I LIBRARY

I UNIVERSITY OF
I CALIFORNIA
SANTA CRUZ

THE MAKING OF SPECIES

OTHER WORKS BY THE SAME
AUTHORS

BY DOUGLAS DEWAR

BOMBAY DUCKS
BIRDS OF THE PLAINS
ANIMALS OF NO IMPORTANCE
ETC ETC.

BY FRANK FINN

ORNITHOLOGICAL AND OTHER

ODDITIES

THE WORLD'S BIRDS
WILD BEASTS OF THE WORLD
GARDEN AND AVIARY BIRDS IN

INDIA

ETC. ETC,

THE MAKING
OF SPECIES

BY DOUGLAS DEWAR, B.A. (Cantab), I.C.S., F.Z.S.
AND FRANK FINN, B.A. (Oxon), F.Z.S., M.B.O.U.
WITH FIFTEEN ILLUSTRATIONS 3 ^

LONDON: JOHN LANE THE BODLEY HEAD
NEW YORK: JOHN LANE COMPANY MCMIX

Turnbull & Spears, Printers, Edinburgh

PREFACE

POST-DARWINIAN books on evolution
fall naturally into four classes. I. Those
which preach Wallaceism, as, for ex-
ample, Wallace's Darwinism, Poulton's
Essays on Evolution, and the voluminous works
of Weismann. 1 1. Those advocating Lamarckism.
Cope's Factors of Evolution and the writings of
Haeckel belong to this class. III. The writings
of De Vries, forming a group by themselves.
They advocate the theory that species spring
suddenly into being ; that new species arise by
mutations from pre-existing species. IV. The
large number of books of a more judicial nature,
books written by men who decline to subscribe
to any of the above three creeds. Excellent
examples of such works are Kellog's Darwinism
To-Day \ Lock's Recent Progress in the Study of
Variation, Heredity^ and Evolution, and T. H.
Morgan's Evolution and Adaptation.

All four classes are characterised by defects.

Books of the two first classes exhibit the

faults of ardent partisanship. They formulate

creeds, and, as Huxley truly remarked, " Science

commits suicide when it adopts a creed." The

The Making of Species

books which come under the third category have
the defects of extreme youth. De Vries has
discovered a new principle, and it is but natural
that he should exaggerate its importance, and see
in it more than it contains. But, as time wears
on, these faults will disappear, and the theory of
mutations will assume its true form and fall into
its proper place, which is somewhere between
the dustbin, to which Wallaceians would relegate
it, and the exalted pinnacle on to which De
Vries would elevate it.

In the present state of our knowledge, books
of Class IV. are the most useful to the student,
since they are unbiassed, and contain a judicial
summing-up of the evidence for and against the
various evolutionary theories which now occupy
the field. Their chief defect is that they are
almost entirely destructive. They shatter the
faith of the reader, but offer nothing in place
of that which they have destroyed. T. H.
Morgan's Evolution and Adaptation, however,
contains much constructive matter, and so is the
most valuable work of this class in existence.

Zoological science stands in urgent need of
constructive books on evolution — books with
leanings towards neither Wallaceism, nor La-
marckism, nor De Vriesism ; books which shall
set forth facts of all kinds, concealing none,
not even those which do not admit of explana-
tion in the present state of our knowledge.—

vi

Preface

It has been our aim to produce a book of this
description.

We have endeavoured to demonstrate that
neither pure Lamarckism nor pure Wallaceism
affords a satisfactory explanation of the various
phenomena of the organic world. We have
further, while recognising the very great value of
the work of De Vries, tried to show that that
eminent botanist has allowed his enthusiasm to
carry him a little too far into the realm of specu-
lation. We have followed up the exposure of
the weak points of the theories, which at present
occupy the field, with certain suggestions, which,
we believe, throw new light on many biological
problems.

Our aim in writing this book has been twofold.
In the first place we have attempted to place
before the general public in simple language a
true statement of the present position of biologi-
cal science. In the second place, we have
endeavoured to furnish the scientific men of the
day with food for reflection.

Even as the British nation seems to be slowly
but surely losing, through its conservatism, the
commercial supremacy it had the good fortune to
gain last century, so is it losing, through the un-
willingness of many of our scientific men to keep
abreast of the times, that scientific supremacy
which we gained in the middle of last century
by the labours of Charles Darwin and Alfred
b vii

The Making of Species

Russell Wallace. To-day it is not among
Englishmen, but among Americans and Con-
tinentals, that we have to look for advanced
scientific ideas.

Even as the Ultra-Cobdenites believe that
Free Trade is a panacea for all economic
ills, so do most English men of science believe
that natural selection offers the key to every
zoological problem. Both are living in a
fool's paradise. Another reason why Great
Britain is losing her scientific supremacy is
that too little attention is paid to bionomics,
or the study of live animals. Morphology,
or the science of dead organisms, receives
more than its due share of attention. It is
in the open, not in the museum or the dis-
secting-room, that nature can best be studied.
Far be it from us to deprecate the study of mor-
phology. We wish merely to insist upon the
fact, that the leaders of biological science must of
necessity be those naturalists who go to the
tropics and other parts of the earth where nature
can be studied under the most favourable con-
ditions, and those who conduct scientific breeding
experiments. Natural selection — the idea which
has revolutionised modern biological science-
came, not to professors, but to a couple of field-
naturalists who were pursuing their researches
in tropical countries. It is absurd to expect
those who stay at home and gain most of their

Vlll

Preface

knowledge second-hand to be the pioneers of
biological science.

We fear that this book will come as a rude shock
to many scientific men. By way of consolation
we may remind such that they will find them-
selves in much the same position as that occupied
by theologians immediately after the appearance
of the Origin of Species.

At that time theological thought was cramped
by dogma. But the clergy have since recon-
sidered their position, they have modified their
views, and thus kept abreast of the times.
Meanwhile scientific men have lagged behind.
The blight of dogma has seized hold of them.
They have adopted a creed to which all must
subscribe or be condemned as heretics. Huxley
said that the adoption of a creed was tantamount
to suicide. We are endeavouring to save biology
in England from committing suicide, to save
it from the hands of those into which it has
fallen.

We would emphasise that it is not Darwinism
we are attacking, but that which is erroneously
called Neo- Darwinism. Neo-Darwinism is a
pathological growth on Darwinism, which, we
fear, can be removed only by a surgical
operation.

Darwin, himself, protested in vain against the
length to which some of his followers were push-
ing his theory. On p. 657 of the new edition

ix

The Making of Species

of the Origin of Species he wrote : " As my con-
clusions have lately been much misrepresented,
and as it has been stated that I attribute the
modification of species exclusively to natural
selection, I may be permitted to remark that in
the first edition of this work, and subsequently,
I placed in a most conspicuous position — namely,
at the close of the Introduction — the following
words : ' I am convinced that natural selection
has been the main but not the exclusive means of
modification.' This has been of no avail. Great
is the power of steady misrepresentation ; but the
history of science shows that this power does not
long endure."

Notwithstanding this protest the Wallaceians
continue on their course, and give to the world a
spurious Darwinism. It is our belief that were
Darwin alive to-day his sympathies would be
with us, and not with those who call themselves
his followers. It was one of Darwin's strong
points that he never avoided facts. If new facts
came to light which were incompatible with a
theory of his, he promptly modified his theory.
Since his death a number of new facts have
come to light which, in our opinion, plainly
indicate that the theory of natural selection
as enunciated by Darwin needs considerable
modification.

We have in this book set forth certain
of these facts and indicated the directions in

Preface

which the Darwinian theory seems to require
modification.

This volume originated as the result of several
conversations we, the joint authors, had last
summer. We discovered that we had a great
many ideas in common on the subject of evolution.
This seemed strange, seeing that our education
had not been on the same lines. One of us took
a degree in natural science at Cambridge, and
subsequently entered His Majesty's Indian Civil
Service, but continued his zoological studies in
India as a hobby. The other, a naturalist from
childhood, nevertheless took a classical degree at
Oxford, then received a technical zoological train-
ing, adopted zoology as a profession, and held
for some years a position in the Natural History
Museum at Calcutta.

Our conversations revealed that we were both
of opinion that biology is in an unhealthy con-
dition, especially in England, and that the science
sorely needs some fresh impetus. Neither of us
had the time to attempt, single-handed, to give
the required impetus, but as one of us happened
to be home on eighteen months' leave, we thought
we might undertake the task in collaboration.

We felt that we might collaborate the more
successfully because the large number of facts
collected by the one of us form the necessary com-
plement to the philosophical studies of the other.

We have endeavoured, so far as possible, to

The Making of Species

avoid technical terms, and have made a special
point of quoting, wherever practicable, familiar
animals as examples, in order that the work may
make its appeal not only to the zoologist but
to the general reader.

It may, perhaps, be urged against us that we
have quoted too freely from popular writings,
including those of which we are the authors.
Our reply to this is that the study of bionomics,
the science of living animals, occupies so small
a place in English scientific literature that we
have been compelled to have recourse to popular
works for many of our facts ; and we would,
moreover, point out that a popular work is not
necessarily inaccurate in its information.

In conclusion, we would warn the reader
against the danger of confounding Inference
with Fact. The failure to distinguish between
the two has vitiated much of the work of the
Wallaceian school of biologists.

Facts are always to be accepted. Inferences
should be scrutinised with the utmost care.

In making our deductions, we have en-
deavoured to act without bias. We shall, there-
fore, welcome any new facts, be they consistent
with, or opposed to, our inferences.

D. D.
F. F.

Xll

CONTENTS

CHAPTER I

PAGE

RISE OF THE THEORY OF NATURAL SELECTION AND

ITS SUBSEQUENT DEVELOPMENT i

Pre-Darwinian Evolutionists — Causes which led to the speedy triumph
of the theory of Natural Selection — Nature of the opposition
which Darwin had to overcome — Post-Darwinian biology —
Usually accepted classification of present-day biologists as Neo-
Lamarckians and Neo-Darwinians is faulty — Biologists fall into
three classes rather than two — Neo-Lamarckism : its defects —
Wallaceism : its defects — Neo-Darwinism distinguished from
Neo-Lamarckism and Wallaceism — Neo-Darwinism realises
the strength and weakness of the theory of Natural Selection,
recognises the complexity of the problems which biologists are
endeavouring to solve.

CHAPTER II

SOME OF THE MORE IMPORTANT OBJECTIONS TO THE

THEORY OF NATURAL SELECTION . . 30

Brief statement of Theory — Objections to the Theory fall into two
classes — Those which strike at the root of the Theory — Those
which deny the all-sufficiency of Natural Selection — Objections
which strike at root of Theory are based on misconception —
Objections to Wallaceism — The Theory fails to explain the
origin of Variations — Natural Selection called on to explain too
much — Unable to explain beginnings of new organs — The
Theory of change of function — The co-ordination of variations
— The fertility of races of domesticated animals — Missing links —
Swamping effects of intercrossing — Small variations cannot
have a survival value — Races inhabiting same area — Excessive
specialisation — Chance and Natural Selection — Struggle for
existence most severe among young animals — Natural Selection
fails to explain mimicry and other phenomena of colour —
Conclusion, that scarcely an organism exists which does not
possess some feature inexplicable on the theory of Natural
Selection as held by Wallace and his followers.

xiii

The Making of Species

CHAPTER III

PAGE

VARIATION . . . . . .52

The assumption of Darwin and Wallace that variations are haphazard
in origin and indefinite in direction — If these assumptions be
not correct Natural Selection ceases to be the fundamental factor
in evolution — Darwin's views regarding variation underwent
modification — He eventually recognised the distinction between
definite and indefinite variations, and between continuous and
discontinuous variations— Darwin attached but little importance
to either definite or discontinuous variations — Darwin's views on
the causes of variations — Criticism of Darwin's views— Variations
appear to occur along certain definite lines — There seems to be
a limit to the extent to which fluctuating variations can be
accumulated — De Vries' experiments — Bateson on "discon-
tinuous variation" — Views held by De Vries — Distinction
between continuous and discontinuous variations — The work of
De Vries — Advantages enjoyed by the botanist in experimenting
on the making of species — Difficulties encountered by the
animal breeder — Mutations among animals — The distinction
between germinal and somatic variations — The latter, though
not transmitted to offspring, are often of considerable value to
their possessor in the struggle for existence.

CHAPTER IV

HYBRIDISM . . . . . .in

The alleged sterility of hybrids a stumbling-block to evolutionists —
Huxley's views — Wallace on the sterility of hybrids — Darwin on
the same— Wallace's theory that the infertility of hybrids has
been caused by Natural Selection so as to prevent the evils of
intercrossing — Crosses between distinct species not necessarily
infertile — Fertile crosses between species of plants — Sterile plant
hybrids — Fertile mammalian hybrids — Fertile bird hybrids —
Fertile hybrids among amphibia — Limits of hybridisation —
Multiple hybrids — Characters of hybrids — Hybridism does not
appear to have exercised much effect on the origin of new
species.

CHAPTER V

INHERITANCE . . . . . 133

Phenomena which a complete theory of inheritance must explain —
In the present state of our knowledge it is not possible to
formulate a complete theory of inheritance — Different kinds of
inheritance — Mendel's experiments and theory — The value and

xiv

Contents

importance of Mendelism has been exaggerated — Dominance
sometimes imperfect — Behaviour of the nucleus of the sexual cell
— Chromosomes — Experiments of Delage and Loeb — Those of
Cue'not on mice and Castle on guinea pigs — Suggested modifica-
tion of the generally-accepted Mendelian formulae — Unit
characters — Biological isomerism — Biological molecules — Inter-
pretation of the phenomena of variation and heredity on the
conception of biological molecules — Correlation — Summary of
the conception of biological molecules.

CHAPTER VI

THE COLOURATION OF ORGANISMS . . .170

The theory of protective colouration has been carried to absurd
lengths — It will not bear close scrutiny — Cryptic colouring
— Sematic colours — Pseudo-sematic colours — Batesian and
Mullerian mimicry — Conditions necessary for mimicry —
Examples — Recognition markings — The theory of obliterative
colouration — Criticism of the theory — Objections to the theory of
cryptic colouring— Whiteness of the Arctic fauna is exaggerated
— Illustrative tables — Pelagic organisms — Objectors to the Neo-
Darwinian theories of colouration are to be found among field
naturalists — G. A. B. Dewar, Gadow, Robinson, F. C. Selous
quoted — Colours of birds' eggs — Warning colouration — Objec-
tions to the theory — Eisig's theory — So-called intimidating
attitudes of animals — Mimicry — The case for the theory — The
case against the theory — " False mimicry " — Theory of recogni-
tion colours — The theory refuted — Colours of flowers and fruits
— Neo-Darwinian explanations— Objections — Kay Robinson's
theory — Conclusion that Neo-Darwinian theories are untenable
— Some suggestions regarding the colouration of animals —
Through the diversity of colouring of organisms something like
order runs — The connection between biological molecules and
colour— Tylor on colour patterns in animals— Bonhote's theory
of pcecilomeres — Summary of conclusions arrived at.

CHAPTER VII

SEXUAL DIMORPHISM . . . . .297

Meaning of the term— Fatal to Wallaceism— Sexual Selection— The
law of battle — Female preference — Mutual Selection — Finn's
experiments — Objections to the theory of Sexual Selection —
Wallace's explanation of sexual dimorphism stated and shown
to be unsatisfactory— The explanation of Thomson and Geddes
shown to be inadequate — Stolzmann's theory stated and criticised

XV

The Making of Species

. — Neo-Lamarckian explanation of sexual dimorphism stated and
criticised — Some features of sexual dimorphism — Dissimilarity
of the sexes probably arises as a sudden mutation — The four
kinds of mutations — Sexual dimorphism having shown itself,
Natural Selection determines whether or not the organisms
which display it shall survive.

CHAPTER VIII

THE FACTORS OF EVOLUTION . . . 345

Variation along definite lines and Natural Selection are undoubtedly
important factors of evolution — Whether or not sexual selection
is a factor we are not yet in a position to decide — Modus operandi
of Natural Selection — Correlation an important factor — Examples
of correlation — Correlation is a subject that requires close study
— Isolation a factor in evolution — Discriminate isolation — Indis-
criminate isolation — Is the latter a factor? — Romanes' views —
Criticism of these — Indiscriminate isolation shown to be a factor
— Summary of the methods in which new species arise — Natural
Selection does not make species — It merely decides which of
certain ready-made forms shall survive — Natural Selection com-
pared to a competitive examination and to a medical board —
We are yet in darkness as to the fundamental causes of the
Origin of Species — In experiment and observation rather than
speculation lies the hope of discovering the nature of these

INDEX ...... 389

xvi

LIST OF ILLUSTRATIONS

HECK'S CURASSOW FEEDING YOUNG BIRD, WHICH HAS
THE PLUMAGE OF THE HENS OF THE GLOBOSE
CURASSOW, ITS FATHER'S SPECIES . Frontispiece

By permission of the Avicultural Society.

FACING PACK

A TUREIT BELONGING TO MR H. P. SCATLIFF . 92

From " The Modern Turbit" published by " The Feathered World"
London.

YELLOW-RUMPED AND CHESTNUT-BREASTED FINCHES,

WITH SPECIMENS IN TRANSITIONAL STATE . 98

On the left, the yellow-rumped finch ; on the right, the chest-
nut-breasted ; birds in state of change in the middle.

By permission of the Avicultural Society.

MALE AMHERST PHEASANT . . . .122

The chief colours of this species (Chrysolophus amhcrstia) are
white and metallic green, so that it is very different in appear-
ance from its near ally the gold pheasant.

HARLEQUIN QUAIL (Coturnix delegorguei) . . 124

By permission of the Avicultural Society.

RAIN QUAIL (Coturnix coromandelicd) . . 124

The markings on the throats of these quails are of the type
usually put down as " recognition marks," but as the Harlequin
Quail is African and the Rain Quail Indian, the two species
cannot possibly interbreed. The pattern, then, can have no
"recognition " significance.

By permission of the Avicultural Society

xvii

The Making of Species

FACING PAGE

BOURU FRIAR-BIRD . . . . .222

Like most of the group to which it belongs, this honey-eater
(Tropidorhynchus bouruensis] is a soberly coloured bird, but is
noisy, active, and aggressive.

By permission of M essrs Hutchinson <&° Co*

BOURU ORIOLE . . . . .222

This " mimicking" oriole (Oriolus boiiruensis] is of the same
tone of colour as its supposed model the Friar-bird of the same
island.

By permission of Messrs Hutchinson dr3 Co.

KING-CROW OR DRONGO . . . .232

This very conspicuous black bird (Dicrurus ater), ranging
from Africa to China, is a striking feature of the landscape
wherever it occurs.

By permission of Messrs Hutchinson &> Co.

232

DRONGO-CUCKOO .....

The fork of the tail in this bird is unique among cuckoos, but
is nevertheless much less developed than in the supposed model,
and may be an adaptation for evolutions in flight, as such tails
usually appear to be.

By permission of Messrs Hutchinson &* Co.

SHIKRA HAWK . . 236

The upper surface of the tail, not shown in this drawing,
exactly corresponds with that of the cuckoo "mimic."

By permission of Messrs Hutchinson &* Co.

HAWK-CUCKOO . . . . .236

This species (Hierococcyx varh(s) is commonly known in India
as the " Brain-fever bird."

By permission of Messrs Hutchinson &* Co

xviii

List of Illustrations

FACING PAGE

BRAZILIAN TROUPIAL .... 284

This species (Icterus vulgaris) is that most frequently seen in
captivity ; the pattern of colour is found in several other allied
forms.

By permission of Messrs Hutchinson &•* Co.

INDIAN BLACK-HEADED ORIOLE . . . 284

Several other orioles besides this (O. melanocephahis] have
the black head.

By permission of Messrs Hutchinson &* Co.

QUEEN WHYDAH ..... 298

This species (Tetraenura regia) is a typical example of
seasonal sexual dimorphism, the male being long-tailed and
conspicuously coloured only during the breeding season, and at
other times resembling the sparrow-like female.

By permission of the Foreign Bird Club.

COURTSHIP OF SKYLARK .... 314

Illustrating display by a species with no decorative colouring
or sex difference.

XIX

THE MAKING OF SPECIES

CHAPTER I

RISE OF THE THEORY OF NATURAL SELECTION AND
ITS SUBSEQUENT DEVELOPMENT

Pre-Darwinian Evolutionists — Causes which led to the speedy
triumph of the theory of Natural Selection — Nature of the
opposition which Darwin had to overcome — Post-Darwinian
biology — Usually accepted classification of present-day
biologists as Neo-Lamarckians and Neo-Darwinians is
faulty — Biologists fall into three classes rather than two —
Neo-Lamarckism : its defects — Wallaceism : its defects —
Neo-Darwinisrn distinguished from Neo-Lamarckism and
Wallaceism — Neo-Darwinism realises the strength and
weakness of the theory of Natural Selection, recognises the
complexity of the problems which biologists are endeavouring
to solve.

DARWINISM and evolution are not
interchangeable terms. On this fact
it is impossible to lay too much
emphasis. Charles Darwin was not
the originator of the theory of evolution, nor
even the first to advocate it in modern times.
The idea that all existing things have been
produced by natural causes from some primordial
material is as old as Aristotle. It was lost

The Making of Species

sight of in the mental stagnation of the Middle
Ages. In that dark period zoological science
was completely submerged. It was not until
men shook off the mental lethargy that had
held them for many generations that serious
attention was paid to biology. From the
moment when men began to apply scientific
methods to that branch of knowledge the idea
of evolution found supporters.

Buffon suggested that species are not fixed,
but may be gradually changed by natural causes
into different species.

Goethe was a thorough-going evolutionist ; he
asserted that all animals were probably descended
from a common original type.

Lamarck was the first evolutionist who sought
to show the means whereby evolution has been
effected. He tried to prove that the efforts of
animals are the causes of variation ; that these
efforts originate changes in form during the life
of the individual which are transmitted to its
offspring.

St Hilaire was another evolutionist who en-
deavoured to explain how evolution had occurred.
He believed that the transformations of animals
are effected by changes in their environment.
These hypotheses were considered, and rightly
considered, insufficient to explain anything like
general evolution, so that the idea failed for a
time to make headway.

Strength of Darwin's Position

As knowledge grew, as facts accumulated, the
belief in evolution became more widespread.
Hutton, Lyell, Spencer, and Huxley were all
convinced that evolution had occurred, but they
could not explain how it had occurred.

Thus, by the middle of last century, all that
was needed to make evolution an article of
scientific belief was the discovery of a method
whereby it could be effected. This Darwin and
Wallace were able to furnish in the shape of
the theory of natural selection. The discovery
was made independently, but Darwin being the
older man, the more influential, and the one who
had gone the more deeply and carefully into the
matter, gained the lion's share of the credit of
the discovery. The theory of natural selection
is universally known as the Darwinian theory,
notwithstanding the fact that Darwin, unlike
Wallace, always recognised that natural selection
is not the sole determining factor in organic
evolution.

From the moment of the enunciation of his
great hypothesis, Darwin's position was an
exceedingly strong one. Everything was in
his favour.

As we have seen, the theory was enunciated
at the psychological moment, at the time when
zoological science was ripe for it. Most of the
leading zoologists were evolutionists at heart,
and were only too ready to accept any theory

3

The Making of Species

which afforded a plausible explanation of what
they believed to have occurred.

Hence the rapturous welcome accorded to the
theory of natural selection by the more pro-
gressive biologists.

Another point in Darwin's favour was the
delightful simplicity of his hypothesis. Nothing
could be more enticingly probable. It is based
on the unassailable facts of variation, heredity,
and the tendency of animals to multiply in
numbers. Everybody knows that the breeder
can fix varieties by careful breeding. Darwin
had simply to show that there is in nature some-
thing to take the part played among domesticated
animals by the human breeder. This he was
able to do. As the numbers of species remain
stationary, it is evident that only a small portion
of the animals that are born can reach maturity.
A child can see that the individuals most likely
to survive are those best adapted to the circum-
stances of their life. Even as the breeder weeds
out of his stock the creatures not suited to his
purpose, so in nature do the unfit perish in the
everlasting struggle for existence.

In nature there is a selection corresponding to
that of the breeder.

It is useless to deny the existence of this selec-
tion in nature, this natural selection. The only
disputable point is whether such selection can
do all that Darwin demanded of it.

4

Strength of Darwin's Position

The man in the street, then, was able to com-
prehend the theory of natural selection. This
was greatly in its favour. Men are usually well
disposed towards doctrines which they can readily
understand.

The nineteenth century was a superficial age.
It liked simplicity in all things. If Darwin could
show that natural selection was capable of pro-
ducing one species, men were not only ready but
eager to believe that it could explain the whole
of organic evolution.

The simplicity of the Darwinian theory has its
evil side. It has undoubtedly tended to make
modern biologists superficial in their methods.
It has, indeed, stimulated the imagination of
men of science ; but the stimulation has not in
all cases been a healthy one.

So far from adhering to the sound rule laid
down by Pasteur, " never advance anything
that cannot be proved in a simple and decisive
manner," many modern naturalists allow their
imagination to run riot, and so formulate ill-
considered theories, and build up hypotheses on
the most insecure foundations. " A tiny islet of
truth," writes Archdale Reid, " is discovered, on
which are built tremendous and totally illegitimate
hypotheses."

Another source of Darwin's strength was the
vast store of knowledge he had accumulated.
For twenty years he had been steadily amassing

5

The Making of Species

facts in support of his hypothesis. He enunciated
no crude theory, he indulged in no wild specula-
tions. He was content to marshal a great array
of facts, and to draw logical conclusions there-
from. He was as cautious in his deductions as
he was careful of his facts. He thus stood head
and shoulders above the biologists of his day.
He was a giant among pigmies. So well
equipped was he that those who attempted to
oppose him found themselves in the position of
men, armed with bows and arrows, who seek
to storm a fortress defended by maxim guns.

Nor was this all. The majority of the best
biologists of his time did not attempt to oppose
him. They were, as we have seen, ready to
receive with open arms any hypothesis which
seemed to explain how evolution had occurred.
Some of them perceived that there were weak
points in the Darwinian theory, but they pre-
ferred not to expose these ; they were rather
disposed to make the best of the hypothesis. It
had so many merits that it seemed to them but
reasonable to suppose that subsequent investiga-
tion would prove that the defects were apparent
rather than real.

We hear much of the " magnitude of the
prejudices " which Darwin had to overcome, and
of the mighty battle which Darwin and his
lieutenant Huxley had to fight before the theory
of the origin of species by natural selection

6

Opponents of Darwin

obtained acceptance. We venture to say that
statements such as these are misleading. We
think we may safely assert that scarcely ever has
a theory which fundamentally changed the pre-
vailing scientific beliefs met with less opposition.
It would have been a good thing for zoology had
Darwin not obtained so easy a victory.

Sir Richard Owen, a distinguished anatomist,
certainly attacked the doctrine in no unmeasured
terms, but his attack was anonymous and so
cannot be considered very formidable. Far more
important was the opposition of Dr St George
Mivart, whose worth as a biologist has never
been properly appreciated. His most important
work, entitled the Genesis of Species, might be
read with profit even now by many of our modern
Darwinians.

For some time after the publication of the
Origin of Species Mivart appears to be almost
the only man of science fully alive to the weak
points of the Darwinian theory. The great
majority seem to have been dazzled by its
brilliancy.

The main attack on Darwinism was conducted
by the theologians and their allies, who considered
it to be subversive of the Mosaic account of the
Creation. Now, when one whose scientific know-
ledge is, to say the best of it, not extensive, attacks
a man who has studied his subject dispassionately
for years, and invariably expresses himself with

7

The Making of Species

extreme caution, the onslaught can have but one
result — the attacker will be repulsed with heavy
loss, and the onlookers will have a higher opinion
of his valour than of his common sense.

The theologians were in the unfortunate posi-
tion of warriors who do not know what it is
against which they are fighting ; they confounded
natural selection with evolution, and directed the
main force of their attack against the latter,
under the impression that they were fighting
the Darwinian theory.

It was the misfortune of those theologians that
it is possible to prove that evolution, or, at any
rate, some evolution has occurred ; they thus
kicked against the pricks with disastrous results
to themselves. When this attack had been
repulsed men believed that the theory of natural
selection had been demonstrated, that it was
as much a law of nature as that of gravitation.
What had really happened was that the fact of
evolution had been proved, and the theory of
natural selection obtained the credit. Men
thought that Darwinism was evolution. Had
the theologians admitted evolution but denied
the ability of natural selection to explain it, the
Darwinian theory, in all probability, would not
have gained the ascendency which it now enjoys.

To us who are able to look back dispassionately
upon the biological warfare of the last century,
Darwin's opponents — or the majority of them—

8

Evolution and Natural Selection

appear very foolish. We must, however, bear in
mind that at the time of the publication of the
Origin of Species both natural selection and evolu-
tion were comparatively unknown ideas. Darwin
had to fight for both. He had to prove evolution
as well as natural selection. Many of the facts
adduced by him supported both. It is, there-
fore, not altogether surprising that many of
his opponents failed to distinguish between
them.

A glance at the Origin of Species will suffice to
show how considerable is the portion of the book
that deals with the evidence in favour of evolution
rather than of natural selection.

Of the fourteen chapters which make up the
book no fewer than nine are devoted to proving
that evolution has occurred. It has been truly
said, that for every one fact biologists have found
in support of the special theory of natural selec-
tion they have found ten facts supporting the
doctrine of evolution. Darwin, then, was in the
position of a skilled barrister who has a plausible
case and who knows the ins and outs of his brief,
while his opponents stood in the shoes of inex-
perienced counsel who had but recently received
their brief, and who had not had the time to
master the details thereof. In such circum-
stances it is not difficult to predict which way the
verdict of the jury will go.

Darwin, moreover, had a charming personality.

9

The Making of Species

Never was a man with a theory less dogmatic.
Never was the holder of a theory more careful of
the expressions he used. Never was a scientific
man more ready to give ear to his opponents, to
meet them half way, and, where necessary, to
compromise. Darwin was not afraid of facts,
and was always ready to alter his views when
they appeared to be opposed to facts. The
average scientific man of to-day makes facts
fit his theory ; if they refuse to fit it he ignores
or denies them.

Darwin continually modified his views ; when
he found himself in a tight place he did not
hesitate to resort to Lamarckian factors, such as
the inheritance of the effects of use and disuse
and of the effects of environment. He conceded
that natural selection was insufficient to account
for all the phenomena of organic evolution, and
advanced the theory of sexual selection in order
to account for facts which the major hypothesis
seemed to him incapable of explaining.

Darwin, moreover, having ample private means,
was not obliged to work for a living, and was
therefore able to devote the whole of his time to
research. The advantages of such a position
cannot be over-estimated, and, perhaps, have not
been sufficiently taken into account in apportion-
ing the praise between Darwin and Wallace for
their great discovery.

To all these factors in Darwin's favour we

10

Huxley

must add his good fortune in possessing so able
a lieutenant as Huxley.

Huxley was an ardent evolutionist, an able
writer, and a brilliant debater. A man of his
mental calibre was able, like a clever barrister,
to make out a plausible case for any theory which
he chose to take up. While nominally a strong
supporter of the Darwinian theory, he was in
reality fighting for the doctrine of descent. Had
any plausible theory of evolution been enunciated,
Huxley would undoubtedly have fought for it
equally earnestly.

A firm believer in evolution, Huxley was,
as Professor Poulton says, confronted by two
difficulties, — first, the insufficiency of the evi-
dence of evolution, and, secondly, the absence of
any explanation of how the phenomenon had
occurred. The Origin of Species solved both
these difficulties. It adduced much weighty evi-
dence in favour of evolution, and suggested a
modus operandi. Small wonder, then, that
Huxley became a champion of Darwinism. But,
as Poulton writes, on page 202 of Essays on
Evolution, " while natural selection thus enabled
Huxley freely to accept evolution, he was by no
means fully satisfied with it." " He never com-
mitted himself to a full belief in natural selection,
and even contemplated the possibility of its
ultimate disappearance/' To use Huxley's own
words : " Whether the particular shape which the

ii

The Making of Species

doctrine of evolution, as applied to the organic
world, took in Darwin's hands, would prove to be
final or not, was, to me, a matter of indifference."

The result of the fortuitous combination of the
circumstances which we have set forth was that
in a surprisingly short time the theory of natural
selection came to be regarded as a law of nature
on a par with the laws of gravitation. Thus,
paradoxical though it seems, practical certainty
was given to a hitherto uncertain doctrine by the
addition of a still more uncertain theory.

"At once," writes Waggett, "the theory of
development leapt from the position of an obscure
guess to that of a fully-equipped theory and
almost a certainty."

Darwin thus became a dictator whose authority
none durst question. A crowd of slavish adher-
ents gathered round him, a herd of men to whom
he seemed an absolutely unquestionable authority.
Darwinism became a creed to which all must
subscribe. It still retains this position in the
popular mind.

The ease with which the theory of natural
selection gained supremacy was, as we have
already said, a misfortune to biological science.
It produced for a time a considerable mental
stagnation among zoologists. Since Darwin's
day the science has not made the progress that
might reasonably have been expected, because
the theory has so captivated the minds of the

12

Growing Opposition to Darwinism

majority of biologists that they see everything
through Darwinian spectacles. The wish has
been in many cases the father to the observation.
Zoologists are ever on the lookout for the action
of natural selection, and in consequence frequently
imagine they see it where it does not exist.
Many naturalists, consciously or unconsciously,
stretch facts to make them fit the Darwinian theory.
Those facts which refuse to be so distorted are, if
not actively ignored or suppressed, overlooked as
throwing no light upon the doctrine. This is no
exaggeration. A perusal of almost any popular
book dealing with zoological theory leaves the
impression that there is nothing left to be ex-
plained in the living world, that there is no door
leading to the secret chambers of nature to which
natural selection is not an " open sesame."

But the triumph of natural selection has not
been so complete as its more enthusiastic sup-
porters would have us believe. Some there are
who have never admitted the all-sufficiency of
natural selection. In the British Isles these have
never been numerous. In the United States of
America and on the Continent they are more
abundant. The tendency seems to be for them
to increase in numbers. Hence the recent
lamentations of Dr Wallace and Sir E. Ray
Lankester. Modern biologists are commonly
supposed to fall into two schools of thought—
the Neo- Darwinian and the Neo-Lamarckian.

The Making of Species

The former are the larger body, and pin their
faith absolutely to natural selection. They deny
the inheritance of acquired characters, and preach
the all-sufficiency of natural selection to explain
the varied phenomena of nature. The Neo-
Lamarckians do not admit the omnipotency of
natural selection. Some of them allow it no
virtue. Others regard it as a force which keeps
variation within fixed limits, which says to each
organism, " thus far shalt thou vary and no
farther." This school lays great stress on the
inheritance of acquired characters, especially
on the inheritance of the effects of use and
disuse.

The above statement of the recent develop-
ments of Darwinism is incomplete, for it fails to
include those who occupy a middle position. If
it be possible to classify a large number of men
of which scarcely any two hold identical views,
it is into three, rather than two, classes that they
must be divided.

Speaking broadly, evolutionists of to-day may
be said to represent three distinct lines of thought.
For the sake of classification we may speak of
them as falling into three schools, which we may
term the Neo-Lamarckian, the Wallaceian, and
the Neo- Darwinian, according as their views in-
cline towards those held by Lamarck, Wallace,
or Darwin.

As adherents of the Neo-Lamarckian school,

The Neo-Lamarckian School

we cite Cope, Spencer, Orr, Eimer, Naegeli,
Henslow, Cunningham, Haeckel, Korchinsky,
and a number of others. It may almost be said
of these Neo-Lamarckians that each holds a
totally distinct theory of evolution. So hetero-
geneous are their views that it is difficult to find
a single article common to the evolutionary belief
of all. It is commonly asserted that all Neo-
Lamarckians are agreed, firstly, that acquired
characters are transmissible ; and, secondly, that
such transmission is an important factor in the
production of new species. This assertion is
certainly true of the great bulk of Neo-
Lamarckians, but it does not appear to hold in
the case of those who believe that evolution is
the result of some unknown inner force. So far
as we can see, a belief in the inheritance of
acquired characters is not necessary to the
theories of orthogenesis held by Naegeli and
Korchinsky. For that reason it would possibly
be more correct to place those who hold such
views in a fourth school. Since, however, a
number of undoubted Neo-Lamarckians, as, for
example, Cope, believe in an inner growth-force,
it is convenient to regard Naegeli as a Neo-
Lamarckian. His views need not detain us long.
Those who wish to study them in detail will find
them in his Mechanisch-physiologische Theorie
der Abstammungslehre.

Naegeli believes that there is inherent in
'5

The Making of Species

protoplasm a growth-force, which makes each
organism in itself a force making towards pro-
gressive evolution. He holds that animals and
plants would have become much as they are now
even if no struggle for existence had taken place.
"To the believers in this kind of ... ortho-
genesis," writes Kellog {Darwinism To-day, p.
278), " organic evolution has been, and is now,
ruled by unknown inner forces inherent in organ-
isms, and has been independent of the influence
of the outer world. The lines of evolution are
immanent, unchangeable, and ever slowly stretch
toward some ideal goal." It is easy to enunciate
such a theory, impossible to prove it, and difficult
to disprove it.

It seems to us that the fact that, so soon as
organisms are removed from the struggle for
existence, they tend to degenerate, is a sufficient
reason for refusing to accept theories of the
description put forth by Naegeli. More truly
Lamarckian is Eimer's theory of orthogenesis,
according to which it is the environment which
determines the direction which variation takes ;
and the variations which are induced by the
environment are transmitted to the offspring.

Spencer and Orr preach nearly pure Lamarck-
ism. The former, while fully recognising the
importance of natural selection, considered that
sufficient weight has not been given to the
effects of use and disuse, or to the direct action

16

Orr's Views

of the environment in determining or modifying
organisms.

The similarity of the views of Orr and
Lamarck is best seen by comparing their re-
spective explanations of the long neck of the
giraffe. Lamarck thought that this was the
direct result of continual stretching. The animal
continually strains its neck in the search for food,
hence it grows longer as the individual grows
older, and this elongated neck has been trans-
mitted to the offspring. Orr writes, on page 164
of his Development and Heredity : " The giraffe
seems to present the most remarkable illustration
of the lengthening of the bones as the result of
the frequent repetition of such shocks. As is
well known, this animal feeds on the foliage of
trees. From the earliest youth of the species,
and the earliest youth of each individual, it must
have been stretching upwards for food, and, as is
the custom of such quadrupeds, it must have
constantly raised itself off its forefeet, and, as it
dropped, must have received a shock that made
itself felt from the hoofs through the legs and
vertical neck to the head. In the hind legs the
shock would not be felt. It is impossible to
imagine that an animal which, during the greater
part of every day of its life (both its individual
and racial life), performed motions so uniform
and constant, would not be peculiarly specialised
as a result. The forces acting upon such an

B 17

The Making of Species

animal are widely different from the forces acting
upon an animal which eats the grass at its feet
like an ox, or one which must run and climb like
a goat or a deer, and the resultant modifications
of growth in the several cases must also be
different. The principle of increased growth in
the direction of the shock, resulting from super-
abundant repair of the momentary compression,
explains how the giraffe acquired the phenomenal
length of the bones of its forelegs and neck ;
and the absence of the shock in the hind-quarters
shows why they remained undeveloped and
absurdly disproportionate to the rest of the
body."

It seems to us that a fatal objection to all
these Neo-Lamarckian theories of evolution is
that they are based on the assumption that
acquired characters are inherited, whereas all
the evidence goes to show that such characters
are not inherited. In these days, when scientific
knowledge is so widely diffused, it is scarcely
necessary to say that all the characteristics which
an organism displays are either congenital or
inborn, or acquired by the organism during its
lifetime. Thus a man may have naturally a
large biceps muscle, and this is a congenital
character ; or he may by constant exercise
develop or greatly increase the size of the
biceps. The large biceps, in so far as it has
been increased by exercise, is said to be an

18

Inheritance of Acquired Characters

acquired character, for it was not inherited by
its possessor, but acquired by him in his lifetime.
We must bear in mind that the period in the life
history of an organism at which a character
appears, is not necessarily a test as to whether
it is congenital or acquired, for a great many
congenital characters, such as a man's beard, do
not appear until some years after birth. As we
have seen, the Neo-Lamarckians believe that it
is possible for an organism to transmit to its
offspring characters which it has acquired during
the course of its existence. But, as we have
already said, the evidence goes to show that
such characters are not inherited. For example,
the tail of the young fox-terrier is not shorter
than that of other breeds of dogs, notwith-
standing the fact that its ancestors have for
generations had the greater portion of their
caudal appendage removed shortly after birth.

We do not propose to discuss at any great
length the vexed question of the inheritance
of acquired characters, for the simple reason that
the Neo-Lamarckians have not brought forward
a single instance which indubitably proves that
such characters are inherited.

Mr J. T. Cunningham, in a paper of great
value and interest, entitled " The Heredity of
Secondary Sexual Characters in relation to
Hormones : a Theory of the Heredity of
Somatogenic Characters," which appeared in

19

The Making of Species

vol. xxvi., No. 3, of the Archiv fiir Ent-
wicklungsmechanik des Organismen, states :
" The dogma that acquired characters cannot
be inherited ... is founded not so much on
evidence, or the absence of evidence, as on a
priori reasoning, on the supposed difficulty or
impossibility of conceiving a means by which
such inheritance could be effected." Such
appears certainly to be true of some zoologists,
but we trust that Mr Cunningham will do us the
justice to believe that our opinion that the in-
heritance of acquired characters does not play
an important part in the evolution of, at any
rate, the higher animals, is based, not on the
ground of a priori reasoning, but on facts.
All the evidence seems to show that such
characteristics are not inherited. If, as Mr
Cunningham thinks, all secondary sexual
characters are due to the inheritance of the
effects of use, etc., how is it that no Neo-
Lamarckian is able to bring forward a clear
case of the inheritance of a well-defined acquired
character ? If such characteristics are habitually
inherited, countless examples should be forth-
coming. Fanciers in their endeavours are con-
stantly " doctoring " the animals they keep for
show purposes ; and it seems to us certain that
if acquired characters are inherited, breeders
would long ago have discovered this and acted
upon the discovery. If Neo- Darwinians are

20

Inheritance of Acquired Characters

charged with refusing to believe that acquired
characters are inherited because they " cannot
conceive the means by which it could be effected,'
may it not be said with equal justice that many
Neo-Lamarckians believe that acquired char-
acters are inherited, not on evidence thereof,
but because if such characters are not inherited
it is very difficult to account for many of the
phenomena presented by the organic world ?

In many of the lower animals, as, for example,
the hydra, the germinal material is diffused through
the organism, so that a complete individual can
be developed from a small portion of the creature.
In such circumstances it seems not improbable
that the external environment may act directly
on the germinal substance, and induce changes
in it which may perhaps be transmitted to the
offspring. If this be so, it would seem that
some acquired characters may be inherited in
such organisms. Very many plants can be
propagated from cuttings, buds, etc., so that we
might reasonably expect some acquired characters
to be hereditary in them. The majority of
botanists appear to hold Lamarckian views ; but
on the evidence at present available, it is doubtful
whether such views are the correct ones.

Plants are so plastic, so protean, so sensitive
to their environment that their external structure
appears to be determined by the external con-
ditions in which they find themselves quite as

21

The Making of Species

much as by their inherited tendencies. In this
respect they differ very considerably from the
higher animals. The peacock, for example,
presents the same outward appearance1 whether
bred and reared in Asia or Europe, in a hot or
cold, a damp or a dry climate, The same plant,
on the other hand, differs greatly in outward
appearance according as it is grown in a dry or a
damp soil, a hot or a cold country. In his recent
book The Heredity of Acquired Characters in
Plants, the Rev. G. Henslow cites several
examples of the celerity with which plants react to
their environment. On page 32 he writes : " The
following is an experiment I made with the
common rest-harrow (Ononis spinosa, Z.) growing
wild in a very dry situation by a roadside. I
collected some seeds, and also took cuttings.
These I planted in a garden border, keeping this
well moist with a hand-light over it, and a saucer
of water, so that the air should be thoroughly
moist as well. Its natural conditions were thus
completely reversed. They all grew vigorously.
The new branches of the first year's growth bore
spines, proving their hereditary character, but
instead of their being long and stout, they were
not an inch long, and like needles. This proved
the spines to be a hereditary feature. In the second
year there were none at all ; moreover, the plants

1 The white, pied, and " Japan " individuals are not more different
from the type than some variations occurring in wild birds.

22

Inheritance of Acquired Characters

blossomed, and, taken altogether, there was no
appreciable difference from O. repens, L"

From this experiment Professor Henslow draws
the inference that acquired characters tend to be
inherited in plants. In our opinion the ex-
periment affords strong evidence against the
Lamarckian doctrine. Here we have a plant
which has, perhaps, for thousands of generations
developed spines owing to its dry environment.
If acquired characters are inherited we should
have expected this spiny character to have
become fixed and persisted under changed
conditions, for some generations at any rate.
But what do we find ? By the second year the
thorns have entirely disappeared. All the years
during which the plant was exposed to a dry en-
vironment have left no stamp upon it. The fact
that the new branches of the first year's growth
bore small spines is not, as Professor Henslow
asserts, proof of their hereditary character. It
merely shows that the initial stimulus to their
development occurred while the plant was still in
its dry surroundings.

In the same way all other so-called proofs of the
heredity of acquired characters break down when
critically examined.

In our opinion "not proven" is the proper
verdict on the question of the possibility of the
inheritance of acquired characters in the higher
animals. One thing is certain, and that is that

23

The Making of Species

acquired characters are not commonly inherited
in those organisms in which there is a sharp
distinction between the germinal and the somatic
cells.

It is nothing short of a misfortune that
Haeckel's History of Creation, which seems to
be so widely read in England, should be built
on a fallacious foundation. It seems to us that
this work is calculated to mislead rather than to
teach.

Our attitude is not quite that of the Wallaceian
school, which denies the possibility of the in-
heritance of acquired characters. In practice,
however, the attitude we adopt is as fatal to
Lamarckism in all its forms as the dogmatic
assertions of the Wallaceians. It matters not
whether acquired characters are very rarely or
never inherited. In either case their inherit-
ance cannot have played an important part in
evolution. All those theories which rely on use-
inheritance as a factor in evolution are therefore
in our opinion worthless, being opposed to facts.
Our attitude, then, is that the inheritance of
acquired characteristics, if it does occur, is so
rare as to be a negligible quantity in organic
evolution.

We may add that the position which we occupy
will not be affected even if the Lamarckians do
succeed eventually in proving that some acquired
characters are really inherited. Such proof would

24

The Wallaceian School

merely help to elucidate some of the problems
which confront the biologist. Thus the question
of the inheritance of acquired characters, while
full of interest, has no very important bearing
on the question of the making of species.

The Wallaceians hold the doctrines which
have been set forth above as those of the Neo-
Darwinian school. It is incorrect to call those
who pin their faith to the all-sufficiency of natural
selection Neo-Darwinians, because Darwin at no
time believed that natural selection explained
everything. Darwin moreover was a Lamarckian
to the extent that he was inclined to think that
acquired characteristics could be inherited. His
theory of inheritance by gemmules involved the
assumption that such characters are inherited.
It is Wallace who out-Darwins Darwin, who
preaches the all-sufficiency of natural selection.
For this reason we dub the school which holds
this article of belief, and to which Weismann,
Poulton, and apparently Ray Lankester belong,
the Wallaceian school. Weismann has put forth
a theory of inheritance, that of the continuity
of the germ plasm, which makes this inheritance
a physical impossibility. We believe that the
Wallaceians have erred as far from the truth as
the Lamarckians have, because, as we shall show
hereafter, a great many of the organs and struc-
tures displayed by organisms cannot be explained
on the natural selection hypothesis. Those who

25

The Making of Species

pin their faith to this, needlessly increase the
difficulty of the problem which they have to
face.

There remains the third school, to which we
belong, and of which Bateson, De Vries, Kellog
and T. H. Morgan appear to be adherents. This
school steers a course between the Scylla of use-
inheritance and the Charybdis of the all-sufficiency
of natural selection. It may seem surprising to
some that we should class De Vries as a Neo-
Darwinian, seeing that he is the originator of the
theory of evolution by means of mutations, which
we shall discuss in Chapter III. of this work.
As a matter of fact the theory of mutations should
be regarded, not as opposed to the theory of
Darwin, but as a theory engrafted upon it. De
Vries himself writes : — " My work claims to be in
full accord with the principles laid down by
Darwin." Similarly Hubrecht writes in the
Contemporary Review for November 1908 :
" Paradoxical as it may sound, I am willing to
show that my colleague, Hugo de Vries, of
Amsterdam, who a few years ago grafted his
Mutations Theorie on the thriving and very
healthy plant of Darwinism, is a much more
staunch Darwinian than either Dr Wallace him-
self, or the two great authorities in biological
science whom he mentions, Sir William
Thistleton Dyer and Professor Poulton."

Having classified ourselves, it remains for us

26

Complexity of the Problem

(the authors of the present work) to define our
position more precisely. Like Darwin we wel-
come all factors which appear to be capable of
effecting evolution. We have no axe to grind in
the shape of a pet hypothesis, and consequently
our passions are not roused when men come
forward with new ideas seemingly opposed to
some which already occupy the field. We re-
cognise the extreme complexity of the problems
that confront us. We look facts in the face
and decline to ignore any, no matter how ill
they fit in with existing theories. We recognise
the strength and the weakness of the Darwinian
theory. We see plainly that it has the defect of
the period in which it was enunciated. The
eighteenth century was the age of cocksureness,
the age in which all phenomena were thought to
be capable of simple explanation.

This is well exemplified by the doctrines of
the Manchester school as regards political and
economic science. The whole art of legislation
was thought to be summed up in the words
laissez faire. The whole sphere of legitimate
government was asserted to be the keeping of
order and the enforcing of contracts. Experience
has demonstrated that a State guided solely by
these principles is wretchedly governed. A large
proportion of recent Acts of Parliament limits the
freedom of contract. Such limitations are neces-
sary in the case of contracts between the weak and

27

The Making of Species

the strong. Similarly the earlier economists con-
sidered political economy a very simple affair.
They asserted that men are actuated by but
one motive — the love of money. All their men
were economic men, men devoid of all attri-
butes save an intense love of gold. Experience
has shown that these premises are not correct.
Love of family, pride of race, caste prejudices
are more or less deeply implanted in men, so
that they are rarely actuated solely by the love
of money.

Thus it is that the political economy of to-day
as set forth by Marshall is far more complex and
less dogmatic than that of Ricardo or Adam

o

Smith. Similarly the political philosophy of
Sidgwick is very different to that of Herbert
Spencer. So is it with the theory of organic
evolution. The theory of natural selection is no
more able to explain all the varied phenomena
of nature than is Ricardo's assumption that all
men are actuated solely by the love of money
capable of accounting for the multifarious existing
economic phenomena. Even as the love of wealth
is an important motive of human actions, so is
natural selection an important factor in evolution.
But even as the majority of human actions are
the resultant of a variety of motives, so are the
majority of existing organisms the resultant of
a complex system of forces. Even as it is the
duty of the economist to discover the various

28

The Aim of the Biologist

motives which lead to human actions, so is it
the duty of the biologist to bring to light the
factors which are operative in the making of
species.

