Skip to main content

Full text of "Darwinism and the problems of life : a study of familiar animal life"

See other formats





/ B 





a Stufci? of jfamUtar animal Xtfe 



Professor at the University Freiburg in Baden 








Up- Ary 





§3 " 

__ . 







4 , 



The present work had its origin in an attempt to 
appreciate the range, the foundation, and the value 
of evolutionary theories. Such a task entailed a 
prolonged study, not only of scientific literature, 
but also of works that belong to neighbouring 

The information gleaned from these fields had then 
to be appraised and put together, and an effort made 
to reduce it into a harmonious system. In doing 

this the various theories had to be examined with 
discrimination, enlarged, and built into the structure. 
It is, therefore, hoped that the reader will meet many 
new thoughts in the work. 

In the preparatory reading the author had to go 
through the whole of the relevant literature in various 
languages. In the book itself he was compelled to 
restrict himself to what had an essential bearing — 
either for or against — on the view it presents. 

The work has not been written solely for those 
who are entirely devoted to the study of science. 
It appeals to all who take an interest in scientific 
questions ; to all educated people who would inform 



themselves as to the actual condition of theories of 

Its chief aim has been to vindicate the value and 
importance of Darwinism. The greater part of the 
work is devoted to proving the truth of this system. 
On the other hand, every care has been taken to 
distinguish between facts and probabilities ; and it has 
been clearly pointed out what general deductions may 
or may not be drawn from Darwinism. The ease 
with which the theory of evolution is grasped too 
readily disposes people to regard Darwinism as the 
one true, natural, and sound view of the world- 
process. And in order to set forth all these questions 
with perfect clearness, it has been necessary to touch 
on fields of inquiry which lie beyond the range of 
biological science. 

The manner of presentation is simple, because the 
work is written for the general reader. No knowledge 
of science is presupposed ; and the reader is briefly 
informed on all the questions that have a bearing on 
the theory of evolution. Everything that would 
interfere with clearness and intelligibility has been 
avoided. Hence, the founders of the various theories 
treated are not, as a rule, named in the text ; though, 
to ensure accuracy, their names are given in foot- 
notes. In these notes will also be found the 
references to the literature relating to the subject, so 



that the reader who desires to go further into the 
matter will find every assistance. With the same 
object of making the text clear the various animals 
have been indicated, as far as possible, by their 
popular names, but their scientific titles will be found 
in the index at the end of the work. 

The difficulty of many of the questions treated 
imposed a yet further condition. Problems that are 
not easily grappled could not very well be put at 
once before the reader. The book gradually educates 
him up to the level of these. Starting from familiar 
objects, it leads him on, almost unconsciously, to 
problems of increasing difficulty, until he is at length 
in a position to form an opinion on even the most 

And as it is the purpose of this work to elucidate 
the theory of evolution only by means of observation, 
to convince those only who have some insight into 
the inexhaustible facts of nature that bear witness to 
it, as many as possible of these facts have been 
introduced. Nature herself shall teach the reader the 
truth of evolution. On this account, the first part of 
the work has been divided, not into problems, but 
according to groups of animals. These animals, 
moreover, are generally the familiar ones of our own 
country. Our indigenous animal-life has been treated 
very fully. Plants have only been dealt with in so 



far as this was necessary for the reader to understand 
the questions. 

The book will, therefore, make the reader acquainted 
with the animals that surround him, and teach him to 
take an intelligent interest in the life of the forest 
and the field. In this we have the most natural 
foundation for the thoughts that reach out to embrace 
the whole of life, and that in the end help to lay 
open the entire world to the human mind. 



Little over half a year has passed since the 

publication of this work. In so short a space of 

time there could not be much advance made in 

science, so that it was unnecessary to make extensive 

alterations in the text for the present edition. In a 

few places there have been additions, relating to new 

investigations ; the third chapter, especially, has been 

considerably modified. No change was needed as 

regards the view that runs through the entire work, 

and is summarily presented in the final chapter. I 

have carefully examined the objections raised on 

several points, but have found them invalid. However, 

I thought it proper to put the chief of them before 

the reader, because I am anxious that he should use 

his own judgment on the facts independently. I have, 

therefore, given the objections in the notes, with a 

few explanatory remarks. Where the objections were 

due to misunderstanding, I have taken care to make 

the corresponding passage in the text clearer, or to 

add further explanations. The purely philosophical 

questions that are dealt with in the later chapters have 

not been enlarged on. A more thorough discussion of 



these questions would spoil the unity of the work ; it 
was necessary only to put, at the limits of my science, 
sign-posts indicating the destination of the roads that 
start from these points, and distinguishing the right 
from the wrong way. For the rest, I believe that 
my treatment of these various questions is not wholly 
superficial, but sufficiently informs the reader on the 
substance of them. I am confirmed in this by the 
testimony of experts. 

I have to express my cordial thanks to my colleagues 
for their friendly interest. 


Freiburg, 15 th March , 1905. 


The quantity of popular evolutionary literature in our 
tongue is — apart from works that deal with the subject 
in its relation to religious controversy — so slight that 
a fresh work of acknowledged competence should be 
assured of a welcome. Professor Guenther’s work 
has, however, an especial title to consideration. He 
has succeeded so well in taking up the position of the 
average untrained observer for his instructive survey 
of our animal world that his book will be singularly 
helpful to thousands who shrink from the usual technical 
manual. The reader will find himself at first looking 
out on a familiar world in a familiar way. Gradually 
he will find the well - known forms and movements 
suggesting alluring problems to his opening vision, and 
he will follow the answers to them, given with a logical 
ease and literary grace that are too uncommon in this 
department, almost without effort. 

Dr. Guenther’s facility has not been purchased, as 
often happens, at the expense of soundness or thorough- 
ness. The limits of the work restrict his plan, but 
within those limits the reader will feel that he is 
following a judicious and entirely informed guide. 
Though full reference is made to the most recent 
speculations of biologists, it is not books and authorities, 
but Nature, that the author holds steadily in view, 
and his personal contributions to its interpretation will 
command respect. 

1 2 translator’s preface 

The circumstance that the work proceeds on a totally 
different principle of interpretation than others that I 
have recently introduced to English readers gave me a 
certain gratification. It is important to make clear that 
the superb procession of organic forms across the stage 
of our planet, which we sum up in the phrase, “ the 
evolution of life,” may be presented either in the terms 
of the older Darwinian theories or of the new ones 
associated with the great name of Weismann. The 
fact of evolution now stands solid and towering above 
all the clash of theories. Even the machinery of natural 
selection continues its vast work — if it does not increase 
it — whether or no we accept the transmission of acquired 
characteristics. It has seemed most expedient to put 
before the general reader a simple and untechnical 
interpretation of evolution from the Weismannic point 
of view (within limits) ; and it would be difficult to 
find a more suitable and attractive one than Professor 
Guenther’s Darwinism. 


London, October , 1905. 



CHAPTER I. — Introduction 

Animal-life in the forest, the field, and the pond. Variations of 
animals in different regions. Connection of animals in the 
same region. Over-production in nature. The relation of 
increase to the danger of destruction. The struggle for 
life. Artificial selection. Natural selection. Transforma- 
tion of species. Different animals of former days as the 
parents of actual organisms. The theory of evolution. 

Its predictions. Variation and heredity. Useful and 
harmful animals. Modification of our animal -world 
through civilisation - - - - - 19 

CHAPTER II. — Mammals 

Life of mammals. Protective value of colour. Origin of 
colour. Hibernation. Store-rooms. Increased produc- 
tion or diminished peril of destruction. Why mammals do 
not multiply more. The play of animals. Explanation 
of play by rest and the accumulation of energy. Human 
play. Imitation in play. Explanation of instinct. Instinct 
and intelligence. Exercise of the mind in the games of 
children. Pleasure in play. Conscious self-deception, 
imagination. Play and art. The animal is at the threshold 
of art. Sense of freedom in play. Games of children. 
Attention. The use of curiosity. The mind of the 
animal and of man - - - - - 52 


Sexual selection. Choice of females. Rejection of the 
hypothesis. Advance of the male’s senses. Selection of 
the strongest suitor. Explanation of coyness and the 
animal coquette. Female selection inadmissible. The 
love -dance. Selection of the apparent strongest. 
Colours as means of distinguishing species. Use of 
sounds. Pairing-calls. Origin and forms of song. In- 
strumental music of the birds. Migration. Speed of 




flight. Do birds tire ? The adaptations of the bird-body. 
Height of the migration-flight. Origin of migratory birds. 
Their strength, their power of presentiment. Routes of 
migrating birds. Their memory and sense of direction. 
Travelling in flocks .... 

CHAPTER IV. — Reptiles and Amphibia 

Principle of animal-classification. The general properties of 
animals explained by heredity and adaptation. Darwinian 
justification of classification. Reptiles and amphibia of 
former ages. Earlier periods of the earth. How and why 
the earth has changed up to the present. How the remains 
of earlier animals have been preserved. Gaps in the 
remains of extinct animals. Primitive man. Conflicts of 
extinct animals. Why the gigantic forms of earlier ages 
became extinct. The death of species. Transformation 
of species. Why ancient species have been preserved. 
Why there are still animals of the simplest type. Pre- 
dominance of a species of animal. Predominance of man. 
Any variation is possible. Origin of flying animals. Life 
of our reptiles. Prey. The creeping of serpents. Re- 
generation, the power to re-form lost members. Its origin 
by natural selection. Frog-spawn. The skin of amphibia. 
Repellent and warning colours on nauseous and poisonous 
animals - 

CHAPTER V.— Fishes 

Origin of terrestrial vertebrates and of lungs. Similarities in the 
structure of animals. Transformation of organs. Creation 
or evolution? Many animals are worse than others in 
this. Selection only creates what is necessary. Atrophy 
of useless organs. Rudimentary organs in man. Degenera- 
tion of organs by panmixis. Indifferent characteristics of 
animals. The differences between species are adaptations. 
Correlation. Animals that are beyond the range of 
selection, Qualities and quantities. Explanation of 
atrophied organs by economy of sustenance and negative 
selection. Impossible to explain many rudimentary organs. 
The biogenetic law. Gills in the human embryo. Pre- 
datory fishes. The rhodeus and the pond-muscle. Senses 
of fishes, their dangers. History of the eel and the salmon. 
Artificial selection of fishes 




CHAPTER VI. — Tracheates 

To the tracheates belong spiders and insects. How insects 
grow. Explanation of the metamorphoses of insects. 
Protective colouring on the wings of butterflies. The 
Lamarckian principle refuted by protective colours. 

Insects that resemble objects. Mimicry. Exhalation 
from male butterflies. Sexual selection. Origin of 

flowers due to insects. Parts of the insect’s mouth. 

Refutation of the Lamarckian principle. The coat of 
insects cannot have arisen by use. Harmonious adapta- 
tions, co-adaptations. Co-adaptations that Lamarck cannot 
explain. Explanation of co-adaptations. Are instincts 
inherited habits? Instincts that can never be affected 
by the will. Spider’s webs. Care of the young. Instincts 
that are only used once. Are mutilations inherited ? Pro- 
tective marks, mildew marks, foresight. Infection of 
embryo. Structure of the embryo. The inheritance of 
acquired characters is difficult to conceive. Untenability 
of the Lamarckian principle - - - - 184 

CHAPTER VII. — Crabs and Molluscs 

Economy of nature. The chemical constituents of bodies. 
Chemical combinations. The elements. The albuminoids. 
Biogens as constituents of living matter. Vital phenomena 
and apparent death. Metabolism. Structure of the living 
substance. Plants the foundation of life. Order of 
sustenance in nature. Flesh-eating is more natural to 
the animal than plant-diet. Are all variations useful to 
animals? Value of selection. Origin of the shells of 
snails. Change of functions. Development of the crab. 

Why the embryonic development of an animal reproduces 
its racial history. Reconstruction of embryogenesis. 
Uncertainty of the biogenetic law. Parthenogenesis, 
the development of unfertilised eggs. Significance of 
the germ - cells. Significance of sexual reproduction. 
Amphimixis. Plural variations - - - - 228 

CHAPTER VIII. — Worms and Ccelenterata 

Genealogical tree of the animals. Descent of animals. Descent 
of man. Preservation of intermediate forms. The earth- 
worm. Regeneration. Leeches. Parasitism. Origin of 




parasites from free animals. Organic changes in parasites. 

How parasites are conveyed. Exchange of hosts. Life of 
the chief parasites : Trichinae, maw-worms, dochmius, 
tape-worms, etc. Danger of fins. Development of the 
liver-distoma. Friendships of animals. Symbioses - 262 

CHAPTER IX.— Protozoa. 

The animal built up of cells. Principle of division of labour. 

The greater the division of labour, the higher the animal’s 
organisation. Multicellular and unicellular animals. The 
protozoa, their form and reproduction. Structure of an 
animal in its development from the ovum onwards from 
rudimentary parts. Origin of the germ-cells. Outlines 
of a theory of heredity. Amphimixis of the protozoa. 

Origin of sexual reproduction. Formation of seed and 
ova. Continuity of the germ-cells. Are any animals 
immortal? Death is not common to all animals. Origin 
of death. Permanent and temporary life. Has life come 
from the stars? Origin of life on the earth, spontaneous 
generation. How it is to be conceived. The first develop- 
ment of living matter. Formation and significance of the 
cell - nucleus. Significance of the fundamental parts. 
Relation of the rudimentary parts in amphimixis. When 
life is extinguished ------ 288 

CHAPTER X. — Extensions of the Principle of 
Selection and other Involuntary Theories 

Why there are numerous species to-day. Isolation facilitates 
the divergence of species. Modification of isolated animals. 
Movement and alteration of animals. Are species formed 
by isolation even without the aid of natural selection ? 
Definite variations. Germinal selection. Changes in the 
nutrition of the embryo are the foundation of variations. 

Do useless organs disappear through germinal selection ? 
Refutation of germinal selection. Effect of external in- 
fluences as modifying principle. Orthogenesis. Rejection 
of same. The mutation-theory. Variations and mutations. 

Do variations proceed indefinitely ? Is there a formative 
energy in organisms ? Mechanicism and vitalism. How 
are the form and purposiveness of organisms explained? 

What is to be understood by chance. Absence of purpose 
in living things. The will to live, the instinct of self- 
preservation 3 2 4 



spicuous shade of colour, otherwise the animals would 
show themselves against the grey soil, and would be 
more easily found and captured. 

All these characteristics of the hare are continually 
improved by natural selection, as only those can escape 
their enemies that are best qualified to do so. But 
as their enemies also are subjected to an improving 
selection, higher qualifications will be required in the 
next generation, and so on. In other words, the hares 
will advance in each generation. It is true that we do 
not directly observe this progress, but that is only 
because our life is too short to appreciate the changes 
brought about by natural selection, which require long 
periods of time. Natural selection cannot act with the 
same intensity as artificial selection. In the case of 
the hare, for instance, not only two or three of the 
swiftest survive, but a large number, and amongst 
these many slow ones that have managed to escape 
destruction by a favourable accident. It is only on the 
average that the speediest survive, and, in fact, when 
we take an average of many years, so that it will be 
thousands of years before any appreciable result can 
be seen. We do not see the grass growing, but we 
can prove that it is longer to-day than it was yesterday. 
So, if we could raise from the dead a man who had seen 
a hare thousands of years ago, he would find a difference 
in the hare of to-day. In point of fact, the skeletons of 
animals belonging to earlier ages prove that they were 
different then from what they are in our time. 

But we should greatly underrate the power of natural 
selection if we attributed to it only the capacity to 



increase already existing characteristics. Just as 
artificial selection can produce white pigeons from birds 
of a grey-blue colour, by choosing in each generation 
the specimens with the largest number of white spots 
in their plumage, so natural selection can endow animals 
with entirely new features. Thus, for instance, our 
hare is not easy to distinguish from the ground on which 
it browses because of its grey colour — which is a mix- 
ture of brown, yellow, white, and black . 1 Now let us 
suppose that a glacial period came over England again, 
as has happened twice in the history of the earth. The 
dark-coloured hares would then easily meet the eyes of 
their enemies on the white snow, but there would be 
varieties with a rather stronger mixture of white in 
their colouring. These would be least easily seen, 
would survive the longest, and bring most young into 
the world ; so that the next generation would in itself be 
of a lighter shade. Amongst these, again, the lightest 
would survive best, and this would be repeated in each 
generation until a pure white coat was produced, as is 
found in the Arctic hare. We must not forget, of 
course, that such a modification of colour could only 
take place if the cold set in gradually, and implied 
above all the coming of longer and more snowy winters. 
Natural selection is powerless in face of sudden changes, 
as it can only modify things gradually. Further, 
selection only acts generally ; every animal does not 
survive that is modified in the desired direction. But 
that the modification can, generally speaking, advance 

1 As mentioned in Weismann’s “ The Evolution Theory.” [English 



in this way is due to the fact that the material to select 
from is inexhaustible, and that immense periods of 
time are available for the process of transformation. 

We see, therefore, that the changes that are brought 
about by natural selection, through the emphasising of 
insignificant characteristics, may become very striking. 
The external difference between grey and white hares 
is very considerable. It is true that one might claim 
the white hares to be a. variety of the grey ones, and 
say that the difference between the two forms is not as 
great as between the hare and the next species, the 
rabbit. But is there any difference between a “ variety ” 
and a “species”? Many writers understand by 
“ varieties ” animals with somewhat different features 
from those of the mother-species, but say that these 
characteristics vacillate, and are not preserved in the 
course of generations — are not constant , as the phrase 
is. We see that this test of the variety does not hold 
good in the case of our white hares ; the whiteness is 
constant, because all reversions are destroyed. And 
when it is said that the variety can always pair with 
the mother-species and produce fruitful offspring, which 
cannot take place between two different species, the 
statement is not entirely correct. Many species can be 
coupled, and beget young that are capable of repro- 
ducing. This is the case, for instance, with the wolf 
and the dog, the carp and the crucian, and other 
animals, which everybody recognises as distinct species. 

We can safely affirm to-day that there are no rigid 
tests for determining whether certain types of animals 
are species or only varieties ; in other words, there 


is no sharp distinction between a species and a 

This modern discovery has thoroughly shaken the 
old Linnean principle : “ There are as many species 
as there were distinct forms created.” We now know 
that species are changeable, and have actually changed ; 
that one species may be formed from another. The 
question is often raised, in the form of an objection, 
why no species has been changed within our experience ; 
in fact, it is urged that history shows the forms of 
animals and plants to be just the same as they were 
6,000 years ago, since the ancient Egyptians depicted 
lions and other animals just as we have them to-day. 
The objection seems to have some strength, but we 
know of several cases in which species have been 
so much modified within the historical period that 
they can no longer be crossed with their earlier 

In the year 1419 rabbits were introduced on the 
isle of Porto Santo, near Madeira, and increased until 
they became a plague of the country. But the de- 
scendants have become very unlike their ancestors, 
and differ from them in their peculiar colour, rat-like 
shape, small size, nocturnal habits, and extraordinary 
savageness. But the most remarkable point is that 
they can no longer be crossed with the European 
rabbit, and have, therefore, formed a new species in 
this comparatively brief space of time. 1 

However, this was an exceptional case. The 

1 The facts are related by Ernst Haeckel, who gave the Porto Santo 
rabbit the name of Lepus Huxleyi. 



conversion of one species into another usually 
requires a longer period than the whole of human 
history, the 6,000 years of which are only an hour 
in comparison with the immense duration of the history 
of the earth. We saw above that it takes a long time 
for grey hares to become white ; and we know from 
geology that, as a matter of fact, all the terrestial 
epochs comprise enormous periods of time. The latest 
of them, the tertiary period, is calculated at several 
hundred thousand years. Geology also gives us the 
best idea of the mutability of species, as we find at 
the bottom of the sea the remains of animals of 
remote ages, which are totally different from the 
animals of our time. Geologists can distribute the 
various strata of the earth’s crust in their chronological 
succession. These strata are the pages of a book that 
it has taken millions and millions of years to write. 
Nowhere in it do we find the animals of our own 
time, or at all events only in the very latest periods 
of the earth’s history ; and the later the remains of 
extinct animals are, from the geological point of view, 
the closer do they come to the living fauna. It seems 
clear, therefore, that the animals of modern times 
were not present at the first creation of life, but only 
came into existence at a later date, and succeeded 
other animals in the dominion of the earth. But 
whence did they come so suddenly, if they were not 
evolved from other animals ? Every animal lies in 
the body of another before birth, in the form of an 
e gg or ovum. But, clearly, before our animals 
appeared there were only forms of a different character ; 


and therefore we may safely conclude that they have 
been evolved from these, and that in the course of 
generations the children have diverged more and 
more from their parents. 

If we go further back in the story of the earth’s 
growth, we find that each period of geology has its 
characteristic animals, which must be the parents of 
the later and the offspring of the earlier forms. When, 
moreover, we pass in review before the eye of the 
mind the animals of the succeeding epochs, we notice 
something else besides the unceasing changes of form. 
The older the period we take, the simpler we find the 
shapes of living things ; and the nearer the period 
approaches to our own time, the more intricate and 
the higher is the organisation. In the earlier periods, 
for instance, we find only the lowest forms of vertebrates, 
and these only very sparingly. Gradually, the number 
of species increases. Lizards, birds, and mammals 
appear ; and amongst these the higher species come 
in succession, the carnivores, the apes, and, finally, at 
the last moment from the geological point of view, 
we find unmistakable proofs of man’s existence and 

Hence geology drives us to the conclusion that the 
animals of our time descend from simpler forms, these 
from yet simpler ones, and so on, so that only the very 
simplest organisms can have arisen at the first creation 
of living things. There was, for instance, a time when 
only the very lowest types of vertebrates, the fishes, 
were present on the earth ; and while a good many of 
these fishes were modified in the following epochs 



without going outside the range of the fish-class, others 
were so appreciably changed as to become salamanders. 
Geology shows, in fact, that at a certain period sala- 
manders were the only vertebrates on the earth beside 
the fishes. We do not find these at the earlier stages ; 
they can only have been evolved from the fishes, as 
these are the nearest to them of all the animals that 
lived at the time, and the structure of the salamander 
approaches so closely to that of the fish that we can 
conceive the period as sufficient for the transformation — • 
a transformation which is far less considerable than the 
conversion of a worm into a salamander. 

From these salamanders the actual salamanders and 
frogs must have descended on the one hand, and 
the reptiles, leading on to the birds and mammals, on 
the other. We may form a picture of the transformation 
of animals with the figure of the tree. At a certain 
period a side-branch, the fishes, grew out of the trunk ; 
the branch grew on, and put forth another side-branch, 
the salamanders, which in turn sent out branches. Thus 
we can compare the growth of the organic world with 
the growth of a tree. At first there was a single trunk, 
the simplest organisms. Branches grew out from the 
trunk, and in turn produced twigs, until a mighty tree 
arose with many branches and innumerable twigs. 

The view that the animal kingdom was developed in 
this way from the simplest forms is called “ the theory 
of evolution .” 1 It is now generally accepted ; there are 

1 Also the theory of descent, or transformism. We must carefully 
distinguish between : i, the statement that living organisms have been 
developed from other forms , and 2, the theory as to how they were 
developed, and by what forces. The first is the theory of evolution, the 



few zoological and botanical works written to-day that 
do not rest on or presuppose this theory. An immense 
amount of proof in favour of it has been accumulated. 
Many predictions that were made on the strength of it 
have been realised by recent research, and prophecies 
of this kind are, when they are fulfilled, the very best 
proof of the correctness of the principles they are 
grounded on. 

If, for instance, the birds were evolved from the 
reptiles, there must have been at a certain stage, since 
the tranformation was gradual, an animal intermediate 
between the reptile and the bird — an animal that was 
really a bird, but still retained unchanged many of the 

second the theory of selection ; but there are a number of other 
theories with regard to the mode and agencies of development. These 
will be given later on. Hence those who accept the theory of evolu- 
tion are not at all compelled to subscribe to the theory of selection ; in 
fact, there are many evolutionists who reject it. This will be quite 
clear if we remember that even in the Bible evolution is, in a certain 
sense, laid down as fact. It is stated in the Mosaic books that all the 
actual races of men, with their great differences in the colour of the 
skin, etc., descend from one couple. Hence theologians have seen of 
late that it is not advisable to reject evolution altogether. In par- 
ticular, a Jesuit writer, Father Erich VVasmann, one of the first 
authorities on ants, has accepted the general theory of evolution in his 
work : “ Modern Biology and Evolution.” He holds that in the 
beginning God created a number of species at all stages of organisation, 
including man. But these species have not remained unchanged. 
They were endowed by the Creator with the capacity and the means of 
evolution. Thus we have an attempt to combine an acceptance of 
evolution with a belief in the verbal inspiration of Scripture. It is not 
likely to satisfy the man who seeks thoroughly to understand the world. 

The theory of evolution was formulated before Darwin ; the theory of 
selection was created by him. But the theory of evolution itself owed 
its great advance to Darwin’s book, chiefly because he provided the 
explanatory hypothesis of selection. Hence it is not improper to 
include both theories under the title “ Darwinism.” 



characteristics of the reptile. Now, we have found two 
well - preserved skeletons of a reptile - bird of this 
character. This “archaeopteryx” has the distinctive 
feathers, beak, pelvis, and feet of the bird, and at the 
same time an articulated lizard-like tail, teeth, and well- 
formed toes on its fore-feet, which project far out from 
the wing and are not found in any actual bird, but only 
in the reptiles. 

A second example : 

Our horse has only one toe, and on this the hoof is 
placed. The other mammals, even the lower ones, 
from which it must have evolved, have several toes ; 
and thus there must have been at a certain stage horses 
that had at least rudimentary traces of the other toes, 
besides the developed one. 

As a matter of fact, we have discovered four-toed 
horses in the geological strata. Indeed, we have 
brought to light in the successive strata skeletons of 
horses that illustrate every stage of transition from the 
ancient four-toed to the modern one-toed horse ; and 
the nearer the remains approach to our own time, the 
less trace do we find of the other three toes. 

We could quote a large number of transitional forms 
from geology, but will be content with these. Let us 
recall to the reader the way in which we arrived at our 
theory of evolution. We sought to show that natural 
selection can transform one species into another, and we 
found that such a process has been going on uninter- 
ruptedly in geology. The question arises, therefore : 
Is it natural selection that thus brought about all these 
transformations? Is this the artist that has produced 


the whole of our living organisms from the simplest 
forms ? 

We may at once say that we answer in the affirmative, 
and that we will justify our answer in the following 
chapters. We shall even go further, and endeavour 
to prove that natural selection is the sole principle 
to be used in explaining the evolution of living things. 
There are other theories in regard to the transforming 
agencies in the organic world, and one of the chief of 
these theories was expounded by Lamarck before 
Darwin’s time, and accepted by Darwin himself. This 
theory affirms that external influences, such as cold or 
heat, have a modifying action on a species of animals, 
and that the modification they produce may be 
transmitted to offspring. It further affirms that an 
organ may be strengthened by exercise, and that this 
improvement in the organ is handed on to offspring, 
and thus by continued use a change of the organ may 
be brought about. According to Lamarck, these factors 
may go so far as to produce new species. 

For the moment we will refrain from testing the 
correctness of this hypothesis, and will return to the 
general starting-point that led us to consider natural 
selection and the theory of evolution. But first of all let 
us put more clearly and succinctly what we have seen 
as to the changes of species by natural selection. 

Natural selection demands two general conditions for 
exerting its influence. In the first place, the offspring 
of a parental couple must differ in some degree from 
each other, or there must be variations ; in the second 
place, the characteristics of the parents must be trans- 



missible to their offspring by heredity. But both these 
are facts that no one can call into question, as they 
come before us every day. We see daily how brothers 
and sisters differ from each other, and at the same 
time how many peculiarities of the father and mother 
are handed on to their children. These two factors 
are the chief means by which natural selection works, 
producing one species from another. We have seen 
above the way in which it does this. 

Let us recall the process. Every species is found to 
be over-productive in reproducing itself ; that is to say, 
it brings into the world a larger progeny than there is 
room for. A great number of these, therefore, must 
fall victims to unfavourable conditions or to enemies, 
and these will be — as a general rule, and apart from 
accident — precisely the least endowed in body and 
intelligence. In other words, those animals will survive 
longest and reproduce most which are in every respect 
— as to inclement weather, enemies, and so on — the best 
able to resist. Thus the fittest among the varieties 
that casually arise will be preserved, and their useful 
characters will be accentuated in the course of many 
generations, since each new generation over-produces 
in turn, and natural selection again chooses the best 
to survive. If the new characters are connected by 
intermediate forms with those of the parental species, 
which may have adapted itself to the struggle for life in 
the original form in some sheltered locality, we may still 
speak of varieties. If the intermediate forms have died 
— an d that will quickly follow — it is clear that animals 
with completely distinct characters will be left, instead of 



animals in which neither the old nor the new features 
were quite distinct ; that is to say, we have now to deal 
with two species. The differences between them may 
become so great in the course of time that crossing the 
two may give sterile offspring, or be altogether 
impossible. Thus we see that varieties are species in 
the making ; species are varieties that have become 

We know now what natural selection is. The best 
equipped animals escape the longest from destruction by 
enemies or from other injury. They are thus enabled 
to leave most offspring, and the next generation shows 
an average improvement. 

Now let us return to the bioccenoses. 

We examined life in a particular region, and 
concluded that the number of animals in it varies 
somewhat, but remains about the same on the average. 
In this we assumed that the locality retains its natural 
condition, and that, especially, man does not intervene 
with his artificial culture. It will be quite otherwise if 
civilisation comes on the scene ; then the impenetrable 
forests will give place to fruitful fields, and boats will 
shoot up and down the river that flows by. This 
transformation of Nature must naturally lead to a change 
in the fauna ; and the question arises to what extent this 
will be modified, and whether man, for instance, can 
extinguish, with his improved methods of hunting and 
his instruments of destruction, the animals that are 
harmful to him and increase those that are useful, in the 
forests which he leaves standing. 

We have to inquire first, therefore, which animals 



are harmful and which useful to man, and, however 
strange it may seem, this question is very far from being 
entirely settled. We do not regard the matter from the 
point of view of the hunter, who takes everything to be 
harmful that menaces his safety, even if it is a question 
of animals which are most useful in every other respect. 
By harmful we mean only what is really injurious to 
civilisation, or that restricts man’s efforts, while 
guarding ourselves against too narrow a view. Game, 
for instance, does a lot of harm in the field and the 
wood, but compensates us so richly with its flesh that 
we readily overlook the mischief it does in the corn 
or on the trees. The field-mouse is always mis- 
chievous, and its enemies are useful to us. The chief 
of these are the owls, which live almost entirely on 
mice. But we might go further, and regard almost all 
our birds of prey, except, perhaps, the hawk and 
sparrow-hawk, as useful on account of their destruction 
of mice. 

We can determine the food of birds of prey with 
some confidence, but it is not so easy in the case of the 
insectivorous birds. It is among insects that we find 
the chief enemies of culture. There are the typographer- 
beetle and the caterpillar of the processionary butterfly, 
the pine lappet-moth and the black-arches — all injurious 
in the wood — the swarm of grass-hoppers, and especially 
the dreaded migratory locust that so often ravages the 
fields. The cockchafer is equally injurious in its adult 
state and when it is a young grub ; and whoever has 
been in a wine-country knows what it means for the 
dreaded phylloxera to get into the vineyards. But it 


would be a mistake to imagine that every insectivorous 
bird is useful. We have a large number of useful 
insects. I need only mention the bee and the silk-worm, 
and the insects that do us a service by destroying their 
neighbours. Many a caterpillar succumbs to the large 
running beetle, many a plant-louse is eaten up by the 
larvae of the lady-bird, and it has been observed that 
trees visited by ants do not suffer from caterpillar-blight. 
But it is especially the ichneumon-flies, slender animals 
with long antennae, darting constantly here and there, 
that protect us from this blight. These insects have 
what is called an “ovipositor” on the hind part of the 
body, with which they stab the caterpillar, and deposit 
their eggs inside it. The larvae of the flies develop from 
the eggs in the flesh of their unfortunate host, and 
gradually feed on its body from within. The process 
goes on for a long time, the caterpillar continuing to 
live and eat, and it is only when it reaches the chrysalis 
stage that the larvae creep out, and enter on that stage 
themselves near, or on, the dead covering of their 
former host. Many a butterfly - collector has been 
disagreeably surprised when he caught an apparently 
sound caterpillar of a cabbage-butterfly in his cage, and 
found one day an empty shell instead of the expected 
chrysalis, with the yellow, oval cocoons of the deadly 
enemy of the caterpillar beside it. 

The ichneumon-wasp is so thorough in its activity 
that it must be put higher than the birds as a destroyer 
of caterpillars. We must not, for instance, have too great 
an idea of the work of the cuckoo, which was formerly 
regarded as the chief agent of destruction of the 



processionary caterpillars, that not only destroy whole 
forests of oak, but also cause violent inflammation on the 
human skin by their hairs. It has been proved that 
most of the caterpillars eaten by the cuckoo were 
already stabbed by ichneumon-flies. Thus they were 
already full of larvae, which would have attacked 
caterpillars in turn after they had crept out. These 
were destroyed by the cuckoo ; and, as they would have 
proved the most effective restriction on the plague of 
caterpillars, we should regard the cuckoo rather as a 
harmful than a useful bird. 

What do we find in the case of other insectivorous 
birds ? 

Unfortunately, we have to class many of them as 
mischievous which were generally regarded as useful. 
The redstart only too often visits the hive for the 
purpose of filling its stomach with the useful honey- 
bearers. The fly-catcher destroys the caterpillar-flies 
— the bitter enemies, as the name indicates, of the 
caterpillar. The kingfisher, of which anglers complain 
so bitterly, feeds mainly on water-boatmen, the stinging 
water-bugs that are very dangerous to the young fishes ; 
it ought, therefore, in this respect to be considered 

But we need not delay any longer in determining 
which animals are useful and which mischievous. I 
believe that the harm done by the higher animals, 
especially mammals and birds, is never serious enough 
to justify us in making every effort to destroy them. 
We have seen that in a bioccenosis all animals are 
related to each other, and that the multiplication of one 


species leads to an increase in the number of its 
enemies. Moreover, it often happens that a dispro- 
portionate spread of any particular species carries its 
own corrective with it ; the animals show symptoms 
of disease, and die off suddenly as if by magic. This 
was seen, for instance, during the great plague of mice 
on the Rhine in the twenties ; and the plague of black- 
arches at the beginning of the nineties also came to a 
sudden stop. 

It is true that the injury already done by these swarms 
of pests is so great that men are not disposed to wait for 
the end, but make every effort to check their progress. 
But it is otherwise with animals which cannot multiply 
in this extraordinary way. These should be spared, I 
think, even if they do a little damage here and there. 

Just as we protect singing birds for their song, we 
should also try to preserve animals that afford pleasure 
to the eye. We ought to forgive the squirrel his taste 
for bird’s eggs, or even for the callow young, for we 
should greatly miss this graceful animal, the ape of our 
forests, if he ceased to enliven our trees. What does it 
really matter if the kingfisher does destroy a few fishes 
a d a y — and generally fishes that are no use to us ! He 
makes up for that by his beautiful appearance. How 
sad it would be if we were to lose for ever the unfor- 
gettable moments that come to the solitary dreamer by 
the stream when he catches sight of this bird with its 
plumage of jewels ! What an impiety to shoot a stork 
because he has stolen a young hare ! When we were 
children the stork was almost a sacred bird to us with 
his inexhaustible poetry. Let us leave him such to 




CHAPTER XI. — The Mechanical Conception of 
Life and its Limits 

An attempt to refute the theory of evolution. Establishment of 
theories and investigation of details. Causes and effects. 

Infinity of same. Impotence of science. Infinite variety 
in the products of organs. The infinite diversity of the 
universe. Purpose. Mechanical and teleological causes. 

There is no end in the development of animals. Sexual 
selection, orthogenesis, and germinal selection are teleo- 
logical. Purification of the theory of selection from 
teleological elements. There are no higher and lower 
animals. A high grade of organisation gives no more 
advantage to an animal than a lower. Natural selection is 
not an absolute principle of betterment. The scientific 
method of research. Infinite diversity of the universe. 
Comprehension of same by concepts. Abstraction of the 
universal. What a natural law is. Ultimate constituents 
of bodies. Comprehension of the world by ultimate 
elements. Mathematics. An ether without properties 
enables us to grasp the world. Does ether exist? Are 
psychic processes to be conceived corporeally ? The 
methods of psychology. Consciousness. The world and 
the soul are only to be conceived as contents of 
consciousness. Transition from science to theory of 
knowledge ------- 358 

CHAPTER XII. — Nature, History, and Morality 

Truth of scientific ideas. Why the universal seems to us more 
essential than the individual. The ideas of animals. Why 
we take ideas for realities. Thinking realities into ideas. 

Is there a real world lying behind the phenomenal world ? 

Natural science itself is a human product and pursues an 
aim. It must not regard itself as the only sound branch 
of science. The historical sciences. Their method. The 
historical elements in natural science. The laws justify 
historical research. The science of evolution rests on 
probabilities. The origin of the human mind. Had 
consciousness a beginning? There never were absolutely 
simple bodies. History and sociology. Origin and 
development of primitive man. Origin of good and 
evil. Origin of conscience. Advance of civilisation by 
tradition. Language. Conflicts of nations. Scientific 




ethics. Restricted and inverted selection in civilisation. 
The evils of war and militarism. Nietzsche’s egoism. 
Darwinian ideas of the social future. Insipidity of the 
Darwinian ideal. Social man according to Nietzsche. 
Natural science knows no idea of duty. It knows nothing 
of values, and can therefore frame no ethic. Preservation 
of existence is not preservation of value. Is there a sense 
of life? Monism. Presuppositions of science. The idea 
of duty is the beginning of all knowledge. Conclusion 

Index - - 



39 ° 





Animal-life in the forest, the field, and the pond. Variations of 
animals in different regions. Connection of animals in the same 
region. Over-production in nature. The relation of increase to 
the danger of destruction. The struggle for life. Artificial 
selection. Natural selection. Transformation of species. 
Different animals of former days as the parents of actual organ- 
isms. The theory of evolution. Its predictions. Variation and 
heredity. Useful and harmful animals. Modification of our 
animal-world through civilisation. 


Who has not visited the forest on a morning in Spring! 

The tall stems of the trees stand out ruddily in the 
green dawn. The blue vault of heaven breaks through 
the tree - tops above. The dew - drops glisten like 
diamonds on the tender moss and the grass - blades ; 
and iridescent prisms flash from the leaves of the 
shrubs. A mist lies on the glade, and covers with its 
veil the flowered-starred ground, while the tips of the 
young firs rise mysteriously from its depths. 

Then the morning wind stirs the tops of the trees. 

A faint rustle passes through the wood. Here and 




there branches and stems give out mysterious creaks 
and groans. 

Now the noises increase. 

On the ground a slight stir catches the ear. It is 
a beetle hurrying by in search of his prey. He runs 
nimbly over the grass and among the bushes. He 
leaps over a scarlet snail, which draws in its antennae in 

alarm, and passes swiftly down an ant-track. Before 

* *» * ** * * * * * 

the.- industrious builders realise the injury done to their 
laborious construction, he has disappeared in the thicket. 

A dreamy .murmur fills the ear. 

Fifes without number are in the air. Their pellucid 
wings glitter in the rays of the sun, and they poise 
motionless, as if hanging by a thread. The whole 
atmosphere seems to vibrate with the tone of the harp. 
An infinite harmony swells the breast of the traveller. 

At last the stillness is sharply rent. 

Like the laughter of some spirit of the forest, the loud 
“ gluck, gluck, gluck ” of the wood-pecker echoes 
through the trees, and the ringing tap tells that his 
fellows are at their carpentering. The cry of the 
chaffinch resounds ; from point after point comes the 
chirp of the wood-pigeon ; and the titmouse utters 
without wearying its tender call. 

Over the clearing is heard the cry of the bird of 
prey. The mist falls on the meadow. And yonder, 
where the thick bush marks off the forest from the 
flower-decked green, a slender deer emerges, lifts up 
its narrow head cautiously, looks all around, and then 
bends its neck towards the grass. 


2 1 

When the sun is at its zenith, life is at its busiest 
in the field. 

A hot fruitful vapour rises from the grass up into 
the blue air, which is filled with the trilling song of 
the lark. The ears of corn stand motionless in the 
dry air ; only here and there a blade stirs and betrays 
the passage of some invisible inhabitant of the field. 

But life is briskest in the field at the point where 
the flower-filled ditches, crowded with rich vegetation, 
are found. Here the bees and wasps hum from flower 
to flower : white, blue, and many-coloured butterflies 
dart about ; and the ground swarms with running insects. 

Beetles creep up the trunks of the willows that stand 
at the border, and their leaves are the pasturage of the 
insatiable caterpillar. On a branch of the tree sits the 
wood-lark, and begins his song. Then inspiration comes 
to him ; he rises, and mounts to the sky, pouring out 
his song in triumph as he ascends. At last he spreads 
his wings, and with long-drawn notes sinks to earth 
once more. 


Now evening approaches, and the rays of the sun fall 
almost level ; the frogs give forth their round song in 
the rush-bordered pond. 

Here, again, is an entirely new picture. 

The great dragon-flies dart rapidly over the water, 
and their dark-blue wings glint like fairy-eyes from the 
rushes. A crowd of gnats and May-flies dance above 
the surface. On it the whirligigs form their endless 
circles, like shining pearls ; and, like long-legged skaters, 
the water-ticks glide hither and thither. 



A red-bellied newt issues from the dark depths to get 
a mouthful of air, and, turning gracefully, sinks again. 
A large swimming beetle appears, and hangs with its 
hind part on the surface. The depth of the water is 
full of water-fleas, which rise up and down unceasingly 
like unnumbered points. 

• «<»•••* 

And when the sun sinks below the horizon, and 
darkness enfolds Nature in its thick veil, a new life 

The call of the screech-owl resounds plaintively in 
the wood, bats fly about in the air, and a gentle rustle 
is heard in the grass. 

Fear falls on the man who enters into the soul of 
the little night-walker, which must make its way in 
the dark, and must be ready at every step to be seized 
by some deadly unseen enemy. Never does the eternal 
carnage in Nature seem so merciless, so terrible, as in 
the night. 

• ••••• 

Each hour of the day has its own life. 

In the forest, the field, or the pond the picture differs 
entirely in the morning, at midday, in the evening, and 
at night. If our path had led us into one of these three 
regions, as we call the various provinces of Nature, at 
another time of the day, we should have encountered 
different animals. Yet the animals of any one region 
are more closely related than those that live in different 
regions at any particular time of the day. Forest, 
field, and pond have their characteristic inhabitants, and 
outside these regions there is a whole series of others. 


2 3 

If we examine the brush instead of the open wood 
we meet animals just as interesting and characteristic ; 
and instead of the field we might have taken the 
meadow, the moor, or the quarry. 

So the life of the pond differs entirely from the life 
of the brook and the great river. Nay, we might even 
confine ourselves to the tiniest compass, and examine 
only a drop of water hanging from the moss. We 
should find that even in this little realm there are 
hunters and hunted, and that countless living things 
find the conditions of their life within these narrow 

Every animal seeks what it needs for its maintenance, 
if not exclusively, at all events mainly, in the particular 
region in which it lives. The wood-pecker will not 
leave the wood, for this alone provides him with 
food in its trees and a sure place for nesting ; nor are 
river-fishes ever found in ponds. 

But all animals are not confined to one region. The 
deer leaves the thicket in the evening to feed in the 
green meadows ; the partridge seeks cover at times in 
the wood ; the water-beetle of the pond may alight in 
running water in its nocturnal flight. 

Other animals have a different habitation at different 
periods of life. 

The young frogs swim about merrily in the water, 
and resemble fishes in appearance and habits. After- 
wards the long oar-like tail is lost, the feet sprout out, 
and the frog assumes the form of a land-animal. It 
lurks for flies at the edge of the pond, and only leaps 
into its earlier element on the approach of danger. 



But Nature may go yet further. It may make the 
habitation of the young animals fatal to them as adults. 

Many insects pass their youth in the water in the 
form of larvae, but after their last cast of skin they 
unfold pairs of wings, and become inhabitants of the air 
and land. And if any mischance brings them back into 
their former element, they are doomed, unless a friendly 
grass -stalk provides the means of safety. May-flies, 
dragon-flies, gnats, and many others are thus adapted 
to two regions. 

Each region, therefore, is filled with a number of 
forms of life. These do not live independently, 
however, but are adjusted to each other. We know, 
in fact, that if water-fleas are plentiful in a piece of 
water, the condition of the fishes will be so much better, 
because they form almost the entire food of the young 
fishes. We must not forget, moreover, that the plants 
in any region are important to the animals contained 
in it. This becomes clear at once when we reflect that 
it is they that form the nourishment of the plant-eating 
animals ; and that they also provide more or less shelter 
for the animals, and especially their young, and so 
cannot be dispensed with. 

Thus each region is a self-contained whole, in which 
plants and animals live in mutual relationship, and the 
diminishing of one species always reacts on another. 
But the foundation of all animal-life is found in the soil, 
the distribution of water and land, light and air, and 
the climate and other factors that we may call the 
physical conditions of the place. The totality of animals 
and plants that live under these conditions and are 


2 5 

dependent on them and on each other, may be called 
the “life- commonwealth,” or bioccenosis } Thus there 
are “ bioccenoses ” of the pond, the river, the wood, and 
so on ; and also biocoenoses of a higher order, such as 
the fauna — that is to say, the animal-life — of an entire 

We need only consider any single animal in a 
bioccenosis to see at once how it is really a member of 
a community. Let us, for instance, examine the life 
of the fox. For this purpose we must learn how that 
crafty thief obtains his prey. But this implies further 
that we cast a glance at the life of the animals he preys 
on ; we must consider the speed of the mice in order 
to appreciate the leap of the pursuing fox ; we must 
know something about the hearing of the hare, to 
understand how reynard can creep up to his victim 
without being perceived. There is an old illustration 2 
of the interesting mutual relations of fox and hare, 
which shows very well how two species react on each 
other in their condition. If we suppose that the hares 
increase in any region that contains only these two 
kinds of animals, the result will be that the foxes will 
multiply in the same district, because the abundance 
of food will make them stronger, and able to rear a 
larger number of young. But the increase in the 
number of foxes will require an increase in the quantity 
of food ; the hares will be less able to escape from 

1 This term was first used by Mobius, of Berlin, and was afterwards 
extended and modified by Hensen and Dahl. Hensen insisted on the 
statistical method as most important in the study of bioccenoses, so as 
to discriminate between the normal and the accidental. 

2 The instance is taken from Darwin. 


their numerous enemies, and will be decimated. When 
the foxes find less to eat, they will decrease again, and 
give more chance to the hares, and thus the balance of 
vital advantage will oscillate between the two species. 
This will bring about in time an unstable equilibrium : 
that is to say, the number of the two species will be 
constantly rising or falling a little above or below a 
certain level, but will remain at the steady average. 

In reality the situation is rather more complicated, 
as the fox does not live on hares only, and the hare has 
other enemies besides the fox. But the fact remains 
that there is this correlation between the animals of 
a certain region ; and it must be so, otherwise a species 
would increase indefinitely. 

Let us suppose that a couple of foxes were left 
to multiply in peace. As a rule the fox has four or 
five young ones, and this for several years in succession. 
But we will take a case in which a couple bring six young 
ones into the world once for all ; and suppose that three 
of these are male and three female, and that these three 
couples have each six young in the following year, so 
that there are then nine pairs, and so on. In ten years 
the number of foxes would have grown to 118,098, and 
this number would be much greater if each couple cast 
young more than once, as is the case in real life. 

As a rule, however, the animal population of a 
district remains constant, apart from the interference 
of extraordinary agencies. If, therefore, each of the 
couples of foxes in a given wood have five young every 
year, and this for seven years, or thirty-five in all, it 
follows that, if the number of foxes is to remain steady, 



thirty-three must die, and only two remain to replace 
the parents. 

It is just the same with all animals and plants. 
Everywhere there are far more born into the world 
than can be supported. Take an apple-tree in blossom. 
If a fresh tree were born of every flower, there would 
soon be nothing but apple-trees on the earth. But 
besides the fruit-trees there are myriads of other plants, 
and each of these has an immense progeny. The 
earth is not large enough to hold this vast wealth ; 
every corner of it is already occupied. Thus it is 
clear that over-production in Nature creates an infinity 
of life only to destroy it. 

We may, of course, admire the “inexhaustible riches” 
of Nature, but on the other hand we must shudder at 
the tragedy of millions and millions of living things 
coming into the world only to die, because there is no 
room for them. However, they all have an unconquer- 
able lust for life, and are impelled by it to fight with 
all their strength for space with those that already occupy 
it. Thus there is bound to be an endless strife in 
Nature. It is the “wealth of Nature” that occasions 
the pitiless, ghastly, despairing struggle, and converts 
the earth into a reeking battle-field. 

However, we will not regard Nature, so cold and 
pitiless, with the warm feeling of a human heart. We 
will seek to detect the causes that lie at the bottom of 
the facts. 

Darwin explained to us the over-production of Nature, 
by showing how large the posterity of this or that living 
thing would be. All animals by no means increase at 



the same rate. While the fox has, on the average, four 
or five young in a year, the hare has eight to ten young 
yearly, in about five casts, and the mouse as many as 
thirty. These figures are far surpassed by the fishes ; 
the carp, for instance, discharges 3,700,000 eggs. But 
the highest number is found in intestinal worms. We 
learn with astonishment that the maw-worm produces 
64,000,000, and the tape- worm 100,000,000, eggs. 

If we now cast a glance at the life of these animals, 
we find that their fertility is directly related to their 
peril. The fox has few enemies, the hare incomparably 
more, and the mouse is, so to say, the piece de 
resistance of all our flesh-eating animals and birds. 
The eggs of fishes are much relished as food by many 
aquatic animals, and the sluggish, defenceless carp only 
too often falls a victim to the predatory fishes. Much 
nimbler is the trout, which has also less enemies to 
fear in its stream, and so only produces 600 eggs 
a year. 

But there are other agencies besides enemies that 
decimate a species. The young foxes pass their early 
days in a warm and sheltering structure ; much worse 
is the lot of the hares, which are laid on the bare 
ground, so that the first arrivals, in the middle of 
March, nearly always perish ; and the ova of fishes 
are exposed to all kinds of accidents, as they are 
very easily washed away or dried up. Remember, too, 
the difficulties that the egg of the cattle tape-worm 
encounters before it can become itself a sexually mature 
animal ! First it has to be ejected in the human 
faeces, and then it must be licked up by a cow, in the 



bowels of which it develops into a young animal. 
This passes into the muscles, and buries itself therein. 
Then the cow must be killed, and its flesh be eaten 
by a human being, for it is only in the human intestines 
that the tiny creature will grow into the adult tape- 
worm. We can easily see that the tape-worm would 
soon become extinct if it were less fruitful. 

We might go through the whole series of animals, 
and we should find in every species a confirmation of 
the fact that every animal’s fertility is proportionate 
to its perils. We may add that it is also proportionate 
to the food and space provided for it, since it is clear 
that, if foxes multiplied as mice do, they would soon 
consume all the animal food in their environment, and 
would be doomed themselves ; whereas vegetarian 
animals, for instance, would find a far more abundant 
diet. It is also obvious that animals with a limited 
habitat must have a low degree of fertility, otherwise 
they deprive themselves of food, light, and space, and 
court destruction. 

We shall explain at a later stage the fact that each 
species produces, on the average, just as many young 
as is necessary for its maintenance, and that, therefore, 
its production increases in proportion to the dangers 
it encounters. Here we need only observe that every 
animal has in itself the power of multiplying in- 
definitely. Thus is brought about the struggle for life, 
the unceasing fight for food, space, and light. 

This struggle only affects the number of organisms. 
It restrains each species within the limits that are set 
to its expansion. But there is another struggle for 

3 ° 


life, the more important one which Darwin immortal- 
ised his name by discovering. It takes place between 
members of the same species, and consists less in an 
active conflict with a recognised enemy than in an 
unconscious effort at self-maintenance. In this struggle 
the best equipped is the victor. Hence Herbert 
Spencer’s phrase, “the survival of the fittest,” is 
preferable to “ the struggle for life.” 

When the foxes in a particular locality are especially 
menacing to the hares, the first of the latter to be 
eaten are those that are slower than their companions, 
or less able to perceive their enemies in time owing 
to defective hearing or smell. The better equipped 
hares survive longer, and so are able to bring a more 
numerous progeny into the world. But since, as we 
know, the parents transmit their qualities to their 
offspring, the new generation of hares will be equally 
conspicuous for speed and sharp senses, if it comes 
entirely from the finer hares. If there are amongst 
the new-comers animals that fall considerably below 
the average, they will be the first victims to the foxes, 
and leave no offspring. However, this does not go 
on until all the hares are so equipped that no fox can 
master them. Among the foxes themselves it is always 
the individuals that can catch the improved hares that 
survive, secure the most food, and so leave a larger 
progeny. Thus the sluggards gradually die out 
amongst the foxes as well, and only those survive 
that can capture the quicker hares. This must be met 
by a new selection among the hares, only those 
surviving and reproducing that are better equipped 



than their parents ; and thus we get a further advance 
of the good qualities of the hare, which grows on and 
on, without end, because there is a corresponding 
advance in the animals that have caused the improve- 
ment — in this case, the foxes. Darwin has shown 
from the example of “ artificial selection ” — selection 
by the hand of man — that such an improvement in 
the characteristics of an animal can probably be brought 
about by “natural selection.” 

Breeders have succeeded, not only in increasing those 
characteristics of domestic animals which they wish 
to accentuate, but even in producing new ones, and 
so in converting an animal gradually into one of a 
quite different appearance. When we look at the 
races of pigeons to-day, it is easy to believe that we 
have before us quite different and independently 
originating species. As a fact, some races of pigeons 
differ from each other more than the pine-marten from 
the stone-marten. What a difference there is in the 
various parts of the body between pigeons ! The beak 
of the turbit, for instance, is hardly visible, while the 
“ carrier * has a long beak with the most curious growth 
hanging from it. In many kinds the feet are clothed with 
very thick plumage, in others they are quite bare. And 
then there are the infinite diversities of colouring ! 

We find just the same if we take other illustrations. 
Look at the difference between a pug and a grey- 
hound, or an English race - horse and a Belgian 
draught-horse! It is the same with cattle and pigs. 
In every case we find races that differ most profoundly 
from each other. 



Now, all these different races are not originally 
independent. It is man who has taken a few primitive 
types and changed them by selection. In the case of 
the pigeon it is certain that all the various races descend 
from one primitive form, the rock pigeon, which is 
distinguished by black bands on the wings. We see 
how these modifications can be brought about in the 
actions of breeders, who are always bringing out new 
races. They do not accomplish this by crossing ; no 
new characteristics can be produced in that way, but 
only the existing ones mixed and distributed. Breeders 
act otherwise. They select from the offspring of a 
couple the animal that shows a slight trace of the 
feature that they wish to produce. Thus, if they desire 
to create a race of dogs with long legs (and there are 
prizes offered by breeding societies for such objects), 
they choose one pup from the litter that has longer legs 
than its brothers and sisters. This is paired with a dog 
from another litter with specially long legs, and the 
same selection is made again amongst their pups. This 
is continued until they get a race of dogs with legs of 
the required length. The object is attained by the 
accumulation of insignificantly small variations. 

According to Darwin, Nature acts in this way, only 
on a higher scale. It selects, not only in the interest 
of one characteristic, but of a number simultaneously. 
So in the case of the hares, to return to our illustration, 
it is not merely a question of making them swifter than 
their enemies, but also of furnishing them with sharp 
senses, and a higher intelligence to use in choosing 
places of security. Finally, they must have no con- 



our own children. How fine it is to watch him in his 
splendid flight ! 

This “ American ” habit of looking only to the useful 
is odious, and unworthy of a poetic and imaginative 
race. We regard with pleasure the re-birth of the 
historical sense the increasing regard for monuments 
of former days. Let us take care, then, to preserve 
the animals that are as much connected with the 
poetry and feeling of our race as historical reminiscences. 

We may now ask how it is that man is able to 
extinguish whole species of animals, a thing which no 
other animal can do? 

It is not so much by powder and shot, not so much 
by snaring and poisoning, as^>y the changes he makes 
in the country. In spite of all snares the number of 
foxes increases steadily in the Black Forest, because 
it is impossible to dig up their homes in the rocks. 
The field-mouse has not diminished in spite of all 
attacks; neither has the lark, though the Italians bring 
them down in swarms. 

It is civilisation alone that changes the fauna of a 
country. If our forests were not cleared, and our 
marshes not dried up, the dry branches would still 
snap under the tread of the bison and the elk, and 
the wolf would still threaten the flocks. Modern 
forestry is slowly but surely destroying the wealth 
of bird-life, as the thinning of the trees and the brush 
deprives the birds of their nesting-places. It is not 
cats, or weasels, or foxes, but the disappearance of 
the thick bushes, that is robbing us of the song of 
the nightingale. This has been recognised of late 




years, and efforts have been made to plant thickets 
alongside the railway on some of the less converted 
estates. In connection with one of these experiments 
in Thuringia nests have been found on an average 
every thirty yards, which is a decided success when 
we consider the dislike of the birds for new plantations. 
However, the times will not wait; cultivated land is 
changing its appearance more and more, and our 
old friends are disappearing. Few of them can adapt 
themselves to the new conditions, like the black-bird, 
which is gradually becoming a town-bird, and now 
pours out its song from the roof of a house or even 
the chimney of a factory, instead of from the top 
of a rain-dewed tree. 

Other birds are not deprived of their nesting places 
in the advance of civilisation ; some, in fact, find them 
in greater abundance. The chaffinch, which nests on 
trees, is never at a loss for a spot, and we hear its 
jubilant cry the most frequently of all. The spread 
of the fields gives more room for nesting to the lark, 
which is also on the increase. This is an excellent 
proof of the correctness of what I said, since its nest 
lies in the ground, exposed to innumerable enemies. 

But most birds, especially our best singers, breed 
in the bush, and they are steadily diminishing owing 
to the destruction of their nesting-places. And the 
same is happening to the fishes. 

The rivers are controlled, and the standing waters, 
in which the inhabitants like to lay their spawn, are 
disappearing. The Rhine-salmon comes less and less 
frequently up-stream, and if it were not for the partial 



remedy of artificial breeding - places, it would have 
vanished from our tables long ago. The Thames 
has long been deserted. 

We can understand now how it is that civilisation 
acts in this way on animal-life. We saw, in considering 
regions and biocoenoses, that physical conditions form 
the essential foundation of an animal-world. But these 
are altered by civilisation, and thus we realise once 
more how fundamental the idea of bioccenosis is. 

What can we do in face of this increasing devastation 
of the country? 

Is a time coming when our forests will again have 
luxuriant under-wood, in spite of the reduction in the 
output of timber ? Possibly. But it seems more 
likely that civilisation will crush Nature under its iron 
feet ; that the days are approaching when the 
nightingale and the robin will be legendary shapes 
in a remote past. Perhaps in those days there will 
be a race on the earth that will tell, with a pitying 
smile, how there were once human beings whose 
heart was more stirred by the song of an unseen 
bird than by the music of artificial automata. 



Life of mammals. Protective value of colour. Origin of colour. 
Hibernation. Store-rooms. Increased production or diminished 
peril of destruction. Why mammals do not multiply more. 
The play of animals. Explanation of play by rest and the 
accumulation of energy. Human play. Imitation in play. 
Explanation of instinct. Instinct and intelligence. Exercise of 
the mind in the games of children. Pleasure in play. Conscious 
self-deception, imagination. Play and art. The animal is at the 
threshold of art. Sense of freedom in play. Games of children. 
Attention. The use of curiosity. The mind of the animal and 
of man. 

Every friend of Nature, everyone who is acquainted 
with the life of the forest and the field, knows that 
there are not too many mammals that now meet the 
eye of the traveller. 

Many a time during a walk through the wood do we 
see something hopping about here and there, and find 
on drawing nearer that a squirrel is hurrying with 
nimble springs to the nearest tree, and climbing up it 
on the side furthest away from us. Now and again we 
discover a hedgehog in his leafy hiding-place, or stand 
by a pond to watch the antics of the water-shrew or 
the water-rat. If fortune favours us, and we keep quite 
still, we may see the field-mouse hurrying over the 

5 2 



It is still better in the evening. Then the lover of 
Nature takes his place at the edge of the wood with 
a telescope or glass. There is a rustle in the bush, 
and a hare springs swiftly into the meadow, looks 
round, and, if all is quiet, hops farther on. A louder 
rustle, and deer come slowly out, to enjoy the succulent 
green or to regale themselves on the toothsome pasture 
of the nearest clover-field. 

But the attentive observer learns a good deal about 
animals without seeing them. Here the bark stripped 
from a slender twig in the thicket betrays the proximity 
of a strong buck ; there he notices the much - trodden 
haunt of the slender deer. On all sides he sees in- 
dications of the presence of plenty of mammals ; in 
the winter, especially, he reads whole stories in the 
footsteps that stand out in the snow. 

Over a broad snow-sheet runs the trace of a hare. 
It can be seen for a long way in an ever curving line. 
Then it is joined by the track of a second hare, though 
the two are distinct. Now there is a trodden spot in 
the snow that catches the eye with its drops of blood 
and scattered wool ; it is the wooing or bucking-place 
of the long-eared game. We look again, and see other 
steps approaching ; a fox has crept up to the timid 
animals. Now there is a deep pit in the disordered 
snow, its pure white flecked with blood. Reynard’s 
stratagem has succeeded. He has got his dinner. 

The life of all our mammals is surrounded by constant 
dangers. Some of them, in particular, have been 
subjected to so sharp a selection by the unceasing peril 
that only the finest can survive the struggle. Thus, 


for instance, the wolf has become so cautious that 
he often escapes from the most careful traps. The 

endless attacks upon this dreaded robber have left only 
particularly cunning specimens in existence. 

As a general rule the day’s work of our mammals is 
very monotonous. Brehm has compared it, in his 
striking way, with that of the birds. The mammals 
are, he says, not such light-livers as the birds. They 
have not the liveliness and the unquenchable joyousness 
of the lovers of the light ; though they have a certain 
comfort and enjoyment of life. Except in their early 
youth they refrain from useless exercise of their bodily 
strength. For the bird, on the contrary, to live is to 
move and to move is to live. The bird is never at rest, 
and would like to turn the whole night into day. Its 
little heart beats more quickly, its limbs are more 
elastic, more wiry, than is the case with the mammals. 
The mammal seems only to experience real joy in life 
when it has packed itself away as comfortably as 
possible, to sleep, or at least to doze. The bird is a 
thing of movement ; the mammal, of sensation. 

This is quite borne out by their organisation. 
The mammal, even when it can attain great speed, is 
tied to the ground, and cannot move anything like so 
independently as the earth-free bird, which can easily 
outstrip our swiftest expresses. So it is with most of 
the arts of movement. What mammal can vie with 
the nut-hatch in climbing, as it runs, head downwards, 
up the trunk? Nor are birds backward sometimes at 
swimming and diving. 

But now for the other side of the matter. How 



much the birds are surpassed by the mammals in the 
life of feeling ! The senses themselves are, with the 
exception of sight, constructed quite differently in the 
two classes. Think, for instance, of the sense of touch 
in the whiskers of the cat, and the sensitiveness of our 
finger-tips. Think of the sense of taste, which is 
almost entirely lacking in the bird, and the extra- 
ordinarily fine scent of the dog, which recognises the 
track of its master amongst a thousand. Even hearing 
is far more advanced in the mammal than in the bird, 
though it has, for the most part, no appreciation of 
music ; but we know that the musical ear has more 
difficulty in detecting faint sounds than the unmusical. 

The intelligence of the mammal has been developed 
along with its senses. A great advance in this is so 
peculiar to them that we might almost call it a 
characteristic of the whole class. 

However, even the keenest intelligence would not 
protect our quadrupeds from destruction, if they were 
not provided by Nature with other means of escaping. 
It is their colour, especially, that causes their enemies 
to overlook them. The hunter often finds that he will 
pass within three yards of a hare in its bed without 
seeing it. And how difficult it is for the unpractised 
eye to distinguish a standing doe from the trees of the 

Tha colour of our mammals varies in all tones of grey 
and brown, and this is the colour of the ground. An 
animal with a lighter shade would soon catch the eye of 
its enemies ; it could not guard against surprises, and 
would be doomed. Hence, if a quadruped of a lighter 



colour were to come from another locality, it would 
either be soon destroyed, or those of its offspring would 
have most chance of surviving which had most greenish- 
brown in their coats. In favourable circumstances the 
species might be acted on by natural selection, and 
“adapted” more and more, until at last its colour was 
in harmony with its environment. 

Where other colours are found at the limits of a 
country, the animals are affected by these. Our winter 
is usually so short that hares are not exposed for too 
long a period to attacks through the contrast of their 
colour with the snow, besides that the grey tones of the 
field and wood rarely disappear. It is otherwise in the 
high Alps. Here, during the long winter, a broad 
unbroken sheet of snow covers the earth, and a brown 
hare could not long escape detection. We can 

understand, therefore, why the Alpine hares are white 
in winter. In fact, this very species shows clearly how 
natural selection modifies an animal. The Alpine hare 
is also found further north in the Arctic hare. While it 
remains brown throughout the winter in the south of 
Sweden, further north it assumes a white coat at this 
season. And the further north we go, the longer does 
the white coat last, always in proportion to the number 
of cold months. In the extreme north, where the snow 
never melts, and where no trees break the dazzling 
white surface, the Polar hare is white at all seasons, like 
almost all the other Arctic animals, the Polar bear, fox, 
owl, and so on. 

These adaptations to the winter have clearly been 
brought about by natural selection. Just as amongst 



our animals those that do not grow a thicker coat in 
the autumn cannot survive the cold of winter, so among 
the Arctic hares those have the best chance of surviving 
which had the strongest shade of white when the fur 
changed. These favoured ones persisted through most 
winters, and so would have the largest progeny. But 
in the southern regions it was no advantage to have 
a lighter shade at the spring change of the fur ; and on 
the other hand, there ought to be no change of colour 
when the earth was still clothed in dazzling white. As 
natural selection continued its work, a species of hare 
was produced in the course of time in which the change 
of coat and colour was proportionate to the length of 
the winter,, so that the animals were in harmony with 
the prevailing tone at each season. 

Other animals have different shades of colour at 
different seasons. Even the doe has a lighter colour 
in summer than in winter, in harmony with the lighter 
shade of the green-clothed forest. 

Some animals can obtain their food, though often 
with great trouble, during the winter, but this is 
impossible for others. These would die if they did 
not pass the cold period in a long sleep in some warm 
spot. It is in the summer only that their diet can 
be had. 

Our hibernating animals pass the winter in nests 
that are completely closed from within, in the hollow 
trunks of trees and underneath the ground. There 
they need no food ; they fall into a death-like sleep, 
and slowly consume their fat. Nature makes this 

hunger-cure possible for them by reducing their 


temperature some 45 degrees (Fahrenheit), and causing 
them to breathe ninety times less than usual. With 
this diminished vital activity it is superfluous to take 

The winter-sleep is not always absolute. Thus the 
dormouse or “seven-sleeper” ( Myoxus glis), which has 
so appropriate a name since its slumbers last for seven 
months, awakens from time to time, and dreamily con- 
sumes some of its store of provisions. Others, such as 
the hamster, awake in their dwellings as soon as the 
ground thaws, but do not open the stopped holes ; they 
eat the corn which the hamster especially stores up so 
abundantly in its home, that the hamster-catchers of 
Thuringia find their chief profit in the grains, which they 
clean, dry, and sell as ordinary wheat. Provision-stores 
are accumulated by almost all hibernating animals, and 
even by some animals that do not really hibernate. The 
squirrel stores its food in the clefts of trees, in bushes, 
and in holes that it digs, and looks it up in winter. 
Nevertheless, a severe winter kills large numbers of 
them. Some of their stores are forgotten, others inac- 
cessible on account of the snow ; and the enfeebled 
animals quickly succumb to their great enemy, the marten, 
from which they could save themselves in summer by 
their speed, and especially by leaping from the highest 
point of the tree, a feat that their pursuer cannot imitate. 

For other animals the winter is the time of plenty. 
It was noticed long ago that heaps of earth-worms 
were stored up in the passages of moles, especially 
during severe winters ; they were not dead, but 
stupefied in such a way that they could not crawl 



away. Formerly, these were regarded as food-stores 
for the winter, but it is now thought otherwise. The 
mole can catch more worms in winter than he can 
eat ; this is all the easier because he can follow the 
chase with less exertion during their winter stiffness. 
He then stores up the superfluous quantity in these 
chambers, which are thus a provision for the summer. 
The fact that 1,280 paralysed worms and 18 grubs 
were once found in a mole-burrow shows that these 
stores may be very considerable. 

The winter-sleep enables the adult animals to live 
through the cold months without food, but the young 
need nourishment if they are to grow ; this is supplied 
at first by the breasts of the mother, but her supply 
of milk again depends on a rich and abundant diet. 
Hence it is that we find the young always making 
their appearance at the time when food is most 
plentiful, and the pairing - season is fixed earlier or 
later to correspond. 

Spring is the love-season for only a part of our 
quadrupeds. The smaller carnivora, such as the 
fitchet- weasel, have it in March, and the fox has his 
“rut” in February; the former are pregnant for barely 
two months, and the latter two and a half, so that in 
both cases the young see the light in May. Other 
animals have the pairing-season late in the year, as 
is the case with the doe, which bears its young for 
forty weeks, and so has its rut in July and August. 

Mammals are far from prolific when we compare 
them with other classes of animals. But that does 
not violate the principle we laid down in the first 



chapter, that each animal has the power to multiply 
so much that, if there were no hindrance, it would 
gradually people the whole earth. Even a species 
that has only six young ones in the course of life 
would increase to 15,000,000 individuals in 500 

We saw that each species bears young in proportion 
to its peril, and that in each case the reproduction 
is sufficient to maintain the species. We might now 
ask whether the rate of reproduction is not increased 
by natural selection. It is obvious that amongst the 
hares of a particular district it is not only the swiftest 
that have to care for progeny, but that those also 
which bear more young than others will dominate in 
the next generation. If one hare has ten young and 
another twelve, is it not more probable that more of 
the twelve will survive than of the ten, and that the 
survivors of the larger brood will carry on the higher 
fertility which they have inherited? 

No. The inference is wrong. We know that species 
have been put in a position to maintain themselves 
by natural selection. In this there are two chief 
methods open to selection. Either the multiplication 
of the species is increased, cr its perils are diminished. 
The effect is just the same in both cases. 

In the case of the hares, and in fact of all the 
mammals, it is the second method that is chosen. 
The animals are cunning and active so as to be able 
to avoid many dangers. Above all, the new brood 
is protected, especially by finding its shelter and food 
inside the mother’s body at first. It is otherwise with 



the fishes. In their case Nature has chosen the first 
method. The ova, which cannot save themselves from 
accident, are poured into the water, where fate decides 
whether any of them will ever reach maturity ; moreover, 
the little fishes that issue from them are exposed to all 
sorts of dangers at a time when the young mammals are 
safe inside the mother’s womb. Hence the fishes must 
produce enormous quantities of eggs. But the result is 
the same in the long run. Both the mammals and the 
fishes have the power of maintaining their kind. 