CHAPTER II

SOME OF THE MORE IMPORTANT OBJECTIONS TO
THE THEORY OF NATURAL SELECTION

Brief statement of Theory— Objections to the Theory fall into two
classes — Those which strike at the root of the Theory — Those
which deny the all-sufficiency of Natural Selection— Objec-
tions which strike at root of Theory are based on mis-
conception— Objections to Wallaceism — The Theory fails
to explain the origin of Variations — Natural Selection called
on to explain too much — Unable to explain beginnings of
new organs — The Theory of change of function — The co-
ordination of variations — The fertility of races of domesticated
animals— Missing links— Swamping effects of intercrossing
— Small variations cannot have a survival value — Races
inhabiting same area — Excessive specialisation — Chance and
Natural Selection — Struggle for existence most severe among
young animals — Natural Selection fails to explain mimicry
and other phenomena of colour — Conclusion, that scarcely
an organism exists which does not possess some feature
inexplicable on the theory of Natural Selection as held by
Wallace and his followers.

i

HE burden of proof is on him who
asserts " is a rule of evidence
which the man of science should
apply as rigidly as does the lawyer.
It is therefore incumbent upon us to prove our
assertion that the theory of natural selection
does not afford an adequate explanation of all
the varied phenomena observed in the organic
world.

3°

Theory of Natural Selection

The theory of natural selection is so generally
understood, that to set it forth in detail in this
place would be quite superfluous.

Darwin, it will be remembered, based his
great hypothesis on the following observed
facts : —

1. No two individuals of a species are exactly
alike. This is sometimes called the law of
variation.

2. All creatures tend in a general way to
resemble their parents in appearance more
closely than they resemble individuals not re-
lated to them. This may be termed the law of
heredity.

3. Each pair of organisms produces in the
course of a lifetime, on an average, many more
than two young ones.

4. On an average the total number of each
species remains stationary.

From (3) and (4) follows the doctrine of
Malthus, namely, that many more individuals
are born than can reach maturity.

Darwin applied this doctrine to the whole of
the animal and the vegetable kingdoms.

In his introduction to The Origin of Species
he writes : — " As many more individuals of each
species are born than can possibly survive ; and
as, consequently, there is a frequently recurring
struggle for existence, it follows that any being,
if it vary, however slightly, in any manner pro-

31

The Making of Species

fitable to itself, under the complex and some-
times varying conditions of life, will have a
better chance of surviving, and thus be naturally
selected. From the strong principle of inherit-
ance, any selected variety will tend to propagate
its new and modified form."

In other words, the struggle for existence
amongst all organic beings throughout the world,
which inevitably follows from the high geometri-
cal ratio of their increase, results in the survival
of the fittest, that is to say, of those best adapted
to cope with their enemies and to secure their
food. Since organisms are thus naturally selected
in nature, we may speak of a natural selection
which acts in much the same way as the human
breeder does. Darwin's theory, then, is that all
the variety of organisms which now exist have
been evolved from one or more forms by this
process of natural selection.

The objections which have been urged against
the theory of natural selection fall into two
classes.

I. Those which strike at its root, which either
deny that there is any natural selection, or
declare that it is not capable of producing a
new species.

II. Those which are directed against the all-
sufficiency of natural selection to account for
organic evolution.

Those of the first class need not detain us

32

Various Anti-Darwinian Views

long, although among those who formulate
them are to be found some eminent men of
science.

Delage alleges that selection is powerless to form
species, its function is, according to him, limited
to the suppression of variations radically bad,
and to the maintaining of a species in its normal
character. It is thus an inimical factor in evolu-
tion, a retarder rather than an accelerator of
species-change. It merely acts by preserving
the type at the expense of the variants, and so
acts as a brake on evolution.

Korschinsky, while possibly not denying that
selection occurs in nature, declares that its
influence on evolution is nil, or, if it has any
influence, that it is a hindering one.

Eimer similarly denies any capacity on the
part of natural selection to create species.

Pfeffer urges a very different objection. He
says that if such a force as natural selection
existed it would transform species much more
rapidly than it does !

Now, in order that the above objections can
carry any weight, one of two sets of conditions
must be fulfilled.

Either all organisms must be perfectly adapted
to their environment, and this environment must
never change, or there must be inherent in each
species a kind of growth-force which impels
the species to develop in certain fixed directions,
c 33

The Making of Species

In either of these circumstances natural selection
will be an inhibitory force, for if the normal
organism is perfectly adapted to its environment,
all variations from the type must be unfavour-
able, and natural selection will weed out the
individuals that display them. No careful
student of nature can maintain, either that all
animals are perfectly adapted to their environ-
ment, or that this never changes. Hence those
who deny that natural selection is a factor in the
making of species, assume the second set of con-
ditions, that species develop in certain fixed
directions, being impelled either by internal or
external forces. How far these ideas are founded
on fact we shall endeavour to determine when
speaking of variation. It must suffice at present
to say that even if any of these views of ortho-
genesis be established, natural selection will have,
so to speak, a casting vote, it will decide which
series of species developing along preordained
lines shall survive and which shall not survive.

Thus we reach by a different line of argument
the conclusion we arrived at in the last chapter :
namely, there is no room for doubt that natural
selection is a factor in the making of species.

We must now pass on to the second class of
objections, those which are urged against the all-
sufficiency of natural selection. So numerous
are these that it is not feasible to consider them
all. A brief notice of the more important ones

34

Darwinism does not explain Variation

should suffice to satisfy any unbiassed person ;
firstly, that natural selection is an important
factor in evolution ; secondly, that the position
taken up by Wallace and his followers, that
natural selection, acting on minute variations,
is the one and only factor in organic evolution,
is untenable.

1. It has been urged that the Darwinian
theory makes no attempt to explain variation,
and that, until we know what it is that causes
variations, we are not in a position to explain
evolution. This of course is quite true, but the
objection is scarcely a fair one, since, as we have
seen, Darwin freely admitted that his theory
made no attempt to explain the origin of varia-
tions. It is not reasonable to object to a theory
because it fails to explain phenomena with which
it expressly states that it is not concerned. On
the other hand, the objection is one that must be
reckoned with, for, as we shall see, it makes a
great difference to the importance of natural
selection as a factor in evolution if variations
appear indiscriminately in all directions, as
Darwin tacitly assumed they do, or whether,
as some biologists believe, they are determinate
in direction, being the result of a growth-force
inherent in all organisms.

2. Very similar to the above-mentioned objec-
tion is that which points out that it is a long
journey from Amoeba to man. It is difficult to

35

The Making of Species

believe that this long course of development from
the simple to the complex is due to the action
of a blind force, to the survival of those whose
fortuitous variations happen to be best adapted
to the environment. The result seems out of
all proportion to the cause. There must be some
potent force inherent in protoplasm, or behind
organisms, impelling them upwards. This objec-
tion is as difficult to refute as it is to establish.
It is purely speculative.

3. A very serious objection to the Darwinian
theory is that the beginnings of new organs
cannot be explained by the action of natural
selection on fortuitous minute variations, and
natural selection can act on an organ only when
that organ has attained sufficient size to be of
practical utility to its possessor. When once
an organ has come into being it is not difficult
to understand how it can be improved, modified
and developed by natural selection. But how
can we explain the origin of an organ such as
a limb by the action of natural selection on
minute variations ?

The theory of the change of function goes
some way towards meeting the difficulty, for by
means of it we are able to understand how certain
organs, as, for example, the lung of air-breathing
animals, might have come into existence. This
is said to have been developed from the
swimming-bladder of fishes. This bladder is,

36

Theory of Change of Function

to use the words of Milnes Marshall, " a closed
sac lying just underneath the vertebral column.
In many fish it acquires a connection by a duct
with some part of the alimentary canal. It then
becomes an accessory breathing organ, especially
in those fish which are capable of living out of
water for a time, e.g. the Protopterus of America.
An interesting series of modifications exists con-
necting the air-bladder with the lung of the
higher vertebrates, which is undoubtedly the
same organ."

This theory, however, does not seem adequate
to explain the origin of all organs. It does
not explain, for example, how limbs developed
in a limbless organism. Wallace tried to
avoid the difficulty by asserting that it is un-
reasonable to ask a new theory that it shall
reveal to us exactly what took place in remote
geological ages and how it took place. To this
the obvious reply is, firstly, that we ought not
to give unqualified acceptance to any theory of
evolution until it does afford us such explana-
tions, and, secondly, that the theory of the origin
of species by means of natural selection is no
longer a newr one. •

Latterly, however, Wallace appears to have
given up all hope of being able to account for
the origin of new organs by means of natural
selection, for he states on page 431 of the issue
of the Fortnightly Review for March 1909 :

37

The Making of Species

" It follows — not as a theory but as a fact— that
whenever an advantageous variation is needed,
it can only consist in an increase or decrease of
some power or faculty already existing." Now,
in order for an increase or decrease to occur,
there must be something in existence to be
increased or diminished. Wallace, it is true,
speaks here only of powers and faculties ; but
it can scarcely be supposed that he believes that
variations as to structure are intrinsically different
from those relating to powers and faculties.

4. Herbert Spencer urges, as an objection to
the theory of natural selection, that favourable
variations in one organ are likely to be counter-
balanced by unfavourable variations in some
other organ. He maintains that the chances are
enormous against the occurrence of the " many
coincident and co-ordinated variations " that are
necessary to create a life or death determining
advantage.

This objection was urged by a writer in the
Edinburgh Review in January 1909, and even
by Wallace himself in the Fortnightly Review
last March against the mutation theory. This
objection, strong though it appears on paper,
exists only in the imagination of the objector.

Those who urge it display a misunderstanding
of the manner in which natural selection acts, and
ignorance of the phenomenon of the correlation
of organs.

38

Correlation

Natural selection deals with an organism as a
whole. Its effect is to permit those creatures to
survive which, taken as a whole, are best adapted
to their environment.

Physiologists insist with ever-increasing em-
phasis that there is more or less correlation and
inter- connection between the various parts of an
organism.

The several organs of an animal are not so
many isolated units. It is impossible to act on
one organ without affecting some or all of the
others.

Variations in a given direction of one organ
are usually accompanied by correlated variations
in some of the other organs. If strength be of
paramount importance to an animal, natural
selection will tend to preserve those individuals
which exhibit strength to a marked degree, and
this exhibition of strength may be accompanied
by other peculiarities, such as short legs or a
certain colour, so that natural selection will
indirectly tend to produce individuals with short
legs and having the colour in question, and it
may happen that this particular colour is one
that renders the animal more conspicuous than
the normal colour does. Nevertheless, on account
of the all-needful strength which accompanies it,
those animals so coloured may survive while
those of a more protective hue perish. Thus,
paradoxical though it seems, natural selection

39

The Making of Species

may indirectly be responsible for characteristics
which in themselves are injurious to the in-
dividual. This is probably the case as regards
the decorative plumage of some male birds.
The phenomenon of correlation was recognised
by Darwin, and has, we believe, played an
important part in the making of species. We
shall deal more fully with the subject in a later
chapter.

5. An oft-urged objection to the theory of natural
selection, and one which weighed very strongly
with Huxley, is that breeders have hitherto not
succeeded in breeding a variety which is infertile
with the parent species. If, Huxley asked,
breeders cannot produce such a thing, how
can we say we consider it proved that natural
selection produces new species in nature ? This
objection, however, loses much of its force in
view of the fact that many perfectly distinct
species are quite fertile when bred together. We
shall recur to this in Chapter IV.

6. The fact that palaeontology has hitherto failed
to yield links connecting many existing species is
a classical objection to the theory of the origin
of species by gradual evolution.

Wallace states this objection as follows, on
page 376 of his Darwinism : " Many of the
gaps that still remain are so vast that it seems
incredible to these writers that they could ever
have been filled up by a close succession of

40

Missing Links

species, since these must have been spread over
so many ages, and have existed in such numbers,
that it seems impossible to account for their total
absence from deposits in which great numbers of
species belonging to other groups are preserved
and have been discovered."

Wallace's reply is to the effect that in the case
of many species palaeontology affords abundant
evidence of the gradual change of one species into
another, the foot of the horse being a well-known
case. The genealogy of this noble quadruped
can be traced from the Eocene four- toed Orohip-
pus, through the Mesohippus, the Miohippus, the
Protohippus, and the Pliohippus, until we reach
the one-toed Equus.

Wallace further points out that in order that
the fossil of any organism may be preserved, the
" concurrence of a number of favourable condi-
tions " is required, and against this the chances
are enormous. Lastly, he urges the imperfection
of our knowledge of the things that lie embedded
in the earth's crust.

The objection based on the lack of " missing
links " loses some of its force if we accept the
theory that species sometimes arise as sports.
Thus, suppose a species with well-developed
horns produces as a mutation a hornless variety,
which eventually replaces the horned form, we
should look in vain for any forms intermediate
between the parent and the daughter species.

41

The Making of Species

On the other hand, it is significant that just
where the links are most needed they are missing.
For example, the splint bones of the horse, taken
in conjunction with the feet of existing tapirs,
which have four toes in front and three behind,
would have led us to infer, without the help of
the geological record, that the horse was a
descendant of a polydactyle ancestor. When,
however, we come to the origin of birds, bats,
and whales, palaeontology fails to give us any
assistance, so that we are in the dark as to the
origin of such really important modifications.

7. The swamping effects of inter-crossing is
an objection which has been repeatedly urged
against the Darwinian theory.

This objection is not so serious as it appears
at first sight. Darwin and Wallace maintain,
firstly, that natural selection acts by eliminating all
individuals except those which present favourable
variations. The favoured few alone survive and
mate with one another, so that there is here no
question of the swamping effects of inter-crossing,
none but well-adapted individuals being left
to mate with one another.

The objection gains greater force when directed
against the theory that evolution proceeds by
sudden jumps. But in this connection we must
bear in mind that the experiments of Mendel
and his followers have demonstrated that some
of the offspring of crosses may resemble their

42

Recurrent Mutations

pure ancestors and breed true inter se. Nor is
this all.

Experience shows that where a mutation, or
sport, or discontinuous variation occurs, it fre-
quently repeats itself ; for example, the black-
winged sport of the peafowl has occurred several
times over and in different flocks of birds. The
sport or mutation must have a definite cause.
There must be something within the organism,
something in the generative cells, which causes
the mutation to arise ; and hence, on a priori
grounds, we should expect the same mutation to
arise about the same time in many individuals.
It seems legitimate to infer that things have
been quietly working up to a climax. When
this is reached there results a mutation. There-
fore we should expect sudden mutations to appear
simultaneously in a number of individuals. To
this important subject we shall return.

8. An almost insuperable objection to the
theory that species have originated by the action
of natural selection on minute variations, is that
such small differences cannot be of a life-or-death
value, or, as it is usually called, a survival value
to their possessor. But if evolution is the result
of the preservation by natural selection of such
slight variations, it is absolutely necessary that
each of these should possess a survival value.

As D. Dewar has pointed out, on page 704 of
vol. ii. of The Albany Review, it is only when the

43

The Making of Species

beast of prey and its victim are evenly matched
as regards fleetness and power of endurance that
small variations in these qualities can have a
survival value. But in the rough and tumble
of the struggle for existence the victim and its
foe are but rarely well-matched. Take as an
example the case of a flycatcher. "This bird,"
writes D. Dewar, "will sometimes take three
or four insects in the course of one flight ; all
are captured with the same ease, although the
length of wing in each victim varies. So great
is the superiority of the bird that it does not
notice the difference in the flying powers of its
puny quarry." It is unnecessary to labour this
point.

9. Species or varieties differing considerably
in colour may exist side by side, as the hooded
and carrion crows, the white and dark breasted
forms of the Arctic skua, the pale and dark forms
of the fulmar petrel, the grey and rufous forms of
the American scops owl (Megascops asio).

It is true that preponderance of one form or
another in certain districts points to some advan-
tage possessed by one over the other, but, for
all we know, it may be due to heredity, and in
any case the co-existence of the two types in part
of their range, or at certain seasons, shows that
selection is not at all rigorous.

The same argument applies to the co-existence
of very differently-coloured species with generally

44

Leaf-butterflies

similar habits, such as that of the jaguar and
puma in South America, and the five very
differently-coloured flycatchers in the Nilgiri
Hills.

In short, there is abundant evidence to show

that considerable differences in colour do not

appear to have any effect on the chances of

survival in the struggle for existence of those

that display them. Yet this is precisely what the

supporters of the Darwinian hypothesis cannot

afford to admit, for they then find it impossible

to account for the origin of such a form as

Kallima, the leaf-butterfly, by the action of

natural selection. As most people are aware,

this creature displays a remarkable resemblance

to a decaying leaf. " These butterflies" (there

are several species which show the marvellous

imitation), writes Kellog, on page 53 of Darwinism

To-day, "have the under sides of both fore and

hind wings so coloured and streaked that when

apposed over the back in the manner common

to butterflies at rest, the four wings combine to

resemble with absurd fidelity a dead leaf still

attached by a short petiole to the twig or branch.

I say absurd, for it seems to me the resemblance

is over-refined. Here for safety's sake it is no

question of mimicking some one particular kind

of other organism or inanimate thing in nature

which birds do not molest. It is simply to

produce the effect of a dead leaf on a branch.

45

The Making of Species

Leaf-shape and general dead-leaf colour-scheme
are necessary for this illusion. But are these
following things necessary ? namely, an extra-
ordinarily faithful representation of mid-rib and
lateral veins, even to faint microscopically-tapering
vein tips ; a perfect short petiole produced by the
apposed ' tails ' of the hind-wings ; a conceal-
ment of the head of the butterfly so that it shall
not mar the outlines of the lateral margin of the
leaf ; and finally, delicate little flakes of purplish
or yellowish brown to mimic spots of decay and
fungus-attacked spots in the leaf ! And, as culmin-
ation, a tiny circular clear spot in the fore-wings
(terminal part of the leaf) which shall represent
a worm-eaten hole, or a piercing of the dry leaf
by flying splinter, or the complete decay of a
little spot due to fungus growth ! A general
and sufficient seeming of a dead leaf, object of no
bird's active interest, yes, but not a dead leaf
modelled with the fidelity of the waxworkers in
the modern natural history museums. When
natural selection has got Kallima along to that
highly desirable stage when it was so like a dead
leaf in general seeming that every bird sweeping
by saw it only as a brown leaf clinging pre-
cariously to a half-stripped branch, it was natural
selection's bounden duty, in conformance to its
obligations to its makers, to stop the further
modelling of Kallima and just hold it up to its
hardly won advantage. But what happens ?

46

A Dilemma

Kallima continues its way, specifically and ab-
surdly dead-leafwards, until to-day it is a much
too fragile thing to be otherwise than very
gingerly handled by its rather anxious foster-
parents, the Neo-Darwinian selectionists." It
is obvious that if natural selection has produced
so highly specialised an organism as the dead-
leaf butterfly, every minute variation must be of
value and have been seized upon by natural
selection.

Thus the Wallaceians are on the horns of a
dilemma. If they assert, as they appear to do,
that every infinitesimal variation has a survival
value, they find it difficult to explain the exist-
ence, side by side of such forms as the hooded and
carrion crows, to say why in some species of bird
both sexes assume a conspicuous nuptial plumage
at the very time when they stand most in need
of protective coloration, why the cock paradise
flycatcher is chestnut for the first two years of
his life and then turns as white as snow. If, on
the other hand, the Wallaceians assert that small
variations are unimportant and have no survival
they are, as Kellog points out, in trouble over
the close and detailed resemblance which the
Kallima butterflies bear to dead leaves.

10. An objection to the Darwinian theory which
has been advanced by Conn, Henslow, D. Dewar,
and others, is that the selection theory fails to
take into account the effects of chance. " If,"

47

The Making of Species

writes D. Dewar on page 707 of The Albany
Review ', vol. ii., "the struggle for existence were
of the nature of a race at a well-regulated athletic
meeting, where the competitors are given a fair
start, where there is no difference in the condi-
tions to which the various runners are subjected,
then indeed would every variation tell. I would
rather liken the struggle for existence to the rush
to get out of a crowded theatre, poorly provided
with exits, when an alarm of fire is given. The
people to escape are not necessarily the strongest
of those present. Propinquity to a door may be
a more valuable asset than strength."

Or again, we may take the imaginary case of
some antelopes being pursued by wolves. The
chase, being prolonged, brings the antelopes to a
locality with which they are not familiar. The
foremost of the herd, the most swift, and there-
fore the individual which should stand the best
chance of survival, suddenly finds himself on soft
boggy ground, which, owing to the depth to
which his feet sink into the soil, seriously
impedes his progress. His fellow antelopes,
now outdistanced, seeing his predicament, take
another course and soon leave him behind, to
fall an easy prey to his foes. Here we have a
case of the perishing of the most fit as regards
the important point of speed.

Writing of plants, Professor Henslow says, on
page 16 of The Heredity of Acquired Characters

48

The Effects of Chance

in Plants : " As the whole of the animal kingdom
ultimately lives upon the vegetable, plants must
supply the entire quantity of food supplied, not
to add innumerable vegetable parasites as well,
for both young and old. Myriads of germinating
seeds perish accordingly, being destroyed by slugs
and other mollusca, and 'mildews/ etc. But far
more seeds and spores — about 50,000.000 of
these it is calculated can be borne in a single
male-fern — never germinate at all. They fall
where the conditions of life are unfavourable
and perish. This misfortune is not due to
any inadaptiveness in themselves, but to the
surrounding conditions which will not let them
germinate. Thus thousands of acorns and other
fruits, as of elder, drop upon the ground in and
by our hedges, road-sides, copses, and elsewhere ;
but scarcely any or even no seedlings are to be
seen round the trees."

Every year thousands of birds perish in the
great migratory flight, others succumb in a
cyclone, a fierce tropical storm, a prolonged
drought, a severe frost. Here death overtakes
multitudes, all that dwell in a locality, the weak
and the strong, the swift and the slow alike.

This objection may be met by saying that in
the long run it is the fittest that will survive.
This is true. The objection is nevertheless of
importance in showing how exceedingly uncertain
must be the action of natural selection if it have but
D 49

The Making of Species

small variations upon which to work. In such
circumstances the mills of natural selection may
grind surely, but they must grind very slowly.

1 1. We must bear in mind that the struggle for
existence is most severe among young animals,
among creatures that are not fully developed.
Nature pays no attention to potentialities. The
weak go to the wall in the conflict, even though,
if allowed time, they might develop into prodigies
of strength.

Moreover, and this is an important point, death
in the case of young creatures overtakes broods
and families rather than individuals.

The above-cited objections to the theory that
species have originated by the action of natural
selection on minute variations, are mostly of a
general nature ; let us now notice briefly a few
more concrete objections. We shall not devote
much space to these in the present chapter, since
we shall be continually confronted with them
when dealing with the subject of animal colouring.

12. Natural selection, as we shall see, fails to
account for the origin of what is known as pro-
tective mimicry. Some insects look like inanimate
objects, others resemble other insects which are
believed or known to be unpalatable. Those
creatures displaying this resemblance to other
objects or creatures, and deriving profit therefrom,
are said to " mimic " the objects or creatures
they copy. They are also called " Mimics."

50

The Origin of Mimicry

It is easy to understand the profit that these
mimics derive from their mimicry. When once
the disguise has been assumed we can compre-
hend how natural selection will tend to improve
it by eliminating those that mimic badly ; but it
seems to us that the theory fails utterly to
account for the origin of the likeness.

13. Similarly, the Neo- Darwinian theory fails to
explain the colours of the eggs of birds laid in
open nests, why, for example, the eggs of the
accentor or hedge-sparrow are blue and those
of the doves are white.

14. The theory fails to give a satisfactory ex-
planation of the phenomena of sexual dimorphism.
Why, for example, in some species of doves and
ducks, thesexes are alike, while in other species
with similar habits they differ in appearance.

1 5. It fails to explain why the rook is black and
why the jackdaw has a grey neck.

These and many other objections we shall
deal with more fully in the chapter on animal
colouration. It must suffice here to mention
them, and to say that our experience teaches us
that scarcely a single species of bird or beast
exists which does not display some characteristic
which is inexplicable on the theory that natural
selection, acting on small variations, is the one
and only cause of organic evolution.

CHAPTER III

VARIATION

The assumption of Darwin and Wallace that variations are
haphazard in origin and indefinite in direction — If these
assumptions be not correct Natural Selection ceases to be the
fundamental factor in evolution — Darwin's views regarding
variation underwent modification — He eventually recognised
the distinction between definite and indefinite variations, and
between continuous and discontinuous variations — Darwin
attached but little importance to either definite or discon-
tinuous variations — Darwin's views on the causes of variations
— Criticism of Darwin's views — Variations appear to occur
along certain definite lines — There seems to be a limit to the
extent to which fluctuating variations can be accumulated —
De Vries' experiments — Bateson on " discontinuous varia-
tion " — Views held by De Vries — Distinction between con-
tinuous and discontinuous variations — The work of De Vries —
Advantages enjoyed by the botanist in experimenting on the
making of species — Difficulties encountered by the animal
breeder — Mutations among animals — The distinction between
germinal and somatic variations — The latter, though not
transmitted to offspring, are often of considerable value to
their possessor in the struggle for existence.

AS we have already seen, the Darwinian
theory, unlike that of Lamarck, does
not attempt to explain the origin of
variations. It is content with the
fact that variations do occur.

Although Darwin did not try to explain how
it is that variation occurs, and was very guarded

52

Nature of Variation

in the expressions he used concerning it, he
assumed that variations are indefinite in variety
and occur indiscriminately in all directions, as
the following quotations from the Origin of
Species will show : " But the number and diver-
sity of inheritable deviations of structure . . .
are endless" (page 14, ed. 1902). " The varia-
tions are supposed to be extremely slight, but of
the most diversified nature." " I have hitherto
sometimes spoken as if the variations so common
and multiform with organic beings under domes-
tication, and in a lesser degree to those under
nature, were due to chance. This, of course, is
a wholly incorrect expression, but it serves to
acknowledge plainly our ignorance of the cause
of each particular variation " (page 164).

Wallace is far less guarded in his expressions.
On page 82 of his Darwinism he speaks of " the
constant and large amount of variation of every
part in all directions . . . which must afford an
ample supply of favourable variations whenever
required."

The double assumption that variations are for
all practical purposes haphazard in origin and
indefinite in direction is necessary if natural
selection is to be the main factor in evolution.
For if variations be not haphazard, if they are
definite, if there be a directive force behind them,
like fate behind the classical gods, then selection
is not the fundamental cause of evolution. It

53

The Making of Species

can at most effect, not the origin of species, but
the survival of certain species which have arisen
as the result of some other force. Its position
is changed ; it is no longer a cause of the origin
of new organisms, but a sieve determining
which of certain ready-made forms shall survive.
Evidently, then, we shall not be able to fully
understand the evolutionary process until we
have discovered how it is that variations are
caused. In other words, we must go considerably
farther than Darwin attempted to do.

Before proceeding to inquire into the true
nature of variations, it behoves us to set forth
briefly the ideas of Darwin on the subject. We
shall then be in a position to see how much
progress has been made since the days of that
great biologist.

It is not at all easy to discover exactly what
were Darwin's views on the subject of variation.
A perusal of his works reveals contradictions,
and gives one the impression that he himself
scarcely knew his own mind upon the subject.
This should not be a matter for surprise.

We must remember that Darwin had to do
pioneer work, that he had to deal with alto-
gether new conceptions. Such being the case,
his ideas were of necessity somewhat hazy ; they
underwent considerable modification as fresh
facts came to his knowledge.

Towards the end of his life Darwin recognised

54

Definite and Indefinite Variability

that variability is of two kinds — definite and
indefinite. Indefinite variation is indiscriminate
variation in all directions around a mean, varia-
tion which obeys what we may perhaps call the
law of chance. Definite variation is variation in
a determinate direction — variation chiefly on one
side of the mean. Darwin believed that these
determinate variations were caused by external
forces, and that they are inherited. He thus
accepted Lamarckian factors. " Each of the
endless variations," he writes, " which we see in
the plumage of our fowls, must have had some
efficient cause, and if the same causes were to
act uniformly during a long series of generations
on many individuals, all probably would be
modified in the same direction."

But Darwin was always of opinion that this
definite variability, this variability in one direc-
tion as the result of some fixed cause, is far less
important, from an evolutionary point of view,
than indefinite variability, that it is the exception
rather than the rule, that the usual result of
changed conditions is to let loose a flood of
indefinite variability, that it is almost exclusively
upon this that natural selection acts.

Darwin also recognised that variations differ
in degree, even as they do in kind. He per-
ceived that some variations are much more
pronounced than others. He recognised the
distinction between what are now known as

55

The Making of Species

continuous and discontinuous variations. The
former are slight departures from the normal ;
the latter are considerable deviations from the
mean or mode ; great jumps, as it were, taken by
nature, as, for example, the pea and the rose
combs of fowls, which were derived from the
normal single comb.

" At long intervals of time," wrote Darwin,
"out of millions of individuals reared in the
same country and fed on nearly the same food,
deviations of structure so strongly pronounced as
to deserve to be called monstrosities arise, but
monstrosities cannot be separated by any distinct
line from slighter variations." Therefore it is
evident that he regarded the difference between
continuous and discontinuous variations as not
one of kind, but merely of degree. To the
discontinuous variations Darwin attached very
little importance from an evolutionary point of
view. He looked upon them as something
abnormal.

" It may be doubted," he wrote, " whether
such sudden and considerable deviations of
structure such as we occasionally see in our
domestic productions, more especially with plants,
are ever permanently propagated in a state of
nature. Almost every part of every organic
being is so beautifully related to its complex
conditions of life that it seems as improbable
that any part should have been suddenly pro-

56

Monstrosities

duced perfect, as that a complex machine
should have been invented by a man in a
perfect state. Under domestication monstrosities
sometimes occur which resemble normal struc-
tures in widely different animals. Thus pigs
have occasionally been born with a sort of
proboscis, and if any wild species of the same
genus had naturally possessed a proboscis, it
might have been argued that this had appeared
as a monstrosity ; but I have as yet failed to
find, after diligent search, cases of monstrosities
resembling normal structures in nearly allied
forms, and these alone bear on the question. If
monstrous forms of this kind ever do appear in a
state of nature and are capable of reproduction
(which is not always the case), as they occur
rarely and singly, their preservation would de-
pend on unusually favourable circumstances.
They would, also, during the first and succeeding
generations cross with the ordinary form, and
thus their abnormal character would almost
inevitably be lost." But, in a later edition of the
Origin of Species, Darwin seems to contradict
the above assertion : " It should not, however,
be overlooked that certain rather strongly marked
variations, which no one would rank as mere
individual differences, frequently recur owing to
a similar organisation being similarly acted on—
of which fact numerous instances could be given
with our domestic productions. In such cases,

57

The Making of Species

if the varying" individual did not actually trans-
mit to its offspring its newly acquired char-
acter, it would undoubtedly transmit to them, as
long as the existing conditions remained the
same, a still stronger tendency to vary in the
same manner. There can also be little doubt
that the tendency to vary in the same manner
has often been so strong that all the individuals
of the same species have been similarly modified
without the aid of any form of selection. Or
only a third, fifth, or tenth part of the indi-
viduals may have been thus affected, of which
fact several instances could be given. Thus
Graba estimates that about one-fifth of the
guillemots in the Faroe islands consist of a
variety so well marked, that it was formerly
ranked as a distinct species under the name
Uria lacrymans. In cases of this kind, if the
variation were of a beneficial nature, the original
form would soon be supplanted by the modified
form, through the survival of the fittest." Here
we seem to have a plain statement of the origin
of new forms by mutation.

Again, we read (page 34) : " Some variations
useful to him (i.e. man) have probably arisen
suddenly, or by one step ; many botanists, for
instance, believe that the fuller's teasel, with its
hooks, which cannot be rivalled by any mechanical
contrivance, is only a variety of the wild Dipsacus ;
and this amount of change may have suddenly

58

Minute Variations

arisen in a seedling. This is known to be the
case with the turnspit dog." x But, as we have
already said, Darwin at no time attached much
importance to these jumps made by nature as a
factor in evolution. He pinned his faith to the
minute, indefinite variations which he believed
could be piled up, one upon another, so that,
if allowed sufficient time, either nature or the
human breeder could, by a continued selection
of these minute variations, call into being any
kind of organism. The importance of selection,
he writes, " consists in the great effect produced
by the accumulation in one direction, during
successive generations, of differences absolutely
inappreciable by an uneducated eye " (page 36).
On page 132 he writes : " I can see no limit to
the amount of change, to the beauty and com-
plexity of the coadaptations between all organic
beings . . . which may have been effected2 in
the long course of time by nature's power of
selection." He expressly states, on page 149,
that he sees no reason to limit the process to
the formation of genera alone.

Athough the theory of natural selection does
not attempt to explain the causes of variation,

1 This short-legged type of dog is sometimes seen among the
ownerless and unselected pariah dogs of Indian towns ; and a short-
legged variety of the fowl may occur sporadically in Zanzibar,
where the long-legged Malay is the prevalent breed.

2 " Effected " appears in the earlier editions, but in the later
editions has given place to " affected," probably a printer's error.

59

The Making of Species

Darwin paid some attention to the subject. He
believed that both internal and external causes
contribute to variation, that variations tend to
be inherited whether the result of causes within
the organism or outside it. He believed that
the inherited effect of use and disuse was a cause
of variation, and cited, as examples, the lighter
wing-bones and heavier leg-bones of the domestic
duck and the drooping ears of some domestic
animals. He supposed that animals showed a
greater tendency to vary when under domestica-
tion than when in their natural state, attributing
the supposed greater variability to the excess
of food received, and the changed conditions of
the life of domestic animals. Nevertheless, he
was fully alive to the fact that "nearly similar
variations sometimes arise under, as far as we
can judge, dissimilar conditions ; and, on the
other hand, dissimilar variations arise under
conditions which appear to be nearly uniform."
In other words, the nature of organisms appeared
to Darwin to be a more important factor in the
origin of variations than external conditions.
Evidence of this is afforded by the fact that
some animals are more variable than others.
Finally, he frankly admitted how great was his
ignorance of the causes of variability. Varia-
bility is, he stated, governed by unknown laws
which are infinitely complex.

It will be convenient to deal with each of
60

Lines of Variation

Darwin's main ideas on variation separately,
and to consider to what extent they seem to
require modification in the light of later research.

Firstly, Darwin believed that variations arise
in what appears to be a haphazard manner, that
they occur in all directions, and seem to be
governed by the same laws as chance. It is
our belief that we are now in a position to make
more definite statements regarding variation than
Darwin was able to.

Biologists can now assert definitely that varia-
tions do not always occur equally in all directions.
The results of many years of the efforts of practi-
cal breeders demonstrate this. These men have
not been able to produce a green horse, a pigeon
with alternate black and white feathers in the tail,
or a cat with a trunk, for the simple reason that
the organisms upon which they operated do not
happen to have varied in the required direction.
It may perhaps be objected that breeders have
no desire to produce such forms; had they wished
to do so, they would probably have succeeded.
To this objection we may reply that they have
not managed to produce many organisms, which
would be highly desirable from a breeder's point
of view, as, for example, a blue rose, hens that lay
brown eggs but do not become broody at certain
seasons of the year, or a cat that cannot scratch.

As Mivart well says, on page 1 18 of his Genesis
of Species, "Not only does it appear that there are

61

The Making of Species

barriers which oppose change in certain directions,
but that there are positive tendencies to develop-
ment along certain special lines. In a bird which
has been kept and studied like the pigeon, it is
difficult to believe that any remarkable spontane-
ous variations would pass unnoticed by breeders,
or that they would not have been attended to and
developed by some fancier or other. On the
hypothesis of indefinite variability, it is then hard
to say why pigeons with bills like toucans, or with
certain feathers lengthened like those of trogons,
or those of birds of paradise, have never been
produced."

There are certain lines along which variation
seems never to occur. Take the case of the tail
of a bird. Variable though this organ be, there
are certain kinds of tail that are seen neither in
wild species nor domesticated races. A caudal
appendage, of which the feathers are alternately
coloured, occurs neither in wild species nor in arti-
ficial breeds. For some reason or other, variations
in this direction do not occur. Similarly, with the
exception of one or two of the "Noddy" terns,
whenever a bird has any of its tail feathers con-
siderably longer than the others, it is always the
outer pair or the middle pair that are so elongated.
It would thus appear that variations in which the
other feathers are especially lengthened do not
usually occur. The fact that they are elongated
in two or three wild species is the more signifi-

62

Breeders' Boasts

cant, because it shows that there is apparently
nothing inimical to the welfare of a species in
having, say, the third pair of tail feathers from
the middle exceptionally prolonged.

This is a most important point, and one
which seems to be ignored by the majority of
scientific men, who appear to be misled by the
boastful talk of certain successful breeders.
Thus, on page 29 of the Origin of Species,
Darwin quotes, with approval, Youatt's descrip-
tion of selection as " the magician's wand, by
means of which he may summon into life what-
ever form and mould he pleases." Darwin
further cites Sir John Sebright as saying, with
regard to pigeons, that he would " produce any
given feather in three years, but it would take
him six years to obtain head and beak."

If it were possible absolutely to originate any-
thing by selection, horticulturists would almost
certainly ere this have produced a pure black
flower. The fact that not a single mammal
exists, either in nature or under domestication,
with scarlet, blue, or green in its hair, appears to
show that, for some reason or other, mammals
never vary in any of these directions.

The fact that so few animals have developed
prehensile tails seems to indicate that variation
does not often occur in that direction, for
obviously a prehensile tail is of the very greatest
utility to its possessor; so that there can be

63

The Making of Species

little room for doubt that it would be seized upon
and preserved by natural selection, whenever it
occurred.

As E. H. Aitken very truly says, "so early
and useful an invention should, one would think,
have been spread widely in after time ; but
there appears to be some difficulty in developing
muscles at the thin end of a long tail, for the
animals that have turned it into a grasping organ
are few and are widely scattered. Examples
are the chameleon among lizards, our own little
harvest mouse, and, pre-eminent among all, the
American monkeys" (Strand Magazine, Nov.
1908).

Even as there are many variations which seem
never to occur in nature, so are there others
which occur so frequently that they may be
looked for in any species. Albinistic forms
appear now and again hi almost every species
of mammal or bird ; while melanistic sports,
although not so common, are not by any means
rare.

Every complete manual on poultry gives for
each breed a note of the faults which constantly
appear, and which the fancier has to watch care-
fully for and guard against. The fact that these
11 faults" occur so frequently in each breed shows
how strong is the tendency to vary in certain
definite directions. It is true that some of these
faults are in the nature of reversions, as, for

64

Albinistic Variations

example, the appearance of red hackles in the
cocks of black breeds of poultry. On the other
hand, some certainly are not reversions, such as
the appearance of a white ring in the neck of the
female of the Rouen duck, which should resemble
the Mallard as regards the plumage of the neck.
Again, the tendency of Buff Orpingtons to
assume white in the wings and tail must be
regarded as a variation which is not in the nature
of a reversion. In short, the efforts of all
breeders are largely directed to fighting against
the tendencies which animals display towards
variation in certain directions.

This tendency to vary in the direction of
whiteness may account for many of the white
markings which occur in nature, as, for example,
the white tails of the Sea Eagle (Haliaetus
albicilla) the Nicobar Pigeon (Caloenas nico-
barica), and many hornbills. Provided that such
variations are not too great a handicap to their
possessors in the struggle for existence, natural
selection will allow them to persist.

It was the belief of Linnaeus, based on experi-
ence, that every blue or red-coloured flower is
likely to produce a white variety, hence he held
that it is not safe to trust to colour for the identi-
fication of a botanical species.

On the other hand, white flowers are not likely
to produce red varieties, and we believe we may
positively assert that they never produce a blue
E 65

The Making of Species

sport. Similarly, white animals appear not to
give rise to colour varieties.

We are never surprised to find that an ordi-
nary upright plant produces as a sport or muta-
tion a pendulous, or fastigiate form. These
aberrant varieties, be it noted, occur in species
which belong to quite different orders.

De Vries points out that laciniated leaves
appear in such widely separated trees and shrubs
as the walnut, the beech, the hazel-nut, and the
turnip.

Another example of the definiteness of varia-
tion is furnished by what Grant Allen calls the
" Law of Progressive Colouration " of flowers.

On pp. 20, 21 of The Colours of Flowers,
he writes, " All flowers, as we know, easily sport
a little in colour. But the question is, do their
changes tend to follow any regular and definite
order? Is there any reason to believe that the
modification runs from any one colour toward
any other ? Apparently there is. ... All
flowers, it would seem, were in their earliest
form yellow ; then some of them became white ;
after that a few of them grew to be red or
purple ; and finally a comparatively small number
acquired the various shades of lilac, mauve, violet,
or blue."

So among animals there are many colour
patterns and structures that appear in widely
different genera, as, for example, the magpie

66

Over-development

colouring in birds. With this phenomenon we
shall deal more fully when speaking of animal
colouration. There is certainly no small amount
of evidence which seems to indicate that, from
some cause or other, an impetus has been given
to certain organs to develop along definite lines,
The reduction of the number of digits in several
mammalian families which are not nearly related
is a case in point. This phenomenon is, as
Cope points out, observed in Marsupials, Rodents,
Insectivores, Carnivores, and Ungulates. He,
being a Lamarckian, ascribes this to the in-
herited effects of use. Wallaceians attribute it
solely to the action of natural selection. The
assumption of a growth-force or tendency for the
development of one digit at the expense of the
others, would explain the phenomenon equally
well. And it is significant that many palaeonto-
logists are believers in some kind of a growth-
force. In the case of certain extinct animals we
seem to have examples of the over-development
of organs. " Palaeontology, " writes Kellog on
p. 275 of his Darwinism To-day, " reveals to us
the one-time existence of animals, of groups of
animals, and of lines of descent, which have had
characteristics which led to extinction. The un-
wieldiness of the giant Cretaceous reptiles, the
fixed habit of life of the crinoids, the coiling of
the ammonities and the nautili, the gigantic
antlers of the Irish stag — all these are examples

67

The Making of Species

of development along disadvantageous lines, or
to disadvantageous degrees. The statistical
studies of variation have made known numerous
cases where the slight, as yet non-significant (in
a life-and-death struggle) variation in pattern of
insects, in dimensions of parts, in relative pro-
portions of superficial non-active areas, are not
fortuitous, that is, do not occur scattered evenly
about a mean or mode according to the law of
error, but show an obvious and consistent tendency
to occur along certain lines, to accumulate in
certain directions."

It seems to us that the only proper attitude to
adopt in the present state of our knowledge is,
not to call in to our aid an unknown growth-
force, but simply to say that there is evidence
to show that variations frequently occur along
certain definite lines only.

Darwin's second assumption was that there is
no limit to which variations may be accumulated
in any direction ; that by adding one minute
variation to another through countless generations
new species, new genera, new families may arise.
This assumption, if applied to continuous or
fluctuating variations, seems opposed to facts.
All the evidence available goes to show that
there is a definite limit to which minute variations
can be accumulated in any given direction. No
one has succeeded in breeding a dog as large as
a horse, or a pigeon with a beak as long as that

68

Speed of Racehorses

of a snipe. In the case of racehorses, which
have been selected so carefully through a long
period of time, we seem to have reached the
limit of speed which can be attained by the mul-
tiplication of insignificant variations. We do not
wish to dogmatise, but we believe that of late
years there has not been any material increase
in the speed of our racehorses.

Mr S. Sidney says, on page 174 of Cassell's
Book of the Horse : u As far as form went {pace
Admiral Rous), the British racehorse had reached
perfection in 1770, when ' Eclipse ' was six years
old." He quotes the measurements of the
skeleton of " Eclipse " in the Museum of the
Royal College of Surgeons as evidence of this.
All the efforts of breeders, then, have failed
appreciably to improve the form of the British
racehorse in the course of over a century and
a quarter.

De Vries has made some important experi-
ments with a view to determining whether or
not there is a limit to the amount of change
which can be induced by the selection of
fluctuating or continuous variations as opposed
to mutations. " I accidentally found," he writes,
on page 345 of Species and Varieties : their
Origin by Mutation, " two individuals of the
* five-leaved ' race (of clover) ; by transplanting
them into my garden I have isolated them and
kept them free from cross-fertilisation with the

69

The Making of Species

ordinary type. Moreover, I brought them under
such conditions as are necessary for the full
development of their character; and last, but
not least, I have tried to improve their char-
acter as far as possible by a very rigid and
careful selection. . . . By this method I
brought my strain within two years up to an
average of nearly 90 per cent, of the seedlings
with a divided primary leaf (such seedlings
averaging five leaves in the adult). . . . This
condition was reached by the sixth generation
in the year 1894, an<^ has since proved to be the
limit, the figures remaining practically the same
through all the succeeding generations. ... I
have cultivated a new generation of this race
nearly every year since 1894, using always the
strictest selection. This has led to a uniform
type, but has not been adequate to produce
further improvement." Similarly, De Vries
found in the bulbous buttercup (Rammculus
bulbosus) a strain varying largely in the
number of petals ; therefore he tried by
means of continuous selection of those flowers
having the largest number of petals to pro-
duce a double flower, but was not able to do so.
He succeeded in evolving a strain with an
average number of nine petals, some individuals
having as many as twenty or thirty ; but even
by breeding only from these last he could not
increase the average number of petals in any

70

Experiments of De Vries

generation beyond nine. This was the limit
to be obtained by the most rigorous selection
of fluctuating variations.

Selection, based on fluctuating variation, does
not, asserts De Vries, conduce to the production
of improved races. " Only temporary ameliora-
tions are obtained, and the selection must be
made in the same manner every year. More-
over, the improvement is very limited, and does
not give any promise of further increase." Not-
withstanding prolonged efforts, horticulturists
have not yet succeeded in breeding a biennial
race of either beetroots or carrots that does not
continually give rise to useless annual forms.
Writing of the beet, De Vries says useless
annual varieties " are sure to return each year.
They are ineradicable. Every individual is in
the possession of this latent quality, and liable to
convert it into activity as soon as the circum-
stances provoke its appearance, as is proved by
the increase of annuals in the early sowings" —
that is to say, in circumstances favourable to
the annual variety.

It will be urged perhaps that these experi-
ments, which seem to show that there is a limit
to which a species can be modified by the
accumulation of fluctuating variations, cannot
have been properly carried out, because all the
various breeds of pigeons and other domestic
animals clearly show that extraordinary differ-

The Making of Species

ences not only can, but have actually been pro-
duced by the selection of such variations. This
objection is based upon the assumption that
breeders have in the past dealt only with fluc-
tuating variations. This assumption does not
appear to be justified. It is exceedingly prob-
able that most, if not all, the varieties of
domesticated animals have originated in muta-
tions. Take, for instance, the modern turbit
pigeon ; this has been derived from the old
Court-bee, described and figured over two
centuries ago by Aldrovandus.

De Vries goes so far as to assert that the
various races of pears are all mutations ; that
each distinct flavour is a mutation, and that it is
impossible to produce a new flavour by selecting
fluctuating variations. Thus it would appear
that in every case of the production of a new
breed a mutation has occurred which has
attracted the fancy of some breeder, and he
has seized upon this and perpetuated it.

All the evidence available tends to show that
there is a limit — and one which is quickly
reached — to the amount of change that can
be produced by the selection of fluctuating or
continuous variations. We, therefore, seem
driven to the belief that evolution is based on
the kind of variation which Professor Bateson
terms ''discontinuous variation" and Professor
De Vries calls "mutation."

72

Bateson on Variation

As long ago as 1894 Bateson published his
Materials for the Study of Variation, in which
he set forth a large number of cases of discon-
tinuous variation which he had collected. He
pointed out that species are discontinuous, that
they are sharply separated one from another,
whereas " environments often shade into one
another and form a continuous series." How,
then, he asked, if variations are minute and con-
tinuous, have these discontinuous species arisen ?
May not variation prove to be discontinuous, and
thus make it clear why species are discontinuous?

On page 1 5 of the above-cited work we find :
"The preliminary question, then, of the degree
of continuity with which the process of evolution
occurs has never been decided. In the absence
of such a decision, there has nevertheless been a
common assumption, either tacit or expressed,
that the process is a continuous one. The
immense consequence of a knowledge of the
truth as to this will appear from a consideration
of the gratuitous difficulties which have been
introduced by this assumption. Chief among
these is the difficulty which has been raised in
connection with the building up of new organs
in their initial and imperfect stages, the mode of
transformation of organs, and, generally, the
selection and perpetuation of minute variations.
Assuming, then, that variations are minute, we
are met by this familiar difficulty. We know

73

The Making of Species

that certain devices and mechanisms are useful
to their possessors ; but from our knowledge of
natural history we are led to think that their
usefulness is consequent on the degree of per-
fection in which they exist, and that if they
were at all imperfect, they would not be useful.
Now it is clear that in any continuous process
of evolution such stages of imperfection must
occur, and the objection has been raised that
natural selection cannot protect such imperfect
mechanisms so as to lift them into perfection.
Of the objections which have been brought
against the theory of natural selection this is by
far the most serious."

Bateson further pointed out that chemical
compounds are not continuous, that they do not
merge gradually each into the next, and suggested
that we might expect a similar phenomenon in
the organic world.

Elsewhere he says : " Let the believer in the
efficacy of selection operating on continuous
fluctuations try to breed a white or a black rat
from a pure strain of black-and-white rats, by
choosing for breeding the whitest or the blackest;
or to raise a dwarf sweet pea from a tall race
by choosing the shortest. It will not work.
Variation leads and selection follows."

But Bateson's views fell upon stony ground,
because zoologists are mostly men of theory and
not practical breeders. They laboured under the

74

Work of Bateson and De Vries

delusion that mutations or " sports " are rare in
nature, and that when these do happen to occur
they must of necessity be swamped by inter-
crossing.

However, the discovery of the Abbe Mendel's
account of his experiments on breeding mongrel
sweet peas has opened the eyes of many
zoologists, so that they have at last learned
what practical breeders have known for untold
years — namely, that sports have a way of per-
petuating themselves. Moreover, Mendel was
able to give a theoretical explanation of his
discoveries, with the result that the believers
in discontinuous variation have largely increased
in number of late.

While we are unable to see eye to eye with
Professor Bateson in all things, we gladly recog-
nise the immense value of his work. Had his
statements in 1894 received the attention they
merited, zoological theory would to-day be con-
siderably more advanced than it actually is.

Professor De Vries has gone farther than
Bateson, having engrafted upon the Darwinian
hypothesis the theory of mutations. He has
done no small amount of experimental work, and
has undoubtedly thrown much new light on the
ways in which species arise. He is purely a
botanist, so that he argues only from plants.
Nevertheless, we believe that some of his con-
clusions are applicable to animals. We are far

75

The Making of Species

from accepting his theory of mutations in toto.
We are, however, convinced that he, like Bate-
son, is on the right track. There can be no
doubt that a great many new forms have
originated suddenly, by jumps, and not by
imperceptibly slow degrees. Before giving a
list of the names of some of the races, both
plant and animal, which appear to have come
into existence suddenly, it will be of advantage
to consider for a little some of the more
important conceptions of De Vries.

That eminent botanist, as we have already
seen, insists on the distinction between fluc-
tuating variations and mutations. The former
correspond, for all practical purposes, to the
continuous variations of Bateson, and the latter
seem to be equivalent to his discontinuous
variations.

According to De Vries, all plants display
fluctuating variation, but only a small percentage
exhibit the phenomenon of mutation. The
most daring of his conceptions is, that the history
of every species is made up of alternating
periods of inactivity, when only fluctuating
variations occur, and of activity when " swarms
of species " are produced by mutation, and of
these only a few at the most survive ; natural
selection, which De Vries likens to a sieve,
determining which shall live and which shall
perish.

76

Varieties and Elementary Species

As we have seen, De Vries does not believe
that new species can arise by the accumulation
of fluctuating variations. By means of these
the race may be greatly improved, but nothing
more can be accomplished. These variations
follow Quetelet's law, which says that, for
biological phenomena, deviations from the aver-
age comply with the same laws as the devia-
tions from the average in any other case, if ruled
by chance alone.

Very different in character are mutations. By
means of these, new forms, quite unlike the
parent species, suddenly spring into being.
Mutations are said by De Vries to be of two
kinds — those that produce varieties and those
which result in new elementary species.

According to De Vries, those species of plants
which are in a state of mutation (he refers to the
species of the systematic botanists) are of a com-
posite nature, being made up of a collection of
varieties and elementary species. His concep-
tion of a variety is a plant that differs from the
parent plant in the loss or suppression of one or
more characters, while an elementary species
differs from the parent form in the possession of
some new and additional character. But we will
allow him to speak for himself: "We can con-
sider (page 141 Species and Varieties) the follow-
ing as the principal difference between elementary
species and varieties : that the first arise by the

77

The Making of Species

acquisition of entirely new characters, and the
latter by the loss of existing qualities, or by the
gain of such peculiarities as may already be seen
in other allied species. If we suppose elementary
species and varieties originated by sudden leaps
and bounds, or mutations, then the elementary
species have mutated in the line of progression,
some varieties have mutated in the line of retro-
gression, while others have diverged from the
parental types in a line of digression or in the
way of repetition. . . . The system (of the vege-
table kingdom) is built up of species ; varieties
are only local and lateral, never of real import-
ance for the whole structure."

De Vries asserts that these elementary species,
when once they arise, breed true, and show little
or no tendency to revert to the ancestral form.
We can, says De Vries, ascertain only by experi-
ment which plants are in the mutating state and
which are not. The great majority, however, are
not at present in the mutating state.

The distinction between fluctuating variation
and mutation has been roughly illustrated by the
case of a solid block of wood having a number of
facets, on one of which it stands. If the block
be tilted slightly it will, when the force that has
tilted it is removed, return to its old position.
Such a gentle tilt may be compared to a fluctu-
ating variation in an organism. If, however, the
block be tilted to such an angle that when left to

78

Mutations

itself the block does not return to its old position,
but tips over and comes to rest on another facet,
we have a representation of the kind of change
indicated by a mutation.

The analogy is far from perfect, for it makes
it appear that the smallest mutation must of
necessity involve a departure from the normal
type more considerable than that of the largest
fluctuating variation. Now, although mutations
ordinarily consist in considerable deviations from
the mean or mode of the type, while continuous
variations are usually minute deviations, it some-
times happens that the extreme fluctuations are
more considerable than some mutations. Hence
" fluctuating " describes this latter kind of
variation more accurately than " continuous "
does.

The test, then, of a mutation is not so much
the amount of deviation as the degree in which
it is inherited. Mutations show no tendency to
a gradual return to the mean of the parent
species ; fluctuating variations do display such a
tendency. A mutation consists, as M. E. East
says, in the production of a new mode or centre
for linear fluctuation ; it is, as it were, a shifting
of the centre of gravity ; the centre about which
those fluctuations which we call continuous varia-
tions occur.

As it is of considerable importance thoroughly
to grasp the true nature of mutations or discon-

79

The Making of Species

tinuous variations, and as some writers do not
appear to realise wherein lies the essential
difference between the two kinds of variation,
we will, at the risk of appearing tedious, give
a further illustration. Let A be a species of bird
of which the average length of the wing is
20 inches, and let us suppose that individuals
belonging to that species occur in which the
length of the wing varies as much as 3 inches
each side of the mean ; thus it is possible to find
individuals of this species with a wing as short as
17 inches, or as long as 23 inches. Let B be
another species of which the average length of
the wing is 1 7 inches, and let us suppose that a
3-inch variation on each side of the mean be
found to occur. Individuals belonging to species
B will occur which have a wing as short as
14 inches, or as long as 20 inches. Thus some
individuals of the short-winged species will have
longer wings than certain individuals of the long-
winged species. Similarly, certain individuals
of a species which display a mutation may show
less deviation from the mean than some indi-
viduals showing a very pronounced fluctuating
variation. In other words, even as by measuring
the length of wing in the above example it was
not always possible to say whether a given indi-
vidual belonged to species A or B, so is it not
always possible to say by looking at an individual
that shows a considerable departure from the

80

Law of Regression

mean whether that departure is due to a mutation
or a fluctuating variation.

It is only by watching the effect of the
peculiarity on the offspring of its possessor that
we are able to determine the nature of the varia-
tion. Where the peculiarity is due to a fluctuating
variation the offspring will display the peculiarity
in a diminished degree ; but if the peculiarity be
due to a mutation, the offspring are likely to
display it in as marked a degree as the parent.

Fritz Mliller and Galton conducted inde-
pendently enquiries into the amount of the
regression shown by the progeny of parents
which have deviated from the average by
fluctuating variation.

Mliller experimented with Indian corn; Galton
with the sweet pea.

Each found that where the deviation of the
parents is represented by the figure 5, that of
their offspring is usually 2, that is to say, the
deviation they display is, on the average, less
than half that of their parents.

Applying this rule to the hypothetical case
given above, if two individuals of species A
having a length of wing of 20 inches be bred
together, their offspring will, on an average, have
a length of wing of 20 inches, since neither
parents showed any deviation from the mean.
On the other hand, the offspring of 2O-inch-wing
individuals of species B would show, on an
F 81

The Making of Species

average, a length of wing of only about i8J
inches. They tend to return to that mode from
which their parents had departed.

But suppose that the deviation of the parents
in this case had been due, not to fluctuating
variation, but to a mutation ; this would mean
that, owing to some internal change in the egg
that produced each parent, 20 inches became the
normal length of wing ; that the normal length of
wing had suddenly shifted from 17 inches to
20 inches.

The result of this would be that their offspring
would have on an average a wing-length of
20 inches instead of i8J inches, that the centre
of variation as regards length of wing had
suddenly shifted from 17 to 20, that, in future,
all fluctuating variations would occur on either
side of 20 inches, instead of on either side of
17 inches as heretofore.

Thus a variation is a fluctuating one or a
mutation according as it does or does not obey
Galton's Law of Regression.

De Vries says that it is of the essence of
mutations that they are completely inherited.
This statement, although substantially true, fails
to take into consideration the factor of fluctuating
variation. For example, in the above instance
if the two individuals of species B had mutated
into forms with a 2O-inch wing, their offspring
will nevertheless vary inter se, some of them

82

De Vries's Dictum

will have wings shorter than 20 inches and
others wings more than 20 inches in length.
But the average wing-length of the offspring of
the two mutating individuals will be 20 inches.

So much, then, for the practical difference
between a mutation and a fluctuating variation.
In Chapter V. we shall discuss the possible
causes of the difference. By way of anticipation
we may say that the suggestion we shall make is
that a mutation is due to some rearrangement
in the particles which represent that part of the
organism in the fertilised egg, whereas a fluctu-
ating variation is caused by variations in the
particles themselves.

De Vries, it should be noted, bases his theory
largely on experimental evidence. His dictum
is "the origin of species is an object of experi-
mental observation." He has, we consider,
proved conclusively that among plants mutations
sometimes occur, and, further, that in a mutating
plant the same mutation tends to occur again and
again. This latter is a most important fact,
because it goes some way towards overcoming
the difficulty urged by Darwin that isolated
sports must be swamped by continual crossing
with the normal type. If mutations arise in
swarms, as De Vries asserts they do, then any
particular mutation is likely, sooner or later, to
cross with a similar mutation and so be able to
perpetuate itself.

83

The Making of Species

The classical example of a mutating plant is
the evening primrose of the species Oenothera
lamarckiana. This is described by De Vries as
a stately plant, with a stout stem, attaining often
a height of 1.6 metres or more. The flowers
are large and of a bright yellow colour, attracting
immediate attention, even from a distance.
"This striking species," he writes, in Species and
Varieties (p. 525), "was found in a locality near
Hilversum, in the vicinity of Amsterdam, where
it grew in some thousands of individuals. Or-
dinarily biennial, it produces rosettes in the first,
and stems in the second year. Both the stems
and the rosettes were seen to be highly variable,
and soon distinct varieties could be distinguished
among them.

The first discovery of this locality was made
in 1886. Afterwards I visited it many times,
often weekly or even daily, and always at least
once a year up to the present time. This stately
plant showed the long-sought peculiarity of pro-
ducing a number of new species every year.
Some of them were observed directly in the
field, either as stems or rosettes. The latter
could be transplanted into my garden for further
observation, and the stems yielded seeds to be
sown under like control. Others were too weak
to live a sufficiently long time in the field. They
were discovered by sowing seed from indifferent
plants of the wild locality in the garden. A third

84

Mutating Plants

and last method of getting still more new species
from the original strain was the repetition of the
sowing process, by saving and sowing the seed
which ripened on the introduced plants. These
various methods have led to the discovery of
over a dozen new types, never previously ob-
served or described." Some of these De Vries
regards as varieties, in the sense in which he
uses the words ; others, he maintains, are real
progressive species, some of which are strong
and healthy, others weaker and apparently not
destined to be successful. All these types proved
absolutely constant from seed. " Hundreds of
thousands of seedlings may have arisen, but they
always come true and never revert to the original
O. lamarckiana type. But some of them, how-
ever, are, like their parent form, liable to muta-
tions." The case of the evening primrose is by
no means an isolated one. De Vries cites several
other instances of plants in a mutating state.
"The common poppy," he says (p. 189), "varies
in height, in colour of foliage and flowers ; the
last are often double or laciniated. It may have
white or bluish seeds, the capsules may open
themselves or remain closed, and so on. But
every single variety is absolutely constant, and
never runs into another when the flowers are
artificially pollinated and the visits of insects
excluded." Similarly the garden carnation some-
times gives rise to the wheat-ear form. " In this

85

The Making of Species

variety," writes De Vries (p. 228), " the flower is
suppressed, and the loss is attended by a corres-
ponding increase in the number of pairs of bracts.
This malformation results in square spikes, or
somewhat elongated heads, consisting only of the
greenish bracts. As there are no flowers, the
variety is quite sterile, and, as it is not regarded
by horticulturists as an improvement on the
ordinary bright carnations, it is seldom multiplied
by layering. Notwithstanding this it appears
from time to time, and has been seen in different
countries and at different periods, and what is of
great importance for us, in different strains of
carnations. Though sterile, and obviously dying
out as often as it springs into existence, it is
nearly two centuries old. It was described in the
beginning of the eighteenth century by Volckamer,
and afterwards by Jaeger, De Candolle, Weber,
Masters, Magnus, and many other botanists. I
have had it twice at different times and from
different growers." Similarly, the long-headed
green dahlia arose twice over some years ago in
the nursery of Messrs Zocher & Co.

Further, the peloric Toad-flax (Linaria vul-
garis peloria) is, De Vries informs us, "known to
have originated from the ordinary type at
different times and in different countries under
more or less divergent conditions." And, as this
variety is wholly barren, it must in each instance
have had an independent origin. Lastly, the

86

Mutation Theory Criticised

purple beech seems to be a mutation which has
originated at least three times over.

Every one interested in biological theory
should read both Species and Varieties and Plant
Breeding by De Vries, works which are of
incalculable value to the horticulturist and agri-
culturist as well as to the biologist.

While not wishing to detract in any way from
the truly splendid work done by De Vries, we
feel constrained to bring several charges against
him.

Firstly, he suffers from the complaint that
seizes nine out of ten originators of new theories.
He pushes his theory to extreme lengths ; he
allows his imagination to run away with him.
We do not think that on the evidence available
he is justified in asserting that every species
passes through alternating periods of comparative
quiescence and periods in which it throws off,
as mutations, swarms of elementary species. He
is justified in asserting that discontinuous varia-
tion is by no means an uncommon phenomenon,
but further than this it does not seem safe to go
at present.

Secondly, he ought to lay more stress on the
fact that Oenothera lamarckiana is a plant which
does not appear to be known in the wild state,
and that it is therefore possibly a hybrid plant,
and the so-called elementary species which it
gives off may be merely the varieties out of

87

The Making of Species

which it has been built up. Boulenger and
Bailey have both studied this plant, and they
have not been able to witness all the mutations
of which De Vries speaks, so that the former
says, " The fact that Oenothera lamarckiana was
originally described from a garden flower, grown
in the Paris Jar din des Plantes, and that, in spite
of diligent search, it has not been discovered
wild anywhere in America, favours the prob-
ability that it was produced by crossing various
forms of the polymorphic Oenothera biennis, which
had been previously introduced in Europe."

It has further been objected that, even if
these various forms which Lamarck's evening
primrose throws off are true mutations, they
ought not to be called new species, for they do
not differ sufficiently from the parent species
to deserve the name of new species. The reply
to this criticism is that De Vries asserts that
mutations produce new elementary species, which
are not the same things as new species in the
ordinary sense of the term. Most Linnaean
species differ from one another to a far greater
extent than do elementary species. It seems
to us quite plain that new species arise, not by
a single mutation, but by two or three successive
mutations which occur in various parts of an
organism.

First arises a well-marked variety, by a single
mutation. Subsequent mutations follow, so that

88

Definition of a Species

a distinct race is produced. And, finally, fresh
mutations occur, so that a new species is eventu-
ally produced.

What De Vries calls an elementary species
the majority of systematists would call a well-
marked variety.

We may take this opportunity of remarking
that the definition of a species is one on which
naturalists seem unable to agree.

So vast is the field of biology, that now-a-days
biologists are compelled to specialise to some
extent. Thus we have botanists, ornithologists,
those who devote themselves to the study of
mammals, those who confine themselves to
reptiles, or insects, or fishes, or crustaceans, or
bacteria, etc.

Now each class of systematists has its own
particular criterion of what constitutes a species.
Ornithologists do not seem very exacting. Most
of them appear to consider a constant difference
of colour sufficient for the formation into a species
of the birds that display such a variation. Those
who study reptiles, on the other hand, do not
allow that a mere difference in colour is sufficient
to promote its possessor to specific rank. Into
these nice questions we cannot enter. For our
purpose a species is a group of individuals that
differ from all other individuals in displaying
certain well-marked and tolerably constant charac-
ters, which they transmit to their offspring.

89

The Making of Species

her front grew from the top and right to the front
of her wattle, and not from slightly behind, as in
almost every other turbit of her day ; thus, as
the wattle developed and grew coarser, the front
became more developed, and made her head
larger without in any way spoiling the sweep of
the profile.

" The same year ' Ladybird ' was bred I bred
eight others from the same pair, and with one
exception all turned out to be hens. There was
only one other hen, however (a dun), that had
this same point, but in a lesser degree than
' Ladybird,' and from these two hens nearly all
my blacks, and several of my blues are de-
scended."

Mr Scatliff, having " spotted " this point,
looked about him for another bird having the
peculiarity, with the object, if possible, of fixing
the same in his strain. He discovered this point
in a pigeon belonging to Mr Johnston of Hull,
and purchased the bird for £20. But it died in
the following spring without producing for Mr
Scatliff a single young one. The next year
Scatliff found that a bird belonging to a Mr
Brannam had the required peculiarity and so
purchased him for £20. But that cock, too, died
before anything was bred from him. Nothing
daunted, Scatliff found that another of Brannam's
cocks displayed the same peculiarity, so purchased
him in 1899 for ^15, but he also died before the

92

A TURBIT BELONGING TO MR. H. P. SCATLIFF
From " The Modern Turbit" published by " The Feathered World" London.

" ScatlifF Strain " of Turbit

year was out. Meanwhile Scatliff had, by mating
up " Ladybird " with the most likely of his own
cocks, succeeded in producing one or two young
cocks with the desired point. By breeding these
with their mother " Ladybird " and their off-
spring again with " Ladybird," Scatliff eventually
succeeded in breeding some turbits, both blacks
and duns, with the required peculiarity fully
developed, but not before he had spent a further
sum of ^"55 on two other cocks, both of which
died before they could be mated with the famous
" Ladybird." However, amid all his misfortunes,
Scatliff informs us that he bought one bird, by
name "Amazement," which did assist him in
fixing his strain. Thus Scatliff spent consider-
ably over ,£100 in purchases, and took eight years
fixing the peculiarity in question. Had " Lady-
bird " been a flower, the peculiarity could probably
have been fixed in one generation by self-
fertilisation.

This furnishes an excellent example of the
trouble which breeders will take, and the expense
to which they will go in order to produce a
desired result. Nevertheless, it appears to be
the fashion for scientific men to decry the work
of the breeder.

Let us now pass on to consider the cases of
mutations which are known to have occurred
among animals.

93

The Making of Species

MUTATIONS AMONG ANIMALS

Some instances of great and sudden variation
in domesticated animals have become classical,
and been detailed in almost every work on
evolution. These are, firstly, the celebrated
hornless Paraguay cattle. This hornless breed,
or rather the ancestor of the breed, arose quite
suddenly.

Many domestic horned breeds of animals,
especially sheep and goats, throw off hornless
sports. Were a hornless breed of buffalo found
in nature, it would undoubtedly be ranked a
new species, and the Wallaceians would doubt-
less exercise much ingenuity in explaining how
natural selection had brought about the gradual
disappearance of the horns ; and palaeontologists,
being baffled in their search for intermediaries
between the hornless species and their horned
ancestors, would complain of the imperfection of
the geological record.

It may, perhaps, be argued that this hornless
mutation was a direct result of the unnatural
conditions to which the Paraguay cattle were
subjected, it may be asserted that since there
are no species of hornless cattle in nature, such
mutations have never occurred under natural
conditions, and hence the Paraguay cattle prove
nothing. As a matter of fact, we know that in
nature a great many mutations occur which are

94

Mutations among Mammals

not perpetuated because not beneficial to the
species. A hornless individual in the wild
state would stand but little chance in fighting for
females against his horned brethren. We must
keep clearly in mind that the theory of mutation
does not seek to abolish natural selection; it
merely affords that force something substantial
to work upon.

The second classical example of a leap taken
by nature is furnished by the Franqueiro breed
of long-horned cattle in Brazil. These furnish
us with an example of a mutation in the other
direction. Then there is the Niata or bull-dog
breed of cattle, which are also South American.
These instances would seem to indicate that
cattle are what De Vries would call " in a mutat-
ing state " in that part of the world.

The other classical examples of great and
sudden variations are the Ancon sheep of Massa-
chusetts, the Mauchamp breed of Merino sheep,
the tufted turkeys, and the long-haired race of
guinea-pigs.

The " wonder horses," whose manes and tails
grow to an extraordinary length, so as to trail
on the ground, may perhaps be cited as a race
which originated in a sudden mutation. They
are all descendants of a single individual,
Linus I., whose mane and tail were respectively
eighteen and twenty-one feet long. But in this
case it is important to note that the parents and

95

The Making of Species

grandparents of Linus I. had exceptionally long
hair.

Coming now to birds we find several undoubted
examples of mutations, or new forms which have
come suddenly into being.

The black-winged peafowl, whose peculiarities
were commented on by Darwin, afford a striking
example of this phenomenon. These birds breed
true when mated together, and are known to
have arisen from common peafowl in no less
than nine instances. The cocks have the wings
(except the primary quills), black glossed with
blue and green, and have the thighs black,
whereas, in the ordinary peacock, the same part
of the wing is nearly all mottled black and pale
buff, and the thighs are drab. The black-winged
hen, on the other hand, is nearly white, but has
a black tail and black speckling on the upper
surface of the body, while her primary quills are
cinnamon coloured as in male peafowl, not
drab as in the normal hens. The young are
white when hatched, the young cock gradually
assuming the dark colour as he matures.

This mutation, which, in one case quoted by
Darwin, increased among a flock of peafowl
until the black-winged supplanted the ordinary
kind, is so distinct in appearance in all stages
that it was formerly supposed to be a true species
(Pavo nigripennis), of which the wild habitat was
unknown.

Mutations among Birds

The Golden Pheasant (Chrysolophus pictus)
produces, in domestication, the dark-throated
form (C. obscurus), in which the cock has the
throat sooty-black instead of buff, and the
scapulars or shoulder feathers black instead of
red. Moreover, the two middle-tail-feathers are
barred with black and brown like the lateral
ones, while in the ordinary form they are spotted
with brown on a black ground. The hens have
a chocolate-brown ground-colour instead of
yellow-ochre as in the normal type. The
chicks are likewise darker.

The common duck, in domestication, when
coloured like the wild mallard, sometimes pro-
duces a form in which the chocolate breast and
white collar of the drake are absent, the pencilled
grey of the abdomen reaching up to the green
neck. In this mutation the duck has the head
uniformly speckled black and brown, and lacks
the light eye-brow and cheek-stripes found in
the normal duck. Both sexes have the bar on
the wing dull black instead of metallic blue.

The ducklings which ultimately bear this
plumage are sooty-black throughout, not black
and yellow like normal ones.

The phenomenon of mutation is not confined
to animals in a state of domestication. The
common Little Owl of Europe (Athene noctud]
has produced the mutation A. chiaradia in the
wild state. In this the irides are dark, instead of
G 97

The Making of Species

yellow as in the normal type, and the plumage of
the back of the wings is longitudinally streaked
with white instead of barred. Several examples
of this form were found, along with normal young,
in the nest of one particular pair of little owls in
Italy, but the whole family were foolishly ex-
terminated by local ornithologists.

The reed bunting (Emberiza schoeniclus) exists
in two distinct forms — one having a much stouter
bill than the other (E. pyrrhuloides). This prob-
ably is an example of a mutation.

The rare yellow-rumped Finch (Munia ftavi-
prymna), of Australia, has displayed a tendency
to change into the allied and far commoner
chestnut - breasted Finch ( M. castaneithorax]
during the lifetime of the individual (Avicultural
Magazine, 1907). Conversely, the male of the
common Red-billed Weaver (Quelea quelea) of
Africa has been found in its old age to assume
the characters of the comparatively rare Q. russi,
its black throat becoming pale buff as in that
form.

Everyone is familiar with the chequered
variety of the common blue - rock pigeon, in
which the wings are regularly mottled with
black instead of being barred. This form some-
times occurs among wild birds, so that it has
been described as a distinct species. It is
important to note that there are red, dun, and
silver chequers as well as blue ones.

98

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Mutations among Birds

A well-marked mutation which appears regu-
larly in nature is the red-headed variety of the
beautiful Gouldian Finch (Poephila mirabilis)
of North Australia. Normally the head of the
cock is black, but in about ten per cent, of the
individuals the cock has a crimson head, while
that of the hen is dull crimson and black.

Mutations which occur with such regularity
are certainly rare. On the other hand, there are
certain mutations which we may expect to see
appear in any species of plant or animal.

Albinistic forms are a case in point, and less
frequently we see white varieties which are not
pure albinos, because the eye retains some at
least of the normal pigment. As examples, we
may cite white dogs, cats, fowls, horses, ducks,
geese, and Java sparrows among domesticated
animals, and the white forms of the Amazonian
dolphin and of the giant Petrel of the South
seas (Ossifraga gigantea] among wild creatures.

In a white mutation the eye may lose all its
pigment, and then we have a true albino. Such
forms on account of their imperfect vision cannot
survive in a state of nature, hence no wild pink-
eyed species are known.

Or the eye may display a partial loss of pig-
ment, as, for example, in the white domestic
forms of the common goose, the Chinese goose,
and the Muscovy duck. Finn saw a case in
which the eyes of a pink-eyed rabbit changed

99

The Making of Species

after death into this type of eye — that is, with
the pupil black and the iris blue. It is to be
observed that this kind of eye sometimes occurs
in coloured horses, rabbits, and dogs. Finally,
we have white mutations in which the eye loses
none of the pigment. These are abundant in
nature, and probably most of the white species
of birds — as, for example, some egrets, swans,
etc. — arose in this way.1 Pure white species are
comparatively uncommon in nature, because,
except in snow-clad regions, white creatures are
easily seen by their adversaries. Most white
birds are of considerable size, and well able to
look after themselves.

Similarly black mutations occur frequently
among animals, both under domestication and
in a state of nature. All are familiar with black
dogs, cats, horses, fowls, ducks, pigeons. Black
mutations, however, do not occur nearly so
frequently as white ones. So far as we are
aware no black mutation has been recorded
among canaries, geese, guinea-fowl, ferrets,
Java sparrows or doves, all of which produce
white mutations.

On the other hand, in the wild state black
species occur more frequently than normal-eyed
white forms. This is probably because such

1 Some egrets, such as the rock-egrets (Demiegrettd) of eastern
tropical coasts, are normally grey, but may be white, and this
whiteness may be confined in individuals to the young or adult
States.

100

Colour Mutations

creatures are less conspicuous than white ones.
As examples of black mutations which occur in
nature, we may cite black leopards, water
rats, squirrels, foxes, barking deer (Cervulus
muntjac), hawk-eagles, harriers, peppered moth
(Amphidasys betularia), etc.

That many black species have arisen as sudden
mutations from lighter-coloured animals seems
tolerably certain from the facts that in Malacca
the black leopard forms a local race ; that some
of the Gibbon apes are as often black as light
coloured ; that the American black bear is some-
times brown, while the other bears, when not
brown, are almost invariably black.

Not uncommon, although rarer than black or
melanistic forms, are reddish or chestnut varieties.
These occur both among tame and wild animals.
Among domesticated creatures, sandy cats, " red "
pigeons, buff fowls, chestnut horses, red guinea
pigs afford examples of this mutation. Among
wild animals many of the species of squirrel, not
naturally red, produce red mutations ; and some of
the grey owls — as, for example, the Indian race
of the Scops (Scops giu] — throw off a red or
chestnut form. As everyone knows, some species
are normally red.

Green or olive species not unfrequently throw
off yellow mutations. As examples of these we
may cite yellow canaries, yellow budgerigars
(Melopsittacus undulatus)^ goldfish, golden tench,

IOI

The Making of Species

and the golden form of the common carp among
captive animals ; and among animals in a state
of nature, yellow forms have been recorded of the
rose-ringed Paroquet (Palceornis torquatus), the
green woodpecker, the pike, and the eel. These
lutinistic forms usually have normally coloured
eyes. Sometimes, but only very rarely, these
yellow forms throw off white sports — as, for
example, the " silver" form of the goldfish.
Finn has seen a white variety of the common
carp. White canaries are excessively rare, while
white budgerigars are unknown.

It is worthy of note that entirely yellow species
of birds and fish are unknown. We would suggest
that the explanation of this is that yellowness is
correlated with some physical characteristic un-
favourable to an organism exposed to the
struggle for existence ; hence individuals which
are yellow are not permitted to survive. In some
species of moths individuals occur in which the
parts normally red are yellow. According to
Bateson, a chalk pit at Madingly, near Cam-
bridge, has long been known to collectors as a
habitat of a yellow-marked form of the six-spot
Bur net Moth (Zygczna filipendulcz). These
lutinistic forms are not confined to one genus
of Butterflies. Moreover, in the Pin-tailed Non-
pareil Finch (Eytkrura prasina) of the Eastern
Archipelago the red tail and other red parts of
the plumage are not infrequently replaced by

102

Mutations among Invertebrates

yellow in wild individuals of either sex and of
any age. In the blue-fronted Amazon parrot
(Chrysotis cestiva) — a most variable bird — the
normally red edge of the pinion is sometimes
yellow. Bateson, in his Materials for the Study
of Variation, gives other examples of this kind
of variation.

As further instances of mutations among
animals which have been observed in nature, we
may mention the valezina form of the female of
the Silver- washed Fritillary Butterfly (Argynnis
paphia) and the helice form of the female Clouded-
yellow Butterfly (Colzas edusa).

The common jelly-fish is an organism which
frequently throws off sports, and some zoologists
are of opinion that the medusoid Pseudoclytia
pentata arose by a discontinuous variation from
Epenthesis folleata or a closely allied form.
Thomson discusses this particular case at some
length on pages 87-89 of his Heredity, and gives
it as his opinion that the evidence in favour
of this latter having arisen as a mutation is
"exceedingly strong."

It is our belief that many species of birds
which occur in nature have been derived from
other species which still exist, but as no one has
ever seen the mutation take place, we cannot
furnish any proof thereof. We merely rely on
the fact that the species in question differ so
slightly from one another that there seems every

103

The Making of Species

likelihood that they have suddenly arisen and
managed to establish themselves alongside of the
parent species.

The Curassows, Crax grayi, C. hecki, each
of which is only known by a very few specimens,
appear to be mutations of the female of the
globose Curassow, Crax globicera. The fact
that when a female hecki bred in the London
Zoological Gardens with a male globicera, the
solitary young one which lived to grow up was a
pure globicera, renders the assumption almost
certain.

The Chamba Monaul (Lophophorus chambanus)
seems to be a mutation of the male of the
common Monaul or Impeyan Pheasant {Lopho-
phorus impeyanus\ the common species of the
Himalayas.

The Three-coloured Mannikin (Muniamalacca)
of South India is probably simply a white-bellied
form of the widely-ranging Black-headed Man-
nikin (M. atricapilla), which has the abdomen
chestnut like the back. Intermediate wild-
caught forms have been recorded.

The African Cordon-bleu (Estrelda phcenicotis)
and Blue-bellied Waxbill (E. cyanogastrd] would
also seem to be mutations, as almost the only
difference between them lies in the fact that
the male of the former has a crimson cheek-
patch, which is wanting in the latter.

The Ringed Finch (Stictoptera annulosa) of
104

Mutating Species

Java, and Bicheno's Finch (S. bichenovii) of
Australia, only differ in the former having the
rump black, while in the latter it is white, and
this difference appears to be of the nature of a
mutation.

So, it might be urged, is the pure white breast
of the male Upland Goose (Chloephaga magel-
lanicd), which part, in the very similar C. dispar,
is barred as in the females, the latter form being
probably the ancestor.

The differences between the silver-grey-necked
Crowned Crane of the Cape (Balearica chryso-
pelargus) and the dark-necked species of West
Africa (B. regulorum) seem also to be not more
than could be accounted for by mutation.

Peculiar forms, such as a rabbit with a con-
voluted brain or a mouse with a peculiar pattern
of molar teeth, have been come upon by
anatomists.

The above-cited mutations are all very con-
siderable ones, and we do not profess to have
mentioned a tenth part of those which have
actually been recorded.

We trust that we have collected and set forth
sufficient evidence to show that the phenomenon
of discontinuous variation is a very general one,
and this would seem to tell against the hypo-
thesis of De Vries that species pass through
alternate periods of comparative stability and
periods when swarms of mutations appear. We

105

The Making of Species

think it more probable that all species throw off
at greater or less intervals discontinuous varia-
tions, and that it is upon these that natural selec-
tion acts.

We further hope that we have succeeded in
making clear what we believe to be the very
sharp distinction between continuous and dis-
continuous variations, even when the latter are
inconsiderable, as frequently happens.

Before leaving the subject of variation it is
necessary to notice the distinction, which Weis-
mann was the first to emphasise, between somatic
and germinal variations.

Every adult organism must be regarded as the
result of two sets of forces ; inherited tendencies
or internal forces, and the action of environment
or external forces. The differences which the
various members of a family show are due in
part to the initial differences in the germinal
material of which they are composed, and in part
to the differences of their environment. The
former differences are the result of what we may
call germinal variations, and the latter the result
of somatic variations. It is scarcely ever possible
to say of any particular variation that it is a
germinal or a somatic one, because even before
birth a developing organism has been subjected
to environmental influences. One of a litter may
have received more nourishment than the others.
Nevertheless, any marked variation which appears

106

Somatic and Germinal Variations

at birth is probably largely germinal. According
to Weismann and the majority of zoologists,
there is a fundamental difference between these
germinal and somatic variations, in that the
former tend to be inherited, while the latter are
never inherited. Weismann believes that very
early in the formation of the embryo the cells
which will form the generative organs of the
developing organism are separated off from those
cells which will go to build up the body, and
become as much isolated from them as if they
were contained in a hermetically-sealed flask, so
that they remain totally unaffected by any
changes which the environment effects in the
somatic cells. Therefore, says Weismann,
acquired characters cannot be inherited.

While the majority of zoologists believe that
acquired characters are not inherited, probably
not many will go so far as Weismann and
declare that the environment cannot exercise
any effect whatever on the germ cells.

Even though acquired characters or variations
are not inherited, it does not follow that they do
not play an important part in evolution. Acquired
variations are the result of the way in which an
organism reacts to its environment. If an organ-
ism is unable to react to its environment it must
inevitably perish. If it is able to react, it matters
not, so far as the chances of survival of the
organism are concerned, whether the adaptation

107

The Making of Species

is the result of a congenital variation or a somatic
one. This will be rendered clear by a hypotheti-
cal example. Let us suppose that a certain
mammal is forced, owing to the intensity of the
struggle for existence, to migrate into the Arctic
regions. Let us further suppose that this organ-
ism is preyed upon by some creature that hunts
by sight rather than by scent. Let us yet
further imagine that this predacious species is
swifter than our animal, on which it preys. It
is obvious that, other things being equal, the
more closely the creature preyed upon assimilates
to its surroundings the more likely is it to escape
the observation of its foes, and so to survive and
give birth to offspring. Now suppose that the
glare from the snow-covered ground bleaches its
coat. This whitening of the fur is a somatic
variation, one which is induced by the environ-
ment. Such an animal will be as difficult to see,
if the bleaching is such as to render it snow-
white, as if its whiteness were due to a germinal
variation. Thus, as regards its chances of sur-
vival, it matters not whether its whiteness be the
result of germinal or somatic variation. But if
the whiteness is due to a somatic variation, its
offspring will show no tendency to inherit the
variation ; they will have in turn to undergo the
bleaching process. If, on the other hand, the
whiteness is due to a germinal variation, the
offspring will tend to inherit this peculiarity and

108

Somatic Variations

to be born white. In such a case, it is unlikely
that the fur of an organism which is naturally
coloured will be completely bleached by the
snow, and, even if it be, the bleaching process
will take time, meanwhile the creature will be
comparatively conspicuous. So that those which
are naturally whiter than the average, that is to
say, those in which the tendency to whiteness
appears as a germinal variation, will be less con-
spicuous than those which tend to be the ordinary
colour. Thus the former will enjoy a better
chance of survival, and will be likely to transmit
their whiteness to their offspring in so far as it
is due to a germinal or congenital variation.

Thus, although none of the whiteness due to
somatic variations is transmitted to the offspring,
such variations are of considerable importance
to the species, as they enable it to survive and
allow time for the germinal variations in the
required direction to appear.

That this case need not be purely hypothetical
is shown by the fact that dun domestic pigeons,
which are of an earthy-brown colour when fresh
moulted, soon fade in the sun to a dull creamy
hue. Thus a coloration adapted to an ordinary
soil could soon be suited to a desert environ-
ment. The ruddy sheldrake also, normally a
bright chestnut- coloured bird, and one that haunts
exposed sunny places, in many cases fades very
much, becoming almost straw-coloured.

109

The Making of Species

Many variations which organisms display are
of a mixed kind, being in part the result of inner
forces and in part due to the action of the en-
vironment. In so far as they are due to this
latter they do not appear to be inherited.

Thus, although we cannot say of many varia-
tions whether they are germinal, or somatic, or
of a mixed kind, it is of great importance to keep
continually in mind the fundamental differences
between the two kinds.

Some somatic variations are due to the direct
action of the environment ; they are merely the
expression of the manner in which an organism
responds to external stimuli.

What is the cause of germinal variations?
This is a question to which we are not yet in a
position to give a satisfactory answer.

The attempt to explain their origin plunges us
into the realm of theory. This doubtless is a
realm full of fascination, but it is an unexplored
region of extreme darkness, in which, we believe,
it is scarcely possible to take the right road until
more of the light of fact has been shed upon it.

In the chapter dealing with inheritance we
shall indicate the lines along which it is likely
that future progress will be made.

CHAPTER IV

HYBRIDISM

The alleged sterility of hybrids a stumbling-block to evolutionists —
Huxley's views — Wallace on the sterility of hybrids — Darwin
on the same — Wallace's theory that the infertility of hybrids
has been caused by Natural Selection so as to prevent the
evils of intercrossing — Crosses between distinct species not
necessarily infertile — Fertile crosses between species of plants
— Sterile plant hybrids — Fertile mammalian hybrids — Fertile
bird hybrids — Fertile hybrids among amphibia — Limits of
hybridisation — Multiple hybrids — Characters of hybrids —
Hybridism does not appear to have exercised much effect on
the origin of new species.

alleged sterility of the hybrids pro-
duced by crossing different species
has long proved a great stumbling-
block to evolutionists. Huxley, in
particular, felt the force of this objection to the
Darwinian theory. If the hybrids between
natural species are sterile, while those of all
the varieties which the breeder has produced
are perfectly fertile, it is obviously quite use-
less for evolutionists to point with pride to the
results obtained by the breeder, and to declare
that his products differ from one another to a
greater extent than do many well-recognised
species.

in

The Making of Species

"After much consideration, and with no bias
against Mr Darwin's views," wrote Huxley to
the Westminster Review in 1860, "it is our clear
conviction that, as the evidence now stands, it is
not absolutely proven that a group of animals
having all the characters exhibited by species in
nature, has ever been originated by selection,
whether natural or artificial. Groups having the
morphological nature of species, distinct and per-
manent races, in fact, have been so produced
over and over again ; but there is no positive
evidence at present that any group of animals
has, by variation and selective breeding, given
rise to another group which was in the least
degree infertile with the first. Mr Darwin is
perfectly aware of this weak point, and brings
forward a multitude of ingenious and important
arguments to diminish the force of the objection.
We admit the value of these arguments to the
fullest extent; nay, we will go so far as to express
our belief that experiments, conducted by a skil-
ful physiologist, would very probably obtain the
desired production of mutually more or less in-
fertile breeds from a common stock in a com-
paratively few years; but still, as the case stands
at present, this little 'rift within the lute' is not
to be disguised or overlooked."

Similarly Wallace writes, at the beginning of
chapter vii. of his Darwinism : " One of the
greatest, or perhaps we may say the greatest, of

112

Alleged Sterility of Hybrids

all the difficulties in the way of accepting the
theory of natural selection as a complete expla-
nation of the origin of species, has been the
remarkable difference between varieties and
species in respect of fertility when crossed.
Generally speaking, it may be said that the
varieties of any one species, however different
they may be in external appearance, are per-
fectly fertile when crossed, and their mongrel
offspring are equally fertile when bred among
themselves ; while distinct species, on the other
hand, however closely they may resemble one
another externally, are usually infertile when
crossed, and their hybrid offspring absolutely
sterile. This used to be considered a fixed
law of nature, constituting the absolute test and
criterion of a species as distinct from a variety;
and so long as it was believed that species were
separate creations, or at all events had an origin
quite distinct from that of varieties, this law could
have no exceptions, because if any two species
had been found to be fertile when crossed and
their hybrid offspring to be also fertile, this fact
would have been held to prove them to be not
species but varieties. On the other hand, if two
varieties had been found to be infertile, or their
mongrel offspring to be sterile, then it would
have been said — These are not varieties, but
true species. Thus the old theory led inevitably
to reasoning in a circle, and what might be
H 113

The Making of Species

only a rather common fact was elevated into a
law which had no exceptions."

Thus the sterility of hybrids was a zoological
bogey which had to be demolished. The plan
of campaign adopted by Darwin and Wallace
was, firstly, to try to disprove the assertion that
the hybrids between different species are always
sterile, and secondly, to find a reason for the
alleged sterility of these hybrids.

Darwin succeeded in obtaining some examples
of crosses between botanical species which
were said to be fertile. These he quotes in
chapter viii. of The Origin of Species. As
regards animals, he met with less success.
" Although," he writes, " I do not know of any
thoroughly well-authenticated cases of perfectly
fertile hybrid animals, I have some reason to
believe that the hybrids from Cervulus vaginalis
and reevesii, and from Phasianus colchicus and
P. torquatus and with P. versicolor are perfectly
fertile. There is no doubt that these three
pheasants, namely, the common, the true ring-
necked, and the Japan, intercross, and are
becoming blended together in the woods of
several parts of England. The hybrids from
the common and Chinese geese (A. cygnoides\
species which are so different that they are
generally ranked in distinct genera, have often
been bred in this country with either pure
parent, and in one single instance they have

114

Fertile Hybrids

bred inter se. This was effected by Mr Eyton,
who raised two hybrids from the same parents
but from different hatches ; and from these two
birds he raised no less than eight hybrids (grand-
children of the pure geese) from one nest. In
India, however, these cross-bred geese must
be far more fertile ; for I am assured by two
eminently capable judges, namely, Mr Blyth and
Captain Hutton, that whole flocks of these
crossed geese are kept in various parts of the
country ; and as they are kept for profit, where
neither pure parent species exists, they must
certainly be highly fertile.1 ... So again there
is reason to believe that our European and the
humped Indian cattle are quite fertile together ;
and from facts communicated to me by Mr
Blyth, I think they must be considered as
distinct species."

Darwin does not seem to have been very
satisfied with the evidence he had collected, for
he said : " Finally, looking to all the ascertained
facts on the intercrossing of plants and animals,
it may be concluded that some degree of sterility,

1 After years of observation of these Indian geese, Finn is
convinced they are now, at all events, pure Chinese ; it is possible
that they really were hybrids in Blyth's time, but that fresh im-
portations of geese from China, such as still occur, may have
ultimately swamped the blood of the common goose. The fertility
of the hybrid geese was, however, known to such early writers as
Pallas and Linnaeus. Darwin himself, at a later date, bred
five young from a pair of such hybrids (Nature, Jan. I, 1880,
p. 207).

"5

The Making of Species

both in first crosses and in hybrids, is an ex-
tremely general result ; but that it cannot, under
our present state of knowledge, be considered as
absolutely universal."

Similarly Wallace writes : " Nevertheless, the
fact remains that most species which have
hitherto been crossed produce sterile hybrids,
as in the well-known case of the mule ; while
almost all domestic varieties, when crossed,
produce offspring which are perfectly fertile
among themselves."

Darwin resorted to much ingenious argument
in his attempt to explain what he believed to
be the almost universal sterility of hybrids, as
opposed to mongrels or crosses between varieties.
He pointed out that changed conditions tend to
produce sterility, as is evidenced by the fact that
many creatures refuse to breed in confinement,
and believed that the crossing of distinct wild
species produced a similar effect on the sexual
organs. He expressed his belief that the early
death of the embryos is a very frequent cause of
sterility in first crosses.

Wallace thus summarises Darwin's conclusions
as to the cause of the sterility of hybrids : " The
sterility or infertility of species with each other,
whether manifested in the difficulty of obtaining
first crosses between them or in the sterility of
the hybrids thus obtained, is not a constant or
necessary result of species difference, but is in-

116

A Biological Bogey

cidental on unknown peculiarities of the repro-
ductive system. These peculiarities constantly
tend to arise under changed conditions owing
to the extreme susceptibility of that system, and
they are usually correlated with variations of
form or of colour. Hence, as fixed differences
of form and colour, slowly gained by natural
selection in adaptation to changed conditions,
are what essentially characterise distinct species,
some amount of infertility between species is
the usual result."

But Wallace has not been content to let the
matter remain where Darwin left it. He has
boldly tried to make an ally of this bogey of the
infertility of hybrids. On page 1 79 of Darwinism
he argues, most ingeniously, that the sterility of
hybrids has been actually produced by natural
selection to prevent the evils of the intercrossing
of allied species. We will not reproduce his
argument for the simple reason that it is now
well-known, or should be well-known, that hybrids
between allied species are by no means always
sterile. The doctrine of the infertility of hybrids
seems to have been founded on the fact that the
hybrids best known to breeders, namely the
cross between the ass and the horse, and those
between the canary and other finches, are sterile.

117

The Making of Species

FERTILE CROSSES BETWEEN SPECIES OF PLANTS

In the case of plants the number of fertile
hybrids between species is so large that we
cannot attempt to enumerate them. De Vries
cites several instances in Lecture IX of his
Species and Varieties : Their Origin by Mutation.

One of these — the hybrid between the purple
and the yellow species of Lucerne which is
known to botanists as Medicago media is, writes
De Vries, " cultivated in some parts of Germany
on a large scale, as it is more productive than
the ordinary lucerne." Other examples of per-
fectly fertile plant hybrids cited by De Vries
are the crosses between Anemone magellanica
and A. sylvestris, between Salix alba and Salix
pentandra, between Rhododendron hirsutum and
R. ferrugineum.

He gives an instance of a hybrid — sEgilops
speltaformis, which, though fertile, is not so
fertile as a normal species would be. It is worthy
of note that Burbank of California has obtained
a hybrid between the blackberry and the rasp-
berry, which is not only fertile, but quite popular
as producing a novel fruit.

STERILE PLANT HYBRIDS

De Vries does not cite nearly so many examples
of sterile hybrids, presumably because they are
not so easy to find. He mentions the sterile

118

Fertile Mammalian Hybrids

" Gordon's currant," which is considered to be a
hybrid between the Californian and the Missouri
species. He also gives Cytisus adami as an
absolutely sterile hybrid, this being a cross
between two species of Labernum — the common
and the purple.

In the case of animals the known hybrids are
so much less numerous that we are able to furnish
a list which may be taken as fairly exhaustive.

FERTILE MAMMALIAN HYBRIDS

Taking the mammals first, we find that, in
addition to those cited by Darwin, there are
several recorded cases of crosses between well-
defined species which are fertile.

There is the hybrid between the brown bear
and the polar bear, which is perfectly fertile. In
the London Zoological Gardens there is a speci-
men of this hybrid, also one of this individual's
offspring by a pure polar bear.

The stoat has been crossed with the domestic
ferret, a descendant of the polecat, a very distinct
species ; the resulting hybrids have nevertheless
proved fertile.

The bull American bison produces with the
domestic cow hybrids known as " cataloes,"
which are fertile. The reverse cross of the
domestic bull with the bison cow does not, how-
ever, succeed at all, which reminds us of what
happens in the case of finch-hybrids.

119

The Making of Species

Bird fanciers when crossing the canary with
wild species of finch, almost invariably use a hen
canary as the female parent, because domesticated
female animals breed more readily than do captive
wild ones.

The domestic yak breeds frequently in the
Himalayas with the perfectly distinct zebu or
humped cow of India, and the hybrids are fertile.
Yet the zebu and the Indian buffalo, living con-
stantly side by side in the plains of India, never
interbreed at all.

Among wild ruminants of this hollow-horned
family, the Himalayan Argali (Ovis ammon) ram,
a giant sheep of the size of a donkey, has been
known to appropriate a herd of ewes of the Urial
(O. vignei\ a very distinct species of the size of
a domestic sheep. Many hybrids were born, and
these, in turn, bred with the pure urials of the
herd.

In our parks the little Sika deer of Japan
(Cervus sika], a species about the size of the
fallow-deer, with an even more marked seasonal
change of colouration and antlers having only
three tines, breeds with the red deer, and the
hybrids are fertile.

In certain parts of Asia Minor the natives
cross the female one-humped camel with the male
of the bactrian or two-humped species. The
hybrids (which are one-humped) will breed with
the pure species ; but, although the hybrids are

120

Fertile Bird Hybrids

strong and useful, the three-quarter bred beasts
are apparently of little value.

FERTILE BIRD HYBRIDS

Coming to birds, we are confronted by a
longer list of fertile hybrids. This is the natural
outcome of the fact that a greater number of
bird species have been kept in captivity.

The oldest known fertile hybrid is that
between the common and Chinese geese above
cited, but many others have since been re-
corded. Even among birds so seldom bred,
comparatively, as the parrot family, a fertile
hybrid has been produced, that between the Aus-
tralian Rosella Parrakeet (Platycercus eximius)
and Pennant's Parrakeet (P. elegans}. The
hybrid was first described as a distinct species,
the Red-mantled Parrakeet (P. erythropeplus).
These two parrakeets, though nearly allied, are
very distinct ; Pennant's being coloured red, blue,
and black, with a distinct young plumage of
uniform dull green ; the rosella in addition to the
above colours displays much yellow and some
white and green. It is, moreover, considerably
smaller and has no distinct youthful dress.

The Amherst Pheasant (Chrysolophus amher-
stice) and the Gold Pheasant (C. pictus) have
long been known as producing hybrids which
are fertile either inter se or with the parents.
Here the species are still more distinct ; not only

121

The Making of Species

are the leading colours of the Amherst white and
green, instead of red and gold, but it is a bigger
bird with a larger tail and smaller crest, and a
bare patch round the eyes.

The Pintail Duck (Daftla acuta] and the
Mallard or Wild Duck and its domestic descen-
dants (Anas boscas), when bred together, produce
hybrids which have been proved fertile between
themselves and with the pure pintail. Any
sportsman or frequenter of our parks can see for
himself the distinctness of the species concerned.

The Pied Wagtail (Motacilla lugubris] and the
Grey Wagtail (M. melanope) have produced
hybrids in aviaries, which have proved fertile.
The two species are distinct in every way, as
all British ornithologists know.

The Cut-throat Finch (Amadina fasciata) and
Red-headed Finch (A. erythrocephala] of Africa
have hybridised in aviaries, and the produce has
proved fertile. The red-headed finch, among
other differences, is far larger than the cut-throat,
and the males have the head all red, not merely
a throat-band of that colour.

The Japanese Greenfinch (Ligurinus sinicus)
which is not green, but brown and grey, with
bolder yellow wing- and tail-markings than our
larger European greenfinch, has produced fertile
hybrids with this latter bird.

The Red Dove of India (Oenopopilia tranque-
barica) has produced hybrids with the tame

122

MALE AMHERST PHEASANT

The chief colours of this species (Chrysolophus amherstiee), are white

and metallic green, so that it is very different in appearance from its

near ally the gold pheasant.

Fertile Bird Hybrids

Collared Dove ( T. risorius] and these have bred
again when paired with the red species. O.
tranquebarica, although presenting a general
similarity to the collared dove, is truly distinct,
being much smaller, with a shorter tail, and dis-
playing a marked sex-difference (the male only
being red, and the female drab). Its voice is
also utterly unlike the well-known penetrating
and musical coo of the Collared Dove.

There is a large class of fertile wild hybrids
produced between forms differing only in colour,
such as those between the Hooded Crow (Corvus
comix) and Carrion Crow (Corvus corone), the
various species of Molpastes bulbuls, and the
Indian Roller (Coracias indica) and Burmese
Roller (C. affinis). Indeed, it may be said that
wherever two such colour-species meet they
hybridize and become more or less fused.

In this connection sportsmen, as mentioned
by Darwin, performed unconsciously a most in-
teresting experiment when, more than a century
ago, they introduced largely into their coverts
the Chinese Ring-necked Pheasant (Phasianus
torquatus] and the J apanese P. versicolor. So freely
has the former bred with the common species
already present there (Phasianus colchicus) that
nowadays nearly all our English pheasants show
traces of the cross in the shape of white feathers
on the neck, or the green tinge of the plumage of
the lower back. The influence of the Japanese

123

The Making of Species

Green Pheasant (P. versicolor) has been very
slight.

It is, of course, open to anyone to assert that
such crosses are not true hybrids, as the species
are not fully distinct, but mere colour-mutations.