But when the maintenance of the species is secured 
in the case of the mammals by reducing the chances of 
destruction, the first method is excluded for them. The 
fishes may mature large numbers of ova within their 
bodies, but only on the understanding that the eggs 
are small. If each egg were to attain the size of a fish 
inside the mother’s body, the number of them would 
have to be very much restricted. Imagine a mother- 
hare with fifty young ones in her body ; though even 
this number is insignificant in comparison with the fishes. 
She would be entirely helpless, would immediately be 
devoured, and the capacity of great fertility would die 
with her. In particular, the young developing within 
her need food, and this would have to be derived from 
the blood of the mother, which is vitally necessary for 
her own maintenance. Finally, the division of the food 
amongst so many would mean less for each of the 
young, and therefore a weaker constitution ; they would 
be destroyed at once, and thus again the disposition 
to high fertility would perish. Think, for instance, 
of human twins, or of triplets. If such children were 



born and reared without proper aid and the control of a 
physician, they would hardly survive. 

Therefore, mammals cannot multiply more rapidly 
because the young developing in the womb need plenty 
of nourishment, and the supply is limited in proportion 
to the size of the mother. The maintenance of mammal 
species is secured by the sheltering of the offspring 
from danger, so that in spite of their small number, they 
can never be all destroyed ; the fishes or tape- worms are 
maintained by bringing forth an enormous quantity of 
eggs, so that, though they are helpless against danger, 
there is every prospect of enough being preserved out 
of so many to carry on the species. But why one 
method is chosen in one species, and the other in 
another, is a question that we will defer until a later 

Mammals are not only sheltered inside the mother’s 
body to begin with, but even for some time after birth 
the mother’s eye watches over them unceasingly. They 
do not need to exert their own strength yet in the severe 
struggle for life. They pass the first weeks of life in 
lively play . 1 

Play is the activity of the young animal ; it devotes 
its whole energy and feeling to it. But even after the 
animal has grown up, and the anxieties of life demand 
all its faculties, there are times when it remembers its 
youth, and indulges once more in play. It is the same 
with human beings. Cricket not only amuses the child, 
but also provides absorbing interest to adults ; and the 

1 The remarks which follow on the play of animals generally follow 
the ideas of Professor Groos, who deals thoroughly with the subject in 
his “ Play of Animals.” 



spirit of invention has devised many other kinds of 
games for man’s recreation after fatigue, and to give 
him pleasure. 

But is it true that recreation is the essence of play ? 
Will not the soldier, who has been following the most 
fatiguing exercises all day long, turn away from play, 
and prefer to refresh his tired frame with sleep ? At 
all events, he will not indulge in physical games. At 
the most he may join in a game of cards. 

We see from this instance that in many cases it is 
not the whole man, body and soul, that needs recreation, 
but only one of the two elements. The mathematician, 
who has been engaged all day in most exacting mental 
work, seeks to rest his tired brain in the evening. But 
during the whole of the day he has felt a twitching of 
the limbs ; his muscular energy has been resting and 
accumulating, and now impels him to bodily exercise. 
If, therefore, we want to understand the meaning of 
play, we must recognise the accumulation of energy as 
the first cause of it, rather than the craving for recrea- 
tion. This will become perfectly clear if we think of the 
games of children, which are the basis of all play. The 
child certainly does not play because it has a craving 
for recreation ; all its thoughts and actions have the 
character of play. Nor would it be more correct to 
say that puppies are seeking recreation when they run 
and tumble about the whole day long. 

It is, therefore, we now believe, an accumulation of 
energy that leads to play. Let us consider how this 
comes about in the case of man. 

The accumulation of energy in man is brought about 


by the multiplicity of his faculties. He does not need 
to use all his powers in the fight for his daily bread. 
One man gains his livelihood by manual labour — he 
is a mason, an iron-worker, or an acrobat ; another 
makes it by mental work — he may be a scholar or a poet. 
In others there is an alternation of the two kinds of 
activity, but one element always rests and accumulates 
energy ; and as the struggle for maintenance does not 
require this energy, a man turns to sham-work for an 
outlet for it. He will imitate real work : he will play . 1 

This manysidedness of faculties in the struggle for 
existence distinguishes all the higher animals from the 
lower. The energy of the lower animals is entirely 
absorbed in the search for food, the avoidance of 
enemies, and the preparations for reproduction. It is 
otherwise with the bird and the mammal. A successful 
raid in the morning will provide a family of foxes with 
food for the whole day, and they laugh at danger in 
front of their shelter. The warm sun falls on the furry 
coats of the sated animals ; the rest has strengthened 
their limbs ; and the body, with no serious demands on 
it, will, in the absence of real employment, make a 
pretence of it . 2 Instead of his real victim, the fox runs 
after his brothers and sisters. He plays. 

But is it really excess of energy that impels the young 

1 This theory, that the essence of play is excess of energy, was first 
expounded by Schiller in his letters “On the aesthetic education of 
man.” I regret that I have not space to reproduce the beautiful 
language of the poet. It is marvellous how many philosophical problems 
— problems that seem to be quite modern — Schiller has treated with 
felicity. Herbert Spencer has expanded his ideas on play. 

2 Spencer joined this idea of pretence or imitation .to Schiller’s 
theory of play. 



animal to play ? Will not even a tired puppy dart into 
the water after a piece of wood ? Are not kittens sent 
over and over again in pursuit of a rolling pebble? Is 
it really excess of energy that makes children play ? No. 
It is not excess of energy ; a very little energy suffices. 
Think of the scholar. He has worked hard all day 
with his mind, yet he sits down to play cards in the 
evening. Here he is devoting himself again to the 
most complicated logical reasoning for the sake of the 

How does the second principle stand? Is the game 
an imitation of real work, which man longs for, but has 
no occasion to do ? 

This idea also must be abandoned when we reflect 
again on the chief form of play — the play of young 
animals. They have no thought whatever of serious 
work ; how, then, can they feel a lack of it, and make 
a pretence of it ? The young squirrels running unceas- 
ingly up and down the tree, the young goats butting 
each other with their heads, and so on, are not making 
a pretence of doing real work, but are impelled by an 
irresistible impulse. All animals have their character- 
istic games even when they grow up in isolation, and so 
have never seen the real work of their species. A 
puppy that is early separated from its mother and 
reared artificially will seize and shake the hem of a 
coat in its characteristic way, just as a grown-up dog 
does with cats, in order to break their necks. 

We have at last found the nucleus of play. It is an 
impulse that caused it. Even in the games that imitate 
the work of the adult, it is an impulse that urges the 



young animal to imitate. The impulse of imitation is 
peculiarly strong in children and young animals. It is 
an impulse that their parents have in their young days, 
and have transmitted to their children. This impulse is 
the same thing as instinct. 

But are we justified in speaking of instinct in the 
higher animals, and even in man ? Are they not 
endowed with reason, and is it not this that controls 
their actions ? 1 

No. There are instinctive actions even in man. Pass 
your hand suddenly before the eye of another, and you 
will see the eyelid close immediately, without the 
other being conscious of it . 2 This closing of the eye- 
lid is called a reflex action, and if we seek to understand 
it we must first examine more closely the nerve-tracks 
in the body. 

There are two kinds of nerves. The first group is 
called the sensory nerves ; these are they that pass from 
the skin to the brain (and spinal cord), and conduct 
thereto every touch from without, every twinge of pain, 
and every impression made on the senses. When the 
brain has received the impression in this way, it 
telegraphs back to the spot whence the message came. 
For this it uses the motor nerves, which pass from the 
brain to the external surface and the muscles of the 

1 Buchner and Brehm attack the idea of instinct generally, but it is 
the old idea of Descartes which assigned reason to man alone, and 
only credited animals with instinct. They both entirely forget that 
there may be other meanings of instinct. Groos draws attention to 

8 In what follows I pass over the various theories of instinct, and only 
jive the one that has been most accepted of late. This is the theory 
of Weismann, and much the most probable. 



body. The proper movement is brought about in this 
way. In our example the wave of the hand would be 
the sense-impression ; this would be conducted by the 
sensory nerves to the brain, and from here the closing 
of the eyelid would be brought about by means of 
the motor nerves. 

But the reflex action does not always consist of a 
single movement ; often many follow upon a single 
impression, and one of these brings about the other. 
This is the case, for instance, when we trip over a stone. 
The shock to the foot is followed by a whole series 
of movements — a stretching of the arms, a throwing 
back of the upper part of the body, and several quick 
movements of the legs. 

Here we have reached the transition to instincts; 
these also are characterised by the fact of a number of 
movements following upon sense - impression. It is, 
therefore, only a complicated reflex action when a 
young, untaught kitten springs instinctively after a 
mouse as soon as it sees it. 

Thus the basis of both reflex and instinctive actions 
is corporeal, and is found in the nerve-tracks. And as 
all the organs of the body can be affected by natural 
selection, it can also bring about changes in the 
connections of these tracks and can increase the 
sensitiveness of the nerves. When we thus discover 
the material groundwork of natural selection, it becomes 
clear that instincts are subject to it, and modified by it, 
and that new ones may be brought into existence by it. 

Anyone who tries to catch a fly with his hand will 
see that the little creature is generally off before the 



hand touches it. Its flight is purely instinctive ; there 
cannot be any question of experience, as even the fly 
that has just issued from the pupa will act in the same 
way. How has this instinct to fly attained such a 
perfection ? Most certainly by natural selection, since 
those flies survived longest that had it in the highest 
degree. Instincts are one of the requisites of an animal’s 
life, and they are therefore subject to natural selection. 

The life of the lower animals is regulated by instincts. 
How complicated these are will be seen when we come 
to deal with insects. But, clearly, natural selection 
must often favour instinctive action in the higher 
animals as well. When the murderous face of the fox 
suddenly appears before the resting hare, there is not 
much time for reflection ; the best thing for the hare to 
do is to spring aside instinctively and make off. But 
does the instinct go any farther? Is the hare’s running 
away also instinctive, and would that be best for the 
hare? Here we must answer no. In running it is 
obviously advisable for the animal to reflect. The 
hare will fly, double, or drop, according to the distance 
of its pursuer ; and this control of the instinct of flight 
by the intelligence will certainly be a great advantage 
to the animal, so that the development of intelligence is 
favoured by natural selection. 

Intelligence does more than instinct; it protects the 
animal even in unforeseen dangers. If you put a 
mole-cricket on a glass plate its instinct makes it try 
to bury itself. Intelligence would tell it after a few 
attempts that it is impossible to scratch up glass, and 
that flight is the better course in such circumstances. 



But would not those animals be in the best position 
that had intelligence and instinct highly developed? 
Will not an animal that makes instinctively for its prey 
the moment it sees it, secure its object more speedily 
and certainly than another that has to reflect on its 
course of action ? 

It is true that instincts in connection with food and 
escape might be so perfectly developed in mammals 
that they would act with absolute precision when they 
were needed. There are wasps that perform the most 
complicated actions in laying their eggs, yet these are 
all purely instinctive, as we shall see in the sixth 
chapter. But instincts like these require the most 
intricate nerve-tracks. 

Let us consider the complicated fashion in which 
mammals seize their prey. Who has not seen how a 
cat, at the sight of a mouse, steals forward, springs, 
thrusts out its paw, seizes its victim, shakes it, and 
finally devours it ? What elaborate nerve-tracks would 
be required in it, if all this were instinctive ! yet there 
are still other habits of the cat. In a word, we see that 
if the complicated life of the mammals were effected 
solely by instincts, the demands on the nervous system 
would be so great as to leave hardly any room for 

We have only the two alternatives : either an 

advanced intelligence or perfect instincts. In the 
mammals it is the former that steadily advances, since, 
as we saw, it can do more than instinct. We might 
even say that the more sagacious animals are, the more 
retrograde are their instincts ; and they are most 



backward of all in man. In the human species the 
most intelligent races have the least developed instincts. 

It is true in all our mammals the intelligence is so far 
advanced that their food and flight-instincts can only 
be in an imperfect condition. But if the alimentary 
instinct is only rudimentary in a mammal, if the whole 
of the mechanism that serves for seizing the victim is 
only feebly developed, how can the animal capture its 
prey from the very beginning? A cat that sees a 
mouse for the first time, and has no instinct to tell it 
how to catch the creature, will certainly not be able to 
do so if it has had no experience in catching mice. 
Now we come to the solution of the problem. In the 
lower animals actions are regulated by instincts, which 
work faultlessly from the very first, according to their 
nature. In the higher animals the instincts are feebly 
developed, and the actions are regulated by intelligence. 
But the intelligence must be trained, like the powers of 
movement. For this a certain period is necessary in 
which every unsuccessful act will not endanger the life. 
This is the period of youth. 

The instincts make their appearance, though im- 
perfectly, in youth ; that is to say, at a time when the 
animal has as yet no serious need of them. During 
this period the animal can improve the inherited, 
imperfect impulses by its own experience ; and if it is 
taken away from the mother and her direction, it knows 
how to catch its prey and protect itself, and will acquire 
in time the requisite adroitness. 

Now, this exercise and training of the faculties takes 
place in the play of the young. We can, therefore, 


7 1 

realise the immense importance of play. It is the 
school in which the animal learns to play its part in the 
struggle for life. Without these early gambols the 
animal would be clumsy and stupid when it leaves its 
mother, and would be quite unfit to meet the stress of 
life. The animal must play, and must therefore pass 
through a period of youth. Thus we are now in a 
position to say that the play is not there because of the 
youth, but that a period of sheltered youth has been 
provided by Nature for the purpose of play. 

Play is, therefore, absolutely necessary for the young 
animal. And in order that it may play often, a feeling 
of pleasure has to be attached to the exercise. It is 
true that the first impulse to play comes from instinct, 
which urges the animal to stir itself, especially in 
directions that have some relation to later life ; and we 
have already seen that the instincts of play are im- 
perfectly developed instincts of food-getting, flight, etc., 
which must appear in youth and afford the little one a 
means of acquiring the bodily adroitness that it needs. 
The exercise of every instinct is pleasant in itself, still 
we may legitimately speak of the lust for food, for 
fighting, and even for murder, and make use of the 
phrase, “to satisfy one’s impulses.” Nevertheless it is 
clear that this feeling is much strengthened in play. It 
is quite certain that even the most incorrigible brawler 
does not feel as much pleasure in his serious fighting 
as boys do in their romping. This is even clearer if we 
take instincts the serious use of which is never agreeable, 
such as flight from an enemy. With what pleasure 
children, and even young animals, chase each other 



about ! In fact, there is one experience that shows 
clearly that the animal feels most pleasure in the very 
form of play which will be of most importance to it 
when it becomes reality. The harmless doe is hunted 
throughout its whole life ; yet when these animals play 
together, we notice that the pursued puts his whole soul 
into it while the chaser is very little interested. It is 
just the opposite with the carnivores. With these the 
chaser is the more spirited. He tastes the whole joy 
of hunting, and in fact, the chase will be the chief 
purpose of his existence in real life. 

What is it, then, that affords the young animal so 
much pleasure in play? Not only the young, in fact, 
but even the adult, which is often seen to play. What 
is the nature of the delightful feeling that play engenders? 

It consists, in the first place, of the pleasure that is 
felt in all energetic action. Then, it is certainly pleasant 
to see that one can do something — that one has power. 
In play a man delights to feel that he is “doing some- 
thing.” It is from this feeling that the pup is so ready 
to tear up boots and other objects ; that the cat rolls 
its ball ; that little birds, and often little children, set 
up prolonged cries, and take considerable pleasure in 

It is, further, the sense of overcoming difficulties that 
adds to the pleasure of play. Swinging, tobogganing, 
sliding down smooth surfaces, etc., which children are 
so fond of, is a sort of escape from the gravitation of 
the earth, and from the friction that makes all movement 
difficult. All these movements fill us with a peculiar 
sense of freedom. 



But play is most advanced in character when the 
playing animal is conscious of its pretended activity ; 
when it knows it is only playing a part. Play is in 
itself only a pretence, since there is no serious occasion 
for the exercise of the instinct. We have to learn next, 
therefore, if the animal knows that it is only making 

This cannot be seriously questioned. Every dog 
that pretends to bite its companions or master knows 
that it is playing. We could give many such instances. 
Remember, too, how animals can dissemble : how a dog 
that has broken something will pretend to be engrossed 
in some action or other, with the most innocent face in 
the world. In this consciousness of pretence we have 
imagination , or the faculty of taking to be real something 
that only exists in idea. In play, therefore, we have a 
conscious self-deception. 

Here we find ourselves at the threshold of art, and 
it will not be without interest to take a peep into this 

In art we have a conscious self-deception, and play 
and art are intimately connected, as the very words 
“ playing the piano,” “playing a drama,” etc., indicate. 
The impulse to play is the real source of artistic 
activity both in primitive races and in children. Thus 
the animal is brought to the very verge of artistic pro- 
duction by its delight in pretence. It does not cross the 
threshold ; because for real artistic creation the aim to 
influence others by one’s make-believe is necessary. 
This purpose is not present in normal play. 

The conscious self-deception in play and art is due to 


a peculiar division of consciousness. Both man and the 
animal know, when they are playing, that it is a pretence, 
yet lend themselves to it. We find in other matters a 
similar division of consciousness, especially in dreams. 
Here we often give ourselves up to the most fantastic 
pictures, yet the consciousness of the awakened man 
often breaks into them, and recognises they are not 
realities. I have often had dreams in which I was 
chased by enemies that gained more and more on me. 
But instead of feeling pain and anxiety I am assured by 
a clear consciousness that it is all a dream, and I sink 
peacefully into my dream again, and see my enemies 
approaching to kill me. I wonder with interest what 
the moment of death will be like, and await the experi- 
ment calmly, saying to myself that my life will not really 
come to an end in it. 

There is a similar duplication of consciousness in 
play and the enjoyment of art. We are often quite 
absorbed in a drama we are witnessing, and only 
brought back to our real selves from time to time 
by consciousness. We have the same experience in 
examining paintings and sculpture. A sort of false 
self is formed in us, full of false feeling, and our 
real self sinks into the background. Yet we retain 
a sense of reality, a real pleasure in the unreal ; but 
it passes into the sphere of the pseudo-self, and lets 
itself be borne by that. 

But why do we never confuse pretence and reality 
in play and in art? Must not our real self recognise 
that the pseudo-self is only a make-believe? 

Our real self knows, or we ourselves know, that 



we are the cause of the phantasm. In this we find 
the highest pleasure of play and art. The projecting 
ourselves into the unreal is voluntary on our part, 
and this feeling of our freedom accompanies us, often 
unconsciously, as long as we indulge in the fiction. 
The reality, on the contrary, presses itself on us 
even against our will ; it gives us a feeling of 

Thus it is the sense of freedom that accounts for 
the highest form of pleasure in play and in art. This 
sense of freedom gives its peculiar colour to the 
world of fancy, and consequently “in conscious play 
the whole pretence of action is converted by the 
accompanying sense of freedom into something higher, 
finer, and lighter, which we cannot confuse with the 
reality of things.” 

In play we feel ourselves really free. We do just 
what we wish to do, and we know that we can halt 
and abandon the play at any moment we desire. 
We do not feel ourselves to be a link in the pitiless 
chain of cause and effect ; we seem to have escaped 
from inexorable necessity. 

All these feelings are found in a rudimentary state 
in the playing animal. Now that we have learned 
the cause and the meaning of play, we will recall the 
chief forms of the play of animals. 

The animal plays on the first day of its existence. 
The stretching of its limbs, the gnawing of objects, 
the rolling about, are nothing but play, with the object 
of teaching the young one to gain control of its own 
body. And the young animal not only learns to master 


itself in play, but also to control its environment. 
It learns to appreciate distances, for instance; we see 
the same in our infants who have to learn gradually 
that the moon, towards which they reach out their 
little hands, is unattainable. It has even been said 
that a human infant learns as much in its first year 
as in all the others put together ; hence the impor- 
tance of this “experimental play.” In this play the 
psychological factor is the joy of “ doing something ” ; 
this is seen most clearly in the destructive tendency 
of young animals, and in their delight in making a noise. 

When the suppleness of the little one increases, and it 
has learned to control its own frame, the play of move- 
ment begins. These serve to give the animal the 

mobility that it will need in the struggle for life. 
Naturally, in this play the particular movements will be 
practised which the animal will find useful later on. 
The squirrel leaps into the air with the most break-neck 
springs ; the marten is equally bent on testing its leaping 
powers. Aquatic animals practise swimming ; animals 
that live in the air take to flying. Even the buck- 
jumping of the kid, which seems to be mere reckless 
delight, has its meaning. On the level ground these 
leaps are puzzling enough ; but on the mountain, the real 
home of the goat, it is quite indispensable for reaching 
the higher rocks. 

With the play of movement is connected the pretence 
of hunting. The carnivores practise this in order to 
creep up to and capture their prey ; and the plant-eaters 
must learn to escape them. Thus the kitten plays with 
the mouse, and learns, by a method that is repulsive to 



us, the way its victim runs, so that it can catch them 
itself when they run free before it, and the mother is not 
present to paralyse them. Deer chase each other for 
hours, and so learn to escape when there is serious 
occasion ; young foxes catch each other and duck to 
avoid each other in front of the den, just as they will do 
afterwards with the unsuspecting hare. 

Then come the fighting-games of the young male. 
These have to make the animals strong and supple, in 
order to beat their rivals in the love-conflict later on. 
The joyous feeling of strength and power may lead in 
this to a frightful mauling of the weaker. 

As we saw, the first impulse to all these games comes 
from instinct. But there is another element that may 
cause the animals to play — the passion for imitating. 
This also is an instinct. We see this at once when we 
look to the fact that every animal confines its imitation 
to its own species. The young fox never tries to imitate 
the bird in flying, but imitates its mother in trying to 
capture it. We might draw up a special category of 
“imitation-games.” In these the young show what they 
can do ; they delight in showing that “ they can do it 
also,” and strive “to do it better.” 

The passion for imitation is an impulse that has 
arisen and is fostered by natural selection, like every 
other instinct. It leads the animal to learn quickly 
what it will need in later life, and so to make experi- 
ments on its own account. A flock of game will escape 
easier if it follows unhesitatingly a leader that has 
scented an enemy, than if each has first to convince 
itself that flight is necessary. 


There is another matter of great importance to animals, 
and must be practised in youth — attention. 

This is indispensable for every animal. How could 
an inattentive animal escape its enemy, or how would 
a carnivore discover and catch its prey without this 
quality ! The cat watches with the most strained 
attention before the mouse - hole. It sits crouched 
waiting for the appearance of its victim, all its muscles 
ready for the unfailing spring and the joint stroke ot 
the paws. 

When there is no serious occasion for attention, 
and it is practised in play, as it were, we call it 
“curiosity.” We see this often enough in animals. 
The essence of it is that the animal sees a strange 
object, and wants to learn what it is. Often enough 
an excessive curiosity leads to the death of the 
observer ; it is well known that one can frequently 
draw quite close to a marten on a tree and shoot it 
without it making an attempt to escape, owing to 
its curiosity at the unusual appearance. Generally, 
however, curiosity is an impulse of great service to 
an animal. It is from curiosity that the young animal 
familiarises itself with its environment, and learns 
to distinguish between what is good and what is 

We might instance quite a number of other kinds 
of play, but will bring the discussion to a close. We 
have, in particular, made no mention of a whole large 
division — love-play. This, however, is not properly 

play, because it does not serve for the animal to 
practise some serious future activity, but is a serious 



activity itself; it is only the psychological factor, the 
joy of power, that often makes its appearance in it, 
that justifies one in speaking of it as a species of 
play. We shall see something about its nature in 
the next chapter. 

In pursuing at such length these observations on 
the play of animals, and taking our cue sometimes 
from the life of man, we have not passed the limits 
of this work. We have learned that many qualities 
of mind that seem to belong to man alone are also 
found in the animal. This shows us how untenable 
is the opinion of those who think they have found 
in man’s mental powers something that distinguishes 
the lord of creation essentially from other organisms 
— something that makes the descent of man from 
other animals impossible. We now know that the 
theory of evolution need not stop short at man ; that 
even his mind is no obstacle to our admitting his 
development from animal ancestors. The mind of 
man does not differ from that of other animals in 
kind but only in degree, and there is nothing to 
prevent us from supposing that it has been raised 
from the animal level by natural selection to its 
present altitude. Just as Copernicus smote the 
conceited belief out of humanity that their kingdom, the 
earth, was the centre of the world, so Darwin has 
put an end to their assumption that they occupy an 
exceptional position on our planet. The earth is a 
stage of a part of the eternal, everchanging world-mass ; 
humanity is a phase of a part of the ever-advancing 
world of organic life. 



Sexual selection. Choice of females. Rejection of the hypothesis. 
Advance of the male’s senses. Selection of the strongest suitor. 
Explanation of coyness and the animal coquette. Female 
selection inadmissible. The love - dance. Selection of the 
apparent strongest. Colours as means of distinguishing species. 
Use of sounds. Pairing - calls. Origin and forms of song. 
Instrumental music of the birds. Migration. Speed of flight. Do 
birds tire ? The adaptations of the bird-body. Height of the 
migration - flight. Origin of birds of passage. Their strength, 
their power of presentiment. Routes of migrating birds. Their 
memory and sense of direction. Travelling in flocks. 

The poets have often introduced the song of the 
bird — as Shelley did — amongst their throbbing lines 
over the destiny of men. It is natural that the poets 
should love the birds. From the bird the art that man 
must slowly learn seems to pour out in rich, inex- 
haustible flood. The woods and the meadows are 
enlivened by the songs of the birds. Where would 
the magic of spring be if there were no singers to 
proclaim its glory to us ? 

We often read in books of travel in distant lands 
that all the splendour of the tropics only awakes a 
longing for our own forests because there is no sweet 
song in the glittering birds that complete the fair 
picture of Nature. Even in Japan, where noble forests 


8 I 

grow like those of Europe, the traveller seems to find 
something wanting. For a long time he cannot tell 
what it is, until at last it dawns on him that it is the 
stirring song of our birds. 1 

But it is not the song alone that makes us love the 
birds. To know a bird’s nest and watch daily the care 
of the parents for their helpless young is a source of 
purest joy to our children. The birds are not far 
removed from children, and resemble them especially 
in their liveliness and their unfailing spirits. They 
seem not only to understand art, but to have also the 
nature of the artist. 

Hence it is that painters feel themselves akin to the 
birds. A man died in Heligoland in 1897 who had 
seen the island for the first time as an artist of twenty- 
three, and was so enchanted with the bird-life circling 
high above, that he devoted himself entirely to the 
study of birds. We shall have much to say of this 
Heinrich Gatke by-and-by. 

But is not that which gives us pleasure likely to 
prove dangerous to the birds themselves? It is true 
that the inhabitants of the air are secured from many 
enemies by their rapid flight and their great agility. 
But does not their song bring them to the notice of 
marauders ? We know that many birds have light 
shades of colour, and these are conspicuous against the 
background, and must betray their possessor from afar. 
How could such a shade be brought about by natural 
selection ? And when we see that, as a rule, only the 
males are brightly coloured, we have a new problem. 

So I have heard from many who have travelled in Japan. 


How could natural selection lead to a different colouring 
of the two sexes ? 

Darwin put these questions long ago, and as an 
answer to them he framed his theory of sexual 
selection as the second great agency in the formation 
of species. We shall understand this best if we compare 
it with natural selection. 

Both by natural and sexual selection certain animals 
have a better prospect than others of leaving offspring 
and so preserving their species in the next generation. 
In the one case it is those animals that have been 
able to escape destruction longest, thus reaching the 
period of reproduction, while the others die off before 
it comes. In the second case it is the males (sexual 
selection affects only the one sex) that attain to union 
with a female, as many of them can never reach love, 
and therefore never reproduce. Natural selection, 
therefore, determines which animals will reach the 
period of reproduction ; and among the selected males 
sexual selection then chooses those that are actually 
to reproduce. In the one case the “bad” are 
destroyed ; in the other case they are condemned 
to sterility. In both cases their kind perishes with 

Thus in natural and sexual selection a few are 
chosen out of a large number of animals. This is 
possible for natural selection because more animals 
are produced than can live ; in sexual selection also 
choice is only possible if the males are so numerous 
that there are not enough females for all, and some 
must go without. As a fact, we do find this pre- 



ponderance of males in Nature , even man is no 
exception to the rule, because there are more boys 
born than girls every year. If the females are in 
the majority in later life, that is because the males 
are at all periods of life exposed to a higher mortality . 1 

Which males, then, are selected ? 

According to Darwin, there is a double struggle 
for the opportunity to reproduce. In the first the 
males fight actively for the possession of the females ; 
the stronger drive away the weaker, the better armed 
conquer the weaponless. In this way, for instance, 
the cock’s spurs and the stag’s antlers would be 
explained by selection. In the second form of selection 
the males are chosen by the females. These are 
supposed not to listen to every suitor, but to choose 
the one that pleases them most. Thus the bullfinches, 
for instance, may once have been the same colour 
in both sexes. Then variations occurred in the males, 
which showed a shade of red in the breast. This 
pleased the females, and the continuous selection of 
the redder ones led to the endowment of the male 
bullfinches with the bright red breast they now have. 

The first kind of sexual selection is based on well- 
known facts, and has never been seriously called 
into question from the Darwinian side ; it is really 
a special case of natural selection. But the second 
category has a number of opponents, among whom 
we find the distinguished naturalist, Dr. A. R. Wallace. 

1 In later years the unhealthy life led by men is to blame for this, 
monotonous labour without regard to the body, and the use of alcohol 
and tobacco. 



This is intelligible enough. Compare this kind of 
sexual selection with natural selection. In the latter 
the idea that there must be selection starts from a 
fact. In the theory, for instance, that the white hares 
have been developed from darker ones by natural 
selection, the fact we start from is that white hares 
show less against the snow than dark ones ; from this 
we are justified in concluding that the lighter the hares 
were, the better their chance of escaping the notice of 
their enemies. But the man who infers from the fact 
that our actual bullfinches have a red breast, that the 
female had from the first a preference for red, and was 
pleased with the increase of colour, is building his theory, 
not on a well-known fact, but on a hypothesis once more. 
Our explanation is simple enough, if we say : The bull- 
finch has a red breast, and consequently the females 
must have always had a preference for red, while the 
blue-throated warblers had a preference for blue. But 
the inference is not scientific, or at least not until we 
have explained why the bullfinch prefers red and other 
animals other colours ; and this we cannot do. 

Could we not say that the bullfinch got its red 
variation by chance, and that it was not exactly the 
colour, but “ the stimulus of novelty,” that acted on the 
females ? But we must not extend this principle, which 
we only know in the life of human beings, to animals, 
especially to those only where we find it convenient. 
The breast of the male bullfinch, which is supposed to 
have been grey, must have shown tendencies to all 
kinds of colours, and if the novelty was appreciated by 
the females, one would have chosen one colour, another 


a different one. There would not have been a develop- 
ment of the colour of the breast in one steady direction, 
namely, towards a bright red. If we suppose that only 
one special novelty pleased, and gave equal pleasure to 
all the females, we are doing violence to Nature. We 
must first show that this novelty pleases the female, and 
why it does so. 

We see, then, that this second kind of sexual selection 
is not satisfactory. How, in that case, can we explain 
the peculiar characters of the male ? What was the 
origin of the brighter colours, the specially developed 
feathers, dances, songs, and perfumes, of the males, in all 
classes of animals ? Can we not give a satisfactory 
explanation of some of them ? We shall see. 

But must we reject altogether this choice on the part 
of the females? Is it not blind chance that brings any 
male to a female and provides it with the fruit of love ? 

No, certainly not. It is not chance that brings the 
male to the object of its love. It seeks it of itself. 
But it is clear that the males which detect the females 
soonest will attain their purpose first, and that those 
with inferior organs of detection will come too late, and 
lose the reward. Thus we see at once that there is a 
sexual selection which falls into the first category of 
that group, and enables us to understand how the males 
of many animals have better sight, hearing, and smell, 
than the females. These organs must, of course, have 
been formed and developed by natural selection, since 
the animals need them for vital purposes ; but sexual 
selection will improve them, as it comes after natural 
i selection and is more exacting. It is, for instance, 



certainly more difficult for a cockchafer to discover 
a female of its own kind than the masses of food about 
it. We understand at once, therefore, why, as a fact, 
the male cockchafer has a finer scent than the female, 
and why he has special olfactory organs on his antennae 
which can be seen externally from their comb-shape. 
We find similar structures in other insects, especially 
several species of butterflies, and in small crabs 
in fact, they are common in the animal world. 
Other sense - organs also have been enhanced in the 
male sex clearly by the same process of sexual selection. 
Many male insects have much larger eyes than their 
females, such as the May-flies and the male bees, the 
drones. We can see the meaning of the large eyes in 
the forehead of the latter. Of the many drones that 
follow the one queen in its nuptial flight, one will be 
particularly favoured in being able to follow the form of 
the queen as she floats in the blue air, and so catches it. 

But it often happens that the males lose the fruit of 
love when they have tracked the female. When other 
suitors come on the scene they will hardly withdraw 
resignedly when they see the place occupied ; they 
will try to make good their lateness by force, and drive 
away their rivals. A struggle of this kind for the 
female often takes place, and the victory naturally goes 
to the strongest and cleverest. On this principle the 
stronger males are again selected, and thus we can see 
why the black-cock or the common cock is so much 
stronger than the hen. In fact, this kind of selection 
may lead to the formation of “weapons,” such as the 
cock’s spurs or the stag’s horns. In the latter case 



the animals with the hardest skulls would win at first, 
and an ever-increasing horn may have been developed 
from the growths on the bones of the head which were 
casually produced by the butting. However it may be 
with these special cases, there is nothing to be said 
against the general principle. 

We have, therefore, given a natural and satisfactory 
explanation of part of the masculine characteristics. 
What are we to do with the rest ? 

The black-cock becomes so intoxicated with its dance 
on the branch of a tree that, though usually so timid, 
it cannot perceive the approach of its enemies. This 
dancing - instinct cannot be due to natural selection, it 
is obvious, since it is injurious to the animal. But 
sexual selection may at least have produced it in the 
beginning, and then the second principle would come 
into effect. The pairing of the cock has reached such 
a pitch because the hen always gave the preference to 
the best dancer. 

As we have rejected this theory, must we despair of 
giving a scientific explanation of the love-dance. 

There are experts who will not admit a conscious 
choice on the part of the females, but have sought to 
replace it by unconscious preference ; in the sense that 
each female would yield itself to the male by which it 
was most stimulated. This stimulation would take the 
form of an enchantment or hypnotism, whether it was 
caused by the beguiling song or the dazzling splendour 
of the male bird. The female would, in a sense, lose 
consciousness from the enchantment, and its resistance 
to the caresses of the male would be broken. 



But why does the female sex show resistance at all 
to love, which ought to be urged with all its force by 
Nature as the great maintainer of life? The desire for 
love is so irresistibly implanted in every living thing 
that a curb is absolutely necessary. It will be easily 
understood that too frequent caresses on the part of the 
male will not serve their purpose, namely to create 
progeny, but will enfeeble the female, and so be 
dangerous to the offspring. Hence Nature has raised a 
barrier to the onrush of the male sex, and this is the 
coyness of the female. When there is a conflict of the 
two powerful instincts, coyness and desire, we describe 
the female as “coquetting.” 

The male has to overcome the coyness of the female, 
and for this the colours, perfume, dance, and song are 
useful to him ; by the improvement of one or other of 
these features a male will be able to ensnare the female 
more quickly than his less brilliant fellows. Among the 
variations that appeared in the male there were some 
that chanced to stimulate the love of the female. In 
this sense the “ choice on the part of the female” can be 
be better understood, yet it is not an explanation. It 
remains a mystery why just this one among many 
variations should affect the female — should affect all 
females, in fact. Further, we do not see how it could 
happen that the character in question should be 
developed steadily in a particular direction by the 
female’s choice. Is it not just as if the female had 
before its mind from the first the image of the complete 
male ornamentation, so that, when the first traces 
appeared, she helped it along, and only looked to 



ornament in the sense of giving the preference to the 
males that came nearest to her ideal ? As a matter 
of fact we should, on this theory, have to suppose that 
the female felt from the first — consciously or uncon- 
sciously — an impulse to a certain end. This end was 
the male ornamentation in its full development, and 
it would be at length attained by the steady preference 
of males that come nearest to the ideal. This 
explanation seems arbitrary and unscientific, because 
neither experience nor science tells us anything of this 
mysterious working for a fixed aim ; and we shall see 
in the eleventh chapter that it must be rejected 

We must seek another explanation of the dance and 
song and colouring. Let us deal first with the 

Is the charming of the black-cock really a means of 
breaking down the coyness of the female? If it were, 
we should have to assume that the cock must convince 
itself during or after the dance that its art has been 
effective ; and above all, we should have to suppose that 
the hen is brought by the dance to look on him with 
a sort of enchantment. As a matter of fact, we see 
nothing of the kind. The females seem to be quite 
indifferent ; in fact, in this particular case of the black- 
cock, they are not very near to the male, and he has 
to pursue them for some distance after the dance. 
Then there is the peacock, whose tail is so much 
admired by human beings ; his females seem to be 
quite unmoved by it, and go on picking up their food 
trivially, however fine he may look. Has anyone ever 



seen a turkey-hen enchanted by the tail and comb of its 
mate ? I do not think so. 

In the case of the turkey, in fact, the idea forces itself 
on us that the male does not dance for the pleasure of 
his wives, but from anger and fighting spirit. The 
inflated, red-combed cock “ dances ” before human 
beings and dogs as well as before his hen. 

I believe that we have here the key to all these 
“courtship-phenomena.” They are connected with the 
fights of the males, and must be explained as serving to 
frighten away rivals. In the first place, it is quite clear 
that double courtship of a female need not always lead 
to fighting. If a male on the quest of love finds a rival 
before him that seems so savage and powerful that he 
himself would probably come off second, he will 
generally not fight, but retire into the background and 
look for satisfaction elsewhere. 

But it is obviously not necessary that every fearsome- 
looking male is particularly strong in point of fact ; 
it is enough that he should seem to be so, as the 
rivals are then not likely to put it to the test. Means 
of frightening others away are not uncommon in the 
animal world. A hunted cat makes its fur stand out so 
as to seem bigger than it is. We can, in fact, readily 
believe that the manes of many animals, such as the 
stag, are intended to make the neck seem bigger and 
stronger, and so may have been brought about by this 
sort of sexual selection . 1 

1 Weismann thinks that the lion’s mane is due to the fact that, in 
the fights of the males, those had the advantage whose necks were 
protected by thicker hair from the teeth of their opponents. This 
theory is unsatisfactory. There are many animals with manes that do 



In the formation of the antlers of the stag it is 
probable that the fearsomeness played a more important 
part than the improvement of them as weapons. It is 
clear that the larger the antlers the more formidable the 
animal looks. As weapons two sharp spikes on the 
head would be more effective, as we see in certain deer 
which have such spikes, and bring down every 
opponent, even the most powerful sixteen-pointers. 

Now let us go a step further. Rival suitors are 
driven away not only by an appearance of strength, but 
by confidence of approach. Who has not seen many a 
little dog frighten away a big cur by attacking boldly ? 
Even a man is intimidated by the self-conscious bearing 
of another. It will be found throughout the whole 
animal world that a reckless onslaught intimidates an 

A male that has stolen a female and shows by his 
manner that it is not advisable to fight with him will 
be avoided. He will show this by inflating himself, 
uttering terrific cries and running about. Do we not 
see this in the turkey-cock? Is it not clear to any 
unprejudiced observer that his capering is a roar-dance ? 
Do the red -skin braves perform their war-dance to 

not bite each other when they fight, such as the stag. My theory, on 
the other hand, meets these cases as well. We might also regard as 
means of frightening combative rivals the knobs on the face of the 
wart-hog, the beards that give a savage appearance to the faces of 
many apes, the two teeth that come through the upper lip of the boar, 
and are useless in fighting because they bend downwards, the antler- 
shaped tentacles of the stag-beetle, which can pinch much less than 
the smaller tentacles of the female, and many other kinds of beetles’ 
tentacles ; possibly also the chirp of the male cricket, and other 



enchant their squaws ? Certainly not. They want to 
strike terror into a lurking foe, and they intoxicate 
themselves with their own power. The latter is the 
psychological element that enters into the dances of 
animals, and sets them to “games.” As a fact, 
means of frightening and intimidating play a great part 
in all fights. Think of the war-cry of the Indians, our 
own “ Hurrah,” the terrific painting of the skins of 
savages, and the military moustache. It was this that 
gave the French warriors their fierce appearance in the 
later Middle Ages, and played a great part in the 
Thirty Years’ War. It does really give a fiercer 
expression to the face, because it draws up the lips at 
the corners of the mouth, over the canine teeth ; and, 
to compare human with animal features, we may recall 
the projecting teeth that were also used for intimidation. 
The martial moustache has been retained in the daring 
Hungarian cavalry. But however it may suit soldiers, 
it does not become the civilian, in whom it forms a 
ridiculous contrast to the otherwise modest and funereal 

In the instances we have given, therefore, it is a 
question of selection of the apparently stronger. I 
believe that this explains the origin of a good many 
masculine characteristics. It may be asked how far my 
theory is supported by observation. Certainly, many 
facts can be quoted in favour of it, such as the well- 
known one that a young black-cock dances very gently 
and stealthily when an older one is about. 

An intimidating conduct on the part of the male will 
have an effect on the female ; it will not only keep away 



other suitors, but will hold the females together. It is 
well known that a stag, or even a cock, treats its 
dependents roughly, and will not let them break loose. 
If, then, a male terrifies the female by its appearance 
and conduct, the latter will be less likely to wander away 
after forbidden fruit, and will not venture to make too 
much resistance to the allurements of the male. Unfor- 
tunately, many animals take Nietzsche’s “ little truth 
to heart: “You are going to the women? Do not 
forget the whip.” Everyone who has had occasion to 
observe the love-making of animals in a zoological 
garden will have noticed that it is more frequently a 
question of being bullied, than of listening tenderly to 
the wishes of the male. In fact, amongst human beings 
it is chiefly the strength that conquers women ; not 
merely strength of body, but the power of thought, of 
mind and will — in a word, the strength of the whole 
masculine nature. But in the case of man it is usually 
a question of choice on the part of the women, and we 
must exclude this element in dealing with the animals, 
and recognise force alone ; whether this is used actively 
for the coercion of the female, or her resistance is broken 
down by the mere perception of it. 

Can we explain all the masculine characteristics in 
this way? Unfortunately, we must admit that we 
cannot. Colours present the greatest difficulty. Many 
colours, of course, may be for the purpose of scaring 
away rivals, such as the red spot over the eye of many 
wild-cocks, which gives it a fierce expression and makes 
it look larger. In the case of man the masculine dress 
at all times is thought to have had its origin in the 



military dress of the particular period ; and this was 
certainly not meant to be merely defensive, but also to 
make the wearer seem formidable — as, for instance, 
skins with animal helmets, waving plumes, etc., or at all 
events to give him a greater appearance of strength and 
life and boldness, in which bright colours would be 
useful. But it is impossible for all the details of the 
composition and design of animal colours to have arisen 
in this way. It is also inadequate to explain the 
undoubted fact that they act as distinguishing characters 
of a species. As such they play a great part in the life 
of animals ; it is easy to see that those animals will 
propagate best which can recognise their kind most 
quickly. Perhaps many light colours arose in this way, 
and they could be preserved and accentuated in the 
male, but not in the female, which absolutely needs a 
neutral tint in order to sit unobserved in the neutral- 
tinted nest or on the ground. Only in this way could 
the mother and her eggs, and later the helpless young 
ones, escape the fatal eye of their enemies. The eggs 
of birds that hatch on open nests are also protected by 
fitting colours that save them from many eyes ; while 
birds that sit in hollows generally have white eggs. 
There is an exception in a number of blue eggs that are 
found in open nests. An attempt has been made 
recently to explain their colour on the theory that the 
blue is particularly favourable to metabolism. 

There are many features that are common to both 
sexes. These are usually confined to particular spots, 
and can do no injury to the animal when it sits quietly. 
In this group we have a whole series of colours that 



are found in the wing-feathers of birds, and are only 
exposed during flight. It is the same with colours 
in the tail, which only meet the eye when it is spread. 

Brighter colours are, as a rule, not found on the 
upper parts of females, but may be developed in the 
male; because even if they carry destruction to many 
of them, the species is in no danger, as the males 
are always in excess. 

But, it will be asked, how can peculiarities of 
colouring serve as marks of the species, when these 
generally act at a distance ? How, for instance, can we 
explain the eyes in the peacock’s tail ? The explanation 
given above seems to fail here ; and as we have 
rejected that form of sexual selection according to 
which “the finest eyes” charm the females most, we 
must find a better explanation. 

We have seen that it is very important for all 
animals to have specific characters, so that the sexes 
may easily find each other, and be not liable to make 
the fatal error of confusing their fellows with their 
foes. It is clear that the specific colours of many 
species have arisen in this way as means of recognition. 
But it is also clear that visible characters do not suffice 
in the case of the birds. The light creature soars high 
up into the air, and is not tied to the ground like the 
mammal. With its keen eyes it looks down on a 
broad expanse of territory. But how can the finest 
eyes pierce through the canopy of leaves to find its 
fellows sitting beneath ? And how can the nocturnal 
birds, such as the owls, find each other so well ? Even 
|:if their eyes can pierce the darkness, they must fail 


to detect their fellows in the wide forest. The mammal 
has an easier task. He follows the track of his 
companion with his nose ; but the air leaves no 

In all these cases sight is of no use in detecting the 
species ; it has to be aided by another sense — hearing. 
The voice is developed as a means of recognising 
the species. But it not only serves the purpose of 
bringing the sexes together ; it is of the greatest 
importance in the common life of the bird. We know 
how powerful the social instinct is in birds, and we 
have learned to appreciate the value of this gregarious 
sense for the maintenance of the species. Apart from 
the fact that the young learn continually from the 
older, they are also protected by them from danger. 
Every sportsman knows that when he is approaching 
a flock of rooks, and one member of the flock sees him, 
it is useless to go any farther. The understanding 
between the flock can only be brought about by voice. 

In the social life of many animals it is extremely 
important to specialise the call, as it is an immense 
advantage to the species if the bird can produce different 
notes. In that case one note will serve to bring the 
flock together, another to warn them of approaching 
danger, a third may be the signal for flight. We are, 
in fact, astonished at the diverse cries of the crows, and 
the different notes of the blackbird, which is often a 
herald of warning even to other animals in the forest. 
Nearly all migratory birds have a peculiar call on their 
long, nocturnal travels, in which some means of keeping 
together is necessary. But it is especially the pairing- 



call, for bringing- the male and female together, that is 
peculiarly developed in most birds. 

From the pairing-cries, which were at first common 
to the two sexes, there were gradually evolved sounds 
that differed for each sex. This was effected by sexual 
selection, which favoured those males that could make 
themselves known at once as suitors to the heated 
females. Quite a number of birds are still at the stage 
of “ sexually different notes.” The grey wood-pecker 
gives out his clear-ringing cry from the highest branch of 
an oak, and is answered from afar by the different note 
of his mate. Even the cuckoo is said to have different 
notes in each sex. When it gives out, in ardent passion, 
its trisyllabic cry “ Cuck-cuck-cuck,” we usually hear 
shortly afterwards the continuous note of the female. It 
is a sign that the love-message of the male has been 

Here we have reached the basis of song — the special 
call of the male — and it will be asked how the further 
development, up to the noble song of the nightingale, 
came about. Again, however, we must depart from the 
theories, as we have rejected “female choice.” More- 
over, the song is not mainly intended for the female, 
since the male usually sings alone, and often, like the 
blackbird, on the top of a tree, and so is easily seen; while 
ithere is no female near to see him. But the song would 
!be just as unintelligible as a means of intimidation ; at 
rthe most, we may assume that it has become so much 
: developed and specialised because it is useful to the 
< male to let his presence be known far around, so that 
( any unpaired companion may know from afar that the 


lady of the district has a spouse. Nevertheless, this 
suggestion must not prevent us from confessing candidly 
that we have as yet no satisfactory explanation of the 
complicated song of the bird. 

And how the songs of the birds differ ! The 
monotonous “ delm, dilm, delm, dilm ” of the willow- 
wren, the rolling flute-like song of the hedge-sparrow, 
the strong exulting note of the chaffinch, the rippling 
song of the black-cap with its bell-like ending, the 
melancholic, varied tones of the song-thrush, and the 
indescribable song of the nightingale ; what variety in 
the fulness of tone, in the change of the notes, in the 
rhythm ! 

Birds not only sing, but many of them play a very 
peculiar instrumental music. Storks clap with their beaks, 
bitterns pump their gullet full of air and give out the 
powerful bellow that has frightened many a traveller. 
The spotted wood-pecker and its black companion fasten 
themselves on the branch of a tree, and with rapid 
stroke of the beak, helped by the vibration of the branch, 
send a humming rattle through the wood. Those who 
go through damp meadows in the spring hear a 
mysterious tone like that of a hautboy vibrating through 
the twilight. This is caused by the snipes, whose tail- 
feathers are set in vibration by the air like the tongues 
of a reed-instrument, as the bird is descending, and with 
a peculiar quiver in its wings sends a current of air 
through them. 

Some birds are able to imitate the sounds of others. 
The jay is a great artist at this work. This pretty 
but thievish bird, with its fine blue epaulettes, often 



delights in imitating, in the most disconcerting way, all 
kinds of bird-voices, as well as the neigh of a foal, the 
bark of a dog, and the swish of the scythe. Its com- 
panion in robbery, the wood-chat, strings together the 
most varied notes, such as the croaking of frogs and 
a number of other sounds, with the bird-songs it hears, 
into a charming song. Imitation plays a great part 
in all songs ; in fact, Wallace believes that the song of 
the bird is entirely due to imitation. That is not 
correct, however. The bird has an instinct to its 
particular song, otherwise there would be no specific 
songs at all. But this instinct, as in the play of animals, 
may not be developed with full precision, and so the 
accession of a second instinct, that of imitation, enables 
the creature to improve its voice by hearing and practice. 

What pleasure the bird takes in its song ! Anyone 
who has watched the singer will know this. It is 
certainly not love alone that inspires its song, as the 
bird sings long after the love-period is over. During 
the hatching, we still hear the note of the chaffinch, and 
the song of the yellow-hammer and the black-cap. In 
the autumn the voice of the blackbird trills out once 
more ; also the song of the willow wren, and the tender 
ripple, like the splash of a tiny waterfall, of the red- 
breast. When the ground is covered with snow in the 
wood, when the fir-branches bend under their load of 
snow, and everything sparkles in the sun, we often hear 
the song of our smallest bird, the wren ; and the water- 
ousel sings its spirited, rippling song by the brook in the 
severest cold of January, and then, to the astonishment 
of the observer, dips into the icy flood. 


Otherwise, all is quiet in Nature in the winter. A 
few grain-eaters, like the titmouse, pick up a precarious 
living. There is only one bird, the cross-bill, that has 
its time of plenty in the winter, as the pine cones are 
then ripe ; and we see the wonderful sight of the red 
and restless gipsy-bird building its nest and rearing its 
young on the snow-covered pines. But all the birds 
that live on insects, and amongst these are our best 
singers, have migrated far away in the autumn, where 
a fresh summer smiles on them under a sky of perennial 

This enormous journey across the Mediterranean to 
Africa only takes them an astonishingly brief time to 
perform, as the little birds can attain a very high speed. 

Henry II. of France found out in the sixteenth 
century how fast a bird can fly. A falcon escaped from 
him at Fontainebleau, and was caught twenty-four hours 
afterwards in Malta. When we calculate the distance 
between the two places, we get a speed of forty-four 
miles an hour ; but this is below the mark, as the falcon 
would hardly do it in one flight and in a straight line. 

The expert whom we mentioned at the beginning of 
the chapter, Gatke, puts the speed of migratory birds 

for instance, that the northern 
blue-throated warbler does its journey from Africa to 
Heligoland in one spring night, because at the time of 
its migration it has been seen in swarms in Heligoland 
while only a few stragglers were found in the rest of 
Europe, and the bird always travels by night. If this 
were so, its speed would be 209 miles an hour. It is 
true that the route and the migration of the blue-throat 

far higher. He maintains, 



are still obscure, but Gatke’s calculation must be too 
hio-h, and we will turn to safer figures. We know from 
exact observation that wild ducks can fly more than 
forty-seven miles an hour, and carrier-pigeons seventy- 
two miles an hour. The highest known speed was 
reached, according to a careful experiment, by a house- 
swallow, which travelled from Ghent to Antwerp in 
1 2 *5 minutes, and so must have done 186 miles an hour. 

The bird can, of course, increase or lessen the speed 
of its flight, according to need. Hence these figures 
cannot tell us anything certain with regard to the 
speed of migration. We know little, moreover, as to 
the duration of the migration. It seems that many birds 
make a halt at suitable spots, but others continue their 
flight without interruption to the end, while the weather 

It is marvellous how a bird can maintain such a 
velocity so long, yet we never see any signs of fatigue 
in migratory birds. It is only a violent storm that 
distresses them, and if they are surprised by one at sea 
thousands of them may perish in the waves. Many 
species of land-birds can alight in a calm sea without 
being drowned. Gatke has seen the snow-bunting, the 
mountain-finch, and the thrush do this. 

Most ornithologists believe that it is the altitude at 
which the migration flight takes place that enables birds 
to make such long stretches ; they say that the birds 
meet less resistance in the upper air. We are also often 
reminded of the special adaptation of the bird for flying 
■ — the air-sacs that are found in its body and the bones 
filled with air, which increase the volume of the animal 



and so lessen its specific gravity. The latter point is 
undoubtedly correct, and it is also true that a thin 
atmosphere offers less resistance to flight than a denser 
one. However, the chief use of the air-sacs, which 
extend in the form of hollow outgrowths of the lungs 
into the body-cavity and the bones, and between the 
muscles, is now thought to be that they spare the bird 
the trouble of respiratory movements during flight. In 
particular, the reservoirs of air between the flying-muscles 
are pressed together like bellows by the movement of 
the wings, and thus to some extent automatically renew 
the air in the lungs. 

Besides this adaptation for flying there are many 
others. The bird is, as we say, a mass of adaptations. 
There is on its breast-bone a strong comb to which 
the flying - muscles are attached ; the whole of the 
shoulder-blade is most beautifully constructed ; and the 
rigid pelvis, formed by the fusion of a number of 
vertebrae, enables it to keep upright while sitting. 
In harmony with the laws of leverage all the heavy 
parts are placed in the centre of the frame ; the crop 
supplies the place of teeth ; the muscles of the leg are 
developed well up in the body, so that the limbs 
themselves are thin and light ; and a particularly good 
digestion enables it to disburden itself at one effort. 
In a word, we could show the adaptiveness of every 
single organ, to say nothing of the feathers. Every 
stroke of the wings lifts the bird up ; and as the 
wings are lifted the air rushes between the feathers, 
so that they meet no resistance. A wind coming 
from the front fills the wings, and enables the creature 



to rise rapidly without any exertion ; and they can 
also easily fly with the wind. 

We see, therefore, that the bird is enormously 
assisted in flying by the nature of its organism. We 
may now inquire whether the statements made with 
regard to the altitude it reaches are supported by 

When we follow the flight of birds of prey they 
seem to rise to immeasurable heights, and even the 
lark often passes beyond our vision into the blue 
sky. But it would be premature to draw any inferences 
from this, as we do not know how far we may not 
be subject to illusion by dazzling. The results of 
balloon observations are more important. In these 
an eagle was once seen at a height of 3,300 yards and 
a lark at a height of 1,500 yards; but there were so 
few birds at this height that we must conclude they 
rarely rise above 1,100 yards. It was also noticed 
that a pigeon, which was dropped from a balloon at 
a great height, first fell downwards, and only found 
sufficient resistance for its wings to use properly in 
thicker strata of the atmosphere. 

However, these facts gives us no information as 
to the altitude of the migration-flight, and unfortunately 
we have not very many observations on this. Gatke 
was one of the few who have seen swarms of migratory 
birds go past, and he gives a superb description of 
one night in October in which this wonderful picture 
unrolled before him. It was a dark, starless night, 
only lit by the rays of the light-house which seemed 
to reach out endlessly into the night. The darkness, 



the perfect silence of Nature, and the consciousness 
of the nearness of the vast sea, awoke a feeling of 
sublimity in the soul of the observer. Then the cry 
of a bird broke the stillness, then a second, and the 
noise grew louder and louder, until at last countless 
flocks of birds of all kinds shone like sparks in the 
beams of the light - house, circling round it like a 
snow-storm, and then disappearing in the impenetrable 
darkness. Larks, starlings, plovers, snipes, and many 
other species were recognised by him. At one time 
an owl appeared, and then passed with loud flap of 
wings into the darkness, accompanied by the plaintive 
cry of a thrush that had been caught in the general 

When the moon and the stars shone, the sight was 
less splendid, as the birds then flew higher, and were 
not caught in the light of the lantern. It seems, then, 
from Gatke’s observations, that the migration does 
not take place at a great height, at least on cloudy 
nights ; and this has been confirmed by recent 
observations . 1 

Aeronauts have let loose various birds from balloons, 
and it was found that in clear weather the birds went 
straight downwards. But if the balloon was above 
a thick stratum of cloud, the birds were puzzled and 
flew hither and thither, and settled on the balloon 
again ; though they immediately left it when it fell 
below the clouds and the earth could be seen. They 
then made for the ground. The same thing happened 
if there was a break in the clouds through which the 
1 Gatke himself held to the theory that the birds fly high. 



earth could be seen from above. In that case the 
birds at once took their direction, passed through the 
opening, and flew downwards. 

If we compare these observations with Gatke’s it 
seems pretty certain that the birds do not need to rise 
high during the migration-flight. It is true that the 
question at what height they fly in clear weather is still 
far from settled, but we may say that, if they fly at 
a lower level in bad weather, yet probably reach their 
end just as quickly, a high level does not seem to be 
necessary for speed. Hence the rapidity of the 
migration-flight is not explained by the theory of the 
thinness of the air. 

A second question now arises. When they are at a 
low level the birds can only see a small part of their 
route, and none at all during the night ; how is it, then, 
that they choose the right way at such enormous 
distances ? We will approach this question in the 
method we have used several times already, and inquire 
how the migratory instinct may have been developed 
in the course of time. 

The actual migratory birds formerly lived, we assume, 
in southern latitudes, and gradually increased until they 
over-populated them, and food became scarce. The 
famine was worse in the dry season, when vegetation 
shrivels up in Africa, and the insects especially, which 
form the chief food of the actual migratory birds, were 
reduced in numbers. The hungry birds were thus 
compelled to abandon their habitation, and travel in 
every direction, seeking food and nesting-places in less 
crowded regions. A number of them came northward ; 



and as fresh arrivals from the south came in later years 
of famine, the place was again too small, and they had 
to spread in all directions, including the north. 

Could the spread towards the north proceed 
indefinitely? No; because the time came when the 
wanderers had passed the winter-limit. When the cold 
season broke on them, the earth became covered with 
snow, the streams froze, and famine set in again. 
What happened to the poor birds ? Those that 
remained, waiting for better days, were destroyed, as 
the lack of food lasted longer than they could endure ; 
others, that fled to the north, east, or west, found the 
same conditions everywhere and perished also ; only 
those were saved that remembered their origin and the 
land of eternal summer, and returned southwards. 

We may confidently assume that these little creatures, 
barely escaping from death, would not at once return to 
the north. But natural selection — for it is with this 
we have to deal — is inexorable. The birds were back 
in fully populated lands, and when the nesting -time 
came in spring there was no room for them ; we know 
that most birds require a certain area for nesting, and 
will suffer no others of the same species within that 
area. The wood-pecker, for instance, and a great 
number of others, including our gentle robin, act in this 
way. What happened to these birds that had become 
strangers in their old home ? Many of them failed to 
breed ; these were the most timorous who would not 
return to the north, and died out through leaving no 
offspring. But there would certainly be bolder ones 
here and there, who would remember how they had 



nested undisturbed in the previous summer, and fly to 
the north once more. 

This was repeated time after time. In a long period 
of time and certainly not without enormous numbers of 
victims, Nature fashioned a provident and hardy race of 
birds ; provident because they would fly south as soon 
as the cold set in, courageous because they ventured 
back to their old nesting-places in the spring. Natural 
selection further regulated the time of flight. The birds 
were not to start too early from the south, or they would 
find their old nesting-place still buried in snow : and not 
too late, or they would not have time to rear their young 
so as to be able to make the great migration. The young 
would accompany the older birds when they gathered 
for departure, and would observe the route so as to be 
able to teach it to their own young afterwards. And as 
those that would not make the flight at the proper time 
were always destroyed, there arose the species of 
migratory birds which still carry out their flight with 
such wonderful exactness . 1 

German ornithologist, Kurt Graeser, has recently given a different 
theory of migration. He believes that the migratory birds are the 
original type, and the non-migratory have descended from them. 
According to him, the first birds lived on a very different land from 
what we have now. It had enormous stretches of water, ice-fields, 
steppes, and forests, which could give no food or shelter to the birds, 
and had to be rapidly covered in order to reach places with plenty of 
food. The primitive birds, therefore, must have had the instinct of 
wandering restlessly and swiftly over the whole earth. Gradually the 
birds would see that certain places were especially favourable for them. 
They flew to these more and more, and from this habit was formed the 
habit of definite migration. Later some of the birds found it better to 
remain in one place, and were adapted by Nature as required. The 
author believes that in time all birds would cease to be migratory, and 
adapt themselves to a different diet and the privation it would entail. 



At first the route was comparatively easy to find ; 
but the further north they spread the more intricate it 
would become, the more strength it would require to 
traverse it, and the earlier the start would have to be 
made. But as they only spread gradually, this advance 
would be quite possible, as only the strongest would be 
able to meet the demands of the longer flight, and 
amongst their progeny, which would go still further 
north, again only the strongest would survive ; so that 
the power of covering long distances in the shortest 

To this theory we may object, in the first place, that there is no 
proof whatever of the earlier condition of the earth compelling the 
birds to cover wide stretches. In fact, it is not at all clear that steppes 
and forests would afford no food and shelter to them. It is just the 
opposite. It is not sufficiently borne in mind by the author that the 
migratory birds live on insects, and that the migration is precisely 
regulated by the alternate abundance of insects in the north and 
south, and that the use of this rich provision of sustenance is an 
admirable adaption. It would be a curious retrogression for the 
migratory birds to adapt themselves to food that is already so much 
sought by other animals. And to adapt themselves to privation ! 
Further, the basis of selection, the over-production of progeny, is lost 
sight of, yet this is the principal ground of the migration. In the 
author’s opinion instincts are inherited habits. We shall refute this 
theory in the sixth chapter ; but even if we admitted it, what was the 
origin of the habit of the primitive birds to fly over the earth ? Among 
the unconvincing objections that the author raises against other 
theories of flight we find the following : “ The birds could not know 
that there was food for them in the south.” But this difficulty only 
exists in the author’s own theory, and for this it is formidable. How 
could the primitive birds know that they would find plenty of food if 
they made long and rapid flight over desert wastes ? Finally, the whole 
theory is impossible because a simple reflection tells us that the first 
birds cannot have been migratory. The birds must have evolved from 
creeping animals ; their ancestors were reptiles, something like the 
present lizards. It must have taken an enormous period of time for 
their flying organs to have become powerful wings; only after vast 
numbers of generations would they be sufficiently advanced to attempt 
long flights without resting. 



possible time, which excites our admiration to-day, was 
gradually developed. The faster the birds travelled, 
the more time they had for breeding, the more young 
they could bring into the world, and the more quietly 
they could rear them. Hence the speed of the flight 
was constantly increased by natural selection. 

Gatke raises the difficulty that every blue-throat that 
must perform this rapid flight lives on the ground, and 
never really makes use of its wings except during 
the migration. Just as a man’s arm becomes weaker if 
it is not used, so it must be with the blue-throat, and we 

cannot see how it will be able to make the enormous 

It is true that disuse enfeebles an organ, but as only 
those blue-throats survived that flew quickly in the 
migration, their strength was increased so much by 
natural selection that disuse could not lessen it much — 
at least, not enough to incapacitate them from flight. One 
thing is clear. If the impairing of the flying-power by 
disuse was inherited \ the blue-throats would certainly 
become weaker and weaker. But this is not the case, 
and so it is clear that Gatke does not impugn natural 
selection, as he supposes, but the Lamarckian 
principle, by his difficulty. We will bear in mind 
this first case in which the principle conflicts with 

The second effect of natural selection was to increase 
more and more the bird’s power of presentiment. The 
wanderers must not wait for the snow and ice to tell 
them that the winter has come, but must take their flight 
before these appear. Thus the marmot foresees the 



winter scarcity of food, and stores up grain in its den in 
the autumn. 

Thirdly, the bird’s sense of direction had to be 
improved. Otherwise how could they find their way on 
the long journey ? 

There is, however, another theory. Remember how 
we conceived the origin of the migration. Among the 
birds that penetrated further north only those survived 
that flew south at the beginning of winter. May not in 
some of the birds an instinct have arisen in the course 
of thousands of years, during which natural selection 
was at work amongst them, to fly straight to the south 
when the cold weather set in ? These birds would thus 
be preserved, and might transmit this instinct — which 
does not differ essentially from the instinct that forces 
the salmon up the river — in increasing power to their 
offspring, And may not an instinct have arisen by 
selection to keep the route unerringly during the migra- 
tion so that the animals will reach the warm countries 
in safety? Certainly the formation of a “magnetic 
sense ” of this kind by natural selection is quite possible, 
and the Siberian traveller, Middendorf, believes it is 
present in migratory birds . 1 Such an instinct is not 
more wonderful in principle than the marmot’s instinct 
to store up grain, or the bees’ instinct to build their 
ingenious cells. 

But we know from observed facts that the migratory 
birds do not regulate their flight by a magnetic sense. 
They do not fly straight, but follow certain paths which 

1 There are many animals with senses that cannot be reduced to 
any of our familiar five senses. 


[ I I 

often change in regard to the four quarters. A mag- 
netic sense would be expected to guide its possessor 
in the straightest possible line. 

The migration - lines of the birds show, on the 
contrary, that the travellers know the way to their old 
home , and that they travel along the same paths as 
their ancestors did. It is clear that the animals, in 
their extension northward, only sought localities that 
promised them sufficient maintenance. A sea-bird, 
though its nesting-places are spread far and wide over 
the shore, will not fly over the land, but along the sea, 
where alone its food is to be had. Now we find that 
the migration-paths of the sea-birds always run along the 
shore and never cross any extensive land, although their 
goal, the winter quarters, could be reached much more 
quickly by land. These circuitous routes are very 
striking in many species. The Richard’s pipit, for 
instance, nests in East Siberia, and migrates from 
Heligoland to West Africa, instead of straight to 
China. 1 How can we understand such an aimless 
direction, unless we admit that the paths of birds follow 
the ancient line of advance, the recollection of which 
has been transmitted from generation to generation ? 
The animals spread gradually further and further north, 
and each time some of the descendants nested in a 
higher latitude than their ancestors. Hence the further 
north a species of migratory birds nests to-day, the more 
nesting-places of their progenitors must they fly over 
during the migration. And as these nesting - places 

Some of these birds, however, must fly to China and Ceylon. We 
must suppose that this variety has spread from the south of Asia. 

I 12 


could only be where there was means of sustenance, 
the line of migration must pass over these localities, 
and so follow the ancient line of expansion. 

This is seen in the paths of all migratory birds. 
River-birds travel along the rivers, though also over 
high mountains, as here also there are streams and 
lakes that afford them sustenance ; while marsh - birds 
go round the marshless hills. Land-birds go straight 
ahead over the country, and only halt at the sea, and 
diverge along its shore. The fact that European birds 
still cross water, namely, the Mediterranean, is ex- 
plained by the circumstance that there was not always 
water where the waves roll to-day. In the earlier 
periods of geology there were bridges of land from 
Africa to Europe, through Malta and Sicily as well as 
at Gibraltar. Over these the birds could advance 
gradually towards the north, and as a fact we find that 
the sea is only crossed by them at these points. 

Let us now picture the migration to ourselves once 
more. A pair of birds travel to the north, rear their 
young there, and return with these in the autumn to 
the old home. In the spring they all return to the 
nesting-place of the previous year, but some of the 
young go still further north to build their nest. The 
journey in autumn will consist of two parts for these. 
They have already done the larger section of it twice 
with their parents ; the second is the stretch from the 
nest in which they themselves were reared to the new 
home that they have made. But both sections of the 
journey are only the first part of the journey for their 
offspring, as these will add to it by advancing further 


II 3 

north. In this way, from the fact of each succeeding 
generation adding a piece, however small, to the original 
journey, we get in the course of an enormous period the 
gigantic travels of our actual migratory birds. And 
as the route is only a little longer in each generation, 
selection does not make too exacting a demand on the 
birds, and there will always be some that can perform 
the longer journey. 

Thus the power of flight has been strengthened 
gradually, and the sense of direction has steadily 
increased up to its present pitch. This sense consists 
especially in a marvellous memory, which has grown 
steadily as the route lengthened. If we did not know 
that it had been built up gradually, we should hardly be 
able to understand to-day how the birds can retain an 
impression of the routes they have only travelled over 
twice with their parents. But this memory is not so 
much a capacity for observing the path over the regions 
they have traversed as the power to keep the various 
directions that they took in their flight, and so there 
must also be a sense of orientation, or direction, that 
enables the birds to keep their way even when they are 
turned aside. That they do not need to any great 
extent to look down on the country is clear from the 
fact that night-time is often chosen for the migration. 
Nevertheless, they do need some sight of the earth, 
however faint and shadowy, otherwise they would rise 
above the clouds, and would not fly so low in bad 

However, this enormous development of memory in 
the migratory birds is not altogether strange. Even 


amongst men there are memory-prodigies. Who has 
not heard of the Hindoo who could repeat, word for 
word, long stories that he had only heard once. If 
circumstances arose that brought about the survival of 
such men alone, there would soon be a race on the 
earth with prodigious memories. 

Nor is there anything mysterious about the sense of 
orientation that enables the bird to keep the right 
direction when its eye cannot see any point to guide it. 
There are men that can find their way in the forest 
without any path or track. We read that the Indians 
never went astray in it. We are, moreover, assured by 
some writers that dogs which have been taken away for 
hours together in closed carriages or trains will find 
their way home by the shortest, and a quite unknown 
route, when they are set free. Here we have something 
exactly similar to the migration of the bird, which, 
though it has been taken a long journey in the darkness 
of night by its parents, has retained the direction so 
well that it can follow the same route without guidance 
in the following year, and never go astray. 

Finally, we must observe that the migratory birds are 
greatly assisted in keeping to the right way by the fact 
that their social instinct is developed especially strongly 
at the period of migration, and vast flocks of them make 
the journey together. Whether some older bird that 
knows the route from having migrated several times 
leads the way, has again been called into question of 
late. This is not necessary, however, as we have seen. 
In any case, it is an advantage to travel in flocks, 
because a large number of birds will be less likely to 



go astray than a few ; and the considerable power of 
communicating which the bird has will certainly help 
them to reach their goal more safely. 