The fact of the intermingling, however, is a fatal
blow to the theory of recognition marks, since it
demonstrates that merely distinctive colouring is
not a preventative of cross-breeding. To this
matter we shall return later.

FERTILE HYBRIDS AMONG AMPHIBIA

Our Crested Newt (Molge cristata) and the
Continental Marbled Newt (M. marmorata]
interbreed in France, in the wild state, and the
resulting hybrid was at first described as a
distinct species, under the name of Molge blasii.
These two newts differ greatly in appearance.
In the Marbled Newt the colouration is brilliant
green and black above, and shows no orange
below, thus differing much from that of the
Crested Newt, which is black above and mottled
with orange beneath, while the crest of the
breeding-male of this species lacks the notches
which are so conspicuous in that of the Crested
Newt.

INSECTS

Among insects, M. de Quatrefages states that
the hybrid progeny of the silk-moths Bombyx

124

By permission of the Aviiuttural Socttty

HARLEQUIN QUAIL RAIN QUAIL

(Coturnix delegorguei) (Coturnix coromandelica)

The markings on the throats of these quails are of the type usually put down

as "recognition marks," but as the Harlequin Quail is African and the

Rain Quail Indian, the two species cannot possibly interbreed. The pattern,

then, can have no " recognition" significance.

Limits of Hybridisation

cynthia and B. arrindia are fertile for eight
generations when bred inter se.

LIMITS TO THE POSSIBILITIES OF HYBRIDISATION
Hybrids can apparently only be produced
between species of the same natural family.
The stories of cat-rabbits, deer-ponies, fowl-
ducks, and similar distant crosses invariably
break down on close examination. A belief in
such remote crosses characterized the ancient
"bestiaries," and still lingers, as witness the
falsely-reputed crosses alluded to above.

This belief has no doubt arisen from the fact
that the domestic breeds of dogs, fowls, etc.,
are popularly confounded with truly distinct
species. Mongrels are well known to be readily
produced, and hence the notion arises that
hybrids between the most widely - separated
species are possible.

In practice, the most remote cross of which
authenticated specimens exist is that between
the red grouse and the domestic fowl (bantam
cock). It is true that the grouse are commonly
ranked by ornithologists as a family distinct
(Tetraonidae] from that of the pheasants and
partridges (Phasianidae), to which the fowl
belongs ; but the relationship is admittedly very
close, and we doubt if general zoologists would
countenance the maintenance of the families as
distinct. Ornithologists are notoriously apt to

125

The Making of Species

over-rate small differences when drawing up a
classification. It would be therefore safe to say,
in the present state of our knowledge, that species
belonging to different natural families cannot
hybridize.

In some cases multiple hybrids have been
produced. Thus, at the London Zoological
Gardens, many years ago, a hybrid between the
Gayal of India (Bos frontalis] and the Indian
humped cow mentioned above was put to an
American bison, and produced a double hybrid
calf.

M. G. Rogeron of Angers bred many hybrids
from a male pochard and a duck bred from a
Mallard and a Gadwall.

More recently, Mr J. L. Bonhote has suc-
ceeded in combining the blood of five wild species
of ducks in one individual.

Mr J. T. Newman has also bred turtle-doves
containing the blood of three distinct species.

A cross, which usually results in sterile
offspring, may in very rare cases produce a fertile
individual ; thus, Mr A. Suchetet once succeeded
in obtaining a three-quarter-bred bird from the
not uncommon hybrid of the tame pigeon and
tame collared dove (Turtur risorius\ which is
usually barren, by pairing it with a dove ; but the
bird thus produced, when again paired with a
dove, was itself sterile.

Some of the cases here given seem to encourage
126

Characters of Hybrids

Darwin's view that domestication tends to elimi-
nate sterility ; but it is doubtful if this can be
upheld. The hybrid between the Muscovy duck
(Cairina moschatd] and common duck is usually,
at all events, sterile, like that between the pigeon
and dove ; yet all these birds have been long
domesticated. The hybrid between the fowl and
the guinea-fowl is likewise barren, nor has the
long domestication of the horse and ass lessened
the sterility of the mule.

Some facts may be noted respecting the
characters of hybrids. In the first place, it is
important to notice that the characters of the
hybrid vary according to the sexes of the species
concerned ; thus, the " hinny," which is bred
from a horse and a she-ass, is a different animal
from the true "mule," which is bred from the
jackass and mare, and is inferior to it.

Similarly, Mr G. E. Weston, a great authority
on British cage-birds and their hybrids, informs
us that when hybrids are bred from a male canary
and a hen goldfinch or siskin — contrary to the
almost universal practice of using the hen canary
for crossing — the progeny are inferior in size and
colour to the hybrids obtained in the ordinary
way.

Hybrids, in animals at all events, differ from
crosses between mutations or colour-variations
in not exhibiting the phenomenon of alternative
inheritance ; they do not follow one parent or

127

The Making of Species

the other exclusively, but always exhibit some
blending of the characters of both, which is,
after all, what might have been expected, since
well-defined species usually differ in more than
one character.

Thus, the cross between the Amherst and gold
pheasants chiefly resembles the latter, but has
the ruff white as in the Amherst, while the crest,
though in form it resembles that of the gold
species, is not yellow as in that species, nor red
as in the Amherst, but of an intermediate tint,
brilliant orange.

The mule between the horse and ass, as all
know, combines the shapes of the two parents,
though in colour it follows the horse rather than
the ass.

When two remote species, one or each of
which possesses some distinctive structural
peculiarity, are crossed, the hybrid does not
inherit such points. The guinea-fowl has a
helmet, and a pair of wattles on the upper
jaw ; the common fowl a comb, and a pair of
wattles on the lower jaw ; but in the hybrid no
comb, helmet, or wattles are present.

The Muscovy drake has a bare red eye-patch,
and the male of the common duck curled middle-
tail feathers ; in the hybrid neither of these
peculiarities is reproduced.

In a cross between nearly-related forms, the
peculiarity of one species may be reproduced in

128

Characters of Hybrids

a modified form in the hybrid ; for instance, in
that between the blackcock (Tetrao tetrioc] and
the capercailzie (7". urogallus], the forked tail of
the former reappears to a small extent in the
hybrid.

Very interesting are those cases in which the
hybrid resembles neither parent, but tends to be
like an altogether distinct species, or to have a
character of its own. Thus the hybrids between
the pied European and chestnut African shel-
drakes ( Tadorna cornuta and Casarca cana), now
in the British Museum, bear a distinct resem-
blance to the grey Australian sheldrake (C. tador-
noides]. In pheasants, also, the crosses between
the common and gold, common and Amherst,
gold and Japanese, and gold and Reeves'
pheasants, widely different as all these birds
are in colouration, are remarkably alike, being
all chestnut-coloured birds with buff median tail-
feathers. These may be seen in the British
Museum. This phenomenon, together with the
above-noted disappearance of specialised features
in hybrids, is possibly comparable to the
"reversion" observed when widely - distinct
domestic breeds are crossed, and so may give
us an idea of the appearance of the ancestors of
the groups of species concerned.

In the few cases wherein several generations
of hybrids have been bred inter se, there seems
to have been no reversion to the original pure
i 129

The Making of Species

types, such as happens when colour-forms are
crossed.

M. Suchetet bred hybrid gold = Amherst
pheasants for four generations, and they retained
the hybrid character. The young bred by
Darwin from a pair of common = Chinese geese
hybrids " resembled," he says, " in every detail
their hybrid parents."

When hybrids have been — as has far more
usually been the case — bred back to one
of the pure stocks, the hybrid characters have
shown, as might be expected, a tendency quickly
to disappear. The three-quarter-bred polar bear
now in the London Zoological Gardens is a
pure polar save for a brown tinge on the back.
A three-quarter Amherst = gold pheasant in the
British Museum is a pure Amherst save for the
larger crest, and a patch of red on the abdomen.
When three-quarter-bred pintail = common duck
hybrids were bred back to the pintail, the off-
spring "lost all resemblance to the common
duck." In the case of the Argali-urial herd of
wild sheep above-mentioned, after the usurping
Argali ram had been killed by wolves, the hybrids
bred with the urials, with the result that the herd
renewed the appearance of pure urial.

Thus, except in the very improbable case of a
family of hybrids going off and starting a colony
by themselves, the effect of hybridism on the
evolution of species seems likely to have been

130

Wild Hybrids

nil. It is, however, curious that three-quarter-
bred animals have rarely, if ever, been recorded
in a state of nature, though a good many wild-
bred hybrids are on record.

This points to some unfitness for the struggle
for existence even in a fertile hybrid. It is
necessary to emphasise the fact that wild hybrids
are always exceedingly rare as individuals, in
spite of what has been said as to the number of
recorded crosses.

More hybrid unions have been noted among
the duck family than anywhere else in the animal
kingdom. Nevertheless Finn never once saw a
hybrid duck for sale in the Calcutta market,
although for seven years he was constantly on
the look-out for such forms ; nor does Hume
record any such specimen in his Game Birds and
Wild Fowl of India.

The hybrid which occurs most commonly as
an individual is that between the blackcock and
capercailzie, which is recorded yearly on the
Continent; but it appears to be sterile, and so
has no influence on the species.

Wild hybrids between mammals are far rarer
even than bird hybrids, the only ones which
seem to be on record being those between the
Argali and Urial above alluded to ; those between
the brown and blue hares and the common and
Arctic foxes.

A consideration of the phenomena of hybridism

The Making of Species

thus leads us to the conclusion that, although
many hybrids are fertile, the crossing of distinct
species has exercised little or no effect on the
origin of species. Even where allied species, like
the pintail and the mallard ducks, whose hybrid
offspring is known to be fertile, inhabit the
same breeding area and occasionally interbreed
in nature, such crossing does not, for some reason
or other, appear to affect the purity of the
species.

Very different, of course, is the effect of cross-
ing a mutation within a species with the parent
form ; the offspring are, as we shall see, likely
to resemble one or other of the parents ; so that,
if the mutation occur frequently enough and be
favourable to the species, the new form may in
course of time replace the old one.

132

CHAPTER V

INHERITANCE

Phenomena which a complete theory of inheritance must explain
— In the present state of our knowledge it is not possible to
formulate a complete theory of inheritance — Different kinds
of inheritance — Mendel's experiments and theory — The value
and importance of Mendelism has been exaggerated — Domi-
nance sometimes imperfect — Behaviour of the nucleus of the
sexual cell — Chromosomes — Experiments of Delage and Loeb
— Those of Cudnot on mice and Castle on guinea pigs — Sug-
gested modification of the generally-accepted Mendelian
formulae — Unit characters — Biological isomerism — Biologi-
cal molecules — Interpretation of the phenomena of variation
and heredity on the conception of biological molecules —
Correlation — Summary of the conception of biological
molecules.

WE have seen that variations may be,
firstly, either acquired or con-
genital, and, secondly, fluctuating
or discontinuous. We have further
seen that acquired variations — at all events in
the higher animals — do not appear to be in-
herited, and therefore have not played a very
important part in the evolution of the animal
world. Discontinuous congenital variations or
mutations are the usual starting points of new
species. It is not unlikely that fluctuating con-
genital variations, although they do not appear
to give rise directly to new species, may play a

The Making of Species

considerable part in the making of new species,
inasmuch as they may, so to speak, pave the way
for mutations.

We are now in a position to consider the
exceedingly difficult question of inheritance. We
know that offspring tend to resemble their
parents, but that they are always a little different
both from either parent and from one another.
How are we to account for these phenomena?
What are the laws of inheritance, whereby a
child tends to inherit the peculiarities of its
parents, and what are the causes of variation
which make children differ inter se and from
their parents ?

Scores of theories of inheritance have been
advanced. It is scarcely exaggerating to assert
that almost every biologist who has paid much
attention to the subject has a theory of inherit-
ance which differs more or less greatly from the
theory held by any other biologist.

As regards the phenomena of heredity we may
say Tot homines tot sententice.

For this state of affairs there is a good and
sufficient reason. We are not yet in possession
of a sufficient number of facts to be in a position
to formulate a satisfactory theory of inheritance.
A complete theory of heredity must explain,
among other things, the following phenomena :—

i. Why creatures show a general resemblance
to their parents.

Phenomena of Inheritance

2. Why they differ from their parents.

3. Why the members of a family display indi-
vidual differences.

4. Why the members of a family tend to
resemble one another more closely than they
resemble individuals belonging to other families.

5. Why " sports " sometimes occur.

6. Why some species are more variable than
others.

7. Why certain variations tend to occur very
frequently.

8. Why variations in some directions seem
never to occur.

9. Why a female may produce offspring when
paired with one male of her species and not when
paired with another male of the species.

10. Why organisms that arise by partheno-
genesis appear to be as variable as those which
are sexually produced.

11. Why certain animals possess the power of
regenerating lost parts, while others have not
this power.

12. Why most plants and some of the lower
animals can be produced asexually from cuttings.

13. Why mutilations are not inherited.

14. Why acquired characters are rarely, if
ever, inherited.

1 5. Why the ovum puts forth the polar bodies.

1 6. Why the mother-cell of the spermatozoa
produces four spermatozoa.

The Making of Species

17. Why differences in the nature of the food
administered to the larvae of ants determines
whether these shall develop into sexual or neuter
forms.

1 8. Why the application of heat, cold, etc., to
certain larvae affects the nature of the imago, or
perfect insect, to which they will give rise.

19. Why the females in some species lay eggs
which can produce young without being fertilised.

20. Why some species exhibit the phenomena
of sexual dimorphism, while others do not.

21. In addition to all the above, a satisfactory
theory of inheritance must account for all the
varied phenomena which are associated with the
name of Mendel. It must explain the various
facts with which we have dealt in the chapter on
hybridism, why some species produce sterile
hybrids when intercrossed, while others give rise
to fertile hybrids, and yet others form no offspring
when crossed ; why the hinny differs in appear-
ance from the mule, etc.

22. It must explain all the facts which consti-
tute what is known as atavism.

23. It must account for the phenomenon of
prepotency.

24. It must explain the why and the wherefore
of correlation.

25. It must tell us the meaning of the
results of the experiments of Driesch, Roux,
and others.

136

Existing Theories Unsatisfactory

26. It must render intelligible the effects of
castration on animals.

Now, no existing theory of heredity can give
anything approaching a satisfactory explanation
of all these phenomena.

It is for this reason that we refrain from criti-
cally examining, or even naming, any of them.

We are convinced that in the present state of
our knowledge it is not possible to formulate
anything more than a provisional hypothesis.

It must not be thought that we consider the
various theories that have been enunciated to be
of no value. Erroneous hypotheses are often of
the greatest utility to science, for they set men
thinking and suggest experiments by means of
which important additions to knowledge are
made.

We now propose to set forth certain facts of
inheritance, and from these to make a few
deductions — deductions which seem to be forced
upon us.

We would ask our readers to distinguish care-
fully between the facts we set forth, and the
conclusions we draw therefrom. The former,
being facts, must be accepted.

The interpretations we suggest should be
rigidly examined, we would say regarded with
suspicion, and all possible objections raised. It
is only by so doing that any advance in know-
ledge can be made.

The Making of Species

By inheritance we mean that which an organ-
ism receives from its parents and other ancestors
— all the characteristics, whether apparent or
dormant, it inherits or receives from its parents.
Professor Thomson's definition — "all the qualities
or characters which have their initial seat, their
physical basis, in the fertilised egg cell " — seems
to cover all cases except those where eggs are
parthenogenetically developed.

The first fact of heredity which we must notice
is that inheritance may take several forms. This
is apparent from what was set forth in the
chapter dealing with hybrids.

In considering the phenomena of inheritance
it is convenient to deal with crosses in which the
parents do not closely resemble one another,
because by so doing we are able readily to
follow the various characters displayed by each
parent. It may, perhaps, be urged that such
crosses occur but rarely in nature. This is true.
But we should bear in mind that any theory
of inheritance must explain the various facts of
cross-breeding, so that, from the point of view of
a theory of inheritance, crosses are as important
as what we may term normal offspring. As
inheritance is so much easier to observe in the
former, it is but natural that we should begin
with them. Our deductions must, if they be
valid ones, fit all cases of ordinary inheritance,
i.e. all cases where the offspring results from the

138

Types of Crosses

union of parents which closely resemble one
another. Now, when two unlike forms inter-
breed, their offspring will fall into one of six
classes.

I. They may exactly resemble one parent, or
rather the type of one parent, for, of course,
they will never be exactly like either parent ;
they must of necessity display fluctuating varia-
tions. The cases in which the offspring exactly
resemble one parent type in all respects are com-
paratively few. They occur only when the
parents differ from one another in one, two, or
at the most three characters. Thus when an
ordinary grey mouse is crossed with a white
mouse the offspring are all grey, that is to say,
they resemble the grey parent type. Although
they are mongrels or hybrids, they have all the
appearance of pure grey mice. This is what is
known as unilateral inheritance.

II. The offspring may resemble one parent
in some characters and the other in other
characters. They may have, for example, the
colour of one parent, the shape of the other, and
so on. Thus if a pure, albino, long-haired, and
rough-coated male guinea-pig be crossed with a
coloured, short-haired and smooth-coated female,
all the offspring are coloured, short-haired, and
rough- coated. That is to say, they take after

139

The Making of Species

the father in being rough-coated, but after the
mother in being pigmented and short - haired.
This form of inheritance is usually seen only in
crosses between two types which differ in but
few of their characters.

III. The offspring may display a blend of the
characters of the two parents. They may be
intermediate in type. They are not of necessity
midway between the two parents ; one of the
parents may be prepotent. The crosses between
the horse and the ass show this well. Both the
mule, where the ass is the sire, and the hinny,
where the horse is the sire, are more like the ass
than like the horse ; but the hinny is less ass-
like than the mule. The offspring between a
European and a native of India furnishes a
good case of blended inheritance ; Eurasians are
neither so dark as the Asiatic nor so fair as the
European.

IV. The offspring may show a peculiarity of
one parent in some parts of the body and the
peculiarity of the other parent in other parts of
the body. This is known as particulate inherit-
ance. The piebald foal, which is the result of a
cross between a black sire and a white mare, is a
good example of such inheritance. This does
not appear to be a common form of inheritance.

V. The usual kind of inheritance is perhaps
a combination between the forms II. and III.

140

Mendel's Experiments

In such cases the offspring* display some paternal
characters and some maternal ones, and some
characters in which the maternal and paternal
peculiarities are blended. An example of in-
heritance of this description is furnished by a
cross between the golden and the amherst
pheasants.

VI. The offspring may be quite unlike either
parent. For example, Cuenot found that some-
times a grey mouse when crossed with an albino
produces black offspring.

The first two kinds of inheritance were care-
fully investigated by Gregor Johann Mendel,
Abbot of Brunn. The results of his experiments
were published in the Proceedings of the Natural
History Society of Brunn, in 1854, but attracted
very little notice at the time.

Mendel experimented with peas, of which many
varieties exist. He took a number of varieties,
or sub-species, which differed from one another
in well-defined characters, such as the colour of
the seed coat, the length of the stem, etc. He
made crosses between the various varieties, being
careful to investigate one character only at a
time. He found that the offspring of such
crosses resembled, in that particular character,
one only of the parents, the other parent ap-
parently exerting no influence on it. Mendel

141

The Making of Species

called the character that appeared in the off-
spring dominant, and the character which was
suppressed, recessive. Thus when tall and short
varieties were crossed the offspring were all tall.
Hence Mendel said that tallness is a dominant
character, and shortness a recessive character.
Mendel then bred these crosses among them-
selves, and found that some of the offspring
resembled one grandparent as regards the char-
acter in question while some resembled the
other, and he found that those that showed the
dominant character were three times as numerous
as those that displayed the recessive character.
He further found that all those of the second
generation of crosses which displayed the re-
cessive character bred true ; that is to say, when
they were bred together all their descendants
exhibited this characteristic. The dominant
forms, however, did not all breed true ; some
of them produced descendants that showed
only this dominant character, others, when
crossed, gave rise to some forms having the
dominant character and some having the
recessive character.

It is thus evident that organisms of totally
different ancestry may resemble one another in
external appearance. In other words, part of the
material from which an organism is developed
may lie dormant.

From the above results Mendel inferred, in
142

Mendelism

the case of what he called alternating characters,
that only one or other of the pair can appear in
the offspring, that they will not blend. If both
parents display one of the opposing characters,
the offspring will of course show it. But if one
parent display one character and the other the
opposing character, the hybrid offspring will dis-
play one only, and that which is dominant. The
other character is suppressed for the time being.
When, however, these hybrids are bred inter se,
their gametes or sexual cells split up into their
component parts, and then the recessives are free
to unite with other recessives and thus produce
offspring which show the recessive character.

His results can be set forth in symbols.

Let T stand for the tall form and D for the
dwarf form. Since the offspring are composed
of both the paternal and maternal gamete, we
may represent them as TD. But dwarfness is,
as we have seen, recessive, so that the offspring
all look as though they were pure T's. When,
however, we come to breed these TD's inter se,
the gamete or sex-cell of each individual crossed
breaks up into its component parts T and D,
which unite with other free T or D units
to form TD's or TT's or DD's. What are
the possible combinations ? A D of one parent
may meet and unite with a D of the other
parent, so that the resulting cells will be pure
D, i.e. DD, and will give rise to pure dwarf

The Making of Species

offspring. Or the D gamete from one parent
may unite with a T gamete from the other
parent, and the result will be a TD cross, but
this, as we have seen, will grow up to look like
a pure T, i.e. will become a tall organism.
Similarly, a T gamete from one parent may
unite with a T gamete of the other, and produce
a pure tall form, or it may unite with a D and
produce a hybrid TD, which gives rise to a
tall form. Thus the possible combinations of
offspring are DD, DT, TD, TT, but all these
three last contain the dominant T gamete, and
so develop into tall offspring ; therefore, ex
hypothesi, we shall have three tall forms pro-
duced to one dwarf form, but of these three
tall forms two are not pure, and do not breed
true. Mendel's experimental results accorded
with what we should expect to obtain if the
above explanation were correct. Hence the
inference that there is such a splitting of the
gametes in the sexual act seems a legitimate one.
Mendel's experiments are of great import-
ance, for they give us some insight into the
nature of the sexual act. But, as is usual
in such cases, Mendel's disciples have greatly
exaggerated the value and importance of his
work. It is necessary to bear in mind that
Mendel's results apply only to a limited
number of cases — to what we may call balanced
characters. In the case of characters which

144

Maturation of the Germ-cells

do not balance one another, which are, so to
speak, not diametrically opposed to one another,
Mendel's law does not hold. A second im-
portant point is, that the dominance is in many
cases not nearly so complete as it should be if
the Mendelian formula correctly represented
what actually occurs in nature. Further, the
segregation of the gametes does not appear to
be so complete as the above hypothesis requires
it to be. The phenomena of inheritance seem
to be far more complex than the thorough-going
Mendelian would have us believe.

Let it be noted that it is not to the facts of
Mendelism, but to some portions of what we
may call the Mendelian theory, that we take
exception.

Before passing on to consider some of the
later developments of Mendelism, it is necessary
for us to set forth briefly certain of the more
important facts regarding the sexual act which
the microscope has brought to light. We
propose to state these only in the merest outline.
Those who are desirous of pursuing the subject
farther are referred to Professor Thomson's
Heredity.

The germ cells, like all other cells, consist of
a nucleus lying in a mass of cytoplasm. The
nucleus is composed of a number of rod-like
bodies, which are called chromosomes, because
they are readily stainable.

K 145

The Making of Species

These chromosomes appear, under ordinary
circumstances, to be joined together end to end,
and then look like a rope in a tangle.

When a cell is about to divide into two, these
chromosomes become disjoined and can then be
counted, and it is found that each cell of each
species of animal or plant has a fixed number of
these chromosomes. Thus the mouse and the
lily have twenty- four chromosomes in each cell,
while the ox is said to have sixteen of them per
cell.

When a cell divides into two, each of these
chromosomes splits by a longitudinal fissure into
two halves, which appear to be exactly alike.
One-half of every chromosome passes into each
of the daughter cells, so that each of these is
furnished with exactly half of each one of the
rod-like chromosomes. In the cell division,
which takes place immediately before the male
gamete or generative cell meets the female
gamete, the chromosomes do not divide into
equal halves, as is usually the case. In this
division half of them pass into one daughter cell
and half into the other daughter cell, so that,
prior to fertilisation both the male and the female
gametes contain only half the normal number of
chromosomes. In the sexual act the male and
the female chromosomes join forces and then the
normal number is again made up, each parent
contributing exactly one half.

146

Experiments of Delage and Loeb

Biologists, with a few exceptions, seem to be
agreed that these chromosomes are the carriers
of all that which one generation inherits from
another. Thus the cardinal facts of the sexual
act are, firstly, prior to fertilisation the male and
the female gamete each part with half their
chromosomes ; and, secondly, the fertilised cell is
composed of the normal number of chromosomes,
of which one-half have been furnished by each
parent. Thus the microscope shows that the
nucleus of the fertilised egg is made up of equal
contributions from each parent. This is quite
in accordance with the observed phenomena of
inheritance.

But Delage has shown that a non-nucleated
fragment of the ovum in some of the lower animals,
as, for example, the sea-urchin, can give rise to
a daughter organism with the normal number of
chromosomes when fertilised by a spermatozoon.
Conversely, Loeb showed that the nucleus of the
spermatozoon can be dispensed with. Thus it
seems that either the egg or the spermatozoon of
the sea-urchin contains all the essential elements
for the production of the perfect larva of a
daughter organism. We are, therefore, driven
to the conclusion that the fertilised ovum contains
two sets of fully-equipped units. Only one of
these seems to contribute to the developing
organism. If this set happens to be composed
of material derived from one only of the parents,

The Making of Species

we can see how it is that we get unilateral in-
heritance in the case of a cross. Where, however,
the units from the two parents intermingle,
although only one set is active in development,
the result will be blended inheritance. Thus, we
may regard the fertilised egg as made up of two
sets of characters — a dominant set, which is active
in the production of the resulting organism, and
a recessive set, which appears to take little or no
part in the production of the organism.

This is quite in accordance with Mendelian
conceptions.

Let X be an organism having the unit char-
acters A B C D E F G, and let Y be another
organism having the unit characters a b c def g.
Now suppose that these behave as opposed
Mendelian units, and that the unit characters
in italics are dominant ones. Then the resulting
individual will resemble each parent in certain
unit characters. It may be represented by the
formula a B c d E f G, but it will contain the
characters AbCDeFg in a recessive form,
so that its complete formula may be written

a Be dEf G\
AbCDeFgj

When these hybrids are paired together it will

.,, , f ABCDEFG

be possible to get such forms as A B C D E F G

and a, l- iGr^ which exactly resemble the
a b c d e i g

148

Experiments of Cu&iot and Castle

respective grandparents, and these should breed
absolutely true, if the segregation of the
gametes is as pure as the Mendel's law seems
to require.

There are, however, certain facts, which recent
experimenters have brought to light, that seem
to show that the segregation is not so com-
plete as the law requires. For example,
the so-called pure extracted forms may be
found, when bred with other varieties, to have
some latent characters. Thus Cuenot observed
that extracted pure albino mice, that is to say,
those derived from hybrid forms, did not all
behave alike when paired with other mice.
Those which had been bred from grey x white
hybrids behaved, on being crossed, differently to
those that had been bred from black x white
hybrids ; and further, those derived from yellow
x white hybrids yielded yet other results on
being intercrossed. Castle records similar pheno-
mena in the case of guinea-pigs, and accordingly
draws a distinction between recessive and latent
characters. Recessive characters are those which
disappear when they come into contact with a
dominant character, but reappear whenever they
are separated from the opposing dominant char-
acter. Latency is defined by Castle as "a con-
dition of activity in which a normally dominant
character may exist in a recessive individual or
gamete."

149

The Making of Species

The ordinary Mendelian pictures a unit
character in a cross that obeys Mendel's law,

as follows : — ^ the dominant character only

showing. It seems to us that each unit character
should be represented as a double entity, thus
D(D), the portion within the bracket being
latent. The cross would appear to be repre-
sented by the formula -o/pv\ since the union

appears to take the form of the transfer of
the dormant latent characters. Now an ex-
tracted pure recessive will, on this hypothesis,

bear the formula T>/T\\ When such recessives
R(D).

are crossed the two dormant portions will
ordinarily change places, and never appear, so
that these extracted recessives will, under
ordinary circumstances, appear to be as pure
as the true pure recessives, which are represented

by the formula •D\-D{
K(K).

Now, suppose that, from some cause or other,
it is possible for the latent D to change places
with the visible R, it is obvious that the impure
nature of the extracted and hitherto apparently
pure recessives will become manifest. This
seems to be what happens under certain circum-
stances to the extracted albino mice. They

Unit Characters

possess latent the character of their dominant
ancestor.

Mendelian phenomena force upon us the con-
clusion that organisms display a number of unit
characters, each of which behaves in much the
same way as a radicle does in chemistry, inas-
much as for one or more of these characters
others can be substituted without interfering with
the remaining unit characters. For example, it
is possible to replace the chemical radicle NH,
by the radicle Na2 ; e.g. (NH3)2SO4 (ammonium
sulphate) may be transformed into Na2SO4
(sodium sulphate).

The conclusion that each organism is com-
posed of a number of unit characters, which
sometimes behave more or less independently of
one another, is one which most biologists who
have studied the phenomena of inheritance
appear to have arrived at. Zoologists are mostly
of opinion that these characters, or rather their
precursors, exist as units in the fertilised egg.
Very varied have been the conceptions of the
nature of these biological units. Almost every
biologist has given a name to his particular con-
ception of them. Thus we have the gemmules
of Darwin, the unit characters of Spencer, the
biophors of Weismann, the micellae of Naegeli,
the plastidules of Haeckel, the plasomes of
Wiesner, the idioblasts of Hertwig, the pangens
of De Vries, and so on. It is unnecessary to

The Making of Species

extend this list. It must suffice that almost
every investigator of the phenomena of inherit-
ance believes in these units, and calls them
by a different name. Moreover, each clothes
them with characteristics according to his taste
or the fertility of his imagination.

These units behave in such a way as to sug-
gest to us an analogy between them and the
chemical molecules. The sexual act would appear
to resemble a chemical synthesis in some respects.
One of the most remarkable phenomena of
chemistry is that of isomerism. It not in-
frequently happens that two very dissimilar
substances are found, upon analysis, to have the
same chemical composition, that is to say, their
molecules are found to be composed of the same
kind of atoms and the same number of these.
Thus chemists are compelled to believe that the
properties of a molecule are dependent, not only
on the nature of the atoms which compose it, but
also on the arrangement of these within the
molecule. To take a concrete example : Analysis
shows that both alcohol and ether are represented
by the chemical formula C2H6O. In other words,
the molecule of each of these compounds is made
up of two atoms of the element Carbon, six of
the element Hydrogen, and one of the element
Oxygen. Now, every chemical atom possesses the
property which chemists term valency, in other
words, the number of other atoms with which

152

Chemical Molecules

it can directly unite is strictly limited. All atoms
of the same element have the same valency.
Monovalent atoms are those which can, under no
circumstances, unite with more than one other
atom. The Hydrogen atom is an example of
such an atom. Divalent atoms, as, for example,
that of Oxygen, can unite with one other atom of
similar valency or with two monovalent atoms.
Similarly, a trivalent atom, such as that of
Nitrogen, can unite with three monovalent
atoms. A tetravalent atom, such as that of
Carbon, can combine with four monovalent
atoms. There are also pentavalent and hexa-
valent atoms. Now, by indicating the valency
of any given atom by a stroke for each mono-
valent atom with which it is able to combine,
chemists have been able to represent the mole-
cule of every compound, or, at any rate, of every
inorganic compound, by what is known as a
graphic or structural formula. Thus, ethylic
alcohol is represented by the formula : —
H H

H— C— C— O— H = C2H60,

H H

and methylic ether by the structural formula : —
H H

H— C— O— C— H = C2H60.

A A

The Making of Species

The formulae indicate a very different arrange-
ment of the nine atoms which compose the
molecule in each case. And to this different
arrangement the differing properties of the two
compounds are supposed to be due. A rough
illustration of the phenomenon of isomerism is
furnished by written language. Thus, three
different words can be made from the letters t,
a, and r, e.g. tar, art, and rat. They also form
tra, which does not happen to be an English
word, although it might have been one.

Among organisms we sometimes observe a
phenomenon which looks very like isomerism.
The classical example of this is furnished by
the butterflies Vanessa prorsa and Vanessa
levana.

At one time these were supposed to belong to
different species, since they differ so greatly in
appearance. Vanessa levana is red, with black
and blue spots. Vanessa prorsa is deep black,
with a broad yellowish-white band across both
wings. It is now known that the levana is the
spring form and the prorsa the summer and
autumn form of the same species. The pupae of
levana produce the prorsa form, but Weismann
found that after being placed in a refrigerator
they emerged, not as prorsa, but partly as levana
and partly as another form intermediate in many
respects between levana and prorsa. Weismann
also succeeded, by exposing the winter pupa to a

Experiments of Grafin von Linden

high temperature, in making it give rise to the
prorsa form, and not to the levana form, as it
would ordinarily do.

Similar results have been obtained with the
seasonally dimorphic Pieris napi. Standfuss,
the Grafin von Linden, and others have obtained
like results in the case of other seasonally di-
morphic butterflies. In some instances it has
been proved that the change in the pigment is a
purely chemical one ; a similar transformation
can be effected in the extracted pigment. But,
we must bear in mind that the changes which
are induced in this way are not confined to
colour ; they occur in the marking and shape of
the wing.

Even more remarkable is the fact that in some
sexually dimorphic species a change of tempera-
ture alters the female, so as to cause her to have
the outward appearance of the male. For
example, it has been found that warmth changes
the colours of the female Rhodocera rhamni and
Parnassius apollo into the colours of the male.

By applying rays of strong light, electric
shock, or centrifuge, the Grafin von Linden was
able to change the colours of the butterflies to
which the caterpillars gave rise. Pictet experi-
mented on twenty-one species of butterflies, or
rather on their caterpillars, and found that in
nearly all cases when the caterpillars ate unusual
food, they developed into butterflies with ab-

The Making of Species

normal colouring. Schmankewitsch made the
discovery that, in the case of the crustacean
Artemia, he could produce either of two species
according to the amount of salt in the water in
which these creatures were placed. He declared
that the anatomical differences between the
species Artemia salina and Artemia milhausenii
depended solely on the percentage of the salt in
the surrounding water. He further stated that
by adding still more salt he could change the
Artemia into a new genus — Branchipus. More
recent observers have cast doubt upon these
results of Schmankewitsch. They, however,
admit that the degree of salinity of the water has
some effect on the form of the Artemia, although
they suggest that factors other than concentration
affect the result. In any case, it is now well-
known that changes in the environment effect
changes in the colouring of many Crustacea.
Pictet has shown that the alternating wet and
dry seasons in some tropical countries are the
cause of, or stimulus that induces, seasonal
dimorphism in some butterflies. He was able to
effect changes in the colouring of certain species
by means of humidity.

The most important cases, from our point of
view, are those in which the application of
heat or cold to a pupa has affected the colour,
shape, etc., of the emerging butterfly. Here we
have but one factor, that of temperature. All

156

Biological Isomerism

the material for the formation of the butterfly is
already stored up in the pupa. The unit char-
acters, or their precursors, are all there, and they
take one form or another according to the stimulus
applied.

Phenomena of this kind can, we think, be
accounted for only on the assumption that the
unit characters affected are each developed from
a definite portion of the fertilised egg, that each
of these portions, these precursors of the unit
characters, is, like a chemical molecule, made up
of a number of particles, and that upon the
arrangement of these particles in its precursor
in the egg depends the form that the unit char-
acter derived from it will take. One arrange-
ment of these particles gives rise to one form of
unit character, while another arrangement will
give rise to a totally different form of unit
character.

Thus, some organisms seem to display a bio-
logical isomerism akin to chemical isomerism,
save that the particles which in organisms
take the place of chemical atoms are infinitely
more complex.

In other words, the precursors in the fertilised
egg of each of these unit characters behave in
some respects like chemical molecules.

In order to avoid the manufacture of fresh
terms we may speak figuratively of the germ
cells as being composed of biological molecules,

'57

The Making of Species

which in their turn are built up of biological
radicles and atoms. These behave in some ways
like chemical molecules, radicles, and atoms, as
the case may be.

It seems legitimate to regard each unit char-
acter in the adult as the result of the develop-
ment of one or more of the biological molecules
which compose the nucleus of the fertilised egg.
These biological molecules are, of course, a
million-fold more complex than chemical mole-
cules. Each biological atom must contain within
itself a number of the very complex protoplasmic
molecules. This view of the structure of the
germ cell seems to force itself upon the observer.
Notwithstanding this, the conception will have no
value unless it seems to throw light on the various
phenomena of heredity, variation, etc.

Let us then try to interpret some of these.

Each chemical element is made up of atoms
which are all of the same kind, but no two
elements are made up of the same kind of atoms,
although chemists are now inclined to conceive of
all the various kinds of atoms as made up of
varying amounts of some primordial substance.
In any case, the molecules of chemical compounds
are made up of various kinds of atoms. With
biological atoms the case would seem to be
different. All would appear to be made up of
the same kind of substance, and the differences
shown by the various unit characters that go to

158

Biological Molecules

make up an organism would seem to be due to
the different numbers and the varying arrange-
ment of the biological atoms which compose the
molecules from which unit characters are derived.
This would be quite in accordance with the
chemical notion of allotropy. Thus, the graphite
and the diamond molecules are both made up of
the same kind of atoms.

But the biological atoms are living, that is to
say, they are continually undergoing anabolism
and katabolism, growth and decay. They
exhibit all the phenomena of life, they must
grow and divide, and they must absorb nourish-
ment ; hence it is not surprising that they should
differ slightly among themselves, that they should
exhibit the phenomenon of variation. Although
probably all are composed of the same living
material, no two are exactly alike, hence the
molecules formed by them will also differ from
one another. Thus we can see why it is that all
organisms exhibit fluctuating variations.

Very different are the discontinuous variations
or mutations. These would seem to be due to
either a rearrangement of the biological atoms in
the biological molecule or the splitting up of
the latter into two or more molecules. This, of
course, is pure hypothesis. Let us take an
imaginary example. Suppose that a biological
molecule contains eighteen biological atoms, and
that these are arranged in the form of an equi-

The Making of Species

lateral triangle, six of them going to each side.
Suppose now, that from some cause or other they
rearrange themselves to form an isosceles triangle,
so that only four form the base and seven go to
each of the remaining sides. Such an arrange-
ment would give rise to a mutation. Suppose now
that, from some cause or other, this triangular bio-
logical molecule were to split up into two triangles,
each having three atoms to each side, we should
obtain a still more marked mutation. We are
far from saying that the atoms in the organic
molecule ever take such forms. We have merely
attempted to give rough but simple illustrations
of the kind of processes which on this hypothesis
might be expected to take place in the germ cells
or the fertilised eggs.

Let us now consider the sexual act from this
aspect. The various molecules (we speak, of
course, of biological molecules) of the male
parent meet those of the female parent, and a
synthesis occurs, which results in the formation
of a new organism. When these two sets of
gametes meet one another, one of several events
may happen. The gametes may refuse to com-
bine. This will occur whenever they are of
very different constitution ; thus it is that widely
differing species will not interbreed. But it may
even happen that gametes of individuals of the
same species may refuse to coalesce on account
of some peculiarity in the composition of one or

1 60

Biological Molecules

other of them. Secondly, they may be able to
form some sort of a union, but, owing to their
diverse nature, the resulting molecules may be
so complex that they cannot be broken up into
equal halves, and as this seems to be necessary
for the sexual act, the resulting organism will be
sterile. Thirdly, the two sets of gametes may
enter into a proper union, that is to say, form
new molecules, but these may be of such different
structure to the molecules of the gametes, that
the resulting offspring will be quite unlike their
parents in appearance. Fourthly, some or all
the groups of radicles in each gamete may be
united so closely that in the sexual act they do
not break up, but enter bodily into the new
resulting organism. In these circumstances the
inheritance of the offspring will follow Mendel's
law. Fifthly, there may be some slight disturb-
ance of the molecule, perhaps one or only a few
atoms will be replaced by those of the other
gamete. This would give us impure dominance.

Thus this hypothesis appears to be compatible
with the various modes of inheritance.

The curious phenomenon known as prepotency
would seem also to be quite in accordance with
the conception.

In chemical reactions the tendency is for the
most stable combinations to be formed, so in
nature.

We may probably go farther and say, not
L 161

The Making of Species

only will the most stable biological molecules be
formed, but the most stable radicles will dominate
the molecule. Hence, if any two animals are
crossed and the offspring show alternate inherit-
ance, the resulting organism will, in the case of
each unit character, display the most stable of
the pair ; in other words, it will take after the
parent which happens to have the greater
stability as regards that particular character.
The difference between the mule and the hinny
would seem to be explicable on this supposition.
If the union were like a simple chemical syn-
thesis it should not make any difference which
way the cross were made. But if the species
crossed are of varying stability, and if their
respective degrees of stability vary with the sex,
it is easy to see that it will make a difference
how the animals are crossed.

In the cases of creatures that obey Mendel's
law, the most stable form of a unit character will
presumably be the dominant one.

One of the most curious of the phenomena of
inheritance is that of correlation. We shall deal
with this more fully in Chapter VIII. It will
suffice here to say that certain characters appear
to be linked together in organisms. Such seem
to be transmitted in pairs. The offspring never
exhibits one of such a correlated couple without
exhibiting the other also.

It would thus seem that certain combinations
162

Biological Molecules

of biological atoms, certain molecules, can only
exist in conjunction with certain other combina-
tions. This is quite in accordance with the
teaching of physiologists regarding the inter-
dependence of the various organs of the body.
We have now reached the stage of the fertilised
ovum. According to our conception it is a series
or conglomeration of the precursors of the unit
characters of the adult. These precursors we
call biological molecules. Each is of a very com-
plex nature. Each seems to be composed of
several portions, only one of which will take
part in the building up of the body of the off-
spring, the other portions remaining latent. We
further conceive that it is possible for the various
radicles which compose these molecules to ar-
range themselves in various manners, and with
each new arrangement a different form of unit
character will be developed. These molecules,
then, are built up from radicles derived from
both parents, the most stable combinations being
formed and one portion of the molecule domin-
ating the whole. Under normal circumstances
this dominant portion of the molecule will give
rise to a character of a definite type. But it
seems that other factors may come into play and
cause a rearrangement of the radicles which
compose it, and this will result in the formation
of a unit character different from that to which it
would ordinarily give rise.

163

The Making of Species

But, it may be objected, if the colour of an
organism be derived from one of these so-called
biological molecules, how is it that it affects the
whole organism, or, at any rate, several of the
other unit characters? The objection may be
met in several ways. In the first place, the
colour-forming molecules may split up into as
many portions as there are units which it affects,
and each portion may attach itself to a unit. Or
the property which we call colouration may not
be derived from a molecule, it may be an ex-
pression in the relative positions of the various
molecules in the fertilised egg. Or the colour-
determining molecule may secrete a ferment or
a hormone, and this may be the cause of the
particular colouring of the resulting organism.
We do not pretend to say which (if any)
of these alternative suppositions is the correct
one. But it seems to us that some such con-
ception as that which we have set forth is forced
upon us by observed facts. This conception
should be regarded not as a theory, but rather as
an indication of the lines along which we believe
the study of inheritance could best be made.

The fertilised ovum has nothing of the shape
of the creature to which it will give rise. It is
merely a potential organism, a something which
under favourable conditions will develop into an
organism.

In the higher animals each individual is either
164

Phenomenon of Sex

of the male or the female sex. A vast amount
of ingenuity has been expended by zoologists in
the attempt to ascertain what it is that deter-
mines sex. Many theories have been advanced,
but no one of them has obtained anything like
general acceptance, because its opponents are
able to adduce facts which appear to be incom-
patible with it.

It is tempting to try to interpret the pheno-
menon of sex on the assumption that the female-
producing biological molecule or unit is an
isomeride of the male-producing cell. Certain
facts, however, seem to negative the idea, as, for
example, the occasional appearance in an indi-
vidual of one sex of characteristics of the other
sex.

Possibly the attempts to explain the pheno-
mena of sex-production on a Mendelian basis
may prove to be more successful. It seems not
impossible that each fertilised egg contains
material which is capable of developing into
male generative organs and material which is
capable of developing into female generative
organs, but that only one kind of material, that
which dominates, succeeds in developing. The
number of what are known as " X-elements "
that happen to be present in the fertilised egg
appear to decide which kind of material is to be
dominant.

But the problem of the determination of sex,
165

The Making of Species

fascinating though it be, is not one that can be
discussed adequately in a general work on
evolution. Those interested in the subject are
referred to Professor Thomson's Heredity, and
to the address given by Professor E. B. Wilson,
of Columbia University, before the American
Association for the Advancement of Science,
which was fully reported in the issue of Science,
dated January 8, 1909.

Stated briefly, then, our conception is, that
the fertilised egg is composed of a number of
entities, to which we have given the name
" biological molecules," because in certain
respects their behaviour is not unlike that of
chemical molecules.

The units which compose these molecules,
being made up of protoplasm, are endowed with
all the properties of life, including the inherent
instability which characterises all living matter.

We suggest that the continuous or fluctuating
variations that appear in the adult organism may
be the result of individual differences in the
biological "atoms" that compose the molecule.

Discontinuous variations, or mutations, on the
other hand, may be the result of a rearrangement
of the atoms within the biological molecule.
Upon what causes this rearrangement it would
not be very profitable to speculate in the present
state of our knowledge. To do this would be to
inquire into the cause of a re-grouping of entities

166

Struggle for Nourishment

of the existence of which we are not certain !
For aught we know there may be an intracellular
struggle for nourishment among the various
molecules and among the atoms which compose
the molecules. If one molecule enjoys any
special advantage over the others the result may
be an unusual degree of development of the
resulting unit character ; in other words, the
result will be a variation in the organism. This
variation may prove favourable or unfavourable
to its possessor.

Certain phenomena seem to point to a struggle
for nourishment between the germinal and the
somatic portions of the egg, between the parts from
which the sexual cells of the resulting organism
are produced and those which give rise to the body
of the organism. Each molecule may strive, so
to speak, to increase at the expense of the others.
Thus, great size in an organism is likely to be
produced at the expense of the germinal cell-
forming molecules. In other words, great size in
an organism would be incompatible with exces-
sive fecundity. This is what we observe in
nature. On the other hand, poor development
of bodily tissue, as in the case of intestinal para-
sites, would be correlated with great fecundity.
Some organisms are mere sacs full of eggs.

Success in the struggle for nourishment of one
molecule might be shared by the other molecules
near to it, hence the phenomena of correlation.

167

The Making of Species

It is thus conceivable that, in a brood consist-
ing of several individuals, a particular molecule
or set of molecules in one of the individuals may
receive more than its share of nourishment, and
this will result in the organs of that individual
which spring from the well-nourished molecules
being exceptionally well developed. Thus arises
the phenomenon of differences between the
members of a litter or brood.

Natural selection will tend to eliminate those
individuals in which the resulting variation is an
unfavourable one. If the environment is such,
as in the case of an internal parasite, that the
production of germ cells is the most necessary
function of the organism, then those individuals
in which the germ-forming molecules increase at
the expense of the body-forming ones will tend
to be preserved. This would cause the pheno-
menon which biologists term degeneration.
The nourishment of the various biological
molecules may possibly depend on their relative
positions in the egg. Those in a favourable
position will then tend to develop at the expense
of the others. This will result in variation along
definite lines. Each succeeding generation will
tend to an increased development of that par-
ticular organ to which the favourably-situated
molecule gives rise. This process may continue,
as in the case of the horns of the Irish elk, until
the development of that particular organ becomes

168

Origin of Mutations

so excessive as to be positively injurious ; then
natural selection will step in and eliminate the
species. But before this happens, something
may cause a rearrangement of the biological
molecules in the fertilised egg, and thus a muta-
tion may arise, which, so to speak, strikes out a
new line.

Finally, on this conception there may be some
sort of connection between fluctuating variations
and mutations. We can picture the fluctuating
variations being piled up, one upon the other,
until there results a rearrangement of the atoms
in one or more of the biological molecules which,
in turn, causes a mutation.

Occasionally this remodelling, as it were, of
one biological molecule may affect certain of the
other molecules, and thus lead to correlated
mutations.

ib9

CHAPTER VI

THE COLOURATION OF ORGANISMS

The theory of protective colouration has been carried to absurd
lengths — It will not bear close scrutiny — Cryptic colouring —
Sematic colours — Pseudo-sematic colours — Batesian and
Miillerian mimicry — Conditions necessary for mimicry —
Examples — Recognition markings — The theory of obliterative
colouration — Criticism of the theory — Objections to the theory
of cryptic colouring — Whiteness of the Arctic fauna is ex-
aggerated—Illustrative tables — Pelagic organisms — Objectors
to the Neo-Darwinian theories of colouration are to be found
among field naturalists — G. A. B. Dewar, Gadow, Robinson,
F. C. Selous quoted — Colours of birds' eggs — Warning
colouration — Objections to the theory — Eisig's theory —
So-called intimidating attitudes of animals— Mimicry — The
case for the theory — The case against the theory — "False
mimicry " — Theory of recognition colours — The theory refuted
— Colours of flowers and fruits — Neo-Darwinian explanations
— Objections — Kay Robinson's theory — Conclusion that Neo-
Darwinian theories are untenable — Some suggestions regard-
ing the colouration of animals — Through the diversity of
colouring of organisms something like order runs — The con-
nection between biological molecules and colour — Tylor on
colour patterns in animals — Bonhote's theory of pcecilo-
meres — Summary of conclusions arrived at.

SINCE the publication of The Origin of
Species, naturalists have paid much
attention to the colouration of animals
and plants, with the result that a large
majority of scientific men to-day hold the belief
that all, or nearly all, the colours displayed

170

Robinson on Protective Colouring

by animals are of direct utility to them,
and are therefore the direct result of natural
selection; a few would add, "and of sexual
selection."

"Among the numerous applications of the
Darwinian theory," writes Wallace, " in the
interpretation of the complex phenomena, none
have been more successful than those which
deal with the colours of animals and plants."

We readily admit that the Darwinian theory
has thrown a great deal of light on the pheno-
menon of animal colouration ; it has reduced to
something like order what was before Darwin's
time chaos. While admitting this we feel con-
strained to say that many naturalists, especially
Dr Wallace and Professor Poulton, have pushed
the various theories of animal colouration to
absurd lengths. As Dr H. Robinson truly says
{Knowledge, January 1909), "It seems to have
been taken for granted, and some even of
Dr Wallace's writings may be interpreted in
this sense, that protective colouring is necessary
to the continued existence of every species, and
that, sexual colouration apart, it is incumbent on
naturalists to offer ingenious speculations in this
sense to account for the appearance even of the
most bizarre and conspicuous beasts. Thence it
has been but a short step to the announcement
of those speculations as further evidence in favour
of natural selection, and of various assumptions

171

The Making of Species

made in the speculative process as indisputable
facts."

The result of this is that men have ceased to
regard the Neo- Darwinian l theories of protective
colouration, mimicry, and recognition markings
as mere hypotheses which seem to throw light on
certain phenomena in the organic world. These
theories have assumed the rank of laws of nature.
To dispute them would seem to be as futile as
to assert that the earth is flat. To take exception
to them would appear to be as ridiculous as to
object to Mont Blanc. To dare to criticise them
is heresy of the worst type.

Be this as it may, scientific dogma or no
scientific dogma, scientific opinion or no scientific
opinion, we have dared to weigh these theories
in the balance of observation and reason, and have
found them wanting. We have examined these
mighty images of gold, and silver, and brass, and
iron, and found that there is much clay in the
feet.

We shall devote this chapter to lifting the
hem of the garment of sanctity that envelopes
each of these images, and so expose to view the
clay that lies concealed.

We propose, first, to set forth in outline what

1 In this chapter we use the word Neo-Darwinism in its usually-
accepted sense, i.e. as a name for that which should be called
Wallaceism, for the doctrine of the all-sufficiency of natural
selection.

172

Cryptic Colouring

we trust will be considered a fair statement of
the various theories of animal colouration which
are generally accepted to-day, then to show
up the various weak points in these, and lastly,
to endeavour to ascertain whether there are not
some alternative explanations in certain cases to
which the generally - accepted theory does not
apply.

Neo- Darwinians divide the various forms of
colouration into three great classes : — ( i ) Cryptic
colouring, or protective and aggressive resem-
blances ; (2) sematic colours, or warning and
recognition colours ; and (3) pseudo-sematic
colours, or mimicry. A tabular statement of
this scheme of colouring will be found on pp.
293-7 of Professor Poulton's Essays on
Evolution.

As regards class (i), Neo-Darwinians point
out that the great majority of animals are so
coloured as to make them very difficult to see in
their natural environment, hence the whiteness
of the creatures which inhabit the snow-bound
Arctic regions, the sandy colour of desert animals,
the spotted coats of creatures which live among
trees, the striped markings of animals which
spend their lives amid long grass, and the trans-
parent blueness of pelagic animals. The theory
is that all kinds of animals, whether those that
hunt or those that are hunted, derive much ad-
vantage from being coloured like their environ-

The Making of Species

ment. The hunted creatures are thereby the
better able to elude the vigilance of their foes,
while those that hunt are in a position to take
their quarry by surprise ; so that natural selection
has caused them all to assimilate to the hues
of their surroundings. Neo-Darwinians point
to the fact that some Arctic animals are brown
in the summer to match the ground from
which the snow has melted, and turn white in
winter to assimilate with their snowy background.
Naturalists further cite, as evidence in favour of
this theory, the case of those creatures which
imitate inanimate objects, such as leaves and
twigs, and thereby escape the observation of
their foes.

Thus, the great majority of animals are sup-
posed to be cryptically coloured, that is to say,
coloured so as to be, if not quite invisible,
at least very inconspicuous in their natural
habitat.

It is, however, generally admitted that many
creatures are not cryptically coloured. Some,
indeed, seem to be coloured in such a way as to
render them as conspicuous as possible. The
Neo-Darwinians declare that there is a reason
for this. "If," writes Professor Milnes Marshall
(page 133 of his Lectures on the Darwinian
Theory], " an animal, belonging to a group liable
to be eaten by others, is possessed of a nauseous
taste, or if an animal, such as a wasp, is specially

'74

Warning Colouration

armed and venomous, it is to its advantage that
it should be recognised quickly, and so avoided
by animals that might be disposed to take it as
food.

" Hence arises warning colouration, the ex-
planation of which is due to Wallace. Darwin,
who was unable to explain the reason for the
gaudy colouration of some caterpillars, stated
his difficulty to Wallace, and asked for sug-
gestions. Wallace thought the matter over,
considered all known cases, and then ventured to
predict that birds and other enemies would be
found to refuse such caterpillars if offered to
them. This explanation, first applied to cater-
pillars, soon extended to adult forms, not only of
insects, but of other groups as well. . . . Insects
afford many admirable examples of warning
colours, and many well-known instances occur
among butterflies. The best examples of these
are found in three great families of butterflies —
the Heliconidcz, found in South America, the
Danaidce, found in Asia and tropical regions
generally, and the Acrceidce of Africa. These
have large but rather weak wings, and fly slowly.
They are always very abundant, all have con-
spicuous colours or markings, and often a peculiar
form of flight, characters by which they can be
recognised at a glance. The colours are nearly
always the same on both upper and under sur-
faces of the wings ; they never try to conceal

The Making of Species

themselves, but rest on the upper surfaces of
leaves and flowers. Moreover, they all have
juices which exhale a powerful scent ; so that, if
they are killed by pinching the body, a liquid
exudes which stains the fingers yellow, and leaves
an odour which can only be removed by re-
peated washing. This odour is not very offen-
sive to man, but has been shown by experi-
ment to be so to birds and other insect-eating
animals.

" Warning colours are advertisements, often
highly coloured advertisements, of unsuitability
as food. Insects are of two kinds — those which
are extremely difficult to find, and those which
are rendered prominent through startling colours
and conspicuous attitudes. Warning colours
may usually be distinguished by being con-
spicuously exposed when the animal is at rest.
Crude patterns and startling contrasts in colour
are characteristically warning, and these colours
and patterns often resemble each other; black
combined with white, yellow, or red, are the
commonest combinations, and the patterns usually
consist of rings, stripes, or spots."

We trust that we shall be forgiven for this
lengthy quotation. Our object in reproducing so
large an extract is to allow the Neo- Darwinians
to speak for themselves. Were we to state their
theory in our own words, we might perhaps be
charged with stating it inaccurately. We should

176

Batesian Mimicry

add that, even as natural selection is supposed to
have been the cause of conspicuous colouring in
some organisms, so has it caused others to assume
intimidating attitudes or emit warning sounds,
such as a hiss, when attacked.

We now come to the third great class of
animal colours — mimetic colours. Mimicry is
of two kinds, known respectively as Batesian
and Miillerian mimicry, after their respective
discoverers.

It has been found that some apparently
warningly coloured butterflies and other creatures
are palatable to insectivorous animals. The
explanation given of this is that these showy but
edible butterfles " mimic," that is to say, have the
appearance of, show a general resemblance to,
species which are unpalatable. This is known as
Batesian mimicry. " Protective mimicry," writes
Professor Poulton (Essays on Evolution, p. 361),
" is here defined as an advantageous superficial
resemblance of a palatable defenceless form to
another that is specially defended so as to be
disliked or feared by the majority of enemies
of the groups to which both mimic and
model belong — a resemblance which appeals
to the senses of animal enemies . . . but
does not extend to deep-seated characters,
except when the superficial likeness is affected
thereby."

As Wallace has pointed out, five conditions

M 177

The Making of Species

must be satisfied before such protective mimicry
can occur : —

" i. That the imitative species occur in the
same area and occupy the same station as the
imitated. 2. That the imitators are always the
more defenceless. 3. That the imitators are
always less numerous in individuals. 4. That
the imitators differ from the bulk of their allies.
5. That the imitation, however minute, is ex-
ternal and visible only, never extending to
internal characters or to such as does not
affect the external characters." {Darwinism,
Chap. ix.).

Thus the mimic is supposed to deceive his
enemies by deluding them into the belief that he
is the inedible species which they once tried to
eat and vowed never again to touch, so nasty
was it. The mimic, then, may be compared to
the ass in the lion's skin. Needless to say, this
mimicry is quite unconscious. It is supposed
to have been developed by natural selection.
Every popular book on Evolution cites many
examples of such mimicry. We may there-
fore content ourselves with mentioning but a
few.

Our common wasps are copied by a beetle
(Clytus arietis), active in movement and banded
black and yellow, and by several yellow-barred
hover-flies (Syrphidae) ; and the bumble-bee
by a clear- winged moth (Sesia fuciformis).

178

Examples of Mimicry

There is, indeed, a whole group of these clear-
winged moths, resembling bees, wasps, and other
stinging hymenoptera. The common Indian
Danaid butterfly, Danais chrysippus, is marvel-
lously reproduced by the female of Hypolimnas
misippus, a form allied to our Purple Emperor.
The male of this is black, with white blue-
bordered patches, the female chestnut, edged
with black and with white spots at the tips of
the wings, as in the Danais. Finn has shown
experimentally that this species is liked by
birds.

Another common Indian Danaid (D. limniace),
black, spotted with pale green, is imitated, though
not very closely, by the female of one of the
" white " group, Nepheronia hippia. Finn found
that this insect was eaten freely by birds, and
that the common jungle-babbler (Crateropus
canorus) was deceived by the mimicry of the
female. The very nauseous Indian swallow-tail
(Papilio aristolochice) is closely imitated by another
swallow-tail (P. polites], both having black wings
marked with red and white ; P. aristolochice,
however, has a red abdomen. This difference
was not noticed by two species of Drongo-shrikes
(Dicrurus ater and Dissemurus paradiseus), to
which the butterflies were offered ; but the Pekin
robin (Liothrix luteus) — a very intelligent little
bird — did not fail to pick out and eat the mimic,
though it was deceived by the marvellously

179

The Making of Species

perfect imitation of Danais chrysippus, by the
female of the Hypolimnas.

Such resemblances can therefore be effective.

The cases of mimicry usually quoted include
very few among mammals, probably, as Beddard
suggests, because the species of that class are
relatively few.

The insectivorous genus Tupaia is supposed to
mimic the squirrels, which it much resembles as
regards form in all respects save the long muzzle ;
the idea being that squirrels are so active that
carnivorous animals find it hopeless to pursue
them.

On the other hand, there is a squirrel (Rhino-
sciurus tupaioides) which is supposed to mimic
the tupaias ! It has a similar long muzzle,
and the light shoulder-stripe which is a common
marking in tupaias. But why the squirrel,
one of the group imitated, should in turn become
an imitator is not explained.

The true interpretation of the resemblance is
probably that both squirrels and tupaias are
adapted to a life in trees. Like profession begets
like appearance : the ground-living shrews much
resemble mice, and the moles find representatives
in mole-like rodents.

Another case, however, wherein true mimicry
may have come into play is that of the South
American deer (Cervus paludosus) which singu-
larly resembles in colouration the long-legged

1 80

Miillerian Mimicry

wolf or Aguara-guazu (Canis jubatus). Both
these species are chestnut in colour, with the
front of the legs black, and the ears lined
with white hair ; both inhabit the same regions
in South America.

The second kind of mimicry — Miillerian mimi-
cry— is where one unpalatable creature resembles
another. This form of mimicry is named after
Fritz M tiller, who suggested the explanation now
usually accepted, namely, that " Life is saved by a
resemblance between the warning colours in any
area, inasmuch as the education of young inex-
perienced enemies is facilitated, and insect life
saved in the process." " It is obvious," writes
Poulton (p. 328 of Essays on Evolution], " that
the amount of learning and remembering, and
consequently of injury and loss of life involved in
these processes, are reduced when many species
in one place possess the same aposematic colour-
ing, instead of each exhibiting a different danger
signal. . . . The precise statement of advantage
was made by Mr Blakiston and Mr Alexander,
of Tokio. ' Let there be two species of insects
equally distasteful to young birds, and let it be
supposed that the birds would destroy the same
number of individuals of each before they were
educated to avoid them. Then if these insects
are thoroughly mixed and become undistinguish-
able to the birds, a proportionate advantage
accrues to each over its former state of existence.

181

The Making of Species

These proportionate advantages are inversely in
the duplicate ratio of the respective percentages
that would have survived without the mimicry/ "

This is rather a cumbrous method of saying
that if there are in a locality a number of young
birds, and each of these has to learn by ex-
perience which insects are edible and which are
not, each will, if it learns by one example, devour
one insect of any given pattern. Now, if two
species of inedible insects have this pattern, they
will between them lose only one member in the
educating process of each bird, whereas if each
species of insect had a colouration peculiar to
itself, each species would lose a whole individual
instead of half a one. There can be no doubt
that such a livery of unpalatability is of some
advantage to its possessors.

It has been shown experimentally that hand-
reared young birds have to acquire their know-
ledge of flavours and colours by experiment.

It is well known that in many species the
male and the female are not coloured alike.
Such species are said to exhibit sexual
dimorphism. In these cases it is usually
the male that is more conspicuously coloured.
Darwin felt that the theory of natural selection
could not satisfactorily account for this phe-
nomenon, so put forward the supplementary
theory of sexual selection. On this hypothesis
the females are supposed to be able to pick and

182

Danger Signals

choose their mates, and to select the most beauti-
ful and ornamental ones, hence the greater
showiness of these in most sexually dimorphic
species. Wallace does not accept this theory.
He thinks it unnecessary. He looks upon the
brilliant colouring of the males as due to their
superior vigour ; moreover, he says that it is the
hen that sits upon the eggs, and so requires a
greater degree of protection than the male, and
therefore natural selection has not permitted her
to develop all the ornaments displayed by the
cock. With the phenomenon of sexual dimor-
phism we shall deal at length in the next
chapter.

Dr Wallace recognizes yet another exception
to the rule that animals are cryptically coloured.
Many creatures possess on the body markings
which tend to render them conspicuous rather
than difficult to see. Where such markings
occur on gregarious animals, Wallace believes
that they have been evolved by natural selection,
either to enable their possessors to recognize one
another, or to act as a danger signal to their
fellows. The white tail of the rabbit is believed
by Wallace to serve as a danger signal. The
first member of the company to espy the approach-
ing foe takes to his heels, and, as he moves, his
white tail catches the eye of his neighbour, who
at once follows him, so that, in less time than it
takes to tell, the whole company of rabbits is

183

The Making of Species

scampering towards the burrow, thanks to the
white under-surface of the tail.

Even as Wallace out- Darwin's Darwin, so does
Mr Abbott Thayer, an American naturalist and
artist, out-Wallace Wallace. That gentleman
seems to be of opinion that all animals are
cryptically or, as he calls it, concealingly or obliter-
atively coloured. Even those schemes of colour
which have hitherto been called conspicuous are,
he asserts, " purely and potently concealing "
when looked at properly, that is to say, with the
eye of the artist.

Lest it be thought unnecessary to criticize a
hypothesis which appears to be based upon the
assumption that animals see with the eye of the
artist, we may say that Professor Poulton writes
approvingly of Thayer's theory. He frequently
alludes to it in his Essays on Evolution, and he
published an account of it in the issue of Nature,
dated April 24, 1902. Moreover the hypothesis
has been enunciated in such scientific journals
as The Aitk (1896) and The Year-Book of the
Smithsonian Institution (1897).

Thayer asserts that all animals, or at any rate
the great majority, including many that are
usually supposed to be conspicuously coloured,
are in reality obliteratively coloured — that is to
say, coloured in such a way that the effects of
light and shade are completely counteracted, with
the result that they are invisible.

184

Obliterative Colouring

It is possible, says Mr Thayer, to almost
obliterate a statue in a diffused light, by putting
white paint on the surfaces in darkest shadow
and dark paint on the most brightly lighted
parts, all in due proportion. Now this is pre-
cisely what nature is supposed by Mr Thayer to
have done for all her creatures.

It is well known that a great many animals, as
for example the Indian black-buck and the hare,
are coloured on the upper side and white below.
This is called by Mr Thayer the principle of the
gradation of colour. It runs, he declares, all
through the animal world, and is "the main
essential step toward making animals incon-
spicuous under the descending light of the sky."

Animals, he contends, are not protectively
coloured to look like clods or stumps or like
surrounding objects, they are simply oblitera-
tively coloured — coated, as it were, with invisible
paint.

To quote from The Century Magazine (1908) :
" Whales, lions, wolves, deer, hares, mice ;
partridges, quails, sandpipers, larks, sparrows ;
frogs, snakes, fishes, lizards, crabs ; grasshoppers,
slugs, caterpillars — all these animals, and many
thousands more, crawl, crouch, and swim about
their business, hunting and eluding, under cover
of this strange obliterative mask, the smooth and
perfect balance between shades of colour and
degrees of illumination."

185

The Making of Species

Nature having thus visually unsubstantialized
the bodies of animals, so that, if seen at all, they
look flat and ghostly, does not stop there. From
solid-shaded bodies they have been converted,
as it were, into flat cards or canvases, and, to
complete the illusion of obliteration, pictures
of the background — veritable pictures of the
more or less distant landscape — have been
painted on their canvases ! Such in effect are
the elaborate ' ' markings of field and forest
birds."

Again he writes : " Brilliantly changeable or
metallic colours are usually supposed to make
the birds that wear them conspicuous, but nothing
could be further from the truth. Iridescence is,
indeed, one of the strongest factors of conceal-
ment. The quicksilver-like intershifting of many
lights and colours, which the slightest motion
generates on an iridescent surface, like the back
of a bird or the wing of a butterfly, destroys the
visibility of that wing or back as such and causes
it to blend inextricably with the gleaming and
scintillating labyrinthine-shadowed world of wind-
swayed leaves and flowers."

According to Thayer, the skunk, which for
years has been an important item of the stock-in-
trade of the advocates of the theory of warning
colouration, is an excellent example of obliterative
colouring, since its enemies are supposed to mis-
take for the sky-line the line of junction between

1 86

Obliterative Colouring

the white fur of the back and the dark fur of the
sides. Similarly the crocodiles are supposed to
mistake a flamingo for the sky at sunrise or at
sunset !

There is doubtless something in this theory of
obliterative colouration.

Any one can see, by paying a visit to the South
Kensington Museum, that an animal which is of
a lighter colour below than above, is less con-
spicuous in a poor light than it would be were
it uniformly coloured. There is then no doubt
that this scheme of colour, which is so common
in nature, has some protective value.

To this extent has Mr Thayer made a valuable
contribution to zoological science. But when
he informs us that obliterative colouring is a
" universal attribute of animal life," we feel
sorely tempted to poke fun at him.

We would ask all those who believe in the
universality of obliterative colouring to observe
a flock of rooks wending their way to their
dormitories at sunset.

Let us now pass on to the examination of the
more orthodox theories of animal colouration.

OBJECTIONS TO THE THEORY OF CRYPTIC
COLOURING

Before criticising the theory of cryptic colour-
ing, we desire to state distinctly that we admit

.8?

The Making of Species

that, where other things are equal, it is of
advantage to all creatures which hunt or which
are preyed upon to be inconspicuous. If difficult
to distinguish amid their natural surroundings,
the former are likely to secure their prey readily,
and the latter have a chance of escaping from
their enemies. Our quarrel is with the theory of
cryptic colouring as it is enunciated by many
Neo-Darwinians, with the theory that every hue,
every marking, every device displayed by an
organism is of utility to the organism and has
been directly developed by natural selection.

The extreme advocates of the theory of cryptic
colouring have greatly exaggerated the degree
in which animals are assimilated to their natural
environment.

We grant that a great many creatures, which
when seen in a menagerie appear very con-
spicuous, are the reverse of conspicuous when
standing motionless amid their natural surround-
ings. As Beddard has pointed out, it is often
not easy to find a sixpenny piece which has been
dropped on the carpet, but the reason for this is,
not that the coin is protectively coloured, but
that any small object, no matter how coloured,
is difficult to distinguish amid a variegated
environment. The assumption of a white
winter coat by many organisms that live in
northern latitudes has been cited, again and
again, as showing how important it is for an

1 88

Fauna of Polar Regions

animal to be protectively coloured. If, it is
urged, those creatures that live in lands which
are covered in snow for half of the year have
become white in winter by the action of natural
selection in order to escape their foes, it is
obviously of paramount importance to all
creatures that they should be cryptically
coloured. Popular books on natural history
convey the impression that during winter the
snow-clad, ice-bound Arctic regions are peopled
by a fauna whose fur or hair rivals in whiteness
the snowy mantle of the earth. The impression
thus conveyed is misleading. It is true that an
unusually large percentage of the animals that
inhabit the polar regions are white in winter, but
the majority of the creatures which dwell there
do not assume the white garb of winter.

As the fauna of the polar regions is a small
one, we are able to give lists of all the birds and
mammals which dwell in the Arctic and the
Antarctic regions. We have arranged these in
in three columns. In the first are placed those
creatures which are white throughout the year, in
the third those that retain their colour through
the winter, while the middle column contains
those forms which change their colouring with
the season.

189

The Making of Species

ARCTIC FAUNA.

MAMMALS.

White.

Changing with the
Seasons.

Coloured.

Polar Bear.
Arctic Fox (some
individuals).
White Whale or

Arctic Fox (most
individuals).
Arctic Lemming.
Stoat.

Arctic Fox (some-
times).
Reindeer.
Musk-ox.

Beluga.

Weasel.
Blue Hare.

Glutton.
Moose.

Sable.

Seals.

Walrus.

Narhwal.

Greenland Whale.

BIRDS.

Ivory Gull.
Snowy Owl.
Gyrfalcon.
Snow Goose.

Black Guillemot.
Ptarmigans.
Snow Bunting
(whitest in
summer !).
Razorbill.

Sea Eagle.
Greenland Red-
poll (very pale).
All Arctic Geese
and Ducks other
than S now

Little Auk (throat
only becomes
white).

Goose.
Raven.
Cormorant.
Brunnich's Guille-

mot.

Puffin.

Fulmar Petrel.

Ross's Gull.

Glaucous Gull

(very pale).
Sandpipers.

190

Antarctic Fauna

ANTARCTIC FAUNA.

MAMMALS.

White.

Changing with the
Seasons.

Coloured.

Antarctic White

None.

Other Seals than

Seal (Lobodon

Lobodon.

carcinophaga),

Whales.

in some cases.

BIRDS.

Sheathbill.

None.

Penguins.

Snowy Petrel.

Cormorant.

Giant Petrel(some

Skua Gull.

individuals).

Giant Petrel

Chick of Emperor

(usually).

Penguin.

Other Petrels.

It will be observed that the third column con-
tains the largest number of forms. It is thus
evident that the whiteness of the Arctic and
Antarctic faunas in winter has been greatly
exaggerated.

The Arctic fox appears in all three columns, as
the creature seems to fall into three races — a
permanently white race, a permanently coloured
race, and a seasonally dimorphic race.

Of the creatures set forth in the middle column
of the above tables all are whiter in winter than
in summer with the exception of the snow bunt-

191

The Making of Species

ing, who sets at naught the theory of cryptic
colouring by turning darker in winter ! The
same may be said of the Alpine chamois.

The advocates of the theory of protective
colouring assert that the creatures which do not
turn white in winter are strong and active animals
which have no enemies to fear.

This contention is met by F. C. Selous as fol-
lows (African Nature Notes and Reminiscences,
p. 9): " According to the experience of Arctic
travellers, large numbers of young musk oxen
are annually killed by wolves. . . . Nothing, I
think, is more certain than that a far smaller per-
centage of so-called protectively coloured giraffes
are killed annually by lions in Africa than of
musk oxen by wolves in Arctic America."

Another difficulty which confronts the Neo-
Wallaceian school is that, ex hypothesi, the
assumption of the white coat was gradual.
Hence the change in the direction of white-
ness cannot, in its first beginning, have been
of perceptible utility to an organism. How
then can natural selection have operated on it ?

The transparency of pelagic organisms is fre-
quently cited as exemplifying cryptic colouring.
We all know that the common jelly-fish is as
transparent as glass. Floating on the surface of
the ocean are millions of tiny organisms, so
transparent as to be invisible to the human eye.
At first sight this certainly appears to be a

192

Pelagic Organisms

remarkable case of protective colouring. Un-
fortunately, nearly all the more highly developed
forms display conspicuous pigment (as in most
jelly-fish) in some part of the body.

" An animal floating about in the sea," writes
Beddard, " perfectly transparent, but decked with
dense black patches, of the size of saucers, would
betray its whereabouts even to the least observant ;
if the observer were stimulated by hunger or fear,
the conspicuousness would not be lessened. . . .
Besides the internecine warfare which is con-
tinually going on amongst the smaller surface
organisms, they are devoured wholesale by the
larger pelagic fish, and by whales and other
Cetacea. A whale, rushing through the water
with open mouth and gulping down all before
him, is not the least inconvenienced by the
invisibility of the organisms devoured in such
enormous quantities ; nor do a solid phalanx of
herring or mackerel stop to look carefully for
their food : they take what comes in their way,
and get plenty in spite of * protective absence of
colouration.'

" If the transparency of the pelagic organisms be
due entirely to natural selection, it is remarkable
that there is so little modification in this direction
among the species inhabiting the bottom at such
depths as are accessible to the sun's rays ; the
advantage gained by this transparency and con-
sequent invisibility would be equally great. And
N 193

The Making of Species

yet this is not the case ; the bulk of the bottom
fauna of the coasts are brilliantly coloured animals,
and those that show any protective colouring at
all appear to be coloured so as to resemble stones
or sea-weeds." l

Before leaving the subject of marine animals,
we may point out that the majority of the
creatures that live in the everlasting blackness of
the depths of the ocean display exceedingly con-
spicuous colouring, and this colouring seems to be
constant. In such cases the colouring cannot be
useful as such to its possessors. The same rnay
be said of the colour of blood, or of the colouring
of the internal tissues of all organisms. We
must not lose sight of the fact that every
organism, and every component part thereof,
must of necessity be either of some colour or
perfectly transparent. It seems to us that since
the appearance of The Origin of Species zoologists
have tended to exaggerate the importance of
colouring to organisms ; they frequently speak
of it as though it were the one and only factor in
the struggle for existence. It is on this account
that they feel it incumbent upon them to find
ingenious explanations for every piece of colour-
ing displayed by every plant or animal.

The tendency to exaggerate the importance to
an animal of its colouring is doubtless in large

1 Animal Colouration, p. 125. A book full of valuable facts
and ideas on this most interesting subject.

194

Unimportance of Colour

part due to the fact that many zoologists are
content to study nature in museums rather
than in the open. Some of those who observe
organisms in their natural surroundings, especially
in such favourable localities as the tropics,
seem to be of opinion that natural selection
has but little influence on the colouration of
organisms.

Thus D. Dewar writes (Albany Review, 1907) :
" Eight years of bird-watching in India have
convinced me that, so far as the struggle for
existence is concerned, it matters not to a bird
whether it be conspicuously or inconspicuously
coloured, that it is not the necessity for pro-
tection against raptorial foes which determines
the colouring of a species ; in short, that the
theory of protective colouration has but little
application to the fowls of the air."

Similarly, F. C. Selous writes, on page 13
of African Nature Notes and Reminiscences :
" Having spent many years of my life in the
constant pursuit of African game, I have cer-
tainly been afforded opportunities such as have
been enjoyed by but few civilised men of
becoming intimately acquainted with the habits
and life-history of many species of animals living
in that continent, and all that I have learned
during my long experience as a hunter compels
me to doubt the correctness of the now very
generally accepted theories that all the wonder-

The Making of Species

fully diversified colours of animals — the stripes
of the zebra, the blotched coat of the giraffe, the
spots of the bushbuck, the white face and the
rump of the bontebok, to mention only a few-
have been coloured either as means of pro-
tection from enemies or for the purpose of
mutual recognition by animals of the same
species in times of sudden alarm."

So also G. A. B. Dewar — a very close
observer of nature in England — writes, in The
Faery Year\ " Few theories in natural history
have received more attention of late years than
protective or aggressive colour, 'mimicry,' and
harmony with environment. . . . To doubt this
use of colour to animals seems like inviting back
chaos in place of cosmos — for abandon the theory,
and a world of colour is straightway void of pur-
pose, a muddle of chance. So we all like the
theory. Some, however, perceive plans to aid
the wearer in every colour, tint, shade, and
pattern. We may be sceptical of a good many
of the cases they cite in support of colour aid,
though attracted by the main idea."

Writing of the commoner British butterflies,
he says: ''After a little practice, any man
furnished with good eyesight can easily dis-
tinguish these butterflies — blues, coppers, small
heaths, and meadow browns — from their perches ;
and so we may be sure that the small beast, bird,
or insect of prey, with sense of colour or form,

196

Gadow on Coral Snakes

could also distinguish them. . . . Quite often,
without even searching for them, I can see
cabbage whites and other butterflies asleep on
perches to which they by no means assimilate."
Mr G. A. B. Dewar suggests that the safety of
the resting butterfly lies in " the position, the
couch on high, . . . not the mask of colour or
marking."

Two short visits to Southern Mexico sufficed
to show Dr Hans Gadow that some of the com-
monly accepted explanations of colour phenomena
are not the correct ones.

Thus writing of coral snakes, he says, on
page 95 of Through Southern Mexico : " They
are usually paraded as glaring instances of
warning colouration, but I am not at all sure
whether this is justifiable. Certainly these Elaps
are most conspicuous and beautiful objects.
Black and carmine or coral red, in alternate
rings, are the favourite pattern ; sometimes with
narrow golden-yellow rings between them, as
if to enhance the beautiful combination. But
these snakes are inclined to be nocturnal in their
habits, and, except when basking, spend most
of their time under rotten stumps, in mouldy
ground, or in ants' nests in search of their prey,
which must be very small, to judge from the
size of the mouth."

Dr Gadow goes on to show that although
black and red are very strong contrasts in the

197

The Making of Species

day-time, the combination ceases to be effective
in the dark. He suggests that red and black is
a self-effacing rather than a warning pattern.
He further points out that several kinds of harm-
less snakes have the same colouring and pattern.
"There seems," he says, "to be no reason why
we should not call these cases of mimicry ; and
yet this is most likely a wrong interpretation,
since such harmless snakes are also found in
districts where the Elaps does not occur, not only
in Mexico, but likewise in far-distant parts of
the world, where neither elapines nor any other
similarly coloured poisonous snakes exist. To
interpret this as an instance of ' warning
colours ' in a perfectly harmless snake, which
has no chance of mimicry, amounts in such
cases to nonsense, and we have to look for a
different explanation upon physiological and
other grounds."

It is, to say the least of it, significant that all
the opposition to the theory of protective coloura-
tion comes from those who observe nature first
hand, while the warmest supporters of the theory
are cabinet naturalists and museum zoologists.

In the case of nocturnal creatures, as Dr H.
Robinson very sagely points out (Knowledge,
January 1909), the value for protective purposes
of any given colouration must depend very
largely on the state of the moon. "It was," he
writes, "a common experience in the South

198

F. C. Selous Quoted

African War that on overcast or moonless nights
the nearly black army great-coat made a picquet
sentry invisible at a distance of a few feet. In
strong moonlight this garb could be seen at a
great distance, whereas a khaki pea jacket, use-
less on a dark night, answered the requirements
of invisibility very well." It is thus evident
that the dark colour of the buffalo and sable
antelope cannot be protective on both dark and
moonlight nights.

The theory of protective colouration is based
on the tacit assumption that beasts of prey rely
on eyesight for finding their quarry. Raptorial
birds certainly do use their eyes as the means of
discovering their victims ; but the great majority
of predaceous mammals trust almost entirely to
their power of smell as a means for tracking
down their prey.

" Nothing," writes F. C. Selous, on page 14 of
African Nature Notes and Reminiscences, " is
more certain than that all carnivorous animals
hunt almost entirely by scent until they have
closely approached their quarry, and usually
by night, when all the animals on which they
prey must look very much alike as far as colour
is concerned."

The herbivora — the quarry for the beast of
prey — too, have a keen sense of smell, so that
they trust their noses rather than their eyes for
safety.

199

The Making of Species

No observer of nature can have failed to
remark how the least movement on the part
of an animal will betray its whereabouts, even
though in colouring it assimilates very closely
to the environment. So long as the hare squats
motionless in the furrow, it may remain un-
observed, even though the sportsman be search-
ing for it ; but the least movement on its part at
once attracts his eye. Thus, in order that pro-
tective colouration can be of use to its possessor,
the latter must remain perfectly motionless. But,
in tropical countries, where flies, gnats, etc., are
a perfect scourge, no large animal is, when
awake, motionless for ten seconds at a time.
The tail is in constant motion, flicking off the
flies that attempt to settle on the quadruped.
The ears are used in a similar manner. Thus
the so-called protective colouring of herbivora
cannot afford them much protection. It is
further worthy of note that the brush-like tip
to the tail of many mammals is not of the same
colour as the skin or fur. It is very frequently
black. Thus we have the spectacle of a pro-
tectively coloured creature continually moving,
as if to attract attention, almost the only part of
its body that is not protectively coloured !

Many species of birds display what is known
as seasonal dimorphism, still more display sexual
dimorphism.

Seasonally dimorphic birds very often assume
200

Sexual Dimorphism

a bright livery at the breeding season ; this
nuptial plumage is by no means invariably con-
fined to the cock, so that we are brought face to
face with the fact that some hen birds, that are
normally inconspicuously coloured, become showy
and easy to see at the nesting time, that is to say,
precisely at the season when they would seem to
be most in need of protection.

In the great majority of cases of sexual dimor-
phism among birds the cock is the more showily
coloured. Now, if it be a matter of life-and-
death importance to a bird to be protectively
coloured, we should expect the showily coloured
cock birds to be far less numerous than the
dull-plumaged hens, since the former are, ex
hypothesi, exposed to far greater danger than
the inconspicuous hens. As a matter of fact,
cock birds in practically all species appear to be
at least as numerous as the hens. Nor can it be
said that this is due to their more secretive
habits. As a general rule, cock birds show
themselves as readily as the hens ; indeed, in the
case of the familiar blackbird, the conspicuous
cock is less retiring in his habits than the more
sombre hen. It may, perhaps, be thought that
the greater danger to which the sitting bird is
exposed accounts for the fact that hens, not-
withstanding their protective colouration, are not
more numerous than the cocks. Unfortunately
for the supposition, in many sexually dimorphic

201

The Making of Species

hens, as, for example, the paradise fly-catcher
(Terpsiphone parodist), the showy cock shares
the burden of incubation equally with the hen.

It frequently happens that allied species of
birds are found in neighbouring countries. The
Indian robins, for example, fall into two species.
The brown-backed robin ( Thamnobia cambayensis)
occurs north of Bombay, while the black-backed
species (T. fulicata) is found south of Bombay.
The hens of these two species are almost indis-
tinguishable, but the cocks differ, in that one has
a brown back, while the other's back is glossy
black. The Wallaceian theory of colouration
seems quite unable to explain this phenomenon—
the splitting up of a genus into local species—
which is continually met with in nature. Equally
inimical to the theory of protective colouration is
the existence, side by side, of species which
obtain their living in much the same manner.
On every Indian lake three different species of
kingfisher pursue their profession cheek by
jowl ; one of these — Ceryle rudis — is speckled
black and white, like a Hamburg fowl ; the
second is the kingfisher we know in England ;
and the third is the magnificent white-breasted
species — Halcyon smyrnensis — a bright-blue bird
with a reddish head and a white wing bar. It is
obvious that all three of these diversely plumaged
species cannot be protectively coloured. It may
perhaps be objected that the piscatorial methods

202

Precis Artexia

of these kingfishers differ in detail. We admit
that this is the case, but would maintain, at the
same time, that these comparatively slight dif-
ferences in habit do not account for the very
striking differences in plumage. We may also
cite the yellow and pied wagtails of our own
country, which may be seen feeding in the same
meadows. Most familiar and striking of all is the
everyday sight of a blackbird and thrush plying
their respective avocations within a few yards of
each other on the same lawn, differently coloured
though they be.

Another weighty objection to the generally
accepted theory of protective colouration is that
some of the creatures which assimilate most
closely to their environment are those which
appear to be the least in need of such protection.

The butterfly Precis artexia, writes F. C.
Selous, 4< is only found in shady forests, is
seldom seen flying until disturbed, and always
sits on the ground amongst dead leaves. Though
handsomely coloured on the upper side, when its
wings are closed it closely resembles a dead leaf.
It has a little tail on the lower wing, which looks
exactly like the stalk of a leaf, and from this tail
a dark-brown line runs through both wings (which
on the under side are light brown) to the apex of
the upper wing. One would naturally be inclined
to look upon this wonderful resemblance to a
dead leaf in a butterfly sitting with closed wings

203

The Making of Species

on the ground amongst real dead leaves as a
remarkable instance of protective form and
colouration. And of course it may be that this
is the correct explanation. But what enemy is
this butterfly protected against ? Upon hundreds
of different occasions I have ridden and walked
through forests where Precis artexia was
numerous, and I have caught and preserved
many specimens of these butterflies, but never
once did I see a bird attempting to catch one
of them. Indeed, birds of all kinds were scarce
in the forests where these insects were to be
found."

Similarly D. Dewar writes (Albany Review,
1907) : " If a naturalist be asked to cite a perfect
example of protective colouring, he will, as likely as
not, name the sand grouse (Pteroclurus exustus).
This species dwells in open, dry, sandy country,
and its dull brownish-buff plumage, with its soft
dark bars, assimilates so closely to the sandy
environment as to make the bird, when at rest,
practically invisible, at any rate to the human
eye. Unfortunately for the theory, this bird
stands less in need of protective colouration than
any other, for it has wonderful powers of flight.
Even a trained falcon is unable to catch it,
because it can fly upwards in a straight line as
though it were ascending an inclined plane, with
the result that the pursuing hawk is never able
to get above it to strike."

204

Striped Caterpillars

Lord Avebury, who is a typical Wallaceian,
points out the connection that exists between
longitudinal stripes on caterpillars and the habit
of feeding either on grass or low-growing plants
among grass. The inference, of course, is that
birds mistake these caterpillars for leaves, or, at
any rate, fail to observe them when feeding, not
only because they are green in colour, but
because their longitudinal stripes look like the
parallel veins on the blades of grass. But the
butterflies of the family Satyrida^ as Beddard
points out, all possess striped larvae, and these
feed chiefly by night, when neither their colouring
nor marking is visible, while during the day
many of them lie up under stones ; other cater-
pillars of this family feed inside the stems of
plants. " Now," writes Beddard (Animal Coloura-
tion, p. 101), " in these cases the colour obviously
does not matter : if, therefore, the longitudinal
striping is kept up by constant selection on
account of its utility, and has no other significa-
tion, we might expect that in these two species
(Hipparc/iia semele and GEnis), and in others with
similar habits, the cessation of natural selection
would have permitted the high standard required
in the other cases to be lowered — perhaps, even,
as has been suggested in the case of cave animals,
the colours being useless to their possessors,
might have disappeared altogether — but they
have not."

205

The Making of Species

Many exceedingly conspicuous birds — as, for
example all the crow-tribe, the egrets, the
kingfishers — flourish in spite of their showy
plumage. Such creatures, while scarcely consti-
tuting a valid objection to the theory of pro-
tective colouration, serve to show that protective
colouring is not a necessity. An animal other-
wise able to take care of itself can afford to
dispense with cryptic colouration. " An ounce
of good solid pugnacity is a more effective
weapon in the struggle for existence than many
pounds of protective colouration."

There used to live in the gardens of the Zoo-
logical Society of London a black cat belonging
to the manager of one of the restaurants. This
animal used to catch birds on the lawn. We
believe that not even Mr Thayer will maintain
that a black cat is cryptically coloured when
stalking on a well-watered lawn ! Nevertheless
the nigritude of that cat did not prevent it
securing a meal.

The case of birds' eggs furnish an excellent
example of the lengths to which Wallace and his
followers have pushed the theory of protective
colouration.

D. Dewar maintains that it is possible to
divide birds' eggs that are coloured, as opposed
to those that are white, into two classes — those
which are protectively coloured and those which
are not The former class includes all those

206

Colours of Eggs

which are laid in shingle or on the bare ground,
as, for example, the eggs of the ring-plover and
the lap- wing.1 He maintains that the variously
coloured and speckled eggs that are laid in cup-
shaped nests are not protectively coloured at all ;
he declares that they are usually very conspicuous
when in the nest, and, moreover, it would be futile
for them to be cryptically coloured, for a bird or
lizard that habitually sucks eggs will examine
carefully the interior of each nest it discovers.

Needless to say, this view does not appeal to
the so-called Neo- Darwinians. Wallace writes,
on page 215 of Darwinism-. "The beautiful
blue or greenish eggs of the hedge-sparrow, the
song-thrush, the blackbird, and the lesser redpole
seem at first sight especially calculated to attract
attention, but it is very doubtful whether they
are really so conspicuous when seen at a little
distance among their usual surroundings. For
the nests of these birds are either in evergreen,
or holly, or ivy, or surrounded by the delicate
green tints of early spring vegetation, and may
thus harmonise very well with the colours around
them. The great majority of the eggs of our
smaller birds are so spotted or streaked with
brown or black on variously tinted grounds that,

1 Even these eggs, closely though they resemble in colouring
the shingle, etc., on which they are laid, are discovered and
eaten by gulls, as Mr A. J. R. Roberts points out in The Bird
Book.

207

The Making of Species

when lying in the shadow of the nest and sur-
rounded by the many colours and tints of bark
and moss, of purple buds and tender green or
yellow foliage, with all the complex glittering
lights and mottled shades produced among these
by the spring sunshine and sparkling rain-drops,
they must have quite a different aspect from that
which they possess when we observe them torn
from their natural surroundings."

The obvious comment on this is that it is very
fine and poetic English, but it is not science. It
is futile to deny what should be obvious to every
field naturalist, namely, that the majority of eggs
laid in open nests are most conspicuous.

D. Dewar thus summarises the main facts
which show that eggs in nests (as opposed to
those laid on the bare ground) are not pro-
tectively coloured :—

11 i. Allied species of birds, even though their
nesting habits are very different, as a rule lay
similarly coloured eggs.

" 2. Eggs laid in domed nests certainly do not
need protective colouring, yet many of these are
coloured.

" 3. The same is true of many eggs laid in
holes in trees or in buildings.

" 4. The protective resemblances of eggs which
are laid in the open are apparent to everyone,
which certainly is not true of those deposited in

nests.

208

Colours of Eggs

"5. Many birds lay eggs which exhibit very
great variations.

"6. Some birds lay eggs of different types,
and these sometimes differ from one another so
greatly that it is difficult to believe that they
could have been laid by the same species." 1

7. It not infrequently happens that one species
lays in the disused nest of another, and the eggs
of the latter are often very different in colouring
from those of the former.

We have up to the present considered the theory
of general cryptic colouration, which declares that
the majority of creatures are so coloured as to be
inconspicuous. We have still to deal with the
hypothesis of special cryptic colouring.

Certain animals look, when resting, very like
an inanimate object, such as a dead leaf or a
twig. This resemblance is said to be the result
of natural selection, since it enables its possessors
to escape destruction ; they are seen, but mis-
taken for something else.

The classical examples of this kind of protec-
tive colouring are furnished by the Kallimas or
leaf-butterflies, which display an extraordinary
resemblance to dead leaves.

Other examples are the stick-insects and the
lappet moth, which looks like a bunch of dry
leaves. It is needless to multiply instances.

1 Journal of the Bombay Natural History Society, VoL xv.
1903-4)) P- 454-

O 209

The Making of Species

In every work on animal colouration numbers of
such cases are cited.

We may grant that in some cases, at any rate,
the resemblance is of value to its possessor, in
that it deceives predatory creatures. But it does
not follow from this that the likeness has origi-
nated through the action of natural selection. In
order that there can be selection there must be
varying degrees of a tolerable resemblance to
select from. How did the initial similarity
arise ? This is a matter upon which Wallaceians
are silent. As Poulton truly says, in discussing
the degree of protection afforded by such re-
semblances, we tacitly endow animals with senses
exactly similar to our own. Are we justified in
so doing ? Most certainly not in the case of the
invertebrate animals, especially as regards the
arthropods, of which the eyes are constructed
very differently from those of human beings.

D. Dewar has often seen a toad shoot out
its tongue and touch a lighted cigarette end,
apparently mistaking it for an insect. Similarly,
he has again and again induced a gecko lizard to
chase and try to swallow a piece of black cotton,
one end of which was rolled up into a ball. It is
only necessary to take hold of the unrolled end
of the cotton and place the rolled-up end a few
inches from the lizard, and gradually draw it
away in order to induce the lizard to attempt to
seize it.

210

Eyesight of Birds

It would therefore seem that all these elaborate
" protective " devices are unnecessary refinements
if regarded as a protection against invertebrate,
reptilian, and amphibian foes. Birds, on the other
hand, appear to have exceedingly sharp eyesight,
so that in order to deceive them the resemblance
requires to be very close. Indeed, as regards
those birds which systematically hunt for their
prey among leaves and grass, it seems doubtful
whether the alleged "protective" resemblances of
caterpillars to twigs, etc. , are sufficient to be of much
use to them. Thus Beddard writes (on page 91
of Animal Colouration) : " Judging of birds by
our own standard — which is the way in which
nearly all the problems relating to colour have
been approached — does it seem likely that we
should fail to see a caterpillar, perhaps as long
or longer than the arm, of an obviously different
texture from the branches, and displaying in
many cases through its semi-transparent skin the
pulsation of the heart, for which we were par-
ticularly searching?"

Now, birds certainly feed very largely on
caterpillars, while they are but rarely seen to eat
butterflies. If, therefore, the aim and object of
these special resemblances is the protection of
the species, we should expect to see them in a
nearly perfect state in caterpillars on which
birds feed very largely, and poorly developed in
butterflies, which do not appear to be greatly

211

The Making of Species

preyed upon by birds, but have to fear chiefly
the comparatively dull-eyed lizards and mammals,
of which the latter hunt mainly by scent. As
a matter of fact, the most striking cases of
resemblance to inanimate objects are seen among
butterflies, which seem to stand least in need of
them.

We have already cited the case of the butterfly
Precis artexia. Even more marked does the
unnecessary elaboration of the likeness seem to
be in the Kallima butterflies.

THE THEORY OF WARNING COLOURATION
All biologists admit that there exist some
organisms which are not coloured so as to be
inconspicuous. Indeed, the colouring of certain
species is such as to render them particularly
conspicuous. Such species are said to be warn-
ingly coloured. They are supposed to be
inedible, or to have powerful stings or other
weapons of defence, or to resemble in appear-
ance organisms which are thus protected. In
the first two cases they are said to be warningly
coloured, and in the last they are cited as
examples of protective mimicry. With the
theory of mimicry we shall deal shortly. We
must first discuss the hypothesis of warning
colouration.

When animals are unpalatable, or when they
possess a sting or poison-fangs, it is, to use the

212

Warning Colouration

words of Wallace, " important that they should
not be mistaken for defenceless or eatable species
of the same class or order, since in that case
they might suffer injury, or even death, before
their enemies discovered the danger or the use-
lessness of the attack. They require some
signal or danger-flag which shall serve as a
warning to would-be enemies not to attack them,
and they have usually obtained this in the form
of conspicuous or brilliant colouration, very dis-
tinct from the protective tints of the defenceless
animals allied to them " {Darwinism, page

232).

For examples of so-called warningly coloured
animals, we may refer the reader to Wallace's
Darwinism, Poulton's Essays on Evolution, or
Beddard's Animal Colouration. An instance
familiar to all is our English ladybird. " Lady-
birds," says Wallace, " are another uneatable
group, and their conspicuous and singularly
spotted bodies serve to distinguish them at a
glance from all other beetles."

In order to establish the theory of warning
colouration, it is necessary to prove that all, or
the great majority of conspicuously-coloured
organisms, are either unpalatable or mimic
unpalatable forms. If this be so, we are able
to understand that the possession of gaudy
colouring may be of advantage to the individual.
But even if this be satisfactorily proved, we

213

The Making of Species

must bear in mind that it does not necessarily
follow that these warning colours can be ac-
counted for on the theory of natural selection.
For, in order to explain the existence of any
organ by the action of natural selection, we must
be able to demonstrate the utility, not only of
the perfected organ, but of the organ at its very
beginning, and at each subsequent stage of
development. This, as we shall show, is pre-
cisely what the Neo- Darwinians are unable to
do. We shall have no difficulty in proving that
it would be more advantageous even to a highly
nauseous creature to have remained inconspic-
uously coloured rather than to have gradually
become more and more conspicuous.

In the first place, let us briefly examine the
evidence on which rests the assertion that all
gaudily-coloured insects, etc., are unpalatable, or
possess stings, or mimic forms which are thus
armed.

In England wasps, bees, and ladybirds are
familiar examples of conspicuous insects.

The banded black and yellow pattern of the
common wasp and the humble bee are regarded
as advertisements or danger signals of the power-
ful sting.

The red-coat with its black spots is similarly
believed to be a warning that the ladybird is not
fit to be eaten.

Caterpillars are usually coloured grey or brown,
214

Examples of Warning Colouration

so as to be inconspicuous ; but numerous ex-
ceptions occur which are brightly coloured, and of
these individuals many have been experimentally
proved to be objectionable as food to most insect-
eating animals, being either protected by an
unpleasant taste, or covered with hairs or
spines.

Familiar cases are those of the abundant and con-
spicuous black and yellow mottled caterpillars of
the European Buff-tip Moth (Pygcera bucephala),
which are much disliked by birds ; and the
gaily - coloured Vapourer Moth caterpillar
(Orgyia antiqua\ with its conspicuous tufts of
hair. Readers will remember that a few years
back these caterpillars were a perfect plague in
London, in spite of the abundance of sparrows,
which feed freely on smooth green and brown
caterpillars.

Oft-cited examples of warning colouration, are
the three great groups of mainly tropical butter-
flies— the Heliconidce of America, the Acrczidce
of Africa, and the Danaince found all over the
world. In all of these the sexes are alike.
They are, every one, strikingly coloured, dis-
playing patterns of black and red, chestnut,
yellow, or white. In most butterflies the lower
surface of the wings is of a quiet hue, in order
to render the organism inconspicuous when at
rest, but in these warningly coloured groups the
under surface of the wings is as gaudy as the

215

The Making of Species

upper surface. Their flight is slow. They are
tough, and exhale a characteristic odour.

Belt showed that, in Nicaragua, birds, dragon-
flies, and lizards seem to avoid the Heliconine
butterflies, as the wings of these last are not
found lying about in places where insectivorous
creatures feed, whereas wings of the edible forms
are to be found. Moreover, a Capuchin monkey,
kept by Belt, always refused to eat Heliconine
butterflies.

Finn investigated the palatability of a number
of Indian insects. He found that most of the
birds with which he experimented objected to
the Danaine butterflies ; but they disliked still
more intensely two butterflies belonging to
groups not universally protected — a swallow-
tail (Papilio aristolochicz) and a white (Delias
eucharis).

Finn further experimented with the tree-shrew
or Tupaia (Tupaia ellioti\ which feeds largely
on insects. He found that this creature refused
most emphatically all these warningly-coloured
butterflies. It would under no circumstances
eat the Danaince, whereas the birds would do so
if no more palatable insects were offered to them
at the time.

Colonel A. Alcock found that a tame Hima-
layan bear indignantly refused to eat a locust
(Autarches militaris) gaily coloured with black,
red, and yellow, and exhaling an unpleasant-

216

Examples of Warning Colouration

smelling froth ; but this bear readily devoured
ordinary brown or green species.

Among cold-blooded vertebrates the common
European salamander, with its bright black and
yellow markings, is a striking example of warning
colouration ; its skin exudes, on pressure, a very
poisonous secretion.

Colonel A. Alcock has described a small
siluroid sea-fish, brightly banded with black and
yellow, and armed with poison spines.

A well-known Indian poisonous snake, the
banded Krait (Bungarus cceruleus), is conspicu-
ously barred with wide bands of black and yellow ;
and in South America there occur numerous
species of coral snakes, in which red is added
to these conspicuous colours.

The only known poisonous lizard — the Helo-
derm of Mexico — is conspicuously blotched with
black and salmon-colour.

Among birds, no instances of warning coloura-
tion have been recorded, though Professor
Poulton has suggested that possibly the striking
and contrasted tints of many tropical species may
be due to this cause. The suggestion is an in-
genious one, but is at present totally unsupported
by evidence.