It was, therefore, an iron necessity that implanted 
lithe instinct of migration in the bird’s breast. Their 
wonderfully developed faculty must have been pur- 
chased at the price of innumerable victims. 

It was necessity also, that compelled our ancestors 
to migrate. They were forced to leave the primitive 
home that had grown too small for them, and was 
^overwhelmed with other peoples. They were driven 
j iinto lands where the hot sun melted down their 
morthern vigour like snow, and where the dark waves 
■of southern races passed over their blond and handsome 
features. So perished heroic races. But others 
iremained, and retain the spirit of the old vikings in 
the life of Europe to-day. 



Principle of animal classification. The general properties of animals 
explained by heredity and adaptation. Darwinian justification 
of classification. Reptiles and amphibia of former ages. Earlier 
periods of the earth. How and why the earth has changed up to 
the present. How the remains of earlier animals have been 
preserved. Gaps in the remains of extinct animals. Primitive 
man. Conflicts of extinct animals. Why the gigantic forms of 
earlier ages became extinct. The death of species. Trans- 
formation of species. Why ancient species have been 
preserved. Why there are still animals of the simplest type. 
Predominance of a species of animal. Predominance of 
man. Any variation is possible. Origin of flying animals. 
Life of our reptiles. Prey. The creeping of serpents. Re- 
generation, the power to re-form lost members. Its origin by 
natural selection. Frog-spawn. The skin of amphibia. Repellent 
and warning colours on nauseous and poisonous animals. 

The man who devotes himself to the study of living 
organisms is overpowered by the inconceivable variety 
of their forms. He would have to despair of ever 

obtaining a grasp of the world of living things if he 
had not in language a means of ranging a vast number 
of forms under one convenient name. With one word 
he can designate countless numbers of animals, each of 
which is different from the other, by ignoring the 
differences between them and fastening on what is 
common to all the individuals. The word “ fox ” 

enables us to grasp a countless number of animals, by 

representing to us the common element of them all. 

1 16 


II 7 

Science pursues the same method. It seeks the 
common element in wider and wider groups of animals, 
and overlooks what is individual. Fox, wolf, weasel, 
marten, are regarded in their common features, and 
described as “carnivores” or carnassia. All “species” 
are distributed in “orders” of this kind. The work 
is carried even further. Some of the orders of animals 
are found to have features in common, and these are 
bracketed together as “classes.” Finally, the “classes ” 
are distributed into “ stems.” Thus the vertebrate 
“ stem ” represents what is common to the five 
“classes,” mammals, birds, reptiles, amphibians, and 
fishes, namely, the possession, first of all, of an internal 
axial skeleton. This feature is not found in the other 
stems, the members of which are at the most covered 
externally with hard parts. 

It is the merit of Darwinism to have established that 
there are in the nature which we really know no 
“species,” but merely a countless number of individuals, 
each of which is unlike the other. Darwin has shown, 
in fact, that the feature which is common to certain 
forms, and enables us to grasp them as a “ species,” is 
not always absolutely fixed. When, for instance, we 
find that a number of individuals agree in having “ long 
ears and so can be formed into a species, differing 
from another or short-eared species, we see also that 
there are other animals with ears of intermediate length. 
Such animals could with equal right be put in either of 
the two species. 

Lut while Darwin has destroyed species as realities , 
he has at the same time fully established the idea of the 


species. Formerly the common element that made it 
possible to distribute organisms into species, orders, 
etc., was taken for granted without discrimination. 
Darwin, and a few students before his time, have tried 
to show why there are common features amongst living 

There are two laws that explain these common 
elements in the animal world. One is the law of 
adaptation; and we shall see later that adaptation to 
precisely the same conditions can bring such very 
different animals as worms and spiders to resemble each 
other. The second is the law of heredity. According 
to this law organisms have more in common, the closer 
their blood-relationship is. Any person can verify this 
from human life. However, it is not as simple as it 
seems at first sight, and we shall see, when we deal with 
the phenomena of heredity, that frequently men who are 
only distantly related resemble each other more than 
brothers and sisters. 

The law of heredity gives a general validity to the 
classification of the animal kingdom, as it was set up 
formerly on the ground of common features ; we have 
much the same arrangement when we classify them 
according to generic relationship. There are, however, 
many exceptions, and these are explained by the first 
law. Animals were formerly classed together which 
resembled each other externally through some similar 
adaptation. But the more thoroughly they were 

investigated, the more they were found to have in 
common with different animals, and they are now 
distributed in other orders and classes. This common 


element, which is due to the law of heredity, affects 
animals far more profoundly than the common features 
due to similar adaptations, which are generally external. 

In our time it is sought to base classification 
exclusively on the law of heredity, all animals being 
regarded as a gigantic family and classified according to 
their degree of kindred. Thus the classification of 
animals has been intrinsically justified by Darwin. 
The common element on which it is now built is 
scientifically explained by the law of heredity. 


In the present chapter we have to deal with two 
classes, the reptiles and the amphibians, and we can 
do this the more easily as both classes have few 
representatives in Europe. Reptiles and amphibians 
require heat. The temperature of their blood rises 
with a higher external temperature, and gives more 
vigour to their vitality. Hence it is that we meet 
more species of the two classes the further south we go, 
and more highly coloured and powerful animals in 
proportion to the length of summer in the district. The 
giants of the reptile class and the largest amphibians 
live in the moist tropical forests, where the rays of the 
sun are almost unendurable to us. The serpents wind 
through the bush like living branches of trees, the 
crocodile lurks in the broad river for the animals that 
come to drink, and the voices of the tropical frogs 
resound at night like the roar of oxen. 

At one time it was different here. 

Many millions of years ago, in what are called the 
Jurassic and Cretaceous periods, there were large 



numbers of huge reptiles in our own latitude. Where 
the wind now sweeps in long waves over the fruitful 
corn-fields, it then lashed the waves of a vast sea. In 
this ancient sea the plesiosaurus, a gigantic reptile with 
legs shaped into huge fins, swam hither and thither. 
A head armed with sharp teeth crowned a neck eight 
yards long. It towered far above the water, and when 
unsuspecting fishes came along, the head shot down 
with terrific force, to emerge again with the captured 

The ichthyosauria were no less deadly to the fishes 
and still more to the cuttle-fishes, or huge polyp-shaped 
molluscs. Something like dolphins in shape and size, 
these reptiles disported themselves in great swarms in 
the sea. There were also reptiles on the land. The 
colossal dinosauri broke with heavy step through the 
thickets, one of them, the cetiosaurus (of which the 
brontosaurus was an American cousin), having a 
ridiculously small head. Another huge animal was the 
iguanodon. Like the modern kangaroo, the monster 
stood on its great hind-legs and heavy tail, and tore off 
masses of leaves with its small fore-limbs to thrust in 
its horse-like mouth. In spite of their huge size the 
dinosauri were harmless vegetarians. They had deadly 
enemies in the megalosauri, gigantic carnivores with 
teeth as sharp as knives. 

Even the third element, the air, had its reptiles at 
that time. The pterosauri flew from tree to tree, 
spreading out the flying membrane that stretched from 
their enormously long fifth finger to the legs, and even 
to the tail. The best known of these flying lizards is 


I 2 I 

the pterodactyl. It was not itself very large, but it had 
relatives with wings that measured eight yards. 

We have to go further back in the history of the 
earth for the period when the amphibians flourished 
most. The largest forms of this class lived in the 
Permian and Triassic periods. These were the 
stegocephala, huge beasts that lay in ambush for their 
victims in the prickly thickets. The yard-long jaws of 
the mastodonsauri were armed with numbers of sharp 
teeth ; their belly and skull were protected by powerful 
armour, and they had, besides the two eyes, a third or 
cyclopean eye in the middle of the forehead. 

The fact that the amphibians were before the reptiles 
in the history of the earth is a proof that the latter 
descended from the former. Geology shows that the 
succession of the five classes of vertebrates was the 
same in the history of the animal world as it is in our 
classification. The earliest geological finds known to 
us are remains of fishes alone, and these increase in 
variety. The first amphibians appear in the Car- 
boniferous period, and they are followed in later epochs 
by the reptiles. In the Jurassic strata we find the first 
bird, the archeopteryx, of which we spoke above; and 
the mammals do not reach the height of their 
development until the Tertiary period. 

But, it will be said, fishes are highly organised animals, 
and according to our theory there can only have been 
extremely simple organisms in the beginning. How 
is it, then, that we find fishes in the oldest strata ? 1 

1 To be quite accurate, in the second oldest, the Silurian. But as 
these fishes have an advanced organisation, it is clear that there must 
have been fishes in the oldest period known to us, the Cambrian. 



For the simple reason that, though these strata are 
the oldest known to us , they really represent terrestrial 
epochs that had many predecessors ; but we have no 
documents relating to these periods. The book of the 
history of organisms only opens for us when there is 
already an immense wealth of forms on the earth. 
Besides fishes, there are crabs, mussels, and other 
animals, the development of which from the lowest 
organisms must have taken enormous periods of time. 
At first there must have been merely particles of 
living substance, and in comparison with the countless 
series of modifications that lead from one of these to the 
fish, the very much shorter series between the fish and 
the mammal is insignificant. We may say, therefore, 
that the pages of the archives of the earth’s history that 
have been preserved only relate to the “ modern period” 
of organic life, and that “ antiquity” and the “ Middle 
Ages” are lost to us, and will never be recovered. 

The earlier of the ecological strata lie below the 
later ; the most recent lie at the top of all. As 
geologists penetrated deeper and deeper in their 
examination of the strata, and still found animal 
remains in the earliest deposits, there suddenly appeared, 
below the earliest fossiliferous layer, one that had no 
organic remains whatever. Experts still differ about 
these empty masses of rock. Many regard them as 
the crust that was formed when the surface of our 
planet, at that time a mass of molten liquid, cooled 
down. At this period of incandescence there cannot 
have been any living things, and we ask for the strata 
that lie between this crust and the deposit that contains 




the earliest animal remains. Here we find a yawning 
gap. No one can say what has become of the missing- 
strata. Many think that they are at the bottom of the 
sea ; others see them in the upper layers of the non- 
fossiliferous rocks, which have destroyed all the remains 
of animals in the incalculable lapse of time, and owing 
to pressure and decomposition. However that may be, 
we must take into account the fact that the whole period 
from the first appearance of life on the earth up to 
the development of these highly organised animals is 
hidden from us. 

Moreover, our discoveries in the periods known to 
us are very defective. 

In the fossil remains or impressions of former animals 
we have, as a rule, only the hard parts of organisms. 
Hence animals that had no hard parts could leave no 
trace of their existence. There is also another 
circumstance that tells us the remains we have represent 
only a small portion of the animals that lived at that 
time. The strata that contain the fossils are formed 
exclusively in water. The rivers carry stones with 
them from the mountains, grind them up into fine mud, 
and convey this to the sea, where it sinks to the bottom 
and covers up any remains of animals that lie there. 
These deposits of mud are gradually converted into solid 
rock containing the animal remains ; and when the sea 
recedes, the rock becomes the basis of new land, and 
may be elevated into a mountain by the creasing of the 
earths surface. If one of these strata is left dry for a 
long period, and then covered by the sea once more, a 
new stratum is formed on top of it. But there will be 


a wide gap between the new organisms and those 
buried in the older stratum, representing the time 
during which the earlier stratum was dry land. Thus 
we can understand the gaps in the passage from one 
species of fossils to another. Further, we can see from 
the nature of this sole means of preserving animal 
remains that land-animals can leave us no trace of their 
existence, or at all events only if they are carried into 
the water by accident and deposited quietly at the 
bottom of it. 

But there will be a still further reduction in the 
number of animal remains preserved. All the seas of 
former days were not fed by rivers that brought mud 
to them, and in those without slimy bottoms animal 
remains would decay. Moreover, remains might not 
be preserved that fell into the water at places where 
the rivers brought down coarse debris into the sea, 
which would grind everything up. 

Further, when the fossiliferous strata were raised out 
of the sea their contents were exposed to fresh dangers. 
An enormous amount was destroyed by weathering, 
rain, floods, and surge, carried away by the rivers and 
ground down into mud again, and so had to begin the 
cycle afresh. And when the crust of the earth burst, 
became creased or folded, and threw up chains of 
mountains, many remains were squeezed until they 
became unrecognisable. 

Besides all this, the sea still holds from us 
incalculable treasures, and there are others in lands that 
have not yet been opened up. When we further 
remember how few of the remains that are found come 



nto the hands of experts, we should not be surprised 
hat we have not fossil remains of all the transitional 
yrpes. We must not expect to find the remains of long 
eries of ancestors of any particular species, showing us 
ow it was gradually converted into a different one. 
Ve must not question the theory of evolution because no 
luman skeletons have been preserved in which the 
ton-human element predominates. 

If, then, such discoveries are made, if the famous 
'teinheim snails 1 bring before us the conversion of one 
pecies into another in all its stages, and if the 
Neanderthal skull and other human remains give us 
nformation as to a primitive humanity, we must learn 
o appreciate the fortunate accident to which we owe the 
reservation. As a matter of fact, however, we shall 
laim full credit for the theory of evolution precisely 
)ecause the evidence of geology, in spite of its 
ncompleteness, affords striking testimony to the truth 
bf it. 

We regard the remains of those monstrous reptiles 
vith astonishment, and ask how it was possible for 
uch powerful creatures to become extinct. We find, 
owever, that towards the close of the Cretaceous 
eriod gigantic sharks appeared, measuring twenty- 
ight yards in length, and we can well believe that 
hey finished off a good many of the ichthyosauri. But 

1 These snails are found in immense numbers in the Steinheim 
eposits. One stem-form has divided into four groups of varieties, and 
he transitional forms have been admirably preserved. The stem-form 
s lowest in the strata, the transitional forms higher up in proportion to 
heir divergence from it. 



how could the sharks develop to such a size, as they 
only appear at a time when the reptiles had long 
dominated the sea, and had been a danger to the 
ancestors — probably much smaller — of the sharks ? 
We can hardly admit that the sharks would be 
developed so much more rapidly than the great marine 
lizards. In fact, we saw in the first chapter, in the 
instance of the fox and the hare, that two species that 
live in a bioccenosis cannot extirpate each other, as 
the strengthening of one species involves at the same 
time more protection for the other. 

An effort has been made to explain by means of 
an example how a species that has lived with another 
for thousands of years may at last bring about its 
destruction. The process is supposed to have taken 
place between the machserodus and the glyptodon, 
mammals of the American Tertiary period. 

The glyptodons were animals about three yards 
long, something like the modern armadilloes, which 
developed a powerful armour as they increased in 
size, and this protected the bearer, like the shell of 
a turtle, and was very thick. It afforded excellent 
protection against most enemies, but not against the 
macha;rodus, a tiger that also grew bigger and bigger, 
and stuck its enormously long canine-teeth, with edges 
like razors, into the glyptodont, in order to suck its 
blood, as its enormous teeth did not allow it to rip 
it up. We can easily understand how armour and 
teeth were improved by natural selection ; in other 
words, how those glyptodons lived longest and re- 
produced most whose armour was impenetrable to 



most of the tigers, and how, when the weaker 
individuals had died out, only those tigers could 
survive whose long teeth could bore through the 
hard coat of the glyptodons. In this way the 
balance would change from side to side for ever, 
and it could never come to pass that “even the 
stoutest armour would no longer protect the victim, 
and the huge glyptodons be gradually extirpated .” 1 
Natural selection could only strengthen the armour of 
the armadilloes if it was near the limit — that is to say, 
if a slight thickening made it impenetrable for a large 
number of tigers. If the latter could suddenly over- 
come all the glyptodons, they must have lengthened 
their teeth to the extent of two generations of 
growth ; and that would be a leap upwards in the 
evolution of the teeth, not a gradual advance. It is 
only on the latter, not on leaps, that we must rely in 
the modification of species by variation. We must, 
therefore, trace the extinction of the glyptodons to 
another cause. One might say, of course, that there 
were limits in the nature of the animal that would 
not allow the indefinite modification of an organ, and 
so after a certain time the armour of the armadillo 
could grow no thicker. Must there not be some 
provision that trees do not grow up into the sky ? 
But we shall see in the eleventh chapter that this 
phrase, however imposing it may seem, explains 

1 Weismann. It is further said that the tigers got the advantage 
of the armadilloes by sticking their teeth into the unprotected neck. 
But that can hardly have been the case, as then natural selection 
would only have to form and strengthen a plate for the neck, and the 
dorsal plate would remain as it was, not being subject to attack. 



nothing, and we will keep clear of all attempts to 
explain things in this way. 

Once the armadilloes disappeared it would be all 
over with the machaerodi as well, since they lived 
exclusively on them ; their long teeth prevented them 
from tearing up or eating other animals like the other 
carnivores. But would it not be possible for the 
teeth to be gradually reduced by natural selection ? 
No; because the teeth were too long for the slight 
reductions that variation might afford to enable the 
animals to adopt a different diet, and so avert famine. 

These two species, mutually affecting each other in 
their modification, could only be destroyed by some 
accident or other extirpating one of them. We can 
only suppose that, as a rule, it is external events 
that come to affect and destroy the relation of two 
species. If, for instance, in our old illustration of the 
fox and the hare, the mice increased enormously from 
some circumstance or other, the foxes, which feed on 
mice also, would propagate more freely owing to the 
abundance of food. If the mice then died off from 
some disease, we should find the numerous foxes 
reduced entirely to eating hares, and they would soon 
extinguish them altogether. 

This illustration shows clearly what must happen 
for a species to be entirely rooted out — namely, some 
sudden accident. Dangers that arise gradually can 
be met by a species, which will be gradually 
modified. The danger must always be just great 
enough for individual variations of the menaced 
animals to escape it ; and in the next generation only 



so much greater that new variations may again arise 
and preserve some animals from it. But if the 
danger arises suddenly, or is suddenly increased, the 
whole species affected by it must die out, as no 
single variation is considerable enough to evade it. 

Thus the disappearance of the mice in our illustra- 
tion is a sudden phenomenon that at once causes the 
hares to face an excessive number of enemies, which 
formerly only took part of their food from the hares. 
There was not time for the hares to change sufficiently 
to meet the numbers of foxes ; their fertility could 
not at one stroke be increased enough to cover the 
enormous disappearance. There was no time for the 
selection of the fittest. If we assume that something- 
of this kind took place in the case of the ichthyosauri, 
we can understand their extinction. The most probable 
contingency is that the sharks came in great numbers 
from another region into the sea where the reptiles 
were, probably driven out by geological changes. 
They increased at the expense of the ichthyosauri 
until the latter were completely extinguished. But 
the sharks could not suddenly reduce their fertility 
and size, and therefore had to go themselves on 
account of the lack of food. 

We see, then, that a species can be extirpated by 
some event that occurs suddenly, in this case by the 
immigration of sharks. Physical changes have a 
similar effect. If vast steppes took the place of the 
rich vegetation of the Jurassic and Cretaceous periods, 
the herbivorous dinosauri would be without food, and 
would be destroyed. We do not know anything about 


their extinction, but must not forget that they might 
be converted into smaller types of animals ; if, that 
is to say, the change in the vegetation took place 
gradually, and the smallest individuals, or those that 
required least food, were constantly selected. Another 
reason why they could not persist in their old size is 
that the very thick skull they had may have been a 
very good protection ; but it meant only a very small 
brain. But a small brain would be quite insufficient 
to keep up the vital energy required in the active 
life on the steppes. 

The pterosauri seem to have been really extirpated, 
not transformed, as we do not find their descendants 
in the birds. These flying lizards had naked bodies, 
and it is possible that a sudden lowering of the climate 
might account for their disappearance. The rapid 
setting-in of severe cold would not give them time 
to protect themselves by developing feathers, as their 
relatives, the birds, had already done. All reptiles are 
sensitive to cold in a high degree, as we see very 
clearly in the lizard, which only displays its full vitality 
in the sun. Hence it is that the giant-reptiles can 
only be maintained in warm countries, the tropical 
zone alone harbouring the mightier specimens to-day. 

Thus a change of climate that alters a country may 
either compel a species to change, or, if it sets in with 
comparative swiftness, extinguish it altogether. But 
there is a third contingency. The species in question 
may migrate. In this way the species that lived in 
Germany during the glacial period retired to the North 
and to the Alps, where they are still to be found. 


1 3 I 

Very few of them adapted themselves to the new 

Physical conditions are bound to modify a group 
of animals when they change themselves, as we saw 
in the first chapter. This applies not only to changes 
of climate, but to volcanic changes, the drying-up of 
seas, the sinking of continents, and the folding of the 
earth’s crust to form mountains. It applies also to 
modifications caused by human culture. Most of these 
factors may come into operation gradually, and modify 
rather than destroy species. In fact, even civilisation, 
which acts comparatively quickly, can modify species 
of animals if the nature of them is such that only slight 
variations are required to let them breathe the new 
atmosphere. We have an instance in the above- 
mentioned case of the blackbird. 

But there are also changes that arise quite gradually, 
yet extinguish a species. When, for instance, a continent 
sinks below the waves, however slowly, the land- 
animals living on it will be destroyed. What happens 
is, not that those animals are selected which are most 
accustomed to the sea, but the animals squeeze into the 
ever-decreasing territory, and when the time of the last 
subsidence comes it is too short to transform them into 
aquatic organisms. 

We see, therefore, that animal species are only 
destroyed when sudden changes set in that make their 
former habits impossible ; in other cases natural 
selection is given time to modify them. 

The word “ sudden ” must not, of course, be taken 
too strictly. When an animal has, in the course of 


hundreds of thousands of years, been transformed from 
an arctic to a tropical organism, from one with a thick 
fur to one with a thin coat, it is clear that a fresh 
lowering of the temperature will be “ sudden ” even 
if it takes several thousand years ; this period would 
not suffice to bring back the thickness of the fur which 
it took such a long time to abolish. Just as we speak 
in geology of “recent” times, although they may be 
hundreds of thousands of years away, so in the 
geological sense the word “sudden” may involve 
enormous periods. It means merely — so rapid that 
even favourable variations have not been able to meet 
the requirements of the change. 

One more question. Can natural selection do every- 
thing, if it has time and material enough ? Is it 
omnipotent in this respect? Can it transform any 
aquatic animal into a terrestrial one, and provide any 
land-animal with wings if it becomes necessary ? This 
is answered in the negative by most scientists. Many 
of them grant some species the capacity of developing 
and deny it to others. They say there are four different 
types of animals : persistent, elastic, rigid and plastic. 
The persistent types retain their form for immense 
periods ; there are still in our seas organisms that can 
be found in almost the same form in the oldest strata. 
Elastic types tend to revert always to the earlier form : 
rigid types have only a very slight power of adaptation, 
and generally perish when their environment changes : 
plastic types continually assume new forms as the 
conditions change, and thus conform themselves into 
new species. 



But it seems very questionable if there really are 
these different types of animals. Even the persistent 
types have been at one time evolved from lower 
organisms, and were therefore once plastic ; their 
persistence is not an eternal and unchangeable feature. 
That many animals have remained unchanged for very 
long periods is clearly due to the fact that this form 
was the most suitable for the environment in which 
they lived. We must not forget that it is not absolutely 
necessary that all the individuals in a species shall be 
modified so as to produce a new one. Let us take the 
case of a species of aquatic animals in a pond. The 
scarcity of food caused by their multiplication will put 
those in a more favourable position that can travel on 
to the land and adopt a different diet. But if a large 
number of the animals leave the water, there is no 
longer any need for the others to become land-animals, 
as they have now plenty of room and food. Natural 
selection means pressure ; new species are only 
formed when they must change in order to avoid 

This is quite clear when we consider the origin of 
migratory birds. Here it was the migration that created 
the species, the animals wandering into new regions for 
which they needed new characters. Migration is an 
important principle in the formation of species generally. 
Thus the flying insects that reached certain small 
islands lost their wings and became a new species, 
because in this case natural selection always favoured 
the worst fliers ; the good fliers were the first to tumble 
into the water. Animals usually only rise to more 


complicated and higher species when they reach special 
localities. We shall see this in a later chapter. 

The physical conditions of our planet are always 
changing, it is true, and on this account the animals of 
to-day are, generally speaking, different from those of 
former times. But, on the one hand, there are un- 
doubtedly spots on the earth in which the changes have 
not been very great, such as certain parts of the deep 
sea ; and, on the other hand, many animals can retain 
their simple form in spite of considerable changes. 
Thus we can understand why the very simple organisms 
from which all living things have been developed are 
still found in every drop of water. 

We will inquire further into the conditions that bring 
about the conversion of part of a species into a more 
complicated one, and leave the other part at the same 
stage of organisation. We have to- day not only the 
final twigs of the tree of evolution. We have worms, 
insects, vertebrates — in a word, living things at every 
stage of organisation. But most animals have changed, 
even when they have not gone beyond the range of this 
fundamental form. The reptiles that live to-day differ 
from those of former times, yet they are reptiles , and 
only a part of them chanced to get into such special 
conditions that birds were developed from them ; and 
these were so favourably placed that they grew in 
number and variety of species, as the new element they 
had found had room for adaptation in the most diverse 
directions. But geology tells us of animals that have 
persisted in almost the same form for incalculable 
periods ; and we must assume that some very exceptional 



conditions made this persistence possible. As a matter 
of fact, such animals are very rare. 

We must not say that the higher animals are better 
adapted than the lower. Higher only means, in the 
scientific sense, more complicated, not better. 1 he 
bacilli that carry on the struggle of life and death with 
man to-day show clearly how they, the lowest organisms, 
have equipped themselves to meet the highest. 

It is said that the Jurassic period was the age of 
reptiles. That is not correct. There were far more 
species that were not dependent on the giant lizards 
than species that were. Was the swarm of insects, or 
were the snails, subject to them ? And if we take their 
size and variety as a symbol of predominance, we should 
have to say that the whales and elephants are the lords 
of the world to-day, if not the insects, which have more 
species than all the other classes. 

No animal species has ever dominated a period of 
the earth’s development, since there were always other 
creatures that were overlooked by them and had no 
relation to them. It is only since the domination of 
man began that we speak with some justice of a king 
of nature, as his civilisation is able to alter the funda- 
mental conditions of animal life. But even here we 
are only partly correct. There are still countless species 
of animals for whom this dominion has no meaning. 

We come to the conclusion that the species that have 
remained unchanged since remote ages have retained 
their form because they had no enemy that compelled 
them to change, and because within the limits of their 
own species they grew to meet the physical conditions 


of the period. They were never faced with the 
alternative of changing or dying. If this alternative 
had been forced on the generations very gradually, 
and always in proportion to the possible latitude of 
variation, we may confidently assume that they would 
not have failed to meet it because of some necessity for 
remaining unchanged. 

We may also suppose that in all species of animals 
any change is possible if there is time enough for it. 
We are bound to admit this if our conception of the 
organic world is a scientific one. The tenth and eleventh 
chapters will tell us more of this. We will only say 
for the present that every particle of living matter has 
the tendency to vary. Every organ, every part of an 
animal, may change ; and this change will in certain 
circumstances become the basis for selection. How 
much the structural plan of an animal may be trans- 
formed is seen very well in the intestinal worms, some 
of which have lost the alimentary canal altogether, and 
take their food through the skin. The nearest character 
will, of course, be used for change. And with what 
enormously different means it may be effected is well 
seen in the wings of animals. In bats and birds the 
fore-limbs have been converted into organs of movement 
in the air ; in the former the skin forms the air-beating 
surface, in the latter the feathers. The birds come from 
the reptiles — probably leaping reptiles. The feathers 
had already been developed, as a warm covering, from 
the scales, and amongst the leapers those certainly had 
the advantage which had the longest quills on the fore- 
limbs, so as to act as parachutes in falling. This was 



the beginning of the organ of flight, and it was steadily 
improved. In this case the feathers afforded an easy 
basis for the making of organs of aerial movement. In 
the flying squirrel it was lateral folds of the skin ; also 
in the flying reptile, in which they were further supported 
by projecting ribs ; and in the flying fish the already 
flattened breast-fins were converted into organs of flight. 
The development of wings in the insects was very 
different. In their case a small projection developed 
at each side from the central body of the coat, and grew 
into two horizontal plates ; with the central part of the 
body these formed a sort of shield that carried them 
through the air, like a parachute, when they leaped. 
The insects were originally jumpers, as the lowest 
species still are. But there are higher species, such as 
the grasshoppers, that only use their wings for leaping, 
so that we can well imagine that the insects that could 
save themselves by the longest leaps away from their 
enemy were those whose lateral plates were most exten- 
sively developed. This use of the plates was fastened 
on by natural selection for further development, and it 
at last produced a joint by means of which the plates 
could be worked backwards and forwards by muscles. 
Thus the wings were made, and were modified in each 
species in harmony with its vital conditions. 1 

Let us return from the past to the present. 

The actions of reptiles and amphibians are mainly 

1 Other experts think that the wings of insects have been formed 
from what are called their trachea-gills. These are small articulated 
plates in the abdomen of May-fly larvoe that live in water, and serve for 
breathing. But the wings are situated right in the middle of the 
insect’s body, and so the theory given in the text is more probable. 


determined by instincts, and they have therefore no 
period of protected youth. When the little reptiles 
issue from the eggs, which have been hatched under 
the action of the sun’s rays in a moist place, they have 
nothing to expect from their parents. All their instincts 
are rigidly formed from the first ; their mobility is 
considerable at once, and the young of the viper 
have their deadly weapon, the poison, from the first 

Still, some of the reptiles, especially the lizards, have 
a certain amount of intelligence. If a caterpillar creeps 
across their path, they know that the victim cannot fly 
away quickly, and they observe it with a certain 
curiosity for some time. Then the head is suddenly 
lifted up horizontally, and the snout, pointing down- 
ward, pounces on the prey. It is crushed with rapid 
movements of the jaws, brought into the right position 
and swallowed, and the little tongue passes for some 
time afterwards over the nose, as if it were smacking 
its lips after the delicacy. A quicker insect, such as 
a grasshopper, is not watched for some time, but is 
captured at one swift bound. 

The serpent takes a great deal more trouble in 
capturing and swallowing his food. The smooth adder 
seizes its prey, which generally consists of lizards, winds 
itself quickly round it in three coils, lifts up its head, 
and opens its jaws wide to swallow the head of the 
victim. But the lizard also knows the only way in 
which it can escape, and opens its mouth wide ; if the 
snake approaches, it tries to seize its lower jaw, and if 
it gets hold of it will not let it go until the snake 



releases it. Very large lizards often escape death in 
this way. 

The defenceless frog, on the other hand, is completely 
at the mercy of its enemy, the ringed adder. When 
one is after him, he makes desperate efforts to escape, 
his usual measured jumps becoming gigantic in his 
anxiety. A plaintive cry comes from his throat, and 
he often abandons himself to his fate by crouching 
down, when he is seized by the snake. If the snake 
grasps his head the end is comparatively speedy, but it 
often seizes the foot first. It then forces itself, as it 
were, over the leg, its teeth gripping further and further 
forward ; as these do not serve for masticating but 
merely for holding, in the snake, and as they are 
directed backwards, they easily allow anything to enter 
the mouth but prevent it from dragging or falling out. 
When one leg has disappeared down the snake’s throat, 
it tries to grasp the other by a quick jerk, and if it 
succeeds its teeth go farther over the frog’s body. The 
head of the snake swells prodigiously, there is a last 
desperate croak from the frog, and the jaws close over 
it like a living tomb. Surprise is often felt that such 
large frogs can be taken into the small head of the 
snake, but it is capable of enormous distension at the 
back ; the anatomic foundation of this is that the bones 
of the lower jaw articulate with those of the upper jaw, 
which are drawn out far behind, and enlarge the gullet 
considerably when they open across. 

Poisonous snakes go to work in a different way. 
These hunt almost entirely during the night, as they 
are generally nocturnal animals. The best way to catch 



the common viper is to make a fire in the wood at 
night. The unusual light attracts them, and they 
approach in amazement and stare curiously into the 
flames. During the day-time they are sluggish, and 
they coil themselves into a disk, with the head lifted 
up threateningly when a man approaches. We do 
not know much about the viper’s method of hunting, 
but it is supposed that it gives the mouse, which is its 
chief article of diet, a deadly bite, and lets it die before 
swallowing it. It also penetrates into the dwellings of 
the mice ; we can imagine the consternation of the little 
creatures when they suddenly see their enemy’s eyes, 
sparkling with death, before them in their holes, and 
have no means of escape. There has been a good deal 
of inquiry into the viper’s terrible weapon — the poison. 
If the wound is immediately sucked out and bound up 
the bite is not fatal, but there are frequent fainting-fits, 
and the final symptoms of the disease only disappear 
after six weeks. The best treatment of the wound is 
with permanganate of potash, and an ancient and 
constantly verified remedy is to drink a large quantity 
of alcohol. 

The movements of the serpent are peculiar. They 
have no limbs, and can only glide along with the aid of 
the whole body. This motion has been compared to 
the progress of a rowing boat, because the serpent’s ribs 
act like oars. The ribs articulate with the vertebral 
column and have free terminations, but are connected 
with muscles in such a way that they are pushed 
forward and pulled back again, which gives rise to 
serpentine motion. Other muscles, however, connect 


1 4 1 

the ribs with the ventral plates, all of which end in 
a sharp edge, directed inwards. Hence when a rib is 
drawn forward, the edge of the corresponding ventral 
scale is brought into a vertical position and must take a 
grip in front ; on account of its sharpness it cannot slip 
back, and when it is drawn to the body by the next 
movement of the ribs, the body itself must slide forward. 
By working the apparatus rapidly and extensively the 
serpent advances quickly enough, but can, of course, 
always be caught up by a human being. The lizards 
also have the aid of this winding of the body in running, 
and make use of the tail for the purpose ; hence a 
lizard with a broken tail cannot get along nearly as 
quickly as one that has the full use of that organ. 

Everyone who has tried to catch one with the hand 
knows that the lizard’s tail is easily broken off. If you 
take hold of it by the tail, you will be sure to find this 
quivering vigorously in your hand, and its former 
possessor hurrying away without it. This is a great 
advantage for the animal ; the number of tailless 
lizards one sees in nature show best how often the 
species is saved in this way. The chief enemy of the 
lizards, the smooth adder, generally catches them by the 
tail when it is after them ; and if the tail breaks off and 
dances about in a lively way before the eyes of the 
snake, the latter eats it and the lizard is saved. The 
best way to catch lizards without injury is to take a long 
grass-stalk, make a loop at the end of it, and slip it 
carefully over the animal’s head. It does not suspect 
its danger, and is captured by lifting up the stalk. 

But nature, which has given this means of escaping 


to the lizard, has also endowed it with the faculty of 
creating a fresh one if it is lost. Three weeks after 
the removal of the tail there is a leathery prominence at 
the wound. This continues to grow, and forms a new 
tail, which is so much like the old one that it takes an 
expert eye to see the difference. However, the new 
one never becomes as long as the old one, and it may 
take two years to become perfectly similar to the old 
one in colour and shape. 

The faculty of re-making lost limbs is called 
regeneration , and it forms a fitting transition from the 
reptiles to the amphibia. These have an even greater 
power of regeneration than the reptiles. It is true that 
a frog’s legs do not grow again if they have been cut 
off, as many peasants believe, when they throw the poor 
creatures into the water again after amputating them ; 
but the tailed relative of the frog, the newt, can 
reproduce a great part of the body. Its legs grow 
again when they have been cut off, the skin always 
heals, and even a new eye is formed when one has been 
torn out. The newts are exposed to the attacks of a 
large number of enemies ; fishes, birds, and their own 
relations, are continually after them, but it is especially 
the large water-beetles that often clip off their legs with 
their sharp jaws, or bite off an eye. Hence the power 
of regeneration is confined to parts of the body which 
are apt to be frequently lost in this way ; this happens 
especially to the newt’s legs. The lizards are not 
easily grasped by the leg by their enemies, and so this 
has not the power to reproduce itself, as their tail has. 

A poisonous snake is never seized by the tail, because 



every animal knows that the only way of avoiding the 
fatal bite is to grasp it by the neck ; and as for most 
animals, and a good many human beings, serpents are 
always serpents, the dread is extended to the adder. 
As a result of this we do not find the faculty of 
regenerating the tail in any serpent. 

Thus we see that the power of regeneration has been 
developed by natural selection wherever it is necessary 
— where a species is constantly exposed to mutilation. 
This faculty is increased in proportion to the frequency 
of the mutilations, and is not found at all where it would 
be of no avail, where the enemies of a species destroy 
the whole animal when they catch it. It is on this 
account that we do not find any faculty of regeneration 
in the frog ; its enemies do not tear off pieces of it, but 
kill the whole animal, as we know to be the case with 
the stork, ringed adder, fox, weasel, hedgehog, and 
the innumerable other enemies of the frog. There is 
one animal, however, that mutilates the frog before eating 
it, and that is the tortoise. These approach the frog 
from the depth of the pond, as it sits unsuspectingly 
on the edge, seize it suddenly by the leg, drag it under 
the water, get the leg as far down the throat as possible, 
and then cut it off from the body with their sharp claws. 
When they have swallowed the leg, they tear other 
parts from their unfortunate victim, until nothing is left 
but the skeleton. In this case it would certainly be an 
advantage to the frog if it could escape after the loss 
of one leg and form a new one. But it is exceptional 
for a frog to be captured by a tortoise, partly because 
they live chiefly on insects, snails, worms, fishes, and 



salamanders ; partly because the animals themselves are 
rare. Natural selection does not provide for exceptional 
cases; it only brings about adaptations that meet average 
needs. A character can only be preserved when the 
majority of the animals that did not possess it would 
come to grief on that account. When a particular 
danger only threatens a species now and again, the 
animal that escapes it through some peculiar character- 
istic will have no prospect of bringing this to predominate 
in the species generally. The characteristic in question 
will soon disappear owing to crossing with others ; while 
the majority, which do not possess it, will survive, 
because the danger is too infrequent to cause it to be 
selected. When we find in the animals that they only 
react by adaptations against dangers that are common 
in their life, this is an excellent proof of the operation 
of natural selection. 

We shall make the acquaintance in later chapters of 
other animals that have a high power of regeneration, 
but will for the moment cast another rapid glance at the 
mammals and birds. If we bring before our minds the 
enemies of the various species of these two classes, 
their methods of attack, we see at once why they 
generally have no faculty of regeneration. It is true 
that the beak may be reproduced in the bird, and it is 
this especially that is exposed to injury, as it is the 
main implement and the weapon of the inhabitant of 
the air. Further, the skin can be regenerated in 
mammals ; and if a wound we have received were not 
closed by scar-tissue, an infection by bacilli would 
inevitably follow. And when we consider the absence 



of regeneration in various parts of animals that have 
otherwise a high power of regenerating, its origin as 
an adaptive phenomenon becomes perfectly clear. The 
newts that re-form eyes and legs cannot regenerate 
internal organs. If we cut the lungs out of a triton, 
or the ovary or any other internal organ, and sew it 
together again, there is no regeneration of the part in 
question. Why ? Because such a mutilation is hardly 
possible in nature, and so could not be provided against. 

While the newt has this admirable power of regenera- 
tion to protect him against his enemies, the frog owes 
its maintenance generally to its enormous fertility. 
Their eggs, the familiar frog-spawn, are not only 
poured into the water in large numbers, but are also 
provided with a peculiar protective structure, which 
consists of a jelly surrounding the egg. This jelly 
prevents the eggs from being dried up or crushed, and 
especially protects them from enemies. Birds, fishes, 
crustaceans, and other animals are unable to eat the 
eggs, because they slip out of the mouth again. Every- 
one knows how difficult it is to handle frog-spawn. 
The transparent balls of jelly also act as lenses for 
focussing the rays of light, and thus attract movable 
plants, such as certain algse, that produce oxygen, 
which is good for the eggs. The jelly also lets the 
rays of light pass direct to the eggs, and keeps them 
there, so that they are practically surrounded by glass- 
houses. The spawn is slightly heavier than water, and 
if a high temperature causes an increased outflow of 
gas from the plants, the bubbles collect on the spawn, 
and bring it to the surface, where it receives the full 



rays of the sun. When it is very cold, the outflow of 
gas ceases, and the spawn sinks to the bottom of the 
water, and is protected there from the wind and frost. 

The wonderful contrivances of the frog-spawn show 
that all the stages of the animal’s career are subject to 
natural selection. Only those animals have a prospect 
of transmitting their character to the next generation 
which lay eggs that will escape the eye of the enemy 
and the injury of bad weather. Whole pages might be 
written on the adaptations of the eggs in the early 
stages of the animals, and we shall see more about 
them later on. 

We must not leave the amphibians without drawing 
attention to one of their best adaptations. This is the 
character of their skin. It is not merely that this 
represents the chief breathing-organ in this class, and 
so enables a lungless frog to survive longer ; it also 
affords the greatest protection to the animal. The 
secretion of the cutaneous glands of the amphibians 
is well known, and a good many legends have been 
told of the salamander, which has been credited with 
the power of remaining unhurt in fire. There is this 
much truth in them, that the animal can remain for 
some time over a gentle fire, as its glands give out 
their secretion more freely under heat. But the pur- 
pose of this juice is to disgust the enemies of the frog. 
This is chiefly attained by the offensive smell, but 
also by the corrosive nature of the fluid. The toad- 
secretion is not poisonous for human beings, though 
it causes inflammation if it touches the eyes, but it 
may be fatal to small animals. 



Most of the amphibians that secrete offensive matter 
are brightly coloured. The fire-salamander catches the 
eye at once with its bright yellow spot on a black 
ground, the newt or water-salamander has a yellow 
belly, like the ringed snake ; the latter have been seen 
to throw themselves on their backs at the approach of 
danger, so that the yellow under-side is suddenly 
presented to the astonished pursuer. 

Light colouring is very common amongst malodorous 
and poisonous animals and plants. Of plants we have, 
for instance, the fox-glove, the laburnum, and many 
poisonous fungi ; but as the flowers of most plants 
are brightly coloured — for reasons that we shall see 
in the sixth chapter — the poisonous flowers are not 
very conspicuous. This is more the case with the 
animals. Besides our amphibia, a number of malodor- 
ous and nasty-tasting butterflies and many marine 
polyps are brightly coloured. Offensive and poisonous 
organisms show red or, more generally, yellow colours ; 
it can hardly be a matter of chance that in the colour- 
language of lovers yellow is regarded as a sign of hatred 
and aversion. 

It is easy to see why natural selection has given a 
striking appearance to poisonous and obnoxious animals. 
It is an advantage to them to be recognised at once as 
inedible and dangerous. What use is it to an obnoxious 
animal if the assailant does not know that it has a nasty 
taste, and has to convince himself of it ? The victim 
has generally to die under the test. So their poison is 
of no use to poisonous organisms if their enemies do not 
know them. The enemies die also after eating them, 


but this is a revenge that cannot bring the slain animal 
back to life. 

In the case of many animals, such as the butterflies, 
one bite is fatal, and hence those poisonous and ob- 
noxious animals were always selected which were 
calculated by their appearance to prevent enemies 
from trying whether they were edible or not. It is 
important, further, that all the marked animals should 
have as nearly as possible the same indication. Then 
carnivorous animals will not test the edibility of any 
new offensive creature that crosses their path, but will 
remember their experience of similar creatures and 
leave it alone. Hence it is that so many poisonous 
organisms have yellow colouring. There are even 
edible animals with the colour because it affords 
them protection ; the value of this adaptation, which 
we will examine more closely in the sixth chapter, is 
obvious. Possibly this is the explanation of the two 
bright yellow spots at the back of the head of the 
ringed adder, which have given occasion for the pretty 
saying, that the snake, as the harmless creature is 
popularly called, wears a crown. 

Natural selection has also given many amphibians 
a protective colouring, instead of the disgusting and 
warning colours. A toad closely resembles a clod of 
earth, the brown frog is not easy to distinguish from 
the soil, and the tree-frog can hardly be detected in the 
green foliage. The latter can change its colour — not 
voluntarily, but it assumes shades from brown to green 
according to its disposition, the weather, and the 



The amphibians and reptiles may live for a consider- 
able number of years, though our own species are not 
so ancient as the crocodile, of which the blacks say there 
are specimens that have sunned themselves on the same 
sand-bank day after day as far back as the memory of 
their fathers and grandfathers goes. It seems, however, 
that the tortoise may live for a hundred years, and toads 
have been kept in confinement for thirty-six years ; they 
are not infrequently kept, as they are the most 
intelligent of the amphibia, and sometimes answer to 
their names. But the stories of toads living for decades 
inside blocks of stone must be relegated to the realm of 
fables. It is true that they can go a long time without 
food, and a much longer time with little food ; this is 
due to their almost perfect digestion. But air and 
moisture are absolutely necessary for them. 

It may happen that a toad falls into the shaft of a well 
during its nocturnal rambles, and, while its companions 
hunt and love and rear their progeny in the garden and 
the field, it is condemned to maintain a pitiful existence 
on a few insects, and so may become as “old as the 

Even the animal has its destiny. 



Origin of terrestrial vertebrates and of lungs. Similarities in the 
structure of animals. Transformation of organs. Creation 
or evolution ? Many animals are worse off than others. 

Selection only creates what is necessary. Atrophy of useless 
organs. Rudimentary organs in man. Degeneration of organs 
by panmixis. Indifferent characteristics of animals. The 

differences between species are adaptations. Correlation. 
Animals that are beyond the range of selection. Qualities and 
quantities. Explanation of atrophied organs by economy of 
sustenance and negative selection. Impossible to explain many 
rudimentary organs. The biogenetic law. Gills in the human 
embryo. Predatory fishes. The rhodeus and the pond-mussel. 
Senses of fishes, their dangers. History of the eel and the 
salmon. Artificial selection of fishes. 

As we make our way down from the sunny heights of 
the forest-crowned hills to the green valley, we often 
halt for a moment, when our eye falls on the brook by 
the way, and catches sight of a trout. We admire the 
ease and restfulness with which the animal meets the 
rush of the water over the stones. 

But there is something more wonderful in the power 

of the fish to penetrate into the depths of the sea, and 

remain there without any exertion of the muscles. As 

a fact, the fish can halt at any depth without moving a 

fin ; it has a special organ that enables it to do this. 

The swimming-bladder is the name of this organ, and 




anybody who has ever killed a fish will remember the 
large structure filled with air. The bladder is sur- 
rounded by muscles, and when it is compressed by 
these the fish descends in the water. As the fish has 
about the same specific gravity 1 as the water, it becomes 
heavier when the air in the bladder is compressed, and 
so descends ; when the pressure is relaxed, the air 
expands in the bladder, the volume of the fish is 
increased, it is specifically lighter, and it rises to the 
surface. Pressure on the front part of the bladder 
causes the head to sink ; pressure at the back sends 
down the tail. 

In about half the species of fishes the bladder is 
connected with the gullet by a duct. This is especially 
developed in the dipneust or mud-fishes, which live in 
tropical waters that dry up in the rainless season. In 
many species the bladder is double. When the water 
disappears from the pond they live in, and they find 
themselves on the mud, the bladder takes over the 
function of breathing from the now useless gills. They 
absorb the oxygen from the air that presses into the 
bladder through the gullet, while the carbonic acid that 
must be given off from the fish’s body passes away by 
the bladder and its duct. 

The mud-fishes are most interesting to us, because 
they show that an organ which seems to make its 
appearance suddenly in the land-vertebrates is really 
found in a rudimentary form in the fishes. If we had 
not the mud-fishes, we should scarcely be able to 

1 The reader will know that we mean by specific gravity the number 
of times that a body is heavier than an equal volume of water. 


imagine how the first land-animals could breathe, as 
they would need an organ in some proportion to their 
size. How could this be formed so quickly, seeing that 
natural selection only builds up gradually from small 
beginnings? The mud -fishes remove the difficulty. 
They afford most striking testimony to the theory of 
evolution and natural selection, as they show that where 
selection required a large organ as the beginning of the 
lungs, it was forthcoming. It is well for us that in 
the peculiar localities where land-animals arose some 
of the transitional forms are still preserved ; the more 
so as geology could give us no information on the 
transformation, since soft parts are never fossilised . 1 

The transition from the fishes to the amphibians is 
seen, not only in the mud-fishes, but in the develop- 
ment of every frog and salamander. The larvae of 
the amphibians, when they issue from the egg, 
breathe by gills, which closely resemble those of the 
mud -fishes. In fact, the whole organisation of the 
larvae is closer to that of the fish than to the adult 
of the species they belong to. 

Even the adult amphibians very much resemble the 
fishes ; all vertebrates must do so, in fact, if they 
have descended from the fishes. We know how 

natural selection, which must have brought about the 
transformation, works. Variations in different organs 
of the parent species, which are trifling at first, are 
emphasised in the course of several generations. 

1 There are, however, recent experts who think the lungs were 
formed, not from the swimming-bladder, but from sac-shaped folds 
or outgrowths of the fore-part of the gut. 



Hence in the comparatively brief period — geologically 
speaking — since the appearance of the fishes, no 
species could be developed from them with a 
fundamentally different structure from their ancestors. 

There are no organisms that descend from the verte- 
brates, and differ from them so widely, as the fishes 
do from the insects ; the chief reason is, that there 
has not been sufficient time for such a transformation. 

We can understand, therefore, why the structure of 
all vertebrates is essentially the same. All of them 
have an internal skeleton, and have the organs of 
nutrition and reproduction on the ventral side, and 
the nervous system on the dorsal side. But the 
similarity goes still further, and this also is clearly 
the effect of natural selection. Selection always 
builds on a given material ; it makes use of actual 
adaptations, preserves them when change is un- 
necessary, and modifies them when some new adapta- 
tion of the species requires it. If, for instance, there 
was already amongst the fishes a skull with the 
function of protecting the brain, there was no need 
for the formation of a new structure to contain the 
ever-growing brain in the classes that developed from 
the fishes. Therefore, the bones of the fish’s skull 
were retained in the new classes, and were enlarged 
and modified according to need. As a fact, even the 
human skull is generally composed of the same bony 
plates that we find in the fishes. It is well known that 
students used to be puzzled by the fact of the upper 
jaw of all vertebrates containing four pieces of bone, 
while in man it had only two, until Goethe discovered 


the two “ intermaxillary bones ” in the child, and 
showed that they fuse together in the adult, and 
cannot be distinguished any longer from the other 
two jaw-bones. 

It is the constant practice of natural selection to 
build on actual material, and that is the quickest way 
of accomplishing anything. Hence, when the amphibia 
took to living on land, and needed support for the 
body and organs of locomotion, the four fins of the 
fish were converted into the limbs of the land animal. 
In the lower fishes the joint of the jaws is formed of 
two bones, which are replaced in the higher ones by 
a greater development of the articulating bones. The 
abandoned bones are found in the higher animals 
only in the internal ear, where they still form a joint 
as the “hammer” and the “anvil”; but instead of 
mastication, it serves for conducting sound. 

We could show that nearly all the organs of the 
vertebrates are found in all the five classes, and have 
always the same fundamental form and structure. We 
have seen in the previous chapter that Darwinism 
explains these similarities, great and small, by the 
law of heredity. The children of a certain couple of 
human parents are more like each other than their 
children will be — or brothers and sisters are more 
like each other than cousins — and it is just the same 
with animals. Birds are nearer to reptiles than to 
amphibians, because if we look upon the actual 
reptiles as brothers of the actual birds, the actual 
amphibians will be their cousins. It was from leptiles 
that the birds descended, and the ancestors of all 



reptiles consisted of a pair of amphibians that reached 
special conditions, and so their offspring formed a 
new class. These amphibians lived about the end 
of the Carboniferous period. Their ancestry coincides 
with that of the other amphibians living at the time, 
whose descendants are found in our frogs and 
salamanders ; earlier still, it is a pair of fish ancestors 
that led to the beginning of the amphibians in a 
particular locality. 

This similarity of organisms is a hopeless puzzle 
for the theory that all our animals were created 
separately. On that theory it is unintelligible why 
some animals so closely resemble others in structure, 
others still more, and others not at all. It can give 
no explanation of these facts. Moreover, it cannot 
explain why certain species seem to be in a much 
worse position than others. Thus, for instance, the 
circulation of the blood is clearly worse in the frog 
than in the bird. The frogs have only one chamber 
to the heart, and this has to receive both the used- 
up blood from the body and the fresh blood from the 
lungs with its new oxygen. The blood mixes in the 
single chamber, and the body is not supplied entirely 
with fresh blood, but with the mixed fluid, which 
passes from the heart into the body. In the bird 
the chamber is divided by a partition ; the fresh 
blood from the lungs passes into the left half, and 
is conveyed in its purity from this to the body, while 
the right chamber receives the used - up blood and 
drives it to the lungs to be renewed. 

The birds, with their constant supply of pure blood, 


are obviously better off than the frogs, in which the 
oxidised blood that should go to the body is always 
mixed with the bad. Why were the frogs placed at 
this disadvantage at creation? Have they less right 
than the birds to a good constitution ? 

Natural selection explains the riddle. From the 
heart of the frog has been developed that of the 
amphibian, then that of the reptile, and from this 
in turn that of the bird. When the amphibians 
appeared, the heart was at the stage of development 
in which we still find it in that class. This structure 
sufficed for those descendants that remained amphibians, 
but not for those that became reptiles and birds. 
In the case of the latter, the heart had to be improved, 
because the more energetic vitality of the two new 
classes required a better supply of blood. Natural 
selection only produces what is necessary ; the amphi- 
bians had to retain the old heart, because they did 
not need a more advanced one. 

But all the organs cannot be retained when a 
species is transformed into a different one. 

When complete land-animals had been formed from 
the fishes, the gills became useless. In fact, they 
would be injurious to the new organisms, as they 
perforate the sides of the gullet, and would allow 
foreign bodies to pass too easily into it. Thus, for 
instance, it often happens to the greedy perch that his 
prey sticks in his gills from trying to swallow it too 
quickly, and both animals perish. As soon, therefore, 
as the gill-clefts ceased to be absolutely necessary for 
breathing, they had to be got rid of by natural 



selection on account of their dangers, which were 
increased by life on land. Here we have for the 
first time the negative action of natural selection. We 
see that it can not only create new organs, but also 
destroy actual ones when this becomes necessary for 
their possessor. 

It often happens that when an organ has to be 
adapted to a new function parts of it will degenerate. 

When the fore - extremity of the reptile was con- 
verted into a wing in its descendants, the birds, it 
was useful to the latter to have the new organ in one 
piece , in order to work it like an oar. Projecting 
fingers would have offered resistance to the air, and 
would have brought continual wounds to the bird by 
getting broken off. Hence, in the interest of the 
flying-organ, the fingers had to disappear. As a 
matter of fact, in the bird’s wing to - day we find 
only the rudiments of five fingers, though the archae- 
opteryx had them well developed and active. There 
are plenty of instances of a similar decay in the 
interest of a unified support ; amongst others, we 
might mention the leg of the birds and the ungulates. 
What seems to be the knee in the fore - leg of the 
horse corresponds to our wrist. The large bone that 
passes from this to the joint of the hoof is the upper 
part of the middle finger ; it has been developed to 
this extent because it can bear the weight of the body 
better as a single support. But at the side of it we 
find two other small bones, which are attached to the 
joint above, and are called the styloid bones. They 
have no function, and cannot be understood except 


as relics of the second and fourth fingers ; we can 
recognise them as such the more confidently as we 
can trace in geology every stage in the gradual 
degeneration of these fingers in the horse’s ancestors. 
These degenerate structures are known as rudimentary 
organs ; they lend great support to the theory of 
evolution. If the animals were created separately, 
why were they endowed with these quite useless 
appendages? We can only understand them when 
we admit that they were fully developed and useful, 
in the ancestors of the particular animal, and that in 
their descendants, which had no further use for them, 
owing to change of habits, they could not entirely 
disappear, because the animals had inherited them 
and transmitted them in their turn. 

We find rudimentary organs of this kind in almost 
every species of animals. Man himself has a large 
number of them — nearly a hundred. Amongst others 
there are the last two ribs, the wisdom-teeth, a process 
of the shoulder-blade — the caracoideum, a vesicle in the 
brain that we call the pineal body, and the worm- 
shaped appendage of the ccecum. The latter is not 
only superfluous, but even dangerous, on account of 
the inflammation (appendicitis) that may be set up in 
it by the penetration of foreign bodies. There were 
vegetarian mammals amongst our ancestors. And in 
plant-eaters the coecum is often indispensable, and is 
often longer than the whole body of the animal. 

In the same way the caracoid process of our shoulder- 
blade is an important bone in reptiles, amphibians, and 
birds ; and in the pineal body we have the last relic of a 



cyclopean eye that was used by the ancient amphibians, 
and resembles a small eye in a certain living reptile in 
New Zealand. The more we examine the anatomy of 
the animals, the more rudimentary organs we discover. 
In the whale the pelvis and hind-limbs remain as 
shrunken relics buried in the flesh ; and amongst the 
serpents there are species that still show rudiments 
of the pelvis. 

In the case of many of these organs the reduction is 
due to natural selection, which has a much greater 
significance in this direction than most experts admit. 
But it does not explain every case ; above all, we can 
only understand with its aid how an organ can be 
reduced to a body that is indifferent for the life- 
purposes of an organism. We have already spoken of 
those island-dwelling insects that have had their wings 
reduced to small relics, because those that could fly well 
were too frequently carried by the wind into the sea. 
In this case natural selection had to reduce the wings 
until the insects could not raise themselves with them 
any longer. There its function ceased. It could not 
make the wings any smaller, because if no insect could 
fly any longer, there was no ground for selection, and 
for the function of flight — the sole cause of selection — it 
was a matter of complete indifference whether or no 
the wings were reduced by another fraction of an inch. 

There are also insects in Europe that never fly. 
These are the females of most of the bombycidae. 
When they emerge from the pupa-covering, they remain 
in the same spot, and are sought and fertilised by the 
active males, and then lay their eggs. The reason for 


this peculiar instinct may be that, in the first place, the 
animal, which is well adapted to the bark of the tree, 
protects itself and its eggs best by remaining still ; and, 
secondly, that the body is too much burdened with 
e gg s to be able to fly. If it is better for the animal not 
to fly, this instinct suffices to prevent it, and natural 
selection has no occasion to reduce the wings, as has 
been done with some of the silk- worms, such' as the 
orgyia, the wings of which have shrunk into small 
relics. But if the disuse of flight depends only on the 
overloading of the body with eggs, we do not very well 
understand the reduction of the wings at first sight. 
Can it be useful for the butterfly to have the nourish- 
ment that usually goes to the wings diverted to the 
rest of the body and the eggs ? When we remember 
the enormous multiplication of the black arches which 
still have wings of the full size, we shall not attach much 
value to this economy of food. Nor can we quite 
admit, in the case of the whale, that those individuals 
always had an advantage whose hind-limbs were a trifle 
shorter than those of their comrades, and so required 
slightly less food. In view of the enormous mass of 
muscle and fat in the colossus, this slight economy 
could never become a matter of life and death, even if 
it is useful at all to the other organs. 

But, we may further ask, is natural selection bound 
actively to reduce an organ that has fallen into disuse ? 
Do we not know that such an organ must deteriorate 
when selection ceases to affect it ? Every organ only 
advances from the fact that the individuals that have it 
in a poorer form are destroyed. When it becomes a 



matter of no consequence whether an organ is in good 
or bad condition, those animals will survive and repro- 
duce who have it in an inferior form ; this inferior organ 
will be transmitted to the young, and the number of 
individuals of that kind will increase in every generation. 
For instance, there is no need for civilised man to have 
good eyes. Those with poor sight can earn their bread 
and bring up a family, by using glasses or adopting a 
field of work in which shortsightedness does not count. 

This process, in virtue of which even the inferior 
specimens are preserved, reproduce, cross constantly 
with the others, and so affect each generation more and 
more, when natural selection ceases, was first pointed 
out by Weismann and given the name of panmixis . But 
the effect of panmixis is not as simple as it seems 
at first sight, and it must not be exaggerated. It 
cannot bring about the reduction, but only degeneration 
of an organ. We will now see how this takes place. 

In a complicated organ, such as the eye, for instance, 
a number of different parts co-operate to discharge its 
particular function. All these parts form a harmonious 
whole, and if the organ is to be improved, they must all 
be modified in the same direction. An orofan of this 
kind is like a regiment of soldiers marching in rank and 
file. Order is only preserved as long as each individual 
remains in his place, or moves just in the same way as 
the rest. If one marches in one direction, another in 
another, the unity of the whole is destroyed, and the 
greatest confusion prevails. 

The harmony of the parts of an organ is secured 
by natural selection. The parts of the eye vary like 


every other living thing. If the eye is to retain its 
efficacy, no part must be greatly altered unless the other 
parts change in the same sense. If one of the parts of 
the eye is suddenly and separately developed in an 
animal that absolutely needs good sight, it fails in the 
struggle for existence, and with it disappears the 
inharmoniously developed eye. There is only one way 
of improving the eye, but there are plenty of ways of 
spoiling it. Hence if selection no longer watches over 
the harmony of an organ, each part will vary on its own 
account ; one part will advance in this direction, 
another in that, and the end of it will be the spoiling 
of the whole organ. 

It is clear, then, that panmixis, or the mixture of all 
possible animal variations without weeding out the bad 
ones, must lead to the degeneration of an organ. But 
does an organ become smaller when selection ceases to 
act ? Diminution of size is the chief characteristic of 
rudimentary organs. 

Certainly, when natural selection no longer prevents 
the reduction of an organ by cutting off all variations 
towards diminution, these will persist and be transmitted 
like the rest. But are there not always variations in 
the direction of increased size ? Why should the 
reducing tendencies suddenly prevail ? Natural 
selection cannot influence variations ; it can only 
accept or reject those that are offered to it. 

As a matter of fact, it has been proved beyond 
question by a number of investigations that variations 
towards increase and decrease — plus and minus 
variations, as we call them — are as a rule equal in 



number. Hence if selection ceases to weed out the 
one group, all the animals will come to reproduce and 
cross with each other ; in the general mixture the plus 
and minus will neutralise each other. The larger 
variations cannot prevail in the succeeding generations, 
because they are affected by just the same number of 
smaller variations. An organ that is subjected to 
panmixis will thus become neither smaller nor larger, 
but remain of the same size. It will become one of 
what are called the indifferent marks of the particular 
species — a mark that has no connection with the 
essential life of the animal, yet is tenaciously retained in 
the structure. Are there any of these indifferent marks 
in the organic world ? 

In the first place, it is always precarious to describe 
certain characters of animals as indifferent. In earlier 
years all that we have recognised to-day as adaptation 
was regarded as a mere mark of the species. Every 
year there are fresh discoveries of adaptations ; we are 
constantly finding an important vital significance in 
parts of animals that had been regarded as of no 
consequence whatever, 

Nevertheless, they may be indifferent organs, and 
we can easily imagine how they may arise. When one 
species is formed from another, a whole series of organs 
are modified to meet the new conditions. But the new 
species will also inherit from the parent species features 
that were necessary to the ancestors in their particular 
conditions, but have no use in the new environment. 

If these organs were in the way of the new life, they 
would, like the gills of the fish and the fingers on the 


bird’s wing, be reduced by natural selection until they 
were harmless ; but if they were of no consequence 
either way to the new species, they would remain 
unchanged in size, because their plus and minus 
variations would neutralise each other. They would 
only change their size in the event of the total size 
of the new species having to be altered. 

The province we have now entered is a very delicate 
one, because, as I said above, we can never know 
whether a characteristic of an animal, the use of which 
is not visible, may not be indispensable all the same. 
In any case, it is certain that indifferent features do not 
form the chief criteria of species and classes, as has been 
said ; nor is it true that the adaptations are not con- 
cerned in the discrimination of species. It has been 
justly replied to these writers that it is precisely the 
adaptations that constitute the species or the class as 
such. What else is left in the whale if we take away 
its adaptation to aquatic life ? What becomes of the 
bird, which, as we saw above, consists entirely of 
adaptations to aerial life? If we look at species in 
this way, we feel inclined to say that there is nothing 
indifferent in an animal. 

Hence we see the rise of new species especially 
in the selection of new adaptations. In this, in- 
different organs may be taken over ; in fact, it is 
possible for them to appear for the first time. Darwin 
himself established a law that he called the law of 
correlation. According to this, the various parts of 
the animal body mutually affect each other in growth. 
Everybody knows, as a matter of fact, that organs that 



seem to have nothing to do with each other may 
influence each other. Thus, when a man is emasculated, 
he retains the high voice of the boy, and never grows a 
beard. Women who are about to become mothers 
suffer from nausea, vomiting, and a number of other 
afflictions. In a word, we have numerous proofs of the 
co-operation of different parts of the body. 

Thus, when an organ has been adapted to new 
conditions and modified in the making of a new 
species, a structure may arise in another part of the 
body from a chain of causes that escapes our scrutiny. 
We put chandeliers in our rooms to light them, for 
instance. But we heat them at the same time, as well 
as illuminate them. This is a constant and necessary 
concomitant of the lighting. We had no intention of 
causing it, but we have to reckon with it because we 
cannot have the gas-light without it . 1 

Owing to correlation many organs may be preserved 
that are of no consequence to the animal’s life. Other 
and important organs prevent them from changing their 
dimensions or quality, because they are in some way or 
other connected with them, and as they themselves must 
remain in the interest of the species, they retain the 
others with them. However, we will make as little use 
as possible of this principle of correlation, because we 
know little about the mutual relations in the animal 
body, and so the whole principle is not well grounded 

1 Many writers explain in this way the colours of the various races 
of men. They think it is a necessary concomitant of the adaptation 
of the skin to different degrees of heat ; the skin does, in point of fact, 
behave differently in relation to perspiration and immunity against 


on facts, and lends itself to abuse and misuse in all sorts 
of cases. Many Darwinians hide behind this principle 
whenever they cannot discover real explanations. 

We saw that an organ from which natural selection 
has removed its hand remains of the same size, but 
deteriorates in quality. How is it with an animal that 
is outside the range of selection? We see this in the 
case of our domestic animals. Apart from cattle, 
horses, pigs, and fowls, and especially dogs, of which 
we produce larger and smaller races by artificial 
selection, and the organs of which have been modified 
by selection, we see that, as a matter of fact, the size 
of domestic animals generally remains the same. Take, 
for instance, the cat, the fallow deer, and the common 
pigeon that is found on every roof. The parts of these 
animals scarcely change in size, though they do in 
another particular — colour. The reason of this is that 
qualities do not vary in two opposite directions, that 
neutralise each other in crossing, but in several. Still, 
there are colours the microscopic structure of which 
compels them to appear either in a light or a dark 
shade, and these will be preserved in panmixis. 

As a general rule, however, the colours of animals 
must be preserved by natural selection ; this is seen in 
many wild as well as tame animals, the variations in the 
colour of which clearly involve no danger to the species. 
Take the varying colours of the common viper, or those 
of the male hedge-lizard. But there are also colours in 
which variation is only possible in one direction so that 
they can never be neutralised. The Alpine hare is 
pure white ; and as there is nothing whiter than white, 



all shades of this animal’s colour must be darker. Here 
we have a clear case where natural selection keeps a 
thing at a certain height. As a general rule, we do not 
find it to do this, but to tend upivards } Nothing is 
absolutely good. The eye of the mammal seems good 
to us, but the bird shows that there are better ones. 
However, even if selection remains at a certain level 
in the case of many qualities, it certainly never does 
that with quantities, as in that case it would have to 
weed out plus and minus variations. But as these 
neutralise each other by panmixis, there is no need 
for the action of natural selection. 

We know now, therefore, that panmixis cannot reduce 
the size of an organ. How, then, can we explain the 
rudimentary organs ? 

This would be easiest to do, it is clear, with the 
Lamarckian principle. The organ that is no longer 
necessary, this theory would say, is no longer used. 
It grows weaker and weaker by the disuse, and is 
transmitted to offspring in an enfeebled condition. 
This continues until the organ entirely disappears owing 
to the steady inheritance of the results of disuse. 

But we saw above that the wings of the blue-throated 
warbler, though they are not used, are found in each 
individual of the strength and size that the long migra- 
tion requires. This circumstance led us to distrust the 
Lamarckian principle, and as we shall conclude in the 
sixth chapter that it is completely untenable, we will not 
delay with it now, but try to explain the rudimentary 
organs by other means. 

1 Or, of course, downwards. 


1 68 

We have already recognised the significance of 
selection in the reduction of organs. I may remind 
the reader of the wings of the island-insects and the 
fingers of the bird. There are snails, too, with small 
shells right at the posterior end. They feed on earth- 
worms, and it is possible that their malformation is due 
to the fact that the snails with the smallest shells were 
best able to follow their prey into their holes. There 
may be many cases that selection can explain, but 
as we saw, it cannot explain all the rudimentary 

Another principle is that of economy of nourishment. 
Every animal, it says, has a limited amount of nourish- 
ment in its body, and if one of its organs is to grow 
bigger, the material for it must be taken from another 
part of the body. If, for instance, in a certain species 
the strongest possible support for the body is required, 
as in swift-running animals of a certain weight, the shin- 
bone must become thicker, as this is always the chief 
support of the body. In that case natural selection will 
always choose the animals with the strongest shin-bones 
(tibiae), and possibly at the same time, indirectly, select 
smaller calf-bones (fibulae) — if, namely, the shin-bone 
has obtained its increase in size at the expense of the 
fibula. Now, there is certainly only a limited quantity 
of nourishment in the bones, and it seems possible that 
for one bone to become larger it must take the food that 
would have gone to the other bone. In this way the 
continuous selection of strong shin-bones might gradually 
bring down the fibula to the dimensions it actually has 
in the horse and the bird. 



But on the other hand, any animal can take up a 
position without displacing another one, and we can 
imao-ine cases in which, when variations occur in the 
tibia and fibula, the former may be larger and the latter 
no smaller, or both bones may be stronger. Such 
variations have then a greater quantity of nourishment 
in the body. But perhaps the growth of the tibia at 
the expense of the fibula is the most frequent and 
normal variation, and natural selection had especially to 
deal with individuals that had a larger tibia and smaller 
fibula. If such variations were more common than those 
that had the greater amount of nourishment, the fibula 
would be bound gradually to disappear. 

We might give a further extension to our principle, 
and say that nature always chooses the nearest way ; 
and appeal to physical forces that also do this. In that 
case the body would be bound first to use up the already 
existing and now superfluous elements in its further 
construction. Yet when we reflect that, on this as- 
sumption, many indifferent characters must disappear, 
we shall not be too hasty in applying our principle. 
We have as yet made so little progress in studying the 
nature of the body ! We must, therefore, modestly 
admit that our actual knowledge is not sufficient to 
explain the rudimentary organs. Selection and economy 
in food may be the cause of the reduction of a good 
many organs, but certainly not of all ; and panmixis only 
explains the deterioration, not the diminution, of an 
organ. Weismann has recently tried to enlarge 
panmixis with his theory of germinal selection, and 
has credited this with the power of making organs 


rudimentary. But we shall see later on that we cannot 
accept this principle. 

However, there has been one result from our inquiry. 
Although we were unable to discover the causes that 
account for the rudimentary organs, their existence is a 
convincing proof of the theory of evolution. We cannot 
understand the existence of these useless organs unless 
we suppose that they had a purpose in the ancestors of 
their possessor, and were then fully developed ; and 
that they had to be transmitted steadily to posterity by 
the force of heredity. These useless appendages can 
never be reconciled with a theory of creation. 

Still greater is the testimony to the evolution of 
organisms of the rudimentary organs that appear and 
disappear in the lifetime of an animal. 

We said at the beginning of this chapter that an 
amphibian shows, in the course of its early development 
from an aquatic to a terrestrial animal, how a salamander 
or a frog must have evolved from a fish in past ages. 
We find similar reproductions of its evolutionary history 
in ancient times more or less in the embryonic develop- 
ment of every animal. All living things descend from 
protozoa, the microscopic beings that we find in a drop 
of water ; and every animal begins its life at the same 
stage, since the ovum entirely resembles one of these 
protozoa. After the protozoa came the polyps, from 
these the worms, and from these again the fishes. Now 
we find in the development of every vertebrate ovum, 
including the human, stages that may be compared with 
those three forms. Haeckel gave the name of “the 
biogenetic law” to this phenomenon, and attached a 



very great importance to it. It is believed to complete 
our geological discoveries. Just as the various epochs 
in the earth’s growth show first lower then higher 
organisms, so we find the same gradation once more, in 
a condensed form, recapitulated in the embryonic 
development of every animal. 

We shall deal more fully with the significance of the 
biogenetic law in the seventh chapter. Here we will 
only point out by means of it why rudimentary organs 
appear and disappear in the evolution of animals. This 
we find to be the case. The human ovum needs nine 
months for its development. In the fourth week it has 
made considerable progress, but is very unlike a human 
being, and much more like an animal. It clearly shows 
slits like the gill-clefts of the fish on each side, and has 
a striking resemblance to the fish in the arrangement 
of the heart, the blood-vessels, and the bony skeleton. 
The clefts are of no use whatever to the unborn child, 
and they soon disappear again. We may confidently 
say that there is no stronger proof of man’s descent 
from the fish than these gill-clefts , which are still 
retained in the descendants of the fish — men — in 
virtue of the law of heredity, although they have 
had no purpose or use for millions of years, and they 
disappear in the further course of development. 

Thus we have got back to the fishes from which we 
started. They are not only of importance as the lowest 
class of vertebrates on account of their structure, but 
their life gives us an interesting illustration of the 
working of natural selection. The struggle for life is 
found amongst them in unsparing form. Except the 


white fishes which feed on green plants, and the carps 
that stick their heads in the mud to find the plants, and 
especially tiny animals, they are all predatory animals, 
and do not even spare their own species. Anglers have 
often found a pike in the stomach of another one, and a 
third pike inside the second one. The pike is the most 
voracious of the fishes, and is rightly described as the 
shark of inland waters. It is even dangerous to small 
ducks ; and young sand-martins, sitting on a branch over 
the water, often find their grave in its stomach. It has 
even been seen to suffocate swans by dragging them 
under water. It is from one to two yards long, and 
weighs up to 70 pounds. It generally chooses the night 
for its predatory excursions. During the day it hides 
amongst vegetation, and only waylays an occasional 
victim. If one comes near it, it darts out, gets its 
fang-teeth into it, releases, and then grasps again and 
swallows it. If the victim hurries away, it leaps after 
it, and is very active in every respect. It fears only 
the stickle-back and the perch, on account of their 
spikes ; but it sometimes captures even the perch, and 
holds it until its spikes drop from exhaustion, and then 
swallows it. 

The perch itself, however, comes next to the pike in 
voracity. It waylays small fishes behind the pillars of 
bridges or at the edge. When a swarm of small fishes 
approaches, it darts amongst them like a hawk, and 
seizes its victim. The perch-pike is less murderous ; in 
spite of its size, it is not as quick as the ordinary perch, 
and its gullet is not expansive enough to take in large 
pieces. But the smooth eel-pout, with flat head and 


I 73 

wicked-looking eyes, is the companion of the pike and 
perch in slaughter. It waits until dark in the thickest 
vegetation in clear, swift-running water. Then it glides 
slowly along, using every stone and piece of wood as 
cover, towards the edge ; it leaves no cover unsearched, 
and darts like an arrow on everything that is eatable. 
The most comprehensive predatory of German waters 
is the shad. It grows to a length of four-and-a-half 
yards, and weighs up to 400 pounds. This is another 
nocturnal fish, but its bristles can also be seen moving 
about in search of prey during the day. It eats ducks, 
and even dogs, and the bodies of children ; even living 
children have to beware of it, as the inhabitants of the 
Danube provinces, where it is still often found, know. 
Much larger, but much less dangerous, is the sturgeon, 
which gives the best caviare. It grows to a length of 
eight yards, and weighs sometimes 1,000 pounds. With 
the equally large and harmless giant-shark, it is the 
biggest fish on the earth. 

The small fishes have their revenge on the larger 
ones by eating them in their early stages, and so 
prevent them from increasing too much to their own 
cost. When the trout has cast its spawn, the bullhead 
gets to work. It places itself vertically over the eggs 
with its head down, makes them rise by a movement 
of its fins, and swallows them one after another. The 
trout in turn has a taste for the young bullhead ; we 
always find the bullhead in a stream which contains 
trout, or vice versa. They keep each other balanced. 

The means by which fishes protect themselves 
against enemies are very varied. The harmless tench 


buries itself in the mud ; the bullhead expands its 
gill-covers so that the spines stand out ; the perch 
elevates its spine-fin, and in the stickle-back the spines 
are raised in a fixed joint so that it does not lower its 
weapons even after death. In this way it is safe from 
most enemies ; only the salmon and torsk can swallow 
it with impunity. It can also protect its young. The 
male, which is the more lively of the two sexes in this 
species, and reveals every emotion by a pretty play of 
colour, builds a nest of root-fibres and vegetable matter 
which he glues together with a sticky substance that 
oozes from his sex-opening. Then, by a show of colour, 
by graceful movements, and, if that does not avail, by 
pushes, he induces a female to lay its 68-80 eggs in the 
nest. When that has been done, the male seeks other 
females to fill up his nest ; and when he thinks he has 
enough eggs, he improves the nest, and watches it most 
carefully. Every creature that comes near is furiously 
driven off ; these are generally of his own species, as 
they have a great liking for the eggs. His watchfulness 
doubles when the little stickle-backs appear. They swim 
away over and over again, and he brings them back in 
his mouth, and puts them back in the nest. He does 
not relax his care until the young can easily support 
themselves, and then he leaves them. 

The bullhead also defends the eggs and the young 
for some time, and the way the Rhodeus amarus takes 
care of its young is most peculiar. This is one of the 
prettiest of German fishes on account of its graceful 
movements, and the male has also such glowing colours 
in the spawning season that the whole animal seems to 



be lit up by an internal fire. The female is recognisable 
at this time by a long ovipositor, into which it forces an 
egg or ovum. With this it swims to one of the larger 
painter’s gapers, which stretch out their respiratory and 
cloaca - opening sluggishly from the sand. The fish 
drops its ovum into this, and the male, its whole body 
quivering, pours its seed over it. The mussel tries to 
get rid of the unwelcome foreign body by violent con- 
tractions, but does not succeed as a rule. The egg 
passes into its gill-chamber, and the little creature that 
develops from it forms a sort of transverse swelling 
behind its head, with two processes that help it to 
strengthen its hold. These projections afterwards 
disappear and the fish abandons the home of its 
childhood, which had sheltered it completely from 

But the mussel has its revenge for this involuntary 
shelter. When the hour comes for its reproduction, 
it thrusts out its brood through the opening. The 
young mussels fall to the bottom of the water, open 
the shell, and send out a long thread. This has a 
sticky surface, and gets entangled with the threads of 
other young mussels, so as to form a firm and com- 
plicated net, from which the little animals hang. If 
a fish — it is generally a rhodeus or a perch — runs 
into the net, the mussels come into contact with its 
body, and immediately bring their shells together, 
and the sharp edges press deep into its flesh. A 
growth is formed in the skin of the fish at the injured 
spot, and at length covers the whole mussel. It then 
lives at the expense of the fish, though it does not 


do it much injury on account of its smallness. Its 
organs are gradually developed, and when it is quite 
ready it releases itself by vigorous movements from 
the skin, and follows the adult life of its species at 
the bottom of the water. It is a remarkable and 
interesting correlation of two very different animals. 

Other fishes meet the danger of destruction by 
producing enormous masses of eggs. In some these 
eggs are poisonous, as in the case of the pike and 
the barbel ; in the latter case, in fact, the whole fish 
is poisonous at the spawning season. It is often 
compared to the pig, as it always remains at spots 
where sewage runs into the water. It is even believed 
that human corpses are its greatest delicacy ; a large 
number of barbel were found on the bodies of the 
slain in the Danube in 1683, at the siege of Vienna 
by the Turks, while none were seen on the bodies of 
animals. Barbel are sometimes taken from the inside 
of dead bodies. 

Fishes know their enemies well. It has been 
observed, in fact, that they have a memory ; that 
fishes at which a diving - bird was set first circled 
round it with curiosity, but when it had caught several 
of them, hid themselves, and were very cautious 
afterwards. They also learn to recognise the servant 
that brings their food ; but the statement that they 
gather for food when the bell rings rests on unsafe 
observations. It is very probable that they have no 
sense of hearing. Their ear serves only as a sense 
of equilibrium ; fishes from which the ears have been 
removed cannot keep themselves upright in the water, 


I 77 

but answer to sounds in the same way as normal 
ones. When fishes come up to be fed, it is because 
they detect the steps of the keeper by the shaking 
and follow them, or else they see him bringing food. 
They have not a great cutaneous sensibility, other- 
wise they would not bite over and over again when 
they have been let loose by the angler . 1 

The fishes have many enemies, but the worst of 
them all is man. It is not so much his various ways 
of capturing fish that decimate the class as his civilisa- 
tion that injures them as it spreads. Sometimes it is 
factories that pour their poisonous waste into the 
waters, and kill thousands of fishes every year. 
Fishes are always very sensitive to bad water. The 
tench is the only one that can thrive in water that 
is poor in oxygen, and the mud-fish, which foretells 
changes of weather twenty-four hours in advance by 
its restlessness. This fish can also take air by the 
mouth at the surface of the water. The air passes 
into the alimentary canal, and is used up there, so 

1 According to the latest works of the American expert, Parker, it 
seems that there are fishes with a sense of hearing. In the first place, 
he says, certain fishes of the order of the “ plectognathi ” (well-known 
specimens of these are the trunk-fish and the globe-fish, the prickly, 
swollen, globular animals that are often seen in show-cases and dealer’s 
shops), must be able to hear, because they make sounds themselves. 
Many of them only do this in the male sex, and so the sounds may be 
only used within their own species. These are conjectures, but Parker 
has proved the sense of hearing with some confidence in the case of 
one fish. This is th zfundulns heteroclitus, or toothed carp, an American 
fish. The very careful experiments that Parker made with the fish 
show that it can hear ; and the same result was obtained on making 
an anatomical examination of its ear. It was much more like the ear 
of the higher, hearing vertebrates in structure than the usual organ of 
equilibrium of other fishes. 



that the alimentary canal serves as respiratory organ 
in this curious fish . 1 

But the regulation of rivers does even more than 
factories in reducing the number of fishes ; it deprives 
the fishes of their spawning-places just as the cutting 
away of the underwood in the forest deprives the bird of 
its nesting-place. The regulation of the rivers dams 
them up and deepens them, and thus does away with 
the shallows and the side-pits. It is just in these places 
that most fishes lay their spawn, as it cannot be swept 
away, and it receives plenty of sun. The pike likes to 
spawn in flooded meadows. The ruffe is the only 
exception. It wanders in troops in the spring from its 
standing waters into the rivers, until it finds plenty of 
reeds, amongst which it lays its eggs. 

Many fishes travel in this way. Even the heavy 
carp turns up the stream, when it is in free water, 
and leaps over high obstacles, in order to lay its spawn 
in quiet water near the source of the river. The 
minnows travel in swarms to the mountains when the 
water becomes too hot for them, and leap over rapids 
and weirs. Sturgeons pass from the sea into the rivers 
in spring. But the most famous travellers are the eel 
and the salmon. 

The reproduction of the eel has only been cleared up 
very recently. Up to that time the most extraordinary 
stories were in circulation about it, as no ova had ever 
been found in it. Some maintained that the eels 
coupled with snakes ; others that they arose from mud 

1 If the animal is taken from the water and squeezed round the 
body, the air rushes out with a loud and plaintive noise. 



or putrified bodies of eels ; others that they were 
formed from dew and honey. The greatest importance 
was always attached to their intestinal worms, which 
were claimed to be their young. 

We should know that our river-eels are all females , 
and that the males, never more than half a yard long, 
live exclusively in the sea or in brackish water. Every 
autumn great swarms of female eels, that have passed 
their fifth year, travel to the sea, while others remain in 
the fresh water, and settle down to their winter sleep 
in the mud. The former make steadily down stream ; 
never on clear nights, and preferably when a storm 
darkens the sky, and the water is lashed by it. When 
they reach the sea, the males join them, and the eggs 
are laid in the deepest parts of the sea, and fertilised by 
the male. The young eels issue from the eggs, but they 
are so unlike the old ones that they have always been 
described — they have long been known — as a particular 
species of fish. 1 They are so completely transparent 
that one can read any kind of print through them, and 
they are not noticed in the water, as a rule ; in shape 
they are flat and lancet-shaped. Gradually, in the 
course of a year, they become darker and serpent- 
shaped, and then — from May to July — the young 
animals travel up stream. They may be seen in count- 
less swarms in the under-current of rivers. It is said 
that in the year 1667 three million pounds of them were 
taken in five hours in the Arno at Pisa. In the Elbe 
a black streak has often been seen moving upwards 

1 Grassi and Calandruccio have shown that the Leptocephalus 
brevirostris is the eel in its early form. 


along the shore ; if water was drawn at this time, it 
was sure to contain numbers of small eels. As the 
large locks now hinder the advance of the young 
eels, fish-ladders have been fixed in the wood in most 
places — that is to say, bands of moss that remain always 
moist, and enable the tiny animals to climb up. The 
higher they penetrate, the more the males hang back ; 
many believe that the fresh water turns the young, 
sexless animals into females, but that has not yet been 
proved. The young mature quickly, and feed by 
preying on fishes, snails, insects, and carrion ; also on 
crabs when they are removing their shells and are still 
soft. Eels have often annihilated all the crabs in a 
given locality. It is a mere myth, of course, that the 
eel goes on pea-fields and feeds on the plants. 

The salmon acts in the opposite way from the eel. 
It spawns in fresh water. In the sea it lives on small 
fishes of all kinds, and becomes very fat. When the 
ice disappears from the rivers, the salmon gather at 
the mouths in companies of thirty or forty, and remain 
for a time in the brackish water, so that the salt-water in 
their bodies may be gradually washed out by the fresh ; 
too sudden a transition would be fatal to them. They 
then press steadily up stream. All obstacles are over- 
come. Weirs and rapids are taken in leaps that some- 
times reach the height of four yards. Only very high 
waterfalls stop them. The young are in front, then the 
older females ; these are followed by the younger males, 
and the rear is formed of the older males — though an 
old and strong fish seems to lead them, as a rule. 
During the whole time they are in fresh water the 


1 8 1 

salmon take no food, and the roe — the ova and seed — 
mature at the expense of the fat and the muscles. The 
old males now develop a bright red colour on the belly, 
and at the tip of their lower jaw is formed a strong, 
upward-pointing hook ; this is often so long that the 
mouth cannot be closed . 1 The swarms separate at the 
spawning places, in the streams that flow into the rivers. 
In the shallow parts of the streams, especially underneath 
small waterfalls, the female brushes aside the pebbles 
with her tail, and lies down in the hollow, to deposit her 
eggs at the bottom. The male remains about a yard 
above, and ejects his seed into the water ; this is con- 
veyed by the current to the ova and fertilises them. 
When the spawning is over, the two sexes, fearfully 
emaciated and exhausted, return to the sea, and 
recuperate there. Many of them, however, perish on 
the way. 

Many salmon pass up river during the spring also ; 
they do not spawn, but feed for a whole year as river- 
fishes, and do not descend to the sea until the next year 
with the comrades they meet in the meantime. They 
have the fattest and reddest flesh, and are called winter 
salmon. They are the dearest. The salmon going up 
stream have also red flesh ; those going down have white 
flesh, and are easy to catch on account of their exhaustion, 
but are less valuable. The worst fishes are the shore 
or black salmon, which never enter fresh water. They 
live on the sea-shore and seem to be permanently sterile. 
Their flesh is quite white and hard. 

Many believe that the hook is used as a weapon in the fight for 
the females. The point is not yet settled. 



The regulation of rivers has greatly reduced the 
number of salmon. The time has gone when more 
than a thousand could be caught at one spot in a day ; 
when servants stipulated in their contracts that they 
should not have to eat salmon more than twice a week. 
In the Rhine it is gradually disappearing, as the mouth 
of the river is almost entirely cut off by Dutch fishermen 
at the time for coming up. In other rivers there has 
been an artificial stimulation for the salmon population. 
There are special places in which not only the eggs that 
have been found are hatched, but the eggs are obtained 
from the body of the ripe female by pressing it (also in 
the case of the trout), and the sperm taken from the 
male is poured over it. The young ones develop in 
vessels full of water, that is kept fresh and circulating, 
until they are big enough to make some resistance, 
when they are put in the streams. In this way 
an artificial substitute is found for the shallow 
waters, and thousands of fishes are reared every 

For a long time our fresh-water fishes were threatened 
with a growing danger of extinction, until at last the 
spread of knowledge enabled us to meet most of the 
difficulties. Angling societies have been formed, and 
fish-culture and protection are spreading more and 
more. Angling is still common enough, and is re- 
garded as a good form of sport. It is true that we 
no longer see boats gliding over the river during the 
night with torches in the bow, throwing a red light 
over the slender form of the salmon-fisher and his 
glistening harpoon ; but the angler sits under the trees 



by the still water absorbed in his work. Lights play 
on the water, and the wide straw-hat of the solitary 
fisher. The fishes splash here and there, and the 
angler waits patiently for the approach of the invisible 
inhabitant of the stream. 



To the tracheates belong spiders and insects. How insects grow. 
Explanation of the metamorphoses of insects. Protective 
colouring on the wings of butterflies. The Lamarckian principle 
refuted by protective colours. Insects that resemble objects. 
Mimicry. Exhalation from male butterflies. Sexual selection. 
Origin of flowers due to insects. Parts of the insect’s mouth. 
Refutation of the Lamarckian principle. The coat of insects 
cannot have arisen by use. Harmonious adaptations, co- 
adaptations. Co-adaptations that Lamarck cannot explain. 
Explanation of co-adaptations. Are instincts inherited habits? 
Instincts that can never be affected by the will. Spiders’ webs. 
Care of the young. Instincts that are only used once. Are 
mutilations inherited ? Protective marks, mildew marks, fore- 
sight. Infection of embryo. Structure of the embryo. The 
inheritance of acquired characters is difficult to conceive. 
Untenability of the Lamarckian principle. 

We now turn to the animals that we meet most fre- 
quently at every turn. These are all alike in having 
the body covered externally with hard parts and jointed, 
like the legs of the “articulates,” as we call the stem to 
which they belong. Some of these animals breathe by 
means of gills ; these are the crustaceans. The others 
breathe by means of what are called tracheae ; to this 
group belong the spiders and insects, which will engage 
our attention in this chapter. The tracheae are a system 
of greatly ramified tubes, which end in a network of 
very fine microscopic branchlets, and pervade the whole 

animal. The air enters into the tracheae by external 




openings or spiracles, reaches every organ and every 
part of the body, and conveys to them the oxygen that 
they vitally need. 

There is an immense number of species of the 
tracheates. We now know some 250,000 forms of 
insects alone, although the tropics, their chief abode, 
have only been superficially explored as yet. Such 
a number as this is only possible because every avail- 
able position in nature is made use of ; and for that 
reason we find particularly complicated and striking 
adaptations among the insects. 

We need only glance at their colours to see full con- 
firmation of this. The collector cannot easily discover 
a tree-locust on a tree, as it is coloured green like a 
leaf ; and its relatives, the grasshoppers, are just as 
difficult to find, as their green-brown tint harmonises 
with the grass-grown ground on which they sit. The 
mole-crickets are quite dark brown ; these are found 
chiefly on brown earth, and dig holes, in front of 
which they sit and sing their concerts. 

We could find an obvious protective colouring in 
almost every species of insect. Moreover, the colour 
changes at different periods of the insect’s life. The 
eggs of most of the insects are green, like the leaf on 
which they are deposited. The larvae that issue from 
the eggs have a protective colouring, which is different 
from that of the adult insect in proportion as their 
habits differ from those of the adult. The larva and 
the imago , as the full-grown, sexually-ripe insect is 
called, often look like two totally different animals. 
This is explained in the following way. 


All the articulates, tracheates as well as crustaceans, 
can only grow periodically , because they are clothed 
with a hard coat of mail. This armour completely 
encloses the animal, and the muscles are attached to 
it, and find in it the necessary resistance for the pull 
on the bones that they effect. 

The coat is too rigid and solid to allow any expansion 
of the body it encloses. The insect can only increase 
in size, therefore, by bursting the shell ; and this it 
does at certain places and times. When the armour 
is thus broken, the soft - skinned animal creeps out 
of it. 

Underneath the shell of every insect there is a layer 
of skin which has the function of secreting the material 
of the coat, much as our salivary glands secrete saliva. 
This skin now forms a new shell while the old one still 
covers it, so that when the insect emerges from the 
broken one, the new coat becomes visible. It is, how- 
ever, soft at first, and the insect can expand and grow 
in it. But it soon stiffens in the air, and then becomes 
a dead mass. Underneath it a new coat is secreted, 
and this will replace it in turn when the time comes. 

The growth of the insect at each cast is accompanied 
by other changes. In many insects the wings make 
their appearance ; they were wanting in the larvae, 
were visible as short stumps at the first cast, and 
increased with each succeeding one until they reached 
their full size at the last; in these cases the insect is 
thus turned into the imago, or adult and mature 
organism. This gradual growth is found in the 
dragon-flies, moths, locusts, and others. 



As the air is cut off from the larvae it was useful for 
them to have different adaptations from the imago. 
While the latter flies easily out of reach of its enemies, 
the creeping larva can be caught at any time, and so 
urgently needed protective colouring so as to escape 
notice in its surroundings. Thus the larvae and 
imagines were selected in different directions according 
to their different conditions of life, and came to differ 
more and more. 

In the case of moths and grasshoppers, there is not 
a very great difference in habits between the larva and 
the imago ; the latter hardly use their wings except to 
lengthen their leaps. Hence the larva does not differ 
so much from the imago, and is merely without the 
wings, or has shorter wings. 

It is otherwise with beetles, flies, bees, wasps, and 
butterflies. The vital activity of these insects chiefly 
centres about their power of flying ; some of them 
hardly move in any other way. But the air is only 
opened to them after the last cast of the skin. The 
gradual transition of the larva into the imago would 
clearly be very much out of place here, as the two 
stages are so very different from each other ; during 
such stages of transition the animal would be neither 
adapted to its larva - surroundings, which it cannot 
leave because of the absence of wings, nor would the 
imperfect characteristics of the imago be of any use to 
it. We understand, therefore, why natural selection 
has cut down these transitional stages as much as 
possible, so as merely to let the larvae grow in the 
first and most of the other casts, without changing 


their form, which protects them so well. Gradually 
only two casts remained for the transformation into the 
totally different imago. All the organs of the imago 
had to be formed in this short period. But this meant 
such a revolution in the animal’s frame that the vital 
functions, movement and nutrition, were impossible. 
Hence we see that the animal remains, during the 
stage between these two casts, in a state of immobility 
that may be compared to that of the ovum. We call 
this the pupa. In the last cast of skin, the pupa 
covering is thrown off, and the wings, which were 
formed under it, make their appearance fully developed. 

Thus bees, flies, beetles, and butterflies only grow in 
the larva stage, as caterpillars or grubs. If we take two 
beetles that seem absolutely like each other, and only 
differ in size, they are not a younger and an older 
animal, but different species. 

The material for studying the adaptation of larvae is 
inexhaustible. When the butterfly-caterpillars leave the 
egg they are generally green, and difficult to distinguish 
from the leaf they are on. Identical colour of this kind 
can, however, only protect small animals ; larger ones 
are sure to attract attention on the grass or the leaves, 
because there is no purely green spot large enough to 
cover them. As a matter of fact, the caterpillars of 
the grass-butterfly (satyridae), when they are of a certain 
size, have light and dark longitudinal stripes over their 
whole body, and thus lie in the same direction as the 
blades of grass and the shadows, which are always 
vertical on the grass. The caterpillars of the hawk- 
moth, which live on bushes and trees, have stripes 



down the sides, which stand at the same angle to the 
length of the body as the side-ribs of a leaf do to the 
central rib. This colouring gives great protection to the 
caterpillars, as it divides their body into sections just as 
the ribs do the leaf. 

In the pupa stage, when the insect cannot fly, it is 
especially important to have protective colouring; and 
it is, as a fact, very common amongst pupae. On the 
other hand, a flying insect cannot have protective 
colouring because of the constant change of the 
animal’s background ; moreover, a flying object is 
always easy to see. Hence it is that the upper 
surfaces of the wings of many butterflies are of a 
light colour, so that the marks for recognising the 
species are well in evidence. But the insects are not 
always flying ; they often rest, and could then, especi- 
ally when they are asleep, be surprised by enemies. 
They therefore need a protective colouring, though this 
is only necessary at the parts that are seen when the 
animal is at rest. 

From this we can understand why nocturnal butterflies 
(or moths) and diurnal butterflies have protective colour- 
ing at different parts of the body. The day-lepidopters 
fold their wings over them when they are at rest, so that 
we only see the under-side. This alone, therefore, has 
a protective colour in their case. We have a striking 
example of this in the tortoise-shell butterflies. In the 
day peacock’s-eye and the black butterfly the very light 
colours of the upper-side of the wings disappear when 
they are folded. The dark brown of the under-side 
now makes the creatures hardly distinguishable in the 



dark corners and crevices in which they rest. The 
colours of large and small tortoise-shell butterflies and 
the painted lady are lighter. They usually sit on the 
road, and seem to disappear suddenly after one has 
been watching the flying, prettily-coloured insects. 

The disposal of the wings is different in the night- 
lepidopters. With these the fore-wings cover the hind 
ones roof-wise, and so we often find very light colours 
on them — as, for instance, in our red underwings or 
tiger-moths — and never on the fore-wings, which alone 
are visible when they are resting. On these there is 
a mixture of different colours, with zigzag streaks and 
lines running between them ; the whole taken together 
gives so good a picture of the bark of a tree or a 
wooden wall that even the experienced naturalist 
often overlooks one of these moths in examining the 
trunk of a tree. The intricate design is always the 
same in every detail, and it has very well been com- 
pared to an impressionist landscape, in which all kinds 
of scrawls seem to be thrown together irregularly, 
though it will be found to be a picture on moving 
away from it a little. Natural selection easily explains 
a colour-design of this kind. All variations in the 
animals are preserved and selected that help on the 
resemblance to the bark. In one part the zigzag 
lines were developed, in another spots, in a third the 
dark ground-colour. As all these selected variations 
repeatedly crossed with each other, their descendants 
came to possess the different features together , and 
steady selection of the combination helped to make 
the deception more complete. 


I 91 

While natural selection thus enables us to understand 
the origin of protective colouring, we can see no 
application in this case of the Lamarckian principle. 
The protective colours of animals cannot possibly have 
been raised to their present condition by continuous use 
and inheritance of the results. In the first place, it is 
impossible for an animal to become green because it 
takes to sitting on leaves ; and in the second place, 
even if the animal knew that it would be an advantage 
to be green, it could not change its colour by an effort 
of will. It has been stated that the light causes the 
colours, and that the animal’s skin photographs the 
surroundings, to some extent. It is striking, for 
instance, that in many day-butterflies, which draw the 
fore-wings between the upward-folded hind wings when 
they rest, so that only the tips of the fore-wings can be 
seen, these are only protectively coloured like the back 
wings just to that extent , while the unseen part of them 
is often very lightly coloured. Thus the back wings 
and the tips of the front wings have exactly the same 
colour-design. And the colouring of the tips of the 
front wings is more or less extensive according to the 
habit of drawing the wings in more or less thoroughly. 
We find this difference in such apparently similar 
butterflies as the large and small tortoise-shells. But in 
the butterflies that do not draw in their front wings the 
whole surface is protectively coloured. 

If, however, it seems on superficial inquiry that the 
light may have produced the colours, and was only able 
to do this on the exposed parts of the wings, we shall 
be compelled to abandon the hypothesis on further 


reflection. We do not see why the light does not 
cause light colours such as those hidden in the folded 
wings. How, moreover, can we suppose it to create so 
intricate a colour-design? And if the skin has the 
capacity to bring about a protective colouring, we may 
very well ask what was the origin of this capacity, as 
very few animals possess it. But we need not delay 
with these theories ; they are completely refuted by one 
single fact. The protective colouring does not arise 
when the animal exposes its wings to the light, but in 
the earlier stage of the pupa. Long before it issues 
from the pupa all the colours are present on the wings 
folded up under the pupa-shell. And in the pupa the 
position of the wings is reversed ; the front wings 
always cover the hind wings, in such a way that the 
protectively coloured under-side of the front wings is 
turned away from the light. Hence the light does not 
touch any of the protectively-coloured parts during the 
development of the colours. We may add that the 
thick, dark pupa-covering does not admit the penetration 
of the rays of light ; and that many caterpillars pass the 
pupa-stage underneath stones, and the night-butterflies 
even underground. 

We must therefore exclude the action of light 
altogether in the formation of the colours of butter- 
flies. The fact that their front wings have protective 
colouring just in so far as they are visible can easily be 
explained by natural selection. We know that selection 
only continues its action until what is necessary has 
been attained. Those butterflies survived which had 
the most deceptive colouring ; but the variations that 



had protective colouring on the unseen parts as well 
were no better off than their comrades. They were 
therefore not specially selected, and they lost their 
shades in their descendants by crossing. 

The animal is still safer when its colouring is 
associated with certain peculiarities of shape so as to 
imitate an object. 

The outer side of the wings of the tortoise-shell 
butterfly has zigzag lines, so that it looks like a decaying 
leaf when at rest. In the lappet-moth there is a most 
deceptive resemblance to a heap of dried oak-leaves 
owing to the colour and the crinkled edges and position 
of the wings. One of our moths, the Xylina vetusta , 
looks just like a broken piece of wood — an effect 
which is increased by the creature “shamming death.” 
There are also many geometer-moth caterpillars that 
closely resemble twigs, and even have warts on their 
bodies that look like the unopened buds on the twig. 
Further, the animals stretch themselves out stiffly when 
at rest, and then rise up at a steep angle from the 
branch on which they are, so that they look just like 
an offshoot of it. 

But the adaptations of insects go a good deal further 
than this. They not only imitate lifeless objects, but 
even other animals that are not likely to be touched. 
Bees and wasps are generally protected by a sting, and 
most animals know these weapons and respect their 
owners. We must not be surprised to learn, therefore, 
that certain harmless insects have the dangerous aspect 
of the stinging insects, and so enjoy the same 
immunity. A species of fly, the Eristalis , strikingly 




resembles the bee, and the hornet is closely imitated by 
the bee hawk-moth, which has assumed the transparent 
wings, the shape, and the yellow abdominal bands of 
its model. This imitation of living models is called 
mimicry, and we find innumerable instances of it in the 
tropics . 1 

The light colours that many insects show when they 
are flying, and that are of great importance to them, 
as it is by means of these that the sexes find each 
other and maintain the species, are often different in 
male and female. In the case of the dragon-flies the 

1 The imitation of objects is very common among tropical insects. 
There is a leaf-butterfly, the callima, the wings of which, when folded, 
not only have the form of a leaf with a stalk, but even a long central 
rib with side branches— looks, in fact, so much like a dried leaf that 
it takes an expert to recognise the animal at rest. There are also 
locusts that have wings most strikingly like leaves, and other locusts 
that are almost indistinguishable from twigs ; many naturalists have 
thought them to be twigs when the natives brought them. 

Mimicry also is wonderfully developed in the tropics. In South 
America there are black, yellow, and red butterflies, the heliconides , 
which are not eaten by birds and reptiles on account of their repulsive 
smell and taste. Other butterflies, originally white, have adopted both 
the appearance and the habits — such as slow flying — of these malodor- 
ous butterflies, and constantly mix amongst their models, which always 
fly in swarms. Thus the white are protected as well as the heliconides, 
though they have not the same nasty taste. 

In this case selection has coloured the females earlier and more 
thoroughly than the males, some of which still have the pure white of 
their ancestors on the hind wing, and some on the upper side of both 
the front wings. Selection does not act as powerfully in the males as 
in the females, and their transformation is slower. The males are 
always more numerous than the females, as a matter of fact, besides 
that one of them suffices for the fertilisation of a number of females ; 
moreover, their death does not involve the destruction of a number of 
eggs. If the species is to be preserved, it is the females especially 
that must be cared for. 



female body is usually of a greenish shade, while the 
males prefer bluish colours ; in the Libellula depressa 
this passes into white, which is the colour of the thick 
abdomen in this species. In others the males have 
beautiful dark blue wings, which give them a fairy-like 
appearance, while those of the females are colourless. 
Among the butterflies the argus and small copper butter- 
flies have their pretty light colouring only in the male 
sex ; the females have an indifferent appearance. 

Other “masculine characteristics” are developed 
among the insects. In many butterflies the males 
give out a strong scent ; it is a charming coincidence 
in nature that the butterflies that seem, in form and 
colour, to be the flowers of the animal world, have also 
very often the perfumes of their models. One can 
easily perceive this odour by holding to one’s nose a 
male cabbage-butterfly, which differs from the female 
by the absence of the black spots and borders on the 
wings ; it gives out an agreeable pungent odour. The 
argus butterflies, the mother-of-pearl, the convolvulus- 
sphinx, and many others, have a male scent. In all 
cases the odour is restricted to special scales. The dust 
of the butterflies, which is so easily brushed off "with 
the hand, consists of very delicate and tiny scales, which 
are for the most part connected with small glands. 
Some especially large glands secrete an odorous matter, 
and let it pass into a peculiarly shaped scale which is 
called a scent-scale. These scales are often closed by 
special structures, so that they only pour out their 
perfume at the will of their owner. It appears, therefore, 
that in this case the perfume is really meant for the 


enchantment of the females, and we are faced again 
with a problem that we cannot solve. In this case 
there is less objection than elsewhere to the second 
form of sexual selection. It is not called upon to 
explain the origin of the perfumes, but only its increase 
in the male sex. The odour certainly came into 
existence as a distinctive mark of the species, as it is 
also found in the female sex, though in so weak a 
form that our nose cannot perceive it. But it can 
easily be proved to be present by placing a female of 
some species of night- butterfly in a wire box before 
the window. A number of males will presently be 
found in it, and they can only have discovered by 
smell the presence of the object of their desire. 
Hence if a female knows the odour as a mark of the 
species, it will be much more affected by it when 
its strength increases. Possibly this is the root of its 

The union of the sexes is sometimes stormy among 
the insects. The females of the large dragon-flies often 
fly in obvious fear from their spouses. In the case of 
other insects it is the male that must be careful. It 
happens only too often that the love-sick male cricket 
is devoured by the callous female. In fact, in the case 
of the mantis or praying insect, a green locust whose 
front legs are lifted up as if in prayer, though they are 
really only for the purpose of grasping its prey, the male 
is generally devoured during , but at least always after, 
union. It has even been observed in the case of this 
species that the female bit the head off the timidly 
approaching male ; the trunk, nevertheless, performed 



its task, and was then in turn taken into the stomach of 
the insatiable female. In the case of the spiders, too, 
the male must approach the female with caution as she 
sits in the middle of her web, because she has a habit of 
biting to death without much examination every living 
thins: that comes into her net. But in this case the 
female signifies its compliance to the hesitating male. 
She travels down, and hangs, head downward, by a 
thread on which the union takes place. 

We have already compared the butterflies to flowers. 
That was merely a superficial comparison, but we shall 
now see that there is an intimate connection between 
insects and flowers, because, strange as it may sound, 
most flowers owe their origin to insects. 

We must go back a little in order to explain this 
statement. In the plants, also, a union of male and 
female generative products is necessary to produce a 
new organism. The male products, which correspond 
to the sperm of the animal, are called “pollen”; it 
consists of an immense number of very tiny grains. 
The pollen of the lily must be known to everyone, as 
it is this that colours the finger yellow when you insert 
it in the flower. This pollen has to unite with the 
female product, which in turn may be compared to the 
ovules of animals. The plant “ egg,” which is found also 
in flowers, but only in small quantities, is in this case 
enclosed in a capsule that is called the “ seed-bud ” or 
germ, and is drawn out in a long stalk called the “ pistil ” 
above. At its upmost point, the “stigma,” a grain of 
pollen touches it in fertilisation, passes gradually through 


the pistil to the egg-, and coalesces with it. Then, as a 
rule, the germ drops off, tumbles to the ground, and the 
fertilised egg within it grows into a new plant. In 
ordinary usage we call the fallen germ the “seed.” 

In the parent-forms of the actual higher plants there 
were male and female blooms, and the pollen was pro- 
duced by the former in vast quantities and scattered far 
and wide by the wind. In this way a grain would fall 
on the stigma of a female plant and it would be fertilised. 
This is still done in the case of a great many plants, 
such as the grasses, the conifers, the birch, the hop, and 
many others. The male blooms were constantly visited 
by insects, as the pollen was an excellent food for them, 
and this visit of the insects became the starting-point 
for natural selection which made the conveyance of the 
pollen to the female flowers safer, instead of leaving it 
to the chances of the wind. 

Fertilisation was easier in those plants which offered 
some attraction to the insects, as after visiting the male 
flowers there were always a few pollen-grains sticking to 
their body, and when an insect in this condition entered 
the corresponding female flower, it was natural for some 
of the grains to be brushed on to the stigma. We can 
understand, therefore, why little pits came to be formed 
in the female blooms of many plants, in which a sweet 
fluid was secreted that attracted the insects. The 
willows have remained at this stage, but in their case the 
male flowers also secrete honey, and thus it is secured 
that both kinds of catkins will be visited by the insects 
and fertilisation obtained. 

However, this form of conveying the pollen left a 



good deal to be desired. It would often happen, for 
instance, that an insect would fly from one male flower 
to another, and not visit a female catkin until much 
later. In this way a great deal of pollen would be 
lost, and so we can understand that a different method 
would lead to better results. We still find in the 
poplars, which have the same kind of catkin-blooms, 
a pistil with a stigma and germ suddenly appearing 
as an abnormality in the middle of a male flower ; this 
union of male and female in one flower is called 
hermaphrodism. These hermaphrodites were pre- 
served by natural selection, as they had a great 
advantage in the conveyance of pollen from flower 
to flower. An insect that covered itself with pollen 
dust in one flower found a pistil in the next one on 
which it could brush the dust, and did not fail by going 
exclusively from one male flower to another. Hence 
the hermaphroditic flowers increased, and a struggle 
sprang up amongst them for the visitors, those being 
most favoured that were most attractive to the insects. 
The chief means was, of course, the honey on which 
the insects fed ; and those flowers had an additional 
advantage that drew attention by their conspicuous 
colours, and so invited the insects from afar. This 
was the origin of almost all our actual beautifully- 
coloured and marvellously-shaped flowers. Nature does 
not revel in a superfluous wealth of colouring ; this has 
only been developed for the sake of the insects, as no 
plant of this kind can reproduce unless it is visited by 
insects. A second source of attraction was provided 
in the scent, which, of course, was especially useful 



during the night. In fact, many plants that are only 
visited by hawk-moths only give out their perfume at 
night when these moths fly. Many will have already 
seen this in the case of the caprifoliacese. 

At first sight it would look as if those flowers were in 
the best position in which the honey was most exposed, 
and which were visited by as many insects as possible. 
But that is not the case. In the first place, many insects 
are so small that they can eat the honey without rubbing 
against the pollen, and so they are useless to the flowers ; 
and in the second place, the flower will have a much 
better chance of being fertilised if only a few species of 
insects visit it. When a certain kind of flower is liked 
by a particular insect, this will be the more likely to 
return to it, and not waste its pollen on other flowers. 
On this account the honey that was at one time exposed 
in many flowers has sunk deeper into them, and thus 
can only be reached by the more intelligent insects. 
The effect is enhanced by the curling of their leaves so 
as to form a tube which varies in thickness, and so 
admits different kinds of insects. In some flowers the 
tube is so narrow that it takes the long proboscis of a 
butterfly to reach the honey. Others have adapted 
themselves to flies, and give out the smell of carrion, 
which attracts these alone. In the aristolochia the long 
and narrow tube is further provided with hairs on all 
sides that point downwards ; these let the fly in, but 
prevent it from escaping. The insect is kept captive 
until it is covered with dust by the stigma at the 
bottom, when the hairs wither, and it can get away. 
In this way the restless fly is compelled to do its duty. 



It would take too long to enumerate all the 
adaptations of the flowers to insects. The most familiar 
of all is the meadow-sage. In this the bees in search of 
honey press on a small mechanism by means of which 
the filaments, at the tip of which the pollen hangs, bend 
down on it and dust their hairs with it. The bee then 
leaves the flower, and another comes which has already 
been covered with pollen in this way. But in the mean- 
time the pistil with the stigma, which had up to that time 
been hidden, has come to the opening. The second bee 
has to rub its body against the stigma in order to reach 
the honey, and so cause fertilisation. 

We thus see that the origin of the flowers affords a 
striking proof of the power of natural selection, and this 
will be particularly clear if we consider the relative 
imperfectness of the adaptations. Selection only acts 
in so far as a change is urgently necessary for the 
preservation of a species. Many flowers can only be 
fertilised by bees, but they also receive the visits of 
many other insects which rob them of their honey with- 
out doing them any service. However, it is clear that 
further contrivances for excluding these other insects are 
not necessary, because the maintenance of the species is 
sufficiently assured by the bees, whose visits are frequent 
enough to fertilise and bring new plants into existence. 

The alteration of the flowers was bound to have an 
influence on the insects. When those of the flowers 
were constantly preserved that had the longest tubes, 
because they kept out mischievous visitors and so were 
most frequently fertilised and left most progeny, there 
must have been a corresponding selection among the 



insects ; the butterflies with the largest probosces would 
have the advantage because they would find most food, 
and their ova and seed would be the most vigorous. 
Thus the characters would mutually affect each other. 

It is not only the proboscis of the butterfly, but also 
the mouth-parts of other insects, that have been modified 
by a correlative selection with the calices of flowers. In 
the ancient insects the eating organs consisted of mas- 
ticators, as we still find in many orders, such as the 
locusts, moths, and beetles, because they chew their 
food. But in the bees a part of the mouth was converted 
into a long licking tongue ; and in the butterflies two 
masticators have blended to form the long tube of the 

In other insects there have been different modifica- 
tions of the mouth-parts. The masticators of the gnats 
have been converted into long stilettoes. The larvae of 
the dragon-flies, which live in the water, have developed 
the lower parts of the mouth as pincers, with a long 
retractile stalk, and able to seize an animal at some 
distance when they are suddenly thrust out. We 
should never come to a stop if we were to examine 
all the adaptations of the mouth-parts of insects. We 
will desist, however, and briefly consider the other parts 
of the insect body. 

The wings have entirely disappeared in the flea ; in 
the fly the back pair has degenerated, and in the 
strepsitera 1 the front pair. In the earwig the wings 

i The strepsitera, to which belongs, for instance, the “Stylops 
melittse,” have some peculiar adaptations. The larvae, which jump 
briskly on their six legs, force their way into the bellies of bees and 



are folded together, and can only be opened with the 
aid of forceps at the extremity of the abdomen. In 
the beetles, only the hind wings are used for flight ; 
the front wings form a cover for them. There is 
equally endless variety in the legs of insects. In the 
mole-cricket the front extremities have been converted 
into shovels ; in the grasshoppers they have become 
a powerful leaping apparatus. 

The skeleton of the articulates, with all these peculi- 
arities, is of the greatest theoretical value. It provides 
ample material for the refutation of the Lamarckian 
principle, as it is Weismann’s merit to have shown. 
We saw above the way in which insects grow. Under- 
neath the shell the skin secretes a new one, but this 
is soft and elastic, and only hardens when the old one 
has been cast off. All the characteristics of the coat — 
its thickness, its different kinds of hairs and other out- 
growths — are already formed before the old coat is cast 
off. When this is done, the new one appears in full 
development ; it hardens and grows no further, as our 
bones do, because it is an excretory product of the 
underlying skin. As soon as the shell comes to light, 
the skin which has produced it loses its connection with 
it ; it has to begin immediately the work of secreting 
a new coat. 

wasps, though not deeply, and become pupae there. From the pupae 
issue the insects that have become males, and fly away with their large 
bird wings. The females do not leave the pupa-covering ; they are 
without wings or legs, and like grubs, and remain in their wasp until 
a male comes to fertilise them. The larvae develop from the fertilised 
ova in the mother’s body, and then break out of the mother’s back, 
and in their turn make their way into wasps. 


These peculiarities of the coat cannot be explained 
by the Lamarckian principle. We will not speak of 
the hairs and protuberances, as to which it is quite 
unintelligible how such structures, which only act when 
they are formed and have never been used, can be 
strengthened by exercise. But let us take a simple 
case. The Lamarckians would explain in the following 
way the hard inner edge of the crab’s pincers, which 
grow in the above manner. The shell of the pincers 
was thin at first. The crab then formed the habit of 
seizing its prey with the pincers, and using them as a 
weapon. By the continuous pressure of the claw-fingers 
on the inner side in bringing them together, the shell 
gradually hardened at the edges, in much the same way 
as the fingers of seamstresses or violinists develop a 
harder skin by pressure. Once the inner edge of the 
crab’s claws had become thicker by this continuous use, 
and it came to have young ones, these would have a 
thicker shell at the part in question from birth, owing 
to heredity, and it would be increased in the course of 
generations until the actual claws were formed. 

The comparison with the skin of the finger seems to 
be helpful, but we have really to deal here with two 
totally different facts. The human skin is alive, and the 
living substance can certainly be strengthened by use, 
as the muscles of the athlete’s arm show. But the 
crab’s shell is dead ; and dead structures do not become 
better, but, if anything, worse by use. They get used 
up, like a steel spring that has been long in use. 

When the coat was still connected with the living- 
skin, when it was still in the process of being formed 



from the skin by secretion, it could not be altered by 
use, because it was the old, overlying shell that was 
then in use. The characteristics of the articulate 
skeleton cannot, therefore, have been developed by use, 
as in each case they were fully developed before use. 
When a crab casts its old coat, it appears in the new 
one, which is still soft, but soon sets. But the soft 
shell has all the protuberances and thick parts, and does 
not differ in the least in structure from the hard one. 
Moreover, it would not help even if the soft shell could 
be modified by use. The soft crab refrains from using 
his soft claws, with which he could do nothing. He 
creeps under a stone and waits idly until the coat is firm 
enough to protect him. 

To this view it has been replied as follows. The 
shell may not be able to thicken from pressure, but the 
skin that is forming the new coat underneath it may. 
Pressure in the old shell affects the underlying skin as 
well, and its function, the secretion of a new shell, will 
be proportionately stimulated, and produce it in a 
thicker condition. Hence when the crab continually 
uses its claws and so presses on the inner side of them, 
this pressure will act through the shell on the skin 
beneath it ; this will do more work, and at the next cast 
of the coat the inner edge of the claws will be thicker. 

But why should the skin act more and not less 
vigorously under pressure ? It is not at all agreed that 
it secretes a thicker and not a thinner coat, when it is 
pressed through the overlying shell. And even if we 
admit that its activity is increased by pressure, how 
did this capacity come into existence ? 


However, we need not linger with these objections to 
the theory. There are certain facts that completely 
demolish it. These facts are the casting of the skin 
of beetles, flies, wasps and butterflies. In all these 
animals the coat of the imago is formed underneath 
the pupa-cover. The legs are pressed against the 
body, the wings folded, and everything enclosed by 
the pupa-skin as in a parcel. But the pupa scarcely 
moves , and so there can be no pressure to act through 
its shell on the underlying imago skin. And even if a 
pupa happened to be exposed to pressure, the stimulus 
would act equally on all parts of it, as in the pupa 
they are all folded together, though in the adult insect 
they must be wide apart and differ very much in thick- 
ness, as they do in point of fact. Finally, it is precisely 
the thin parts of the imago coat that lie directly under- 
neath the pupa skin ; many of the thick parts are 
protected from pressure by the overlying wings. 

It is clear, therefore, that in the secretion of the 
imago coat the skin cannot possibly be influenced by 
pressure. Nor even immediately after the emergence of 
the insect. The imagines of the insects enumerated 
may expose their coat to all kinds of pressure, as much 
as they will, the underlying skin will never be caused 
thereby to secrete a stronger coat, because in these 
insects it has no further activity in the imago. No 
butterfly ever casts its skin ; this is done by it several 
times as a caterpillar, and once as a pupa. None of 
the characteristics of the coat of a bee, the wing- 
nervures, the thick and thin parts, the various kinds 
of hairs, the eye-facets — none of these things can 


20 7 

have arisen by use and the inheritance of its results. 
The whole coat, with all these prominences, is a 
dead structure ; it can only be worn out by use, as it 
has no living parts to replace or increase what has been 
used up. The animals retain this shell until they die ; 
no new one is formed underneath it, and there is no 
coat-producing skin there to be influenced by pressure 
or use. Hence the peculiarities of the imago coat of 
these insects cannot possibly be explained by the 
Lamarckian principle. 

But they are explained by natural selection. Every 
living thing varies, and so there will be a slightly 
different imago formed under the pupa-cover of each 
separate insect. When the animals issue forth, their 
variations come to light, and are selected or rejected 
according as they are useful or otherwise. They will 
either be preserved and accentuated by continuous 
selection, or they will disappear. And as the 

Lamarckian principle cannot possibly have formed 
the details of the coat of these insects, but natural 
selection may have done so, we have a right to assume 
that the shell of the Crustacea and of the insects with 
gradual growth was not brought about by the “ inheri- 
tance of functional modifications,” but by a process of 

There are certain adaptations which many experts 
think cannot be explained by natural selection, but only 
by the Lamarckian principle. These are what are 
known as “harmonious adaptations” or co-adaptations. 

There were in former ages stags with antlers six and 
a half yards high. The animals could, of course, only 


support these heavy antlers on their heads if they had 
skulls of proportionate thickness and necks strong 
enough to sustain the ponderous head. Even the 
animals’ shoulders and other parts of the body must 
have been powerfully developed. We see, then, that 
strong antlers involved a whole series of co-adaptations ; 
that is to say, it was not enough for variations with 
larger antlers to appear among the stags, but in these 
very cases there would have to be also a number of 
other organs modified in a definite direction. But this 
could not be expected in variations. They depend on 
chance ; each varies on its own account, and there is 
no hand guiding them from some higher standpoint. 
If one amongst a litter of stags has larger antlers, it is 
possible that it may also chance to have a stronger 
collar, but some of the other parts will certainly be 
found to be weaker ; it is too much to expect from 
chance that so many organs should vary in the same 
direction. The reader will be able to follow the 
argument best by imagining a game with twenty dice. 
The different numbers that come out on top will 
represent the variations arising at each throw — 
corresponding to each litter of young. As it is 
demanded in the case of the stag that some animals 
shall appear with, let us say, ten definite variations, we 
must require that ten of our dice will throw the number 
six. Certainly one of the dice, possibly two, will throw 
a six after several attempts, but it is improbable in the 
highest degree that ten dice will give that number, 
however often they may be thrown. 

The Lamarckian principle meets the difficulty. 



When from any cause the antlers of the stag became 
larger, they exercised a pressure on the skull, which led 
to its thickening, and the other parts of the body would 
be equally strengthened and modified by the pull of their 
burden. These variations were transmitted to offspring, 
and if a still stronger pair of antlers arose in the next 
generation, and was selected, it found better support, and 
would in turn improve this by its pressure, and so 
the advance would gradually continue. 

This kind of explanation seems simple enough, but 

there are certain co - adaptations that it cannot cover. 

This is the case with the insects once more. We have 

already seen that the cutaneous skeleton of these 

animals is dead, and can only be used up, not 

strengthened, by exercise. Now, the peculiar fiddling 

apparatus of the field-cricket only makes its appearance 

at the last cast of the skin. It consists of two very 

different parts — a bow, which is represented by a 

specially modified nervure of the wing, and the side 

across which it is drawn. The latter is a part of the 

inner surface of the hind leg, which is equipped with a 

number of little teeth ; it is these that give out the 

chirping sound when they are rubbed. Here we have 

a co-adaptation that the Lamarckian principle cannot 

explain. Two organs that lie in different parts of the 

body are modified in the same direction, so that one 

can only co-operate with the other ; but they can neither 

have arisen nor been improved by use. They only 

make their appearance at the last cast of the skin, and 

when they rub together they only wear themselves, 

since they are dead structures, and the underlying 


2 10 


skin cannot be stimulated by the pressure to form 
stronger parts, since its function ceased at the last 
cast of the skin. 

In the same way we find many other co-adaptations 
in the coats of bees, wasps, butterflies, etc., in which 
the last cast is the abandonment of the pupa-skin, when 
they first receive their specific features, such as wings 
and so on. Hence when we find on the fore-legs of 
bees and wasps certain structures consisting of two 
parts forming a ring with teeth in its inner side, through 
which the antennae are drawn to be cleaned, we have a 
structure that cannot have arisen by use. The same 
may be said of the mouth-parts of these insects. In 
the gnat there are at least eight parts that are all 
modified in the same sense as stabbing - bristles and 
suctorial apparatus ; they are all about the same length, 
and can only act in conjunction. The antlers of the 
large stag with the thick skull and the proportionately 
modified other parts are not more wonderful than the 
parallel development of the mouth-parts of the gnat. 
When the Lamarckian principle is admitted on the 
crround that it is said to meet difficulties that natural 
selection cannot explain, we see that this is not the case. 
At all events, it does not do away with the difficulty of 
co-adaptations, because there are co-adaptations that it 
cannot explain. 

But are co-adaptations really inexplicable by natural 
selection ? Selectionists say they are not, and they 
are quite right. In the first place, artificial selection 
shows that harmonious variations do actually take place. 
Think of the dachshund, which has been brought to its 


2 1 r 

present form by a continuous selection of the shortest- 
legged pups. In its variations there were always 
corresponding modifications of the other organs, such 
as, broader paws, thicker legs, and changes in the 
bony structure and length of the body. The latter 
feature is absolutely necessary to secure mobility in a 
low animal, as we see in the case of all short-legged 
or legless animals, like the marten, the lizard, or the 
serpent. Just as, in the selection of the dachshund, 
all the corresponding variations appeared quite spon- 
taneously, without the vital activity of the developing 
variety being drawn upon, that might also happen in 
the parallel case of natural selection, and therefore in 
the selection of the giant antlers of our stag. We must 
not forget, moreover, that an organism is a harmonious 
whole, in which continuous selection has brought about 
an ever improving co-adaptation and co-operation of 
the various parts. Hence, when the variation of a 
longer bone occurs in a leg, the corresponding muscles, 
blood-vessels, and nerves are also usually longer. It 
has even been discovered that when fly-maggots are 
kept without food, the flies that issue from them are 
smaller than usual, but have a complete harmony of the 
various organs. Selection has led to this harmony, and 
it preserves and increases it ; every organism that lacks 
it will be crushed out as a cripple. Moreover, natural 
selection can often develop similar organs in different 
directions. We see this in the legs of the leaping 
mammals, in which the hind legs are much longer than 
the front. 

Further, co-adaptations may often be brought about. 


by combination. It is clear that natural selection may 
attain the same end by different means. When, for 
instance, the herons began to seek their food at the 
bottom of the water, selection favoured not only those 
with long legs, but also those with long bills and long 
necks. The end was reached by all three modifications, 
and so they were equally selected. The continual 
crossing of the three characters gave rise to the actual 
herons, which have all three of them. 

Finally, we need not suppose that the co-adaptations 
must arise simultaneously , and it is precisely in this that 
the chief difficulty was found. Remember our illustra- 
tion from the dice. We can easily get our ten sixes if 
we throw until a six turns up, then leave this standing, 
and throw again until another six appears, and so on 
until we have got our ten sixes. 

Natural selection may act in the same way. In the 
giant stag first large antlers were favoured ; they were, 
of course, not immediately so heavy that the animals 
with weaker skull and neck were incapacitated, because 
all variations are small at first. When a race of stags 
with large antlers had thus been formed, and continued 
to increase, the time came when only the individuals 
with strong skulls could carry the antlers with ease. 
Then the thicker skulls were selected. Thus all the 
co-adaptations might be selected successively ; even if 
they were wanting at first, they were bound to appear 
in the course of a long period, and would then be 
favoured. But even if they were wanting at first, 
the animals with the larger antlers were not necessarily 
incapacitated. We must not forget that use in the 



course of an individual life certainly strengthens an 
organ, though the result of it is not, in my opinion, 
inherited. As the antlers of a stag need years to grow, 
and their weight does not increase so very much in 
each year, the head and neck will become stronger 
under their increasing burden, so that an old sixteen- 
pointer can bear a considerable weight. However, 
this strengthening by use can only advance to a certain 
point, as we see in the old illustration of the man who 
carried a calf every day and so was able to lift it even 
when it had grown into an ox. The man could never 
have lifted two oxen, even if he had begun with two 
calves. Hence there came a time in the development 
of the giant stag when the antlers were so heavy as to 
interfere with the mobility of the animals ; then the 
animals were selected which had a stronger constitution 
from birth. 

Hence, as the co-adaptations do not need to appear 
simultaneously, but may be selected successively during 
long periods, they present no difficulty to natural 
selection. The Lamarckian principle is not only 
inapplicable to a number of co-adaptations, but it 
is wholly unnecessary for explaining harmonious 
adaptations . 1 

1 Weismann further instances the many co-adaptations of the ant 
and bee-workers, whose frame cannot have been formed by the 
inheritance of the effects of use, because the workers inherit nothing t 
since they do not reproduce at all. The queens, which give birth to 
the workers along with the rest, have a totally different structure. 
Weismann explains the case by a selection of stocks. Those stocks were 
always preserved, the workers of which took most care of the eggs and 
the stock. At the same time those queens were selected which were not 
only the best queens, but also brought the best workers into the world. 


There is still one province in which the Lamarckists 
think their principle is indispensable ; this is the province 
of instincts. It is said that we cannot understand these 
except as inherited habits. 

We saw above that instincts are Grounded on com- 


plicated reflex actions. It is just as difficult, moreover, 
to put limits between instincts and voluntary actions as 
it is between reflex actions and instincts. It is certain 
that actions which were at first voluntary and have 
often been repeated become at last instinctive. There 
is the pianist, for instance, who practises a piece 
consciously and with an effort of will. In the end 
he will play the piece quite instinctively, often while he 
is thinking of other things altogether. With many 
people it is entirely instinctive to take out their watch at 
night, or to clean their teeth — in fact, to perform a large 
number of actions which were at first controlled by the 
will. That voluntary actions may become instinctive by 
frequent repetition is as certain as that organs become 
stronger by exercise. 

Hugo von Buttel-Reepen, the leading authority on bees, has shown 
at length how we may conceive the origin of the bee-state by selection. 
At first there were a few living females, which laid their eggs in 
sheltered hollows and provided them with food, as many wasps still do. 
Then those females were selected that remained with the eggs and 
watched them until the young issued. The next point was that the 
first females to come from the eggs took a part in the watching of the 
rest of the eggs and larvse. After this there was a more and more 
complete division of labour, in virtue of which the older female was 
turned exclusively into an egg-laying machine, and the others worked 
for the community. The great advantage of the state is that, even if 
numbers of the feeders of the swarm are destroyed, there is always a 
sufficient number left to supply its needs. The limits of the present 
work unfortunately forbid me to enlarge further on this interesting 


2I 5 

It has been claimed that voluntary actions of this 
kind that have become instinctive, or habits such as 
these, may be inherited. That, however, is not found 
to be the case with the pianist ; his son must learn the 
art himself laboriously. It is the same with reading 
and writing. 

Thus we see from the start that all voluntary 
actions that have become instinctive are not inherited. 
It is true, say the Lamarckians, that all habits are not 
transmitted, but the instincts we find in the animal 
world are inherited actions that have passed from 
voluntary to instinctive. There are instincts so wonder- 
ful that we can only conceive them as impulses perfected 
by intelligence, which have reached their present height 
by the inheritance of such usage during a long series of 

But when we examine the impulses of animals, we 
find that in a large number of them this conception 
is quite impossible. There are instincts which it is 
impossible to imagine as having ever been initiated by 
the will of the animal, or having been improved by use. 
This is clear in the course of one of the most original 
impulses — that of flying from enemies. 

When a fly darts away from the hand that tries to 
capture it, this is certainly not a voluntary act that has 
become a habit by practice and been transmitted as such 
to posterity. It can hardly be supposed that the fly 
knows what it is to be killed. Nor can it ever learn by 
experience how swiftly it must fly, as every insect that 
does not get away promptly loses its life. Finally, the 
action is clearly seen to be unintelligent from the fact 


that the fly constantly returns to the same spot, although 
it has barely escaped frorm the hand of the catcher 
a number of times. The fly is certainly not an 
intelligent animal, otherwise it would know that the 
spot was dangerous. Clearly, in its flight we have an 
instinct that causes the animal to fly away quickly, by a 
sort of reflex action, when a body approaches it rapidly ; 
an instinct that was not initiated by intelligence, nor 

We must equally discard the Lamarckian principle 
as an explanatory factor in dealing with the instincts 
that accompany protective colouring. The murderous 
mantis, which is of a green colour like the surrounding 
grass, steals very slowly on its prey. The xylina , that 
looks like a piece of wood, shams death ; that is to say, 
remains quite motionless, and finds excellent protection 
in this way. Can these animals know that their 
colour is only useful to them if they act in accordance 
with it ? 

Butterflies that are not eaten on account of a nauseous 
taste or smell are distinguished, as we saw, by glaring 
colours. They fly slowly, because it is best for them 
to be seen clearly, so as to be recognised from afar as 
inedible before a bird can seize them. No one, surely, 
will suppose that these animals are conscious of the 
advantage they have in flying slowly. 

There are, nevertheless, intelligent tracheates whose 
instincts might seem to have been originally acts of 
intelligence, which they have improved by reflection, 
and have transmitted the results to offspring. I refer, 
especially, to the spiders. 



When a garden -spider is preparing its web, it first 
climbs to a high point, gives out two threads from its 
spinning glands and attaches them. It then lets itself 
down by the two, either to a branch that lies right 
below it or in a slightly oblique direction ; it accom- 
plishes the latter movement by swinging itself about. 
One of the two threads is again attached and drawn 
tight ; the other is bitten off, and is carried by the wind 
until it reaches a branch that lies on a level with the 
upper point. The spider crawls up it, draws it tight, 
and attaches it. It then lets itself down and prepares 
the second vertical thread. It furnishes the horizontal 
thread either in the way we have described or by 
making a circuit, passing from one point to the other 
on the ground, spinning its thread all the time and 
drawing in the long thread with its fore - legs and 
fastening it. When it has thus prepared the frame of 
the net, it runs to the centre of the horizontal thread, 
and lets itself down vertically to the lower one, and thus 
forms the diameter-line. Then come the radii from the 
centre ; these are fastened to all the required points, 
when the spider has reached them by means of the 
existing threads. Last of all the concentric lines are 
made by passing from one radial line to another. The 
whole web is often made in a single night. 

The work of the house-spider is simpler. It draws 
threads backwards and forwards across a corner, and 
lurks in the tube it has spun. Very remarkable, again, 
is the conduct of the large water-spider. It breathes 
the air, although it lives in the water, and has in the 
hairy coat that clothes its abdomen a means of retaining 


air underneath the water ; this gives it a bright silvery 
appearance. The water-spider makes underneath the 
water a diving-bell as large as a wall-nut, bringing 
down in succession from the surface the air-vesicles it 
has wound round. It usually lives in these bells, and 
stores its prey there. 

If it were said that intelligence prompted the spider 
to modify its web in this way, and practice had made 
it perfect, the claim would not apply to the bell that 
the water-spider constructs for its young, which is 
closed below as well. The spider cannot possibly know 
that the eggs and the young that issue from them need 
air. But if the one web has been produced without 
intelligence and practice, it may very well be the same 
with the other. 

We are, in fact, compelled to exclude the influence 
of intelligence in this care of the young by the 
tracheates, because the parents only make the shelter 
for them, and never see their offspring, and so cannot 
know their needs. The black water-beetle spins two 
plates, lays its eggs inside, and weaves the edges to- 
gether. It thus forms a raft, one side of which is drawn 
up in the shape of a little horn, so that it always floats 
with this uppermost. Still more complicated is the case 
of the predatory wasps. These powerful creatures fall on 
an insect, probably a caterpillar, paralyse it by a sting, 
and drag it into their nests, where they lay the spoil 
in a cell, deposit an egg on it, and cover up the cell. 
The larva develops from the ovum, and feeds on the 
victim, which has been prevented from decaying by 
being merely paralysed. Sometimes, indeed, the egg 


2 19 

is suspended over the victim by a thread, so that the 
convulsive movements of the caterpillar may not injure 
the larva, which can always retreat by the thread. 
Here again we must discard the supposition that the 
wasp executes all these details because it knows what 
will be good for the larva. And the instinct cannot 
have been perfected by practice, because they lay very 
few eggs in the course of their life. 

There are, moreover, plenty of instincts that only 
act once in the lifetime. In these cases it is frequently 
clear that the Lamarckian principle entirely fails, because 
here there is no practice whatever and consequent 

An insect only passes into the pupa stage once in 
the course of life, so that this act and the preparations 
for it have not been practised. But these preparations 
are amongst the most wonderful and most complex 
instincts. The matter is comparatively simple in many 
of the day butterflies, such as the common white ones. 
These, while in the caterpillar stage, spin a thread 
round themselves, and hang down by it from a wall. 
The thread must be just as long as the thickness of 
the pupa, otherwise it may either be pressed or fall 
out. How can the caterpillar know how thick it will 
be in the pupa stage ? And how can it practise spinning 
its thread when it only does this once in life ? 

The larva of the large stag-beetle passes into the 
pupa stage in a hollow ball of clay prepared by itself 
with polished walls. In the insect that will become 
the male this is much longer, because of the large 
antler-shaped jaws, than in the case of the future females, 


whose tentacles are small. Here the constructive 
instinct differs for the two sexes. But in neither case 
can we suppose that the larva knows what sort of 
tentacles ft will have. The clay-ball, moreover, is only 
formed once in life, and there is no possibility of 

One of the most complicated pupa-coverings is the 
web of the small nocturnal peacock’s eye. In this case 
there is a hole for creeping out in the spun capsule, but 
in order that the enemies of the pupa may not crawl 
in by it a bundle of stiff silk-bristles, with points directed 
outwards, is spun over the hole, and acts as a weel. 
The bristles are easily pushed aside by the butterfly 
when it issues forth, but they prevent an entrance from 
without. Here, again, there can be no question of 
practice, as the caterpillar only makes the web once 
in its life, and makes it — must make it — correctly on 
this single occasion. The intelligence of the caterpillar, 
moreover, has certainly nothing to do with the work, 
as it cannot know that it will need special protection 
during the pupa stage, and that this complicated 
structure on its home will keep off its enemies. 

We see, therefore, that the Lamarckian principle 
entirely fails to explain many instincts. There are 
instincts that can never have been acts of will and 
intelligence, and others in which the element is entirely 
wanting to make them instinctive even if they had 
once been voluntary actions — namely, practice or 
repetition — as they are only performed once during 
life . 1 If the complex instincts we have described cannot 

1 Instincts of this kind are Weismann’s chief objection to Lamarckism. 


22 I 

have been brought about on Lamarckian principles, we 
must discard them in the case of all instincts. 

But we have already seen, in the second chapter, 
that instincts present no difficulty to natural selection. 
Instincts vary, just as the parts of the animal body 
do, and so can be selected and improved. They are 
adaptations, and are often only of use in the circum- 
stances in which their possessors ttsually live ; they are, 
therefore, relatively imperfect, as we should be bound 
to expect in view of their origin by selection. A 
cricket that saves itself in nature by digging swiftly 
into the ground repeats the movement even on hard 
gravel or on a glass plate, when it would do better to 
run away. A bee stings a human being, whose skin 
closes over the wound, and retains the sting with its 
barb, which is fatal to the bee. Its sting is only 
provided against its chief enemies, the insects, whose 
coat remains open after the wound is inflicted, and lets 
the sting out again. The imperfectness of these 
instincts tells very clearly of their origin by natural 

Hence, though many scientists retain the Lamarckian 
principle because a number of the characteristics of 
animals seem to them inexplicable without it, we have 
seen that these characteristics are also found in circum- 
stances where the Lamarckian principle cannot be 
admitted at all. We found this in the case of the 
skeleton of insects and their co-adaptation. We now 
find it also in their instincts. 

The Lamarckians, however, retain their theory ex- 
clusively, though they know it cannot be proved. How 



often it used to be said that mutilations were inherited, 
yet all the alleged proofs of it have been found invalid ! 
There is not a single case in which a pup has been born 
with its tail cut off, or an individual born, amongst the 
Semitic races that practise circumcision, with that 
particular mutilation, though it has been practised by 
them for thousands of years. It has been found just 
as impossible to prove a case of a change that had 
occurred in an animal’s lifetime being transmitted to 
its young. We sometimes read in sporting papers that 
red spots have been found on the young in the womb 
of a deer at the spot where the ball struck the mother. 
That would be a very sudden inheritance of acquired 
characters ! Many people still believe that pregnant 
mothers can influence their offspring by fear, that the 
child will have burn-marks if the mother has seen a bio 


flame before birth ; it is quite arbitrary to call the red 
spots burn-marks, instead of blood-marks, or anything 
else. It is also thought that crippled limbs from a fall 
can be inherited. 

These beliefs have not been sustained by scientific 
inquiry. The many cases that have been investigated 
by experts have generally been explained in the sense 
that the feature in question was already in the family as 
a congenital characteristic. Not a single case has been 
established scientifically in which an acquired character, 
a mutilation or a habit, to which there was not a 
predisposition, was transmitted to children. 

It is, of course, a different matter with infection and 
poisoning. These affect the germ ; they taint the 
whole body, and do not leave the ova and sperm 



untouched. But in these cases the germ is not modified 
in a particular direction, but is diseased , like the whole 
body. This is what we have in cases of syphilis or 
alcoholic poisoning. The infection of the germ is 
brouo-ht about either by minute organisms that pene- 
trate to it, or by alcohol, which naturally reaches the 
germ as it courses through the whole body. 