The skunks are often cited as an excellent
example of warning colouration among mammals.
Skunks are most conspicuously arrayed in black
and white — the latter above, not below, as is

217

The Making of Species

usual — and have bushy tails, which they carry
erect. Although less powerful and ferocious
than other members of the weasel family, to
which they belong, skunks are notoriously pro-
tected by their abundant secretion of a very fetid
liquid.

For further examples of warning colouration
we would refer the reader to Beddard's illumin-
ating book, entitled Animal Colouration.

It should be noticed that in all the cases which
we have cited the colouration is not only con-
spicuous, but is found in both sexes, whereas in
many undefended animals the male may be just
as strikingly coloured, but the female is not.

We may take it as proved that there is a very
general relation between gaudy colouring and
inedibility, or rather unpalatability, among insects.
It may safely be said that any species of insect
which lives, either as an adult or as a larva, in the
open will perish in the struggle for existence if,
being conspicuously coloured, it is neither in-
edible nor armed with a weapon such as sting, nor
provided with a thick cuticle, nor resembles in
appearance some creature which is protected.

But from this it is not legitimate to conclude,
as Neo-Darwinians do, that these brilliant colours
have been slowly brought into being by natural
selection.

Why should any creature, having by the
"luck" of variation and heredity acquired some

218

Warning Colouring a Drawback

quality — be it strength, pugnacity, sting, or un-
pleasant taste — which renders it comparatively
immune from persecution, proceed to advertise
the fact by assuming a gaudy or striking colour ?
It would surely be better for such an organism to
remain inconspicuous. By becoming showy it is
visible to every young bird who, not having yet
learned that the creature in question is unfit for
food, seizes and perhaps kills it. It is true that
the young bird vows that never again will it
touch another such organism. But of what avail
to the dying example of warning colouration is
the resolution of the young bird ? Moreover, the
organism in question, by being conspicuous, also
advertises itself to those few enemies which will
eat it. There are always, as Professor Poulton
justly remarks, animals which are enterprising
enough to take advantage of prey which has
at least the advantage of being easily seen and
caught.

It is possible to cite cases where animals, not-
withstanding the fact that they possess natural
defences, become the prey of others in some
exceptional cases.

The salamander can be eaten with comparative
impunity by the toad, a creature very likely to
meet with it.

The toad itself may be eaten ; Finn saw the
Indian toad (Bufo melanostictus) eat another of
its own kind. He further observed that the

219

The Making of Species

Indian water-snake (Tropidonotus piscator) and
the "Crow pheasant" cuckoo (Centropus sinensis),
in the free state, and the Indian Roller (Coracias
indica) and the Pied Hornbill (Antkracoceros), in
captivity, eat the warningly-coloured toad. On
the other hand, a captive Racket-tailed drongo
rejected toads when offered to it. The common
cuckoo is well known to feed on hairy and
" warningly-coloured" caterpillars.

Finn has also seen the glossy cuckoo in
Zanzibar devouring black-and-yellow caterpillars.
Moreover, in America crows are found to
select deliberately highly polished and strongly
flavoured beetles. Yet again, wasps are preyed
upon by bee-eaters, and also eaten by our
common toad. In India, Finn found, by many
experiments, that the common garden lizard,
or " bloodsucker" (Calotes versicolor\ would
eat, both in captivity and in freedom, all
" warningly-coloured " butterflies, not only the
Danaince, but even Delias eucharis and the pre-
eminently nauseous Papilio aristolochice. That
this reptile is a great enemy to butterflies is
rendered probable by the frequent occurrence of
specimens of these insects with its semicircular
bites in their wings.

Further, Finn found that bulbuls, the com-
monest garden birds in India, ate the Danaince
readily in captivity, even when other butterflies
could be had, which was not the case with most

220

Conspicuous Animals Attacked

other birds. Bulbuls did, however, usually
refuse the Delias and Papilio mentioned above.

The Skunk is preyed upon in America by the
Eagle-owl (Bubo virginianus) and the Puma.

Thus, animals provided with natural defences
are not immune from attack.

Hence natural selection cannot have en-
couraged the survival of individuals which dis-
played a conspicuous colour, for the sake of
the " warning."

We must not forget that many creatures armed
with powerful weapons possess the unobtrusive
drab, brown, or green colouration which is
associated with concealment from foes.

There can be little doubt that, but for the fact
that the hive-bee can inflict a sting more severe
than that of the wasp, this useful insect would
have been cited as a case of a protectively
coloured creature. Notwithstanding its sober
brown colouring, the hive-bee is recognised and
avoided.

Professor Poulton records that the dull in-
conspicuous caterpillar of the moth (Mania
typica) is rejected by reptiles. It must be
admitted, however, that these cases among
insects are very rare.

The smooth newt (Molge vulgaris), a relation
of the salamander, is protected by a poisonous
skin ; nevertheless the creature has a dark brown
back and spends most of its time on land. Its

221

The Making of Species

black-spotted, yellow under-surface may have
some protective value in the water. Neither
the pike nor the common European water-tortoise
will eat this newt.

Toads are nearly all very inconspicuous ;
nevertheless they are well protected by the acrid
secretion from the skin glands ; moreover, they
are both recognised and avoided by those pre-
dacious creatures to whom they are distasteful.
Hawks, although as a rule plainly coloured, are
certainly recognised by all other birds. It would
seem, therefore, that "warning colours," like the
similar striking hues of many domestic animals,
are incidental attributes. It has been possible
for their owners to develop them, because for the
most part let alone.

Eisig, long ago, pointed out that the brightly
coloured pigment in the skin of these warningly
coloured insects is in certain cases of an excretory
nature. Therefore the inference which should be
drawn is, as Beddard points out on page 173 of
his Animal Colouration, " that the brilliant
colours (i.e. the abundant secretion of pigment}
have caused the inedibility of the species, rather
than that the inedibility has necessitated the
production of bright colours as an advertisement"
In other words, Neo- Darwinians put the cart
before the horse !

In some cases these brilliantly coloured insects
may be survivals of an age in which there were

222

By permission of Messrs. Htttchittson &• Co.

BOURU FRIAR-BIRD

Like most of the group to which it belongs, this honey-eater

(Tropidorhynchus bouruensis)\s a soberly coloured bird,'but

is noisy, active, and aggressive.

By permission of Messrs. Hutchinson &• Co.

BOURU ORIOLE

This " mimicking" oriole (Oriolus bouruensis) is of the same tone of colour
as its supposed model the Friar-bird of the same island.

Aposematic Sounds

no birds. When these came into being and
began to prey upon insects, the conspicuously
coloured species which were not inedible or
very unpalatable would soon become extinct,
while those that were inedible would survive as
warningly-coloured insects. In other cases it is
not improbable that these warningly-coloured
creatures have arisen by mutations from more
soberly - hued insects. It is conceivable that
every now and again a mutation occurs which
renders its possessor conspicuous. This will
result in the early destruction of these aberrant
individuals unless their newly-acquired gaudi-
ness is either correlated with, or the result of,
distastefulness.

In the case of warning colouration, the Neo-
Darwinians have, as usual, pursued their theory
to absurd lengths. Professor Poulton, for
example, extends it to sounds and attitudes.
"Sound," he writes, on page 324 of Essays on
Evolution, " may be employed as an Aposematic
character, as in the hiss of some snakes and some
lizards. Certain poisonous snakes when dis-
turbed produce by an entirely different method
a far-reaching sound not unlike the hiss.
Thus the rattle-snake (Crotalus) of America
rapidly vibrates the series of dry, horny, cuticular
cells, movably articulated to each other and to
the end of the tail. The stage through which
the character probably arose is witnessed in

223

The Making of Species

another genus which vibrates its tail among dry
leaves, and thus produces a warning sound.
The deadly little Indian snake (Echis carinata)
('the Kuppa') makes a penetrating swishing sound
by writhing the coils of its body one over the
other. Special rows of the lateral scales are
provided with serrated keels which cause the
sound when they are rubbed against each other.
Large birds, when attacked, often adopt a
threatening attitude, accompanied by an intimi-
dating sound which usually suggests more or less
closely the hiss of a serpent, and thus includes an
element of mimicry. . . . The cobra warns an
intruder chiefly by attitude and by the broadening
of its flattened neck, the effect being heightened
in some species by the 'spectacles.' In such
cases we often witness a combination of cryptic
and Aposematic methods, the animal being con-
cealed until disturbed, when it instantly assumes
a warning attitude.

" The benefit of such intimidating attitudes is
clear : a venomous snake gains far more advan-
tage by terrifying than by killing an animal it
cannot eat. By striking, the serpent temporarily
loses its poison, and with this a reserve of defence.
Furthermore, the poison does not cause imme-
diate death, and the enemy would have time to
injure or destroy the snake."

At first sight this reasoning may seem very
convincing. But consider for a moment the

224

Intimidating Attitudes

process by which the hiss originated and gradu-
ally increased by natural selection. We must
suppose that the rattle-snake was formerly
incapable of making any sound. One day a
variety appeared in which the skin was slightly
hardened, so that when the creature moved its
body rapidly there issued a slight sound. This
must have caused an enemy to refrain from
attack ; it thus lived to transmit this peculiarity
to its offspring, and those which made more noise
than their ancestors escaped, while those that
made less succumbed to their enemies. For our-
selves, we find it quite impossible to believe that
the rattle was thus gradually evolved by means
of natural selection. Indeed, we are inclined to
think that neither the hiss of the cobra nor its
" intimidating attitude" has any terrifying effect
on its adversary. In the case of the cobra we
are able to cite positive evidence that dogs and
cattle show no alarm at the attitude.

" Dogs," writes D. Dewar of this display,
" regard it as a huge joke. Of this I have
satisfied myself again and again, for when out
coursing at Muttra we frequently came across
cobras, which the dogs used invariably to chase,
and we sometimes had great difficulty in keeping
the dogs off, since they seemed to be unaware
that the creature was venomous."

Colonel Cunningham writes, on page 347 of
Some Indian Friends and Acquaintances : " Sport-
p 225

The Making of Species

ing dogs are very apt to come to grief where
cobras abound, as there is something very alluring
to them in the sight of a large snake when it sits
up nodding and snarling ; and it is often difficult
to come up in time to prevent the occurrence of
irreparable mischief."

Colonel Cunningham also states that many
ruminants have a great animosity to snakes, and
are prone to attack any that they may come
across.

We may therefore well be sceptical as to the
value of intimidating attitudes to those creatures
which are in the habit of striking them.

MIMICRY

In a work of this kind it is neither possible
nor necessary to consider in great detail the
mass of evidence which has been advanced in
favour of the theory of mimetic resemblance.

Chapters vii. and viii. of Professor Poulton's
Essays on Evolution contain an up-to-date state-
ment of the facts in favour of the theory. Pro-
fessor Poulton believes that in all cases mimetic
resemblance is the result of the action of natural
selection.

He admits that there is no direct evidence in
its favour, but asserts that "the facts of the
cosmos, so far as we know them, are consistent
with the theory, and none of them inconsistent
with it" (page 271).

226

Theory of Protective Mimicry

We are not at all sure that no facts are against
the theory of protective mimicry. We shall
presently set forth some which to us seem, if not
actually inconsistent with the theory, at least to
point to the conclusion that the phenomenon
may be explained otherwise than as a product of
natural selection.

Let us first briefly state the case for the theory
of protective mimicry.

1. It is asserted that the mimicking species
and that which is mimicked are often not nearly
related. For example, the unpalatable larva of
the Cinnabar Moth {Euchelia jacobaece) is said to
mimic a wasp, because it has black and yellow
rings round its body.

4 'The conclusion which emerges most clearly,"
writes Poulton (p. 232), "is the entire indepen-
dence of zoological affinity exhibited by these
resemblances." This is supposed to be proof
that Darwin was wrong when he asserted that
the original likeness was due to affinity. Says
Poulton : " The preservation of an original like-
ness due to affinity undoubtedly explains certain
cases of mimicry, but we cannot appeal to this
principle in the most remarkable instances."

2. It is asserted that species which are
mimicked are invariably either armed with a
sting, well defended, or unpalatable, so that it
is against the interest of insectivorous creatures
to attack them. It is further asserted that the

227

The Making of Species

species imitated are " even more unpalatable than
the generality of their order."

3. It is pointed out that the most distasteful
groups of butterflies — the Danaidce, the Acrceincz,
the Ithomiince, and the Heliconincz — consist of
large numbers of species which closely resemble
one another. This is said to be due to Mlillerian
mimicry. Mayer states that in South America
there are 450 species of inedible Ithomiincz which
display only 15 distinct colours, while the 200
species of Papilio, which are edible, exhibit 36
distinct colours. Nevertheless, he says, there is
no lack of individual variability among the former
hence their conservatism as regards colour cannot
be attributed to their having but little tendency
to vary.

4. It is asserted that although in many cases
the mimetic resemblances extend to the minutest
detail, nevertheless they are not accompanied by
any changes in the mimetic species except such
as assist in the production or strengthening of a
superficial likeness.

Pictures illustrating such cases of mimicry are
figured on pp. 241, 247, and 251 of Wallace's
Darwinism (1890 edition).

5. It is stated that mimetic resemblance is not
confined to colour, but extends to pattern, form,
attitude, and movement ; that deep-seated organs
are affected when the superficial resemblance is
intensified, but not otherwise. Poulton cites

228

Evidence for the Theory

Clytus arietis, the " wasp-beetle," as an example
of this.

6. It is asserted that mimetic resemblances are
produced in the most diverse ways ; that the
modes whereby the similarity in appearance is
brought about are varied, but the result is
uniform.

" A lepidopterous insect," writes Poulton
(p. 251), "requires above all to gain transparent
wings, and this, in the most striking cases that
have been studied, is produced by the loose
attachment of the scales, so that they easily and
rapidly fall off and leave the wing bare except
for a marginal line and along the veins (Hemaris,
Trockilium)."

7. It is alleged that the imitator and imitated
are always found in the same locality. If they
did not do so no advantage would be derived
from the resemblance. It is further alleged that
where the mimicking species is edible it is in-
variably less abundant where it occurs than the
species it imitates.

8. It is pointed out that it sometimes happens
that where in the mimic the sexes differ in
appearance, the male copies one species, the
female quite a different one. This is said to be
because the deception would be liable to be de-
tected if the mimicking species became common
relatively to that which is imitated. " We there-
fore find that two or more models are mimicked

229

The Making of Species

by the same species " (Essays on Evolution,

P- 372).

Occasionally the female mimics two other
species, i.e. she occurs in two forms, each like
a different species.

It sometimes happens that the female alone
mimics. This is said by Wallace to be due to
her greater need of protection. When she is
laden with eggs her flightjis slow, and therefore
she requires a special degree of protection.

9. It is said that in some species we find a
non-mimetic ancestor preserved on islands where
the struggle for existence is less severe, while
on the adjacent continent mimicry has been
developed.

10. It is alleged that in the cases where moths
resemble butterflies the former are either as
diurnal as the butterflies or are species which
" readily fly by day when disturbed."

11. It is asserted that some seasonally di-
morphic forms are examples of mimicry only in
one state, in the form that comes into being at
the time when the struggle for existence is most
severe ; that is to say, in the dry season, in
Africa, when insect life is far less abundant than
in the rainy season.

In other cases the mimicry of the dry- weather
form is said to be far more perfect.

Instances of this phenomenon are set forth in
Professor Poulton's Essays on Evolution.

230

Alternative Theories

It will be observed that we have quoted very
largely from Professor Poulton's work. Our
reason for so doing is that he appears to be the
most prominent advocate of the theory of protec-
tive mimicry, and his work, which was published
in 1908, may be taken as the latest Neo-Dar-
winian pronouncement on the subject.

Hence if we can show, as we believe we can,
that his arguments are not sound, we may take
it that we have demonstrated that the theory in
its present form is untenable.

It is worthy of notice that Professor Poulton
sets forth three other suggestions which have
been proposed as substitutes for natural selec-
tion as an explanation of the phenomena of
mimicry.

The first is the theory of External Causes,
namely, that the resemblance is due to some
external cause, such as food or climate.

The second is the theory of Internal Causes,
which states that mimetic resemblance is due to
internal developmental causes.

The third is the suggestion that sexual
selection has caused the origin of these re-
semblances.

He then proceeds to demolish these to his
own satisfaction, and adds triumphantly, " The
conclusion appears inevitable that under no
theory, except natural selection, do the various
resemblances of animals to their organic and

231

The Making of Species

inorganic environments fall together into a
natural arrangement and receive a common
explanation " (p. 228).

To reasoning of this description there is an
obvious reply. Even if it be granted that the
alternatives to the theory of natural selection
as set forth by Professor Poulton are untenable,
it does not follow that natural selection affords
an adequate explanation. If A, B, C and D are
charged with theft and the prosecutor proves
that neither A nor B nor C committed the theft,
this will not suffice to secure the conviction of
D. It is quite possible that a fifth person, E, may
be the culprit.

Much of the popularity of the theory of natural
selection is due to the fact that biologists have
not yet been able to discover a substitute for it.

It seems to us that the proper method of
making progress in science is not to bolster up
natural selection by ingenious speculations, but to
look around for other hitherto undiscovered
causes.

OBJECTIONS TO THE THEORY THAT THE SO-
CALLED CASES OF MIMICRY OWE THEIR
ORIGIN TO NATURAL SELECTION j

It is obvious that for one creature to resemble
another can be of little or no benefit to either
until the resemblance is tolerably close. It is,

232

By permission of Messrs. Hutchinson & Co.

KING-CROW OR DRONGO

This very conspicuous black bird (Dicrurus ater), ranging from Africa
to China, is a striking feature of the landscape wherever it occurs.

By permission »_/ Messrs. Hntchinson &• Co.

DRONGO-CUCKOO

The fork of the tail in this bird is unique among cuckoos, but is nevertheless

much less developed than in the supposed model, and may be an adaptation

for evolution in flight, as such tails usually appear to be.

Objections to the Theory

therefore, insufficient to prove the utility of the
perfected resemblance. We may readily grant
this and yet maintain that the origin of the
resemblance cannot be due to the action of
natural selection.

The Drongo-cuckoo (Surniculus lugubris] dis-
plays so great a likeness to the King Crow
(Dicrurus ater) that it is frequently held up by
Neo-Darwinians as an excellent example of
mimicry among birds. But D. Dewar writes,
on page 204 of Birds of the Plains : "I do not
pretend to know the colour of the last common
ancestor of all the cuckoos, but I do not believe
that the colour was black. What then caused
Surniculus lugubris to become black and assume
a king-crow-like tail?

" A black feather or two, even if coupled with
some lengthening of the tail, would in no way
assist the cuckoo in placing its egg in the
drongo's nest. Suppose an ass were to borrow
the caudal appendage of the king of the forest,
pin it on behind him, and then advance among
his fellows with loud brays, would any donkey of
average intelligence be misled by the feeble
attempt at disguise? I think not. Much less
would a king- crow be deceived by a few black
feathers in the plumage of a cuckoo. I do not
believe that natural selection has any direct con-
nection with the nigritude of the drongo-cuckoo."

Darwin was fully alive to this difficulty when
233

The Making of Species

he wrote : "As some writers have felt much
difficulty in understanding how the first step
in the process of mimicry could have been
effected through natural selection, it may be
well to remark that the process probably com-
menced long ago between forms not widely
dissimilar in colour" (Descent of Man, loth Ed.,
p. 324). Such a statement is of course quite
inconsistent with the Neo-Darwinian position.
" The conclusion which emerges most clearly,"
writes Poulton (Essays on Evolution, p. 232), "is
the entire independence of zoological affinity
exhibited by these resemblances ; and one of the
rare cases in which Darwin's insight into a bio-
logical problem did not lead him right was when
he suggested that a former closer relationship
may help us to a general understanding of the
origin of mimicry. The preservation of an
original likeness due to affinity undoubtedly
explains certain cases of mimicry, but we cannot
appeal to this principle in the most remarkable
instances."

It is unnecessary to labour this point. It is
surely evident to everyone with average intelli-
gence that, until the resemblance between two
forms has advanced a considerable way, the like-
ness cannot be of utility to either, or at any rate
of sufficient utility to give its possessor a survival
advantage in the struggle for existence. Until
it reaches this stage, natural selection cannot

234

The Brain-fever Bird

operate on it. It is therefore absurd to look upon
natural selection as the direct cause of the origin
of the likeness. When once a certain degree of
resemblance has risen, it is quite likely that in
some cases natural selection has strengthened
the likeness.

The second great objection to the Neo-
Darwinian explanation of the phenomenon
known as mimicry is that in many cases the
resemblance is unnecessarily exact. Even as
we saw how the Kallimas, or dead-leaf butter-
flies, carried their resemblance to dead leaves
to such an extent as to make it appear probable
that factors other than natural selection have had
a share in its production, so do we see in certain
cases of mimetic resemblance an unnecessarily
faithful likeness.

The common Hawk Cuckoo of India (Hiero-
coccyx varius) furnishes an example of this :
" The brain-fever bird," writes Finn, on page 58
of Ornithological and Other Oddities, " is the
most wonderful feather copy of the Indian
Sparrow-hawk or Shikra (Astur badius). All the
markings in the hawk are reproduced in the
cuckoo, which is also of about the same size, and
of similar proportions in the matter of tail and
wing ; and both hawk and cuckoo having a first
plumage quite different from the one they assume
when adult, the resemblance extends to that too.
Moreover, their flight is so much the same that

235

The Making of Species

unless one is near enough to see the beak, or can
watch the bird settle and note the difference
between the horizontal pose of the cuckoo and
the erect bearing of the hawk, it is impossible to
tell them apart on a casual view." Moreover,
the tail of the cuckoo sometimes hangs down
vertically, thus intensifying the likeness to the
hawk.

It is quite possible that the brain-fever bird
derives some benefit from the resemblance ;
indeed, it has been seen to alarm small birds,
even as the hawk-like common cuckoo frightens
its dupes, but, as D. Dewar pointed out, on page
105 of vol. 57 of the Journal of the Society of
Arts, " this is not sufficient to explain a likeness
which is so faithful as to extend to the marking
of each individual feather. When a babbler
espies a hawk-like bird, it does not wait to inspect
each feather before fleeing in terror ; hence all
that is necessary to the cuckoo is that it should
bear a general resemblance to the shikra. The
fact that the likeness extends to minute details in
feather marking, points to the fact that in each
case identical causes have operated to produce
this type of plumage." This conclusion is still
further strengthened by the fact that the likeness
extends to the immature plumage, that is to say,
exists at a time when it cannot assist the cuckoo
in its parasitical work.

Poulton meets this objection as follows :
236

Ky pet tn

LO.

SHIKRA HAWK

The upper surface of the tail, not shown in this drawing, exactly corresponds
with that of the cuckoo "mimic."

By permission of Messrs. Hittchinson &• Co.

HAWK-CUCKOO

This species (Hierococcyx varius) is commonly known in India as the
" Hrain-fever bird."

Hypertely

" All such criticism is founded on our imperfect
knowledge of the struggle for existence. The
impressions and judgments of man are immensely
influenced by the 'corroborative detail,' giving
' artistic verisimilitude to a bold and unconvincing
narrative.' Indeed, the laughter which is in-
variably raised by this passage from The Mikado
is, I have always thought, not only or chiefly
due to the humour of the application, but to the
way in which a great and familiar truth breaks
in upon the listener with all the pleasing surprise
which belongs to epigram. Birds, the chief
enemies of insects, are known to have powers
of sight far superior to those of man, and, from
our experience of them in captivity, it may be
safely asserted that their attention is attracted by
excessively minute detail. Until our knowledge
of the struggle for life is far more extensive than
at present, the argument founded on Hypertely
may be left to contend with another argument
often employed against the explanation of cryptic
and mimetic resemblance by natural selection.
Hypertely assumes that there are unnecessary
details in the resemblance, that the resemblance
is perfect beyond the requirements of the insect ;
the second argument maintains that birds are so
supremely sharp-sighted that no resemblance,
however perfect, is of any avail against them.
In the meantime the majority of naturalists will
probably reject both extremes, and believe that

237

The Making of Species

the enemies are certainly sharp-sighted and
successful in pursuit, but that perfection in detail
makes their task a harder one, and gives to the
individuals possessing it in a higher degree than
others, increased chances of escape, and of be-
coming the parents of future generations."
(Essays on Evolution, p. 302.)

This long quotation requires careful considera-
tion, since to us it appears to be typical of the
kind of reasoning resorted to by Neo- Darwinians.

Note the reference to our " imperfect know-
ledge of the struggle for existence." This is
almost invariably the last refuge of the Neo-
Darwinian when worsted in argument. We
fully admit that there is still much to be learned
of the nature of the struggle for existence, but
such a statement sounds very curious when
uttered to those who pin their faith to the theory
which sees in the principle of natural selection
an explanation of all the phenomena of the or-
ganic world. Natural selection, be it remembered,
is but a name for the struggle for existence.

" Birds," says Professor Poulton, " are the
chief enemies of insects." This may be so.
But we greatly doubt whether they are the
chief enemies of butterflies and moths, among
which the most perfect examples of mimicry are
supposed to occur.

We have watched birds closely for some years,
but believe that we could almost count on our

238

Birds capturing Butterflies

fingers the cases in which we have seen a bird
chase a butterfly.

Professor Poulton, being aware of this ob-
jection, sets forth, on pp. 283-292 of Essays on
Evolution, the evidence he has gathered in favour
of the view that birds are the chief enemies of
butterflies and other lepidoptera.

As the result of five years' observation in S.
Africa, Mr G. A. K. Marshall was able to record
some eight cases of birds capturing butterflies.
In three cases the butterfly seized was warningly
coloured, or, at any rate, conspicuous ! In two
of these eight cases the bird failed to capture
its quarry !

Says Mr Marshall, "the fact that birds refrain
from pursuing butterflies may be due rather to
the difficulty in catching them than to any wide-
spread distastefulness on the part of these

insects."

During six years' observation in India and
Ceylon, Colonel Yerbury records some half
dozen cases of birds capturing, or attempting to
capture, insects. He writes : " In my opinion
an all-sufficient reason for the rarity of the
occurrence exists in the fact that in butterflies
the edible matter is a minimum, while the inedible
wings, etc., are a maximum."

Colonel C. T. Bingham in Burma states that
between 1878 and 1891 he on two occasions
witnessed the systematic hawking of butterflies

239

The Making of Species

by birds, although he observed on other occasions
some isolated cases.

This appears to be the sum total of the
evidence adduced by Professor Poulton as
regards the capture of butterflies by birds.
This seems to us an altogether insufficient
foundation upon which to build the theory that
the cases of resemblance between unrelated
species have been effected by natural selection.

It is, however, to be noted that probably
among birds the most dangerous enemies of
butterflies are not those that habitually catch
insect prey on the wing. Such are experts in
the art of fly-catching, and would despise the
comparatively meatless butterfly. One often
comes across butterflies with an identical notch
in each wing, which leaves little room for doubt
that those particular butterflies had been snapped
at, while resting^ by a bird. Among birds the
chief enemies of butterflies and moths are pro-
bably to be found in those that hunt for their
food in bushes and trees.

Thus, what we do know of the nature of the
struggle for existence offers but poor support to
the Neo-Darwinian explanations of the cases of
so-called mimicry in nature.

Professor Poulton's idea of pitting the argu-
ment of hypertely against that of the alleged
supreme sharp-sightedness of birds is ingenious,
but is not likely to satisfy very many people save

240

Observing-powers of Birds

those content to live in a fools' paradise. If
birds are supremely sharp-sighted, and pay
attention to excessively minute detail, the diffi-
culty of accounting for the origin of protective
mimicry on the natural selection hypothesis
becomes all the greater.

The question whether or not birds are good
observers is a most interesting one. Unfor-
tunately, hitherto, but little attention has been
paid to the subject. The evidence available
seems to point to the fact that birds, like savages,
have sharp eyes only for certain objects — that is
to say, for the things they are accustomed to
look out for. All observers of nature must have
noticed how quick a butcher-bird is to catch sight
of a tiny insect upon the ground at a distance of
some yards from his perch.

On the other hand, it is said that when there
is snow upon the ground wood pigeons will
approach quite close to a man wearing white
clothes and a white hat, provided he keep
perfectly still. Finn once witnessed in Calcutta a
sparrow pick up a very young toad, obviously by
mistake, for it dropped it at once with evident
distaste. Birds of prey are supposed to have
remarkably good eyesight ; yet they can readily
be caught by a net stretched out before their
quarry. They are not trained to be on the
watch for such things as nets, and so do not
appear to notice one when erected.

Q 241

The Making of Species

It is thus our belief that the very perfection
and detail of some so-called mimetic resemblances
are a very serious objection to the theory of
protective mimicry as enunciated by Professor
Poulton and other Neo- Darwinians.

There is yet a further objection to this theory,
one which, in our opinion, is fatal to the hypo-
thesis in its generally accepted form.

A number of cases occur where two species, in
no way related, show close resemblance to one
another under such circumstances that neither
can possibly derive any benefit from the likeness.
The theory of protective mimicry is quite unable
to explain these cases. This fact leads to a
suspicion that, in the instances where the theory
does at first sight appear to offer an explanation,
the resemblance may also be due to mere
coincidence.

We may perhaps call the cases which the
theory of mimicry is unable to account for " false
mimicry," but in so doing we must bear in mind
the possibility that some, at any rate, of the
examples of so-called mimicry may, on further
investigation, prove to be nothing of the kind.

"FALSE" MIMICRY AMONG MAMMALS

The Cacomistle of Mexico (Bassaris astuta),

one of the raccoon family, has a grey body and

long black-and-white ringed tail, just like the

ring-tailed Lemur of Madagascar (Lemur catta) ;

242

False Batesian Mimicry

both are arboreal and about the same size, and
this lemur's colouration is exceptional in its
family.

The banded Duiker-buck of West Africa
(Cephalophus doriae\ has the same very unusual
colouration as the thylacine or marsupial wolf of
Tasmania, light brown, with bold black bands
across the hinder part of the back, and the
animals are about the same size.

The dormouse of Europe closely resembles a
small American Opossum (Didelphys murina),
and a larger opossum (D. crassicaudata) is very
like the Siberian Mink (Mustela sibirica).

The Flying Squirrel of North America (S«#r0/-
terus volucella) is closely copied by the Flying
Phalanger (Petaurus breviceps) of Australia.

It will be readily seen that in no one of these
cases can the likeness be of utility to either the
" model " or the " copy."

FALSE BATESIAN MIMICRY AMONG BIRDS
There are many instances of this phenomenon
among birds. The New Zealand Cuckoo (Uro-
dynamis tritensis) shows a far closer resemblance
to the American Sparrow-hawk (Accipiter cooperi)
than to any New Zealand hawk, and in fact
closely mimics this quite alien bird.

The stormy petrel, a purely oceanic bird,
closely resembles in size, colour, and style of
flight the Indian Swift (Cypselus affinis), a purely

243

The Making of Species

inland creature ; both are sooty black, with a
conspicuous white patch on the lower back.

The Pied Babbling Thrush (Crateropus bicolor)
of Africa is singularly like the Pied Myns.(Gr<zu-
lipica melanoptera) of Java, both being of about
the same size, with white body and black wings
and tail quills. This, we may add, is a very
unusual colouration among small birds.

The black - headed Oriole (Oriolus melano-
cephalns) of India is very similar in appearance
to the common Troupial (Icterus vulgaris) of
Brazil ; indeed, the troupials, a purely American
group, are so like the old world orioles in colour
that they usurp their name in America.

The little insectivorous lora (&githina tiphia]
of India strongly resembles in size and colour
a Siskin (Chrysomitris colambiana) from South
America, the males in both being black above
and yellow below, while in the females the black
is replaced by olive-green.

Another Indian babbler (Cephalopyrus flam-
miceps), yellowish-green, with orange forehead, is
closely copied by, or copies, the well - known
Brazilian Saffron -finch (Sycalis flaveola).

In Fergusson Island, near New Guinea, there
is a ground pigeon (Otidiphaps insularis) which
is black with chestnut wings, like several of the
powerful ground cuckoos of the genus Centropus,
but no species of these cuckoos so coloured
appears to inhabit the island.

244

False Batesian Mimicry

In Africa there is a tit (Parus leucopterus)
which has the same very unusual colouration as
an East- Indian bulbul (Micropus melanoleucus),
both being black with a white patch on the wing-
coverts. These two birds are about the same
size. As showing the purely coincidental char-
acter of such resemblances, we may mention that
this same rare pattern occurs again in our Black
Guillemot (Uriagrylle) and in the Muscovy Duck
(Cairina moschata).

We have already quoted Gadow (p. 198) on
" false mimicry " among snakes. He also gives,
on p. 1 10 of Through Southern Mexico, an example
of this phenomenon among amphibia. It is, he
writes, " impossible to distinguish certain green
tree-frogs of the African genus Rappia from a
Hyla, unless we cut them open. If they lived
side by side, which they do not, this close resem-
blance would be extolled as an example of
mimicry."

We should be very greatly surprised if abun-
dant examples of "false mimicry" are not found
among insects. We trust that this remark will
stimulate some entomologist to pay attention to
the subject.

It is the essence of Mullerian mimicry that
both model and copy are immune from attack
from enemies. Unfortunately for the theory,
similar resemblances occur among birds of prey,

245

The Making of Species

where neither party can benefit from the associa-
tion. This gives rise to what we may perhaps
call false Mtillerian mimicry. Thus the goshawk
and peregrine falcon resemble each other in
being brown above and streaked below in im-
mature plumage, and having barred underparts
and a grey upper plumage when adult.

Having stated the more important objections
to the theory of protective mimicry, it now
remains for us to deal specifically with each head
of evidence offered in its favour.

1. With regard to the assertion that the model
and its copy are often not nearly related, we have
shown that among mammals and birds instances
of resemblance between widely-separated groups
occur under such circumstances that neither party
can derive any benefit therefrom.

2. As regards the assertion that species which
are mimicked are either well-defended or un-
palatable, this certainly does not hold good with
regard to some at any rate of the coincidental
resemblances among birds which we have
pointed out ; even if these pairs of similar
species lived in the same country it would re-
quire considerable ingenuity to say why one
should mimic the other.

3. As regards the argument that the inedible
species of Ithomiince, etc., display only fifteen
colours, while the less numerous edible Papilios

246

Theory of Mimicry Criticised

display more than double this number of colours,
we may draw attention to the fact that those
birds which are most immune from attack are
precisely those which display the smallest range
as regards colour, eg., hawks, owls, crows, gulls,
storks, and cranes. As we have already sub-
mitted, no question of Miillerian association
comes in here.

On the other hand, the eminently edible
families of game-birds and ducks display great
variety of colour, in the males at all events.

4. As regards the statement that although
in many cases the mimetic resemblances extend
to the minutest detail, they are not accompanied
by any structural changes except such as assist
in the production of a superficial likeness, we may
refer to the case we have already cited of the
New Zealand cuckoo, which, though it so closely
copies an American hawk, is typically cuculine in
structure. Here, of course, there can be no
question of advantage to the " mimicking "
cuckoo in the resemblances.

5. In answer to the argument that mimetic
resemblance extends to form, attitude, and move-
ment, as well as colour, and that deep-seated
organs are affected only when the superficial
resemblance is thereby intensified, we may draw
attention to such cases as the following : —

(a) The harmless Indian Snake (Lycodon aulicus)
is closely similar to the well-known Krait (Bun-

247

The Making of Species

garus cceruleus), also Indian ; but the resemblance
extends to a structural detail which can hardly
have mimetic value — namely, the harmless snake
has long, fang-like front teeth, though these are
unconnected with poison-glands. Animals which
come into contact with the krait and its mimic
are hardly likely to inspect their teeth.

(6) A considerable number of birds of the
shrike group — known as Cuckoo-Shrikes (Cam-
pophaga] — closely resemble cuckoos in plum-
age ; but even if they derive any benefit from
mimicking birds which are credited with being
mimics already, they cannot profit by the fact
that the shafts of the rump-feathers in both groups
are stiffened ; this being a peculiarity which would
not be perceptible until the bird was in the grasp
of an aggressor.

(c] As a third case of coincidence we may
refer to the tubercle in the nostril of the Brain-
fever-bird {Hierococcyx varius\ as a minute detail
of hawk-like appearance, though not present in
the particular species imitated.

6. The argument that mimetic resemblances
are producd in the most diverse ways, but the
result is uniform, loses much of its force when
we consider the various methods by which
short-tailed birds appear to have long caudal
appendages.

In the peacock it is the upper tail coverts
which are elongated ; in the Stanley Crane

248

Theory of Mimicry Criticised

(Tetrapteryx paradisea) it is the innermost or
tertiary quills of wing ; in one of the egrets
some of the feathers of the upper back grow
to a great length and form a train ; in the Bird
of Paradise (JParadisea apoda) the long flank
plumes are commonly mistaken for the tail.

In these cases there can be no question of
mimicry.

7. We have shown that the idea that imitator
and imitated are always found in the same area
is absolutely fallacious. In birds, for example,
the most striking resemblances appear to occur
between species that dwell far apart.

8. We can cite, as parallel to the case of a
mimicking species of which the male copies one
model and the female another, the strange
similarity between the barred brown plumage
of the female blackcock and that of the female
eider-duck. The males of these species, although
both black and white, differ greatly in appear-
ance ; but the male blackcock is admittedly very
like the male of another species of sea-duck — the
scoter.

9. Against the supposed ancestral non-
mimetic forms existing on islands we can pit
the " mimetic" orioles in small islands and their
non-mimetic cousins on the mainland. In
Australia an oriole of what appears to be an
ancestral style lives beside, but declines to
mimic, a friar bird of a very pronounced type.

249

The Making of Species

10. The case of certain diurnal moths mimick-
ing butterflies appears to be explicable without
the aid of the theory of protective mimicry.
When two species adopt the same method of
obtaining food, it not infrequently happens that
a professional likeness springs up between them.
Of this the swifts and swallows afford a striking
illustration.

11. As a set-off to the cases where the alleged
mimicry is confined to certain seasons of the year,
we may cite the case of the pheasant-tailed
Jagana (Hydropkasianus chirurgus), which in its
winter plumage might easily be mistaken, when
on the wing, for the paddy bird or Pond Heron
(Ardeola grayii\ both being of like size and
having a brown back, long green legs, and white
wings. Moreover, they are to be found in
the same localities in India. At the breeding
season, however, they are absolutely different
in plumage.

Yet another argument commonly adduced in
favour of the theory of protective mimicry is that
local variations of the imitated species are some-
times followed by the imitator ; thus the butterfly
Danais chrysippus shows a white patch on the
hind wings in Africa, and this is followed by
its mimic.

But the same thing occurs, quite irrationally,
so to speak, among birds. The peregrine falcon
and hobby of Europe are only winter migrants

250

Recognition Colours

to India, where they are replaced as residents by
the Shaheen (Falco peregrinator) and Indian
Hobby (F. severus). Both these differ from the
migratory forms by being blacker above and
chestnut below, instead of cream colour. Thus
the resemblance occurs in each race. A similar
distinction, as noted by Blyth, exists between
the Common Swallow (Hzrundo rustica) and the
Swallow (H. tytleri) of Eastern Asia, the latter
having the whole ventral surface rufous instead
of only the throat. Yet no one will suggest that
swallows mimic falcons, or that there is mimicry
between the peregrine and hobby. It is obvious
that such parallel changes occur independently
of mimicry.

The Water-rail (Rallus aquaticus) and Baillon's
Crake (Porzana bailloni) of Europe are distin-
guished from their allies of Eastern Asia by
having the sides of the head plain grey, whereas
the Eastern Asiatic forms (R. indicus and P.
pusilla) have a brown streak along each side of
the face. Here, again, we have an instance of
birds of the same family varying together with
geographical distribution.

" RECOGNITION " COLOURS

One of the prettiest conceits of the Wallaceian
school of zoologists is the theory of recognition
markings.

" If," writes Wallace, on page 2 1 7 of Darwinism,
251

The Making of Species

" we consider the habits and life-histories of those
animals which are more or less gregarious, com-
prising a large proportion of the herbivora, some
carnivora, and a considerable number of all orders
of birds, we shall see that a means of ready
recognition of its own kind, at a distance or
during rapid motion, in the dusk of twilight
or in partial cover, must be of the greatest
advantage and often lead to the preservation of
life. Animals of this kind will not usually
receive a stranger in their midst. While they
keep together they are generally safe from
attack, but a solitary straggler becomes an easy
prey to the enemy ; it is therefore of the highest
importance that, in such a case, the wanderer
should have every facility for discovering its
companions with certainty at any distance within
the range of vision.

" Some means of easy recognition must be of
vital importance to the young and inexperienced
of each flock, and it also enables the sexes to
recognise their kind and thus avoid the evils
of infertile crosses ; and I am inclined to believe
that its necessity has had a more widespread
influence in determining the diversities of animal
colouration than any other cause whatever. To
it may probably be imputed the singular fact that
whereas bilateral symmetry of colouration is very
frequently lost among domesticated animals, it
almost universally prevails in a state of nature ;

252

Recognition Colours

for if the two sides of an animal were unlike,
and the diversity of colouration among domestic
animals occurred in a wild state, easy recognition
would be impossible among numerous closely
allied forms."

As examples of recognition colouration, Wallace
cites, among others, the white upturned tail of the
rabbit — a " signal flag of danger," the conspicuous
white patch displayed by many antelopes, the
white marks on the wing- and tail-feathers of the
British species of butcher-birds, the stone-chat,
the whin-chat, and the wheat-ear.

Wallace therefore asserts, firstly, that recog-
nition marks not only help herbivorous animals
to keep together, but act as a danger signal ; the
member of a flock which first catches sight of the
enemy takes to its heels, displaying its white
flag, which is the signal of danger to the other
members of the flock. Secondly, that recog-
nition marks prevent the evils of infertile crosses.
Thirdly, that the necessity of being able to recog-
nise one another has rigidly preserved bilateral
symmetry among animals in a state of nature.

As regards assertion number one, we would
point out that where a flock of herbivora is being
stalked by a beast of prey, the member of the
flock nearest to the enemy — that is to say, the
hindmost member — will probably be the first to
observe him. As that creature will be more
unfavourably situated for escape than the rest of

253

The Making of Species

the herd, it will not be to their advantage to
follow the line it has taken. Moreover, being at
the rear of the flock, it is not in a good position
to take the lead, and its pursuer is likely to see
the danger signal before its friends do. It would
thus seem that " danger signals," while possibly
sometimes of service to their possessors, are on
the whole ornaments which might profitably be
dispensed with. Natural selection can scarcely
be charged with the production of a character of
such doubtful utility to the organism.

Moreover, flourishing species of many
gregarious animals do not possess any " signal
flag of danger," while, on the other hand, a great
many solitary species display markings that
render them very conspicuous when in motion.
Take the case of the famous Indian Paddy Bird
(Ardeola grayii). This, when at rest, is coloured
so as to be very difficult to distinguish from its
surroundings, but flight transforms it, for it then
displays its milk-white pinions, which would
make a perfect danger signal, if only it were not
peculiarly solitary in its habits. Its gregarious
brethren, the Cattle Egrets (Bubulcus coromandus),
on the other hand, display no danger signal.

That these recognition marks prevent the
intercrossing of allied species and the production
of infertile hybrids appears to be pure fiction.
As we have already shown, hybrids between
allied species are by no means always infertile.

254

Interbreeding of Allied Species

Moreover, species which differ only in colour
seem usually to interbreed in those parts where
they meet.

"This interbreeding," writes Finn, on page 14 of
Ornithological and Other Oddities, " occurs where
the carrion crow (Corvus cor one) meets the hooded
crow (Corvus cornix), where the European and
Himalayan goldfinches (Carduelis carduelis and
C. caniceps) encounter each other, and where the
blue rollers of India and Burma (Coracias indicus
and C. affinis) come into contact, to say nothing
of other cases."

Of these other cases, the Indian bulbuls of the
genus Molpastes form a very remarkable one.
In all places where two of the so-called species
meet they appear to interbreed, and so freely do
they interbreed that at the points where the allied
species run into one another it is not possible to
refer the bulbuls to either species. Thus William
Jesse writes of the Madras Red- vented Bulbul
(Molpastes hcemorrhous) (page 487 of The Ibis
for July 1902): "This bird, although I have
given it the above designation, is not the true
M. hcemorrhous. I have examined numbers of
skins and taken nests and eggs time after time,
and have come to the conclusion that our type is
very constant, and at the same time differs from
all the red-vented bulbuls hitherto described.
The dimensions tally with those given by Gates
for M. hczmorrhous, while the black of the crown

255

The Making of Species

terminates rather abruptly on the hind neck, and
is not extended along the back, as is the case
with M. intermedius and M. bengalensis. On the
other hand, as in the two last species, the ear
coverts are chocolate. Furthermore, I may add
— although I attach little importance to this—
that the eggs of the Lucknow bird which I have
seen are, without exception, far smaller than my
eggs of genuine M. intermedius from the Punjab.
My own opinion is that the Lucknow race is the
result of a hybridisation between the other three
species."

Further, in Bannu, Mr D. Donald saw M.
intermedius and M. leucogenys paired at the same
nest. That gentleman could not possibly be
mistaken on the point, as the latter species has
white cheeks and yellow under tail-coverts, while
the cheeks of the former species are dark-coloured
and the patch of feathers under the tail is red.
Similarly, Whitehead and Magrath, writing of
the birds of the Kurram Valley (Ibis, January
1909), record that the former shot no fewer than
twelve bulbuls, which undoubtedly appear to be
hybrids between these two species. As these
hybrids differ considerably inter se, there seems
no room for doubt that they breed with one
another and with the parent species.

Wallace's third statement, that if the two sides
of animals in a state of nature were alike, easy
recognition would be impossible among numerous

256

Symmetry in Nature

closely allied forms, reminds us forcibly of the
sad case of the boy whose tailor was his mother.
Humanum est errare : she made her son one
pair of trousers that fastened up behind, so that
the poor boy when wearing them never knew
whether he was going to or coming home from
school ! If animals are able to recognise their
mates, their bilateral symmetry does not seem
necessary to enable them to distinguish their
fellows from allied species.

It is, indeed, true that asymmetrically marked
animals are very rarely seen in the wild state,
while they are the rule rather than the exception
among domesticated species. But this appears
to be due, not to the necessity of recognition
markings in nature, but to the fact that those
animals that display a tendency to massed pig-
ment perish in the struggle for existence, since
this massing of pigment appears to be correlated
with weakness of constitution. In other words,
this massing of pigment is an unfavourable varia-
tion, which under natural conditions dooms its
possessor. In the easier circumstances of domes-
tication, animals which are irregularly pigmented
are able to survive, so that, among them, the
almost universal tendency to the massing of pig-
ment can be followed without let or hindrance.

It is unnecessary to say more upon this subject.
The few facts we have set forth suffice to destroy
this particular excrescence on the Darwinian theory.
R 257

The Making of Species

THE COLOURING OF FLOWERS AND FRUITS

Extremely interesting though the subject be,
we are unable to consider at length the generally
accepted theory that the colour markings and
perfumes of wild flowers are the result of the
unconscious selection exercised by insects.

While not denying that many flowers profit by
their colouring, that these colours may sometimes
serve to attract the insects, by means of which
cross-fertilisation is effected, we are not prepared
to go to the length of admitting that all the
colours, etc., displayed by flowers and floral
structures are due to the unconscious selection
exercised by insects. It is one thing to admit
that the colour of its flowers is of direct utility to
a plant ; it is quite another to assert that the
colour in question owes its origin and develop-
ment to natural selection. Our attitude towards
the generally accepted explanation of the colours
of flowers is similar to that which we adopt
towards the theory of protective mimicry among
animals. In certain cases we are prepared to
admit that the mimicking organism derives benefit
from the likeness ; but this, we assert, is no proof
that natural selection has originated the likeness.

The theory that flowers have developed their
colours in order to attract insects to them, and
thus secure cross-fertilisation, is based on the

258

Cross- versus Self-fertilisation

assumption that cross - fertilisation is advan-
tageous to plants. It is questionable whether
this assumption is justified. True it is that
numbers of experiments have been performed,
which show that, in many cases, flowers which are
artificially self-fertilised yield comparatively few
seeds. But experiments of this kind do not
prove very much.

To place on the stigma pollen from the anthers
of the same flower, in case of a plant which for
many generations has been cross-fertilised, is to
subject the plant in question to a novel experi-
ence— an experience which may be compared to
transplanting it to another soil. The immediate
effect may appear to be unfavourable, although,
if the experiment be persisted in, the ultimate
results may prove beneficial to the plant.

That this is the case with some flowers that
are artificially fertilised is asserted by the Rev.
G. Henslow. This observer states, that had
Darwin pursued his investigations further, he
would probably have modified his views regard-
ing the benefits of self-fertilisation. Darwin's
statement that " Nature abhors perpetual self-
fertilisation " seems to be as far from the
truth as that which declares " Nature abhors a

vacuum."

From the mere fact that cross-fertilised flowers
yield a greater quantity of seed than they do
when self- fertilised, it does not necessarily follow

259

The Making of Species

that cross - fertilisation is advantageous. The
amount of seed produced is probably not always
a criterion as to the advantages of the crossing
to the plant. Some flowers yield most seed
when fertilised by the pollen from flowers
belonging to a different species !

It is significant that some plants produce
cleistogamous flowers, that is to say, flowers
which invariably fertilise themselves. Such
flowers never open ; so that the visits of insects
are precluded.

According to Bentham, the Pansy ( Viola tri-
color) is the only British species of Viola in
which the showy flowers produce seeds. The
other species are all propagated by their cleisto-
gamous flowers. The genus Viola is an ad-
vanced species : it would therefore seem that
the production of cleistogamous flowers is an
advance on the production of entomophilous
flowers. Cleistogamous blossoms are obviously
more economical.

In the case of the malvas, epilobias and
geraniums, where we see, side by side, races
of which the individuals produce insect-fertilised
flowers and those that are characterised by self-
fertilised flowers, the latter are quite as thriving
as the former.

The common groundsel, which, according to
Lord Avebury, is "rarely visited by insects,"
flourishes like the green bay tree, as many

260

Insects and Flowers

gardeners know to their cost. The same may
said of the pimpernels. In this connection it
is important to bear in mind that the anemo-
philous, or wind-fertilised, angiosperms, as, for
example, the grasses, are believed to be de-
scendants of insect-fertilised or entomophilous
forms.

A weighty objection to the theory that the
colours of flowers have been developed because
they attract insects has been urged by Mr E.
Kay Robinson, namely, that among wild flowers
the most highly coloured ones are the least
attractive to insects.

"Show me," writes he, on page 222 of The
Country-Side for March 20, 1909, "the insect-
collector who will seek for specimens among the
brilliant scarlet poppies. Of what use is the
dog rose, with its large discs of pinky-white,
to him ? On the other hand, does he not find
that by far the most attractive flowers are the
almost invisible spurge laurel blossoms in
February and March, the fuzzy sallow catkins
in March and April, the bramble blossom in
midsummer, and the ivy's small green flowers
in autumn ? Of these only the bramble has any
pretensions to colour, and if you try, as I have
tried, the experiment of picking off every petal
from sprays of bramble blossoms you will find
that its attraction to moths does not appear
diminished.