The Lamarckian principle cannot, therefore, help us 
in explaining certain characteristics of animals, because 
it does not explain many of them ; in the second place, 
it cannot be proved ; and in the third place, it is not an 
explanation at all. 

Natural selection rests on two causes, both of which 
have been demonstrated — on the variations of animals 
and their inheritance, and on over-production and the 
destruction of a certain percentage which this entails. 
But of the two postulates of the Lamarckian principle 
only one has been established, and this only in certain 
cases. This is the statement that an organ is strengthened 
by use and enfeebled by disuse. The second postulate 
— that these changes affect the germ in precisely the 
same sense — is a hypothesis that has not only never 
been proved, but itself requires explanation. 

We must certainly admit that the ova — and also the 
sperm — that mature within an animal are infinitely com- 
plicated structures ; and that in each ovum there is an 
enormous number of minute particles, each of which 
forms a certain organ when an animal develops from the 
ovum. But these particles are not miniatures of the 
subsequent organ ; they have a totally different form. 

Hence the stimulus that modifies any organ of the 


mother must penetrate to the ovum, must make its way 
through all the particles, without affecting them, and 
must influence precisely that particle which will form the 
same organ in any child that may develop from the 
ovum. But as the particles have quite a different form 
from the organ in question, the stimulus, when it has 
reached its object, must suddenly transform itself in a 
mysterious fashion, much as electricity is converted into 
sound in the telephone. 

Let us take the case of a woman strengthening the 
muscles of her arm by bending and stretching it. Even if 
this stimulus penetrates as far as the ovum, there is no 
arm there for it to strengthen in the same way, there 
is merely a minute point that will form the muscle later 
on, but at the time has nothing muscular about it. The 
stimulus must, therefore, transform itself in order to 
influence this point so as to produce a stronger arm 
subsequently than it was originally calculated to do. 

By what means, moreover, will such a stimulus be 
conveyed ? By the nerves ? By the blood ? These 
can at the most only convey a fuller or thinner supply 
of nourishment to the ovum. How, then, can they be 
the means of influencing just one particle, and that in 
a q7ialitative sense ? When a woman, for instance, 
injures her eyes by too much sewing, the most that can 
be done is for the particle which will form the eye of 
her child to receive a worse supply of nourishment. 
But why should that make the child’s eye short-sighted, 
instead of smaller ? 

There are other hypotheses as to the conveyance of 
the stimuli that affect the body to the ovum, but they 



are all grounded on precarious conjectures, not on facts. 
Hence the chief postulate of the Lamarckian principle 
itself requires explanation. Then there are the 
numerous categories of facts in which the principle 
entirely fails. There are so many characters of animals 
that have never been exercised because they only act 
when they are already there — such as colouring. How 
could any conceivable exercise of the salivary glands 
bring about the poisonous character of many serpents ? 
Use can at the most cause the glands to secrete a 
larger quantity , but not a different product ? And how 
could the spines of the hedgehog arise from its being 
often bitten in the skin by its enemies ? The thorns 
that protect plants from being eaten are also just as 
impossible to explain as due to use. 

We must, in fact, be very careful with the word use 
or exercise. We often read in Lamarckian literature 
that pressure will in one case lead to a less development 
of the parts pressed, and in another case to a stronger 
development . 1 The first postulate of the theory is 
therefore unsafe in many cases. It lends itself far too 
much to being used as a mere phrase that explains 
nothing. This organ must have been strengthened by 
exercise, they say, knowing neither if it was in reality 
much used, nor if exercise would modify it in the 

1 Thus in Plate’s works pressure generally has a strengthening effect, 
but in the case of the hermit-crab, the abdomen of which is buried in 
a snail-shell, the steady pressure is regarded as having a weakening 
effect and leading to the disappearance of its coat at this part. In 
general, however, Plate makes a moderate and judicious use of the 
Lamarckian principle. Pie recognises its weak points, but thinks it 
is necessary for the explanation of certain phenomena. 


particular direction. And when the same stimulus is 
said to weaken in one case and strengthen in another, 
we shall do best to discard an explanation that is 
unworthy of the name. 

It might still be said : We admit that the chief 
postulate of the Lamarckian principle has never been 
proved, but that is because we know so little about the 
conveyance of stimuli in the body. Still, the principle 
has one advantage. It unites a large number of cases 
under a single head. Thus we trace all the cases of 
falling to terrestrial magnetism without knowing its real 

But it is precisely the element which gives any value 
to such a concentration — the embracing of all falls that 
we observe under one law — that is lacking in the 
Lamarckian principle, which always leaves gaps that 
it cannot explain. And apart from the fact that the 
principle cannot explain the origin and transformation 
of the organic world as a whole, it proves useless even 
in small groups of cases, and it has to leave gaps in 
those where its action seems most probable, such as the 

There is only one phenomenon in the organic world of 
which selection does not give an entirely satisfactory 
explanation. I mean the rudimentary organs. But 
even here the Lamarckian principle is of no use to us, 
as it cannot have acted in many of these cases, and so 
we know that rudimentary organs may be brought about 
without its aid. There are some in the coat of insects ; 
I need only recall the degenerated wings of the orgyia, 
which consist mainly of shell. In this case the inactivity 


22 7 

ought to preserve rather than injure the wings, since 
dead structures are all the better for being spared, as 
anyone can see in the matter of his clothes. Hence, 
the wings ought to have been used up and atrophied 
precisely in the case of the flying insects, and have been 
preserved in the case of the non-flying, such as the orgyia. 
There are many rudimentary organs in the coat of 
insects. To these the Lamarckian principle is inappli- 
cable, and so once more we must discard it as unsafe and 
only explaining a part of the instances. 

To conclude ; no case has ever been known of the 
inheritance of the effects of use and disuse, and so the 
Lamarckian principle has not a single established fact 
to support it. Its possible sphere of action is very 
limited ; even amongst a given class of phenomena it 
has always to leave inexplicable gaps. There is an 
enormous number of instances to which it has no 
application. Of the two postulates on which it is based, 
the first is only certain in a few cases, and at the most 
merely possible in the majority. The second postulate 
is not an established fact, but a pure theory ; a theory, 
moreover, that is difficult to imagine, and in its turn 
postulates all sorts of phenomena and relations of most 
of which nothing is known. Finally, the Lamarckian 
principle is an obstacle in the way of a unified conception 
of things, such as it is the chief aim of the theory of 
evolution to build up, and can never be reconciled with 
it. We shall see more of this in the eleventh chapter. 

But I think we have now said enough to deprive the 
Lamarckian principle of all power to modify the forms of 
the organic world. 



Economy of nature. The chemical constituents of bodies. Chemical 
combinations. The elements. The albuminoids. Biogens as 
constituents of living matter. Vital phenomena and apparent 
death. Metabolism. Structure of the living substance. Plants the 
foundation of life. Order of sustenance in nature. Flesh-eating 
is more natural to the animal than plant-diet. Are all variations 
useful to animals ? Value of selection. Origin of the shells of 
snails. Change of functions. Development of the crab. Why the 
embryonic development of an animal reproduces its racial history. 
Reconstruction of embryogenesis. Uncertainty of the biogenetic 
law. Parthenogenesis, the development of unfertilised eggs. 
Significance of the germ-cells. Significance of sexual reproduction. 
Amphimixis. Plural variations. 

In every pond there are living at a certain depth 
innumerable tiny creatures up to the size of a pin’s head. 
They pass up and down unceasingly, and travel back- 
wards and forwards through the water. Every hour 
swarms of them are devoured by their countless enemies, 
yet we see no sign whatever of a diminution of their 
numbers. The heat of summer broods over the pond, 
the vapour rises to the clouds, aquatic plants come to the 
surface and wither in the heat ; in a short time there is, 
instead of the pond, a dry earth-pit covered with animal 
remains. In the autumn the rain sets in, the ground is 
moistened, little pools are formed, and soon the rich 

colours of autumn are reflected on the surface of the 




pond. The little creatures have returned as if by 
magic, and fill the water once more. Other aquatic 
animals were unable to sustain the drought, but they are 
there again as soon as the water covers the bottom ; 
the interval seems to have had no effect on their life. 

These minute animals, which fill the ponds and 
seas in such numbers that every cast with a fine net 
brings up a mass of their bodies from the bottom, are 
called water-fleas. They belong to the gill-breathing 
articulates, the Crustacea. They have a shell, and 
grow by casting the skin, like all other articulates. 

The small crustaceans play an important part in the 
life of a pond, as most of the fishes and a good many 
other animals could not exist without them. These 
build up their frames with the flesh of the little 
crustaceans. The water-fleas form a tooth in the great 
cog-wheel of the earth’s round. It turns on and on; 
substances are formed from stone and water ; from these 
is built up the living matter that appears first of all in 
the tiniest organisms ; from these are made larger and 
larger animals which will decay in turn, until the turn of 
the wheel is complete, and the stone and water are there 
once more to provide material for the fresh start. 

In order to understand better this “economy of 
nature,” we must begin a little further back. 

We know that the mass of the earth, with all the 
rocks, the water, and the air that surrounds our planets, 
consists of elements , of which more than seventy are 
known. These can combine in so many different ways 
as to produce the immense variety of forms of matter 
that we see every day. Such elements are, for instance, 


oxygen, hydrogen, nitrogen, carbon, all the metals, 
sulphur, phosphorus, and others. 

These elements may unite in two different ways to 
make up the materials we find in nature — in simple 
viixtures or in chemical combinations. 

A mixture can easily be understood. We may take a 
piece of copper, for instance, file it down, and mix it up 
thoroughly with ground sulphur so as to form a greyish- 
green powder. This seems to be quite homogeneous, 
but we find that it is not if we examine it under the 
microscope. If we apply a higher power, we see clearly 
that the new powder consists of grains of sulphur and 
copper, lying side by side. 

But if we heat the mixture until it becomes incan- 
descent, and then let it cool, we get a black substance 
in which we cannot detect, under the most powerful 
microscope, a single grain of sulphur or copper. A new 
body has been formed, and this cannot at once be 
separated into its constituents, as the mixture could be. 
The new body has also different properties from its 
constituents ; they have, as we say, entered into a 
chemical combination. In the present instance the 
compound is called sulphuret of copper. 

There are vast numbers of these chemical compounds 
in nature. Water is one, for instance ; it consists of 
hydrogen and oxygen. On the other hand, the 
elements that form the chemical compounds are rarely 
found in a free state in nature. Iron, for example, is 
never found pure, but always combined with sulphur in 
sulphuret of iron or other forms. 

It is possible to break up chemical compounds into 



their constituents by a method that we call “analysis.” 
But this analysis can only continue until we reach the 
elements. It is the characteristic of these that, however 
much you subdivide them, the particles are always of 
the same kind. They consist of a single form of matter. 
Take gold, for instance; however small it is ground up 
or chemically divided, it remains gold. 

We have now analysed all the substances on the 
earth, including the substance of which living things are 
composed. It has been found that the living substance 
contains just the same elements that we find in the 
lifeless crust of the earth, in the inorganic world, as we 
say. It is true that only a few of the elements — twelve 
in number — are found in living matter ; these are, 
especially, carbon, hydrogen, sulphur, nitrogen, and 
oxygen. But while the elements of organisms are the 
same as those of the inorganic world, they enter into 
different compounds in living things from those we find 
anywhere else. Of these compounds it is especially the 
albuminoids that distinguish the living substance and are 
never absent from it. They are very elaborate com- 
pounds ; we have succeeded in analysing them, but 
not in building them up from their known elements, 
because we do not know the arrangement of these, 
nor the forces and concomitant circumstances in which 
the elements enter into an albuminous combination — 
in the way that we found heat uniting sulphur and 
copper into sulphuret of copper. 

Thus there is no difference in principle between the 
composition of living and lifeless matter. Nor is there 
any essential difference between the forces at work in 



each substance. The only difference is that we always 
find in the organic world certain very complex chemical 
compounds, especially the albuminoids, that are not 
found in the inorganic. 

But important as the results of long chemical research 
are, we must not exaggerate them. The living sub- 
stance is as enigmatic as ever, because we only know 
its composition after death. The analyses that have 
acquainted us with its constituents had to kill it before 
any result could be obtained. We may, nevertheless, 
assume that the organic substance consists chiefly of 
albuminoids in life as well as after death, but their 
behaviour is very different in the two cases. We can 
preserve dead albumen for a long time, if we keep 
bacteria away from it, without decomposition setting 
in, whereas the albuminous matters in the living 
state are continually breaking up even under normal 
conditions, and the more readily the stronger the 
stimuli that act on them. We must, therefore, 
draw a profound distinction between living and dead 

This has induced many scientists to discard the name 
“ living albumen,” and replace by the term “ biogen.” 
We know very little of the real composition of these 
biogens. As they pass into dead albumen when the 
organism dies, it is very probable that they closely 
resemble it in texture, and especially that they contain 
no different elements. But certainly the grouping of 
their elements is different from in dead albumen ; it 
is, in particular, looser, as only in that way can we 
explain the ready disintegration of the biogens. It is 



precisely in this looser texture that we find the centre 
of gravity of the whole life. 

The living substance has distinctive properties which 
we call the phenomena of life , and which are familiar 
enough to everyone as nutrition, movement, irritability, 
and so on. When these properties disappear we say 
that the organism is dead. 

All the vital phenomena, however varied they may 
be, are based on one property of the living matter, 
namely, its interchange or circulation. The funda- 
mental quality in this is “ metabolism ” ; that is to say, 
the living substance breaks up of itself unceasingly and 
regenerates itself, and in doing so thrusts out matter 
from itself and takes in new matter from without. As 
- it is the living albuminoids that behave in this way, we 
may say : Life consists in the metabolism of the biogens. 

This metabolism ceases when life has left the body. 
We have, in fact, every reason to believe that the 
metabolism is suspended in “sham death,” even when 
it is voluntary, as in the case of the Indian fakirs. 
The trance or simulated death of the fakir may last 
for six weeks. Many of the animals, also, fall every 
year into an apparent death-condition, and awake to 
new life in proper conditions. The seeds of plants 
may lie for years without vital functions, yet germinate 
when they are put in moist earth. The very finest 
methods have failed to detect any trace of giving-off 
matter in these seeds. But it is untrue that the 
grains of wheat taken from Egyptian tombs thousands 
of years old grow into plants. They decay when they 
are put in water. 


The constant renewal of the disintegrating biogens 
is effected, therefore, by the taking-in of matter. This 
must, of course, contain the elements of which the 
living substance is composed. These elements, we 
know, are found in inorganic nature. Thus the 
organism is like a laboratory, in which chemical com- 
pounds are constantly set up and taken to pieces again. 
The requisite elements are taken from the earth, the 
water, and the air. These are first of all united in 
simple combination in the organism, and from these 
more complex ones are formed, and so the activity 
of the living substance goes on until the albuminoids 
are produced. The albuminoids are converted into 
living albumen, or biogens, by rearrangement of their 
constituents. Here the highest point is reached. The 
series of changes then descends once more. The living 
albumen becomes dead, this disintegrates, more and more 
simple compounds appear, and in the end combinations 
of the simplest nature. 

But, we may now ask, who represents the chemist in 
this living laboratory, the man who chooses and brings 
together the requisite substances ? 

The new biogens are formed from the old. The 
dead albumen that is imported into the body is con- 
verted into living by the biogens. When these have 
created new biogens, they break up, but owing to 
their activity before death the body loses none of its 
living albumen. 

However, the conversion of dead into living albumen 
is only the last part of the work done in the body. 
Who selects the matter that is to be taken into the 



body out of the number of substances found in nature, 
and who converts them into dead albumen by 
progressive combinations ? 

First of all, we must explain that the forces that can 
do this are only present in the plants. These alone 
have the power to select the requisite elements for 
making albuminoids out of water, air, and earth ; 
animals have lost this power. The latter must always 
obtain their albumen ready made, and their biogens 
will then convert it into living albumen. Animals 
perish if only supplied with inorganic matter, as their 
biogens then find no albumen that they can convert 
into particles like themselves. They cannot make a 
beginning with inorganic material, as their substance 
has not the power to put it through the long series 
of combinations that are necessary for the production 
of an albuminoid. 

Thus the whole animal world is based on the plants. 
These alone have retained the power to form living 
matter out of inorganic substances ; they are now the 
sole laboratory in which albuminoid substances are 
prepared. This can be done, however, only by the 
green plants ; the others, such as the fungi, need organic 
nourishment, like animals. The green in the plant 
consists of microscopically small granules of chlorophyll ; 
they have the power, under the influence of sunlight, 
of gradually creating organic matter from the necessary 
elements of the air, earth, and water. The plants are 
the foundation of life. They alone can cover the steady 
return of living substance into inorganic matter, during 
its disintegration, by re-forming organic from the 


inorganic. They thus exercise their power, not solely 
for themselves, but also for the whole animal kingdom. 
The animals can only cover their loss of organic sub- 
stance from disintegration by obtaining albuminoids 
ready made, which they merely convert into living 
matter. They either take their food from the plants, 
or they satisfy their need of organic food by devouring 
their fellows, and these must have built up their frames 
on vegetal matter. The groundwork of all life is found 
in the plants ; without them the animal world is 

Let us now consider a world in miniature, a pond, in 
order to see the successive steps in the provision of 
food. There must first of all be plants, if any living 
substance is to be formed at all. In the pond these are 
chiefly algae, tiny green vesicles, which often swim freely 
about. These algae form the food of the water-fleas, 
the crustaceans of which we spoke at the beginning of 
this chapter. Most of the other animals live on these 
fleas, as also do the fishes, which feed almost exclusively 
on water-fleas in their earlier stages. The fleas are, 
therefore, an important connecting link in the economy 
of Nature. 

Even from this instance we see that it is not the 
higher plants that form the groundwork of the nutritive 
scale. This will easily be understood from the fact that 
the higher plants are very complex structures, with their 
stem and roots, leaves and flowers ; they must have 
been developed at a late date, when there were already 
plenty of animals. Thus the first “ angiosperms ” — or 
all our foliage-trees and shrubs, and many of our herbs 



— only appeared about the Tertiary period, and so come 
after many groups of vertebrates, such as the reptiles, 
had reached their greatest height. In fact, the whole 
intricate mechanism of the plants — the leaves, flowers, 
etc. — only came as an adaptation to life on land ; marine 
plants have remained at the primitive stage of seaweeds 
and algae. 

The plant-eaters are, of course, older than the flesh- 
eaters, since the first animals can only have had organic 
food in the shape of plants. But we must not generalise 
too much on the strength of this fact. Once the world 
was filled with the tiniest animals, the higher animals 
could be developed from them, and grow and advance 
at their expense. It has been rightly pointed out that 
animal food comes more naturally to the animal than 
plant-food. Every animal has been accustomed to an 
animal diet in its earlier period, whether this consisted 
of the yolk of an egg or the milk of the mother. The 
break from this early diet to plant-food with its hard 
substance, the cellulose, is very considerable, and we 
can understand why the higher plants have been 
avoided and the earlier vegetal diet retained. 

The chief difficulty in following the food-series occurs 
in connection with the land-animals. In the sea there 
are lower algae that are eaten by the smallest animals, 
and these in turn are devoured by the larger. Here 
nearly all are carnivores ; vegetarians are very rare 
amongst the larger salt-water animals. We can thus 
see that these tiny, lowly algae provide the organic 
matter for the whole animal life of the sea, since this 
is prepared from inorganic substances by the algae 


alone ; it then passes through the whole series of 
animals until it reaches the great monsters of the 

It is otherwise on the land. Here there are none of 
the lower algae and the minute animals that we call the 
protozoa. We have, therefore, to construct a different 

It is clear that all the higher characteristics that the 
plants developed on land first put in their appearance as 
root, stalk, leaves, and fibres, without being devoured 
by the animals. The leaves were not used as food 
until some time afterwards. It is probable that at first 
the land-plants only served as food for the animals after 
they had decayed, and so been modified by bacteria. 
The earthworms, which are certainly ancient species of 
animals, still feed in this way. Other animals may have 
lived directly on the fungi, which were certainly nearer 
to the diet they had been accustomed to from their early 
days than the green plants. The fungi have a similar 
composition and nutritive value to the animals. They 
have no green colouring matter, but feed on organic 
matter that the green plants have made. 

There is only a step from the eating of decayed 
plants to the eating of carrion, and this comes close to 
flesh-eating. We can best understand the flesh-eating 
animals if we assume this to have been the development 
of their diet. We are speaking, of course, only of the 
original animals ; in the higher ones the food changes 
according to the adaptation. Thus our former state- 
ment, that a flesh diet comes more naturally to an 
animal than a vegetal diet, is not inconsistent with the 



ruminants. Natural selection can certainly cause the 
adult animal to adopt a diet different from that it was 
accustomed to in its youth. 

We have a good illustration of such a development 
of diet in the second great group of animals with which 
we have to deal in this chapter, the “molluscs.” The 
chief representatives of this stem amongst us are mussels 
and snails. Of the latter, the land-covered snails eat 
fungi or mould, and the road-snails fungi. But a few 
species in each family have taken to a flesh diet. They 
can, of course, only catch slow animals such as earth- 
worms or other snails. And it is only certain species 
of snails that they eat, while avoiding the rest, possibly 
because they are protected by a strong slimy secretion. 

The mucus is a general characteristic of the snails. 
Our water-snails use it for creeping on the surface, 
many experts believe, and as a fact this seems to be 
the simplest explanation of the mysterious progress of 
the pond-snail on the surface of the water, with its 
body bent downwards. The snails which seem to 
have the flat part hanging in the air, and to creep on 
this, give out a long slimy thread and glide along this. 

The water-snails have a peculiar organ that enables 
them to rise or sink without effort, as the fishes do. 
This is their breathing organ, a cavity in the body that 
opens externally by an orifice. The animal sinks by 
compressing the cavity, and rises again by dilating it. 

The respiratory cavity is the lung of our molluscs, and 
is found both in the land and water-snails, as the latter 
are land-animals that have passed into the water, and 
must come to the surface to breathe and close the cavity 


below. However, the ancestral forms of the snails are 
in the sea, and are gill-breathers. How were the lungs 
formed when they came to live on land ? The organ 
for breathing air could not be large enough from the 
start to perform its function. How was it possible, 
then, for variations which represented the rudiment of 
an organ that could not yet act, and so were useless , to 
be preserved and favoured by selection ? 

Here we have what is considered to be the radical 
objection to the theory of selection ? The action of 
natural selection is made possible by the variations that 
bring about differences between animals, and cause some 
of them to be retained and others extinguished on the 
ground of their better or worse qualities. But these 
variations are insignificant in themselves. Hence if an 
animal only differs very little from its fellows, we can 
hardly say that it has on that account more chance of 
surviving or perishing than they. 

Let us take an instance. In the craw-fish the eyes 
are fixed on mobile stalks, and so the animal, the whole 
fore part of the body of which is rigid, is able to see over 
a larger area. In its ancestors the eyes were set deep 
in the head, as is still the case with the centipedes and 
the smaller crabs. According to our theory, those 
crustaceans must have been selected whose eyes stood 
out a little higher than those of their fellows, so that 
they were favoured in the struggle for life. But, it may 
be asked, could this trifling elevation of the eyes really 
be such an advantage to its possessor ? The field of 
vision would only be the smallest degree larger than in 
the other crabs. If individuals arose amongst those 



early crabs that had eyes already projecting on small 
stalks, we should acknowledge that these had an 
advantage, as they would perceive their enemies or 
their food quicker than the others. In a word, the 
changes that any organ or character of an animal shows 
at birth must generally be so slight that they can have 
no selective value ; that is to say, their owners cannot 
be so much better situated on account of them as to 
escape the destruction that falls on their fellows. 

Above all, it is said, we cannot see how complex 
organs and instincts can have a selective value from the 
beginning. The trunk is indispensable to the elephant. 
It uses it as a weapon, conveys food to its mouth with 
it, and cannot lift objects from the ground, or drink, 
without it ; these are all actions that it could not perform 
without the trunk on account of its short and stiff neck. 
But the trunk is only useful at its actual length. If the 
ancestors of the elephant had noses of ordinary length, 
like the tapirs, they would hardly be able to perform one 
of the above functions, and they would not have any 
advantage in variations that added a small fraction of an 
inch to them. We cannot admit, therefore, that the 
first slight lengthening of the nose was so useful that 
the elephants which did not possess it were the first to 
perish. In other words, we do not see that these nasal 
variations would have any selective value. 

However, let us take an instance from amongst our 
own animals. Take the shell of the snails. This is 
certainly useful to the animals, as they can withdraw 
into it and find shelter from their enemies and from bad 

weather. But the shell did not appear at its full size all 



at once ; it must have been small at first, so that the 
animal could not retire into it. Thus the shell was of no 
use at first, and so the snails in which it first made its 
appearance could not have been favoured by natural 

Nevertheless, the origin of the snail’s shell by natural 
selection is not so unintelligible at all. It has been said 
that the ancestors of the snails were animals that 
migrated from the depths of the sea into the surge-zone. 
These were at first devoid of shells, and clung to the 
rocks with their foot. The force of the surge must 
have destroyed numbers of them, tearing the animals 
from the rocks and dashing them against the stones. 
Those had an advantage, therefore, which had some 
feature that modified the force of the surging masses of 
water. This was a slimy layer that made the back of the 
animal smooth, so as to give no point of resistance to the 
water. All snails do, as a matter of fact, secrete this 
slime, and we can conceive this faculty to be increased 
by selection. But selection altered the quality, as well 
as increased the quantity, of the secretion. It was useful 
for this to become thicker and thicker, and thus at last 
the shell was formed, covering the snail like a shield. 
Each small variation was useful from the first, as we 
saw, and as the variations affected the whole dorsal 
surface of the body they led in time to the formation of 
a structure covering the entire animal. When the snail 
took to further migration and to the land, other 
variations would be selected until the snails’ house was 
formed, however small it may have been. 

We must be careful in urging the objection that many 



organs could not have had a selective value from the 
first. Even such complicated structures as the wings of 
birds and insects could arise gradually, as we saw in the 
fourth chapter, and were clearly useful from the start. 
Further, it has been rightly pointed out that sudden 
crises may occur in animals after periods of rest. 
During these the utmost demands are made on the bodily 
and mental constitution of the animals in the general 
devastation, as the stronger often fall upon the weaker 
members of the same species. Large numbers of 
animals perish in a severe winter, and we may assume 
that even a slight variation in the thickness of the fur or 
the feathers may save an animal from destruction. It 
has also been said with truth that in the migratory birds, 
for instance, slight advantages in the power of flight 
may do much, as the effects accumulate in the course of 
the long journey. Cyclists know that if they are to win 
a race every small part of their machine must be as light 
as possible. 

It is often difficult to imagine how an organ can have 
arisen by natural selection, yet we detect a means on 
further reflection. The origin of the wings and 
of the snail’s shell seemed for a long time to be a 
hopeless enigma, but the solution was at length dis- 
covered. If we can find the answer to these really 
difficult questions, we may hope to do the same for the 
remaining problems in connection with the evolution of 
animals or organs. But above all we must not at once 
throw the blame on the theory of selection when we 
cannot find the solution, but must remember the 
imperfect condition of our knowledge. We cannot 


determine the origin of any organ with certainty , as we 
have no absolutely certain documents. We construct 
the development of animals and their organs with the 
highest probability, once we have established the fact 
that they must have been evolved. The soundness of 
the theory of selection is by no means shaken by 
quoting organs the origin of which we are not at 
present able to explain. 

We will not attempt at the moment to settle com- 
pletely the difficulty that arises about the selective 
value of variations. We will merely refer to a 
subsidiary principle which provides a simple solution 
of the difficulties that are found in regard to the 
usefulness of the first variations of many organs. This 
is the principle of change of function. 

We became acquainted with this principle in describ- 
ing the conversion of the swimming-bladder of the fish 
into the lungs of the amphibia. Something similar 
happened in the development of the land-snails. In 
the marine snails the gills lay in a cavity that opened 
externally, and there were several blood-vessels in the 
wall of it. In the pulmonary snails also the respiratory 
organ is a cavity which differs from the preceding one 
chiefly in the absence of gills, and in the fact that the 
blood-vessels in its lining are so numerous and ramified 
that the air can give its oxygen, which penetrates through 
their thin walls, to the blood. These lungs are one of the 
best conceivable instances of the gradual transformation 
of one organ into another. They show, in the first 
place, that here, where natural selection needed an 
extensive organ from the first, there was one ready to 



meet the requirement ; and in the second place, it is 
clear that here the smallest variations had selective 
value, because as they passed on to the land every 
advance in the ramification of the blood-vessels in the 
lining of the cavity meant a richer supply of oxygen, 
and secured a longer life. 

There are plenty of examples of organs that had at 
first a certain function, and were enabled from their 
constitution to take up a secondary one. If a change 
took place in the habits of the animal, this second 
function might become the principal one ; in fact, the 
first might gradually disappear, and the organ would 
be correspondingly modified. We have a process of 
this kind in the limbs of the craw-fish. It has feet on 
what is called its tail, as well as the five pairs of legs, 
of which the first bear the claws. The animal’s tail 
is really its abdomen, and must not be compared to the 
tail of the vertebrate ; the alimentary canal runs through 
it. The legs on this abdomen were at first clearly for 
swimming, but were also used by the female for 
carrying the eggs. The second function became more 
important when the animal took to crawling as its chief 
method of locomotion, and so the abdominal legs 
became smaller and smaller by selection, and are now 
only useful for carrying the eggs ; even in the male 
they are used in connection with reproduction. 

Other legs of the craw-fish have undergone an even 
greater transformation. All the limbs of the Crustacea 
were originally legs, even the feelers, or antennae, that 
act as organs of smell or touch, and the masticating 
apparatus. Most of the masticating organs look very 


much like feet, except that the first masticators are shaped 
like two strong teeth. But, it will be asked, how do we 
know that these and the antennae were originally legs, 
when they have no resemblance to legs ? 

The answer to the question is given by embryology. 
In the case of a good many Crustacea the ovum produces 
an animal that is very different from the adult, and is 
known as a nauplius- larva. It is unarticulated, and has 
a simple organisation and only three pairs of legs, with 
which it swims about with a kind of hop. The larva 
gradually grows ; its hind end lengthens and breaks 
into joints, on which new limbs sprout out ; these differ 
in number according to the number possessed by the 
adult of the particular species. But the original three 
pairs of limbs of the nauplius are converted into the 
two pairs of antennae and the first masticators. These 
have therefore been developed from legs, as we clearly 

There are crustaceans that have become parasites ; 
they cling to other animals, and feed on their vital 
fluids. These have changed their form so completely 
that they may be taken for a piece of the intestine or 
at all events a worm, but never for a crustacean. The 
most curious, perhaps, is the sacculina , a crustacean that 
settles on the abdomen of a marine crab and is shaped 
like a sac ; widely branching root-fibres proceed from 
this and penetrate the whole interior of the crab and 
suck its blood. Yet this organism, so little like an 
animal, is a crustacean ; in its youth it has the form 
of one, and it emerges from the egg as a nauplius that 
cannot be distinguished from the nauplii of other 



crustaceans. In fresh water, also, there are crustaceans 
that have assumed the most curious shapes owing to 
parasitism, such as the Achtheres percarum, a parasite 
of the perch. 

The Crustacea are particularly striking illustrations of 
the biogenetic law that we mentioned in the fifth chapter. 
The crustacean reproduces in its ontogeny — its develop- 
ment from the ovum — the course of its phylogeny, or 
ancestral development in past ages. 

In the above-mentioned parasites we can understand 
why they cannot give up the free-living stage of their 
ancestors in their development. How could they reach 
their host — how could the animal, for instance, that 
comes from the sacculina egg reach its crab, if it could 
not swim freely about at the beginning of its career, and 
then settle like a plant on its victim ? 

There are only a few animals in which it was 
necessary to retain the ancestral stages. In many 
cases it will be an advantage to the animal to be as 
fully developed as possible when it leaves the egg, so 
as to reach sexual maturity quickly and provide off- 
spring. The whole development has, therefore, to take 
place in the egg, as is the case with the birds, and 
individuals of this kind are protected by the shell of 
the egg or within the mother’s womb. But a develop- 
ment of the animal within the egg implies a certain size 
in the egg, because, whilst the free-swimming larva can 
obtain from without the necessary nourishment for its 
growth, the animal in the egg is restricted to the supply 
of food inside the shell, or to the substance that we 
call the yolk. Eggs with much yolk can, in view of 


their size, only be produced in small quantities ; but on 
the other hand, the amount of nourishment provided 
enables the young in them to run through the stages 
of development more quickly than the free larvae, which 
have to struggle laboriously for the matter with which 
to build up their frames. 

When an animal is brought by natural selection to 
develop in the egg instead of as a free larva, a number 
of changes will follow. All the characters that can only 
be of use to a free-living larva are cut out in the 
embryonic development as so much waste of time and 
material, and only those ancestral stages will be retained 
that are necessary for the further development of the 
specific marks of the animal. Here we come to the 
essence of the biogenetic law. It is not a law of 
absolute and universal validity, like the law of gravity, 
otherwise every animal would have to reproduce exactly 
in its embryonic development the stages of its ancestry, 
which is not the case. It is no more than a postulate 
of the action of natural selection. All the characters of 
animals must arise in connection with others already 
existing ; nothing can be developed suddenly and 
without intermediate stages. Hence if a new organ has 
been formed from a previous one by gradual modifica- 
tion, it must follow the same line in its development 
from the ovum to the adult, because the ontogeny also 
can only proceed gradually. Thus the biogenetic law 
demands that just as an animal could only develop 
further in its ancestral history on the strength of 
qualities already existing in its predecessors, so in its 
individual growth it must build gradually on the actual. 



And this is, in the present case also, the succession of 
ancestral stages. 

When an adult animal is modified by natural selection, 
this modification will be the last to appear in the 
development of its descendants. It is always the 
terminal stages of animals that are vitally affected by 
selection. But the further the modification of the new 
species proceeds, the more will the embryonic develop- 
ment be affected. The organs that assume an increasing 
importance and range in the transformation will no 
longer find time for their development in the final 
embryonic stages, and their formation will be pushed 
further and further back, since those animals will always 
have the advantage in which the organ is formed first, 
and so most completely developed. Thus the most 
important organ in man is the brain. This enormously 
complicated structure naturally requires a very long time 
for its construction, and so we can understand why it 
should be one of the first organs to appear in the 
embryonic development, and why in the human embryo 
its size is altogether out of proportion to the small body. 
But it is utterly wrong to conclude from this that the 
human embryo with its large head and small body 
must prove according to the biogenetic law that man’s 
ancestors were similarly misshapen. 

In the transformation of species many new organs 
become larger and more important than the old ones, 
and these will accordingly, if they continue to be 
necessary but can be quickly developed, only be formed 
at the close of the embryonic life. This in itself will so 
modify the individual development that it will be almost 


impossible to gather the ancestral history from it. 
But the effect will increase if many of the organs of the 
ancestors are no longer necessary, and are not found in 
the adult animal. It is true that these will still have 
to appear in a rudimentary fashion in the embryonic 
course, but those animals will be steadily selected in 
which they take a shorter time and are less in size, as 
they then leave more room to the other organs. In the 
end they will be forced out of the embryonic develop- 
ment altogether. This must, of course, take place 
gradually, and if we find the gill-clefts of a fish still 
appearing, and then disappearing, in the human embryo, 
it only proves that the time when our ancestors had the 
fish form is not yet very remote, from the geological 
point of view . 1 

Finally, natural selection will modify the ontogeny by 
means of new structures arising. Thus in many ova 
and larvae special contrivances have been selected ; and 
as the embryonic development proceeds it must be 
affected still more owing to the particular method of 
receiving nourishment and the special position. The 
insect pupa is a new structure of this character ; the 
insects cannot possibly have had pupa-like ancestors, 
as they would never have been able to nourish them- 
selves. We saw in the preceding chapter how the 
formation of the pupa came about. 

All these divergences, modifications, and new forma- 
tions, of which there is an immense number, must alter 

1 For a brief account of the line of man’s ancestry the reader may 
consult Haeckel’s “ Last Words on Evolution,” of which an English 
translation has just appeared. (A. Owen & Co.) [d rans.] 


25 1 

the course of the individual development to such an 
extent that in no single case will it faithfully recapitu- 
late the ancestral history. It is only rarely that the 
biogenetic law will help the student to trace the stem- 
history of an animal. That is not the purport of the 
law. It serves rather to make more intelligible the 
action of natural selection, which can only build upon 
previous structures in the transformation of animals. 
When we find ancestral traits in the embryonic 
development of an animal, it is a proof of the theory 
of descent, but we must not demand such fortunate 
accidents. The ontogenetic evidence for phylogeny has 
been so much distorted by natural selection that it is 
probably the worst we have. It can only rarely serve 
to illumine the darkness that lies on the past history of 
organisms, and then generally only in conjunction with 
the other two sources of evidence, the structure of 
animals and the geological discoveries. 

We started from the larva-form of the crustacean, the 
nauplius. In that shape many crustaceans, such as the 
small hoppers and the branchiopods, leave the egg, and 
gradually pass into the adult form in the course of their 
free life. Other crustaceans pass through the nauplius 
stage in the ovum, and issue from it at a more advanced 
larva stage, the zoea, which has a larger number of legs 
and an abdomen. This is the case with most of the 
higher crustaceans, such as the sea-crabs, which would 
otherwise have to delay too long in the larva-stage on 
account of their elaborate articulation and numerous 
extremities. It is clearly better for the animal if the 
time is not too protracted until it begins to lay eggs, 


and so to maintain the species ; because during that 
period it is exposed to all sorts of dangers. The craw- 
fish, which is closely related to the marine crab, issues fully 
formed from the egg. This, again, is an adaptation, 
because the animal lives in running water, and cannot 
use a larva-form which from its structure is intended 
to float in the water. The stones afford shelter to the 
young animal, and it can take refuge under them. It 
is already a miniature of the adult. 

Among the lower crustaceans, also, the copepoda 
and water-fleas, there are differences of development. 
The copepods, which swim about in countless numbers 
in most ponds, lay a large number of eggs, and carry 
them about for a long time in a little sac. These 
numerous eggs have to be small, on account of the 
lack of space and the slight quantity of food available 
for each ; and as they contain little yolk, the animal 
can only develop in them up to the nauplius-stage, and 
must then issue forth. It is otherwise with the water- 
fleas or daphnidae. In their case only a few eggs are 
laid, and they have consequently more yolk. They also 
lie in a special breeding-chamber under the mother’s 
shell, and are washed with a fertilising fluid. Thus we 
can understand how, in the case of the daphnid, the 
whole nauplius-stage can be passed in the egg, and 
from it issues a completely developed water-flea, only 
differing from the adult in size. 

The number of the enemies of the daphnidae is 
enormous, and as the animals lay only a few eggs, they 
could not survive if they had not a special adaptation 
in connection with their fertility. They multiply 



parthenogenetically : that is to say, they lay eggs which 
develop without being fertilised by a male. From 
these eggs females only are produced, and they in turn 
lay eggs that do not need to be fertilised. Hence the 
water-fleas that appear in the spring are followed by 
several generations of the same sex ; towards the end 
of the summer their number is enormous, and then at 
last males are developed from a few of the eggs. 
These fertilise the eggs of the last generation of females, 
which are only laid in small numbers, generally only 
one or two. They are larger than the summer-eggs, 
and have plenty of yolk, because they have not the 
benefit of the fertilising water of the mother. They 
have a thick shell, and fall to the bottom, where they 
may be frozen in, or may lie uninjured without water. 
In the following spring they produce the first generation 
of females. 

Parthenogenesis brings up the number of daphnidae 
in the course of the summer to a huge figure. We saw 
in the first chapter that a couple of foxes will, if they 
have three male and three female young, and these 
three pairs give birth to the same number and so 
on, increase in ten years to 118,098 individuals. But 
if the first pair of foxes only gave birth to females, and 
these could multiply parthenogenetically, the number 
would rise in ten years to 60,466,176, or incomparably 
more. With larger figures the effect is still more 
stupendous, as there is question of a geometrical pro- 
gression. Hence the increase due to parthenogenesis is 
so great that though the numbers of winter eggs in 
each case is small, the total is very large on account of 


the number of parents. They serve to secure the 
maintenance of the species during the unfavourable 

The daphnidae are not the only animals whose eggs 
develop without being fertilised by the male. Quite a 
number of other species are associated with them in 
this respect. Many species of small mussels increase 
parthenogenetically as a rule ; amongst many of them 
no males have yet been discovered, though they have 
been carefully watched for years in an aquarium. 
Parthenogenetic reproduction is also found in the 
branchiopods and some other species of Crustacea, the 
gall-flies whose sting causes the gall-nuts on our trees 
and shrubs, and many lice, including the dreaded 
phylloxera. They are especially animals that enjoy 
from time to time very favourable conditions, which 
they can make use of for most prolific reproduction, 
and then pass into very dangerous and unfavourable 
conditions, which they survive in the shape of fertilised 
and hard-shelled eggs. Hence in this case fertilisation 
is not directed merely to the multiplication of the species. 
The best instance of this is the phylloxera. 

In the spring the egg of the phylloxera produces a 
female which multiplies parthenogenetically to an immense 
extent, as the animals have an unlimited supply of food 
in the shape of the vine-tendrils. All these females are 
wingless, but after several generations the eggs produce 
winged females which fly from stock to stock and spread 
the species. They lay two kinds of eggs. The larger 
produce females and the smaller males. Both are very 
small and wingless, and cannot feed themselves. After 



their union the tiny female lays a single egg, which lasts 
through the winter, and makes a beginning of a new 
parthenogenetic generation in the following spring. 

In this case it is clear that the union of male and 
female does not lead to multiplication. On the contrary, 
there is only one egg, and so one individual, from each 
pair. If the phylloxera depended on sexual propagation 
alone, it would soon become extinct. Its propagation 
and multiplication are exclusively parthenogenetic. 

But why do the males appear at all, we may ask, 
when the phylloxera reproduces so much better 
parthenogenetically ? And when we see that these 
animals can dispense with sexual generation, why is 
the same process not possible in other cases ? What 
advantage is it to organisms that a new individual can 
only be formed by the union of the generative products 
of two sexes ? 

We call the ovum and the sperm by the common 
name of “germ-cells.” They are both the germs of 
the new individual, and originally either the ovum, as 
in our illustration, or the spermatozoon, could develop 
quite independently into an animal. We shall see more 
about this later on, but may point out here that the 
spermatozoon and the ovum are structures of equal 
value as regards heredity. The ovum contains the 
bodily and mental characteristics of the mother and her 
ancestors ; the spermatozoon the features of the father 
and his ancestors. And just as a new individual can be 
formed in the ovum from these characteristics by a 
certain composition, as the above examples show, so 
there is no essential reason why one should not be 


formed in the same way from the spermatozoon. The 
fact that the latter is much smaller and differently 
shaped from the former is due to an adaptation which 
we shall deal with later. This distinction only appeared 
when it was no longer possible for the ovum or 
spermatozoon alone to develop into a new animal, and 
a conjunction of the two was needed. The blending of 
the two germ-cells, the spermatozoon and the ovum, is 
called amphimixis} 

It was the introduction of this into the organic world 
that deprived the two germ-cells of their independence ; 
from that time there could be no reproduction without 
union of the sperm-cells and ova. 

As a matter of fact, amphimixis provides the start in 
the formation of new individuals in the case of most 
animals. But this is only its subsidiary purport, and 
not the ground of its introduction, since the germ-cells 
can grow into new individuals without amphimixis, as 
we see in the daphnidae and phylloxerae. Its chief 
significance is that before a new individual is formed 
the characteristics of two animals must be blended. 
The qualities of the father are contributed by the 
spermatozoon : those of the mother by the ovum. 
Thus the new individual has a selection of paternal 
and maternal traits and of the ancestors on either side. 
The nose, for instance, may follow that of the father, 
or of the mother, or of any ancestor. How it is that 

1 Weismann has shown that amphimixis (a name he has himself 
invented) has originally nothing to do with propagation. It was he 
who first adduced the parthenogenetic animals in proof of this con- 
ception, and we shall generally follow him in our further observations 
on amphimixis. 



of the many noses that are in a sense contained in the 
fertilised ovum only one is developed and not several, 
and what forces cause one property to be derived from 
the father, another from the mother or an ancestor, are 
questions involving general theories of heredity with 
which we shall deal later. We will be content here to 
establish the fact that there is a mechanism in the 
fertilised ovum that builds up harmoniously the new 
individual from the many characteristics it contains, 
by always selecting one quality out of several equivalent 

The great value of amphimixis is, then, that it adds 
new and different paternal qualities to those that the 
new organism receives from the mother, so that it has 
a choice, and has a greater variety in its composition 
than it would have without amphimixis. It is true 
that even parthenogenetic offspring do not entirely 
resemble the mother, because each ovum contains 
variations, and many of the mother’s characteristics 
appear slightly changed in her progeny. Nevertheless, 
"such offspring will be more uniform in structure than 
:others that suddenly receive a series of characteristics of 
a totally different individual. 

For these the constant re-combination of characters 
in the offspring is of the greatest value ; it gives a wider 
field of operation to natural selection. It enormously 
increases the adaptive capacity of the animals, and the 
variations from which one animal would arise here, 
and another there, are united in one individual. It is 
lue to amphimixis, therefore, that co-adaptations do not 
need to be selected slowly and successively, but may 


appear simultaneously, as we saw in the instance of 
the heron, in which one animal is favoured on account 
of the length of its neck, another on account of the 
length of its bill, and their offspring may inherit both 
features. In this way amphimixis may easily bring 
about a difference between two similar structures. A 
hare, for instance, may inherit short fore legs from a 
short-legged mother and long hind legs from a long- 
legged father ; and as this combination is useful in view 
of its leaping, it may be further selected. Thus co- 
adaptations are facilitated and accelerated by amphimixis; 
the animals that are subject to it will be selected first, 
and so we can see why amphimixis would be retained 
in most animals, and why it is so wide-spread. 

But it is also useful to organisms in another respect. 
When an organ varies in any animal — let us say it becomes 
larger — it may, of course, become smaller in the next 
generation, but may just as well become larger. Many 
experts believe, in fact, that there are definite directions 
of variation ; that some internal or external principle 
often presses them in the direction they have once 
taken. We will discuss later on the possibility of this, 
but we can in any case imagine that variations, especially 
those that are only in two opposite directions, may take 
the same direction for some time. 

If any organ does vary in this way it may very often 
be injurious to its possessor and bring about its 
destruction. Excessive variations of this kind must 
often appear, as chance may frequently lead to the 
variation of an organ in a particular direction during 
several generations. Amphimixis prevents animals from 



being destroyed on the ground of these excessive 
variations ; it does not allow too great an advance of 
the variations, because it crosses these animals with 
others that have not the variation in question, or have 
one in the opposite direction, so that the normal 
standard is reached again in their offspring. Thus 
excessive variations tend to disappear in the general 
crossing, as amphimixis has an equalising effect. 

We have already seen that the indifferent characters 
of animals are preserved in the general crossing, because 
the plus and minus variations neutralise each other. 
Without amphimixis the variations would diverge in all 
possible directions, and each animal would separate 
further and further from the others. It would be 

impossible to comprise a definite group together as a 
species. Definite species are maintained entirely by 
amphimixis. As the law of heredity explains the 
resemblances of animals, so amphimixis explains that 
its action marks off definite specific types from each 
other in the world. 

A further result of this levelling tendency of am- 
phimixis is that isolated changes, even if they are 
useful, cannot modify the species, because they are lost 
in the general crossing. It is only when the majority 
of a species that live together vary that the character 
in question will be impressed on the whole species by 
natural selection; in other words, only plural variations 
are taken into account by natural selection. The 
majority have, of course, only to influence the survivors. 
If, say, a third of a species is extinguished every year, 
iit is sufficient if a little over a third of the species has 


the favourable variation, as the new character will then 
predominate in the surviving two-thirds and be continu- 
ously incorporated by amphimixis in the animals that 
do not possess it, but survive, because the destruction 
of the species is not great enough to involve them. 
Thus amphimixis conveys a favourable variation to 
animals that did not possess it. It qtiickly generalises 
useful varieties, and the modification of the species 
proceeds more rapidly than it could do without am- 
phimixis. But it is clearly of great importance for a 
useful variation to spread quickly to a large number of 
animals, because of the great dangers that the animals 
encounter from other sides against which the new 
variation affords no protection. It is also due to 
crossing that organs which have fallen into disuse 
slowly disappear in all individuals of the species. 

When we are asked if it is not expecting too much 
of chance to demand that a variation shall occur in the 
majority of the survivors, we can answer “ No.” There 
are many changes that must be in one of two opposite 
directions, and in these cases plural variations are quite 
natural. There are many other variations in which 
totally different characters may appear plurally, such as 
the three lengthened parts of the heron we spoke of 
previously and various shades in the protective colouring 
of butterflies’ wings, if they increase the deception in 
any way. In the case of many organs the only question 
is whether they are better or worse, and all variations 
that fall in the first category are preserved as plural 

In this way a gradual transformation of the species 



is brought about. Still, natural selection may, of course, 
act with such intensity as to give predominance to a 
small number of animals that possess a variation, and 
leave all their fellows to be destroyed. Thus in very 
severe cold a few deer with particularly thick coats may 
be preserved. 

It is due to amphimixis alone that the species remain 
within their limits for thousands of years. If the 
variations were not constantly neutralised, they would 
long ago have modified animals so much that they 
would no longer have the least resemblance to their 
ancestors. If it were not for amphimixis there would 
not be to-day any fishes resembling the fishes of earlier 

On the other hand, amphimixis allows no division 
of a species. How can a new species be developed 
from an older one, and this be preserved, if the 
promiscuous crossing is continually at work destroying 
or generalising all new characters? In that case, we 
can safely say, there would not be a number of different 
species if there were not a force that prevented the 
crossing of the members of the new species with those 
of the parental stock. We have alluded several times 
already to this force. It is isolation. We shall deal 
with it in the tenth chapter, and see why there are 
many different species, when we have learned why the 
species may be arranged in a system according to their 
greater or less resemblance, and why there are unifying 
types of species. But we have other questions to 
answer first. 



Genealogical tree of the animals. Descent of animals. Descent 
of man. Preservation of intermediate forms. The earth-worm. 
Regeneration. Leeches. Parasitism. Origin of parasites from 
free animals. Organic changes in parasites. How parasites are 
conveyed. Exchange of hosts. Life of the chief parasites, 
trichinae, maw-worms, dochmius, tape-worms, etc. Danger of 
taenia. Development of the liver - distoma. Friendships of 
animals. Symbioses. 

We have already passed in review three stems of the 
animal world : the vertebrates, articulates, and molluscs. 

We may regard these three groups as sisters, as they 
proceed side by side from a fourth or parental stem. 
This consists of the worms or vermalians. 

The worms are primitive forms whose origin goes 
back long before the geological records commence. 
It is their simple organisation that makes it possible 
tor stems to develop from them in three such different 

We have, then, so far considered the three chief 
branches of the tree of organic development, and we 
now come to the trunk in which the three branches 
unite. From this point we shall follow the stem down 
to the lowest point of its roots. That is as far as the 
eye and microscope can reach. The ultimate fibres of 



the roots are so fine that they lie entirely beyond our 
range of vision. 

The protozoa represent the point at which the root 
becomes thick enough to be seen by us. These are 
the simplest organisms known to us, and their origin 
goes back to an incalculably distant period. From them 
were developed the ccelenterata, which we will consider 
at the close of this chapter. After these come the platodes 
— animals that approach closely to the coelenterates in 
structure ; in both, for instance, there is only one aperture 
in the body, and this has to act both as mouth and anus. 

From the platodes (or “flat worms”) descended the 
round worms, which have mouth and anus, and an 
alimentary canal suspended in a spacious body-cavity. 
However, their organisation is still very simple. Their 
type of structure is retained fundamentally in all the 
higher animals, as they are the ancestors of the verte- 
brates on the one side, and the molluscs and articulates 
on the other. We may mention as a fourth daughter- 
stem the echinoderms, the star-fish and sea-urchins, of 
which there are many species in the sea. 

It was a fortunate chance for science that the 
transitional forms from the vermalians to each of the 
four stems are still in existence. Where they are 
missing, the gap is filled by larvae forms. Thus the 
larva of certain molluscs and of the echinoderms 
resembles a certain order of worms, the microscopic 
rotifers that are found in all water. The lowest forms 
of the vertebrates lead on to a group of animals called 
the tunicates, which have a good deal of affinity to the 
worms in their structure. 


The round worms do not represent the highest class 
of the vermalians. There is a much more advanced 
section, the annelides. To this group belongs the earth- 
worm ; it has a very elaborate structure, but its marine 
relatives are much more highly organised. They are 
predatory animals with sharp eyes, and swim briskly in 
the water in search of their prey. 

From the annelids have come the articulates : the 
crustaceans on one side, and the tracheates on the 
other. Of the former no transitional form has been 
preserved, but this is not so with the latter ; in fact, 
this particular animal, the peripatus , is the most typical 
instance of a transitional form that we know. Half- 
annelid and half-myriapod, it seems to have one organ 
of the worm-type and another of the tracheate. The 
peripatus is found in various species, but only a very 
few ; and this is true of all transitional forms. It is 
clear that animals of this kind, which have neither the 
adaptations of their ancestors nor their descendants in 
complete form, are easily crushed out by the two, and 
can only be preserved in sheltered localities. When 
we recollect, in addition, the eternal changing and re- 
adapting in nature, we are surprised that any typical 
transitional form has chanced to survive to our time ; 
but we must not ask the theory of descent to justify 
itself by producing actual instances of transitional forms. 

When we say that the vertebrates have been 
developed from the vermalians, it must not be sup- 
posed that any living animals, such as the maw-worms, 
were their ancestors. We cannot assume that these 
ancestors had relatives whose descendants are still 



preserved quite unaltered. The maw - worms, for 
instance, have many adaptations that they have 
acquired since that time in the course of the earth’s 
development, and we do not know if they had not at 
that time adaptations that they have since lost. Thus 
we cannot form any absolutely safe picture of the 
primitive worms that became, in certain circumstances, 
the ancestors of the vertebrates. We can only say that 
they had the worm-type ; that their principal organs 
had, in general, a structure and arrangement more 
closely resembling that of the worms than any other 
living animals. 

Thus the statement that “ man descends from fishes ” 
does not mean that we have ancestors who resembled 
any of the actual fishes, but that at a certain period they 
were gill-breathing, aquatic animals with a structure to 
which the nearest approach is found among the fishes of 
all actual animals. So, again, man does not descend 
from the apes, as is often said, but from beings that 
must probably have resembled the actual apes more than 
man. The apes have not been fixed in their organisation ; 
they have diverged steadily from their ancestors by 
constantly acquiring new adaptations. Their ancestors 
were probably brothers of man’s ancestors, but that does 
not justify the above statement. On the strength of 
this probability we may, at the most, say that man and 
the ape have a common ancestor . 1 

There are scientists who do not admit that man had ape-like 
ancestors. They believe that the apes are no more clearly related to 
man than the ruminants or carnivores, or, especially, the kangaroos. 
1 his view, however, has few supporters, and its arguments are not at 
all convincing. 



The most familiar representative of the present stem 
is the earth-worm. It is true that most people’s 
acquaintance with this animal is superficial, as its 
subterraneous habits prevent more than a few from 
knowing it thoroughly. For a long time, in fact, the 
animal, which is not merely harmless but extremely 
useful, was decried as injurious, and there are still 
people who kill it whenever they find it. 

Darwin was the first to show that the earth-worms 
are indispensable to the plants. He pointed out that 
they act as ploughs in loosening the earth. The 
animal feeds on the digestible elements in the soil. It 
eats its way through them, as it were, passing them the 
whole length of its alimentary canal, and then ejecting 
them, which is always done on the surface. Thus the 
finer constituents of the soil are constantly brought to 
the top by the worms, and we have always good soil 
there. The many passages that the worm leaves 
behind it in its travels loosen the ground more and more, 
and as they fall in, the elements of the soil rub together 
and grind one another. Finally, leaves and other 
bodies are drawn by the animals into their tubes, ground 
up, and brought to the surface again. However strange 
it may sound, we have to admit that the whole mass of 
the fruitful surface of the earth has passed through 
the alimentary canal of earth-worms, and passes through 
the same process every few years. 

Man’s attempts to trap the worm have, fortunately 
for it, hardly any success. But the defenceless animal 
has a good deal to suffer from other enemies. Besides 



moles, shrew-mice, birds, lizards, amphibians, insects, 
and many others, it is the myriapods, especially, that 
pursue it into its own tubes. We often see the worm 
creep in terror from its passages in full daylight to 
escape these dreaded enemies. 

The danger of being captured is less fatal to the 
earth-worms than to other animals, as they have a 
great power of regeneration, and can lose a part of their 
body without perishing, because they can replace it. 
One can cut a worm into two parts, and one part — 
often the second one as well — will always regenerate the 
lost piece. If it is cut into several pieces, there is never 
more than one new animal, and often none at all ; and if 
it is cut longitudinally into two halves both of them 
very soon die. 

Here again we see that the power of regeneration 
is an adaptive phenomenon, and does not act in rare 
situations. What generally happens is that a piece is 
torn off an earth-worm, and the rest of it retreats 
underground. This mutilation would soon extinguish 
the animals if it were fatal to them ; and the other 
injuries happen too rarely for natural selection to have 
provided a remedy against them. 

In the near relatives of the earth-worm, that live in 
water, such as the lumbriculus , the regenerative power 
is much higher. One of these animals has been cut 
into fourteen pieces, and thirteen of these formed new 
worms. These animals are devoured on all sides, and 
their enemies, the water-insects, have sharp jaws with 
which they cut pieces out of them. There are various 
species of aquatic worms, and in each of them it can be 



shown that the regenerative force is proportionate to the 
kind of mutilation to which they are most frequently 

Thus the leeches, which are dreaded and not much 
exposed to mutilation, have no power of regeneration. 
The medicinal leech is still very common in France and 
Hungary, and is a great trouble to bathers, as it gathers 
in swarms at the first splash. Much less troublesome 
are the large leeches that are found in the ponds, and 
known as horse-leeches ; these may be taken in the 
hand without fear. Their teeth cannot bite through the 
human skin ; they can only pierce the mucous lining of 
the nose, the mouth, and other parts. One species of 
the horse-leech, the Atilastomum gulo , feeds on snails, 
and does not generally indulge in blood-sucking : the 
other species, the Hceniopis vorax , may become a great 
nuisance by getting into the throats of horses and cattle 
when they bathe, and attaching themselves to the soft 
parts. But this hcemopis plague is only found in North 

There is also in our ponds a worm about as thick as 
a violin-string, and sometimes a foot in length. It looks 
like a horse-hair, and, as a matter of fact, the rustics 
have in many places fastened on to it the legend that it 
is a living horse-hair, travelling about in the water and 
able to penetrate the human skin. In reality the animal 
is quite harmless, and is, in fact, unable to maintain 
itself ; it lives only a short time, and uses this for laying 
its eggs. From these develop tiny larvae with a pointed, 
zigzag boring apparatus, which pass through the skin 
of May-flies and gnat-larvae, live in them for some time, 



and surround themselves with a capsule. If the larva 
is eaten by a larger insect, the capsule bursts in its 
stomach, the worm becomes free, and develops to the 
adult stage in its new host ; it abandons this home in 
wet weather, and returns to the water to lay its eggs. 

The life-story of this Gordius aquaticus brings us to 
one of the most interesting phenomena of the animal 
world, parasitism. There are many parasites among its 
relatives, the nematodes, which form the lower class of 
the round worms ; but there are still more amongst the 
platodes. Generally speaking, the vermalian stem is 
the richest in parasites in the whole animal world, the 
articulates alone approaching them in this respect. In 
comparison with the parasites of these two stems, the 
rest are insignificant ; the protozoa alone of other groups 
provide a large number, including the notorious malaria 
parasites. In the plant world again we have the bacteria 
and other fungi. 

Rudolf Leuckart, the chief authority on the subject, 
defines parasites as creatures that find food and shelter 
in a living organism. According to this definition there 
are, of course, parasites amongst the plants, some with 
other plants, some with animals, as hosts. In our view 
of the origin of living things all parasites must have 
descended from free-living organisms. 

This statement can easily be proved in the case of 
animal parasites. We have already seen something of 
parasitic crustaceans. We saw that they pass their 
youthful stages as free organisms, and can hardly be 
distinguished from those of other crustaceans. We may 
now add that we find a large number of transitional 


forms amongst the parasitic crustaceans, some of which 
are entirely like the free animals, and differ from them, 
perhaps, only in having longer claws, with which they 
attach themselves for a time to other animals and derive 
their food from them. But the longer the animals live 
on their hosts the more profoundly are they modified ; 
the legs, which are no longer necessary, degenerate 
more and more, the sense organs disappear, even the 
alimentary canal may atrophy, and the animals feed, as 
the sacculina does, in plant fashion, by means of roots 
passing into their host. The structure is also entirely 
changed by the enormous development of the sexual 
organs, which are of great importance in every parasite. 

Of the tracheates there are lice and fleas, which 
ordinary folk call insects. Here again there are animals 
that have been most curiously modified. We have an 
instance in the Pentastomum tamioides. This animal, 
which looks very much like a tape-worm, as its name 
suggests, and has very little of the characteristics of a 
spider, to which it really belongs, lives — though rarely — 
in the nasal cavities of the dog. The eggs pass through 
the nostrils to the ground, and when a hare or rabbit 
takes them into its stomach with the grass, larvae issue 
from them, pass through the stomach into the liver of 
the ruminants, and cover themselves with a membrane, 
inside which they cast their skin several times in the 
manner of the articulates. When they have grown 
bigger, they break the capsules, and disperse through 
the various passages of the liver. They then bury 
themselves in capsules once more, and if their host is 
devoured by a dog or a fox they develop into sexually 


mature animals inside it. They are often so numerous 
in the hare as to cause its death. They are less 
dangerous to man, who also may be infected with them, 
the eggs being received on the hand from the dog’s 
sniffing and being passed to the mouth. 

This pentastomum is a thorough parasite, and changes 
its host ; this, as we shall see presently, is characteristic 
of the majority of intestinal worms, which are, so to say, 
the most complete parasites. We can, however, find 
transitional forms even amongst these, leading gradually 
to them from their free-living relatives. Amongst the 
nematodes many species are still perfectly free ; among 
the platodes the tape-worms descend from the suctorial 
worms, and these are closely related to the turbellarians, 
small, flat, dark or light worms that we find in every 

Parasites are, therefore, animals that have adapted 
themselves to living on other animals. This kind of 
life is clearly a very safe one. Living in the warm 
interior of the host, the parasite is almost entirely 
sheltered from climatic troubles, and has nothing to 
fear from direct enemies. Finally, it riots in an abund- 
ance of food, and this is often brought to him already 
digested. This is the case with the parasites of the 
alimentary system, which are surrounded with a 
constant stream of nourishment, and have often even 
lost their own alimentary canal, as the food can pass 
directly through the wall of their body, without having 
to undergo further changes within the body of the 

Thus we find no alimentary system either in the 


tape-worm or the echinorkyncus / and in the nematodes 
it is at least very much simplified, and is devoid of the 
subsidiary glands such as the liver and other appendages. 

The locomotive organs of the parasites are equally 
degenerate, and are replaced by clinging apparatus. 
There is bound to be such an apparatus in external 
parasites, otherwise the unwelcome guest could easily 
be rubbed off when they are not concealed from their 
host by a thick coat of hair. And clinging organs 
are necessary in intestinal parasites, as they could 
not stand against the pressure of the fluid food 
if they were not attached, and would be forced out at 
the anus. It is only the maw-worms and other thread- 
like worms that can maintain themselves in the £ut 
owing to their shape alone. As they are long, at the 
end thin, and round, the chyle runs past without bearing 
them along with it. 

Being cut off from the outer world, the parasite has 
no need of sense-organs, and is usually without them. 
Its respiratory organs are less altered, and hence it is 
that the gill-breathing Crustacea only attach themselves 
to aquatic animals, and the air-breathing tracheates 
only, as a rule, to land-animals. The ancestors of the 
intestinal worms breathed through the skin, and this 
has been preserved in their descendants, who can do 
so because they are constantly bathed in the fluids 
of their host that contain oxygen. It is due to this way 
of breathing that they are found both on land and 

1 These are round worms, often of a considerable size ; their snout is 
equipped with spines with which they fasten themselves to the wall 
of the gut. They are generally found in fishes and aquatic birds, 
more rarely in mammals, and very rarely in man. 



water-animals, and are therefore the most widespread 
of all parasites. In many of the tracheates parasitism 
has gone so far that their respiratory organs have been 
affected. Thus the pentastomum we referred to above 
has lost its tracheae, and breathes through the skin, 
like the worms. 

We have now seen that the nature of parasitism 
entails a simplification of many organs, but other organs 
are all the more elaborately developed in parasites. 
These are the sexzial organs. In the first place, it 
is very easy for the parasite to supply them with plenty 
of food. It is devoid of so many organs that require 
their proportion of the food in other animals. Hence 
we find, as a matter of fact, the sexual organs of 
parasites swell in proportion to the thoroughness of 
their parasitism. When we study the anatomy of a 
distomum we have some difficulty in finding the other 
organs on account of the pronounced sex organs. In 
the tape-worm the other organs occupy an evanescent 
space in comparison with the testicles, the ovary, and 
their glandular appendages. 

It is not merely possible, but necessary, for the 
parasites to have this preponderant development of the 
sexual organs. It is just as difficult for the parasite to 
maintain its species as it is easy to support itself. 
When the host, especially of internal or fixed para- 
sites, perishes, the parasites must die also, as a rule. 
Hence its ova must always be conveyed to new animals. 
In the case of the sacculina this is comparatively simple, 
as we saw in the last chapter. From the egg is 
developed an active larva, which seeks a new host. But 


how can this be done on land, and in the vertebrates 
that shelter most of the parasites? In some cases, such 
as the gourd-worm ( distomum ) and the broad tape-worm, 
an active larva develops from the egg, falls into the 
water and enters a mollusc or a fish. But in this the 
animal has not reached its definitive host, the sheep or 
man. The larva has to be conveyed from the interior 
of the aquatic animal to the stomach of the mammal, 
and this is done by the former being eaten, consciously 
or unconsciously, together with the larvae by the eater. 

This passive transition, which we shall study more in 
detail afterwards, is the only possible means of surviving 
for most parasites. In only a few cases is an active 
larva developed from the egg ; as a rule the eggs must 
be licked up and taken into the mouth of a host, and 
even then the end of the parasite’s development is not 
reached. The host must be eaten, and the larva; pass 
in its flesh into the interior of their principal host, where 
they come to sexual maturity. Thus chance plays a 
great part in the maintenance of parasitic species, and 
in view of the slender prospect that the individual egg 
has of ever being developed, we can understand why 
they are laid in such vast numbers, sometimes up to 

The eggs, which lie on the earth after leaving the 
host and usually have to wait a long time before they 
reach the stomach of an animal, need a high power of 
resistance. As a rule they have a shell and plenty 
of yolk ; this in turn requires organs in the mother’s 
body that are capable of meeting these demands. 
Hence there are yolk-bodies and shell-glands, as well as 


large ovaries, which greatly complicate the sexual 

In fact, we very often find both sexes united in one 
parasite, and we then call the animal an hermaphrodite. 
This is not difficult to understand. The parasite is 
often alone in its host, as is generally the case with 
the tape-worm ; and it has then to develop both 
spermatozoa and ova, or remain barren. Sometimes, 
it is true, there may be two or more tape- worms in one 
host, and this is more frequent in the case of other 
parasites. Then mutual fertilisation is possible. 
Hermaphrodism has been introduced amongst the 
parasites to prevent the animals that live in isolation 
from perishing without doing something towards the 
maintenance of the species. 

We have now examined the organisation and habits 
of parasites from our point of view, but there is one 
point we have not yet considered — the change of hosts. 
This plays a very important part in parasites, and we 
have already referred to several that pass their early 
stage in one animal and come to sexual maturity in 
another. An attempt has been made to explain this 
remarkable phenomenon by regarding the first host 
as the original one, in which the parasite became 
sexually mature in former ages. After the rise of the 
vertebrates it adapted itself to these, so that the 
parasites taken with the flesh of the first host into the 
alimentary canal of the second did not die, but only 
reached sexual maturity there, as the conditions are 
the best conceivable for parasites in the vertebrate. A 
good deal can be said in support of this view, especially 


the fact that the stages of the parasites in the first hosts 
have some resemblance to their primitive forms, from 
which we may infer that these stages were at first 
sexually mature animals. 

However, we will not linger over these theories, 
but pass on to study the life-story of some of the 
chief parasites. In this we shall see what a wonderful 
adaptiveness there is in these creatures. 

One of the worst human parasites is the trichina. 
The man who is visited by this dire guest has often to 
pay for it with his life. It is chiefly on its account that 
the examination of meat has been introduced, and 
this and the now prevalent custom of killing in 
abattoirs have greatly diminished the danger from 

The trichina is found in a large number of animals, 
but only one of these, the pig, calls for our notice. It 
often lives in great quantities in the flesh of pigs, in the 
shape of a small white point ; this is a capsule, and the 
tiny worm is rolled up spirally inside it. If the pig’s 
flesh containing the capsules enters a man’s stomach, 
the capsules burst and the little worms issue forth ; they 
travel into the small intestine and there reach sexual 
maturity within a few days. The females give birth 
to an enormous number of young, and then die. The 
young pass through the wall of the intestine, which they 
can easily do on account of their small size and pointed 
shape, and travel gradually by the blood-vessels into the 
man’s muscles. There they feed for a time on the 
decaying muscular matter, until this in turn secretes a 
membrane to protect itself against the parasites. This 



membrane is strengthened by the worms themselves, 
and coloured white by deposits of lime. The animals 
have now entered on a condition of repose, and will 
only re-awaken into life when the muscles they reside 
in reach the stomach of a new animal. When this 
capsule stage is reached — about three months from the 
first infection — the danger is over. But many people 
die before this through the irritation of the intestines, 
and especially through the inflammation of the muscles 

When the trichinae enter human beings their career 
is virtually over, because no one can be infected by 
eating human flesh. It is otherwise with the animals. 
Rats are the chief victims of these parasites, as in their 
case the cycle of migrating and capsulating begins 
afresh, the dead or diseased rats being eaten by their 
fellows. This would not affect human beings if the rats 
did not make their way into pig-styes, where they are 
'■eaten by the pigs when they die, or even when alive. 
Thus the worms capsulated in the rat’s flesh pass into 
the stomach and the muscles of the pig, and may come 
to infect human beings. 

Among the nematode worms there is a large number 
•of parasites. Most of those in Europe that can infest 
human beings are of a harmless character. The human 
maw-worm, the female of which measures up to ten 
inches, and the much smaller oxyuris (two-fifths of an 
dnch), are common in children. These two species have 
mo temporary host; their eggs, and often the whole 
;animal, are passed by human beings, and if they find 
itheir way into the human intestines once more, they 


develop at once . 1 This can easily happen in bed, and 
also in other ways. One of the chief transporters of 
them is the fly, which settles on excrements as well as 
on food. 

But though these worms are often present in great 
quantities, they are generally only a nuisance and very 
rarely dangerous. The latter applies more frequently 
to a relative of theirs, the Dochmius duodenalis. This 
worm, somewhat larger than the oxyuris, has strong 
jaws with which it attaches itself to the wall of the 
intestine ; it pierces this with the stiletto it has in its 
mouth and causes frequent hemorrhage, sometimes 
causing death and always anaemia. The ova of the 
parasite are ejected by the anus, and develop in mud 
or moist earth into tiny larvae, which give fresh dochmii 
when they re-enter the human intestines. Hence the 
disease occurs particularly in people who are compelled 
to drink muddy water, like the Egyptians, or any who 
work much in moist soil, such as brick-makers. It is on 
this account that the workmen in the St. Gothard tunnel 
had to suffer so much from dochmii. It was through 
the tunnel that the worm was introduced into Germany. 

In these instances we have followed a simple develop- 
ment of parasites, but we now turn to animals with a 
much more complicated life - story. These are the 

1 In the case of the oxyuris the eggs develop very quickly, so that 
self-infection is always occurring, but the egg of the maw-worm needs 
months before it will develop into a new animal if re-introduced into 
the human body. In this case, therefore, the infection is not so direct 
as in the oxyuris ; it usually comes aboutfthrough drinking meadow- 
water, or putting grass in the mouth, which may also bring one the 
much more mischievous echinococcus that we will describe presently. 



platodes (“ flat- worms ”). We will begin with the most 
familiar order, the tape-worms. 

There are two tape-worms especially that are parasites 
on the human intestines, the Tania solium and the 
Tania, saginata. Both consist of a series of connected 
segments, very narrow at the head and broadening 
towards the end. At the end, also, the sections are 
sexually mature, and contain a vast number of fertilised 
eggs ; these are detached from time to time, and pass 
out with the excrement. The sections of Tania solium 
are comparatively inert after ejection, but those of 
Tania saginata can crawl about ; they often make their 
own way out of the anus, and have been seen to climb 
up the wall of a room. 

The two also differ in the armament of the head. In 
Tania solium there are four suctorial disks which cling 
to the wall of the intestine, and are assisted in this by 
a fringe of hooks. The latter are not found in Tania 
saginata , yet it is more difficult to get rid of, as its 
suctorial disks are larger and more powerful. Often 
a slight remedy will bring away the greater part of the 
body, but that is no use to the patient, as the head is 
able to form new parts. 

If the sections of Tania solium that contain the eggs 
lie on the fields amongst human excrements and are 
eaten by pigs, which do not disdain such food, the shells 
of the eggs burst in the pig’s stomach. A tiny creature 
emerges, bores its way through the wall of the intestines, 
and gradually reaches the muscles. Here it assumes 
an oval shape, and forms a membrane round itself, 
which is further strengthened by a secretion from the 


pig’s muscles. Fluid passes into the capsule from the 
surrounding tissue, so that it may swell to the size of 
a pea. The animal itself remains at the globule-stage, 
and grows very little inside it. It forms the head of a 
future tape-worm, and remains at this stage in the 
muscles of the pig. At this period it is known as 
a scolex or measle-worm. 

If the infected flesh of the pig is eaten by a human 
being, the measle-worms are set free, and the small tape- 
worm head makes its way into the intestine, and attaches 
itself to the wall. The vesicle hangs on to it for some 
time, but is at last cast off, and the head begins to form 
the segments until the animal has reached its full size 
of more than three yards. 

The development of the 7^-8^- yards long Tania 
saginata is similar to this. But in this case the eggs 
must be taken into the stomach of a cow, if they are 
to become scolices ; the pig digests them. Hence it 
is that in this case the parts of the worm have 
developed the power of motion, as the cow does not 
eat faeces like the pig ; but it can very well happen 
for the cow to swallow a part of a taenia clinging to 
a blade of grass, or grass covered with its eggs. But 
there is a second difference of more importance to 
human beings. While the eggs of Tama saginata 
may safely be eaten by human beings, as they cannot 
develop in their alimentary canal, it is otherwise with 
Tania solium. In the latter case infection is possible, 
as the eggs produce larvae in the human intestines as 
well, and these pass into the muscles, and enclose 
themselves in capsules as large as peas. If they 


28 l 

reach the eye — which has often happened — they 
cause blindness, and it is still worse if they reach the 
brain. Hence a man who is infected with Tania 
solium is in a condition of great danger to himself 
and those about him, as new infection is very possible. 
It also happens that in vomiting the sections pass 
from the intestine into the stomach, and the larvae 
are set free there. This is a moment of great 
danger to the patient, as it is always the larva- 
stage that may cause death ; the adult tape- worm 
is not dangerous. A man with Tania solium 
should, therefore, get rid of it as soon as 


Still worse are the scolices of the Tania echinococcus. 
This tape-worm is only one-fifth of an inch in length, 
and is found in large numbers in the intestines of 
the dog. The detached parts are very active ; they 
climb up stalks of grass, and are likely to be eaten 
by hares, as well as by cattle, sheep, or pigs. The 
larvae that develop pass into the muscles, but before 
the formation of the head begins, they grow so large 
and soak up so much fluid that they cause blisters as 
big as a child’s head, which are generally fatal to the 
victim. The head of the echinococcus does not begin 
to form until after this swelling. Man may eat these 
larvae with impunity, as they do not develop into tape- 
worms in his intestines ; they do so, however, in the 
dog. But if the eggs of the echinococcus get into the 
human mouth and stomach — and the dog will often 
give them an opportunity to do this, as it licks its 
anus as often as it does the hands (or even the 


mouth) of its master 1 — the large vesicle is formed in 
the muscles, generally in the liver, but sometimes in 
the brain. Death follows in most cases. 

Thus the Tania echinococcus and the Tania solium 
are found in man in the shape of scolices, and these 
particular tape-worms are accordingly to be dreaded. 
Another parasite of the human intestine is the broad 
tape-worm, the Bothriocephalus latus , which grows to 
a length of thirteen yards. We have referred pre- 
viously to its migration. Differently from the tania , 
it develops from the egg a larva that enters a fish, 
if it reaches water, and incapsulates itself, without 
forming a vesicle. It at once forms the head of the 
future tape-worm, which develops in a new host that 
has eaten the fish. Human beings get the worm by 
eating underdone pike or turbot. 

This kind of migration brings us to the other 
parasitic platodes, the suctorial worms. They are 
rarely found in man, and are never dangerous — in 
Europe, at all events . 2 But they are a great plague 
to other animals, such as sheep, birds, and frogs. 
The fluke or gourd-worm, shaped like the kernel of 
a gourd, the Distomum hepaticum , is found in the 
sheep’s liver, or rather in its gall-duct. Its eggs pass 
by the gall-duct into the gut, and then out with the 
excrements. If they fall into water, minute, lancet- 

1 People should, therefore, be careful with dogs. They should at 
least wash their hands after touching them, and should never let dogs 
kiss them. 

2 In Egypt the Bilharzia hcematobia is one of the most dangerous 
parasites. It lives in the human blood-vessels, especially the portal 
and urinary veins. 



shaped creatures develop from them ; these swim 
about, and bore into a water-snail, in the interior of 
which they grow into tube -like bodies. Inside the 
tubes are a quantity of small, tadpole-shaped creatures. 
These abandon the tube and the host, and seek a 
new victim, inside which they incapsulate themselves ; 
though they may do this, without migrating, on 
aquatic plants. If the sheep eat these plants, the 
distoma develop from the capsules in their intestines, 
and pass on to the liver. The other species, which 
have incapsulated in a second host, reach sexual 
maturity when the new host is eaten. 

The adaptations of the distoma are enormously 
varied, and may be very complicated. Especially 
interesting is the Distomum macrostomum , which is 
found in birds. When the eggs of this animal reach 
the plants that grow on the edge of brooks and ponds, 
they are swallowed by the snails, which gnaw the 
plants. In these they develop into curious tubes that 
surround the intestines of the snail, and also run out 
into its feelers, which they distend and distort into thick 
tubes. Inside the tubes, especially those in the antennae, 
the young distoma are developed, and the tubes contain- 
ing them now become coloured with green and white 
bands, and move about. The movement increases, the 
snails antennae burst, and the tubes fall to the ground, 
where they creep about and look very much like insect- 
larvae, or caterpillars. The birds really take them to be 
edible animals of that kind, swallow them, and so take 
the brood of distoma into their bodies, where they reach 
sexual maturity. Here we have a most peculiar case of 


adaptive colouring - . Most animals need their colouring 
as a protection against their enemies, but in this case we 
have organisms that are coloured for the purpose of 
getting eaten. However, the life-story of the animals 
enables us to understand this remarkable adaptation. 

We will not explore any further the interesting field 
of parasitism. We have examined the various forms of 
parasites and their habits so closely, because they make 
it so clear that there are no insuperable limits fixed to 
the variations of animals. As a matter of fact, we dare 
not say that natural selection could not give wings to a 
horse. If there were some necessity and sufficient time 
for such a transformation of the horse, the required 
variations would certainly not fail. The creation of a 
pegasus is not more wonderful than the transformation 
of a spider into a tapeworm-like animal. Natural selec- 
tion is omnipotent in the creation of forms of life. It 
is restricted by no limit that lies in the nature of things. 

• •••••• 

There is a certain resemblance to parasitism in a 
phenomenon that leads us on to the ccelenterata. This 
is symbiosis , or community of life. 

When we put water and plants from a pond into an 
aquarium, we often notice on the glass, some time after- 
wards, a green tube, as thin as a needle, with long 
threads hanging from the end of it. If a water-flea 
touches one of these threads, it remains sticking to it, 
and is conveyed into the tube, where it disappears. 

This small, tubular creature is the green water- 
polyp, one of the few fresh-water representatives of 
the coelenterata, which are found in many brightly 



coloured species in the sea — medusae, anemones, 
sponges, etc. — and are one of its chief ornaments. 
One other relative of the green polyp, the brown 
polyp, is often found in our waters, and also the 
fresh-water sponge, which is often found on pieces of 
wood and branches at the bottom of ponds. 

Let us return to the animal we mentioned first, the 
hydra, or green polyp. When we examine it with the 
microscope, we find that its colour is due to very small 
granules that pervade the animal. These granules are 
independent organisms, algae, that live in the polyp, 
without suffering any injury, or doing any to the hydra. 
The joint living is beneficial to both organisms. The 
algai have a pretty well-assured maintenance in the 
ccelenterate, while this in turn benefits by the oxygen 
they secrete. Here we have a case of symbiosis — a 
joint life of two organisms, based on mutual advantage. 

There are a large number of these symbioses. Certain 
marine Crustacea, that live in snail-shells, always carry 
on them anemones, ccelenterates that secrete a stinging 
substance when they are touched that paralyse many 
organisms. The sea - anemones have this advantage 
from the transportation that it enables them to obtain 
food more easily than they would do otherwise, since 
they have no power of locomotion. On the other hand, 
the crustaceans are protected by the anemones from 
their enemies, because if one attempts to drag them 
from their shell, the coelenterate plies its batteries and 
the assailant has to withdraw. There is another 
instance of symbiosis in the relation of ants and lice. 
We generally find ants running about on plants with 


certain species of lice on them, and it is easy to see 
that the lice have the advantage of being protected from 
many enemies by the presence of these stalwart com- 
panions. On the other hand, the ants are fond of the 
faeces of the lice, which are as sweet as honey . 1 

Symbioses between plants and animals, or between 
plants and fungi, are much more common than between 
two species of animals. That is easily explained. 
Animals are rivals in the struggle for life, but plants 
have a different kind of food and respiration ; in fact, 
the latter difference makes the proximity of plants 
healthy, and often indispensable, for animals. The 
fungi are in the same position as the animals. 

Hence besides the hydra, certain protozoa are 
inhabited by green algae ; and the best known instance 
of a symbiosis between fungi and algae is found in the 
lichens, which are not single organisms, as one would 
infer from their appearance. 

1 There are also symbioses between higher plants and animals. Thus 
in South America the trees are threatened by the leaf-cutter ants. 
They cut off the leaves with their shear - like jaws, and gather them 
into heaps, on which they grow fungi. Certain plants, the imbauba, or 
chara, are protected from these enemies by harbouring fighting ants of 
a different species, which drive off the leaf-cutters when they come. 
But in order to induce the tree-ants to remain outside the tree, so as 
to perceive the approach of the enemy — which would often be impossible 
if they were always inside — the tree has developed special nutritious 
pods at the threatened points — the stalks of young leaves — which the 
ants constantly gather for their young inside, and so they are always 
found at these spots. 

This case, again, cannot be explained on the Lamarckian principle. 
The nutritious pods that are formed by the plant for the ants, and that 
are wanting on trees related to the imbaubas which have no ant-guests, 
cannot have been produced either by the will of the plant or the 
repeated bites of the insects. Hence the explanation of symbiosis as 
an inherited habit does not hold in this instance. 



Symbiosis exhibits an entirely new side of natural 
selection to us. In this case the principle that seems to 
be the foundation of all life, the struggle of all against 
all and the crushing of one organism by another, is 
thrust aside. Symbiosis teaches us the omnipotence of 
natural selection more clearly than any other phenomenon 
in nature. 



The animal built up of cells. Principle of division of labour. The 
greater the division of labour, the higher the animal’s organisation. 
Multicellular and unicellular animals. The protozoa, their form 
and reproduction. Structure of an animal in its development 
from the ovum onwards from rudimentary parts. Origin of the 
germ-cells. Outlines of a theory of heredity. Amphimixis of 
the protozoa. Origin of sexual reproduction. Formation of seed 
and ova. Continuity of the germ-cells. Are any animals 
immortal? Death is not common to all animals. Origin of 
death. Permanent and temporary life. Has life come from the 
stars? Origin of life on the earth, spontaneous generation. How 
it is to be conceived. The first development of living matter. 
Formation and significance of the cell-nucleus. Significance of 
the fundamental parts. Relation of the rudimentary parts in 
amphimixis. When life is extinguished. 

To a certain extent we may compare organisms to 
edifices in our towns. Just as our buildings differ 
enormously in size and structure, yet are generally 
composed of the same elements, the bricks, so we find 
the same elementary units in all vegetal and animal 
bodies. In the course of its embryonic development 
every organism is built up like a house. Its life 
begins with one structural element. To this numbers 
of fresh ones are added until at last the highest point 
is reached ; the living thing has attained its full size, 
and it would be idle to attempt to count its constituent 




The fundamental elements of organisms are called 
cells . 1 With a few exceptions the cells are too small 
to be seen with the naked eye ; they can be seen with 
the microscope as corpuscles of various shapes. But all 
of them contain a frothy, fluid substance, protoplasm. 
Inside this is a tiny vesicle, the nucleus. This in turn 
has the same texture as the protoplasm of the sur- 
rounding cell-body. Only the nucleus is enclosed by 
a delicate membrane, while there is no membrane 
enclosing the entire cell, at least not in most animal 
specimens. Plant -cells have always a membrane, 
sometimes a comparatively thick one. 

Thus the principal characteristic of a cell is its 
nucleus. But this is not the whole of its contents ; it 
has other invariable elements besides the nucleus. The 
nucleus itself is not a simple structure, but always 
contains certain compact particles which are comprised 
together under the name of “chromatin.” It is believed 
that these contain the matter that is the vehicle of 
heredity. On this view they are the most important 
parts of the cell. 

Thus the protoplasm of which the cell consists 
contains a number of deposits, and this shows that 
it is not a formless mass. It is especially the frothy 
character of the protoplasm that gives it a definite 
structure . 2 We know from the seventh chapter that 

1 The cell was discovered in 1667 by Robert Hooke, who examined 
a cork, and found that it was composed of cells like a honey-comb. 
The term “cell” is still retained, though we now know that the cell is 
a solid particle, and often has no membrane at all, so that it has no 
resemblance to the honey-comb cell. 

2 1 he theory of the frothy structure of protoplasm was advanced by 
O. Butschli, and has generally displaced other theories. 


the chemical constituents of the organic substance are 
living albuminoids, the biogens. Now, we know that 
this substance has a definite form, protoplasm. 

Although the cells may differ widely in form and size, 
the organs of animals would not be so varied as they are 
if the cells could not give out different kinds of products. 
Our skin and viscera consist directly of cells, but they 
only form the basis of the muscles and bones. 

But, it will be asked, how can the cells create 
anything new ? 

These elementary units of the organic body feed and 
grow naturally in virtue of the nourishment circulating 
in the body. However, they do not need the food 
solely for their own growth and the maintenance of the 
vital activity ; from one portion of it they form special 
substances which they eject at their surface. Thus the 
skeleton of the articulates was formed as a secretion of 
the cell-layer of the underlying skin, and our bones and 
muscles, also, are the secretory products of large numbers 
of cells. These products have a function ; they serve 
for support or movement, like the bones and muscles, or 
for the conducting of stimuli, like the neural substance. 
On the other hand, the cells that have produced these 
substances renew and nourish them. 

The great advantage of this kind of organ-construction 
is in the division of labour , a principle that is also found 
in civilised life, and forms its foundation. It is at work 
not only in the body politic, but in every warehouse and 
factory. This alone makes it possible, for instance, to 
build a good house ; this can only be done if one part 
of the workers looks after the building, another the 



wood-work, a third the locks, another the painting’, and 
so on. Then each section knows its own business, and 
can pursue it with effect. 

The whole organisation of the higher animals rests 
on the principle of the division of labour. If each cell 
had to discharge all the vital functions, they would 
restrict each other. The secretory product only dis- 
charges one function, and so is not distracted by other 
duties in doing so. 

The lower we descend in the animal scale, the less 
division of labour do we find. Thus, in the animals 
with which we concluded the preceding chapter, the 
polyps, we find only two kinds of cells — as a rule, at 
least — which clothe the inner and outer surfaces of the 
sac-shaped body. The internal layer of cells accom- 
plishes digestion ; the external keeps the animal in 
touch with the outer world. Both of them are equally 
engaged in movement. In the further course of animal 
evolution the external stratum of cells was differentiated 
into skin and nerves ; the internal divided into the 
alimentary canal, with its dependent glands, and the 
muscles and bones. 

In harmony with the theory of descent we must 
assume that in certain ancestors of the polyps there 
was as yet no division of labour ; that each cell had 
to discharge every function. And these mulberry- 
shaped animals must in turn have had ancestors that 
consisted of a single cell. 

The embryonic development of every animal establishes 
some such series of ancestors. Every animal begins 
life as a single cell, the ovum. To this succeeds a 



homogeneous cluster of cells ; and from this is 
developed the polyp stage, consisting of two layers of 
cells. The development then continues its course. 

Geology can tell us nothing about the first living 
things. Apart from the fact that they must have 
appeared at a time of which no evidence has been 
handed down to us, they may have had no hard parts, 
and so could not possibly be fossilised. 

But may not these lowest animals have survived to 
our own time, without having abandoned their unicellular 
character ? As a matter of fact, there are not only 
polyps to - day, but there are millions of minute 
organisms in every drop of water that consist of a 
single cell. These are the protozoa . 

Since the whole body of the protozoa is a single cell, 
it cannot be large, nor have different organs, as the 
organs consist of several cells of different kinds. It is 
all the more wonderful to find that natural selection has 
created an infinite variety of forms among the protozoa. 
There are the amoebic, small pieces of protoplasm with 
a nucleus, which move about something like beer-froth 
on a glass plate. If a tiny alga-granule lies in the way 
of one of these animals, it moves towards it and surrounds 
it, and the alga finds itself inside the amoeba. Gradually 
we see a change in the alga-granule. Its digestible 
parts are assimilated by the protoplasm of the amoeba, 
and the indigestible remainder is thrust out at some 

The movement of the amoebae is merely a sort of 
flow, with constant changes of its shape, but the 
“flagellates” have on their cell-body one or two lashes 



which carry the animal along swiftly by beating the 
water. These, and still more the higher protozoa, the 
‘‘ciliated infusoria,” need a special motor apparatus, 
because their cell -body is surrounded by a delicate 
membrane ; it gives more firmness to the animal, but 
prevents the flowing movement of its substance. While 
the flagellates have their lashes or whips, the whole 
skin of the ciliated infusoria, or special parts of it, is 
covered with countless hairs or “cilia,” which strike the 
water in a uniform direction, like a row of oars, and 
force the animal forward. Further, the clothing of 
the skin of these animals prevents them from feeding 
as the amoebae do, and so the infusoria have a special 
opening in the skin, through which the food can enter 
the protoplasm and be ejected again. Round this 
aperture, especially in the sedentary vorticelke, there 
are long lashes that cause a small whirlpool in the 
water and so bring the food down into the animal. 
Naturally, unwelcome foreign bodies are often brought 
into it in this way, and have to be ejected again. 

Thus we see that the single cell is capable of very 
different adaptations, and so we cannot be surprised if 
the cells that compose the higher animals assume such 
enormously different forms. But while the cells of the 
latter are usually selected only in one direction, the cell 
of the protozoa has to advance in every possible direc- 
tion. In the protozoa the one cell discharges all the 
vital functions, locomotion, nutrition, respiration, and 

1 he latter function is accomplished in a very simple 
way in the unicellulars. Let us take the amoeba, for 


instance. The particle of protoplasm that constitutes 
the animal contracts from two opposite sides. It 
becomes thinner and thinner in the middle, until the 
cord that has kept the two halves together gives way. 
During the division the nucleus also has been drawn 
out and constricted, so that when two animals are found 
instead of the one, each of them has a half of the 
nucleus. The two pieces of the amoeba then quickly 
feed themselves up to the normal size of the species, 
and each half of the nucleus attains the size of the 
whole one. The essence of reproduction is the same 
in all the protozoa : the animal splits into two halves, 
and thus the “mother” divides into two “daughters.” 

The cells of the higher animals multiply in the same 
way as the protozoa. The only difference is that in 
their case the cells remain united after the cleavage, 
whereas in the protozoa they become independent, and 
go their own ways. Hence the development of a multi- 
cellular animal is as follows. The ovum, which always 
consists of one cell, divides into two daughter-cells ; 
these again divide into two, and thus four are produced. 
After the next cleavage there are eight, then sixteen 
cells, and so on, until we have a compact cluster of 
cells. The cells then arrange themselves ; they lay 
themselves in two strata, and form a sac. Thus they 
reach the polyp stage, and the differentiation continues. 
Some of the cells secrete muscular matter, others the 
skeletal matter, until the whole complicated animal is 

What a wonderful development ! How is it possible 
that from this repeated cleavage we get, not an irregular 



cluster of homogeneous cells, but a harmonious whole, 
the very different parts of which always come to lie at 
the right spot ? We must admit the impotence of science 
in face of these embryonic mysteries. We know nothing 
of the forces at work here ; but we can say with some 
confidence that no supernatural power controls the 
development of an animal, so that each separate process 
shall bring it a step nearer the complete construction. 
The co-operation of the parts has clearly been brought 
to its present height by natural selection, and the forces 
at work in embryonic development are certainly not 
different from those that we know in organic nature as 
attraction and repulsion, strain and release. 

We saw in the sixth chapter that there are in the 
ovum minute particles that represent the rudiments of 
the future organs. We may now add that it has been 
claimed that these particles are the chromatin that is 
found in the nucleus of every cell, and so of the ovum, 
in the shape of a number of minute corpuscles . 1 We 
know that this chromatin also divides in the cleavage 
of the cell, and this is done by so fine a piece of 
mechanism that one daughter-nucleus receives jzist as 
many halves of the particles as the other. If this 
substance represents the rudiments of the future organs, 
as we have good reason to believe, the ontogeny of an 
animal would run somewhat as follows. In the first, 

1 We know from the following experience that the nucleus is the 
chief constituent of the cell. It has been proved experimentally that 
in protozoa that were cut into pieees, only those parts remained alive 
and grew into fresh animals which contained a fragment of the nucleus. 
Pieces without nucleus died ; even pieces of an amoeba without nucleus 
could not creep along, but floated about aimlessly in the water. 


and generally in a few of the further, cleavages of the 
ovum the halves of all the rudimentary parts pass into 
each daughter-cell, and they complete each other, so 
that the first segmentation-cells have still the power of 
constructing the whole organism, because they have the 
rudiments of all the organs. But in the further course 
of development the rudimentary parts, which have not 
yet made any use of their power to form organs, enter 
into action. When the number of cells is large, the 
dividing cells receive all the rudimentary parts, but 
these do not remain united in the nucleus of the new 
cells ; some of them pass into the protoplasm of the 
cells, and thus give a definite character to them. When, 
for instance, the development has proceeded far enough 
for the construction of the alimentary canal to have 
begun, the alimentary basic parts pass out of the 
nuclei and give the new cells the character of alimen- 
tary cells. The cells that afterwards separate from 
these are, therefore, devoid of the alimentary parts. 
As they divide further, the other bases of the various 
organs pass out of their nuclei ; the nerve-parts convert 
certain cleavage-cells into neural cells, and so on. In a 
word, the basic or rudimentary parts continue to work 
until the construction of the organism is completed. 
Naturally, this description of the process does not rest 
on observation, but is a theory, founded by Weismann ; 
but it must be admitted that it makes the embryonic 
development intelligible . 1 

This continuous transfer of the basic parts does not 

1 The above is an outline of Weismann’s “germ-plasm theory,” the 
most elaborate theory of heredity that we have. 



29 7 

affect all the cells. In the very first segmentations of 
the ovum, in which none of these parts come into play, 
but are equally distributed among the daughter- cells, 
certain cells were separated that retained all their 
rudimentary parts, and therefore the power to build 
up a complete organism. These were the germ-cells . 
While the great mass of the cells differentiated more 
and more in the course of development, these remained 
inactive, or only divided in such a way that all the 
rudimentary parts were retained in their daughter- 
cells. Hence the germ-cells persist through the whole 
embryonic development, and only come into prominence 
when it is over, and the animal is fully formed. The 
inactive basic parts that they have all retained then 
enable them to produce a new organism under proper 

Thus the multicellular animals multiply by means of 
germ-cells. How has this method of propagation arisen 
out of that of the protozoa ? 

In the protozoa the single cell is also the germ-cell, 
as it has to undertake all the vital functions. Every 
cleavage of the unicellular being is a reproduction. 

d here is a certain animal in our fresh waters called 
the “pandorina.” It consists of sixteen cells, all 
homogeneous, and each of them discharging all the 
functions. Each of the sixteen can reproduce the 
animal, by detaching itself from the cluster and sub- 
dividing until it makes sixteen cells. Hence in the 
pandorina each cell can act as a germ-cell. There is 
no division of labour. 

The next step brings us to the “volvox,” a green 


globule about the size of a pin’s head, consisting of a 
number of cells. It is often found in large quantities 
in our ponds. In this animal we have the first division 
of labour. Most of the cells have taken charge of the 
functions of movement and nutrition ; a few others of 
a different shape are responsible for reproduction. 
These lie in the centre of the other cells, and can 
by repeated cleavage create a new animal, which 
detaches itself from the mother and swims about. If 
the parent has given up all its germ-cells, it dies off, 
since its other cells cannot produce germ-cells. 

There does not seem to be anything more wonderful 
in the reproduction of the protozoa. Two quite equal 
halves are formed by cleavage, and each of them has 
only to grow, not to form anything new. It is the same 
with the pandorina, only in this case the cleavage is 
repeated three times, and produces sixteen cells which 
remain united. It is in the volvox that the marvel of 
heredity first appears. Here the germ- cell reproduces 
not only its kind, but also the very different cells of the 
body. But there is no sudden leap from the protozoa 
to the volvox. There are many protozoa in which the 
fore end differs a good deal from the hind end ; and 
when such an animal divides, each half must reproduce 
features that it does not possess. Mere growth could 
not convert fragments of these animals with different 
parts into whole individuals. 

We can more or less understand the mystery of 
heredity with the aid of the above theory. Even the 
protozoon contains rudimentary parts in its nucleus, 
which can build up the different parts of the cell 



body. When the animal divides, each piece receives 
halves of all the basic parts, and therefore those also 
that can supply the part that is wanting in each half. 
So it is with the pandorina. In the volvox two cells 
result from the germ. One of them contains all the 
rudimentary parts in a state of quiescence ; this is the 
germ -cell, the rudimentary parts in which wait until 
the animal is fully grown. But the other cell con- 
tinues to subdivide, and as it does so the rudimentary 
parts come into play, and produce the various volvox- 
cells with all their peculiarities. The process is the 
same in all the higher animals. There is always one 
section of the cells arising from the ovum that contains 
all the rudimentary parts in a state of slumber, as it 
were ; these are the germ-cells. On the other hand, 
the parts come into play in the body-cells, and give 
distinctive characters to various groups of cells. At 
the same time these cells lose the particular rudi- 
mentary parts from their nuclei, and can never build 
up an entire organism, as the germ-cells do . 1 

We have not taken into account the fact of sextial 
generation. But we said in the seventh chapter that 

x This is Weismann’s theory. There are many exceptions, in which 
body-cells have in their nucleus the quiescent basic parts of all the 
sections of the body. We see this, for instance, in the phenomena 
of regeneration. Here, if certain parts of the body are cut off, the 
rudimentary parts that were quiescent in the cells of the contiguous 
parts come into play, and re-build the last fragment. Plants have 
rudimentary particles at all possible parts of the body, because any 
sprout can reproduce a new plant. In fact, in certain plants, such as 
the begonia, even the leaf-cells have these quiescent rudimentary 
particles. If a begonia-leaf is set in moist soil, new plants grow 
from it. 


“ amphimixis ” has originally nothing to do with 

This is perfectly clear in the case of the protozoa. 
If we glance at the transitional forms between the 
unicellulars and the multicellulars, we shall see how 
“sexual” reproduction came gradually to spread. 

In the unicellulars the whole animal has to unite 
with another to give amphimixis. This is really what 
happens. Two protozoa, apparently of the same size 
and appearance, put their cell bodies together, and 
coalesce into one mass. After a time they separate 
again, and the process of amphimixis is over. Here 
we see clearly that amphimixis does not aim at 
multiplication in its original form, because there are 
two animals both before and after it. 

Do the protozoa confirm the view we adopted in 
the seventh chapter that it is the object of amphimixis 
to give the new organism a choice of the character- 
istics of two “ parents,” so as to make it more 
capable of different adaptations ? That is really the 
case. The various characteristics of an animal’s frame 
are based on the rudimentary particles of the germ ; 
in the case of the protozoa, in which body and germ 
are one, this means in the nucleus of the cell. Now 
it has been noticed that during the conjunction of two 
protozoa the nucleus of one of them divides, and 
transfers one half to the body of its companion, where 
it blends with the half that has remained there. 
Hence when the animals separate once more, the 
nucleus of each contains a half of the rudimentary 
particles of the other protozoon as well as half of 


3 QI 

its own. These particles are, therefore, mixed and 
combined afresh through the amphimixis. 

Moreover, the protozoa have two nuclei. It is only 
the smaller of these that contains the rudimentary 
particles and mixes them in the manner described. 
The larger one has only the function of attending to the 
animal’s nutrition, movement and respiration. During 
the amphimixis it dissolves, and is afterwards recon- 
structed by the small nucleus. 

As a rule there is a cleavage, and therefore a multi- 
plication, of the protozoa that have separated after the 
conjunction has been completed. But the chief method 
of reproduction amongst them is non-sexual, that is to 
say, cleavage without amphimixis. In the multicellular 
animals amphimixis is always followed by multiplication. 
How could the germ-cells, the only ones that can enter 
into amphimixis in such cases, return to the bodies of 
their bearers after the act ! If the amphimixis is to 
have any result, two germ-cells must leave the parent 
bodies, combine, and produce directly a new animal, 
which will have the united rudimentary particles. 

This is how the process of amphimixis takes place in 
the pandorina, which has no division of body and germ- 
cells. Any cell in the cluster may in this case detach 
itself, combine with another that has separated from 
some other animal, and with it build up a new animal. 
Reproduction after amphimixis is only occasional in the 
pandorina ; as a rule it multiplies sexually, as stated 

How does the process take place in the volvox, in 
which there are two different kinds of cells, body and 


germ-cells ? In this case, naturally, the germ-cells 
alone enter into amphimixis. The division of labour 
has advanced so far in the volvox that the germ-cells 
which reproduce the animal in the non-sexual way 
we have described cannot enter into amphimixis. A 
different kind of germ-cells has been provided for this ; 
these also are found in the cell cluster of the volvox, but 
they are only formed from time to time. In fact, there 
has been a division of labour even amongst these sexual 
germ-cells. There are two kinds of them produced in 
the same animal, so that at the proper moment a volvox 
has four sorts of cells — body-cells, asexual germ-cells, 
and two kinds of sexual germ-cells. 

One of the lattet kinds is comparatively large, and is 
only formed in small numbers ; and they resemble the 
asexual germ-cells. The cells of the other kind lie in 
packets, each containing several, in the volvox body. 
These cells are very small and have mobile lashes, like 
the body-cells. They break away, when they are 
mature, and seek another volvox, and combine with its 
sexual germ-cells of the first kind. The product of the 
fusion then dissolves, and develops into a new animal. 

In the volvox we have the same features that we find, 
essentially, in all the higher animals. In these, how- 
ever, the asexual germ-cells have generally disappeared ; 
they are common only in the plants, in the shape of 
spores. With the disappearance of the asexual germ- 
cells the animal is now reduced to one method of 
reproduction, that following upon amphimixis. Never- 
theless, the cases of parthenogenesis show that natural 
selection can impart even to the sexual germ-cell, the 



whole structure of which is framed so as only to divide 
and develop after amphimixis, the power of developing 
without union. Apart from these the importance of 
amphimixis led to the disappearance of the asexual 
germ-cells, and the animals were forced to effect 
amphimixis if they wished to multiply. 

It will have already occurred to the reader that the 
inactive sexual germ-cells of the volvox correspond to 
the ova of the higher animals, and the active germ-cells 
to the spermatozoa ; even in man the latter have retained 
the lashes of their flagellate period. But, whereas in 
the volvox the same individual produces both kinds of 
germ-cells, as is the case with many other animals, which 
we call hermaphrodites, we find most animals divided 
into male and female, each with only one kind of germ- 
cells. These are matured at special parts of the body, 
namely, in the ovaries or testicles, as the case may be. 
They have diverged more and more from each other in 
structure. In this the chief principle was the division of 
labour. The germ-cells had to find each other, and had 
to provide a certain amount of nourishment for the 
development of the young after combining. The first 
function devolved on the spermatozoa, which are 
endowed with mobility according to the requirements of 
each species. As a rule they are equipped with mobile 
lashes, and are produced in enormous quantities, which 
is facilitated by their smallness. They can be small, 
because they do not need to contribute any nourishment 
for the new organism, but only the paternal characters 
that are found in their nucleus. The food is provided 
by the ovum, and so this may attain considerable 


size. The yellow of the hen’s egg, for instance, is at 
first a single cell while it is still inside the hen. The 
nucleus of this cell is small, but the cell body takes up 
an immense amount of yolk, and then the whole is 
surrounded by the white and the shell ; these are later 
products, superadded to the yellow. When the egg is 
laid, it is, of course, fertilised, and there have already 
been a number of cell cleavages, so that the white dot 
on the yellow yolk, the “ scar ” as it is called, is really 
a somewhat advanced embryo. 

Continuous adaptation has brought about great differ- 
ences in the form of the spermatozoon and ovum in the 
various animals. It is obvious that those animals will 
always be favoured by selection whose germ-cells were 
the surest to find each other ; animals whose sperma- 
tozoa, for instance, were not active enough to reach the 
female ova could not reproduce, and their sluggish 
sperm-cells would die with them. Thus we can under- 
stand why in the case of organisms that eject their seed 
into water, it is produced in large quantities and is very 
mobile. In these cases it is largely a matter of chance 
whether a single spermatozoon will find its ovum. 
When it does reach one, the physico-chemical nature 
of the two cells attracts them to each other and fuses 
them together. Even then it is no light task for the 
mammal spermatozoa to pass up the oviducts to the 
ovum in the ovary, and this explains their number and 

However, I have not space to deal with either the 
great diversity of form in the animal ova and sperm- 
cells or the interesting relation in which we always find 



them to the life of the particular species. Their admir- 
able adaptations are easily understood. They are the 
maintainers of the species ; in a sense they are its most 
essential element. If we recall our account of the 
embryonic development, it is clear that the germ-cells 
of living animals must have existed, in a sense, since 
the beginning of life. The germ-cells are never created 
afresh ; they are always formed by segmentation from 
the germ-cells of the parents. Let us, for a moment, 
ignore the fact that there are two kinds of germ-cells, 
and consider the process of phylogeny (or ancestral 
development) in the case of an organism that has only 
one kind of germ-cells. These cells contain the basic 
particles of a new organism. They divide and sub- 
divide. One portion of the cells again receives all the 
basic particles, the other portion only a part of them, 
and this grows less and less as the cleavage proceeds, 
because the organs are gradually formed. The cells of 
the various organs cannot give birth to an entire organ- 
ism, because they contain only a few of the basic 
particles ; they have the most diverse functions, and 
afterwards die off. Not so the germ-cells. These form 
a chain that may be infinite in length. They perish, of 
course, if the animal they are in perishes, and they can 
also be destroyed by poison like all living matter ; but 
under the proper conditions they go on to build up a 
new organism, and so on. Hence they have been com- 
pared to a root stretching under the ground, that brings 
forth plants above the surface under certain circum- 
stances and at certain times. These plants grow and 

perish, but the root remains ; it grows on and on, and 



thus constitutes the persistent ground-work of the 
changing forms of life. 

Hence the germ-cells are the main trunk of the 
organic world. In them are contained the basic par- 
ticles ; and as these vary they give birth to ever-new 
forms of life. If the new variation is useful in the 
struggle for life, the animal is preserved, and with it 
the germ-cells. These produce their kind, in unbroken 
continuity, and so continue their life - creating action. 
It is the germ-cells that vary of themselves , and so 
determine the whole variability of organisms. The 
body-cells cannot affect them ; they merely represent 
the house which, by its superiority or inferiority of 
structure (which, however, it owes to the germ-cells), 
enables them to continue their course, or suffers them 
to be cut off 1 

As each germ-cell forms another germ-cell, together 
with the organism, this does the same, and the process 
may go on indefinitely, there seems to be something 
immortal in the germ-cell. How is it with the protozoa? 
In these the body and the germ are one ; the germ-cell 

1 There is a novel of Grant Allen’s, “A Terrible Inheritance,” in 
which a young man suddenly remembers certain details in the life of 
his mother before marriage, and the youthful escapades of his father, 
without having been told anything about them. The story is, to some 
extent, an attempt at a practical application of the Lamarckian prin- 
ciple, and really amounts to a reductio ad absurdum of it. While the 
youth was merely a germ-cell in the mother’s ovary — and in the father 
— she is supposed to have suffered a powerful emotion that was deeply 
imprinted on her. The germ-cell is supposed to have been influenced 
in the same way. The cell shared the experience in a sense, and its 
memory-elements are supposed to have been so acted upon that when 
the cell became a human being, he could recall the conduct of the 



does not build up a temporary body-shell, but only germ- 
cells. These are, of course, bodies, but there is nothing 
temporary formed from them ; they in turn create only 
cells that have the power to live on. Every protozoon 
multiplies by dividing into two. If dangers are avoided, 
these animals will continue to live, divide into others, 
and so on ; in a word, it is possible that one of these 
animals may never become a corpse. The protozoa 
seem to have, as Weismann puts it, a potential 
immortality ; that is to say, they have in their frame 
a capacity for living indefinitely. This is, of course, 
only a capacity. No one questions that they may come 
to a violent end. But it is not in the nature of their 
structure that they are menaced with senile decay and 
death, and that life itself gradually uses up their sub- 
stance, as is the case with the body-cells of the higher 

It has been objected to this view, that the protozoa 
have no natural death, that at each cleavage the indi- 
viduality of the mother comes to an end. “ Individual ” 
means “indivisible,” and it is clear that the mother dies 
when it divides into two daughters, as these are two new 

Weismann, however, considers that the characteristic 
of death is not the destruction of individuality, but the 
appearance of a corpse. We will not stay to discuss 
whether this conception is correct, but will go to the 
heart of the problem. The protozoa have, Weismann 
says, the faculty of not being permanently used up by 
metabolism, and this can be called metaphorically, with 
some propriety, immortality. But is there really in the 


protozoa nothing that ever compels them to become 
corpses ? This seems to be correct. There can be no 
such necessity in the protozoa, otherwise there would be 
no protozoa to-day that are fragments of their ancestors, 
though the parts have fully developed in turn. When 
a protozoon is split into two daughters there is certainly 
no corpse to be seen, and it is the same when the 
daughters in turn subdivide. Here we have a difference 
between unicellulars and multicellulars. In the latter 
it is only the small particles in the germ-cells that are 
immortal. The germs divide. But only one part, the 
newly divided germ-cells, have the power to carry on 
the life. The other part, the body-cells, are used up 
by metabolism, and must perish. The unicellulars 
divide, but in their case both halves can carry on the 
life indefinitely. 

Natural death is not, therefore, a necessity for all 
organisms, but has only made its appearance with the 
multicellulars. In their case the germ-cells convey the 
living substance to their descendants ; when they leave 
the body, it is useless for the maintenance of the species, 
as it has not the power to create new organisms. 
Weismann believes that we have here the chief 
reason of the introduction of death into the organic 
world. The body becomes superfluous and disappears, 
like all useless organisms, when it has secured the 
maintenance of the species by the transmission of its 
germ-cells. However that may be, we see that the 
division of labour amongst the several groups of body- 
cells could not be very considerable unless they made 
no claim to indefinite duration. Many cells, in fact, have 


precisely the duty of dissolving themselves ; and it is 
possible that most cells only do their work so well at 
the cost of using themselves up in the process. They 
can do this, because the propagation of the species is 
secured by the germ - cells, which perform their duty 
the more confidently when the body they are in is in a 
good condition. The more advanced the body is in 
organisation, the better will be the nutrition of the germ 
apd the greater its security from dangers. 

It may be asked whether there is not some such division 
of labour within the one cell of the protozoa ; whether 
there are not in these animals also parts that can only 
discharge their function for a certain time, and must then 
decay and be reconstructed by the permanent parts of 
the cell. 

This is really the case. In many of the protozoa only 
the nucleus and a small part of the protoplasm are 
divided in non-sexual multiplication, for the greater part 
of the cell-body dies. Hence there are a number of 
protozoa in which we constantly find dead parts. In 
fact, it looks as if dead parts are continually being 
extruded from all protozoa. It has been proved by 
careful experiments that protozoa perish if they are 
impeded in their amphimixis. Thus amphimixis is 
necessary for the protozoa . 1 It is true that they usually 
propagate asexually, but from time to time their body has 
to effect an exchange of basic particles with another one. 

1 I cannot go any further here into the introduction of amphimixis 
into the organic world. Weismann has attempted to trace it to its 
ultimate roots. He believes that it arose in the earliest, unnucleated 
living things, and had a favourable influence on their metabolism. It 
was, therefore, a process of adaptation. 


But if any protozoa must submit to amphimixis in 
order to preserve the species, there are in the group 
parts that are subject to natural death. We have 
described above how in the amphimixis of the unicellulars 
the large nucleus, which undertakes the vital functions, 
dissolves, and thus represents the corpse. It does not 
alter the case essentially that this corpse is small in pro- 
portion to the animal ; in many of the higher animals 
the germ-cells are much larger than the body — as in the 
case of the frog’s eggs. The question is whether there 
are any animals whose whole substance lives on con- 
tinuously and is not dissolved by its metabolism. 
That is clearly not the case with the protozoa. We are, 
therefore, not justified in drawing a line between the 
unicellulars and multicellulars, and saying that the former 
are immortal and the latter not. 

However, the protozoa are not the lowest organisms. 
In them the living matter is already differentiated, 
particularly into nucleus and cell-body. In our view 
there must have been animals from the beginning of 
life in which there was no differentiation. It is a 
question whether there are now any unnucleated 
organisms of this kind, as a nucleus has been found 
even in the smallest animals. That is, of course, not 
conclusive, because the simplest living things may be 
below the limit of visibility. However that may be, we 
can at least picture to ourselves animals whose repro- 
duction consists merely in dividing without leaving any 
residue, and in which there is not any amphimixis. 
We must not forget, of course, that even in such 
animals the living matter as such is not immortal, 


3 ii 

since it is its property to be always breaking 

There cannot, therefore, be any living thing of which 
the substance, as such, is lifted above time. Yet we 
speak of immortality, because there is a continuity of 
life. Our own body is breaking up constantly through- 
out life, yet we do not speak of this as death ; in fact, 
we hardly perceive the constant process. 

In the seventh chapter we dealt with the activity of 
the living matter, of the biogens. These have to break 
up, it is true, but they have the power to build up one or 
more new biogens before they die, and this secures a 
continuity of the life. We can picture to ourselves the 
activity of the biogens, in the growth and decay of an 
organisation, in something like the following way. At 
first they create several of their kind before they break 
up, and thus effect the growth of the animal. Then 
each produces only one biogen, and thus they maintain 
the organism at its height. Finally, they are unable to 
make any new biogens before they decay, and so they 
bring about the death of the organism. 

Life can only continue to exist because there are 
biogens the action of which is never paralysed in all 
their generations. There are biogens that can maintain 
life in continuity, and so bring about an immortality of 
life. But in the multicellulars and unicellulars this can 
only be done permanently by some of the biogens ; by 
the others it can only be done to a certain point — until 
death. We can, however, conceive living things of the 
simplest character, the bodies of which consist entirely 
of such biogens. These animals might not improperly 


be called immortal, because no part of their body 
perishes without providing a substitute ; in other words, 
no part forms a corpse. 

We know too little of the biogens and their activity 
to be able to say why all biogens are not indefatigable 
in creating a substitute. It has been suggested that the 
temporary biogens can only achieve this by drawing on 
their own energy. They differ so much in the structure 
of their elements that some irregularity is unavoidable 
in the co-operation of the various parts. In the course 
of their life these irregularities increase, and at last a 
time must come when the biogens are shaken to the 
foundations of their structure. They then break up. 
That is the meaning of death. 

We are led to conclude, then, that the introduction of 
death into the world was useful, because the living 
matter was bound to give up all claim to eternal con- 
tinuity before it could be so differentiated that its 
possessor could escape violent death. However, some 
of the biogens had to retain the power of continuous 
creation, in order to maintain life upon the earth. 

Just as death was introduced by natural selection, so 
the moment of its occurrence is carefully regulated. In 
each animal species natural death only sets in when the 
maintenance of the species is secured. The duration 
of life is strictly proportioned in all organisms to their 
reproductive powers. But I have not space to discuss 
this in detail here. 

Life will not continue for ever on the earth. A time 
will come when the earth will course through space, 
a frozen mass, and a violent end will come to all 


3 X 3 

organisms . 1 The moon already shows us what the 
fate of our planet will be. And as the earth will 
necessarily change until it becomes incapable of sup- 
porting organic life, so there must have been a moment 
in its past development when no plant or animal could 
be found on it. In this case it was the glowing heat — 
in the former the icy cold — that precluded the presence 
of life. Neither extreme can be borne by life; it can 
only maintain itself between the two poles, and will 
perish if one of them approaches nearer. We may 
now ask when life made its appearance, and whence 
it came. 

We saw that the living substance is continually being 
built up out of inorganic matter, but that this can only 
be effected by living matter already in existence. If 
we go far back in the history of the earth we come to 
a point when it was a molten mass and could not 
possibly contain life. Whence did this come, then ? 
It might be possible for life to be conveyed from some 
other body to the earth after it had cooled down. A 
few scientists have suggested this , 2 supposing that it 
may have been brought to the earth by meteorites. 
It has been replied to them that delicate organisms 
could hardly endure the icy cold of space, and then 
the incandescent heat of the meteor as it passes through 
the earth’s atmosphere. The objection is not entirely 
sound. Particles of charcoal and soil have often been 

1 Verworn urges this as a difficulty against Weismann, but he is 
clearly wrong. The cooling of the earth causes a violent death, and 
is not inconsistent with potential immortality, or a capacity for enduring 
life. T his naturally presupposes external conditions. 

2 Lord Kelvin, Richter, and Helmholtz. 


found inside meteorites, and if these could stand the 
heat we may grant that also of the living substance. 
Nor is the fact that the meteorites provide no food or 
water a reason for denying- that they might contain 
life. Grains of seed can remain a long time without 
water or food. 

It has also been said that this “cosmozoic theory” 
does not answer the question of the origin of life, but 
only postpones it. If we put life off to another planet, 
we have to ask how it was born there. 

But this also is wrong. It might be said that life 
was not born on that other planet, but brought from a 
third one. In a word, it might be said that the living 
substance has existed from all eternity, like matter and 
motion. This theory, that life had no beginning, that 
it is eternal, gives an answer to the question. 

But there are more effective objections to the 
cosmozoic theory. In the first place, we see that the 
plants build up living matter from inorganic matter 
every day. If the living substance can thus be created 
daily, it cannot be eternal. Still less will we believe in 
the eternity of the organic substance if we reflect that 
organisms can perish. An eternal matter ought to 
be imperishable. Inorganic matter, which is eternal, 
cannot be entirely destroyed. It changes — we can 
do what we will with it — into another form of inorganic 
matter, but this also is eternal. It is otherwise with 
living matter. This can be destroyed as living matter ; 
it does not then change into another form of living 
matter, but into inorganic matter. 

As we see every day with our own eyes how living 



substance is formed from lifeless, and changes back 
into it, we may assume that it had its first origin in 
inorganic matter. We have the more right to do this 
since no element has yet been found in living matter 
that is not found in the inorganic world. There is no 
essential difference between the albuminoids and other 
compounds. Finally, we know that all compounds are 
made up of simple elements. The whole of science 
is based on this fact. It would be contrary to all 
experience if compounds suddenly appeared that were 
not formed from others, but had existed for all 
eternity without any connection with nature, as it 
were . 1 

We are thus driven, by a number of considerations, 
to the conclusion that life was born on our planet. And 
as there can only have been inorganic matter on our 
planet from the first, life must have been evolved from 
it; nothing can be made out of nothing. It is no 
objection against our theory that we have not 
yet succeeded in artificially producing living matter or 
animals. How could we hope to do this when we know 
neither the structure of living albumen nor the forces 
that create it. The fact that no living matter has yet 
been produced artificially only shows that a certain 

1 There is still another important theory of the origin of life, that 
of Preyer. This takes the idea of life in a wider sense than we 
usually do. It regards the molten planet as a living organism, 
and so postulates a continuity of life. In the form to which we 
now give the name of living matter, Preyer himself admits that 
it was formed by spontaneous generation. It is a question whether 
we should be justified in speaking of the movement of inorganic 
masses as life. It is a question of terms, and we will not enlarge 
on it. 


experiment has failed ; it does not show that there may 
not be other unknown methods by which living albumen 
can be constructed. In a word, we can quite understand 
the failure of all the attempts made up to the present to 
create living matter, because in the actual condition of 
our knowledge of life they are merely shots in the 

It is possible, in fact, that life could only be formed 
on our planet when it was at a certain stage of 
development that has long since passed away. The 
distinguished physiologist Pfliiger has formulated and 
firmly established a theory in that sense. He 
believes that the first steps towards life could only be 
taken when the earth was still entirely or partially in a 
molten condition. This would be a justification of the 
old saying that life was born from fire. 

I cannot, unfortunately, go into Pfluger’s theory at 
any length, as it requires a thorough knowlege of 
chemistry. I will merely give a general outline 
of it. 

There are certain elaborate compounds, known as 
“cyanic compounds,” which are easily broken up, and 
have a good deal of analogy with living matter. These 
compounds are only formed at an incandescent heat. 
They may, therefore, have been formed when the earth 
was still incandescent at its surface. In consequence of 
their decomposibility they soon entered into relations 
with other compounds. And when the steam descended 
on the earth, and the masses of water began to form, the 
cyanic compounds combined with the fluid element and 
the salts dissolved in it, and thus gave rise to the living 



albuminoids. Tiiese were very simple at first, and not 
yet differentiated into cells ; but they had from the 
beginning the faculty of metabolism. 

Thus the origin of life was determined by the condi- 
tion of the earth. The living substance is part of the 
matter of the earth, and has been formed therefrom by 
spontaneous generation. It was just as necessary an 
evolution as that of the rocks, when the conditions of it 
were given. Throughout the whole universe there is 
an endless chain of causes and effects, and the origin of 
life comes within this inexorable chain. The further 
development of the living substance and the moulding 
of it into the more advanced plants and animals was 
another necessary consequence of the condition of the 
earth at the time. These transformations were effects 
of causes that in turn sprang from other causes. We 
have long known that all that happens in organic nature 
is determined by necessary, endless chains of cause 
and effect. It is the immortal merit of Darwin to 
have brought life also within this series. 

We may now picture to ourselves the first development 
of life. We begin with the living substance, the origin 
of which we have outlined above. In the beginning 
were the biogens. These must be conceived in the 
form of living things with a metabolism like that of the 
actual plant. Their constant break-up would have led 
to the destruction of all life if they had not had the 
power of creating their like out of inorganic matter. 
I hey cannot, of course, have had any chlorophyll, the 
green substance that effects the construction of organic 
matter from inorganic in most of our actual plants. 


Chlorophyll is much too complex a structure for us to 
suppose it to have been present from the first. No, 
these biogens were clearly like the actual nitrogenous 
bacteria, very simple organisms, that can convert lifeless 
into living matter. 

The next step in the development of life was that the 
biogens, which were at first quite homogeneous, clustered 
together like stars. External conditions were acting 
constantly on all these primitive beings, because it is 
the nature of the living substance to be flexible and 
modifiable. We can thus understand that the activity 
of the biogens, in creating their like before they broke 
up, would be greater in warm and well-lit places than in 
less favourable ones. Here we have the first cause of 
differentiation. If we further remember the great diver- 
sity of the earth’s surface, we can see that this of itself 
would lead to a considerable variety among the living 
things, since each locality would have a different effect 
on the changeable living matter. Thus the Lamarckian 
principle was active at the beginning of biological 
evolution. Even when a group of biogens divided 
and formed two, the halves retained the modifications 
that had been imprinted on the parent by external 

But it would be otherwise when a differentiation set 
in among the biogens in a given group. The moment 
a favourable division of labour was introduced amongst 
them, the organism would be in a better position, and 
would be picked out by natural selection. By this 
division of labour one biogen would be better able to 
discharge one vital function, a second another one, and 


3 l 9 

so on. The advance of this division of labour was more 
and more favoured, and at length the organism was so 
much differentiated that when it divided it gave rise, 
not to two homogeneous halves, which could at once 
become complete organisms in turn, but to two different 
halves, each of which, in order to form the parts 
wanting in it, and found in the other half, needed a 
sort of depot, in which were found the biogens that 
could create the half that was wanting. This store is 
the nucleus of the cell ; in this are the basic particles of 
each section, and thus we come to the stage of cellular 

As from this stage the missing parts were formed by 
the basic particles at cleavage, which were contained in 
the halved nucleus, the Lamarckian principle ceased to 
act. However much the protoplasm of a protozoon is 
modified, the daughter-cells do not receive any part of 
the modified substance at cleavage ; it is the basic 
particles that build up the protoplastic parts as it grows 
into the mature animal. And if the protoplastic parts 
are formed afresh at each segmentation by the basic 
particles, they can only change when there is a change of 
the latter. But we have seen that the basic particles 
change of themselves, and are not modified by bodily 

The basic particles consist of living matter, and so 
can change, grow and divide. In the earliest nucleated 
organisms there can only have been a few of them, and 
when changes occurred in them by chance, they created 
different organisms. Let us take the case of a simple 
protozoon with a cell-body containing four different 


parts. On our theory there were four basic particles in 
the nucleus of this animal, and these would form the 
four protoplastic sections. Now, if one of these four 
particles divided into two, and the one resulting particle 
differed somewhat from the other, we should have five 
basic particles ; and in the next protozoic cleavage we 
should have protozoa with cell-bodies containing five 
different parts. 

We can conceive in this way that the multiplication 
and differentiation of the basic particles would give rise 
to more and more complex organisms right up to the 
vertebrates. The root of the variations is, therefore, 
in the basic particles. The more complex their com- 
position becomes, the more highly differentiated will be 
the organism whose organs they construct during the 
embryonic development. But we can say nothing very 
confidently as to the causes of their alteration and 
multiplication. Weismann, to whom we owe the whole 
of this theory of heredity, believes that the food that 
must be supplied to them, as to all organic substance, 
whether in the nucleus of the ovum or of the protozoon, 
may vary in quantity from some accident or other, and 
that a basic particle changes, multiplies, or disappears, 
according to this variation in its supply of nourishment. 
With it must vary the section of the body that it 
builds up. 

Thus the basic particles are never created afresh, but 
are always formed from pre-existing ones. When they 
have constructed an organism, their variations come to 
light in it and in the struggle for life, because the form 
of the particular organism is changed in harmony with 



their change. It is then settled whether the variation is 
to survive or not. If it is of such a character that the 
organism can sustain the struggle for life, it is preserved 
and transmitted to offspring ; if not, the animal 
perishes, and with it disappear the variations of its 
basic particles. Thus in the course of time those 
of the innumerable variations of the basic particles 
will survive that prove useful in the developed 

There is only one more reflection to make. What is 
the conduct of the basic particles during amphimixis ? 
As the ovum contains the basic particles of the mother 
and her ancestors, and the spermatozoon those of the 
father and his ancestors, the number of them must be 
doubled when they unite. It will be fourfold at the 
next amphimixis, and so on, until at last they fill the 
cell-nucleus in immense numbers. We saw in the 
seventh chapter that there are several basic particles 
in the ovum for each organ, and that both the ovum and 
the spermatozoon are capable of constructing several 
different beings. We saw further that there is a force 
which, in a way unknown to us, always selects the one 
basic particle of each organ that is to build up the 
particular organ. But even if this force prevents the 
doubling or tripling of an organ in the developing body, 
nevertheless the basic particles must increase so much 
in a few generations by the eternal doubling at 
amphimixis that there will at last be no room for them 
in the nucleus. 

To fix a limit to this indefinite increase of the basic 
particles there must be some arrangement of the germ- 


cells . 1 Both the ovum and the spermatozoon must pass 
through a maturing process before union, the essential 
point of which is that it reduces the basic particles by 
one half. In the ovum and spermatozoon before union 
half of the basic particles are expelled from the cell, so 
that when the fusion has taken place, there is only the 
normal number, and this is preserved in the same way 
at each successive amphimixis. If we suppose that a 
male cell contains ten basic particles and the corre- 
sponding female cell the same number, amphimixis 
would produce twenty, the next fusion forty, and 
so on, if there were nothing to prevent the in- 
crease. But as five particles have been eliminated 
from the spermatozoon and ovum respectively before 
amphimixis, they remain ten in number after 
union. The same process has been observed in the 

We have now formed some idea of the origin and 
evolution of life. We have seen that certain biogens 
in a continuous series have the power of producing 
other biogens before they break up, so that the 
continuity of life is maintained. Whether this power 
is really lifted above time, or whether the living 
substance, which had a beginning, will also of its 
own nature have an end, in the sense that in the end 
— though after an incalculable period — even the 

1 Weismann pointed out the well-known reduction cleavage of the 
ovum of this character. He postulated the same process for the 
sperm-cell, because in his opinion the basic particles must be reduced 
by half in this also before amphimixis. His theory was soon verified, 
and the reduction cleavage of the spermatozoon was discovered. 



strongest biogens will age, and thus bring life to a 
natural termination, we do not know. But we can 
affirm with some confidence that one day a violent 
death will make an end of all terrestrial life. The 
cooling of our planet is proceeding with inexorable 
necessity, and the day will come when the warm 
earth of our time will course through space as a cold 
and waterless sphere. All life will perish in this 
state of icy rigidity. 



Why there are numerous species to-day. Isolation facilitates the 
divergence of species. Modification of isolated animals. Move- 
ment and alteration of animals. Are species formed by isolation 
even without the aid of natural selection? Definite variations. 
Germinal selection. Changes in the nutrition of the embryo are 
the foundation of variations. Do useless organs disappear through 
germinal selection? Refutation of germinal selection. Effect 
of external influences as modifying principle. Orthogenesis. 
Rejection of same. The mutation theory. Variations and 
mutations. Do variations proceed indefinitely? Is there a 
formative energy in organisms? Mechanicism and vitalism. 
How are the form and purposiveness of organisms explained? 
What is to be understood by chance. Absence of purpose in 
living things. The will to live, the instinct of self-preservation. 

We can now picture to ourselves how life began on 
our planet, and how it has been evolved. In virtue 
of the fundamental property of organic substance, 
variability, a process of transformation has been 
possible that maintained organisms even amid the 
changing conditions of the surface of the earth. We 
recognised natural selection as the power that 
continuously adapted living things to their new 
environment. And as we came to the conclusion 
that organisms arose entirely, or at least mainly, from 
adaptations, we are bound to say that selection alone 

has done all the work of transforming life. 

3 2 4 


However, we saw at an early stage that the theory 
of selection will not explain everything in the present 
condition of science. It could not satisfactorily 
explain the various characters that are peculiar to 
one sex. The auxiliary principle, sexual selection, 
which we called to our aid, was so unsatisfactory that 
we sought to reduce it again to natural selection. We 
also failed to explain many of the rudimentary organs 
because we had to reject, on the strength of 
Weismann’s objections, the Lamarckian principle 
that might have shed light on them. On the other 
hand, when we came to the question why there are 
sharply distinct species, we discovered an agency 
that really solved the problem — amphimixis. 

However, there seemed to be other difficulties in 
the way of amphimixis. The origin of one species 
from another — in other words, the divergence of 
species — seemed to be inconsistent with it. How 
can a new property, even when it only arises amongst 
one section of a species, maintain itself and lead to 
the founding of a new species, if the differently 
constituted individuals are always crossing with the 
modified ones ? The new feature ought to be 
absorbed by the majority in this general crossing. 

But we have had frequent occasion to remind the 
reader of a power that can prevent crossing, and so 
maintain the incipient specific character. This agency 
is isolation. We will now deal with the importance 
of isolation in the formation of species, to which 
attention was first drawn by Moritz Wagner. 

The most common effect of isolation is that a 


number of animals are separated spatially from the 
great mass of their fellows, so that there can be no 
further crossing. If these isolated animals come into 
a different environment, selection will modify them in 
a different direction from that taken by their distant 
fellows. Remember the origin of land vertebrates. 
As the fishes dispersed, passed up the rivers, and 
reached their higher waters, some of them may have 
swum into a piece of water that was not usually 
connected with the rivers. When the water fell once 
more, the wanderers were cut off from their species. 
Selection had another effect in their new home. In 
the hot season most of the water dried up, and this 
was the occasion of the conversion of the swimming 
bladder into lungs. 

It must have happened very frequently during the 
millions of years of the earth’s history that wandering 
animals were cut off from their fellows. In this way 
floods and evaporation must have given occasion over 
and over again to the formation of new species of 
aquatic animals. Land-animals also must have been 
separated by inundations. Suppose, for instance, that 
the overflow of the Rhine into a certain valley killed 
all the deer in it, and only left survivors on the 
mountains at each side. When the water subsides 
again, the deer will remain in their separate localities, 
because we know that they keep always to a rather 
restricted area, and do not willingly leave it. Gradu- 
ally, the increase of the animals on the mountains will 
bring some of them down into the valley once more. 
But if they had a different environment on one range 


of mountains from on the other, each species will have 
been changed by natural selection, possibly so much that 
they can no longer be crossed, or not with any effect. 
Thus there will be two different species of deer in this 
Rhine valley. 

Inundations will often cover a large area, and this 
must have happened more frequently in former years 
when there was no regulation of rivers. These floods 
would certainly often drive animals into a new environ- 
ment. If, for instance, a river floods half a wooded 
region, and only spares the extreme corner of it which 
borders on a wide steppe, the animals in the part of the 
wood that has not been flooded will remain forest 
animals, but those that live in the narrow strip of wood 
will gradually become steppe animals, because their 
continued expansion will drive them on to the open 
grass. It is not necessary for the animals to be driven 
into other regions by the flood in order to be modified ; 
it is enough if they find a new enemy in their new home. 
In the struggle with this enemy, the branch species will 
be made to differ from the parental species, which will 
not be affected by the same agency. 

If we bear in mind the continuous geological changes 
that have taken place in the earth’s surface since the 
enormously remote period of the origin of life, we can 
understand that the isolations must have been frequent 
enough to account for the infinite variety of organic 
species. Lands have sunk beneath the sea, others have 
emerged from the waves ; at one place mountain ranges 
have been elevated, at another great valleys scooped 
out. Land joined on to land and water to water, then 


separated afresh, and reunited later on. Storms swept 
over the earth. Violent hurricanes rooted up whole 
forests. Desert-storms buried whole stretches of green 
land under sand. Tropical heat alternated with arctic 
cold : floods with drought. 

When animals that had long been separated came 
together again, they were generally so different in 
structure and appearance that they could no longer 
cross in such a way as to mingle the characters of one 
species with those of the other. Even minute changes 
in the spermatozoa of the male prevent it from pene- 
trating any longer into the ovum and fertilising it. 
Moreover, animals are most apt to unite with those of 
their own species ; they have a sort of racial feeling that 
generally prevents them from crossing with animals of 
a different form. An unfamiliar appearance or scent 
restrains animals from mixing, and this is especially 
true of animals that come together after a long separa- 
tion. We know that mammals and birds that have 
been kept in captivity for only a brief period have not 
only no love to expect from their kind when they are 
released, but are actually persecuted. Even the finest 
changes in animals often act powerfully on the 
sense-organs of their free-living fellows. 

It is not only geological alterations of the earth’s 
surface that lead to the division of animal species by 
isolation, but organisms may be transported into regions 
from which they cannot return to their old home and 
their fellows. In modern times animals have often 
enough been transplanted by men into distant localities. 
The Porto- Santo rabbit is a proof of the fact that a 


Species can be so altered by isolation as to be incapable 
of crossing with the parental species. In fact, long 
before man crossed the waves on his vessels, organisms 
were conveyed into remote districts. Sometimes small 
water-snails clung to the legs and feathers of swimming 
birds, and were taken far across the sea to strange 
islands, where they entered the water once more and 
found their proper conditions. In the same way other 
aquatic animals travelled far and wide — the minute 
eggs, especially, that were easily caught in the feathery 
coats of the swimming birds and taken away uncon- 
sciously. Land animals also could be dispersed by 
birds in this way. 

It was by no means necessary to have living vehicles 
to convey animals into distant and isolated districts. It 
might often happen that a branch of a tree with small 
animals sitting on it would fall into the river, be carried 
out to sea, and be borne by the currents to distant 
localities. In this way, as a matter of fact, branches 
have come from America to the coast of Europe. The 
eggs, especially, which are comparatively insensitive to 
external influences, and the seeds of plants, might be 
conveyed in this way. It is certain that many newly- 
formed islands have been thus populated. 

Not only may the sea transport germs in this way, 
but many a flying animal has been taken a considerable 
way by stormy winds. Insects and birds often get into 
currents of air that carry them to distant localities, and 
they often find such a favourable environment there that 
they do not think of returning even when it is possible 
to do so. 


The transport of animals into distant lands is often 
very useful for their extension. Especially when the 
wanderers reach an island that offers them a virgin 
habitat — one that has few or no animal species in it — 
they may spread in all directions. And as there are all 
kinds of spots in the new district, their descendants 
in turn may separate into new species, each locality 
modifying its inhabitants in a different respect. This 
will happen particularly to slow-moving animals, such 
as the snails, every valley and every wood giving a 
specific modification to its inhabitants. There is no 
reason to fear the levelling of the new characters by 
crossing with their kind of other districts in the case 
of such slow animals, as they have long coupled with 
others like themselves before they reach a different 

There are many other means of isolation besides 
these. The isolation may only hold during the period 
of reproduction ; birds, for instance, that otherwise 
mingle together in quest of food may rear their young 
in remote districts. In such cases a differently coloured 
ground may change the colour of the animals. It was 
an isolation of this kind that gave rise to the migratory 
birds. The isolation need not always involve an 
absolute separation of the daughter species from the 
parental species. It is enough if one part of a species 
leaves its proper territory, and takes up residence in a 
contiguous one of different characters, that meets its 
needs. Although there is still a good deal of crossing 
at the frontier, there will as a rule be a steady and pure 
development of the new species away from it. 


Up to the present we have only seen a preparatory 
principle in isolation, which makes possible the formation 
of new species. This formation may be brought about 
by natural selection after the isolation. 

There are also cases in which isolation alone may lead 
to the formation of a new species. If a fertilised female is 
forced into an isolated district and lays her eggs there, 
the young developed from them will not, as a rule, differ 
from the parental species. But if the female happens 
to have some peculiar characteristic, it will transmit 
it to the offspring ; in time the feature will become a 
characteristic of the isolated animals, as it can no longer 
be absorbed by crossing. In this way isolation may 
lead to the formation of a new species without the aid 
of natural selection. The isolated variety would be still 
more strongly modified if the characteristic in question 
were to be accentuated in the offspring ; in other words, 
if there were some force in the organisms that caused 
variations to advance in a definite direction in the 
offspring. We have already found several times that 
the transformation of species would be brought about 
much more speedily by a principle of this kind than 
without it, and we will now inquire whether or no we 
may infer the existence of such a force. 


We have spoken of selective value in the seventh 
chapter and seen that it is difficult to conceive how 
every little variation can be helpful to its possessor in 
the struggle for life. If that is not the case, how can 
the variation be preserved and increased? How could 
the elephant s trunk be developed from the original nose, 


since even the most favourable variation of the latter 
could not perform a single function of the trunk ? 

The whole difficulty would be avoided if we could 
suppose that variations that have once arisen have 
in themselves a tendency to advance in the same direction 
in each generation ; in that case, if the elephant’s nose 
happened to be rather longer than those of its fellows, it 
would be still longer in this elephant’s offspring, and if 
the family became isolated, each succeeding generation 
would have longer noses. In the end a point would be 
reached when the nose would be long enough to be of 
service. Then selection would set in, and still further 
develop it. 

If there were definitely directed variations, it would 
be easier to solve a number of other problems. The 
importance of amphimixis would be greatly enhanced. 
By means of it different directions of variation would be 
brought together in one individual, and co-adaptations 
would be effected much more quickly. At the same 
time, amphimixis would convey both upward and 
downward variations to a number of individuals, and 
thus generalise useful characteristics, and prevent 
injurious ones from spreading, with fatal consequences 
to their possessors. 

There are many advantages in the theory of definitely 
directed variations. Many scientists, in fact, believe 
we need the hypothesis, as the theory of selection is, 
they say, unable without it to explain the origin of 
species. We will now see if there is sound reason for 
crediting nature with definitely directed variations. 

The expert who has made most use of the principle of 




selection, Weismann, has attempted to apply it to the 
germ-cells . 1 He thinks that here also there is a selection 
at work — “germinal selection.” The result of this is to 
preserve definite directions of variation in the germs. 

We have already seen several times that there are 
in the germ -cells, which an animal has in its sexual 
glands, tiny particles that represent the rudiments of 
the future organs, in the sense that, if an animal is 
developed from the germ-cell, they determine the several 
parts of the body and stimulate their construction. 
Hence every part of an animal’s frame is present 
rudimentarily in the germ-cell. 