261

The Making of Species

The fact that insects do visit many con-
spicuously coloured flowers does not show that
the colour attracts them, when the fact is borne
in mind that they neglect others which are
equally coloured, while the flowers which they
particularly haunt are inconspicuous. Con-
spicuous flowers which have abundance of
nectar attract insects, of course, but so do
inconspicuous flowers which have nectar. If
they have no nectar, neither the conspicuous
nor the inconspicuous flowers attract insects
other than pollen or petal eaters, whose visits
are not good for the plant. This shows that
the nectar attracts the insects and that the
colour of the flowers makes no difference."

In autumn many leaves assume bright and
beautiful tints. These are not believed to be
in any way useful to the plant. The autumnal
hues and shades are regarded, and rightly re-
garded, as the garb of death and decay. Such
colours are the result of the oxidation of the
chlorophyll or green colouring matter of the
leaves. Why should not the colours of the
petals of the flowers, which wither and fade
long before the green leaves do, be due to a
similar cause? The bright colours of fruits
are supposed to have been effected by natural
selection in order to attract fruit-eating animals.
Surely a hungry animal does not require that its
food be brightly coloured in order to find it ! We

262

Honey

must remember that during the greater part of the
year most animals have no occupation save that
of finding their food. Inconspicuously coloured
fruits, like those of the ivy, are frequently eaten
by birds. The bright colours of some ripening
fruits are undoubtedly the colours of decay.
Many fungi and seaweeds have bright colours.
It is never hinted that these are of any direct
utility to their possessor.

Every flower, every plant, every organism
must be of some colour.

Many flowering plants produce honey. This
is said by some botanists to have been directly
caused by natural selection, because the honey
attracts insects. Possibly those who take up
this attitude are putting the cart before the horse.
It is probable that honey, like oxygen, is an
ordinary product of the metabolism of the plant,
and that the visits of bees and other insects to
such plants are the result rather than the cause
of the honey being there. Boisier found that
some plants, for example, Potentilla tormentilla
and Geum urbanum, gave honey in Norway, but
very little near Paris.

He further discovered that by supplying certain
plants copiously with water he could induce them
to produce more than their normal output of
honey.

As is their habit, Neo- Darwinians have
pushed their pet theory to absurd lengths in its

263

The Making of Species

application to flowers. They assert that the
visits of insects are responsible for not merely
the general colour of every flower, but also the
various lines, spots, and other markings of
flowers. The lines that frequently occur on the
petals are supposed to guide the insects to the
honey! This particular refinement of Neo-
Darwinism, to quote Kay Robinson, " needs
little discussion. Insects have very poor sight.
You can see this when a bee or a butterfly flies
bang against a whitewashed wall ; when a wasp
pounces upon a black spot on a sunlit floor, mis-
taking it for a fly ; or when a settled dragon-fly
will allow you to poke it in the face with the end
of a walking-stick, although it will be off like a
flash if you raise your arm. There is, therefore,
large reason to doubt whether insects can even
see the fine lines in the throats of flowers which
are supposed to guide them to the nectar. It is
rather absurd, too, to suppose that such lines can
be needed, since insects come in swarms to in-
conspicuous and apparently scentless flowers or
to * sugared' tree-trunks in the dark. Where
there is nectar, insects which have come to the
feast from a distance need no pencilled lines to
guide them over the last quarter of an inch of
their journey."

Neo- Darwinians further assert that the scents
of flowers have been developed by natural selec-
tion because they serve to attract insect visitors

264

Scents of Flowers

to the flowers. In support of this contention
it is urged that the most highly scented flowers
are not usually the most conspicuous ones, since
it is not necessary for a flower to be both highly
coloured and strongly scented. Again, those
flowers which open at night are usually very
highly scented.

Plausible though this view seems, there are
weighty objections to it. These are so admirably
summarised by Kay Robinson in the issue of
The Country-Side for March 27, 1909, that we
feel we cannot do better than reproduce his
words : —

"It is true that many flowers which are
strongly scented are visited by insects, but these
flowers have abundance of nectar, and the insects
come in spite of the scent, and not on account of
it. They visit unscented flowers, provided that
they have nectar, equally freely ; and they do
not visit flowers which have scent without nectar.

" Moreover, fruits are more generally scented
even than flowers; but what explanation have
those, who attribute the scents of flowers to the
tastes of insects, for the scents of fruits ? Insects
which visit fruits are only robbers. Therefore,
if we say that plants have scents for the purpose
of attracting insects, we accuse all plants which
have scented fruits of attempted suicide.

" There are hosts of plants, again, with scented
leaves. Here also the insects are only robbers,

265

The Making of Species

and it is quite clear that the scent is not useful
in attracting insects. If, therefore, you adopt the
insect theory to explain the scents of flowers, you
must invent entirely new theories to explain the
scents of fruits and leaves."

It is thus evident that the ordinarily accepted
explanation of the colours, scents, and markings
of flowers is far from satisfactory.

Mr E. Kay Robinson has put forth in recent
issues of The Country-Side (March 20, 27, and
April 3, 1909) quite a new explanation of the
phenomena, and one which deserves careful con-
sideration. He maintains that " the real, primary,
and original meaning of the colours, markings,
nectar and scents of flowers is not to attract
insects, but to deter grazing and browsing
animals."

" I say," he writes, " that grazing and browsing
animals avoid eating conspicuous flowers. I have
watched a flock of five hundred sheep pass across
a yard-wide strip of close-nibbled turf on the
Norfolk coast, grazing as they passed, and the
number of open daisy blossoms after they had
passed seemed the same as before they came.
Every one of five hundred sheep had eaten some-
thing from that yard of grass, and not one had
eaten any of the hundred and thirty odd daisies.

" Every summer the farm horses are turned
into the same old pasture, and as the summer
wanes the field always presents the same appear-

266

Kay Robinson's Theory

ance — the green grass close-grazed, the tall butter-
cups left standing high.

"Once, leaning over a gate with friends, I
pointed out that a flock of sheep grazing in a
sainfoin field were nibbling the greenstuff close,
but were not eating the flowery stalks, when one
sheep near us accidentally pulled up a whole
sainfoin plant by the roots and proceeded to
munch it upwards. Inch by inch the stem passed
into its jaws, and I began to be afraid that it was
going to establish an ' exception ' to my rule.
But, just when the bright cluster of pink sainfoin
blossom was within two inches of its teeth, it
gave an extra nip, and the flower head fell to the
ground, and the sheep resumed its search for
greenstuff.

" I do not say that this would always happen
— I should be sorry for any theory which depended
upon the intelligence of a sheep — but it was a
very striking object-lesson to my two companions;
and any one who looks around during this summer
with an inquiring mind will find plenty of evidence
that grazing, browsing, and nibbling animals avoid
flowers, and stick to greenstuff when they can
get it.

" I do not say that all animals avoid the same
flowers. Horses, for instance, may dislike large
flowers like roses and conspicuous yellow flowers
like buttercups, but they will bite off flat clusters
of minute white or pale yellow flowers, such as

267

The Making of Species

yarrow or wild parsnip. These distinctions made
by certain kinds of beasts will probably in the
future be found to afford valuable evidence as to
the regions of origin of our flowers and animals.
Such plants as the yarrow and the wild parsnip,
for instance, probably did not originate in the
home of the wild horse, because they are not
protected against it.

" As a general rule, however, there is abun-
dance of evidence that plants with conspicuous
flowers gain a large advantage in the struggle for
existence, because grazing and browsing animals
avoid them ; while there is no real evidence at
all that conspicuous flowers attract insects."

Kay Robinson extends this explanation to the
shape, the scent, and the nectar of flowers. He
admits that many flowers are adapted to the visits
of insects, but this is, he asserts, but a secondary
result. The " real, primary meaning " of the
shapes of flowers of curious configuration is, he
insists, " a deterrent to grazing or browsing
animals."

According to him plants, like the snap-dragon,
which have " blossoms in the semblance of a
mouth," are avoided by grazing animals, because
they mistake such flowers for mouths, and have
no wish to be bitten! Orchids, he asserts, "are
strongly deterrent to grazing and browsing
animals, which are looking for greenstuff, and
regard these gaudy, spidery, winged blossoms as

268

Kay Robinson's Theory

live creatures." " If this is not the truth," he
asks, " will any adherent of the theory that we
owe the shapes of flowers to insects explain why
some of our common British orchids are so like
bees, spiders, etc. ? Some which have no parti-
cular resemblance to any insect still exhibit weird
shapes, suggestive to the human mind of living
things, such as lizards, etc. The reason why they
look like bees, spiders, lizards, and various un-
classed creatures is quite simple. Grazing
animals are looking for greenstuff, and do not
wish to eat living creatures which may bite or
sting or taste nasty. Thus the orchids have
acquired the power of looking like creatures.

" Every one," he continues, " who is familiar
with the blossom of the wild carrot — a flat head
of minute, dull-white blossoms — must have
noticed how very often the centre blossom in
each head is purplish or reddish-black. This
makes it very conspicuous in the middle of the
flat white flower head. Now what conceivable
use can this barren little blackish blossom —
scarcely bigger than a pin's head — be to the
wild carrot plant if we regard the flat head of
white flowers as an attraction to the sight of
insects ? If, on the other hand, we rightly regard
the flat head of white blossoms as an advertise-
ment to grazing animals that it is not wholesome
greenstuff, but innutritious blossoms liable to be
infested with ants and other stinging insects, we

269

The Making of Species

see at once the great use of this small blackish
flower in the middle. It looks like an insect, and
possibly in the home of the wild carrot there is
some minute blackish insect with a peculiarly
villainous smell or taste — or perhaps a potent
sting — which grazing animals carefully avoid
whenever they can see it. Thus the wild carrot
flourishes ; though here in Britain — where the wild
carrot has established itself now — we may fail at
first to see the exact meaning of the trick. I
think, however, that, when we understand it, it
fits admirably into the theory that the shapes
and colours of flowers are primarily useful as
deterrents to grazing and browsing animals and
not as attractions to insects.

" Thus we see," he concludes, "that the queer
shapes of these orchids, which are a great stum-
bling-block in the way of those who preach that
we owe the shapes of flowers to the tastes of
insects, become a strong confirmation of my
theory that we owe the shapes of flowers to graz-
ing and browsing animals."

Of the nectar of flowers, Kay Robinson
writes : " Since this is eagerly sought for by
hosts of insects, whose visits are in most cases
useful to the flowers, it seems only natural to
suppose that we see cause and effect in this
connection.

" Here, however, I will outline my theory of
the origin of nectar and of flowers in general.

270

Kay Robinson's Theory

" I think there is no doubt whatever that all
the parts of a flower are modified leaves. The
original type of flowering plant — I think we may
safely assume — had a single stem and produced
its seed at the summit, as the crown of its year's
endeavour. The flower, before it became what
we would recognise as a flower, was a cluster of
protecting leaves round the seed-making parts of
the plant. To the production of the seed the
whole energies of the plant were devoted, and
into the cluster of leaves at the top of the stem
all the essences of the plant were concentrated.
If during the coming spring you handle and
examine the leaves at the end of the strong
shoots of thorns or fruit bushes, you will find that
the surface of the young leaves is quite sticky If
you observe browsing animals also, you will dis-
cover that — contrary to expectation — they do not
like strong-growing, juicy shoots, evidently pre-
ferring mature leaves lower down the branch.
This shows, I think, that plants have the power
of protecting their new shoots by crowding into
them the volatile oils and essences which they
produce as a protection against animals. Now
nectar appears always to be distasteful to grazing
and browsing animals ; and they also dislike
scented flowers. I think, therefore, that it is
reasonable to suppose that the nectar and scents
which now distinguish so many flowers were first
produced as an exudation of concentrated sap

271

The Making of Species

upon the surfaces of the protecting leaves round
the seed-making parts of the original flowers.
As these leaves became more efficiently protective
by assuming colours, shapes, and markings which
warned animals of their character, so their
apparatus for producing scent and honey became
specialised ; and at this point the insect appeared
upon the scene as a factor in the life's success of
the plant."

Such, then, is Kay Robinson's bold and original
theory. In some respects it seems far-fetched.
The natural inclination is to ask, " Is it possible
that cattle can be so stupid, so blind, as to really
believe that a snap-dragon is the mouth of an
animal, or that an orchid is a spider ? "

At present we know so little of animal psy-
chology that we are not yet in a position to give
an answer to this question. Horses, we know,
are apt to be frightened by the most harmless
things, such as a piece of brown paper lying on
the road. Mr Robinson's theory should give a
stimulus to the study of the mind of animals—
a study which, if properly undertaken, will
probably throw a flood of light upon some of
the problems of evolution. Mr Robinson's theory
equally with the ordinarily-accepted hypothesis,
utterly fails to explain the first origins of colours,
scents, etc. When once a flower has acquired a
certain amount of colour, it is easy to understand
how that flower may attract insects or repel

272

Kay Robinsons Theory

grazing animals. But how can the origin of the
colour or other characteristic be explained ?

We asked Mr Kay Robinson how he would
account for the great success in the struggle for
existence of some species of grasses on which
herbivorous animals feed so largely. He replied,
in the issue of The Country -Side, dated April 3,
1909:—

" The grass has a manner of growth which
defies the grazing animal. Its long, thin leaves
are constantly pushing upwards from the ground,
and, if they are grazed down one day, they will
have pushed up again the next. Moreover, when
the outside blade of grass has exhausted its power
of growing, there is another blade inside it with
many inches still to grow, and another inside that
which has scarcely begun to grow, and yet another
further in which has not yet seen daylight ; and
so on. In a state of nature grazing animals are
nowhere so numerous on any given patch of
ground from day to day as to keep down the
grass. If they were, carnivorous animals would
stay there to eat the grazing animals, and grow
fat and multiply. Thus the grazing herds are
scattered and wandering, followed wherever they
go by the beasts of prey; and in their absence
the grass pushes ahead, so that when the grazing
animals return its clump is larger and its roots
are stronger, and it is better able to survive
attack than before.

s 273

The Making of Species

" The method of the clovers and trefoils is quite
different. When circumstances are favourable
and enemies few, they will form large-leaved
luxuriant clumps, with fine heads of blossom ;
but where grazing animals abound they have
the power of adapting themselves to altered
circumstances. They creep so closely along the
ground that the teeth of the grazing animal can-
not pick them up between the surrounding grass,
and they produce leaves so small and short-
stalked that to eat them would be like nibbling
the pile off velvet. Any clover or trefoil thus
growing in self-defence is accepted as the
' shamrock ' of Ireland ; and it is certainly a
fine emblem for a race which regards itself
as surviving in spite of incessant oppression.

" These are the reasons, however, why the
grasses and clovers or trefoils continue to enrich
old pastures when most of the other plants dis-
appear, with the exception of daisies and butter-
cups, and the acid sorrels."

We should be glad to hear how Mr Robinson
accounts for the conspicuous flowers in the
species of "prickly pear" (Euphorbia), which is
so abundant in India, and which is not browsed
upon by animals.

We regret that we are not able to devote more
space to this most interesting theory. We can
only add that, even if it fail to become widely
accepted, it is of great value as showing that it

274

Accepted Theories Unsatisfactory

is possible to offer a plausible explanation of a
large number of phenomena, which nine out of
ten botanists explain in a very different way.

So satisfied are the majority of naturalists with
the " insect theory," that they seem of late years
to have paid but little attention to the subject of
floral colouration. This affords a striking instance
of the pernicious influence which Neo- Darwin ism
is exercising on the minds of men to-day. It
tends to stifle research instead of stimulating it.

We have now dealt with the theory of protective
colouration, the theory of warning colouration,
the theory of mimicry, and the theory of recogni-
tion markings. We have shown that although
many organisms undoubtedly derive profit from
the fact that they are difficult to see in their
natural surroundings or from their resemblance
to other organisms, the hypothesis that this in-
conspicuousness or the mimicry of these animals
has been caused by the natural selection of small
variations is untenable.

Warning colours, we have shown, although a
disadvantage to their possessors, are sometimes
seen in nature because they are accompanied by
unpalatability. The theory of recognition mark-
ings must, we fear, be laid to rest in the burial
ground of exploded hypotheses.

The extreme popularity of the existing theories
regarding animal colouration and their very

275

The Making of Species

general acceptance are to be attributed, firstly,
to their simplicity ; secondly, to the fact that they
have thrown light on many phenomena which
previously had seemed inexplicable ; thirdly, that
if we assume, as the great majority of biologists
do, that evolution has been effected by the
accumulation of numerous variations, small in de-
gree and indefinite in direction, we seemed forced
either to accept Neo-Darwinism or admit that the
whole subject of animal colouration baffles us, in
other words, to reject what appears like cosmos
and substitute for it chaos.

With a few exceptions, books that deal with
the colours of organisms, while emphasising
the evidence in favour of the generally-accepted
theories, seem almost entirely to ignore the host
of facts that do not appear to fit in with them.

This is largely due to the almost unavoidable
bias of the human mind when obsessed by a pet
theory. There are none so blind as those who
will not see. It is also, in part, the consequence
of the prevalent neglect of the scientific method
of comparison which leads men to theorise on
insufficient evidence. This, of course, is a natural
result of specialisation in biology. Naturalists
are in the habit of confining their study to the
habits of the animals of one particular country
and then making far - reaching generalisations
therefrom.

As an example of the kind of theorising to
276

White Down of Nestlings

which this method leads, we may cite the often-
quoted theory which ascribes the green colouring
of some arboreal fruit-eating pigeons to adapta-
tion to an existence among tropical foliage, and
ignores the fact that in America tree-haunting
pigeons are never of this colour, and that it is not
by any means universal even among the old-
world pigeons.

Similarly, a theory has been advanced (W. P.
Pycraft, Knowledge, 1904, p. 275) that the white
down of some nestling birds, is an adaptation
to resisting the heat of the sun in open nests.
This is at once negatived by the fact that young
owls, usually hatched in shaded places, are also
generally white, while young cormorants, living
in open nests, are black ; yet the allied darters,
with the same breeding haunts in some cases,
have white young. Lest it should be thought
that black has some especial value in a nestling
living exposed, we may mention that young
petrels, which are born in holes, have black or
dark down.

As we have already pointed out, naturalists
in too readily accepting the theory that varia-
tion is minute in degree and indefinite in
direction, have raised quite unnecessary diffi-
culties, even for the selection hypothesis. We
have cited certain facts, which seem to show that
variations, as a rule, are not indefinite in direc-
tion ; of these the most striking is furnished by

277

The Making of Species

birds in which the tail feathers are greatly
elongated. Were variations indeterminate, we
might reasonably expect to find that the
elongation occurred in one particular feather or
pair of feathers in one species, in another pair in
a second species, in a third pair in a third species,
and so on. But this is not the case ; no bird has
one single long feather in its tail, and when two
are elongated, as is so commonly the case, these
are almost invariably the middle or the outside
pair; e.g., in the European bee-eater and pheasant
it is the former, in the swallow and blackcock,
the latter.

Exceptions are so rare that they may almost
be said to prove the rule ; e.g., although most
terns have the outer-tail feathers elongated, in
some of the Noddy Terns (A nous, Gygis) the
third pair, in others the fourth pair, of tail
feathers are the longest. This must mean one of
two things, either that the variation, as regards
length in tail feathers, other than middle or outer,
does not ordinarily occur, or that it occurs, but is,
in some way, inimical to the welfare of the
species. The latter hypothesis does not seem
probable, as the Noddies are particularly
abundant birds where they occur, that is to
say, in the tropical seas ; therefore, we can only
conclude that that particular variation has not
occurred in birds as a whole.

We have adduced abundant evidence to show
278

Cranes

that mutations or discontinuous variations occur
in nature ; and as these afford much more favour-
able material on which natural selection can act,
it is reasonable to suppose that they have played
a considerable part in evolution.

When discussing the phenomena of inheritance,
we attempted to show that, not improbably, these
discontinuous variations are due to some re-
arrangement in the constituent parts of the unit
characters, or biological molecules, as we have
called them.

In this connection we may mention the
apparently singular phenomenon of different
species in the same natural group, exhibiting
either a definite excess or deficiency of plumage
on the head. Among cranes, most species are
more or less bald ; but the Demoiselle (Antkro-
poides virgo) has a fully- feathered head with
long side-plumes, while the head of the Stanley
Crane (A . paradisea) appears to be swollen, so
abundantly is it feathered The crowned cranes,
although bare - cheeked, have double crests,
the two parts of which have been respectively
compared to a pen -wiper and a bunch of
toothpicks !

Among the guinea-fowls, several species are
crested, while others, as, for example, the
domestic one, are bare-headed. Now, on the
theory of evolution, by accumulation of minute
variations, phenomena such as these are difficult

279

The Making of Species

of explanation ; but, on the assumption that a
slight rearrangement of the biological atoms in
the molecule may produce very diverse results, as
we see in the case of chemical molecules, and
of seasonally dimorphic butterflies, there is
no particular ground for surprise at such a
phenomenon.

In this connection we may cite the significant
fact, so well known to canary breeders, that two
crested birds when mated tend to produce a bald-
headed one.

If the colour of any part of an organism be
due to the internal arrangement of the constituent
parts of the biological molecule from which it is
derived, we should expect any rearrangement of
the component parts to produce quite a different
colour. In other words, we should expect occa-
sionally to see colour-mutations. These are pre-
cisely what we do see. Similarly, if the scheme
of colouring of an organism be due to a certain
grouping of biological molecules, we should ex-
pect the same scheme of colouring to occur in
organisms which are not nearly related. This,
too, we observe in nature.

Many of the phenomena of mimicry, and all
the cases which we have cited as pseudo-mimicry,
seem to us to be referable to this.

Take, for example, the magpie colouration in
birds — that is to say, a scheme of colouring in
which the body is white, and head, wings, and

280

Magpie Colouring

tail black. This occurs in the following birds
belonging to the most diverse groups : —

The Magpie.

The Magpie Tanager (Cissopis leveriana).

The Magpie Robin (Copsychus saularis\ cock
only ; in the hen the black is replaced by brownish
grey.

The Pied H oney eater (Entomophila picata).

The Chaplain Crow (white-bodied form of the
hoodie crow).

The New Ireland Swallow Shrike (Artamus
insignis).

The Magpie Goose (Anseranas melanoleucus).

Combinations of this kind, in which the black
is replaced by brown or grey, are excessively rare.

On the other hand, we see in several birds the
combination in which the white is replaced by
yellow : —

The Common Troupial (Icterus vulgaris).

The Black-headed Oriole (Oriolus melano
cephalus).

The Black-and-yellow Grosbeak, male only.

What we may call imperfect magpie coloura-
tion, i.e. where the head becomes white, occurs
in several species of birds. The head of a black
species sometimes becomes white as a mutation ;
in the domestic Muscovy duck, for example, an
individual is sometimes produced having a white
head, although the black of the remainder of the
plumage remains unchanged.

281

The Making of Species

As examples of this scheme of colouration we
may cite —

Black-and-white Fruit Pigeons (Myristicivora).

Several Gannets (Sula capensis, S. serrator,
etc.)

Swallow-tailed Kite (Elanoides furcatus).

Several Storks (Euxenura maguari, Anastomus
oscitans, P seudotantalus cinereus).

Moreover, a common variety of the barn-door
fowl has also a white body and black primaries
and tail, showing that this scheme of colour may
arise as a mutation.

A further elimination of black in the tail and
body leads us to white birds with more or less
black wings :—

White Storks (Ciconia alba, C. boyciana, and
Euxenura maguari).

The White Crane (Grus leucogeranus).

The Snow Geese (Chen nivalis, C. rossi).

The Common Gannet (Sula bassana).

The White Buzzard (Leucopternis).

The Scavenger Vultures (Neophron].

A recurring combination in mammals is black,
with a white marking on the breast.

Most of the bears, even young brown bears,
show a tendency to this. It is also found in the
Tasmanian devil, and in varieties of our domestic
cats, rats, and dogs ; also in the domestic duck.

The white-spotted pelage, not uncommon in
deer, especially fawns, is curiously repeated in

282

Albinos

the Australian carnivorous marsupials, known
as Native Cats (Dasyurus).

In domestic animals we frequently find the
following localisation of white — white socks,
collar, breast, and muzzle. The arrangement
occurs in cats, dogs, rabbits, guinea-pigs and
mice, also in the horse and pig, but without
the collar. The arrangement is not seen in
goats, cattle, or sheep, nor in wild animals of
any kind. This would lead to the conclusion
that the combination is correlated with some
character unfavourable to survival under natural
conditions.

Many variations which frequently occur among
both wild and domestic animals do not persist in
nature.

As instances of such variations we may men-
tion pure albino forms, that is to say those in
which pigment does not occur in the eyes.

It is easy to see why this variation is not
allowed to persist in nature. Its possessors are
handicapped by bad eyesight, and so have no
chance of surviving in the struggle for existence.
It is thus that natural selection acts. On the
other hand, white species with pigmented eyes are
fairly numerous. These enjoy normal eyesight,
but labour under the disadvantage of being easily
seen by their foes. Hence we find that white
species generally either occur in a snowy habitat,
or are powerful and both able and ready to

283

The Making of Species

defend themselves. In this connection it is inter-
esting to notice that in New Zealand all birds,
whether introduced or indigenous, are particularly
liable to albinism. Owing to the fewness of their
enemies these albinistic forms are able to persist.

A variation, or rather a mutation, that fre-
quently occurs among domesticated birds, but
which is seen in very few wild species, is that
which takes the form of white primary feathers
on the wing. This variation must often occur in
nature, but it rarely establishes itself, apparently
because white feathers do not resist wear so well
as coloured ones do.

Black-and-yellow colouration occurs in several
widely separated species of birds. The arrange-
ment of the two colours follows to some extent
the same rules as the black-and-white combination.

Several birds have a yellow body with black
head, wings, and tail, such as —

The Black - headed Oriole (Oriolus melano-
cephalus).

The Black-and-Yellow Grosbeaks (Pycnor-
hamphus icteroides, P. affinis) (cock).

The Common Troupial (Icterus vulgaris).

In others the black on the head is nearly or
quite suppressed, that on the tail remaining to a
greater or less extent ; such are —

The Golden Orioles (Oriolus galbu la, O. kundoo,
etc.).

Several species of Icterus.
284

Byfermtssion of Messrs. Hntchinson &• Co.

BRAZILIAN TROUPIAL

This species (Icterus vulgaris) is that most frequently seen in captivity ;
the pattern of colour is found in several other allied forms

By permission of Messrs. Hutchinson &• Co.

INDIAN BLACK-HEADED ORIOLE
Several other orioles besides this (O. melanocephaltts) have the black head.

Biological Molecules and Colour

Several fly-catchers of the genus Piezorhynchus
(males only).

We have said sufficient to show that certain
combinations of colours recur in nature in species
which are neither nearly related to one another
nor subjected to similar environment. For such
phenomena it is difficult, if not impossible, to
account on the theory that natural selection,
acting on minute variations, is responsible for
all the varied colouring of the animal kingdom.
The facts, however, are in accordance with the
supposition that the organism is the result of the
growth and development of a number of units or
biological molecules which exist in the fertilised

If there be any truth in the supposition,
the colouration of every animal must be due to
the development of one or more of these mole-
cules. Colouration may be expression of the
arrangement of all the molecules in the fertilised
egg, or it may be due to the development of a
number of molecules whose function is to deter-
mine the colouring of an organism, or it may be
the result of the development of one such mole-
cule, which perhaps splits up in such a way that
a portion attaches itself to each of the other
molecules.

But it is idle to speculate on this point. As
we have already insisted, the tendency to build

285

The Making of Species

up elaborate theories on very slender foundations
is a too frequent failing of zoologists. We desire
merely to emphasise the fact that the phenomena
of animal colouration almost force us to the con-
clusion that the colouring of each organism is the
result of the development of a number of units.

It may be objected that, if this be the case, the
number of the units which contribute to the colour
of any organism must be exceedingly large, since
we see in nature an almost limitless number of
different schemes of colouring. If the colour of
each animal be the result of the development of
a few units, it might be thought, firstly, that the
diversity of schemes of colouration which we
observe in nature could not possibly occur ;
and secondly, that, under such circumstances,
the colour pattern of a bird or beast should
be of the nature of a mosaic, each colour being
sharply defined and separated from every other
colour, instead of the colours shading one into
the other, as is so frequently the case.

Such objections would be based on a miscon-
ception as to the nature of the units which com-
bine to produce the colouration of an organism.
These units show themselves as centres of develop-
ment of colour, as points from which the colour
or colouring they represent spreads, until it
meets and mingles with other patches of colour
which are being developed from other centres.
The colour produced at one centre may spread

286

Mr Tylor Quoted

more rapidly than that which forms at another ;
this, of course, will result in a preponderance in
the organism of the colour which is produced at
the former centre.

Further, we must bear in mind that the develop-
ment of each colour-producing unit is largely
affected by conditions external to it, as we shall
see when dealing with Sexual Dimorphism.

More than one naturalist, who has paid careful
attention to the subject of animal colouration, has
perceived that through the apparently endless
diversity of the colouring of organisms something
like order runs.

Over thirty years ago Mr Alfred Tylor called
attention to this important fact. That observer,
whose views met with the approval of Wallace,
was of opinion that colour follows structure, and
that in a many-hued animal it changes at points
where the function changes.

"If," writes Mr Tylor, "we take highly
decorated species — that is, animals marked by
alternate dark or light bands or spots, such as
the zebra, some deer, or the carnivora, we find,
first, that the region of the spinal column is
marked by a dark stripe ; secondly, that the
regions of the appendages, or limbs, are differ-
ently marked ; thirdly, that the flanks are striped
or spotted, along or between the regions of the
lines of the ribs ; fourthly, that the shoulder and
hip regions are marked by curved lines ; fifthly,

287

The Making of Species

that the pattern changes, and the direction of the
lines, or spots, at the head, neck, and every joint
of the limbs ; and, lastly, that the tips of the ears,
nose, tail, and feet, and the eyes are emphasised
in colour."

More recently Mr J. Lewis Bonhote has
devoted much attention to this important subject.
The results of his researches are summarised on
page 185 of vol. xxix. of the Proceedings of the
Linncean Society, and on page 258 of the Proceed-
ings of the Fourth International Ornithological
Congress, 1905. Mr Bonhote states that the
presence or absence of colour tends almost in-
variably to make its appearance, first of all, on
certain definite tracts, common to mammals and
birds alike, which he calls pcecilomeres.

" Pcecilomeres," he writes, " are situated on
the following parts, viz., chin, malar stripe, max-
illary stripe, a spot above and slightly in front of
the eye, a spot below or slightly behind the eye,
the ear, crown of the head, occiput, fore-end of
sternum, vent, rump, thighs, wrist, shoulders
(above and below).

" Now, there is hardly any species of bird on
which one or more of these poecilomeres is not
' picked out ' (to use a painter's expression) in
some colour different from that of the surround-
ing parts, and, in fact, most of the so-called
recognition or protective markings will be found
on these patches.

288

Poecilomeres

" On the other hand, among many species the
differentiation of colour on the pcecilomeres is
not so conspicuous as to attract the eye or to
serve in any way for protection or mimicry, yet
we still find them marked by differences of colour
so slight that, unless especially looked for, they
would never be noticed.

"Or, again, some species occasionally, but not
invariably, show a few white feathers on certain
parts of their body, and, when such is the case,
it will be found that these white feathers appear
on the pcecilomeres. . . . There is hardly a
species in which examples of these pcecilomeres
may not be found. . . . The Kingfisher (Alcedo
ispida] shows the various head pcecilomeres very
clearly, and as examples of inconspicuous differ-
ences on these tracts, the rump of the hen sparrow
(Passer domesticus] and hen chaffinch (Fringilla
ccelebs), the malar stripe and dark ear-patch of
the hen Yellow Bunting (Emberiza citrinella),
and the dark ante-orbital patch of the Barn Owl
(Strix flammea) are familiar examples. And,
lastly, as an instance of the class where a few
white feathers frequently, but not invariably,
appear, the young of the cuckoo (Cuculus cano-
rus) forms a good example.

" These spots may, however, appear in a tran-
sitory manner, as, for instance, where a change
of plumage (not necessarily moult) is occcurring."

As an instance of this, Bonhote cites the case
T 289

The Making of Species

of a young male Shoveler (Spatula clypeata), " in
which the metallic colour on the head first showed
itself on the post-orbital and auricular pcecilo-
meres, gradually meeting and joining up across
the head with the crown and occipital pcecilo-
meres, and then finally spreading forwards. And
it may be well to note that the joining up of the
auricular and post-orbital pcecilomeres formed
a metallic patch similar in size and position to
that found in the male Teal (Querquedula crecca\
and, further, in the last stage, when the whole
head, except the portion round the beak, was
metallic, the markings are similar to those found
permanently in the hen Scaup {Fuligula marila).

Now, these resemblances taking place in the
normal pure-bred wild shoveler, the question of
reversion does not come in, and no one would
suppose these resemblances due to anything
more than transitional variation, and it is the
object of this portion of the paper to show that
variation in colour follows along definite lines."

Mr Bonhote continues : " As a further illus-
tration of how widely spread these lines are
throughout the mammalian and avian kingdoms,
we may note the assumption of the brown head
in the case of the Black-headed Gull (Larus
ridibundus\ which invariably follows each year
on lines similar to those related in the case of
the shoveler, and . . . the method by which, on
the approach of winter, the stoat assumes his

290

Biological Molecules

white dress, is (although the change is from
brown to white) again conducted along precisely
similar lines." Mr Bonhote argues with great
force that, as the process occurs in two animals
so widely separated, the fundamental cause must
be a deep-seated one. There can be no doubt
that these pcecilomeres of Bonhote are connected
with our biological molecules. Each of these
pcecilomeres is the result of the development
of one of these unit characters ; each is to be
regarded as the centre of activity, the sphere of
influence of a biological molecule, or the portion
of one, which controls the colouring of a definite
region of the organism. In the case of creatures
which display the same colour throughout, these
molecules all give rise to the same kind of
colouring ; in the case of animals which display
a variety of colours and markings the various
molecules give origin to various colours. But
we must bear in mind that the final colour to
which each colour-producing molecule gives rise
depends to some extent on circumstances other
than the constitution of the molecule. Thus it
is that the young in most organisms differ in
colour and marking from the adults. On this
also depends the phenomena of seasonal and
sexual dimorphism. The same colour-producing
molecule may give rise to one colour under one
set of conditions and to a totally different colour
under another set of conditions.

291

The Making of Species

It is a significant fact that under abnormal
conditions the feathers of birds tend to disappear
precisely on those spots where the pcecilomeres
of Bonhote occur.

Thus in a sickly cage bird the feathers
frequently show a tendency to fall off on the
following spots : crown of head, lores, jaws,
head generally, rump, vent and thighs.

Many wild birds — as, for example, the cranes
— display patches of naked skin on the head,
and these are usually situated on pcecilomeres.
Similarly, natural excessive developments of
plumage tend to occur on the pcecilomeres, or,
rather, the spots characterised by pcecilomeres—
for example, the train of the peacock. Loral
plumage, it is true, is seldom long, but is often of
a peculiar nature.

Colour mutations tend to occur on the pcecilo-
meres. Thus it is that these pcecilomeres often
form the distinctive characters and markings of
allied species. This is precisely what we should
expect if the pcecilomeres correspond to bio-
logical molecules and mutations are the result of
the rearrangement of the constituent parts of
these molecules.

Still more significant is the fact that the colour-
markings in hybrids tend to follow pcecilomeres.

Bonhote has performed a large number of
experiments in hybridising ducks. Some of his
hybrids were produced from three pure ancestors,

292

Biological Molecules

as, for example, the pintail, the spotbill, and the
mallard ; others from two ancestors. Some of
these hybrids were crossed with other hybrids,
and others with the parent forms, hence Bonhote
secured a number of hybrids, each of which had
a distinctive appearance ; but all the variations
appearing among the hybrids were found to start
on one or more of the pcecilomeres.

Certain of the hybrids showed a resemblance
to one or other of the parent species, others were
unlike either parent, and resembled either no
known species or species other than their parents.

When a hybrid shows a resemblance to a species
other than that to which either parent belongs, it
is said to exhibit the phenomenon of atavism or
reversion, — the individual is supposed to have
been " thrown back " to an ancestral form.

The true explanation of the phenomenon would
seem to be that, as the result of the crossing,
biological molecules in the fertilised egg have
been formed which, on development, give rise to
combinations of colour like those seen in other
species.

Thus the phenomena of " mimicry " and " re-
version " are, we believe, due to the fact that in
the fertilised egg of both the pattern and its copy
a similar arrangement of biological molecules
obtains. If we regard the sexual act as re-
sembling in many respects a chemical synthesis,
the phenomenon need not surprise us.

293

The Making of Species

To sum up, the observed facts of animal
colouration seem to indicate that there are in
each organism some twelve or thirteen centres of
colouring, which we suggest may correspond with
portions of the fertilised egg. From each of
these centres the colour develops and spreads,
so that every part of the organism is eventually
coloured. These centres of colouring are not
altogether independent of one another. Some-
times they all give rise to the same hue, in which
case we have a uniformly-coloured organism, such
as the raven. More often from some one colour
develops, and from others another colour ; if
these two colours happen to be black and white,
the result is a pied organism, which displays a
definite pattern due to the correlation of the
various colour-producing biological molecules.

Thus it occasionally happens that two widely
different organisms exhibit very similar mark-
ings, and therefore resemble one another. When
this resemblance is believed to be of advan-
tage to one or other of the similarly-coloured
species, naturalists call it mimicry, and assert that
the likeness is due to the action of natural selec-
tion ; but where neither organism can profit by
the resemblance, zoologists make no attempt to
explain it What we suggest is that the coloura-
tion of an animal depends upon the structure, or,
at any rate, the nature, of the parts of the egg
which produce these centres of colour. But this

294

Biological Molecules

is not by any means the only cause that deter-
mines the colouration of the organism. If it
were, young creatures in their first plumage
would invariably resemble the parents, the two
sexes would always be alike, and there would be
no such phenomenon as seasonal dimorphism.

As a matter of fact, the portions of the egg (we
call them, for the sake of clearness, colour-produc-
ing biological molecules) which give rise to the
pcecilomeres exhibit themselves merely in the
shape of tendencies ; the ultimate form the
colouring will take depends to a large extent
upon other and extraneous circumstances, such
as the secretion of hormones.

Thus it is that organisms seem to display an
almost endless diversity of colouration. But
beneath all this diversity we see something like
order. It occasionally happens (why, we do not
know) that one, or more, of the biological mole-
cules which make up the nucleus of the fertilised
ovum becomes altered in the sexual act, with
the result that a discontinuous variation or muta-
tion appears in the resulting organism. The
mutation may be a favourable one, or one which
does not affect in any way the chances of an
organism in the struggle for existence, or an
unfavourable one. In the last of the three cases
the organism will perish early and not leave
behind any offspring exhibiting its peculiarity.

It is thus that natural selection acts. Natural
295

The Making of Species

selection weeds out relentlessly all organisms
which display unfavourable variations. It is
thus obvious that many species may, and we
believe do, exist which possess characters of no
direct utility to them, or even slightly harmful
ones. For this reason Wallace and his fol-
lowers fail in their attempts to prove that
every patch of colour in every organism is of
direct utility. Natural selection has to take an
animal as it finds it — the good with the bad. If
an organism as a whole is not wanting — that is to
say, if it is able to hold its own against other
organisms, and is fitted to fill any place in nature
— that organism will probably survive, although it
may be defective in many respects. As its name
implies, natural selection is a mere selecting
agency. It has to choose from what is presented
to it. It is not, as many seem to think, a manu-
facturer or inducer of variations. Natural selec-
tion can no more make an animal vary in any
given direction than the human breeder can. Its
power is limited to the destroying of all variations
which do not pass the test prescribed by it.

296

CHAPTER VII

SEXUAL DIMORPHISM

Meaning of the term— Fatal to Wallaceism— Sexual Selection—
The law of battle — Female preference — Mutual Selection —
Finn's experiments— Objections to the theory of Sexual
Selection — Wallace's explanation of sexual dimorphism
stated and shown to be unsatisfactory — The explanation of
Thomson and Geddes shown to be inadequate — Stolzmann's
theory stated and criticised — Neo-Lamarckian explanation
of sexual dimorphism stated and criticised — Some features of
sexual dimorphism — Dissimilarity of the sexes probably arises
as a sudden mutation — The four kinds of mutations — Sexual
dimorphism having shown itself, Natural Selection determines
whether or not the organisms which display it shall survive.

IN some species the sexes are so similar in
appearance that it is not possible to tell
by mere outward inspection to which
sex a given individual belongs.
In other species the sexes differ so widely in
external appearance that it is difficult to believe
that the male and the female belong to the same
species. Between these two extremes are a
great number of species in which the sexes are
more or less dissimilar. Those species in which
the sexes differ in appearance are said to be
sexually dimorphic. The phenomena of sexual
dimorphism are fatal to that form of Neo-
Darwinism which sees in natural selection an

297

The Making of Species

explanation of all the peculiarities of animal
structure and colouration.

It is not easy to understand how natural selec-
tion can have caused marked sexual dimorphism
in a species where the habits of the sexes are
the same, in the Paradise Flycatcher ( Terpsiphone
paradisi), for example, where the cock and the
hen obtain their food in the same way, and share
equally the duties of nest-building, incubation, and
feeding the young.

Of course, in all species where each individual
carries only one of the two kinds of sexual organs,
there must of necessity be some slight difference
between the individuals that carry the male organ,
which performs one function, and those that carry
the female organ, which performs another function.

But in many species the sexes display differ-
ences which have no direct connection with the
generative organs — for example, the deer, where
the stag alone has horns.

Those characters which differ with the sex,
but are not directly connected with the organs
of reproduction, are known as secondary sexual
characters.

In nearly all species where the male and
female differ in beauty, it is the male who
surpasses the female. Natural selection is,
in many cases, not able to explain the origin
of these differences, or why, when they occur,
the male should be more beautiful than the

298

By permission of the Foreign Bird Club

QUEEN WHYDAH

This species ( Tetraenura regia) is a typical example of
seasonal sexual dimorphism, the male being long-tailed
and conspicuously coloured only during the breeding
season, and at other times resembling the sparrow-like
female.

Theory of Sexual Selection

female. This Darwin saw. In order to account
for the phenomena of sexual dimorphism, he
formulated the theory of sexual selection. This
hypothesis is based on the assumption that there
is, in all species of animals, a competition among
the males to secure females as mates. It is not
difficult to understand how this competition
arises in polygamous species. Assuming that
approximately equal numbers of males and
females are born (an assumption which appears to
be justified as regards the majority of species), it
is clear that for every male who secures more
than one wife, at least one male will be obliged
to live in a state of single blessedness.

But how can there be competition in the case
of monogamous species ? The sexes being ap-
proximately equal in number, there are sufficient
females to allow of a mate for every male.

Such is the nature of things, said Darwin, that,
even under these circumstances, there is com-
petition among the males for females.

" Let us take any species," he writes, on page
329 of The Descent of Man (Ed. 1901), "a bird
for instance, and divide the females inhabiting a
district into two equal bodies, the one consisting
of the more vigorous and better-nourished in-
dividuals, and the other of the less vigorous and
healthy. The former, there can be little doubt,
would be ready to breed in the spring before the
others ; and this is the opinion of Mr Jenner

299

The Making of Species

Weir, who has carefully attended to the habits of
birds during many years. There can also be no
doubt that the most vigorous, best nourished,
and earliest breeders would on an average
succeed in rearing the largest number of fine
offspring. The males, as we have seen, are
generally ready to breed before the females ; the
strongest, and with some species the best armed
of the males, drive away the weaker ; and the
former would then unite with the more vigorous
and better-nourished females, because they are
the first to breed. Such vigorous pairs would
surely rear a larger number of offspring than the
retarded females, which would be compelled to
unite with the conquered and less powerful males,
supposing the sexes to be numerically equal ; and
this is all that is wanted to add, in the course
of successive generations, to the size, strength,
and courage of the males, or to improve their
weapons."

From this competition among the males there
arise, firstly, contests between the males for
mates ; secondly, the preference of the females
for favoured males.

It is a matter of common knowledge that at
the breeding season the males of nearly all, if
not all, species are very pugnacious. Two
males often engage in desperate fights for one
or more females ; the victor drives away his foe
and secures the harem. In such contests the

300

The Law of Battle

stronger male wins, and thus emerges that par-
ticular form of sexual selection which Darwin
termed "the law of battle."

" There are," writes Darwin, on page 324 of
The Descent of Man, " many other structures and
instincts which must have developed through
sexual selection — such as the weapons of offence
and the means of defence of the males for
fighting with and driving away their rivals —
their courage and pugnacity — their various orna-
ments— their contrivances for producing vocal
or instrumental music — and their glands for
emitting odours." The former characters have,
according to Darwin, been developed by the law
of battle, and the latter, since they serve only
to allure or excite the female, by the preference
of the female.

" It is clear," continues Darwin, " that these
characters are the result of sexual and not of
ordinary selection, since unarmed, unornamented,
or unattractive males would succeed equally well
in the battle for life and in leaving a numerous
progeny, but for the presence of better-endowed
males. We may infer that this would be the
case, because the females, which are unarmed and
unornamented, are able to survive and procreate
their kind. . . . Just as man can improve the
breed of his game-cocks by the selection of those
birds which are victorious in the cockpit, so it
appears that the strongest and most vigorous

301

The Making of Species

males, or those provided with the best weapons,
have prevailed under nature, and have led to
the improvement of the natural breed or
species."

"With mammals," says Darwin (loc. cit.,
p. 763), "the male appears to win the female
much more through the law of battle than
through the display of his charms."

In the case of birds, however, feminine prefer-
ence comes more into play. It is well known
that cocks display their charms to the hens at
the breeding season, and Darwin believed that
the hen selected the most beautiful of her rival
suitors.

"Just as man," he writes (p. 326 of The
Descent of Man, new edition, 1901), "can give
beauty, according to his standard of taste, to his
male poultry, or, more strictly, can modify the
beauty originally acquired by the parent species,
can give to the Sebright bantam a new and
elegant plumage, an erect and peculiar carriage,
so it appears that female birds in a state of
nature have, by a long selection of the more
attractive males, added to their beauty or other
attractive qualities."

Thus the theory of sexual selection is based
on three assumptions. Firstly, that there is in
all species competition among the males for
females with which to mate. Secondly, that
this results in either "the law of battle" among

302

Selection by Females

the males, or selection by the female of one
among several admirers. Thirdly, that the
female selects, as a rule, the most attractive of
her suitors.

The evidence upon which Darwin founds this
theory may be thus summarised : —

1. In cases where the sexes differ in appear-
ance, or power of song, it is almost invariably
the cock who is the more beautiful or the better
singer, as the case may be.

2. All male birds that possess accessory plumes
or other attractions, make a most elaborate dis-
play of these before the females at the mating
season, hence "it is obviously probable that
these appreciate the beauty of their suitors."

3. Darwin was able to cite specific instances
in which the hens showed preference.

In the case of polygamous species there can
be no doubt that there is considerable competition
among males for their wives. It cannot be said
that the contention is so well established in the
case of monogamous species. D. Dewar suggests
that circumstances may occur in which the hens
have to fight for the cock, or in which the male is
in the happy position of being able to select his
mate. He states his belief that in many cases
the selection is mutual, as in the case of human
beings.

"I have seen," he writes, on page 13 of
Birds of the Plains, " one hen Paradise Fly-

303

The Making of Species

catcher ( Terpsiphone paradisi) drive away another
and then go and make up to a cock bird. Simi-
larly, I have seen two hen orioles behave in a
very unladylike manner to one another all
because they both had designs on the same cock.
He sat and looked on from a distance at the

contest."

Darwin quotes, on page 500 of The Descent
of Man, a case of a male exercising selection :
"It appears to be rare when the male refuses
any particular female, but Mr Wright of Gelders-
ley House, a great breeder of dogs, informs me
that he has known some instances : he cites the
case of one of his own deerhounds who would
not take any notice of a particular female mastiff,
so that another deerhound had to be employed."

Similarly, Finn records, in the Country -Side
for August 29th, 1908, that the male Globose
Curassow ( Crax globicera) in the London Zoo-
logical Gardens, which bred with the female
Heck's Curassow (C. hecki), as related on p. 104,
selected the hen of this very distinctly coloured
form or species in preference to any of the
typical hens of his own kind.

The cases on record of cocks being in a position
to select their mates are comparatively rare, while
instances of selection on the part of the hens are far
more numerous.

Hence it would seem that the sex, which is in
a minority, and so has the opportunity of select-

3°4

Male Attractiveness

ing a mate, does exert a choice and prefer one
particular individual ; and that, for the reasons
pointed out by Darwin, it is in most cases the
female who is in the position of being able to
pick and choose her mate. It is, as Darwin
truly said, far more difficult to decide what
qualities determine the choice of the female.
He believed that it is " to a large extent the
external attractions of the male, though no doubt
his vigour, courage, and other mental qualities
come into play."

Darwin argued that it is the love of hen birds
for "external attractions" in cock birds that
has brought into being all the wonderful plumes
that characterise such birds as the peacock.
" Many female progenitors of the peacock," he
writes, on page 66 1 of The Descent of Man
(ed. 1901), " during a long line of descent, have
appreciated this superiority, for they have un-
consciously, by the continued preference of the
most beautiful males, rendered the peacock the
most splendid of living birds."

This conclusion has been vigorously attacked.
It is argued, with some show of reason, that it
is absurd to credit birds with aesthetic tastes
equal, if not superior, to those of the most
refined and civilised of human beings.

Is it likely, it is asked, that a bird, which will
nest in an old shoe cast off by a tramp, can
appreciate beauty of plumage ?
u 305

The Making of Species

As Geddes and Thomson say (page 29 of
The Evolution of Sex\ " When we consider the
complexity of the markings of the male bird or
insect, and the slow gradations from one step of
perfection to another, it seems difficult to credit
birds or butterflies with a degree of aesthetic
development exhibited by no human being with-
out special aesthetic acuteness and special train-
ing. Moreover, the butterfly, which is supposed
to possess this extraordinary development of
psychological subtlety, will fly naively to a piece
of white paper on the ground, and is attracted
by the primary aesthetic stimulus of an old-
fashioned wall-paper, not to speak of the gaudy
and monotonous brightness of some of our garden
flowers. Thus we have the further difficulty,
that we must suppose the female butterfly to
have a double standard of taste, one for the
flowers which she and her mate both visit, the
other for the far more complex colourings and
markings of the males. And even among birds,
if we take those unmistakable hints of real
awakening of the aesthetic sense which are
exhibited by the Australian bower-bird or by
the common jackdaw in its fondness for bright
objects, how very rude is his taste compared
with the critical examination of infinitesimal
variations of plumage on which Darwin relies.
Is not, therefore, his essential supposition too
glaringly anthropomorphic ?

306

Male Attractiveness

" Again, the most beautiful males are often
extremely combative ; and on the conventional
view this is a mere coincidence, yet a most
unfortunate one for Mr Darwin's view. Battle
thus constantly decides the question of pairing,
and in cases where, by hypothesis, the female
should have most choice, she has simply to yield
to the victor."