These basic particles, which Weismann calls deter- 
minants , because they afterwards determine an organ 

1 Weismann was influenced by the “ theory of histological selection ” 
of Wilhelm Roux. Roux attributed the purposive structure in the 
histological, microscopic texture of animals to “ a struggle among their 
elements.” We know that sustained exercise or stimulation in the life 
of the individual strengthens. The cells are enabled to grow better 
under stimuli. Hence when we find a graceful framework in the bones 
of the leg, the arches of which always run in the direction of the 
greatest pressure and strain, as in the construction of an edifice, it must 
have been brought about by the fact that the cells which lay in the 
direction of the pressure and strain were most stimulated, and so 
formed the strongest bony matter. On the other hand, the intermediate 
cells were less stimulated, would grow and act less, and the nourish- 
ment they needed would be absorbed by the better situated cells, so 
that they would eventually perish. It is thus that the curves in the 
osseous structure run only in the direction of the greatest strain. The 
cells that lie there have an advantage in the struggle of parts, as they 
grow under the constant stimulation, and build up bony substance 
at the expense of the adjacent cells, which gradually die off. 

Histological selection gives us a luminous explanation of microscopic 
structure. But in our opinion it only acts during individual develop- 
ment. What it accomplishes is not inherited, but has to be created 
afresh in each organism. 


of the body, consist of living matter, and so must receive 
nourishment. Their food must be matter that is 
found in the germ-cell, or passes into it from the body. 
This matter must, of course, be fluid and must flow 
round the determinants. 

Nowhere in nature do we find absolute equality, and 
so the fluid nutriment will not equally reach all parts of 
the germ-cell. Hence a determinant will receive some- 
times a fuller and at other times a thinner supply of food. 
If it finds plenty of food, it will grow strong and sound, 
as all living matter does when it is well nourished. 
Another determinant will chance to have a worse 
supply of food, and become weaker. 

When the determinant is thus enfeebled by happening 
to receive a poor supply of nourishment, it will, if an 
animal is developed from the germ, have less power to 
build up the organ it represents, and the organ also will 
be feeble. And when a determinant is strengthened in 
the germ by a plentiful supply of food, it will afterwards 
build up its particular organ in greater strength. Thus 
we see that the variations we find in children of the 
same mother at birth are due to chance differences in 
the supply of food to the ova. While the ova lay unde- 
veloped within the mother’s body, the determinants were 
differently fed by the varying stream of nourishment, 
and when they afterwards come into action they show 
differences in the building up of their respective organs. 
Hence the accidental irregularities in the supply of food 
in the germ are the roots of variations. 

All living matter is able to accomplish work in pro- 
portion as it is strengthened by food. We can thus 


conceive that a determinant, which has increased in 
size within the mother through the good supply of food, 
will, by reason of its size, attract more food to itself in the 
daughter. When the mother’s germ-cell divides to form 
the daughter-cells, we know that in the earlier segmenta- 
tions of the ovum all the determinants are split into 
halves, because first of all must be formed the germ-cells 
of the daughters, and these must contain all the basic 
particles. When the determinants come into action in 
the later segmentations, and gradually build up the 
body of the daughters, some of the first cells divided, 
the germ-cells retain all their determinants in a quiescent 
state. Hence if a determinant became larger in the 
mother owing to a good supply of food, it maintained 
this size in the germ-cells of the daughters as well, as 
after cleavage it always grew again to its normal size. 
And, being larger, it needed more nourishment than the 
neighbouring determinants that remained small. Owing 
to its volume it, as it were, drew to itself the stream of 
food circulating in the germ. On account of this supply 
of food it became still larger, and retained its size in the 
ovum of the grand-daughter, where it again attracted 
food, and became larger still. The size increased in 
each generation, the determinant grew larger and larger, 
and hence the part of the body that it built up showed 
a corresponding steady increase or, in other words, a 
definitely directed variation. 

Does this enlargement of a determinant and the 
corresponding organ proceed indefinitely? If this were 
the case, there could be no such thing as a specific 
type. As the nutrition is exposed to irregularities 


at each part of the germ, one part of the innumer- 
able determinants would become steadily larger and 
the other part constantly smaller. In the same way 
the organs of the developed animal would change in 
all directions simultaneously. It would be impossible, 
in view of this eternal ebb and flow of the determinants, 
for an animal species to remain the same for a 
considerable period, as we actually find. 

Hence Weismann is compelled to attribute to the 
germ-substance a faculty of self-correction; that is to 
say, generally speaking, a determinant will, if it receives 
a somewhat richer supply of food, check it by its own 
force, so that it will be neglected, and the determinant 
in question will become weaker again. By this self- 
regulation the determinants save themselves from 
changing incessantly with every variation in the food- 
supply. The force of self-correction is only overcome 
in rare and exceptional cases of the access of a heavy 
stream of nourishment. Then they grow constantly 
larger, and with them the organs they bring into 

If the enlargement of the particular organ is useful 
for the organism, its possessor is preserved by natural 
selection, and therefore also the growing determinant. As 
the individuals that vary in this way are selected they 
come in time to dominate the species. But if the 
enlargement of the organ is injurious, the animal in 
question is destroyed and the upward movement of the 
determinant is cut off. 

Up to the present we have only considered the 
quantitative changes of the determinants and their organs. 


Irregularities in the food-supply may also lead the 
determinants to vary in quality , and so give rise to 
qualitative variations in the parts of the body 
subsequently. This is believed to be brought about 
by a difference in the growth within a determinant of 
the many biogens that compose it ; this leads to an 
alteration of the structure of the determinants. 

Germinal selection thus seems to explain the dis- 
appearance of useless organs. These also have, of 
course, one or rather several 1 determinants in the 
germ-plasm. And while decreasing determinants of the 
necessary organs are rooted out with the animals they 
are in, as they are insufficiently equipped for the 
struggle for life with their undersized necessary organs, 
on the other hand the decreasing tendency is preserved 
in useless organs, because their possessors are not 
extinguished by selection. In this case enlargements 
of useless determinants are cut off. Such growing 
determinants take the nourishment away from the others, 
and cause them to be smaller. But they must not 
become smaller, since they build up important and 
indispensable organs. Hence rising tendencies in the 
determinants of useless organs are cut off, and only 
those are preserved that keep them down and reduce 
them in size. In this way the determinants and their 
organ must gradually disappear within the species. 

Here we have the principle of selection. There is 
a kind of struggle for nourishment among the deter- 
minants in the germ. If one of them has become large 

lr lhe eye, for instance, must have several determinants, otherwise 
each part could not vary of itself. Hence there must be an immense 
number of determinants in the germ. 


owing to some chance increase in its food-supply, it is 
particularly favoured in the struggle. If it becomes 
smaller, it is gradually crushed out, because the food 
is taken from it by its neighbours. 

Hence on this theory there can only be a limited 
amount of nourishment in the germ. If it were 
inexhaustible, a tendency to increase in the determinant 
of a useless organ would not be prejudicial to its neigh- 
bours, as they also would have sufficient food. In this 
way organs would not be reduced to a rudimentary 
condition, since the rising and falling variations of the 
determinants would neutralise each other in the general 
crossing, as we have already seen. 

According to the theory of germinal selection, there- 
fore, the amount of nourishment in the germ is limited. 
But each determinant must have enough to maintain 
itself. When, therefore, the determinant of a useless 
organ becomes weaker and weaker in each succeeding 
generation, what becomes of the food that formerly went 
to it? As we saw that a determinant only becomes 
stronger by taking food away from its neighbours, so 
when they become weaker, it must mean that their 
neighbours have taken food from them. Thus the 
determinants that are contiguous to the determinant of 
a useless organ will absorb the nutrition that formerly 
went to it. They will grow ; and as they become 
stronger they will, according to the theory, continue 
to grow, and so will their respective organs. Hence, 
on this theory, the parts adjacent to a rudimentary 
organ in the body must steadily increase in size. For 
the same reason the parts surrounding a growing organ 


must decrease in size, though not to such an extent as 
to cause injury to the organism. But there is no trace 
to be found in reality of either process. Therefore, the 
hypothesis of a germinal selection cannot be sound. 

A number of experts have raised objections to this 
hypothesis of germinal selection . 1 It has been pointed 
out that we must assume that a determinant which 
has increased in size owing to an accidental addition 
to its food-supply will sink to its old level as soon as 
this addition ceases. It is quite arbitrary to ascribe to 
a living force — such as the determinant is — the power to 
retain the increased size it has obtained from a better 
food-supply when this supply has diminished. If a 
gymnast strengthens his arm by exercise, it will not 
remain at its full strength if he afterwards abandons 
daily practice. If such complex structures as the 
muscles of the arm are not able to maintain the force 
they have acquired in this way when the exercise is 
abandoned, how much less will this be possible for a 
minute particle of living matter, which is so much 
exposed to vacillations in its supply of food ? 

It is just as arbitrary to identify size and force. A 
determinant that has increased in size owing to better 
nourishment has not necessarily acquired a greater 
power of obtaining food than the neighbouring deter- 
minants that have remained small. We should be 
equally justified in assuming that the shrinking deter- 
minants are so much the “ hungrier.” There is no 
direct physiological relation between force and size. 

1 Professor Emery of Bologna and Professor Thomson of Aberdeen 
are the only two distinguished authorities who have fully subscribed to 
the theory. 


We might put a long list of questions to germinal 
selection. Whence comes the greater amount of 
nourishment that overcomes the self-regulation of the 
determinants, and thus represents the real source of the 
variations ? To what extent can a determinant grow 
without injuring its neighbours ? How is it that 
irregularities of the food-supply within a determinant 
do not often lead to a complete transformation of it, 
instead of merely altering its quality a little? 

But we have seen that we must reject the theory of 
germinal selection, and may quit the subject. In the 
next chapter we will return to it for a moment, in 
order to disprove it once more from a different point 
of view. 

Let us now look about us for other principles to 
explain how organs reach a certain height owing to 
constant definitely directed variations, so that at some 
stage they acquire selective value and may be further 
advanced by selection. 

There are experts who say that external influences 
may not only affect an organism in the course of the 
individual life, but that these modifications are trans- 
mitted in a weaker form to its offspring, and are 
accentuated in these, since they remain exposed to the 
same influences. Thus in the course of generations the 
external agency, which always remains the same, will 
modify the animal more and more in a definite direction. 
This steady variation in one direction owing to external 
influences is called orthogenesis. 

Orthogenesis is, clearly, a subdivision of the 


Lamarckian principle, and as we have rejected the one, 
we need not linger in discussing the other. However, 
we will say a few words about orthogenesis, as in 
speaking of the Lamarckian principle we dealt almost 
exclusively with the inheritance of changes brought 
about by the actions of the animals, their energy and 

Animals are said to be permanently affected chiefly 
by the following external agencies : climate, the char- 
acter of the soil, and food. Thus the stimulus of cold 
may provoke a thicker coat of hair in many animals. 
This will be transmitted to the young, and as the cold 
continues to affect them in turn the hair will grow longer 
and longer. In this way the animals will vary in one 
definite direction as long as the stimulus lasts. 

It has been alleged in support of this view that many 
poisons make organisms more sensitive the longer they 
act on them. That, however, only shows an increase 
of the action of a stimulus during the individual life, not 
that the increase is inherited. 

But there is an experiment that seems to prove the 
inheritance of a stimulated effect. In this the pupae of 
a butterfly, the large tortoise-shell, were exposed to a 
cold of 1 5 0 Fahr. The butterflies that were developed 
from them were much darker than the normal specimens. 
A couple of these modified animals were crossed, and 
from the ova, which were developed under entirely 
natural conditions, came caterpillars that afterwards 
changed into tortoise-shells of a shade similar to that 
of the parents, or slightly lighter. 

Had the modification ot the parents by cold been 



transmitted to the offspring ? It is not necessary to 
suppose this. We can just as well imagine that the 
lower temperature affected the whole pupa, and even 
penetrated to the germ-cells contained in it. As the 
wings especially were affected by the cold, that may 
have been the case with their determinants in the 
germ-cells ; these being so profoundly influenced that 
even after the cessation of the cold they brought about 
modified wings. “ Medium influences,” such as climate, 
for instance, can often not only modify an animal, but 
also penetrate it and modify its determinants. 

Thus the experiment does not prove that the 
modifications of an organ brought about by a 
stimulus will on their side influence the corresponding 
determinants in the germ ; the stimulus may reach 
them directly. We do not know how far or how 
often these medium influences on the germ may act, 
and so we will not linger over this principle, once it 
has helped us to take away an apparent support of 
the Lamarckian theory. 

The explanations offered us by the hypothesis of 
an orthogenetic action of constant stimuli are not 
satisfactory. The Lamarckians say, for instance, that 
certain mammals, such as whales and walruses, have 
almost entirely lost their hairy coat owing to the 
constant action of the water. In other animals the 
water is said to have formed horny plates on the 
mucous lining of the palate, as in the tortoises, the 
duck-bills, and the whales. We may ask, then, why 
the water has not reduced the fur of the otter, the 
beaver, the seal, and the water-rat, and why we find 


no horny plates on the palate of the crocodile, the 
dolphin, and other aquatic animals ? The external 
influence is the same in the case of all these animals. 
Why is there a different reaction in the various animals ? 

And there is yet another question. What is the 
extent of the influence of external stimuli ? If the 
water causes horny plates on the palate of certain 
animals, they must continue to grow indefinitely. If 
apes have acquired certain protuberances by sitting, 
these will go on growing until they become monstrous 
swellings, if the effect of the stimulus is increased 
with each generation. 

It has been said in reply that an organism at length 
inures itself to these permanent stimuli, and ceases to 
react on them. But this only raises another difficulty. 
What is the basis of this power of adaptation ? Perhaps 
it will be said that it depends on a certain adaptive 
power of the body. But how did this come about ? 
And when the animal has become inured in this way 
what is the service of it ? Moreover, it must last for a 
longer or shorter period in different animals. 

In a word, we see that the action of external stimuli 
in the transformation of organisms must be very slight. 
The real force must lie within the animals themselves. 
It is due to this that the body responds to external 
stimuli in so far as it is to the interest of the animal. 
The adaptiveness of living things, which must have a 
scientific explanation, puts out of court all the Lamarckian 
hypotheses, and therefore also orthogenesis. 

* • • • • • • 

It is the opinion of many authorities that natural 



selection alone does not suffice to explain the origin of 
species, and that we are compelled to postulate a pur- 
posive internal formative energy in organisms. But 
before we deal with these writers, we will describe a 
recent theory which does not directly reject natural 
selection, but greatly restricts its sphere of influence. 
This is the “mutation theory” of the botanist, Hugo 
de Vries. 

De Vries questions especially whether the actual forms 
of life are due to ordinary variations. He says that 
they are not inherited pure , and appeals to artificial 
selection, as, for instance, in many kinds of grain. These 
are never independent of selection, because as soon as 
cultivators cease to watch and select them, they quickly 
return to the parental species. Thus no character can 
be fixed by natural selection to such an extent that it 
will remain as a permanent quality of the new species 
when selection has ceased. 

There is a second reason why natural selection cannot 
have created the actual forms of life from variations. 
The variations, he says, are restricted ; they cannot 
increase indefinitely, and can at the most only double 
the original character. We have, for instance, con- 
siderably increased the amount of sugar in the beet 
by selection, but that is all. Further, there has been 
no increase in the size of gooseberries since 1852, 
though one cannot see any reason why they should 
not have become as large as pumpkins. There must 
be an internal limit to variability. 

Hence de Vries believes that ordinary variations 
cannot have produced the actual species. They must 


be due to special variations, which he calls mutations. 
These mutations have long been recognised ; they 
rarely occur, and the feature of them is that the 
organism is modified by them at a bound, in several 
directions at once. Thus, amongst a number of plants 
that de Vries was cultivating, most of which varied in 
the usual manner, there were some that departed from 
the species in several directions simultaneously, and so 
were very conspicuously altered. When de Vries 
crossed these “ mutations ” with each other they 
produced plants of just the same kind. In other words, 
contrary to the variations, the mutations retained their 
new characters from the beginning when purely cultivated. 

Species have been brought about, he thinks, by these 
mutations. Owing to certain internal causes the species 
have, he thinks, suddenly divided into several with a 
number of new characters which they all retained. 
These mutations take no particular direction ; they are 
partly useful, partly indifferent, partly injurious to the 
organism. Natural selection weeds out the unfit, but 
has no influence on the survivors. It cannot improve 
the latter ; it must take the individuals as they are, 
modified simultaneously in several directions. 

Thus, whereas we have so far considered the trans- 
formation of species to be due to the fact that each 
organ was slowly modified in connection with its 
environment, in the sense of adaptation, this new theory 
suddenly shatters the whole conception. When we 
reflect on this we are disposed to join those who reject 
the mutations as the formers of species. We know 
that the species are made up of adaptations, and these 


can only gradually have been evolved from variations. 
The complete adaptations cannot possibly have arisen 
from a modification of the organism by mutation ; that 
would be an excessive trust in the fortune of chance. 
On this theory a mutation of a butterfly’s wing would 
imply that all its parts suddenly developed different 
colours. But we must not expect that in this hap- 
hazard variation the colours would harmonise in such 
a way as to form a picture of a leaf ! Even if an 
imperfect leaf-design were formed, it would not be 
improved at the next mutation, as the colours of all the 
parts would change at once ; even if the colours that were 
wanting before now made their appearance, the parts 
that had been rightly coloured would be destroyed. 
Let us recall our illustration of the twenty dice. 
Suppose the adaptation consisted in all the dice showing 
the six. The shaking of them in the cup and throwing 
them would represent a mutation. However many 
times we try the experiment we shall scarcely succeed 
in making all the dice show the six. It can only be 
done by throwing each die separately until it gives a 
six, and then letting it stand. But that is just the way 
in which variations occur, and the fixing of them is left 
to natural selection. 

Another objection to the theory of de Vries is that 
the mutations must be neutralised by amphimixis with 
normal animals, as they occur in so few individuals. It 
will very rarely happen for them to be of so favourable 
a character and at the same time for such a crisis to 
come upon the species that all the individuals without 
the mutation will perish. 


Hence the multiplicity of our actual species cannot 
be due to mutations. What can we say to de Vries’s 
objections to variations ? 

It has been rightly pointed out that these objections 
are unsound. In the first place, we have really pro- 
duced new races of dogs and pigeons by artificial 
selection, and these have retained their new characters 
when crossed with their own kind. We may therefore 
assume that in natural selection also the modified 
animals will retain their characteristics when the 
selection has ceased. But even that is not necessary. 
Selection does not cease to act even in pronounced 
species ; it watches unceasingly over the animals, and 
continues to act on them. Hence the variations, even 
if they had a tendency constantly to slip back, must 
lead to new species, as natural selection always cuts 
off all instances of reversion. 

Secondly, even if after a time we reach a limit that 
we cannot pass in artificial selection, it does not follow 
that this is the case in nature as well. We can only 
continue to select as long as the harmony of the various 
parts is preserved, and we do not know what other parts 
of the body we must attend to in our selection if the 
object we are breeding is to have unusual features. If 
we want to increase the gooseberry to the size of a 
pumpkin, it is certainly not enough to select the trees 
that have the largest berries. If we want very large 
berries we must also have changes in the plant’s fibres 
for conveying water and sap, the branches must be 
thicker in a word, there must be a number of changes 
that are not entirely within our knowledge or control. 


But if we reflect on monstrosities in nature, the parasites, 
and the deep-sea animals (some of which have mouths 
of extraordinary proportions, others have stomachs that 
can take in a larger fish than the devourer, and others 
have eyes on the end of long stalks), we must ascribe 
to variations a faculty of indefinite advance. Natural 
selection may produce the greatest monstrosities if they 
are capable of life and are adapted to their environment. 
Japanese breeders have even succeeded in creating cocks 
with tail-feathers four yards long by artificial selection. 

We turn now to those writers who ascribe the 
development of the organic world to a formative energy 
that was present in living matter from the beginning. 
This energy is supposed entirely of itself to impel 
organisms to assume more and more advanced forms. 
Living things would have the forms they exhibit to-day, 
on the whole, even if they had been subject to quite 
different influences, and if the geological changes of the 
earth had been different. Natural selection, they say, 
does not create species by adapting animals to new 
conditions, but the animal forms were built up by the 
internal force, without any influence from external 
conditions. This was done by the species diverging 
from each other in characteristics of no value in animal 

We need not delay long with this theory, because we 
know that the foundation of it is unsound. We have 
seen that the species is first and foremost a collection 
of adaptations. But adaptations cannot arise from some 
independent formative energy working on its own 


account. It is of their very essence that they be in 
harmony with the external conditions of life, and these 
are brought about by a totally different force — the force 
that effects the geological changes of the earth. As it 
is a fact that the organisms have always been modified 
in correspondence with the geological changes of the 
earth’s surface, since the adaptations always harmonise 
with the new condition of the earth, the two forces 
must go together like two mutually regulated clocks. 
And as the forces have nothing to do with each other, 
we can only explain their agreement by postulating a 
third force that controlled them from the start. If we 
do this we abandon all attempt at scientific explanation. 

If we want to explain a phenomenon satisfactorily we 
have to bring it into line with a more general and better 
known phenomenon within our experience. But we 
must not ascribe to this phenomenon any characteristics 
which we do not really know to be present in it ; and 
in experience we are only acquainted with the corporeal 
and with movement, matter and force, the material of 
chemistry and physics. 

What do we mean by reducing one phenomenon to 
another ? It means that we can show the one to be a 
necessary consequence of the other. The phenomenon 
to be explained must have a cause, of which it is the 
necessary effect. We have, therefore, satisfactorily 
explained a phenomenon when we show that it is the 
effect of another of which we know by experience that 
under certain known conditions it is bound to produce 
the effect in question, and that these circumstances are 
actually given. Thus we explain the luminosity of 


lightning by showing that electricity is generated by the 
friction of certain bodies, that from this a luminous 
spark must arise, and that these conditions are realised 
in a storm. 

In the same way we give the most satisfactory 
explanation of the phenomena of life when we trace 
them to the known processes of physics and chemistry. 
However, our actual biological knowledge is much too 
scanty for us to give this explanation in full. But we 
may ask if it is possible in a general way to give a 
physico - chemical explanation of the processes of life, 
or if it is not in the very nature of life to elude such an 
explanation. Here we find two contradictory opinions. 
One holds that a physico - chemical explanation of life 
is possible ; that is mechanism. The other denies that 
it is possible ; this system is known as vitalism. 

All that we have said hitherto was based on the 
mechanical conception. The principle of natural 
selection, which we have chiefly employed, enabled us 
to give a mechanical interpretation of the organic world. 
If living things came into existence and were trans- 
formed by natural selection, we need only physico- 
chemical forces to explain the process. 

The Vitalists say, however, that natural selection is 
just as incapable as any other mechanical principle to 
explain life. Let us see which property of organisms 
it is that the Vitalists declare to be particularly 
inexplicable by physico-chemical means. 

In the first place, they object that the Mechanicists 
have never yet succeeded in giving a purely physico- 
chemical explanation of the vital phenomena. But this 


merely implies that our present means and knowledge 
do not suffice for constructing a mechanical explanation ; 
it does not follow that there will always be insuperable 
difficulties in the way of it. On the contrary, we have 
already good reason to say that a mechanical explanation 
of life is possible. We have already given a physico- 
chemical analysis of some aspects of the vital processes 
which were formerly attributed to a vital force. There 
are certain substances that are only found in the living 
body, yet have been artificially produced by chemistry. 
Uric acid is the best known of these. 

The Vitalists reply that we must put outside the 
category of real vital phenomena all aspects of the vital 
processes that can be conceived as purely mechanical. 
But it has been rightly pointed out to them that the 
problem before us is : Can the vital processes be 
conceived as physico-chemical? If the Vitalists say it 
is the characteristic of vital phenomena to be incapable 
of being conceived as physico-chemical, they are begging 
the whole question. 

I have already said that we do not know under what 
conditions the chief elements of the organic body, the 
albuminoids, are produced. Living albumen is still an 
unsolved problem for us. Hence our knowledge of the 
living substance is as yet much too scanty for us to 
construct successfully a mechanical explanation of the 
vital processes. 

It has been established by careful research that the 
same amount of force is used up by an adult organism 
in its vital activity as is taken into it with its food. 
Hence all the actions of the body are exactly 



proportioned to the amount of force contained in the 
food taken. But if these actions proceeded from a 
special vital force, the amount of energy introduced in 
the food would be superfluous in the body. 

Thus Vitalism is inconsistent with the law of 
the conservation of energy. It has, therefore, been 
modified into what is known as Neo-Vitalism. Generally 
speaking, this theory admits that the same physico- 
chemical forces are at work in living things as in 
inorganic nature. But while the mechanical processes 
alone are found in the inorganic world, living things 
are also subject to other principles which are not found 
in inorganic nature. 

We shall see something of this “teleological” 
governing force in the next chapter. Here we will 
only say that a unified conception of the organic and 
inorganic worlds is preferable to the Vitalistic, especially 
as we know only mechanical events as facts. The 
Vitalists do not help us to understand the organic 
world. They only question whether the problem can 
be solved mechanically. 

There are, they say, two characteristics of organisms 
in particular that cannot be understood mechanically — 
their form and their purposiveness. 

It is true that all living things have a form, not only 
the individuals as a whole, but even in their smallest 
parts. The forms of organisms are conditions of 
equilibrium. If we recall the simplest forms of living 
things, those of the tiny protozoa, we find that they 
are generally globular. The round shape is the foi m 
of equilibrium of a fluid body, and we saw at an earlier 


stage that protoplasm is fluid. Thus the form of the 
lowest organisms may be compared to that of a drop 
of water. The shapes of other protozoa are explained 
by the membranes that cover them, which cause the 
departures from the globular form by their inequality 
in thickness and extensibility. The forms of the lowest 
organisms are, therefore, parallel to forms in the 
inorganic world. In fact, in the latter there are forms 
that are far more difficult to understand than those of 
the protozoa — the crystals. 

But how do we explain the forms of the higher 
organisms ? 

We have seen that these forms have been developed 
from the lower ones. No extraordinary forces were 
employed in this evolution ; the new organisms 
were in each case the outcome of an accidental, local 
coincidence of physico-chemical conditions. 

But is not chance itself incapable of being understood 
mechanically ? 

No. Chance, in our sense of the word, has nothing 
to do with the miraculous. Every accident, on which 
we count, is the ultimate effect of a whole chain of 
successive causes and effects, in all of which only 
natural forces are at work. We are, therefore, quite 
convinced that “ chance ” is to be explained physico- 
chemically ; though we grant that the causes which 
have determined it are not known to us. We have an 
excellent illustration of the matter in a ball that has 
been thrown on the ground. Chance determines at 
what spot it will stop rolling ; in other words, the spot 
cannot be calculated in advance, because the various 


forces and conditions that impel the ball towards it are 
not known to us. 

The Vitalists say that none of the marvellous forms 
of the organic world can have been brought about by 
chance, any more than the chance agencies that effected 
the geological changes of the earth’s surface could have 
constructed a Parthenon or a steam-engine. But it has 
been pointed out that even these structures owe their 
origin to chance. Did James Watt go to work with the 
idea of making a steam-engine ? Not at all. He came 
by his first thought by chancing to observe the pressure 
of the steam in lifting up the lid of a kettle. He then 
confirmed his observations by assiduous experiments, 
and so he and his successors erected machines that 
advanced step by step, always selecting the useful and 
rejecting the useless. The Greek style of architecture 
arose in the same way. Natural selection acts 
analogously. We will, therefore, regard its explanation 
of the forms of the higher organisms as satisfactory. 

Does the purposive reaction of organisms to external 
stimuli point to the presence of an internal vital 
force ? 

It is suggesed that such a force, independent and 
self-existent, must react purposively on all influences, 
just as a magnet attracts all pieces of iron. But we 
know that this purposive force often fails in living 
things. An amoeba will take into its body and retain 
for some time a particle of stone lying in its path, just 
as it does with food. The relation of flowers and 
insects also is often unsuitable. Many animals have 
died out because they could not adapt themselves 


suitably to their suddenly altered conditions oflife. We 
saw that, generally speaking, animals have the power of 
suitable reaction or adaptation only in their customary 
environment. A mole-cricket tries to bury itself in a 
glass plate instead of running away ; a bee stings a 
human being, though the sting will be fatal to itself, 
and so on. If the purposive reaction in the vital force 
of animals were independent of the external world they 
would be armed against all contingencies ; and that is 
not the case. Far more probable is our hypothesis that 
the animal’s power of adaptation has arisen by gradual 
development under the controlling influence of external 

Matter and force determine the series of cause and 
effect, as we know from experience. To this no 
exception has been found. On the other hand 
there are many exceptions to the purposive power of 
organisms ; and that shows it is not determined by any 
internal law. 

We have a proof of non-purposive development in the 
rudimentary organisms. Humanity would be far better 
off if the human frame contained no ccecum. How 
frequently, moreover, the “purposive power” goes 
astray during embryonic development, and brings into 
the world hydrocephalous children and other deformities. 
Then there is the power of regeneration ; it would be 
of great service to all animals, but is found well 
developed in very few. Do not some animals have a 
larger measure of it than others? Why, then, are 
they particularly favoured ? In a word, the vital force 
raises so many new difficulties that are not raised by 


the mechanical conception that we are bound to prefer 
the latter. Selection is precisely proved in a most 
striking way by the imperfectness of the adaptations. 

Finally, the objection has been raised against the 
mechanical theory that all evolution pre-supposes some- 
thing that cannot be explained physico - chemically. 
This is the will to live. The struggle for life is not 
imposed from without on organisms ; it is rooted in 
their own will. Selection would accomplish nothing — 
it would effect no improvement if living things did not 
strive to maintain themselves and reproduce. 

We cannot accept this view. The will to live is 
synonymous with the impulse of self-preservation. 
This is an instinct, and we said that there is no difficulty 
in attributing the origin of instincts to natural selection. 
Moreover, the will to live and to reproduce is not 
primary. It is certainly not present in the lowest 
protozoa. These have no will to nourish themselves. 
They travel about and take into their bodies everything 
that comes in their way. If the particles are digestible 
they are used for building up the animal ; if not, there 
was no use in absorbing them. When the lowest 
mobile algae swim towards the light, they do not do 
this in virtue of a will to live, but because an attractive 
force has been developed in their frame by selection that 
impels them towards the light, which is important to them. 

Still less can we speak of a will to reproduce. The 
cleavage of an amoeba clearly means merely that when 
it has absorbed a certain quantity of food it breaks up of 
itself, just as steam on the window runs down at length 
in drops. 


A considerable number of animal characteristics have 
been produced by a purely passive selection. Protective 
colours, for instance, are of this kind. In this case the 
least conspicuous animals are preserved without any 
action on their part. 

Now that we have shown the untenability of the 
bases of this theory, we need not go into its consequences 
in detail. When it is said that the basic particles 
were fully developed by their impulse to act, that the 
action of the will in the body leaves behind it an 
hereditary disposition, and that the animal organisation 
is embodied volition, we can only say that these 
statements postulate the Lamarckian principle which 
we have rejected. 

We conclude, therefore, that the value of natural 
selection consists in its enabling us to form a unified and 
mechanical view of the world. In order to appreciate 
this fully, we will now go on to consider the nature and 
the significance of mechanism. 



An attempt to refute the theory of evolution. Establishment of 
theories and investigation of details. Causes and effects. Infinity 
of same. Impotence of science. Infinite variety in the products 
of organs. The infinite diversity of the universe. Purpose. 
Mechanical and teleological causes. There is no end in the 
development of animals. Sexual selection, orthogenesis, and 
germinal selection are teleological. Purification of the theory 
of selection from teleological elements. There are no higher 
and lower animals. A high grade of organisation gives no more 
advantage to an animal than a lower. Natural selection is not an 
absolute principle of betterment. The scientific method of 
research. Infinite diversity of the universe. Comprehension 
of same by concepts. Abstraction of the universal. What a 
natural law is. Ultimate constituents of bodies. Comprehension 
of the world by ultimate elements. Mathematics. An ether 
without properties enables us to grasp the world. Does ether 
exist ? Are psychic processes to be conceived corporeally ? The 
methods of psychology. Consciousness. The world and the 
soul are only to be conceived as contents of consciousness. 
Transition from science to theory of knowledge. 

As we have in the previous chapter refuted the 

objections to the theory of selection, we may now state 

our position in the following theses : 

The present living inhabitants of our planet have 

been gradually developed from the simplest forms in 

the course of long terrestrial epochs. The latter 

themselves have been developed from inorganic matter. 

The evolution was and is the work of natural selection, 

a principle that rests on the general laws of nature, and 



so enables us to understand organisms on a mechanical 

We have already observed several times that there is 
no longer any serious objection urged against our first 
thesis, or against the general theory of evolution. It is 
true that objections continue to be raised by a few men 
of science. A book appeared recently in Germany that 
spoke of “the break-up of the theory of evolution.” But 
the gist of the work was merely that we cannot establish 
with certainty the descent of the various classes of 
animals. The objection overlooks the fact that the 
theory of selection has done enough as a scientific 
theory when it shows in a general way the reasons 
why we must suppose one species to have been evolved 
from another; of this we have plenty of instances. 
The fact that we cannot for the moment determine the 
stages of development of the various classes makes no 
difference to the general theory ; in fact, even if it were 
true that we could not reconstruct, even in broad out- 
line, the genealogical tree of an animal group, this 
would not in the least affect the truth of the theory of 
selection. The detailed efforts to construct the genea- 
logical trees of the animals lie outside its province ; they 
are not scientific at all in the same sense. They come 
within the range of a totally different science — history. 
We shall see this better if we consider the historical 
side of the theory of evolution. 

Objections of this kind, therefore, do not injure the 
theory of selection or of evolution ; they merely show 
that in many cases it is difficult, if not impossible, to 
trace the ancestry of an animal. But no reasonable 

360 Darwinism and the problems of life 

man of science has denied this. The transformation of 
one species into another can only be established with 
certainty in a few cases — such as that of the Porto- 
Santo rabbit. That is natural enough, as this trans- 
formation lasts far too long and is far too gradual to 
come under human observation. We may, therefore, 
readily grant that we cannot establish the selective value 
of variations in particular cases. We cannot do this 
solely because we do not know what is of value in the 
life of the animal. And if that is impossible with living 
animals the conditions of whose life are known to us, how 
can we be expected to show the selective value of 
variations in animals that have evolved to their present 
forms in earlier ages. We do not know the accidents — 
the isolations — that determined selection to modify them 
in a particular direction, and so cannot know what has 
selective value for this particular direction. All that we 
can say is that a variation will have selective value if it 
favourably influences the strength of the particular 
animal, as that will lead to an increased multiplication 
which must be gradually prepared. It is clear, at all 
events, that there must be a large number of small 
variations with selective value, and that it is incorrect 
to say that there are hardly any variations with selective 

The action of natural selection cannot be directly 
observed in nature, we must admit. But this admission 
does not cover a defect of the theory of selection. 
There are many theories the truth of which cannot 
be established by direct observation. It is said that 
light is due to the vibration of the minute particles 


that fill the universe. But has anyone ever seen this 
vibrating ether ? It is the same with the theories that 
explain the nature of electricity and magnetism. The 
value of scientific theories is not that they can be 
verified by direct observation, but that they bring all 
the material under one point of view, and so make 
it intelligible. Natural selection prevails wherever 
there is life. 

• •••••• 

Can science make the whole world intelligible to 
us, then ? 

When a man of science seeks to explain a 
phenomenon he looks for the cause of it. When he 
has discovered this cause his task is not over ; the 
question then arises, what was the cause of this cause ? 
Even when this is settled the work is not ended. 
Every cause is at the same time the effect of another 
cause. We never reach an ultimate cause that is 
cause only and not effect, because the chain of cause 
and effect, the various links of which are the 
phenomena of the universe, is infinite. 

We have, for instance, discovered the cause of the 
erosion of the sea - coast in many places to be the 
waves of the sea, the cause of these to be the lifting- 
up of the surface of the water, and the cause of this 
again to be the attraction of the sun and moon. 
Science presses onward, and brings more and more 
links of the chain of causes out of the depths of the 
perplexing ocean of events. Will the whole chain 
ever be brought to light? No, that can never be. 


It is the very nature of the infinite that we can set 
no limit to it, before or after. 

We may go further. The distance from the earth 
to the sun is very considerable, but it can be 
expressed by a definite figure, and so is finite. When 
the sun is at its zenith and we stand on a chair, we 
are really a little nearer to it, but may say that the 
difference is insignificant in view of the colossal 
distance. However, the cosmic chain of causes is 
really infinite. No matter how many causes we 

determine, we do not come a single step nearer to 
infinity. Hence the results of scientific research are, 
in comparison with the reality, not only very slight, 
but almost nothing, and will ever remain so. 

When we inquire into the nature of the matter 
that composes the whole world we are face to face 
with infinity once more. However much we sub- 
divide bodies we always come to other bodies, and 
never to anything that gives us an insight into their 
essence. That is easily understood, as it is the 
property of every body to be divisible ; hence the 
smallest particles must always be bodies and nothing 

Hence bodies are divisible to infinity. And in this 
process we encounter a second infinity. No part of 
a body is like another, so that when we break up 
matter, we discover an infinite diversity of its particles. 
It may be said that that is not true; that when we 
analyse matter we come to the elements, some 
seventy in number, of which all matter is composed. 


Thus the ultimate particles of bodies would not be 
infinitely varied. But who can tell us that these 
ultimate elements, the atoms, do not differ from each 
other? No one has ever seen an atom. We know, 
at all events, that when we break up an element such 
as gold we do not produce absolutely identical 
particles ; they always differ in contour, in size, or 
other characters, as we see clearly when we examine 
them carefully, if possible with a microscope. It is 
true that they have much in common, but they are 
not therefore equal. If it is said that their differences 
are so slight that we may overlook them, the state- 
ment is arbitrary, and not based on the nature of 
things. It is not at all evident in nature that the 
general is more important than the individual. 

When we see a couple of horses at a distance they 
often seem to be alike, but we find on going nearer 
that they are different. It is certain that the particles of 
the elements differ more from each other than our 
feeble eyes can detect. Finally, for all we know it may 
be that if we pushed our analysis far enough we should 
come to elements with nothing in common. 

The third infinity is the diversity of phenomena and 
bodies that meets our eyes. A science that would 
investigate the world cannot master its material ; the 
infinitely numerous and varied bodies and processes 
cannot be described in detail, much less investigated. 

Must we then fold our arms ? Can we never grasp 
reality as it is. 

No. No human mind can grasp the world as it is. 


It must first make it intelligible — must transform it. 
Then it may succeed in grasping the world. 

Mechanism endeavours to understand the world, and 
has succeeded to a certain extent. But before we inquire 
how it solves the riddle of the universe, we must first 
make clear the unity of the world, even in relation to 
organisms, which it implies. We have, therefore, to 
exclude entirely from the organic world the non- 
mechanical theory. 

• •••••• 

We saw something in the previous chapter of theories 
that deny the identity of living with lifeless matter. 
We rejected these theories. Now we will deal with 
the common ground-work of them all. 

They hold that the chief characteristic of living sub- 
stance is its aiming at an end. They think that there is 
latent in every ovum a force that comes into play in the 
development of the ovum, and controls the evolution so 
as to attain the end — the fully-formed organism. In the 
same way, they say, there was a force in living matter 
from the start that aimed at advancement, and has con- 
tinually realised its end — the creation of higher forms — 
until it produced man as the crown of its work. 

We give the name of teleology to the view that the 
evolution of living things was controlled by a plan 
or end. 

There is, of course, causality in the teleological system. 
But it differs from that we have already considered. In 
ordinary causality the cause thrusts the effect from it, as 
it were ; causes and effects follow each other eternally, 


without there being any aim that influences the whole 
series. What often seems to us to be the goal or end 
of the series is only a link in it, followed uninterruptedly 
by other links. Thus, for instance, the construction of 
a living thing from the ovum is not a halting-place in 
the series of causes ; they continue their endless course 
beyond it. 

But in teleological causality there is such a thing as an 
end or purpose. It is true that here also cause and 
effect follow necessarily on each other, but the end has 
the power of attracting causes and effects to itself so that 
they do not run beyond but realise it. According to the 
teleological view the construction of an organism is the 
end which the whole embryonic development is aiming to 
realise. The end, as it were, observes and controls the 
series of causes, and is realised in the ultimate effect. 
The very first causes were controlled by a fact that was 
still in the future. The ordinary causes, which we have 
discussed, can only produce an effect when they them- 
selves have already been brought into existence as an 
effect. Teleological causes or ends act before they are 
themselves realised. 

We rejected in the previous chapter the notion that 
organisms aim at the realisation of ends. Seeking an 
end would be the greatest conceivable form of purposive- 
ness. But the rudimentary organs, the erratic instincts, 
and the many imperfections in nature prove that the 
evolution of animals is not wholly controlled by pur- 
posiveness. Moreover, how is it that an end is merely 
sought in some animals and realised in others? We 


may recall, for instance, the vascular system of the 
amphibians and birds ; the former have clearly a much 
more ingeniously constructed heart than the latter. 

In the individual development of an animal, where 
there seems to be an end, the processes are regulated 
by natural selection, a mechanical principle. The germ 
cells give rise to others in unbroken succession and also 
the bodies surrounding them, which are continually 
dissolved again into inorganic matter. Thus the 
causal series of the living matter continually sends out 
side-branches, as it were. The main trunk endures 
uninterruptedly as life ; the effects of the side-branches 
lead into the inorganic world and continue indefinitely 
there as lifeless processes. 

If the construction of a living thing were the aim of 
the germ cells, impelling them to realise it by their 
development, how is it that it so often fails ? Why are 
there mis-births? Why, above all, is the “end” no 
longer fully attained when natural selection has ceased 
to act ? Surely the degenerations effected in panmixis 
show clearly enough that the ontogenesis is not aiming at 
an immutable purpose. If natural selection ceases, the 
harmony of development is always, though gradually, 
disturbed, and some misshapen object formed. Civilised 
man is always inferior in strength, hearing, and sight to 
his ancestors and his savage fellows. How is it that the 
end has suddenly lost its force in his case? 

It is clear, therefore, from panmixis that there is no 
end controlling the development of animals with a view 
to its own realisation. Such an end would not be 


dependent on natural selection, a principle that it really 
excludes. The development of civilised man is becoming 
less and less purposive ; the fact that men are not yet 
more short-sighted and weaker is because panmixis has 
not yet lasted long enough to bring about conspicuous 
degenerations, and because natural selection has not 
entirelyabandoned man even in regard to his bodily frame, 
as in the majority of cases excessive weakness or short- 
sightedness prevents a man from earning his living and 
so from reproducing. The majority are always con- 
tributing new blood to the “higher orders,” and this 
improves the corporeal debility that distinguishes the 
latter on account of their condition and occupations. 

Science, especially, has no need of teleology, because 
it cannot regard as facts causes that act before they are 
themselves realised. According to the teleological view 
the evolution of the actual organisms must aim at a 
remote end, and this end must accomplish their trans- 
formations. If that were so we should have to give up 
all idea of a scientific investigation of the organic world. 
We could not study this end, as the future does not 
exist, and so we can never determine in what way the 
end regulates the modifications of animals; we cannot 
detect their real causes. 

For these reasons we must reject the teleological 
causes that are supposed to influence the beginning 
from the end, these “ final causes ” as they are called in 
opposition to the “ efficient causes,” which proceed 
gradually onward. We can safely do this, because the 
principle of selection enables us to give a purely 


mechanical explanation of the evolution of living 


We know that the theory of selection is a mechanical 
principle. Just as the pebbles are rolled about in the 
stream, the smaller ones going farther and the larger 
remaining behind, so we find the action of natural 
selection. Chance — or causes and effects that are 

unknown to us, but which we know to be of a 
mechanical nature — determines whether the whole 
species is to be transformed or whether it divides. 

The principle of selection itself has been generally 
recognised as mechanical. But this has been denied 
of its two postulates. It has been said that the varia- 
tions are not universal, or do not diverge in all directions, 
but only in a few. If the variations were universal why 
could we not produce, for instance, a cock’s spur on a 
pigeon by selection ? 

We need not delay with this difficulty, as we settled it 
in dealing with the mutation-theory in the previous 
chapter. We cannot breed a spur on the pigeon 
because we do not know what varieties of pigeons to 
select for the purpose. That the occurrence of varia- 
tions is not the same in every species is clear from the 
fact that many animals of very different classes have 
assumed the same form. I need only mention the 
parasitism of the spiders, crabs, and worms . 1 

1 If we wish to form a scientific and harmonious conception of the 
world, we can only use mechanical principles in explaining it. 
Mechanical natural selection can do nothing without postulating 
variations. Hence if we wish to explain the organic world mechani- 


Against heredity the objection has been raised that 

ordinary variations were not preserved, and that it was 

cally, the variations must depend absolutely on mechanical grounds. 
If it is assumed that the variations only follow definite directions and 
are restricted — if, in other words, there are limits in the organisation of 
animals that prevent the variations from passing a certain measure — 
they are no longer mechanical ; in that case there is a force in 
organisms that avoids unserviceable and aimless changes — a purposive, 
teleological force. Variations do not then depend on chance — which 
alone would be mechanical — but are directed according to definite 
internal principles. 

Thus we see that variations cease to be mechanical as soon as they 
are assumed to be definitely directed and limited. Natural selection 
is then no longer a mechanical principle, and a unified conception of 
the world is impossible. As soon as a Mechanist recognises variations 
of that kind he abandons the possibility of a harmonious system, and 
is no longer a Mechanist. It is just the same if he recognises other 
principles that can be shown to be teleological, as we shall show 
presently of sexual selection and the Lamarckian principle. If he 
would remain a Mechanist he must abandon them in this case. That 
is mere logic and consistency. But even if one holds the mechanical 
system to be impossible and unattainable, these theories are none the 
less useless, if they are teleological. He considers the development of 
living things to be due to a purposive internal force, and so must 
regard natural selection, the Lamarckian principle, etc., as merely 
subsidiary. These theories have real value only for a Mechanist, and 
they must, therefore, be mechanical. 

It is said that if there are no limits fixed in the nature of the animals, 
natural selection would be able to equip the horse with wings and 
create all the fantastic forms of our legends and fairy tales. How do 
we know that it cannot? Is the legendary dragon more wonderful than 
the ichthyosaurus or the plesiosaurus ? Does it not show an unlimited 
capacity when a sort of tape-worm is developed from a spider, and a 
being that scarcely looks like an animal out of a crab? The point is 
worthless on other grounds. The transformations of the animal world 
are due to the fact that those survive which are most in harmony with 
their conditions at the time. Hence when it is said that certain animals 
ought to have arisen, one must have had some knowledge of the 
conditions of life of the evolving sped s at the time. But we do not 
know them — in the case of the horse, for instance. Horses with wings 
would only be developed if the conditions of the horse were such that 
the best leapers survived (compare the origin of the insects). But that 
can hardly have been the case. 

2 A 


not the adaptations, but the indifferent characters, that 
were retained in the species. We have already settled 
these difficulties. 

Hence natural selection with its two postulates is a 
purely mechanical principle that has never been unsettled 
by any solid objections. And as we have concluded that 
it alone accounts for the evolution of living things, we 
can answer “yes” to the question whether the organic 
world can be conceived in a purely mechanical sense and 
whether it can form part of a unified cosmic system. At 
the same time we admit that it is not yet possible to give 
a satisfactory explanation of the vital phenomena. 

However, it is only pure natural selection that serves 
to explain the organic world. All the auxiliary theories 
are teleological. 

This is true in the first place of sexual selection, or at 
least of the second category of sexual selection — choice 
on the part of the female. In this instance we should 
have an end acting before it is realised. When a 
musical apparatus was developed in the cricket, for 
instance, we may very well ask how the females came 
to be attracted by this particular sound at its first 
occurrence, while they take to flight at all other sounds ? 
Even if it is said that curiosity drew them to the new 
sound, it has not yet been explained how it is that the 
females yield more readily to the fiddling crickets than 
to their silent fellows. In every case we have to assume 
that the chirping sound pleased the females. The same 
must be done when it is sought to explain any of the 
other masculine characteristics. The females must have 


some sense for them before they are developed, if they 
are to be recognised at once and selected ; and they 
must be equally sensitive to any increase in the 
characters. Hence the male characteristics act before 
they exist ; in other words, sexual selection even in its 
simplest form is teleological . 1 

The Lamarckian principle, also orthogenesis, rest on 
teleological foundations. The statement that certain 
organs have attained their higher development by 
inheriting the effects of exercise supposes that the 
organism in question acts consciously, and that there 
is a special disposition in the animal’s body. And when 
explanations are offered us such as that pressure causes 
the skin to become thicker in some animals and thinner 
in others, that is to credit the organism in question with 
a purposive adaptability and regulate this so as to attain 
the end that is to be explained. The Lamarckian 
principle postulates a force in animals, in each case, that 
strives to attain an end, and exercise and other agencies 
merely help it to attain it. 

The third auxiliary theory to natural selection, 
germinal selection, may also be described as a 
teleological principle. In the first place this hypothesis 
supposes that the germ has a purposive faculty of self- 
correction, controlling the advancing and retreating 
movements of the determinants in most cases. But 
purposive forces within a determinant must above all 
things prevent too unequal a nourishment of the various 

1 We have already shown on p. 82 that female choice seeks to attain 
an end. 



biogens that compose the determinant. Irregularity in 
the nourishment of the biogens of a determinant would 
alter their quality. But why does the unequal growth 
of the biogens, owing to irregularities of nutrition; never 
disturb the harmony in the determinant, as is the case 
with panmixis? In fact, the harmony of the parts 
should be far more profoundly disturbed in the deter- 
minants than in degenerating organs. In the latter 
case the controlling influence of natural selection never 

entirely ceases, while irregularities in the food-supply of 
the determinants can never be controlled by natural 
selection, as they only give occasion to selection to come 
into play when they give rise to variations : in other 
words, they always precede selection. Hence when we 
see, for instance, that the determinants of a bird’s feather 
are almost never modified in such a way as to produce 
scales or other malformations instead of a feather, we 
must assume that there is a purposive force in the 
determinants also that ensures the harmony of the 

But our task is not completed when we reject the 
teleological auxiliary theories from natural selection in 
order to have a purely mechanical principle. Teleolo- 
gical phrases and terms are only too easily slipped into 
the theory of selection itself. In fact, we ourselves 
have not been quite exact in our expressions in the 
nine preceding chapters. We had to do this so as not 
to confuse the reader by using unfamiliar phrases. The 
teleological always comes more naturally to us than 





the mechanical, as we are accustomed to looking for 
ends and purposes. But as we have given only- 
mechanical processes in the character of facts, we need 
now merely rectify our form of expression. 

In the first place we must give up the term 
“purposive.” There can be no question of “purposes” 
in a scientific investigation. We can only speak of a 
structure in an organism as purposive in the sense that 
the animal has the faculty of self-preservation in its 
momentary circumstances. 

We must also be careful in using the word “evolu- 
tion.” When we speak of the evolution of the animal 
world, the thought involuntarily forces itself on us that 
they have advanced from lower to higher forms. But 
we have no right to speak of “lower” or “higher” 
forms. We should in that case have to suppose that 
there was from the first a principle in the living 
substance that gradually creates the higher forms, and 
we have rejected that view. By higher and lower 
animals we can only mean more complex and sivipler. 

Natural selection is not a principle of progress, always 
creating higher animals. Selection merely seeks to 
adapt organisms better to their environment. But 
greater complexity of organisation has no relation to 
good adaptation. We pointed out previously that man 
is not better adapted than the bacillus. From the 
point of view of the birds man must be a very 
imperfect being. 

If greater intricacy of structure were the same thing 
as better adaptation, natural selection would gradually 


have to give all animals a complex organisation, since 
it always seeks the better adaptation of all animals. 
But we still have protozoa living in a drop of water. 

In fact, many highly organised animals have become 
extinct, while their more simply constructed relatives 
have survived. 

There may be occasions in which the more complex 
organisms are at a disadvantage in comparison with the 
simpler. Natural selection will then modify organisms 
in the direction of greater simplicity. In our view of 
the development of the earth there will really be such 
a time one day. The water on our planet is constantly 
decreasing, and the time will come when there will not 
be sufficient left to support human life, when the bones 
of the last man will bleach in the unclouded glare of the 
sun. But in the last drops that will linger in holes in 
the vast desert of the earth there will certainly still be 
infusoria. After a time even these creatures will not 
find water enough ; they will perish, and only simpler 
organisms still will be maintained, until at last all living 
matter has returned to its mother and changes into 
lifeless mineral once more. 

The fact that there are to-day animals at such 
different stages of organisation is due, as we now know, 
to special accidents that isolated certain animals. Even 
the step that seems greatest to us, the formation of 
multicellular organisms, must have taken place at a 
particular locality — whether it was that certain protozoa IB 
reached running water and so the connected ones were 3 
less easily washed away, or that they reached a pond 


that was poor in oxygen and could only make a 
sufficient use of the oxygen by sticking together. The 
imagination has a wide field in these problems, but we 
cannot say whether the construction of multicellulars 
only took place once or on several occasions. 

As natural selection is not a force that of itself creates 
more complex organisms, so it is not an absolute 
principle of progress. It is scientifically illogical to say 
that animals are “ improved ” by natural selection. 
“Good” and “bad ’’are antithetic and dualistic terms 
that have no place in a unified conception of the world. 
The word “ improve ” would only have a meaning if we 
recognised any value in the nature of animals. But 
that is entirely wrong. The man of science has only to 
determine the processes of the world and discover their 
causes. For him there are only changes in the world. 
There can only be an “ improvement ” if we recognise 
an end, the good. Mechanism has nothing to do with 

Even if we could recognise value in the nature of 
animals, we could never say whether certain changes 
that we observe in animals are improvements or no. 
Selection adapts animals to their environment at the 
moment, and we do not know if these will not change, 
in which case the opposite modifications will have to be 
selected. For instance, if the animals with the thickest 
coats survive in a very cold climate, we cannot say that 
the selection of the thick coat is an improvement for 
the animals. If that were so the cold would have to 
remain unchanged, whereas the climate may become 


warm again. If it does the animals with the thinnest 
coats will be in the best position. 

When we reflect on the past history of animals and 
find that a long time ago thick-coated animals were 
selected because the cold persisted, we cannot even 
then speak of an improvement. We have not to consider 
the chains of cause and effect in relation to what they 
eventually lead to, as that would be teleological. We 
have to look on each change only as the effect of a past 
cause. When we are studying the past, we must leave 
the present out of account. It would be unscientific to 

predict the persistence of the cold. 

• • • • • • • 

We have now purified the theory of selection of all 
teleological elements and prepared it for incorporation 
in Mechanism. We may now return to the question 
from which we started, and ask if Mechanism gives us 
a satisfactory explanation of the world and how it does 
so. We have to examine its method, and as this is at 
the same time the method of all natural science — in 
its higher forms — we shall learn to appreciate scientific 
method generally. 

We have already seen that it is the infinity of the 
world that prevents the human mind from comprehending 
it. We will now go more fully into the point. 

When the man of science approaches the object of his 
investigation, the world, he feels himself surrounded by 
a bewildering wealth of forms that he can never compass. 
The corporeal world is infinite in its variety and 
inexhaustible. No-one thing' is like another ; everything 


represents an object that can never be entirely replaced 
by another. Quite apart from the incalculable distance 
of the stars, one cannot even count in detail the bodies 
contained within a limited space. No stone is quite 
like any other, no tree like another, no leaf, indeed, 
exactly like another. It is, therefore, quite impossible 
to describe every single thing in the world. 

But even when we abandon the idea of grasping the 
whole universe, and turn to the study of a small part of it, 
we encounter insuperable difficulties. Every part of the 
world, no matter how small, has so many differences 
latent in it that they cannot be counted. The more 
thoroughly we study a single body the more vast do we 
find the number of differences in it. If we continue to 
analyse a body, we bring to light at each analysis new 
things that were unknown to us. And as each surface 
has its colour, and this always differs, we can never 
exhaust the shades of colour of even the smallest 

This enormous diversity in nature not only prevents 
science from comprehending the world, but no human 
being could orientate himself in the world if language 
did not come to his assistance. Language enables the 
human mind to take in a large number of details by 
imposing the same name on them all. The whole 
infinitely varied population of the earth, differing in 
each individual, can be grasped by the term “man”; so 
those predatory animals of the forest, not one of which 
is quite like another, by the term “wolf.” We gather 
together all the objects in inorganic nature by means of 


names, just as we take certain metals of which there 
are only pieces that differ in size, shape, contour, 
and colour, under the name “iron.” 

How is this comprehension of individually different 
bodies possible ? By regarding only that which objects 
have in common and overlooking the individual features. 
When, for instance, we give the name “gold” to a 
large number of objects, we look merely to the common 
brilliance, the colour, and the weight, and do not take 
account of the difference of the pieces of gold in size, 
angles, surfaces, etc. 

Science continues the work of language, as it were. 
It brings together a number of bodies by regarding 
merely what they have in common. In this way it 
creates scientific concepts. A certain number of the 
countless particular things in the world, which have 
certain common features, are “conceived.” But science 
has something further to do. It must give definite 
formulae to its concepts, so that we may know what 
is the common element in the particulars that the 
concept embodies. That is done by a number of 
propositions or judgments. The scientific conception 
must always be capable of conversion into judgments. 
Judgments of this kind on the concept “diamond,” for 
instance, would run : transparency, refraction, hardness, 
definite angles of the surfaces, etc. 

A good deal is accomplished by these concepts. 
Large numbers of diverse things have been made 
comprehensible. But the number of these concepts, 
in turn, is immense, and science would have done 


only half its work if it were content with these. There 
must be subordinating concepts, expressing the common 
element in a certain number of concepts. Thus gold, 
silver, iron, and other minerals are grouped together as 
“metals.” As science extends its range, and looks to 
the common element in the subordinating concepts 
themselves, it seeks at last to pursue its method to 
a point where it is impossible for direct observations to 
determine the common features. 1 hus we not only 
conceive the seventy elements to consist of homo- 
geneous atoms, but also that these seventy different 
kinds of atoms are at bottom composed of the same 
particles, or primitive atoms [such as electrons]. The 
diversity in the structure of the elements is due to a 
difference in the grouping of these in the atom of the 
element. Hence the ultimate particles make up the 
whole material world. They are the common element 
in all matter. 

Not only the bodies, but also the phenomena, in 
nature are infinitely varied. When we speak of 
“storms,” we are grouping together a large number 
of different phenomena, with respect to the common 
feature in them. Phenomena also are grasped by 
science through general concepts, which express the 
common element in them. 

However, these concepts require something further. 
They must be free from space and time, if they are 
really to embody all that has happened, is happening, 
or will happen, in the world. They must have a 
universal application, because it is only then that they 


can express an infinite number of phenomena, and it is 
precisely infinity that has to be overcome by the 
formation of concepts. We can, of course, only form 
our concepts in a limited number of instances, but we 
must make them capable of expressing all phenomena 
of the kind ; they must apply universally. To the 
concepts which take the form of judgments and apply 
to certain phenomena of all time we give the name of 
natural laivs. A natural law embraces an infinite 
variety of particular processes, and embodies what it 
is important for us to know in them. 

Just as a large number of concepts of things are 
arranged under one comprehensive object-concept, so 
we find in the case of law-concepts, or natural laws. 
In the end science comes to formulate one ultimate law, 
which embraces all the phenomena of all time. The 
other laws are only special cases of this law. 

Thus the final outcome of science is the formulation of 
an ultimate object-concept, which is common to all bodies, 
and an ultimate natural law, that embraces all pheno- 
mena. When that is accomplished, the infinite diversity 
of the world is overcome. We have then no longer to 
grasp endless series of causes and effects ; we merely 
' conceive the one law that dominates the whole series. 
Our mind no longer needs to arrange in itself the incal- 
culable number of different bodies and occurrences — a task 
it could never accomplish ; it has now to deal with one 
body and one phenomenon. Thus the infinity of the world 
is mastered. We can now make all the bodies in the 
universe intelligible at any time by means of a certain 


combination of ultimate things ; in other words, we can 
express all bodies in arithmetic formulae. Numbers are 
always comprehensible ; they have no particular features 
in themselves, and so lack the diversity of forms that is 
found in reality. We know, especially, that we can 
count in a series as long as we like, and we will never 
come to anything essentially new. Like bodies, we can 
also represent all phenomena by certain arithmetic 
formulations of the one law, which is all we have to 

But this comprehension of the world will only be 
possible if the “ ultimate things ” are fundamentally 
distinct from the bodies that we know. All the objects 
known to us change. Each of these changes passes 
through an incalculable number of stages, and the 
ultimate things, which must be calculable, cannot be 
changeable. They must not be transitory. They must 
also be indivisible , as all division is change. Finally, 
they must be exactly alike in size and quality. Each 
ultimate thing must be capable of being replaced by 
another without the least change taking place ; other- 
wise they cannot be used in mathematical formulae. 

Mechanism endeavours to realise this ideal of know- 
ledge. There is only one thing that is common to 
all others and enters into the composition of all that 
begins to exist — ether. There is only one law that 
embraces all phenomena — the movements of ether. 
Ether is a space-filling but imponderable medium, con- 
sisting of minute particles, which are simple, immutable, 
indivisible and homogeneous. All the phenomena in the 


world, electricity, light, and the rest, are special forms of 
ether-movement; even matter is to be regarded as an 
ether-movement, since the ultimate particles that make 
up all bodies are centres of condensation in the ether. 

It is the task of science, therefore, to determine the 
various categories of ether-movement, and to express 
light, electricity, and even matter in mathematical formulae. 

Will it ever be possible to analyse bodies so finely as 
to bring the ether-particles to light? No. Apart from ' 
the fact that every portion of a body must be itself a 
body, not incorporeal ether, the latter entity has no 
features of reality. In the reality that surrounds us 
there are only divisible and transitory things, of which 
no one absolutely resembles another. Each body, how- 
ever small, has its individuality ; this becomes all the 
clearer the more thoroughly we study it. Thus the 
apparently similar grains of sand betray their individual 
differences under the microscope. But the ether- 
particles cannot have individual characteristics, and 
so they are quite unimaginable. The world speaks 
to us through all our senses with its infinite character- 
istics , 1 and we cannot picture to ourselves bodies with- 
out properties, such as the ether-particles must be. 

1 Thus the ether-particles explain phenomena and matter. But the 
ultimate elements of matter also, the primitive atoms, are something 
unreal, because they must be absolutely identical, and because no 
further body can be produced by subdividing them. In fact, the 
atoms themselves cannot have individuality. But we know that there 
cannot be anything that is not individual, and that no body is 
absolutely identical with another. We must, therefore, regard even 
the atoms only as a device of knowledge. We see here the value of 
such a contrivance. Chemistry has made marvellous achievements 
precisely through its atomic theory. 


They are in contradiction with the reality that we 

It has been said that when we exhaust the air under 
a glass-bell and the light remains in it, we see the 
vibrating ether. But it has been rightly answered that 
even then we do not see ether, but light alone. 

There is no ether, because there is nothing in the 
world without properties. Ether can never be the 
object of research ; it is only a means of understanding 
the world. 

We come to the following important conclusion. 
Natural science does not represent reality to us as it is. 
Reality, as it reveals itself in the world, is absolutely 
incomprehensible to any science or any human being, 
because it is infinite. Science cannot deal with it as it 
is ; it has to transform and simplify it. It does that at 
the very outset of its work. Its first concepts do not 
picture reality, but apply to it ; this is done by leaving 
out of account a part of what distinguishes reality — the 
individuality of each particular thing. As this work of 
transforming to render intelligible proceeds, and more of 
the individual characters fall out in the higher concepts, 
science departs further and further from the visible 
reality. Its ultimate concept, which has to embrace 
all, and so must have nothing individual about it, can 
have nothing in common with reality. It is not a 
reality, but an indispensably necessary means for grasping 
the whole world. 

Natural science is occupied with bodies, and forms 



its concepts on these, so that they exclude anything 
incorporeal. Hence it has nothing to do with psychic 
phenomena. These can never be understood from the 
observation of bodies and their processes, because the 
corporeal can never explain anything but the corporeal. 
Science canj never tell us how the simplest sensation 
comes about. Even if we had an exact knowledge of 
the mechanism of the brain, even if we knew all the 
movements of the atoms in feelings of desire and pain, 
we should only be witnessing the movements and shocks 
of bodies. It is true that the sensations are connected 
with these, but they tell us nothing about the origin and 
nature of the sensations. Being incorporeal, the sensa- 
tions lie beyond our range of observation. 

The psychic processes are dealt with by psychology. 
This science, again, is confronted with an infinite variety. 
No one can dream of picturing to himself all his pains 
and pleasures, his ideas and judgments. Each psychic 
process occupies a certain time, and so passes through 
an incalculable number of stages. 

In order to master this diversity, psychology forms 
concepts in relation to the universal in the particular 
psychic processes. It endeavours to find the elements, 
or the simplest constituents, of the psychic life, of which 
we must conceive all the psychic phenomena to be 
composed. “ Sensations” have been advanced as these 
elements, and it is said that the will and the ideas, in 
fact, all the psychic processes, are made up of these 
elements. But experience knows nothing of “sensa- 
tions ” that may constitute such diverse processes as a 


will and ideas. Hence in this sense the sensations are 
merely scientific devices, like the ether-particles of the 
physical scientist. 

We saw that Mechanism has accomplished its task 
in making the world intelligible to us. Psychology 
makes a similiar effort to solve its problem, but, being 
a younger science it has not achieved nearly so much 
as physical science. We may now ask whether it is 
not possible to bring together the ultimate concepts of 
both these worlds, and so attain a perfectly unified and 
harmonious knowledge. 

We have rejected the opinion of the materialists who 
hold the psychic processes to be the object of physical 
science. Can we say the reverse of this ? Does not 
the corporeal world consist of psychic processes ? 

The reader who has never reflected on problems of 
this kind will think the very question is an absurd one. 
We are accustomed to regard the world about us as 
existing quite independently of us. But that is certainly 
not the case. 

All our knowledge of the material world comes 
through our senses. But all that passes through our 
senses can only give us sensations. The various 
properties that make up the complete image of a body 
are merely so many sensations within ourselves. A 
piece of gold seems to be a body, but this body is 
made up of the sensations of yellow, hard, heavy, cold, 
etc . 1 It is the same with all bodies. Hence men in 

'These sensations, of course, must not be confused with the psychic 
sensations that make up will and ideas in the sense described above. 

2 u 


whom one sense is missing have a totally different idea 
of the world from ourselves. If the missing sense is 
restored to them by an operation, they can hardly 
recognise their world with it. A blind man whose sight 
has been restored cannot recognise the bodies about him 
until he has touched them. 

Sensations give us information of the external world 
when they reach our consciousness. How often do we 
not look at our watch without noticing the position of 
the hands, or touch an object without perceiving its 
existence ! When we are asleep the world has ceased 
to exist for us. 

When other men tell me that the world continued to 
exist while I was asleep, their movements and voices 
create nothing in me but sensations, and of these I only 
know what reaches my consciousness. Even my own 
body is only known to me by processes of consciousness; 
when I am not conscious of it, it does not exist for me. 

There is no sense, no reality, in the world that we 
can bring into opposition to consciousness. There 
is nothing that is not a content of consciousness. That 
is a truth that cannot be shaken ; in fact, it seems to be 
the eternal immutable foundation of the clashing 
structures of theories about knowledge. All that we 
experience and live, all that we see and feel, consists 
of conscious processes. 

Here we refer to ordinary, individual sensations, familiar to everyone 
under this name. We shall not go into the question whether there are 
conscious and unconscious sensations. When it is said that the sensa- 
tions must reach our consciousness, we are merely following the usual 
form of speech. 


This is not the place to treat the question whether 
the processes of consciousness bring the external world 
before us as it really is, or whether this real corporeal 
world, the “thing in itself,” is not something quite 
different from what we imagine ; whether it does not 
merely set our conscious processes in motion without 
revealing itself. Or whether in the end conscious 
processes can only be evoked by other conscious 
processes ; whether there is no external world corre- 
sponding to them, and its causes and effects only exist in 
our thoughts. These questions would lead us into 
endless controversies. We have only raised the point 
to see whether Mechanism can be reconciled with 
psychological science, or whether it dissolves in it. 

That is not the case at all events. The material 
world is a process of consciousness, it is true, but so are 
the psychic phenomena. We may make it clear in the 
following way. 

The material world can only be conceived as a content 
of consciousness. Consciousness is, as it were, the 
subject and bodies are the objects ; that is to say, the 
bodies are the objects to be known and consciousness is 
the perceiver. But my consciousness perceives not 
only the bodies apart from my own body, but also this 
itself ; it may even become an object of knowledge itself. 
But that is not the whole function of the knowing 
subject. My whole psychic life with all its processes may 
become the object of the cognitive faculty of conscious- 
ness, otherwise there could be no psychology, which 
needs objects to investigate. Thus we see that 


consciousness encloses in itself not only the whole 
corporeal world, but also the whole life of the soul. 
This cognitive power is devoid of all personality. But 
we cannot suppose that the all-embracing, impersonal 
subject, which enfolds the whole of existence, appears 
in isolation ; for us it is always connected with a part of 
the psychic life. In this sense one might call psychology 
a higher science than physical science. But the reason 
is merely that we cannot study the whole of the psychic 
life simultaneously , and make it the object of knowledge. 
However, we will not go any further into this difficult 

We have seen that reality contains two separate pro- 
vinces, the material world and the psychic life, nature and 
mind. Either province may become the material or the 
object of science, and the scientific method may be 
applied to either — the method that enables us to grasp 
the enormous diversity of objects by grouping many of 
them together with respect to their common features. 
As the two sciences proceed to form more and more 
comprehensive concepts in this way, each of them comes 
at length to the ultimate and all-embracing concept — 
ether for the material world and psychic sensations for 
the spiritual world. In this way physical science and 
psychology put the keystone on their respective 
structures, and have then to elaborate and develop 
their systems in detail. To throw light on and 
reconcile the two ultimate concepts is the task of a 
new science, which has to bring reality into unity 
without taking into account the antithesis of body 


and soul. It is consciousness that encloses in 
itself all existence, the material and the spiritual 
world, since both provinces can only be conceived as 
processes or states of consciousness. In consciousness 
we have a unity and a truly “ monistic ” stand-point. 
But consciousness, the all-perceiving subject, can never 
become the object of an empirical science. When we 
wish to study it, we have to leave aside the scientific 
method and turn to philosophy. This is the last 

and the highest science. It is the foundation on 
which every theory that aims at comprehending reality 
must rest. It is the undying merit of Immanuel Kant 
to have shown us the way to it. 



Truth of scientific ideas. Why the universal seems to us more 
essential than the individual. The ideas of animals. Why we 
take ideas for realities. Thinking reality into ideas. Is there 
a real world, lying behind the phenomenal world? Natural 
science itself is a human product and pursues an aim. It must 
not regard itself as the only sound branch of science. The 
historical sciences. Their method. The historical elements in 
natural science. The laws justify historical research. The science 
of evolution rests on probabilities. The origin of the human 
mind. Had consciousness a beginning ? There never were 
absolutely simple bodies. History and sociology. Origin and 
development of primitive man. Origin of good and evil. Origin 
of conscience. Advance of civilisation by tradition. Language. 
Conflict of nations. Scientific ethics. Restricted and inverted 
selection in civilisation. The evils of war and militarism. 
Nietzsche’s egoism. Darwinian ideas of the social future. 
Insipidity of the Darwinian ideal. Social man according to 
Nietzsche. Natural science knows no idea of duty. It knows 
nothing of values, and can therefore frame no ethic. Preservation 
of existence is not preservation of value. Is there a sense of 
life? Monism. Presuppositions of science. The idea of duty 
is the beginning of all knowledge. Conclusion. 

The world is infinite and immeasurable, and no science 

will ever be in a position to describe it. Science would 

not yet have accomplished anything if its work had 

merely consisted in describing or picturing the world. 

It could only attain to a knowledge of the world by 

transforming reality and simplifying it so as to make it 

39 ° 


intelligible to the human mind. But it follows from our 
theses that reality is infinitely varied on the one hand, 
and that scientific theory stands higher in proportion to 
its simplicity on the other, or that scientific theory is the 
more perfect the less reality it reflects in its concepts. 

This statement in no way diminishes the importance 
and objectivity of science. Although the scientific 
concepts are not pictures of reality they are very closely 
related to it. There cannot be any unscientific 
arbitrariness in science because its concepts are 
universally valid. They are unconditionally true , not 
because they depict reality but because they apply to it. 

How is it, then, that it is not obvious to everyone 
that ideas do not correspond to individuals ? How is it 
that so many people think there is some reality 
corresponding to the idea “ wolf,” whereas the idea has 
only been found by the mind transforming the reality in 
order to grasp it ? 

It is because, in the first place, man’s senses have 
only a limited power of discrimination. Widely 
differing objects often seem to us to be alike ; even on 
closer examination we often see only their common 
features, and do not see their individuality until we look 
carefully for it. Many bodies, such as grains of sand, 
seem alike to us however closely we examine them ; it 
takes a lens or a microscope to show that not one of 
them is absolutely similar to another. But that our 
senses perceive common features first and foremost, and 
that our intelligence always recognises first the common 
features of the objects about us, is clearly a faculty that 



we owe to natural selection. How could we orientate 
ourselves in the world if every single object about us 
were something peculiar and had its special name? We 
should have to describe and count so much that we 
could never make ourselves known to another ; he would, 
in fact, never have a clear idea of the body we were 
speaking of, unless we could bring before him a number 
of bodies which are familiar to him in their common 
features. There would be no language if there were no 
general terms. 

We must assume that the nerve-centre that receives 
a sense-impression was so constituted from the first, even 
in the animals, as to perceive especially the common 
features. The fox must have general ideas of “ hare ” 
and “ man,” in order to know which to pursue and which 
to flee. If all things appeared to him to be unlike each 
other, everything he met would be something new, and 
he would not know how to act in relation to it. 

The simpler the life of an animal is, the less advanced 
are its senses and the more comprehensive its concepts. 
For the frog there are only “ stationary ” and “ moving ” 
things, and of the latter only “large” and “small. 
The former it avoids, the latter it pounces on. 

The development of an animal’s senses is always in 
proportion to its habits of life. Hence there are 
animal senses that can detect the individual better than 
the corresponding sense in man. Take, for instance, 
the dog’s sense of smell. As a general rule animals 
recognise individual realities better the more advanced 
their senses are. Man has created devices for improving 


his senses, optical instruments, which enable him to 
detect the special features even in the smallest bodies. 

However, common features always come much more 
naturally to man’s perception than special ones, because his 
senses are adapted to them. Thus it seems to him that the 
general features alone are essential, and physical science 
is thought to be the most natural of all sciences because 
it starts from the proper nature of the sense-impressions. 

Hence in order that man may orientate himself in the 
world, numbers of things have to be brought together 
in virtue of their common features and provided with a 
common name. And as most things have not a very 
great interest individually, because this is not necessary 
for the purposes of human life, they generally have only 
generic and not proper or individual names. When we 
speak of the individual we have only the generic name 
— “ wolf,” for instance — and so this name or concept 
seems to us really to coincide with the individual in 

But there are also things in the world that have an 
individual interest. They have generic names, but also 
proper names, and in this case it is clear that the con- 
cepts are not perfect images of the individuals. We 
see this especially in the case of man. If we try to 
express the individual “ Shakespeare ” by the idea 
‘ poet or “ man, ’ we see at once that these ideas do 
not represent the great poet, and do not embody pre- 
cisely those features that make Shakespeare Shakespeare. 
When we say “ poet ” instead of Shakespeare we are 
really doing just the same as when we say “ wolf” of a 


particular wolf, or when we express a certain plant or a 
certain piece of gold by the corresponding concepts. 
There are also stones that have an individual interest, 
and here again it is clear that they are not fully 
expressed by their generic ideas. Take, for instance, 
the diamonds Orloff, Star of the South, or Kohinoor. 

The concepts are not definite pictures, because they 
do not mirror reality ; but we think this into them, 
and thus they appear to be pictures. When we speak 
of wolves, we always think involuntarily of a particular 
wolf. When we say “ man,” we think of a particular 
man — with a medium-sized, straight nose and other 
definite features, just as when we make sketches of 
the objects. 

Thus the reality is always forcing its way into our 
narrower concepts, but it does this less in the case 
of those with wider range. It must be difficult to 
imagine a “vertebrate” — impossible, if one has never 
seen one. Try to form a mental picture of an 
“animal,” without thinking of the features of the 
protozoa, worms, insects, birds, or other organisms. 

Thus we see that the concepts are less definite and 
depart more from the reality the “better” or more 
comprehensive they are. The ultimate concepts, that 
embrace everything, cannot become mental pictures ; 
there is nothing of reality in them. 

It is true that when we think of “ether,” we picture 
to ourselves tiny balls, pushing and attracting each 
other, and in a state of perpetual motion ; such an idea 
enables us to grasp a mechanical process in the world. 


But we must never forget that when we do this we 
think something into ether that is really not in it. The 
ether-particles cannot be balls, otherwise they would 
differ in size and be divisible ; they would, in fact, be 
bodies with the properties of bodies, and that is just 
what we must avoid. The ether-particles must have 
nothing individual about them, and therefore they are 
unimaginable, and have nothing in common with 
reality; they lie behind reality, and are metaphysical. 
Their movements also are unimaginable, as we can 
only picture to ourselves movements of bodies ; we 
know no such thing as movements of incorporeal 

But, it may be objected, is not reality only apparently 
individual ? Is there not, behind the reality that we see, 
something that represents the true reality ? And may 
not this be simple and non-individual ? If that were so, 
it would be the task of science to pass from the apparent 
world which we see to the true homogeneous world 

But such a statement has little value, since no one 
can prove it. On the contrary, it is highly improbable. 
The commencement and the advance of the scientific 
formation of concepts is — as no one will question — an 
artificial modification of reality. Only the individual 
exists, only that appears at a definite spot, is never 
repeated, and is gone for ever once it is destroyed. 
When the human mind brings together a number of 
these bodies, by looking only to their common features, 
it has no idea of picturing them altogether. How could 


it happen that after forming higher and higher concepts, 
depicting less and less of the things comprised, suddenly, 
when the whole thought-process was over, the “ ultimate 
things ” once more contained the complete reality ? 
When man began and continued to form concepts, he 
regarded the world from which he started as the sole 
reality ; he by no means sought after a “ metaphysical,” 
true reality. It would be a piece of good fortune that 
we would have to put down to magic if at the 
conclusion of his process of thought the final result 
represented the true and different and hitherto unimagined 

No, it is incredible. We must assume that science, 
which ever presses on, and must press on, towards 
greater simplicity, and so is always analysing bodies 
afresh without ever coming to an end, imagines the 
process of division to be complete. In that case we 
need not assume that in the continued disintegration of 
bodies we shall come at length to parts that are not 
bodies. We shall then see that the ether-particles were 
created by the human understanding, because it needed 
them in its effort to understand nature. 

Physical science is described as empirical, and the 
designation is correct. But we must not on that account 
suppose that science never goes beyond the range of 
experience. It deals with probabilities as well as exact 
observations. When it deduces a “law” from a 
number of phenomena that it has observed, it assumes 
that this law will hold also for other phenomena of the 
same category ; and this assumption in turn implies 


that there are general laws which apply universally and 
unconditionally. This, of course, can never be proved. 

It is possible that new observations might be made 
that compel science to rearrange all its laws. However 
that may be, physical science is not absolute and 


unconditional, because it supposes that what is true in 
a thousand cases will not prove untrue in the next one . 1 

Thus science is influenced by considerations that do 
not arise of themselves from reality ; it is also a product 
of the human mind, and endeavours to achieve its task 
of making reality intelligible. Hence physical science 
has no right to oppose other sciences which modify 

reality in order to attain their ends. 

• • • • • • • 

The concepts which are formed with regard to the 
universal alone cannot contain the particular. As the 
laws of physical science deal with what applies always 
and everywhere they cannot answer the question, what 
exists at a particular point of space, what happens in 
detail, and how that which exists came into being. 

These questions are dealt with by the historical 
sciences — or history, in the widest sense of the word. 
Physical and historical science complete each other. 
Hence we find scientific elements in history and 
historical elements in science. 

The historical elements increase in physical science 
in proportion as its ideas approach reality and depart 

1 The laws of science must not admit a single exception. In their 
case the law is not confirmed, but completely destroyed, by the 


from individual things. There is absolutely no historical 
element in the idea of ether, because even if it 
represented something real it would be useless to 
raise any historical question about it. Every ether- 
particle must contain just the same as the others, and 
so it is absurd to seek the particular features of one 
of them. 

However, even in scientific concepts which are 
very comprehensive, but not all-embracing, there are 
historical elements. The sciences that deal with these 
concepts start, in a sense, from a historical fact. Optics, 
for instance, treats of light. But if we have had some 
experience of light, we always think of the light we 
know in that way. If there were anyone who had 
never seen light, he could form absolutely no idea 
of its real nature, no matter how accurately he knew 
the figures and formulae that represent the vibration 
of ether when it causes light. The further question 
arises, moreover, when and where light came into 
existence. Such questions cannot be settled by the 
methods of physical science. 

We could show in greater detail how the historical 
elements in natural science increase in proportion as 
the various parts of the total science decrease in com- 
prehensiveness. But we have not space to do this, 
and will be content to consider the sciences that deal 
with life. 

The problem with which we are concerned, the 
origin of species, is of an historical character. It is 
a question of a process that once took place. Hence 



when we seek to determine this process of evolution 
in detail we have to use a different method from that 
of physical science. We must act on the historical 
method. In point of fact, we rely on documents, as 
the historian does. They share the character of all 
documents of being less valuable the more remote 
they are . 1 

It is not our purpose here to study the principles 
of the historical method. The historian is equally 
unable to represent the incalculable diversity of reality. 
He must select definite points. He will choose 
particular events — or, as every individual thing is 
itself too vast to comprehend — certain particular 

1 The objection is raised that Professor Haeckel has been 
endeavouring for some forty years, with very moderate success, to have 
the natural sciences called “historical" instead of merely “descriptive" ; 
in other words, that it is the chief part of their task to tell us, not the 
actual nature of things, but how they became what they are. The 
reader who has followed me so far will see for himself the error of this 
objection. In the first place, ether can never be studied historically, 
because it had no origin. Anyone who' takes up a manual of physics or 
chemistry will see that in these it is nearly always a question of what 
the law is — what is valid independently of time — not what has come into 
being. There are, of course, historical questions in these sciences, but 
very rarely; their investigations are almost always purely scientific. On 
the other hand, zoology and botany use both methods. In my contrast 
of the two methods, I aim merely at a logical appreciation of them; I 
am not bringing into opposition sciences that differ according to 
their material. I merely say that all our sciences may employ both 
methods, but that one finds the one method more suitable, another the 
other method. The first method determines what holds good indepen- 
dently of all time, by discovering the common element in phenomena ; 
the second determines what has taken place once, regarding, not the 
common but the individual features, and interpreting it according to 
the documents. The two methods are, therefore, of a precisely 
opposite character. 


The historian first chooses his theme. This is 
usually a fact or event that interests him and seems 
worth study. He then examines the antecedents of 
this event, and selects those that have a bearing on 
his subject. Thus a student who is writing a history 
of the preparatory period of the Reformation will not 
speak of fashions in dress or the price of food, but will 
confine himself to the points that have some relation 
to the Reformation. Again, the evolutionist who is 
studying the origin of the vertebrates will only 
describe those of the innumerable changes in the 
animal world that may be regarded as stages in the 
formation of the vertebrates. That is not an 
unscientific procedure — not teleology in the sense we 
described above. The historian neither forces the 
chain of causes towards his aim, nor fancies that they 
sought this end from the first ; he merely studies only 
those meshes in the network of causes and effects that 
lie before the phenomenon whose origin he is investi- 
gating. This way of studying it arranges agencies in 
a straight line, and makes them seem to be aiming at a 
certain result. 

The evidence for the evolution of animals differs 
from that we consult in human history. Most of it 
is of such a character that we have first to justify our 
action in regarding it as evidence. This justification 
is furnished by the laws of science. The law which 
says that organisms are constantly changing, and that 
every living thing descends from some other one, gives 
us the right to regard the remains of the different 


animals of earlier ages as the ancestors of living 
animals, and to determine the historical lines of 
development. The law which says that animals 
resemble each other in proportion to their blood- 
relationship gives us the right to take their structure 
as evidence of their ancestral history. And there are 
still other laws. 

However, these laws only justify historical investi- 
gation ; they do not supply the place of it. They 
apply wherever there are organisms, and therefore they 
cannot discuss the particular process of the modifica- 
tion of a species. A law that has only held good in 
one particular case is an impossibility, because every 
law is formulated by regarding the common element in 
a number of phenomena. Hence the laws of science 
can never bridge over the interval between two 
distinct stages of organic evolution ; indeed, one 
might be acquainted with all the laws that apply 
to organic evolution yet have no idea of the real 
course of this development. 

The laws can never tell us, for instance, how birds 
were developed from reptiles. Again, if there were 
a law which said that in the rise of a nation there 
were always great men who led the people, we should 
not understand from this law alone why Luther in 
particular appeared at the Reformation, or Bismarck 
at the rise of modern Germany, and why these 
special individuals led the people. 

It is in the very nature of the evidence for animal 
evolution to be grounded on greater or less probabilities. 



On that account we shall always find differences of 
opinion as to the value of the historical investigation 
into the transformations of animals. There are recent 
zoologists, for instance, who would confine their science 
to the establishment of laws, and would reject all 
“ galleries of ancestors ” as not affording any 

But that is a one-sided and unjustifiable appreciation 
of science. Even probable transformations in the 
organic world are certainly very interesting. As long 
as man reflects on himself, he will long to know some- 
thing of his earlier history. Every discovery will be 
welcomed that throws light on the obscure condition 
of primitive man. 

In the nine preceding chapters we have made 
simultaneous use of scientific and historical methods 
of research. 

We have, on the one hand, investigated the common 
features in the particular evolutions of living things, 
and thus formulated laws. The most comprehensive 
law that we discovered was that those organisms 
especially survive which are best adapted in their 
structure to their actual environment . 1 This is the 
principle of selection. We found that it holds good 
wherever there are living things. We next tried to 
prove that other laws of evolution do not hold. We 

1 Natural selection is a law because it presents the common element 
in all evolutions, and it applies wherever there are organisms ; but it 
differs from other scientific laws in not definitely presenting the common 
element. It has to use the qualifying clauses “on the average,” or 
“as a general rule.” 


therefore concluded that it must be the sole agency 
that effects the modification of animals. 

On the other hand we sought to determine the 
particular processes of animal evolution by means of 
historical inquiry. For this purpose we used such 
evidence as the structure of animals, fossil remains, and 
so on. We were given the right to do so in virtue of 
natural laws. In this way we succeeded in determining 
the period — if only approximately — and the locality in 
which a certain modification of animals must have taken 
place, and to some extent we were able to follow the 
course of this transformation. 

The provinces of natural science and psychology are 
entirely distinct, as the one forms its concepts on 
phenomena that occupy space and the other does not, 
but the distinction does not hold in regard to historical 
investigation, Bodily and mental phenomena are in 
time, change, pass through stages, and are individual. 

As we have adopted the view that man has animal 
ancestors, we must trace his mind also to them, though 
it is at least a lower stage of development in the animals. 
We saw in the second chapter that, as a matter of fact, 
man’s mental processes are found in a more rudimentary 
form in the animal. 

As we cannot admit that the mind is formed in any 
animal out of nothing, we must ascribe psychic phenomena 
to the protists. We must even go further. We have 
accepted the view that living things were developed 
from inorganic matter. Did psychic phenomena begin 
at once with the appearance of living substance ? That 


is scarcely possible. Living matter, we believe, evolved 
from lifeless. But the psychic processes cannot have 
developed from it, because we know that bodies alone 
can be formed from bodies, never anything spiritual. 

Thus we are forced to ascribe psychic phenomena 
even to inorganic matter. Why they are not recognis- 
able in it, or why they are so different even in the lowest 
animals, it is impossible for us to say. They are subject 
to transformations which become so considerable in the 
course of long ages that something entirely new seems 
to have come into existence. That is all we can 

But this process of transformation only applies to the 
psychic processes, not to consciousness. It is absurd 
to conceive consciousness as evolving from material 
things, and as having any beginning at all. We know 
that we cannot imagine anything either corporeal or 
spiritual, anything real at all, that is not a content of 
consciousness. Time and space exist only in conscious- 
ness. How, then, can consciousness, without which time 
cannot be conceived, have arisen in time? How can 
bodies and psychic phenomena, which always presuppose 
consciousness, have given birth to it ? 

It will be clear to every one who has properly con- 
ceived the world as existing in time and space only as a 
content of consciousness that the creative power cannot 
arise from the thing created, the subject from the object, 
the perceptive power from the thing perceived. 

Consciousness cannot be imagined, because it is 
itself the imaginative force. Consciousness is the 



cognitive force, which creates the objects of its 
knowledge in the very act of perceiving them. Its 
knowledge is action . 1 

It is not our purpose to go into philosophical 
questions. We merely wish to point out the limits 
of the theory of evolution, and show that there is 
something that cannot be subjected to either scientific 
or historical investigation. 

There is one more point that we must make clear. 
We were justified in accepting the view that the 
more complex animals have descended from the less 
complex. The multicellular have been evolved from 
the unicellular, these from unnucleated animals, and 
these in turn from inorganic matter. But we must 
not forget that even the simplest organisms possess 
an infinite diversity, and that each of them has its 
individuality, which can never be completely replaced 

1 The reader who has never reflected on these questions will do well 
to think of himself. What do I know of the world ? What is 
absolutely real and certain about it ? It is absolutely certain that 
there are sensations in me, but that is all. The world, my fellows, and 
all they tell me, are so many sensations in me. It might all be a 
dream ! I know for certain only that something is taking place, that I 
have sensations. I can imagine that I am dreaming of the world, my 
life, and my fellows. This figure should be most helpful to conceive 
the matter. 

My own body and my whole psychic life are only sensations in 
me. This comprehensive sensation, embracing all that occurs, is 
consciousness. It is impersonal, and not bound up with any particular 
man, for his very individuality is a content of consciousness. 

This view does not do away with the reality of the world. The 
world holds its reality as a content of consciousness. All its phenomena 
remain as we know them, and the relations of its various parts and 
phenomena to each other remain, because consciousness dominates 
the whole. 


by another. Even in inorganic matter every particle 
is an “ individual.” It has innumerable properties 
and diversities, and does not entirely resemble any 
other particle. All bodies have been formed from 
other bodies, or — more correctly — all bodies are 
constantly changing, yet never lose their nature as 
bodies. Hence in nature we have only processes of 
transformation. If a protozoon seems to be simpler 
than a human being, and an element still simpler than 
a protozoon, we must never forget that even the 
“simplest” bodies are much too complex to be 
grasped by us just as they are, without any mental 
modification. No theory of evolution, therefore, 
enables us to understand the nature of matter ; that 

can only be done by a mental process of transformation. 
• •••••« 

There is a further province of evolution that we 
must touch on before we conclude — the evolution of 
the human race, the history of civilisation. 

The scientific method has been applied here also, 
and we give the name of “ sociology ” to this treat- 
ment of the history of civilisation. The aim of this 
science is to gather the common features of the 
various forms of human society, and formulate laws 
in virtue of these. 

Thus we can study the common elements in the 
evolution of different races, and draw up laws which 
apply wherever there are nations. In fact, as these 
laws must be independent of time, they must be valid 
in the past and the future, and they enable us, to some 


extent, to forecast the future of the human race and to 
lay down certain guiding rules that may be useful in 
preparing the future. 

Sociology cannot, indeed, ever replace or displace 
history. It can never tell us the real course of particular 
racial developments. For instance, a sociological law 
to the effect that races living on the sea-coast must 
utilise the sea, because that is their only chance of 
survival, cannot give us any information on the interest- 
ing questions, how the first boat was built, who was its 
inventor, and what gave him the idea. 

Nevertheless, in human history natural laws, which 
include the laws of sociology, give us the right to use 
certain evidence, so that we can reconstruct, in its 
general outlines, a history of humanity that has a high 
degree of probability. Let us try to determine the basis 
of this history, which is of considerable importance to us. 

The first men lived in isolation or in families. Their 
special habits — we need not go into them in detail — 
were such that those had the advantage who entered 
into close relations with their fellows, as they could then 
help each other, and take better care of their offspring. 
Thus natural selection would favour the more coherent 
social groups. 

In this way men of a greater social disposition were 
always selected. Those who continued to wander singly 
through the forests were not so well placed in the 
struggle for existence as those in community, and they 
gradually but steadily disappeared. Again amongst the 
social groups those individuals were constantly weeded 


out who menaced the communal life. If they were too 
numerous the whole community collapsed, either from 
internal troubles or in conflict with more coherent 
groups. If these individuals were few, they were driven 
away or destroyed by their fellows, and were unable to 
sustain the struggle in isolation. Thus it is the first 
condition of all social life that no member shall endanger 
the life of another. Hence all primitive men that had 
murderous thoughts against their fellows would be 
gradually weeded out. 

The more coherent the communities, the more com- 
plex the social instincts would become by means of 
selection. The property of one’s fellows would come 
to be respected as well as their persons, and it was 
not long before thieves were put to death. In a 
word, all variations with lower social instincts came 
to be destroyed, and only the most social variations 

Thus from the start those individuals were selected 
whose instincts were the most useful to the community. 
When one of these individuals committed murder, he 
acted contrary to his instinct, and an action contrary to 
one’s instinct is always, even in the animals, accompanied 
by a feeling of pain, as we saw in the second chapter. 
This feeling may have been the beginning of conscience. 
The closer the co-operation in the community, the more 
confidently were those preserved who did not disturb 
the communal life — those, in other words, whose feeling 
of discomfort was strongest if they ever acted against 
the social instinct. In this way an increasing number of 


men were selected whose conscience was pricked, not 
only if they committed murder, but also if they were 
guilty of theft or any other crime against the community. 
That they were able to act at all against the instinct was 
due to the fact that selection favoured not only the more 
social, but also the more intelligent, members. Intelli- 
gence — and intelligence alone — can bring a man to act 
against instinct; just as in the case of the animals it is 
only the most sagacious, such as the dog, that can act 
contrary to their instincts. However, this disadvantage 
of intelligence is insignificant in comparison with its 
many advantages. 

Hence in the first human societies “good ” and “ bad ” 
were synonymous with socially useful and prejudicial. 
Primitive men would not be conscious of such ideas. 
The “ good ” acted unconsciously on their instinct ; they 
were chosen by selection, and the “ better ” were 
favoured amongst their descendants. As the human 
intelligence continued to develop, and gave birth to 
speech, to think and act in a socially useful way became 
a matter of course to them, to such an extent that they 
would regard social conduct as the rule in life, as moral 
or “good, without being conscious of its utility. They 
then endeavoured to foster “ good ” conduct by punish- 
ment and education, and here^again they were assisted 
by selection, which favoured the “best” races. 

The origin of conscience by natural selection is 
confirmed when we turn to study the races that are still 
at a low level of culture. Amongst these, “ good ” and 
bad often mean something quite different from what 


they do with us, and conscience pricks them in regard to 
other actions. It is not necessary to go into details. 
One can read in any manual of anthropology that in 
many races murder, pillage, and even theft are not 
regarded as evil ; that an Indian will feel remorse, for 
instance, because he has not killed anyone, but never 
because he has done so. Adultery, again, is often so 
general that the neglect of it is regarded as a disgrace, 
and it is well known how the men offer their wives to 
their guests in many races. The cannibal never feels 
remorse for having eaten anyone. On the other hand, 
many savages feel remorse for an action that is in our 
eyes indifferent or even good. In fine, one needs little 
acquaintance with ethnography to see that “good” or 
“ bad ” have not a common value for all men, and that 
all men have not got an inner voice that tells them what 
is “good.” 

Educated people have a more sensitive conscience 
than those of a lower condition, and this again is ex- 
plained by natural selection. They usually marry 
refined partners ; at all events they rarely choose those 
with crude feelings and a disposition to gross conduct 
without the check of remorse. Thus, amongst the 
educated, the individuals with the gentler instincts are 
always selected for reproduction, and therefore 
those in whom any violent deed will be followed by 

We could expand this idea much further, but that 
is not our purpose. We wished merely to show that 
conscience offers no difficulty to the man who accepts 


natural selection. It can be understood as an instinct, 
and instincts arise and grow by natural selection. 

But we should be one-sided if we tried to explain the 
higher civilisation solely by selection of the more socially 
disposed and the more intelligent. There is a second 
factor to be considered, even a more important one. 
This is tradition. 

Tradition is found almost exclusively amongst human 
beings. It may be that among the higher animals a 
method of catching prey, or building the nest, or 
singing, is maintained by tradition, perhaps even 
furthered by it, the young learning from the old ; but 
this hardly calls for consideration. It is quite otherwise 
with man. In his case tradition has a solid foundation 
in speech, in drawings and the work of the hand. It is 
due to this that the skill which one man has acquired 
during life is not lost when he dies, but taught to his 
descendants ; they can learn it in a short time, and 
advance it in their turn. In this way tradition brings 
about a certain mental transmission of acquired 
characters, though this has nothing to do with the 
Lamarckian principle, since nothing is inherited. 

Let us take an instance. 

In a certain coast-land a man worked throughout his 
whole life at some contrivance for enabling people to 
travel on the sea. Towards the close of his life he 
invented a boat. If there were no tradition, the 
invention would die with him, and the human race 
would have to wait until some germ-variation happened 
to occur that qualified the man developing from it to 


build a boat once more. Tradition made it possible, 
not only for others to copy the boat, and for their children 
to learn the art, so that it became a lasting possession of 
the people, but also for improvements to be made, since 
the children did not need to reflect all their lives on how 
to make a boat, like the first inventor ; they learned 
the work in a shorter time, and were thus able to devote 
their lives afterwards to improving it, and could transmit 
this knowledge to their descendants. 

The whole of our higher civilisation would be im- 
possible without tradition. Our books inform us of the 
achievements of former ages, and inscriptions and draw- 
ings acquaint us with long extinct races. The objects 
of civilisation are our property, and we build further 
upon them. We have implements from the very dawn 
of humanity the essential parts of which still represent 
the foundation of all creative work. Language, like a 
great river, brings on its waves the achievements of 
earlier generations down to our own time ; it unites all 
generations in an unbroken chain. All this is so 
obvious that we need say no more of the subject. 

What has been attained through tradition may be 
modified and improved by natural selection. Let us 
return to our illustration of the boat. It is quite clear 
that the race whose boats have been improved owing to 
tradition beyond those of a neighbouring, hostile race, 
will be able to defeat the latter in a sea-fight, and so 
spread into its territory. With the people will go the 
traditional possession, the better boat. Thus in a sense 
this has conquered the inferior outcome of tradition. 


To give another instance, let us suppose that a race 
has acquired by tradition such admirable political and 
juridical forms that its co-operation is lifted to a higher 
level. If a neighbouring race lives under worse political 
and juridical conditions, it is probable that the first race 
will conquer when war breaks out, because its more 
coherent nature leads to more energetic and harmonious 
operations on the part of its army. If the law of the 
conquerors is forced upon the losers, this survives, while 
the inferior law disappears. 

The struggle of traditionary benefits may, of course, 
be peaceful ; the best acquirement may conquer without 
strife or blood-shed. Suppose, for instance, that the 
excellent position of a state leads to the prolific multiplica- 
tion of its citizens ; this constantly increasing community 
will gradually oust its neighbours in the most peaceful 
way. With it survives its political system. 

Thus it is possible to trace the probable course of the 
evolution of civilisation and ground it on scientific laws. 
Opinions will differ as to the value of the attempt. On 
the one hand it will not be entirely convincing because 
it is no more than probable ; on the other hand it will 
be very difficult to provide it with a purely scientific 
foundation. Words like “improve,” “valuable” and 
“ progress ” will be only too apt to creep into it, and 
these meanings will involuntarily be imputed to the laws 
of evolution. We are accustomed enough to regard 
nature in the light of what is “ valuable ” and “ valueless,” 
and will be much more apt to use these terms in dealing 
with civilisation. It is a question if we can ever speak 


of changes of civilisation — which is the only way to put 
it scientifically — without considering them in relation 
to some standard of value that is regarded as generally 

However, we may grant the possibility of a history of 
civilisation on scientific lines, but we must entirely reject 
the notion of a scientific ethics. It has been said that 
the laws of science must apply always, even in the future, 
as they are independent of time. Hence we should be 
able to determine the laws of evolution in virtue of 
which the human race has not only changed, but will 
continue to change. We know that the fittest survive 
in the struggle for existence. The point is, therefore, 
to establish what is the fittest in particular cases. When 
that has been done, men will be disposed to aim at that 
particular adaptation in order that they may survive. 
We must, of course, also determine the general direction 
of human development, and must know what will be 
the best adaptation in ages to come. If we can obtain 
definite knowledge on these points, laws must be framed, 
States constructed, and the social order regulated, in 
relation to them. That is the language of the sociologist. 

Above all things, nothing must be done in opposition 
to natural selection, because it is this that always confers 
their greatest advantages on living things. It is a false 
humanity to spare those with hereditary disease, as in 
this way the disease is spread. It is not necessary to 
put them to death, but merely to prevent them from 
marrying, so that the disease-germs may die with them. 
If, for instance, some years ago, all consumptives had 


been prevented from having children, there would soon 
be no people with unsound lungs. We look too much 
to the individual. We ought to care for the soundness 
of the species, as nature does, and then the individuals 
also would be sounder. 

Other institutions show us an inverted selection. 
War brings about a “ survival of the weakest,” as it 
is precisely the strongest elements that perish in them, 
while the weaklings can continue to bring forth their 
puny children in peace at home. It is, therefore, 
unspeakably perverse and ridiculous to say that a little 
blood-letting from time to time does a nation good, and 
keeps down over-population. Apart from the fact that 
with the vast sums spent on the army waste lands might 
be cultivated, and numbers of families provided with 
new and secure dwellings, this blood-letting deprives 
the nation of its soundest blood, and every battle 
lessens the vital force of the next generation. 

Our whole military system should be abandoned. 
From the fact that the strongest enter military service, 
they generally lose the time for founding a family, while 
the less strong civilians have young earlier. Thus the 
weaker children come earlier and are more numerous, 
and this gradually enfeebles the race. 

Finally, we have a case of inverted selection in the 
Catholic principle of clerical celibacy. In Catholic 
countries the stupid survive, as a glance at such lands 
is said to show. As a general rule in a Catholic 
country, those are chosen for the clergy who are above 
the average of intelligence that suffices for peasants 


and artisans. But these more intelligent men are 
prevented from reproducing. In this way for centuries 
the more intelligent have been taken out of each 
generation, and their better germ - qualities have 
perished with them, because they were forbidden to 
have children. Thus the intelligent were continuously 
selected for destruction, the stupid were enabled to 
pass on their inferior germ-qualities to the next genera- 
tion, and the mental level of the race was bound to be 
gradually lowered . 1 

However, the scientific treatment of the evils of our 
time seems to be fairly justified. What must we make 
of the positive moral laws of sociology ? 

We must point out in the first place that there is a 
view which predicts the greatest future, not for society, 
but for the individual. This is the well-known philo- 
sophy of Friedrich Nietzsche, though founded before 
him by Max Stirner. 

1 We may regard celibacy from another, I would almost say a more 
fitting point of view. We are told that the peasants give to the clergy 
those of their sons who are least suitable for agricultural work. In 
other words, the weaker are selected for barrenness, and so celibacy 
must tend to strengthen the next generation. In the same way it may 
be contended that military training is of great service to our young 
men. It would certainly be better for humanity if nations did not 
face each other armed to the teeth, but we are still very far from this, 
and standing armies are at present inevitable. Moreover, it may be 
objected to the proposal to condemn weaklings and the diseased to 
infertility that it is impracticable. In my opinion all these questions 
should be settled by the historical method, because the work of natural 
science is merely the theoretical interpretation of the world. This will 
be made clear in what follows. 

I was, therefore, surprised when a reviewer in a New York Journal 
observed that my point of view — which he calls Darwinian-ethical — 
can hardly be maintained on practical grounds. That is not my point 
of view, as I think I have clearly stated. 


We see from this that Darwinism may not only lead 
to the prosperity, but also to the decadence, of a society, 
as Nietzsche’s “egoism” is built up rigorously on a 
basis of selection. In fact he attributes a more 
energetic action to selection than the social Darwinists 
do. Nietzsche especially rejects the precept of love of 
one’s neighbour as “a morality of slaves.” It is hatred 
alone that makes the fittest to survive. “ The strong 
drift just as necessarily away from each other as the 
weak do towards each other.” Strong and masterful 
men must arise who feel themselves bound by no 
restrictions and follow unsparingly the primitive instinct 
of man towards violence, with no regard for science or 
morality. Science bids fair to-day to rob man of all his 
self-esteem. Astronomy dwarfs him by reducing him 
to insignificance in the great universe. Away with 
science, then, since it hinders the development of man 
and the beyond-man ! “Nothing is true; all is 

The State is an evil. Men cannot give the rein to 
their violence in it, until they at last turn it against 
themselves and mutilate themselves. This was the 
origin of conscience, another evil, according to 
Nietzsche. The primitive human instinct to fierce- 
ness cannot express itself externally and is reflected 

But a time is coming when men will live as masters 

once more. When one great State embraces the whole 

world and no enemies threaten it, the older selection 

will no longer be a condition of existence. Then 

2 n 


morality will have survived ; men will dare to express 
their individuality, and their long repressed egoisms 
will explode. There will be a fierce struggle for the 
light of the sun. No values will be recognised. The 
day of the beyond-man will have come. 

We will not go further into the subject, as this is not 
the place to deal with the ideas of Nietzsche. We 
merely wanted to point out that they are based on 
selection. As a matter of fact, little can be said against 
them from the scientific point of view. The Darwinist 
believes that the struggle for life creates the best — let 
the phrase pass for the moment — and is most effective 
when it is most destructive. Away, then, with what- 
ever limits the struggle ! Away with the State and the 
whole of civilisation ! Away with our physicians and 
hospitals, which run counter to selection, by preserving 
the weak ! Epidemic diseases are the most drastic 
selective agencies ; they suffer only the very soundest 
to survive, and the generation that follows their ravages 
is the healthiest conceivable. 

How will it be when one state embraces the whole 
world ? Then all selection will cease, and everything 
will be done in accordance with laws framed by men 
for the attainment of certain ends. But the laws of 
Nature that they interrupt can achieve more than man. 
Hence we ought to prevent the formation of such a 
state and all institutions that restrict the struggle for 


Can Nature’s eternal laws be corrected or suppressed 
by the puny hand of man ? A natural law is some- 


thing that holds good everywhere and at all times, and 
cannot be suddenly destroyed by the very objects to 
which it applies. 

It is true that the laws of nature hold good always, 
and cannot be influenced by civilisation. Selection 
would act even in a state that covered the whole world. 
It merely demands that those shall survive who are 
most in harmony with their actual environment. In a 
universal state the conditions would be different from 
what they are to-day. Selection would then allow those 
individuals to multiply most who are best and quickest 
able to secure maintenance and found a family. Even 
if the state extends equal care to all its members there 
will always be variations in the fertility of the citizens, 
and the more fruitful will tend to predominate. 
Whether they will be the more intelligent is another 
question. It is, in fact, pretty clear that in such a 
universal state, where cleverness would be no advantage 
and would not put a man in a better position to found a 
family, and where selection would no longer favour men 
according to their degree of intelligence, ability would 
diminish. In the end the citizens might become too 
stupid to maintain the state. It would break up, and 
then selection would once more favour the more 
intelligent ; they in turn would build up a state, which 
would meet the same fate, and so on in an endless cycle. 

However that may be, we can see clearly how 
difficult it is to build up a science of morality, or ethics, 
on the principal of selection. We can hardly determine 
what is “ better ” for our own time ; how much less 


can we do it for the future. How can we say with any 
confidence what the conditions of life will be in the 
future with which the coming race will have to 

The Darwinists who would deduce a system of ethics 
from their theory say that moral laws are only safely 
established when they are natural laws. We have seen 
how a law of nature is formulated. Individual 
phenomena are considered in their common features, 
and these are then embodied in a law. Moral laws 
must be framed in the same way. The individuals have 
then to range themselves under the law, like an example 
of a genius under the generic title. Hence a scientific 
ethics would have to demand that everyone should be 
as far as possible an “average man.” Only what he 
has in common with his fellows is essential ; his 
individual and distinctive traits must be as slight as 
possible, if he is to be as moral as possible — in the 
scientific sense. Science, which overlooks individuality 
in the formation of its concepts and regards it as 
unessential, must demand that the men who would 
realise its ideal shall have little or no individuality. 

As a matter of fact, we find confirmation of this when 
we read about future states and Darwinian ideals. No 
account can be taken of the individual ; he must merge 
into the general. The “general” or common interest 
is the basket of the “ social ” state. 

Nietzsche has given us a masterly description of the 
Darwinian ideal of the coming race in his “ last men.” 
It shows the complete insipidity of the theory that looks 


only to the common interest and suppresses the 
individual . 1 

“ The earth will then have become unimportant, and 
the ultimate man, who makes everything important, will 
hop about on it. His species is ineradicable, like that 
of the flea ; the ultimate man lives longest. 

“‘We have devised happiness’ — say the ultimate 
men, and wink knowingly. 

“ They have left the regions where it was hard to 
live ; for warmth is required. They still love their 
neighbour, and rub against him ; for warmth is required. 

“It is regarded by them as sinful to turn sick or be 
mistrustful ; they walk warily. It is only the fool who 
still stumbles over stones and men ! 

“ A little poison now and then — that makes pleasant 
dreams. And much poison at last, for a pleasant death. 

“ They still labour, for labour is an entertainment. 
But they take care that the entertainment does not 
hurt them. 

“ They no longer become poor or rich ; both are 
too troublesome. Who of them still wants to rule? 
Who of them still wants to obey ? Both are too 

“No herdsman, but one herd ! All want the same. 
All are equal. He who thinks otherwise goes 
voluntarily into the madhouse. 

“‘Formerly all the world was insane’ — say the 
most subtle of them, and wink knowingly. 

“ They are wise, and know all that has happened ; 
l “ Thus spoke Zarathustra ” (Commons’ translation). 


so there is no end of their derision. They still fall 
out, but are soon reconciled — otherwise it would spoil 
their stomachs. 

“They have their little pleasures for the day, and 
their little pleasures for the night ; but they have a 
regard for health.” 

This is the pass that things will come to if the 
Darwinian - ethical ideals are realised. A “ deadly 
generalness ” will dominate the world. Happiness and 
unhappiness are antitheses, and there should be no 
antitheses in the scientific world of ideals. Nothing 
low — but nothing high : no hatred — but no love : no 
depth — but no altitude : an eternally monotonous life, 
without struggle and without victory. 

We see, then, that the ideal of a scientific guidance 
of men means, to everyone who esteems individuality, 
an intolerable mediocrity. But that is not the only 
objection to a scientific ethics. It can be shown that 
it has no right to exist at all. 

Every system of ethics must prescribe something 
to a man ; it must tell him his duty. That is evident. 
If moral laws are to be laws of nature, they must, 
like the latter, have a universal validity. They then 
show what exists, and must exist, everywhere ; it is 
the very essence of natural laws that they act 
necessarily. But if moral laws, being natural laws, 
must be realised of themselves always and every- 
where, there is absolutely no purpose in directing a 
man to act according to them. If a thing is so, it is 
superfluous to make it a duty for a man to bring it about. 


In reality the world has no place for duty from 
the scientific point of view. The cosmic process 
goes on inexorably. There are no ends towards 
which the eternal changes are working ; and there 
is no force that can arrest or control the rolling 

The stars travel on in the infinite universe. They 
exist at one moment of the world’s history, and are 
gone the next. On a small body in a corner of the 
universe certain beings were produced in one of 
these moments, to grow rigid for ever with their 
planet in the next. Such is the story of mankind. 

How ridiculous and aimless it must be, in view of 
this conception of things, to direct a man how he 
shall act. As if he could make the slightest change 
in the inexorable march of cause and effect ! How is 
it possible to set before a man aims that he shall 
strive to realise, when there is no “teleological” 
occurrence in the world, when even human actions 
are determined by causes that lie behind , not before 
them ? 1 The utmost that science can say is that an 
ethic, a setting-up of ends to be attained, has no 
meaning. It can only direct a man to let himself be 
borne in peace on the stream of cause and effect, 
without doing anything, because his action could have 
no aim and no result. The only possible scientific 
ethic is resignation. 

Is it true that the laws of Nature are the sole 

1 There can, of course, be no question of free will to the 
scientifically-minded man. 


moral laws because they alone lead to ever-increasing 
values? We have already rejected this idea so often 
that we need not enlarge on it here. The principle 
of selection is not a principle of progress. It does not 
lead up inevitably to the “highest being,” to man; he 
is the accidental outcome of one branch of the organic 
system. Even in the evolutionary series, of which 
man is the terminus, we cannot speak of progress ; 
it would not be scientific, but anthropomorphic. In 
the eyes of science man is not “higher” than the 
other animals. It is precisely one of the elements 
of the success of the scientific view that it brings 
man into level with other living things. It is illogical 
suddenly to raise him again to the position of the 
“highest being.” 

Further, it is entirely wrong to say that selection 
gives increasing value to the frames of animals, because 
it makes them increasingly fit to maintain their exist- 
ence. Maintenance of existence has nothing to do 
with maintenance of value. Science has only attained 
its great results by studying the world independently 
of all considerations of value. It sees nothing but 
changes. Certainly, its organisation will seem valuable 
to an animal when it sees that it fares better in life 
than its fellows owing to it. In the same way, man 
will attribute value to everything that is useful to 
himself. But this way of thinking is not scientific. 
The scientist has only to determine that there are 
human beings and animals, and that some survive 
and others perish on account of their bodily character- 


istics. He cannot wish that certain animals, or even 
man, may maintain their existence as long as possible. 
Worth is only conceivable as the opposite to worth- 
lessness. Dualistic ideas of that kind should have no 
place in a monistic system . 1 

We have now reached the fundamental objection to 
all scientific ethics. Science regards cosmic processes 
merely as changes, and pays no attention to values. 
It abandons its methods entirely and contradicts itself 
when it begins to recognise values. Hence it cannot 
have an ethics, because this has no meaning unless 
the moral laws that it sets up, and especially the life 
of man and the improvement of it, are regarded as 
having worth. 

Thus for science — to repeat our conclusion — there is 
no such thing as an aim, an end, or a value in the 
world. There are only changes in accordance with 
eternal laws. The laws are beyond the control of 
any human being. The whole history of humanity 
consists of certain changes that take place on a speck 
of dust, and occupy only a second of the world’s time. 
All man’s actions, all his struggles and efforts, are so 
many phenomena that follow necessarily upon other 
phenomena ; they are as void of worth as the fall of 
the meteor, or the roll of pebbles on the beach. 

The whole cosmic process is aimless. There is no 
such thing as a sense of life. 


1 For the same reason, the phrase “ worthy of selection ” is unfor- 
tunate. It does not give one a very scientific impression when we 
find sociological writers speaking incessantly of values. 


Yes, in a scientific conception of the world there is 
no sense of life. But that does not mean that there is 
no such thing anywhere as a sense of life. If science 
affirms that, it is passing beyond its sphere. 

We have seen that the scientific conception of the 
world does not present reality itself, but an inter- 
pretation of it. We have also seen that there is a 
second way of conceiving it — the historical. History 
looks first and foremost to individuals, and shows that 
in reality no individual can be substituted for another. 
History has a perfect right to read an ethic from 
reality — an ethic that lays on each personality the 
task that he alone and no other can perform. But 
it is not our place to enlarge on this. 

If science tells us to reject the historical conception 
of life it is illogical. When it censures the historical 
method, it assumes it to be of less value than its own, 
and thus once more oversteps its province. 

Briefly, we see on all sides that science lands itself 
in contradictions the moment it goes beyond its sphere. 
Its task is merely to give us a knowledge of the world. 
In doing this consistently it has attained marvellous 
results, and has formed a “ monistic ” or unified view of 
the world. The foundation of the monistic structure 
and all the columns and buttresses that support it 
imply a disregard of all values. Hence monism cannot 
frame an ethic unless it abandons all its supports, which 
are inconsistent with values. In that case, monism 
breaks down. 

When, therefore, we find practical counsels, aims, 


and values in monistic works, we have no longer 
monism before us, but dualism — dualism, in fact, of 
the most positive character. We cannot recognise 
two systems as equally valid ; we must leave only one 
standing. But we destroy it when we turn to the 
second, even though we demand that it shall be based 
on the first. 

There is one further point. 

Not only has empirical science, which recognises 
no values, no right to deny worth and the sense of 
life generally, but it is itself subordinate to the sciences 
that endeavour to determine values. Before it begins 
its work some standard of value has to determine 
whether its procedure is to have any meaning. This 
standard is the value of truth. Knowledge of the 
world must be of value to a man before he applies 
himself to the empirical sciences that help him to 
attain it. And the methods of acquiring this know- 
ledge, which disregard all values, must have a value 
for him. 

Thus all science presupposes a will to attain the 
truth, a will to reach the goal of knowledge. Over 
the portals of every science are inscribed the words : 

Thou Shalt. 

We have now reached the end. 

These last considerations have shown us that we 
are justified in believing in a sense of life, and that 
there must be duties, since the idea of duty precedes 
all knowledge. 


But science has nothing to do with these problems. 
It is of its very nature to pass no judgment on the 
value of other methods of investigation. 

It presses on to its goal, the comprehension of the 
world, regardless of all else. It gives an impulse 
to the human mind that bears it on to ever greater 
heights. The vision steadily enlarges. The individual 
disappears ; the world lies at the feet of the spectator 
in its broadest outlines. 

But we press onward. It bears us beyond the world 
to a height whence we can survey the entire universe. 
He who would see over the whole world must pass 
beyond it. 

There, in pure ether, the mind is able at last to 
grasp the infinite all. 


A chtheres percarum, 247 
Adaptation, law of, 118 
Aim not known in science, 425 
Air-sacs in birds, 100 
Algae, 236 
Albumen, 237 
Albuminoids, 231 
Alpine hare, adaptation of, 54 
American notions, 47 
Amoebae, 292, 294 
Amphimixis, uses of, 256-61 
Analysis, chemical, 231 

,, the task of science, 396 
Angiosperms, 236 
Annelides, 264 

Antennae of the Crustacea, 245 
Antlers, 84, 89 

„ of the giant stag, 207-13 
Ants, 285-6 

Archaeopteryx, 39, 121, 157 
Arctic hare, evolution of the, 32, 54 
Argus butterfly, the, 195 
Aristolochia, 200 
Art, analysis of, 71 
„ animal destitute of, 71 
Articulates, 184 
Artificial selection, 29, 166 
Asexual germ-cells, 302 
Atoms, 365 

Attention in animals, 76 
Aulostomum gulo, 268 

Bacillus, adaptation of the, 373 
Bacteria, nitrogenous, 318 
Balloons, birds dropped from, 102 
Barbel, the, 176 
Basic particles in the germ, 319 
Bee hawk-moth, the, 194 
,, queens and workers, 213 
,, state, origin of the, 214 
Bees and plants, 200 
Beetles, wings of, 203 
Beyond-man, the, 417 
Bilharzia hcematobia, 282 
Biocoenosis, 23, 42 
Biogenetic law, the, 17 1, 247 
Biogens, 232-4, 31 1 

,, evolution of the, 317 

Bird, anatomy of the, 100 
,, evolution of the, 38, 136 
,, life of the, 52 
,, song of the, 78, 94-6 
,, soul of the, 79 
Bittern, the, 96 
Black-arches, the, 43, 160 
Blackbird, the, 48 
Black-cock, the, 85, 87 
Blue-throat, the, 107 
Bombycidae, the, 159 
Botkriocephalus latus, 282 
Brain and mind, 384 

,, development of the, 249 
Branchiopods, 254 
Brontosaurus, the, 120 
Bullfinch, the, 81-2 
Bull-head, the, 173, 174 
Buttel-Reepen on the bees, 214 
Butterflies, 187, 189-93 

Cabbage-butterfly, the, 195 
Callima, 194 
Caprifoliaceas, 200 
Caracoideum, the, 158 
Carp, eggs of the, 26 
Cast of the skin in insects, 187 
Cat and the mouse, 67, 68 
,, why its fur stands out, 88 
Caterpillars, 188 
Catholic clergy, 415 
Causation, infinity of, 361 
Cause and effect, 349 
Celibacy, evils of, 415 
Cell, the, 289 
„ cleavage of the, 294 
Cellular animals, 319 
Cellulose, 237 
Cetiosaurus, the, 120 
Chaffinch, the, 48 
Chance, 353 

Change of function in organs, 244 
„ of hosts in parasites, 275 
Chlorophyll, 235, 317 
Choice, female, 80-7, 95 
Chromatin, 289 
Classification of animals, 1 17 
Co-adaptations, 207 



Coat of insects, development of the, 

Cock, spurs of the, 84 
Cockchafer, the, 84 
Cold, effect of, on butterflies, 341 
Cold-blooded animals, 1 19 
Colour as protection, 53-5 
Colours, animal, origin of, 91 

„ of animals and selection, 166 
„ of insects, 185 
Combinations, chemical, 230 
Common features expressed in ideas, 

Concepts, 378 

„ of animals, 392 
Conscience, evolution of, 408 
„ variations of, 410 
Consciousness, 386 

„ not evolved, 404 

„ unimaginable, 404 

Coecum, the, 159 
Co-operation in the body, 165 
Copepoda, 252 
Copper butterfly, the, 195 
Coquetting, 86 
Correlation, law of, 164 
Cosmic process, the, 425 
Cosmozoic theory, 314 
Courtship of animals, 82-8 
Coyness, 86 
Crab, legs of the, 245 
„ pincers of the, 204-5 
Craw-fish, the, 240, 245 
Creation, theory of, 155 
Cretaceous period, 119 
Cricket, pairing of the, 196 
Cries of birds, 94 
Crocodile, age of the, 149 
Cross-bill, the, 98 
Crustacea, 184 

Cuckoo, as destroyer of insects, 45 
„ cry of the, 95 
Curiosity in animals, 76 
Cyanic theory, the, 316 
Ciliated infusoria, 293 
Circulation of blood in the bird, 156 
,» » frog, 155 

Civilisation, effect of, on animals, 
42 , 47 

Civilisation, evolution of, 406 

Dachshund, the, 210 
Daphnidae, 252 

Darwin and over-production, 26 
Darwinian ethic, the, 417, 420 
Darwinism, definition of, 38 
Death, nature of, 307-11 
„ utility of, 312 

Definite variations in animals, 258, 

Degeneration of organs, 156-8 
Descartes on instinct, 64 
Descent, theory of, 37 
Descriptive science, 399 
Design on butterflies’ wings, 191 
Determinants, 333 
De Vries, Hugo, 344 
Differentiation of life-forms, 318 
Dinosauri, the, 120, 129 
Direction, sense of, in birds, 1 10-12 
Distomum hepaticum , 274, 283 
Distomum macrostomum , 283 
Divisibility of bodies, 362 
Division of labour in organisms, 290 
Dochmius duodenalis , 278 
Dragon-fly, the, 19, 22, 194, 196 
Dreams and art, 72 
Dualism, 427 
Duty, idea of, 422, 427 

Ear-bones, the, 154 
Earth, end of the, 312, 3 23 
Earth’s history, periods of the, 122 
Earthworm, the, 238 

„ use of the, 266 

„ regeneration in the, 267 

„ summer store of the, 56 

Earwig, the, 202 
Echinoderms, 263 
Echinorhyticus , 272 
Economy of nourishment, 168-70 
Eel, reproduction of the, 178-80 
Eel-pout, the, 172 
Efficient causes, 367 
Eggs, colours of, 92 
„ number in certain animals, 26 
„ of reptiles, 138 
„ poisonous, 176 
„ provision for development of, 59 
Egoism, 417 
Egyptian plants, 34 
Egyptian seeds do not grow, 233 
Elastic types, 132 
Elements, chemical, 229 
Elephant, trunk of the, 241, 332 
Embryo, development of the human, 

Embryonic adaptations, 249-51 

„ development, evolution- 
ary aspect of, 170, 248-51 
Empirical science, 396 
End in organisms, 364 
Eri s/alis, 193 
Eternity of matter, 314 
Ether, 381 

,, invisibility of, 382 


43 [ 

Ether-particles, metaphysical, 395 
Ethics, 419 

Evolution, the theory of, 37 
„ a slow process, 360 

„ based on probabilities, 401 

„ nature of evidence for, 400 

„ not a purposive process, 


Evolution of life-forms, 318 
External influence on organisms, 340 
Extinction of species, causes of, 

Fakir, sham death of the, 233 
Falcon, the, 98 
Feathers, origin of, 136 
Feeling in the mammal and the bird, 

Female choice, 81-7 
Fertilisation of plants, 197-9 
Fertility of animals, 26, 58 
Fibula, the, 168 

Field-cricket, apparatus of the, 209 
Field-mouse, the, 43 
Final causes, 364 
Fingers of the bird, 157 
Fins, evolution of the, 154 
Fishes, eggs of the, 59 
Fitchet-weasel, the, 57 
Flagellates, 292 
Flea, the, 202, 270 
Flesh-eating, beginning of, 238 
Flight, instinct of, 66, 215 
Flowers and insects, relation of, 197 
Fluke, the, 282 
Flying fish, the, 137 
„ squirrel, the, 137 
Flying muscles of birds, 100 
Food instincts, 66-8 
Forestry and birds, 47 
Formative energy in organisms, 344 
Forms of living things, 352 
Fossils, absence of early, 122-3 
,, formation of, 123 

,, scarcity of, 123-4 

Fox, the, 23, 28 
Free will, 423 

Freedom, sense of, in play and art, 73 
Frog, the, 21 

„ adaptations in the, 145 
Frog-spawn, 145 
Fundulus heteroclitus , 1 77 
Fungi, 235, 238 

Future society, the Nietzschean 
forecast, 419 

Gall-fly, the 254 
Galleries of ancestors, 402 

Game, injuries done by, 43 
Games, nature of, 60-377 
Gatke, H., 79 

„ on speed of migration, 98, 


Genealogical trees, 359 
General concepts, 379 
„ terms, use of, 392 
Generic names, 393 
Geology, evidence of, 35 
Geological succession of animals, 

Geometer-moth caterpillars, 193 
Germ-cells, 255, 297 

,, not teleological, 366 

,, selection in the, 333 

Germ-plasm theory, the, 296 
Germinal selection, 333-40 

,, _ ,, teleological, 371 

Gill-clefts in the human embryo, 171 
Gills, evolution of the, 156 
„ of snails, 244 
Good and bad, meaning of, 375 
Gordius aquaticus , 268 
Gourd-worm, the, 274, 283 
Graeser, Kurt, on migration, 105 
Grant Allen on heredity, 306 
Grasshopper, the, 137, 185, 187 
Groos, Professor, on animal play, 60 
Growth of insects, 186 
Glyptodont, the, 126-8 

Haeckel, Professor, 399 
Haemopis vorax, 268 
Hairy coat, disappearance of, 342 
Hamster, winter sleep of the, 56 
Hare, the, 23, 28, 31 
Harmful animals, 43 
Harmonious adaptations, 207 
Hawk-moth caterpillar, the, 188 
Hawks, 43 

Hearing in the fish, 176-7 
Heart, the, 155 
Heliconides, the, 194 
Heligoland, migratory birds of, 98, 


Henry II., falcon of, 98 
Hereditary disease not to be spared, 

Heredity, 41, 256 
„ law of, 1 18 
„ nature of, 298 
Hermaphrodism, 275 

„ in the plant, 199 

Hermit-crab, the, 225 
Heron, the, 212 
Hibernating animals, 55-7 
Highest being, man as the, 424 



Histological selection, 333 
Historian, work of the, 399 
Historical science, 397 
History of civilisation, 414 
Honey in plants, 199 
Horse, evolution of the, 39 
„ toes of the, 157 
Horse-leech, the, 268 
Humanity, true and false, 414 
Hydra, 285 

Ichneumon-flies, 44 
Ichthyosauria, the, 120 
Iguanodon, the, 120 
Imago, 185, 187 
Imagination, 71 
Imbauba , 286 

Imitation, instinct of, 64, 75 
Immortality of the germ-cells, 306 
„ ,, protozoa, 307-10 

Incomprehensibility of the world, 


Indifferent marks of organisms, 

Individuality, 406 
Individual the only reality, 395 
Infection of germs, 223 
Infertility of mixed crossing, 328 
Infinity, 362 
Infusoria, 293 

„ will survive man, 374 
Inheritance of acquired characters, 
204, 222-4 

Inheritance of impressions, 340 
Inherited habits, 214 
Inorganic matter has psychic pheno- 
mena, 404 

Insects, adaptations of, 185 
„ growth of, 186 
,, origin of wings of, 137 
Insectivorous birds, 43-5 
Instinct and intelligence compared, 


Instinct, nature of, 64-6 
Instincts, origin of, 214 
Instrumental music of birds, 96 
Intelligence, animal, 55 

„ and instinct, 66-7 

„ of insects, 216 

Intermaxillary bones, the, 154 
Intestinal worms, eggs of the, 26 
Isolation as an evolutionary factor, 
261, 325-31 

Jay, song of the, 96 
Japan, no singing birds in, 78 
Judgments, 378 
Jurassic period, 119 

Kant, 389 

Kingfisher, the, 45, 46 

Lamarck, theory of, 40 
Lamarckian principle, the, 167, 191 

Lamarckian principle, the teleologi- 
cal, 371 

Language, scientific value of, 377 
Lappet-moth, the, 193 
Lame, 185, 187 
Last men, the, 420 
Laws of science, 397, 401 
Leaf-cutter ants, 286 
Leech, the, 268 
Legs, development of, 168 
Leptoccphalus breviroslris , 179 
Lepus Huxleyi, 34 
Leuckart, R., on parasites, 269 
Libcllula depressa, 195 
Lichen, the, 286 
Life, duration of, 312 
„ origin of, 313-6 
„ historical conception of, 426 
,, nature of, 232 
„ phenomena of, 233 
Limbs, evolution of the, 157 
Linnean principle, the, 34 
Lion, mane of the, 88 
Living substance, 232 
Lizard, intelligence of the, 13S 
„ tail of the, 141 
Love-dance, the, 85, 87 
Love-play, 76 
Lumbriculus, 267 
Lungs, origin of the, 152 
„ of snails, 240, 244 

Mach/ERodus, the, 126-8 
Magnetic sense in the bird, 108 
Males, fights of the, 84 
Mammal and the bird compared, 52 
Man and the animal not specifically 
different, 77 
Mantis, the, 196, 216 
Marmot, the, 107 
Marten, the, 29 
Masticators, evolution of, 202 

„ of the Crustacea, 246 
Mastodonsauri, the, 12 r 
Material world, a process of con- 
sciousness, 387 
Materialism, 385 
Maturing of the germ-cells, 322 
Maw- worm, the, 265, 272 
„ eggs of the, 26 
May-flies, 19, 22 
Meadow-sage, the, 20 r 



Measle-worms, 280 
Mechanism. 350, 369 
Mediterranean, former bridge over 
the, no 

Medium influences, 342 
Megalosauri, the, 120 
Memory of birds, 1 1 x 
„ of fishes, 176 
Memory prodigies, 112 
Metabolism, 233 
Middendorf, 108 
Migration of birds, 98-115 

„ „ „ altitude of, 99-103 

„ „ „ cause of, 103-5 

„ „ „ speed of, 98-9 

Migrations of animals, 328 
Migration routes, 109-10 
Migratory instinct, the, 103-15 

„ „ origin of the, 


Military system, evils of the, 415 
Mimicry, 193-4, 216 
Mind and matter, 387-8 
,, in the animal, 77 
Mixtures, chemical, 230 
Mole-cricket, the, 185, 203 
Monism, 389, 425, 426 
Monstrosities, 348 
Moral laws, 422 

„ sense, evolution of the, 408 
Morality, science of, 419 
Mortality greater in males than 
females, 81 
Mosaic narrative, 38 
Moth, the, 187, 190 
Moustache, the military, 90 
Mucus of the snail, 239, 242 
Mud-fish, the, 151, 177 
Mussels, parthenogenetic, 254 
Mutation theory, the, 344 
Mutilations, not inherited, 222 
Mutilation of animals, 140-5 
Myoxus git's, 56 

Natural laws, 380 

„ selection, 28-9, 40 

„ and sexual selection, 79-82 

„ selection, description of, 41 

„ selection, is it omnipotent ?, 


„ selection, mechanical, 368 

Nauplius-larva, the, 246, 251 
Neanderthal skull, the, 125 
Nematodes, 271, 277 
Neo-Vitalism, 352 
Nerve-tracks, 65 
Nerves, motor and sensory, 64 
Nesting-places of birds, 48 

Newt, regeneration in the, 142 
Nietzsche, F., 416 

Nightingale, disappearance of the, 

Novelty, stimulus of, 82 
Nucleus, importance of the, 295 
Nut-hatch, the, 52 

Ontogeny, 247 
Optics, 398 

Organisation, degrees of, 374 
Orgyia, the, 226 
Origin of life, 313-18 
„ of species, 398 
Orthogenesis, 340 

,, teleological, 371 

Ova, number and development of, 
26, 359 

Over-production, 25 
Ovum, the, 255, 303 

„ structure of the, 223 
Owl, the, 43 
Oxyuris, the, 277 

Painter’s gaper, the, 175 
Pairing-cries, 95 
Pairing of insects, 196 

,, season, date of the, 57 
Pandorina, the, 297 
Panmixis, 161 

Parasites, alimentary organs of, 272 
,, respiratory organs of, 272 
„ sexual organs of, 273 
Parasitism, 246, 269-84 
Parthenogenesis, 253-7 
Passive selection, 357 
Peacock’s-eye butterfly, the, 189, 220 
Peacock, tail of the, 87, 93 
Pentastomum tanioides , 270 
Perch, the, 172 
Perch-pike, the, 172 
Periftaius^ 264 
Persistent types, 132 
Pfliiger on the origin of life, 316 
Phylloxera, the, 43, 254 
Phylogeny, 247 

Physical changes of the earth, 327 
„ conditions of life, 22, 49 
„ science, 396 
Pigeons, species of, 29-30 
Pike, the, 172 
Pineal body, the, 158 
Pine lappet-moth, 43 
Plagues of animals, 46 
Plant-eating animals, 237 
Plant, evolution of the, 197-9 
,, importance of the, 235 
Plastic types, 132 

2 E 

434 INDEX 

Plate on heredity, 225 
Platodes, 263, 279 
Play, analysis of, 60-77 
„ animal, 60-77 
Plural variations, 259 
Plesiosaurus, the, 120 
Plectognathic fishes, 177 
Poisoning of germs, 223 
Poisonous butterflies, 148 

„ organisms, colours of, 147 
„ . snakes, 139, 143 

Polar animals, colour of, 54-5 
Political systems, development of, 

Pollen, 197 
Polyp, the, 284, 291 
Pond, inhabitants of the, 21 
Pond-mussel, the, 175 
Pond-snail, the, 239 
Porto Santo rabbit, the, 34 
Potential immortality, 307 
Presentiment of the bird, 107 
Preyer on the nature of life, 315 
Proboscis of butterfly, 201-2 
Processional butterfly, 43 
Proper names, 393 
Protective colours of insects, 189 
Protoplasm, 289 
Protozoa, the, 170, 263, 292 
Psychic phenomena, 384 

„ „ in inorganic 

matter, 404 

Psychic phenomena in the protists, 


Psychology, 384 
Pterodactyl, the, 121 
Pterosauri, the, 120, 130 
Pupa, the, 188, 206 
Purpose in organisms, 354 
„ in science, 373 

Racial colours, cause of, 165 
Reality, nature of, 395 

„ not given in natural science, 


Recreation not the essence of play, 

Red breast in birds, 81, 82 
Redstart, the, 45 
Reduction cleavage, 321 
Reflex action, 64, 214 
Regeneration of organs, 142 
Regions of nature, 20 
Regulation of rivers, 177 
Reproduction, essence of, 294 
„ rate of, 58 
Reptiles, age of, 135 
Rhine salmon, 48 

Rhodeus, the, 175 
Richard’s pipit, the, 109 
Rigid types, 132 
Ringed adder, the, 139, 148 
Rivers, artificial control of, 48 
Rock-pigeon, the, 30 
Rudimentary organs, 158-70 

„ parts in germs, 295 
Ruffe, the, 178 
Rut of animals, 57 

Sacculina, 246 
Salamander, the, 37 

„ and fire, 146 
Salmon, spawning of the, 180-1 
Satyridm, the, 188 
Scar in the egg, 304 
Scars, use of, 144 
Scented butterflies, 195 
Schiller on play, 62 
Science, objectivity of, 391 
Scientific explanation, nature of, 361 
Scolices, 280-1 
Sea-anemones, 285 
Seed of plants, 198 
Selective value, 329 
Self-correction of determinants, 336 
Self-deception in play and art, 71-2 
Self-preservation, instinct of, 356 
Sensations as psychic elements, 384 
Sense-impressions, 65 
Sense of life, 426-7 
Senses, action of the, 391 
Serpent, habits of the, 138 

„ movements of the, 140 
Sexual characters, 82-5 

„ generation, nature of, 299 
„ selection, 80-3 

„ „ teleological, 370 

„ union, reasons for, 256 
Shad, the, 173 
Shamming death, 193, 216 
Shell of the snails, origin of the, 241 
Silurian strata, animals in the, 121 
Skeleton of the articulates, 203 
Skull, development of the, 153 
Smooth adder, the, 14 1 
Snail, the, 239 
„ breathing of the, 244 
Snails with small shells, 168 
Snipe, noise of the, 96 
Social instincts, culture of, 408 
„ instinct in birds, 112 
Society, growth of, 407 
Sociology, 406 

„ laws of, 407 
Species, nature of a, 33, 1 1 7 

persistence of, 132-3, 135 



Species, characters of, 93-5 
Spencer, H., on play, 62 
Spermatozoa, 255, 303 
Spider, the, 217 

„ pairing of the, 197 
Spiracles, 185 
Spiritual world, the, 388 
Spontaneous generation, 315, 317 
Spring as the love-season, 57 
Squirrel, winter store of the, 56 
Stag, antlers of the, 84, 89, 207-13 
Stag-beetle, the, 89 

,, larva of the, 219 
State, Nietzsche’s idea of the, 417 
Stegocephala, the, 121 
Steinheim snails, the, 125 
Stickleback, the, 174 
Stigma, the, 197 
Sting of the bee, 221 
„ of insects, 193 
Stirner, Max, 416 
Stork, the, 46 

„ noise made by, 96 
Strepsitera, 202 
Struggle for life, the, 25, 27 
Styloid bones, 157 
Sty lops melitta, 202 
Subjectivity of knowledge, 405 
Sudden changes in nature, 13 1 
Survival of the fittest, 28 
Swimming-bladder of fishes, 150-1 
Symbiosis, 284 

Tadpole, the, 21 
Tania echinococcus , 281 
Tania saginata, 279, 280 
Tania solium, 279, 280 
Tape-worm, the, 279-82 

„ development of the, 26-7 

„ eggs of the, 26 

Teleological principles, 352 
Teleology, 364 

Temperature of ancient Europe, 1 19 
Thing in itself, the, 387 
“Thus spoke Zarathustra,” 421 
Tibia, the, 168 
Tiger-moth, the, 190 
Toad, age of the, 149 
,, secretion of the, 146 
Tortoise, the, 143 

Tortoise-shell butterfly, the, 189, 191, 

Tracheae, 184 
Tradition, 41 1 
Trance, 233 
Transformism, 37 
Transitional forms, 264 
Tree of life, the, 37 

Tree-frog, the, 148 
Tree-locust, the, 185 
Trichina, the, 276 
Tropical frogs, 119 
Trout, eggs of the, 26 
Trunk-fish, the, 177 
Truth, the will to attain, 427 
Turkey, the, 88, 89 
Types of animals, 132 

Ultimate concepts, 394 
„ elements, 379, 381 
Universal concepts, 380 
Unnucleated organisms, 308 
Uric acid, 351 

Use and disuse, effects of, 223, 225 

Value, idea of, 413 

„ no standard of, in science, 375 
Variations are in all directions, 368 
, , not definitely directed, 369 

,, in organisms, 40 

,, plus and minus, 162 

,, roots of, 334 

Variety, nature of a, 33 
Vermiform appendage, 158 
Vertebrates, similarity of, 153 
Viper, the, 140 
Vital force, 355 
Vitalism, 350 
Voluntary action, 214 
Volvox, the, 297 
Vorticellas, 293 

Wallace, Dr. A. R., on sexual 
selection, 81 

War-dance of animals, 89 
War, evils of, 415 
Wart-hog, the, 89 
Wasmann, Father, 38 
Wasps, predatory, 218 
Water-beetle, the, 218 
Water-flea, the, 20, 22, 229, 236, 252 
Water-ousel, the, 97 
Water-polyp, 284 
Wasmann on co-adaptations, 213 
,, on heredity, 299 

,, on instinct, 64 

,, on the extinction of 

species, 127 

Whale, rudimentary organs of the, 

Wild cocks, 91 
Will to live, the, 356 
■Willow, fertilisation of the, 198 
Willow-wren, song of the, 96 
Winged horses, possibility of, 369 
Wings, 100 

43 ^ 


Wings, evolution of, 136-7, 157 
Winter sleep of animals, 55-7 
Womb, development in the, 59-60 
Wood-chat, song of the, 97 
Woodpecker, the, 18, 21 

„ noise of the, 96 
Work and play, 61 

,, mental and physical, 61-2 

World, infinity of the, 390 
Wren, the, 97 

Xylina vetusta , 193, 216 . 

Yellow as warning colour 
Yolk of the egg, 247, 304 

Zoea, 251 


•tr ' 

. r 47 

Class ' Book 

Aec. 8 <> 432 »™. . Copy 

1L Q4 


r w