Darwin, with characteristic fairness, quotes
some instances which appear to be opposed to
the theory that the hen selects the most beauti-
ful of her suitors. He informs us that Messrs
Hewitt, Tegetmeier, and Brent, who have all
had a long experience of domesticated birds,
" do not believe that the females prefer certain
males on account of the beauty of their plumage.
... Mr Tegetmeier is convinced that a game-
cock, though disfigured by being dubbed and
with his hackles trimmed, would be accepted as
readily as a male retaining all his natural orna-
ments. Mr Brent, however, admits that the
beauty of the male probably aids in exciting the
female ; and her acquiescence is necessary. Mr
Hewitt is convinced that the union is by no
means left to mere chance, for the female almost
invariably prefers the most vigorous, defiant, and
mettlesome male " ; and, in consequence, when
there is a game-cock in the farmyard, the hens
will all resort to him in preference to the cock
of their own breed. Darwin thinks that "some

307

The Making of Species

allowance must be made for the artificial state in
which these birds have long been kept," and
cites in his favour the case of Mr Cupples' female
deerhound that thrice produced puppies, and on
each occasion showed a marked preference for
one of the largest and handsomest, but not the
most eager, of four deerhounds living with her,
all in the prime of life.

The question what is it that determines the
choice of the female is obviously one of con-
siderable importance, and it was to be expected
that many zoologists would have conducted
experiments with a view to deciding it. This
legitimate expectation has not been realised.

The matter of sexual selection remains to-day
practically where Darwin left it. Wallace rejects
the whole theory, and believes that natural
selection alone can explain all the phenomena of
sexual dimorphism. To such an extent does the
enticing idea of the all-puissance of natural
selection dominate the minds of scientific men
that but few of them have paid any attention to
the question of sexual selection. This neglect
of the subject affords an example of the baneful
results of the too-ready acceptance of an enticing
theory, " Natural selection explains everything,
why then investigate further ? " seems to be the
general attitude of our present-day naturalists.

Edmund Selous and D. Dewar have made
some observations on birds, and the Peckhams

308

Pearson's Investigations

on spiders, in a state of nature. Such observa-
tions demonstrate that selective mating occurs
in nature, but, for the most part, fail to show what
it is that determines the choice.

D. Dewar, however, states (Birds of the Plains,
p. 42) that the coloured peahens in the Zoo-
logical Gardens at Lahore show a decided pre-
ference for the white cocks, which are kept in
the aviary along with normally coloured cocks.
He gives it as his opinion that "the hens select
the white cocks, not because they are white, but
because of the strength of the sexual instincts of
these latter. The white cocks continually show
off before the hens ; the sexual desire is developed
more highly in them than in the ordinary cocks,
and it is this that attracts the hens."

The only zoologists who have investigated
experimentally the question of sexual selection
appear to be Karl Pearson and Frank Finn.
The former tried to determine, by actual measure-
ments, whether there is any preferential mating
among human beings as regards physical char-
acteristics. " Our statistics," he writes, on page
427 of The Grammar of Science, "run to only
a few hundreds, and were not collected ad hoc.
Still, as far as they go, they show no evi-
dence of preferential mating in mankind on
the basis of stature, or of any character very
closely correlated with stature. Men do not
appear, for example, to select tall women for

3°9

The Making of Species

their wives, nor do they refuse to mate with
very tall or very short women." As regards
eye-colour, Pearson seems to have arrived at
somewhat more definite results. " We con-
clude," he writes (p. 428), "that in mankind
there certainly exists a preferential mating in the
matter of eye-colour, or of some closely allied
character in the male ; in the case of the female
there also appears to be some change of type due
to preferential mating. . . . The general tendency
is for lighter-eyed to mate, the darker-eyed being
relatively less frequently mated."

But Pearson's experiments seem to show that
as regards stature and eye-colour there is "a
quite sensible tendency of like to mate with
like." "In fact," writes Pearson, "husband and
wife for one of these characters are more alike
than uncle and niece, and for the other more
alike than first cousins." He adds, " Such a
degree of resemblance in two mates, which we
reasonably assume to be not peculiar to man,
could not fail to be of weight if all the stages
between like and unlike were destroyed by
differential selection."

Two obvious criticisms of the results obtained
by Prof. Pearson occur to us. The first is that
his conclusions do not seem to be in accordance
with the popular notion that fair-haired men
prefer dark hair in a woman, while dark-haired
men prefer fair-haired women, and vice versa.

310

Finn's Experiments

The second is that the human animal is not a
typical one. Husbands and wives are selected
for mental and moral qualities rather than
physical ones. The same may, of course, be to
some extent true of animals, but in these there
must of necessity be far less variation as regards
mental attributes. Moreover, the question of
income is much bound up with human matrimonial
alliances ; a rich man or woman has the same
advantage in selection as is possessed by an
animal endowed with more than the average
physical strength of its species.

Finn adopted the plan of experiment suggested
by Prof. Moseley. His apparatus consisted of a
cage divided into three compartments by wire
partitions, so that a bird living in one of them
could see its neighbour in the next compartment.
In the middle compartment he placed a hen
Amadavat (Sporceginthus amandava), and in each
of the other compartments he put a cock bird.
Under such circumstances, the hen in the middle
compartment will sit and roost beside the cock
she prefers. The male amadavat, he writes, in
The Country-Side, vol. i. p. 142, "is in breeding
plumage red with white spots, and the hen brown.
The red varies in intensity even in full-plumaged
birds, and I submitted to the hen first of all two
male birds, one of a coppery and the other of a
rich scarlet tint. In no long time she had made
her choice of the latter bird ; the other, I am sorry

311

The Making of Species

to say, very soon died ; and, as he had appeared
perfectly healthy, I fear grief was accountable
for his end — a warning to future experimenters
to remove the rejected suitor as early as
possible. In the present case I took away the
favoured bird, and put in the side compartments
he and his rival had occupied two other cocks,
which differed in a similar way, though not to
the same extent. Again the hen kept at the
side of the rich red specimen, so, deeming I
knew her views about the correct colour for an
amadavat, I took her away too, and tried a
second hen with these two males. This was an
unusually big bird, and a very independent one,
for she would not make up her mind at all, and
ultimately I released all three without having
gained any result.

Subsequently I made another experiment with
linnets. In this case all three were allowed to
fly in a big aviary-cage together, a method which
I do not recommend.

In this case, however, the handsomest cock,
which showed much richer red on the breast, had
a crippled foot, and proved, as I had expected,
to be in fear of the other ; nevertheless, the hen
mated with him. It must be said, in justice to
the duller bird, that he did not press the advan-
tage his soundness gave him, but with a less
gentle bird than the linnet this would have
happened."

312

Finn's Experiments

It is obvious that there is a wide field for
observation on these lines. In the case of large
birds the experiment could be made still more
conclusive by confining the three birds to be
experimented on in a single enclosure, divided
into three compartments by fences. The males
should be placed each in a separate compartment,
and have a wing clipped so as to prevent them
leaving their respective compartments, while the
hen should be allowed the power of flight so that
she can visit at will any compartment.

Finn has also recorded (loc. cit.) some other
observations bearing on the question of sexual
selection. He writes: —

" One cannot observe or read about the habits
of birds very much without finding out that,
whatever may be the value of beauty, strength
counts for a great deal. Male birds constantly
fight for their mates, and the beaten individual,
if not killed, is at any rate kept at a distance by
his successful rival, so that, if he be really more
beautiful, his beauty is not necessarily of much
service to him. I was particularly impressed
by this about a couple of years ago, when I
frequently watched the semi-domesticated mal-
lards in Regent's Park in the pairing season.
These birds varied a good deal in colour ; in
some the rich claret breast was wanting, and
others had even a slate-coloured head instead of
the normal brilliant green. Yet I found these

3'3

The Making of Species

' off-coloured ' birds could succeed in getting and
keeping mates when correctly-dressed drakes
pined in lonely bachelorhood ; one grey-breasted
bird had even been able to indulge in bigamy.
That strength ruled here was obvious from the
way in which the wedded birds drove away their
unmated rivals, a proceeding in which their wives
most thoroughly sympathised.

" Evidently, beauty does not count for much
with the park duck, and the same seems to be the
case with the fowl. As a boy, I often used to
visit a yard wherein was a very varied assort-
ment of fowls. Among these was one very
handsome cock, of the typical black and red
colouring of the wild bird, and very fully
1 furnished ' in the matter of hackle and sickle
feathers. Yet the hens held him in no great
account, while the master of the yard, a big
black bird, with much Spanish blood, provided
with a huge pair of spurs, was so admired that
he was always attended by some little bantam
hens, although they might have had diminutive
husbands of their own class.

" It must be remembered, however, that these
ducks and fowls had an unnaturally wide choice.
In nature, varieties are rare, and the competing
suitors are likely to be all very much alike ; this
makes matters very difficult for the observer,
who may easily pass over small differences which
are plain enough to the eyes of the hen birds."

3J4

Display of Undecorated Cocks

Finn observed that a young hen Bird of
Paradise (Paradisea apoda) in the London Zoo-
logical Gardens, mated with a fully adult cock in
the next compartment although a young cock in
female plumage in her own compartment did his
best to show off.

It would thus seem that the very limited
evidence at present available is not sufficient to
sustain the theory that the hens select the most
attractive of their suitors. It is significant that
plainly-coloured species of birds show off with as
much care as their gaily-plumaged brethren ;
and, if they be nearly allied, assume similar
courting attitudes. Thus the homely-attired
males of the Spotted-bill (Anas poecilorkynckaj,
Gad wall, and Black Duck (Anas superciliosa),
show off in precisely the same way as does the
handsome mallard.

Howard describes and figures in his excellent
and beautifully illustrated monograph the elabo-
rate display at the pairing season of some of our
plain-coloured little warblers. The skylark has
also a notable display.

The common partridge assumes a nuptial atti-
tude similar to that of the pheasant, and, although
the cock of the former species has nothing brilliant
to show off, the hen partridge pays far more atten-
tion to the display of her suitor than does the hen
pheasant.

The fact that some cock birds show off after the

The Making of Species

act of pairing seems to tell against the theory of
sexual selection, or at any rate to indicate the
purely mechanical nature of the performance.
Finn has witnessed this post-nuptial display
at the Zoological Gardens (London) in the
pied wagtail, the peacock, the Andaman Teal
(Nettium albigulare), the Avocet, the Egyptian
Goose (Chenatopex <zgyptiaca\ and the Maned
Goose (Chenonetta jubata).

Another objection to the theory that the bright
colours of cock birds are due to feminine selection
is presented by those birds which breed in im-
mature plumage. Darwin admits that this objec-
tion would be a valid one " if the younger and
less ornamental males were as successful in
winning females and propagating their kind as
the older and more beautiful males. But," he
continues, " we have no reason to suppose that
this is the case."

Unfortunately for the theory of sexual selection,
there is evidence to show that the cock Paradise
Fly-catcher ( Terpsiphone parodist) in immature
plumage is quite as successful in obtaining a
mate as is the cock in his final plumage. The
cock of this beautiful species has a chestnut
plumage in his second year, and a white one
in the third and subsequent years of his life.
Nevertheless, a considerable proportion of the
nests found belong to chestnut cocks.

Darwin was of opinion that any novelty in

Plumage of Herons

colouring in the male is admired by the female ;
and in this manner he sought to overcome some
difficulties to his theory which certain birds
presented.

Writing of the heron family, he says :—
"The young of the Ardea asha are white, the
adults being slate-coloured ; and not only the
young, but the adults of the allied Buphus
coromandus in their winter plumage are white,
their colour changing into a rich golden buff
during the breeding season. It is incredible
that the young of these two species, as well as
of some other members of the same family,
should have been specially rendered pure white,
and thus made conspicuous to their enemies ; or
that the adults of one of these two species should
have been specially rendered white during the
winter in a country which is never covered with
snow. On the other hand, we have reason to
believe that whiteness has been gained by many
birds as a sexual ornament. We may therefore
conclude that an early progenitor of the Ardea
asha and the Buphus acquired a white plumage
for nuptial purposes, and transmitted this colour
to their young ; so that the young and the old
became white like certain existing egrets, the
whiteness having afterwards been retained by
the young whilst exchanged by the adults for
more strongly pronounced tints. But if we
could look still further backwards in time to

31?

The Making of Species

the still earlier progenitors of these two species,
we should probably see the adults dark-coloured.
I infer that this would be the case, from the
analogy of many other birds, which are dark
whilst young, and when adult are white ; and
more especially from the adult of the Ardea
gularis, the colours of which are the reverse
of those of A. asha, for the young are dark-
coloured and the adults white, the young having
retained a former state of plumage. It appears,
therefore, that the progenitors in their adult con-
dition of the A. as ha, the Buphus, and of some
allies have undergone, during a long line of
descent, the following changes of colour : firstly
a dark shade, secondly pure white, and thirdly,
owing to another change of fashion (if I may so
express myself), their present slaty, reddish or
golden-buff tints. These successive changes are
intelligible only on the principle of novelty
having been admired by the birds for the sake
of novelty."

This reasoning may appear far-fetched and un-
convincing. It seems, however, quite likely that
the hen may select as her mate the suitor who
is conspicuously different from the others, not
because she admires novelty, but because his
conspicuousness attracts her attention and en-
ables her to make up her mind quickly to take
him and thus rid herself of the other troublesome
admirers, who are all very much alike.

318

Sexual Dissimilarity

It is perhaps worthy of note that, after the
most successful of her suitors has succeeded in
securing the hen, it may happen that a dis-
appointed rival makes love to her in the absence
of her lord and master and thereby nullifies the
effect of her previous selection.

It is to be observed that, even if we take it as
proved, as Darwin believed, that the hens alone
exercise a choice of mates, and that they select
the most beautiful of their suitors, we are still
far from arriving at an explanation of the fact
that the males alone have acquired beauty.
Admitting that the hens always mate with the
most beautiful cocks, we should expect the off-
spring of each union to be all more or less alike
in beauty — that is to say, more beautiful than the
mother and less so than the cock. How are we
to explain the one - sided inheritance of this
beauty ? Why is it confined to the cocks ?

In order to meet this objection Darwin had to
call to his aid unknown laws of inheritance.
" The laws of inheritance," he writes (Descent of
Man, p. 759), " irrespectively of selection, appear
to have determined whether the characters
acquired by males for the sake of ornament, for
producing various sounds, and for fighting
together, have been transmitted to the males
alone or to both sexes, either permanently or
periodically, during certain seasons of the year.
Why various characters should have been trans-

The Making of Species

mitted sometimes in one way and sometimes in
another is not in most cases known ; but the
period of variability seems often to have been
the determining cause. When the two sexes
have inherited all characters in common, they
necessarily resemble each other ; but, as the suc-
cessive variations may be differently transmitted,
every possible gradation may be found, even
within the same genus, from the closest simi-
larity to the widest dissimilarity between the

sexes."

This statement, although it does not throw any
light upon the problem, is somewhat damaging
to the theory of sexual selection. If it be
admitted that dissimilarity between the sexes
is due to the fact that the males have varied in
one way and the females in another way, there
seems no necessity for invoking the aid of
feminine preference.

Even greater is the difficulty presented by
those species in which the males alone are pro-
vided with horns or antlers. " When," writes
Darwin (Descent of Man, p. 767), "the males
are provided with weapons which in the females
are absent, there can hardly be a doubt that
these serve for fighting with other males ; and
that they were acquired through sexual selection,
and were transmitted to the male sex alone.
It is not probable, at least in most cases, that
the females have been prevented from acquiring

320

Wallace's Theory

such weapons on account of their being useless,
superfluous, or in some way injurious. On the
contrary, as they are often used by the males for
various purposes, more especially as a defence
against their enemies, it is a surprising fact that
they are so poorly developed, or quite absent,
in the females of so many animals."

We have, we believe, demonstrated that
Darwin's theory of sexual selection is unable to
account satisfactorily for all the phenomena of
sexual dimorphism. But, as we have seen, it is
quite possible that sexual selection is a real
factor of evolution.

We trust that what we have said will stimu-
late some leisured naturalist to study the question
of male and female preference.

We now pass on to consider briefly some of
the other attempts that have been made to ex-
plain the phenomena of sexual dimorphism.

WALLACE'S EXPLANATION OF SEXUAL
DISSIMILARITY

Wallace does not accept the theory of sexual
selection. He admits that the form of male
rivalry, which Darwin calls " the law of battle,"
is "a real power in nature," and believes that
" to it we must impute the development of the
exceptional strength, size, and activity of the
male, together with the possession of special
offensive and defensive weapons, and of all
x 321

The Making of Species

other characters which arise from the develop-
ment of these, or are correlated with them "
(Darwinism, p. 283). But the view that the
female selects the most beautiful of her suitors
has always seemed to Wallace "to be un-
supported by evidence, while it is also quite
inadequate to account for the facts." For
example, the accessory plumes of birds " usually
appear in a few definite parts of the body. We
require some cause to initiate the development in
one part rather than in another."

Wallace considers that natural selection is
able to explain all the phenomena of sexual
dimorphism. He points out that, when the sexes
are dissimilar among birds, it is almost invariably
the female which is duller coloured. The reason
for this is, he believes, that the hen birds, while
sitting, "are exposed to observation and attack
by the numerous devourers of eggs and birds,
and it is of vital importance that they should be
protectively coloured in all those parts of the
body which are exposed during incubation. To
secure this, all the bright colours and showy
ornaments which decorate the male have not
been acquired by the female, who often remains
clothed in the sober hues which were probably
once common to the whole order to which she
belongs. The different amounts of colour ac-
quired by the females have no doubt depended
on peculiarities of habits and environment, and on

322

Wallace's Theory

the powers of defence and concealment possessed
by the species."

In support of his contention, Wallace asserts
that all species of birds, of which the hens are as
conspicuously coloured as the cocks, nest in holes
or build domed nests. The plumes and other
ornaments, which the cocks of certain species
display, Wallace would attribute to a surplus of
strength, vitality, and growth power, which is
able to expend itself in this way without injury.

"If," he writes, "we have found a vera causa
for the origin of ornamental appendages of birds
and other animals in a surplus of vital energy,
leading to abnormal growths in those parts of
the integument where muscular and nervous
action are greatest, the continuous development
of these appendages will result from the ordinary
action of natural selection in preserving the most
healthy and vigorous individuals, and the still
further selective agency of sexual struggle in
giving to the very strongest and most energetic
the parentage of the next generation." (Dar-
winism, p. 293.) "Why," he says, "in allied
species the development of accessory plumes
has taken different forms we are unable to say,
except that it may be due to that individual
variability which has served as the starting point
for so much of what seems to us strange in form,
or fantastic in colour, both in the animal and
vegetable world."

323

The Making of Species

Wallace's view that the dull plumage of the
hen bird is due to her greater need of protection
is based on the assumption that the hen bird alone
takes part in incubation.

Is this assumption a correct one?

It certainly is not in all cases. As D. Dewar
has stated in Birds of the Plains, the showy
white cock Paradise Fly-catcher (Terpsiphone
paradisi] sits in broad daylight on the open nest
quite as much as the hen does. And this may
prove to be true of many other species of
birds. Again, the cocks of the various species
of Indian sunbirds are brightly coloured while
the hens are dull brown. In these species the
hen alone sits on the eggs, but, as the nest is
well covered-in, the hen might display all the
colours of the rainbow without being visible
to passing birds. Moreover, as D. Dewar
pointed out in a paper read before the Royal
Society of Arts (Journal, vol. Ivii., p. 104),
although, in most species of Indian dove, the
sexes show little or no dissimilarity, there is one
species (CEnopopelia tranquebarica) which ex-
hibits considerable sexual dimorphism. But the
nesting habits of this peculiar species are in
all respects similar to those of the other species
of dove. Why then the marked dissimilarity of
the sexes ?

Another objection to the theory of Wallace is
that urged by J. T. Cunningham (Archiv fiir

324

Wallace's Theory Criticised

Entwicklungsmechanik der Organismen, vol.
xxvi., p. 378), namely, that the secondary
sexual characters in those species which possess
them show an entire absence of uniformity in
nature and position. " Why," asks Cunningham,
' 'should the male constitution of the stag show
itself in bony excrescences of the skull, in the
peacock in excessive growth of the other end of
the body ? Why should the larynx be modified
in one mammal, the teeth in another, the nose in
another ? Why is the male newt distinguished
by a dorsal fin, the male frog by a swelling on
the fore foot ? "

Another objection to the explanation of sexual
dimorphism suggested by Wallace, is that in
many species of bird, as, for example, the house
sparrow and the green paroquets of India, the
external differences between the sexes are so
slight that it is unreasonable to believe that they
are the result of natural selection. It seems
impossible to hold that the Rose-ringed Paroquet
(Palaeornis torquatus) — a species which nests in
holes — would have become extinct if the hens had
developed the narrow rose-coloured collar that
characterises the cocks.

Darwin pointed out that while Wallace's
hypothesis might appear plausible if applied to
colour, it can scarcely be said to explain the
origin of such structures as the musical apparatus
of certain male insects, or the larger size of the

325

The Making of Species

larynx in some birds and mammals. We thus see
that suggestions offered by Wallace, although
they contain a modicum of truth, fail to explain
the phenomena of sexual dimorphism.

The fairest possible criticism of these views is
that of Darwin : —

"It will have been seen that I cannot follow
Mr Wallace in the belief that dull colours, when
confined to the females, have been in most cases
specially gained for the sake of protection.
There can, however, be no doubt, as formerly
remarked, that both sexes of many birds have
had their colours modified, so as to escape the
notice of their enemies ; or in some instances, so
as to approach their prey unobserved, just as
owls have had their plumage rendered soft, that
their flight may not be overheard " ( The Descent
of Man, p. 745).

THE THEORY OF THOMSON AND GEDDES

Thomson and Geddes have attempted to
explain sexual dimorphism on the hypothesis
that males are essentially dissipators of energy,
while females tend to conserve energy. They
point out that the spermatozoon is a small
intensely active body, which dissipates its energy
in motion, while the ovum is a large inert body
— the result of the female tendency to conserve
energy and to build up material. The various
ornaments and excrescences which appear in

326

Views of Thomson and Geddes

male organisms are the result of this male ten-
dency to dissipate energy. In the spermatozoon
the dissipated energy appears in the form of
active movement ; in the adult organism it takes
the shape of plumes and other ornaments, of song
and contests for the females.

This theory, however, does not explain what
we might call the haphazard nature of sexual
dimorphism. If sexual dissimilarity is due to the
tendency of the male to dissipate energy, why do
we see very marked dimorphism in one species,
and no dimorphism in a very nearly allied
species? Why are the males larger than the
females in some species, and smaller in other
species ? Again, how is it that in certain species
of birds — the quails of the genus Turnix, the
Painted Snipe (Rhynckaa), and the Phalaropes —
it is the female who possesses the more showy
plumage ? Moreover, this theory, equally with
that of Wallace, does not explain why the ex-
crescences which characterise the male appear in
various parts of the body in different species.

STOLZMANN'S THEORY

Stolzmann has made an ingenious attempt to
explain why in birds the cock is so frequently
more conspicuously coloured than the hen. He
asserts that among birds the males are more
numerous than the females, and that this pre-
ponderance is not advantageous to the species.

327

The Making of Species

Those males which have not managed to secure
a mate are apt to persecute the females while
sitting on the eggs, to the detriment of these
latter. Natural selection, says Stolzmann, is
concerned with the well-being of the species
rather than of the individual. Hence anything
that would tend to lessen the number of males
would be a good thing for the species, so that
a peculiarity, such as bright plumage, which
renders the males conspicuous, or ornamental
plumes, which cause their flight to be slow, and
so leads to their destruction, will be seized upon
and perpetuated by natural selection. He points
out that the cock of one species of humming-
bird— Loddigesia mirabilis — has not only longer
tail feathers, but a shorter wing than the female,
and must, in consequence, find it comparatively
difficult to obtain food, and be more liable to fall
a victim to birds of prey than the hen. Stolz-
mann further suggests that the excessive pug-
nacity of male birds at the breeding season may
lead to the destruction of some individuals, and
so prove of advantage to the species.

Several objections seem to present themselves
to this most ingenious theory.

In the first place, there does not appear to
be any satisfactory evidence to show that more
cocks than hens are born.

We may grant that a superfluity of cocks is
injurious to any species, since the unmated ones

328

Stolzmann's Theory

are likely to persecute the hens ; we may also
grant that many cocks are handicapped in the
struggle for existence by the excessive growth
of certain of their feathers, but we fail to see
how this excessive development has been caused
by natural selection in the manner suggested by
Stolzmann. Although it may be advantageous
to the species for the cocks to be showy, natural
selection can perpetuate this only by weeding
out the least conspicuous of the cocks. But it
is the more gaudy ones, those, according to
Stolzmann, whose presence is beneficial to the
species, which will be eliminated by natural
selection. So that, in this case, that force will
act in a manner contrary to the interests of the
species, if Stolzmann's idea is a correct one.

The theory in question would therefore seem
to be untenable. Nevertheless there is doubt-
less some truth in the notion that too many
males spoil the species. Thus, excessive showi-
ness and high mortality among the males may
be beneficial to the species. But we must not
forget that the more beneficial it is, the stronger
must be the tendency of natural selection to
eliminate the males that possess the desired
peculiarity.

NEO-LAMARCKIAN EXPLANATION

J. T. Cunningham makes an attempt to ex-
plain the phenomena of sexual dimorphism on

329

The Making of Species

Neo-Lamarckian principles. His theory is set
forth in a paper entitled The Heredity of
Secondary Sexual Characters in relation to
Hormones, which was read before the Zoological
Society of London, and published in full in the
Archiv fur Entwicklungsmechanik der Organ-
ismen. " The significant correlation of male
sexual characters," he writes, " is not with any
general or essential property of the male sex,
such as katabolism (or the tendency to dissipate
energy, as we have called it), but with certain
habits and functions confined to one sex, but
differing in different animals. ... In those
animals which possess such (i.e. secondary
sexual) characters, the parts of the soma (i.e. the
body) affected differ as much as they can differ ;
any part of the soma may show a sexual differ-
ence : teeth in one mammal, skull in another ;
feathers of the tail in one bird, those of the neck
in another, and so on. But in all cases such
unisexual characters correspond to their functions
or use in habits and instincts which are asso-
ciated, but only indirectly, with sexual produc-
tion. These habits are as diverse and as
irregular in their distribution as the characters.
The cocks of common fowls and of the Phasi-
anidae generally are polygamous, fight with each
other for the possession of the females, and take
no part in incubation or care of the young, and
they differ from the hens in their enlarged

330

Cunningham's Theory

brilliant plumage, spurs on the legs, and combs,
wattles, or other excrescences on the head. In
the Columbidae per contra the males are not
polygamous, but pair for life, the males do not
fight, and share equally with the females in
parental duties.

" Corresponding with this contrast of sexual
habits is the contrast of sexual dimorphism,
which is virtually absent in the Columbidse.

" I think, then, the only scientific explanation
is that the difference of habits is the cause of
the sexual dimorphism, and that the special
sexual habits which occur in some species but
not in others are the causes of the sexual char-
acters. . . . The habits in question always involve
certain definite stimulations applied to those parts
of the body whose modification constitutes the
somatic sexual characters. The stimulations are
confined, as the characters are confined, to one
sex, to one period of life, to one season of the
year, to those animals which have the characters,
to those parts of the body which are modified."
Mr Cunningham believes that these stimulations
cause hypertrophy or excessive growth of the
part affected, and that this peculiarity is trans-
mitted to the offspring. And thus he supposes
all the ornaments and excrescences of the males
of various species to have arisen.

As evidence in favour of his view, he points
out that these excrescences are, in many species,

The Making of Species

not only functionless but absolutely injurious, as
in the case of the comb and wattles of the jungle
cock and his domestic descendants, which merely
serve as a handle for enemies to seize.

Cunningham asserts that the only objection to
his theory is the dogma that acquired characters
cannot be inherited. This assertion is, however,
not correct. It is, indeed, a very serious objection
that all the evidence available seems to show that
acquired characters are not inherited, but this is
by no means the only difficulty.

Before mentioning these further objections, let
us say a word on the subject of the inheritance
of acquired characters. Mr Cunningham himself
compares the formation of a splint or spavin
in a horse as the result of special strain, to
the acquisition of secondary sexual characters.
Unfortunately for Cunningham's theory, but
fortunately for mankind in general, spavined
horses and mares do not beget spavined off-
spring. If, then, spavin is not inherited, is it
not unreasonable to assert that the thickening
of the bone that develops on the head of a
butting animal is inherited?

Another objection to Cunningham's theory is
that many birds which show off their plumage
most vigorously possess no ornamental plumes.
As Howard has recorded, many of our dull-
coloured British warblers show off in the same
manner as bright-coloured birds do. If the

332

Existing Theories not Satisfactory

exercise has caused the development and in-
heritance of plumes in some species, why not
in the others ?

Again, Cunningham is not correct in saying
that sexual dimorphism is " virtually absent " in
the Columbidae. Few birds display so striking a
sexual dimorphism as the Orange Dove (Chryscena
victor) of Fiji, in which the male is bright orange
and the hen green. We have already cited the
case of the curious sexually dimorphic red turtle-
dove. Now, the courting attitudes and actions
of this species are precisely the same as those of
other allied turtle-doves ; why, then, have these
exercises caused only one species to become
sexually dimorphic ?

Our survey of the more important attempts
which have been made to explain the phenomena
of sexual dimorphism leads to the conclusion that
these still require elucidation. We have weighed
each theory in the balance and found it wanting.

The outstanding feature of sexual dissimilarity
is the apparently haphazard manner of its occur-
rence.

We have already alluded to the case of the
doves in India. In that country four species are
widely distributed — namely, the Spotted Dove
(Turtur suratensis), the Ring or Collared Dove
( Turtur risorius), the Little Brown Dove ( Turtur
cambayensis\w\& the Red Turtle-dove (CEnopopelia

333

The Making of Species

tranqebarica). The habits of all these four
species appear to be identical, nevertheless in
the first three the sexes show little or no dis-
similarity in outward appearance, while in the
last the sexual dimorphism is so great that the
cock and hen were formerly thought to belong to
different species.

Another very curious case is that of the South
American geese of the genus Chloephaga, in
which some species, as the familiar Upland or
Magellan Goose of our parks (C. magellanica),
have the sexes utterly unlike, while in others, as
the Ruddy-headed Goose (C. rubidiceps\ they are
quite similar to each other.

The ducks furnish us with another very good
example of the apparently haphazard nature of
sexual dimorphism. In the Common Mallard or
Wild Duck (Anas boscas] the cock is far more
showily coloured than the hen, but in all the
species most nearly allied to it the males are as
inconspicuous as the females, e.g. in the Indian
Spotted-bill (Anas pozcilorhynchd), the Australian
Grey Duck (A. superciliosa), the African Yellow
Bill (Anas undulata), and the American Dusky
Duck (A. obscura). As the dusky duck inhabits
North America, where the mallard is also found,
the case is particularly striking.

Among mammals the lion and the tiger and the
sable and roan antelopes (Hippotragus niger and
H. equinus) furnish familiar examples of nearly-

334

Hormones

related species, in one of which the sexes are
alike and in the other dissimilar in appearance.

Another important point to be borne in mind
is the intimate correlation that exists between the
reproductive organs and the general appearance
of the organism, more especially of the secondary
sexual characters. These last, in most cases, do
not show themselves until the maturity of the
sexual organs. The well-known effects of castra-
tion illustrate this connection. Again, females in
which the reproductive organs have ceased to be
functional often assume male characters.

It has lately been proved by experiment that,
in many cases at any rate, the development of
the ornaments, etc., characteristic of the sexes
is due to the secretion by the sexual cells of
what are known as hormones — that is to say,
secretions which excite development of the
secondary sexual characters. The tendency to
produce the external characteristics of the sex
to which an organism belongs is inherited, but
the actual development thereof is in many cases
dependent on the secretion of these hormones.
Accordingly, if a male individual be completely
castrated it ceases to develop the external
characters of its sex. The evidence upon which
the doctrine of hormones is based is admirably
summarised in the above - quoted paper by
Cunningham. Into this evidence we cannot
go. It must suffice that the doctrine is quite

335

The Making of Species

in accordance with all the observed results of
castration.

It is worthy of notice that the various features
which characterise the sexes in sexually dimor-
phic animals are not associated with any par-
ticular organ or parts of the body, nor do they
necessarily affect the same part in allied species.
" We cannot say," writes J. T. Cunningham,
" that any part of the soma (i.e. the body tissue) is
specially sexual more than another part, except
that such differences between the sexes are
usually external. They usually affect the skin,
and especially epidermic appendages, and the
superficial parts of the skeleton, or whole limbs
and appendages ; or the difference may be one
of size of the whole soma. In mammals and
birds the male is often the larger, sometimes very
much so, but there are cases in which the female
is larger. There is no general rule."

Another important point is, that females,
although they themselves show no trace of the
male character, are capable of transmitting it to
their progeny. This can be proved by crossing
a hen pheasant with a cock barn-door fowl ; the
male offspring of the union display the plumes so
characteristic of the cock pheasant. Theise can-
not have been derived from the barn-door-fowl
father ; they must have come from the dull-
coloured hen pheasant.

In this connection we may mention the curious
336 '

Eye-colour, Comb, and Spurs

fact recorded by Bonhote, on page 245 of the
Proceedings of the Fourth International Ornitho-
logical Congress, that in the case of ducks de-
scended from crosses between the pintail, the
mallard, and the spotbill, the drakes in full
breeding plumage showed a mixture of pintail
and mallard characteristics, while, in their non-
breeding plumage, the colouring of the spotbill
is predominant.

An important point, and one which does not
seem to have been pointed out by any zoologist,
is that eye-colour, comb, and spurs in birds and
horns in mammals do not stand in the same
relation to the sexual organs as do the other
external characteristics. For example, the cas-
trated Nilgai (Boselaphus tragocamelus) acquires
horns, but not the characteristic male colour.
In the common Indian Francolin Partridge
{Fr anco Linus pondicerianius), the cock differs from
the hen only in the possession of spurs. The
same applies to the various species of Snow
Cock ( Tetraogallus}. There is a breed of game-
cocks which display plumage like that of the
hen, but such birds have the comb and spurs
developed as in normally feathered cocks.

The white eye of the white-eyed Pochard
Drake (Nyroca africana), and the yellow eye of
the cock Golden Pheasant (Chrysolophus pictus],
which are purely male characters, show them-
selves earlier than the male plumage. Occasion-
v 337

The Making of Species

ally a hen golden pheasant assumes the plumage
of the cock, but she never acquires the yellow
eye.

Many birds when kept in captivity lose some
of the beauty of their plumage, and this is
usually attributed to the sexual organs becoming
impaired and reacting on the somatic tissue.
But this explanation cannot in all cases be the
correct one, because the linnet, although losing
the male plumage in captivity, lives long and
well in a cage and breeds readily with hen
canaries.

Another curious fact is that the male plumage
sometimes appears pathologically in hen birds,
more especially in those which have become sterile
from age or disease. This phenomenon occurs
comparatively frequently in the gold pheasant,
and more rarely in the common pheasant, the
fowl, and the duck.

Phenomena such as these seem to suggest
that in some cases the bright colours of the male
may be pathological, that the hormones which
the male sexual cells secrete may exercise an
injurious effect on the somatic or body tissues.
Decay is known to be accompanied by the
production of brightly coloured pigment in the
case of leaves. Finn suggests that the white
plumage which the cock paradise fly -catcher
assumes in the fourth year of his existence may
be a livery of decay, a sign of senility.

338

The Four Kinds of Mutations

It is our belief that sexual dimorphism arises
frequently, if not invariably, as a mutation.
Mutations may be of four different kinds.

Those which appear only, or especially, in con-
junction with the male organs, for example,
whiteness in domesticated geese allowed to
breed indiscriminately.

Those which appear only, or especially, in con-
junction with the female organs ; mutations of
this description appear to be very rare, but it
may be noted that in fowls allowed to breed
indiscriminately, as in India, completely black
hens are common, but completely black cocks
are rarely, if ever, seen. This indicates an
association between blackness and femininity.

Those which appear in the same manner in
both sexes. The great majority of mutations
appear to be of this kind.

Lastly, those that appear in both sexes but
take a different form in the case of the two
sexes ; thus in cats a mutation has given rise
to sandy males and tortoise-shell females. The
mutation which has produced the black-winged
peacock shows itself in the form of a black wing
in the cock, while it causes the plumage of the
hen to be grizzly white.

We shall deal with the phenomenon of correla-
tion at some length in the next chapter. It is a
subject to which sufficient attention has not been
paid. Even as certain characters are correlated

339

The Making of Species

in certain species, so in some cases are certain
characters correlated with sex.

Why this should be so we are not in a position
to say ; this, however, does not affect the indis-
putable fact that such correlation does exist.

Physicians in the course of their practice
sometimes come across very curious cases of
correlation in human beings.

" It is," writes Thomson (Heredity, p. 290),
" an interesting fact that an abnormal element in
the inheritance may find expression in the males
only or in the females only. If we could under-
stand this we should be nearer understanding
what sex really means.

" Haemophilia, or a tendency to bleeding, is
a heritable abnormality, partly associated with
weakness in the blood-vessels, which do not
contract as they should and are apt to break,
and partly connected with a lack of coagulating
power in the blood. It is usually confined to
males. But as it passes from a father through a
daughter to a grandson, and so on, it must be a
latent part of the germinal inheritance of the
females, though for some obscure physiological
reason it fails to find expression in them, or has
its expression quite disguised. Colour-blindness
or Daltonism has been recorded (Horner) through
the males only of seven generations. Dejerine
cites another case (fide Appenzeller) in which all
the males in a family history had cataract through

34°

Unilateral Transmission

four generations. There are other instances of what
is sometimes awkwardly called the unilateral trans-
mission of abnormal qualities. Edward Lambert,
born in 1717, is said to have been covered with
1 spines.' His children showed the same
peculiarity, which began to be manifest from
the sixth to the ninth month after birth. One
of his children grew up and handed on the
peculiarity to another generation. Indeed, it is
said to have persisted for five generations, and
in the males only — unilateral transmission."

In our view, these abnormalities are of such a
kind that they are only possible in connection
with the male organ ; in other words, they are
mutations of the first of the four kinds cited
above — those which appear only in connection
with the male organ.

It is a curious fact that the general rule in
nature seems to be that the male is ahead of the
female in the course of evolution. The sexes
may be alike at a given period in the life-history
of the species. Presently a mutation appears
which is confined to the male alone ; thus arises
the phenomenon of sexual dimorphism. The
next step in the evolution of the species is
frequently a mutation on the part of the female
which brings her once again into line with the
male, and so the sexual dimorphism disappears,
for a time at any rate, A good example of this
is furnished by the sparrows ; in the common

The Making of Species

sparrow of a large part of Africa (Passer
swainsonz) both sexes are very plain, like the
hen of the house-sparrow ; in this species (P.
domesticus), as every one knows, the cock, though
by no means brilliant, is noticeably handsomer
than his mate ; while in the Tree-sparrow (P.
montanus) both sexes have a plumage of mascu-
line type, much like that of the cock house-
sparrow.

If we consider in conjunction with one another
the various facts we have cited above, we begin
to grasp the nature of the phenomena of sexual
dimorphism.

Let us consider an imaginary case of a defence-
less little bird which builds an open nest. Let
us suppose that it is inconspicuously plumaged.
Now suppose that a mutation of the first kind
shows itself, a mutation which affects the cock
only and makes him more conspicuous. Let
us further suppose that the cock does not
share in the duties of incubation. It is quite
possible that, in spite of this apparently unfavour-
able mutation, the species may survive, for, as
we have seen, it does not affect the hen, and
she, since she alone incubates, stands the most
in need of protective colouring. Moreover, as
Stolzmann has suggested, the species can pos-
sibly afford to lose a few males. But suppose
that both cock and hen share in the duties of
incubation, it is then quite likely that the muta-

342

Greater Value of Females

tion will cause the species to become extinct,
by the elimination of all the males. Or, let us
suppose that the mutation in the direction of
showy plumage affects both sexes, then in such
a case the species will almost certainly become
extinct. If, however, the hypothetical species
nested in holes in trees, it is quite possible that
it might survive notwithstanding its showy
plumage.

Whether, as Wallace suggests, the hen does
most of the incubating, and is exposed to special
danger when sitting on her eggs in an open nest,
or, as Stolzmann urges, it is of advantage to the
species that there should not be too many males,
the result is the same, that the species can afford
to allow the cock to be more gaily attired than
the hen. In either case the colouration of the
cock becomes a matter of comparatively little
importance to the species, and this, coupled with
the fact that the male tends to mutate more
readily than the female, will explain why, in
most species which exhibit sexual dimorphism,
it is the cocks that are the more conspicuous.
In certain species the cocks alone incubate, and
these then become more important than the
females to the race, so that they have not been
permitted to become showy, while the hens have
been allowed more freedom in this respect.
The extreme variability of the Ruff (Pavon-
cella pugnax] in breeding plumage points to the

343

The Making of Species

fact that his colour is a matter of comparative
indifference to the species; in consequence plenty
of latitude is allowed to his tendency to vary.

Our view, then, is that evolution proceeds by
mutations, which may be large or small.

The mutation is the result of a rearrangement
in part or parts of the fertilised egg, and this re-
arrangement shows itself in the adult organism as
a change in one or more of its characteristics.
The mutation may be correlated with only one
of the sexual organs, and when this is the
case, it gives rise to the phenomenon of sexual
dimorphism. The appearance in the adult of
certain, if not of all, characteristics is affected by
causes other than the nature of the biological
molecules from which they are derived. The
tendency to develop in a certain direction is
there, but something else, such as the secretion
of hormones from the sexual cells, is frequently
necessary to enable a given tendency to fully
develop itself. Thus it is that castration often
affects the bodily appearance of those animals
operated on. When a mutation appears, natural
selection decides whether or not it shall persist.

344

CHAPTER VIII

THE FACTORS OF EVOLUTION

Variation along definite lines and Natural Selection are un-
doubtedly important factors of evolution — Whether or not
sexual selection is a factor we are not yet in a position to decide
— Modus operandi of Natural Selection — Correlation an im-
portant factor — Examples of correlation — Correlation is a
subject that requires close study — Isolation a factor in evolu-
tion— Discriminate isolation — Indiscriminate isolation — Is
the latter a factor? — Romanes' views — Criticism of these —
Indiscriminate isolation shown to be a factor — Summary of
the methods in which new species arise — Natural Selection
does not make species — It merely decides which of certain
ready-made forms shall survive — Natural Selection compared
to a competitive examination and to a medical board — We
are yet in darkness as to the fundamental causes of the
Origin of Species — In experiment and observation rather
than speculation lies the hope of discovering the nature of
these causes.

WE have so far considered three factors
of evolution. The first of these is
the tendency of organisms to vary
along definite lines. This is a most
important factor, because, unless variation occurs
in any given direction, there can be no evolution
in that direction. Variations are the materials
upon which the other factors, or causes, of evolu-
tion work. The second great factor is natural
selection. Natural selection may be compared

345

The Making of Species

to a builder, and variations to his materials.
The kind of building that a builder can construct
depends very largely on the material supplied to
him. The Forth Bridge could not have been
built had those who constructed it had no material
given them but bricks and mortar. Wallaceians
regard natural selection as a builder who is sup-
plied with every kind of building material — stone,
bricks, wood, iron, aluminium, in any quantities
he may desire. They therefore regard natural
selection as the one and only cause which deter-
mines evolution. This, however, is a wrong
idea. Natural selection should rather be likened
to a builder who is supplied with a limited variety
of building materials, so that considerable restric-
tions are imposed on his building operations.
The doors, windows, fireplaces, etc., are supplied
to him ready-made. He merely selects which of
these he will use for each building.

The third factor of evolution which we have
considered is sexual selection. As we have seen,
sufficient attention has not been paid to this sub-
ject, so that we are not yet in a position to say
how much, if any, influence it has exercised on
the course of evolution.

In addition to these three factors, there are,
we believe, some others. Before proceeding to
a consideration of these, it is important to study
carefully the modus operandi of natural selection,
or, in other words, the nature of the struggle for

346

The Struggle for Existence

existence, as many of the statements contained
in recent books on evolution seem to us to be
based upon a mistaken conception of this
important factor.

As usual, Darwin's disciples have failed to
improve upon the account he gave of the nature
of the struggle for existence. This is set forth in
Chapter III. of the Origin of Species.

" The causes," writes Darwin (new edition,
p. 83), " which check the natural tendency of
each species to increase in number are most
obscure. Look at the most vigorous species ;
by as much as it swarms in numbers, by so much
will it tend to increase still further. We know
not exactly what the checks are even in a single
instance." This is perfectly true. Nevertheless
elaborate theories of protective and warning
colouration and mimicry have been built up on
the tacit assumption that the checks to the multi-
plication of all, or nearly all, species are the
creatures which prey upon them. Possibly no
Wallaceian asserts this in so many words, but it
is a logical deduction from the excessive pro-
minence each one gives to the various theories of
animal colouration ; for, if the chief foes of an
organism are not the creatures which prey upon
it, how can the particular shade and pattern of
its coat be of such paramount importance to it ?

We shall endeavour to show that there are
checks on the increase of a species far more

347

The Making of Species

potent than the devastation caused by those
creatures which feed upon it. Let us, however,
first briefly set forth some of the checks on
the multiplication of organisms which Darwin
mentions in the Origin of Species.

" Eggs, or very young animals," he says,
"seem generally to suffer the most, , but this is
not invariably the case." This is, as we have
already insisted, a most important point to be
borne in mind, especially when considering the
various current theories of animal colouration.
When once the average animal has become adult
its chances of survival are enormously increased.

A second check mentioned by Darwin is the
limitation of food supply. <c The amount of food
for each species," he writes (p. 84), " of course
gives the extreme limit to which each can
increase ; but very frequently it is not the
obtaining food, but the serving as prey to other
animals, which determines the average numbers
of a species. Thus there seems to be little
doubt that the stock of partridges, grouse, and
hares on any large estate depends chiefly on
the destruction of vermin. . . . On the other
hand, in some cases, as with the elephant and
rhinoceros, none are destroyed by beasts of
prey."

We are inclined to think that neither the food
limit nor the beasts of prey are a very important
check on the multiplication of organisms. The

348

Checks on Increase

lion, for example, was never so numerous as to
reach the limit of its food supply. Before the
white man obtained a foothold in Africa vast
herds of herbivores were to be seen in those
districts where lions were most plentiful. This
is a most important fact, for, if the numbers of
a species are not determined by those of the
animals that prey upon it, the particular colour of
an organism is probably not of any direct im-
portance to it. This cuts away the foundation
of some of the generally accepted theories of
animal colouration.

" Climate," writes Darwin (p. 84), "plays
an important part in determining the average
numbers of a species, and periodical seasons of
extreme cold or drought seem to be the most
effective of all checks. I estimated (chiefly from
the greatly reduced numbers of nests in the
spring) that the winter of 1854-55 destroyed
four-fifths of the birds in my own grounds,
and this is a tremendous destruction when
we remember that 10 per cent, is an extra-
ordinarily severe mortality from epidemics with

man."

In our opinion, Darwin did not lay nearly
enough stress upon the importance of climate as
a check on the increase of species. We have
seen that he stated his belief that it is the most
effective of all checks. But even this is not a
sufficiently strong statement of the case. It

349

The Making of Species

seems to us that before this check all other
checks pale into insignificance.

Darwin failed to notice the potent effects of
damp. Damp is more injurious to most species
than even cold or drought, as every one who has
tried to keep birds in England knows. All en-
tomologists are aware how harmful damp is to
insects. Caterpillars seem to take cover under
leaves to avoid damp rather than to hide them-
selves from birds, since these make a point, when
searching for insects, of invariably looking care-
fully under leaves.

It is a well-known fact that a wet winter in
England causes much mortality among rabbits.
The increase of the rabbit in Australia is usually
attributed to the fact that the little rodent has
not so many predatory creatures to contend with
there as it has in Europe. This is not so. In
Australia the rabbit has to fight against eagles,
other large birds of prey, carnivorous marsupials,
feral cats, monitor lizards and large snakes, to
say nothing of the well-organised and persistent
attacks of man.

Were predacious creatures the most important
foes of the rabbit it would never have obtained a
firm foothold in Australia. Damp appears to be
its chief enemy. In Australia this does not exist.
Hence the remarkable increase of the species.
Stronger evidence it would not be possible to
advance of the potency of damp as a check on

Checks on Increase

the increase of a species and of the comparative
powerlessness of the attacks of raptorial creatures.

The failure of the sandgrouse to establish a
footing in England is, we believe, due to the fact
that it is constitutionally unfitted to withstand our
damp climate.

The camel is an animal that revels in dry
habitats, hence the difficulty of keeping camels
in damp Bengal, although they seem to thrive
well enough in the drier parts of India.

"When a species," writes Darwin (p. 86),
" owing to highly favourable circumstances, in-
creases inordinately in numbers in a small tract,
epidemics — at least, this seems generally to occur
with our game animals — often ensue ; and here
we have a limiting check independent of the
struggle for life. But even some of these so-
called epidemics appear to be due to parasitic
worms, which have from some cause, possibly
in part through facility of diffusion amongst
the crowded animals, been disproportionately
favoured : and here comes in a sort of struggle
between the parasite and its prey."

Thus inadequately does Darwin deal with that
bar to the increase of organisms, which is only
second in importance to the effect of climate.
The check occasioned by disease and parasites
is one to which naturalists have as yet paid but
little attention. The result is a very general
misunderstanding of the true nature of the

351

The Making of Species

struggle for existence, in other words, of the
modus operandi of natural selection.

The tsetse-fly in Africa is a far more important
check on the increase of some animals than the
lions and other beasts of prey. There are in
that continent large tracts of country, known as
tsetse-fly belts, in which neither horse, nor ox,
nor dog can exist. If races of these animals
were to arise which could withstand the bite of
the tsetse-fly, these species might increase more
rapidly than the rabbit in Australia has done,
nor would it matter if the creatures in question
were bright crimson, or any other conspicuous
colour.

Take the case of the lion in Africa. The chief
bar to the increase in numbers of this species
appears to be the teething troubles to which the
whelps are liable. Now suppose that a mutation
were to occur in the lion. Suppose that several
members of a litter were all bright blue, and that
these suffered from no teething troubles. They
would probably all grow up, and although at
some disadvantage as hunters on account of their
conspicuous colouring, they would nevertheless
probably increase at the expense of the normally
coloured lions, because of the immunity of their
offspring from death from teething troubles.
Zoologists would then be at a loss to explain
their bright colouring. We should have all manner
of ingenious suggestions raised, namely, that in the

352

Checks on Increase

moonlight these creatures were really not at all
conspicuous, indeed that they were obliteratively
coloured. In other words, a totally wrong ex-
planation of their colouring would be given and
accepted. It is our belief that many of the
explanations put forward and accepted of the
colouration of existing species are wide of the mark.

As all bee-keepers are aware, the disease
known as foul-brood works more havoc among
their bees than all the insectivorous creatures
put together.

Similarly throat disease among wood-pigeons
does more towards keeping their numbers down
than all the efforts of predacious birds.

A check on multiplication not mentioned by
Darwin is that which is sometimes imposed by
the individuals of the species on one another.
Thus, in some animals, as, for example, the
hyaena, the male occasionally devours his own
young ones.

A check of a similar nature results from the
habit which the Indian House Crow (Corvus
splendens) has of interrupting the pairing opera-
tions of its neighbours.

We are now in a position to sum up briefly
the more important requisites for success in the
struggle for existence.

These are not so much specialised structure as
courage, a good constitution, mental capacity and
prolificacy.

z 353

The Making of Species

Few animals possess all these characteristics
in a pre-eminent degree, for, to use the words of
Mr Thompson Seton, " Every animal has some
strong point or it could not live, and some weak
point or the other animals could not live."
Courage may be of two kinds — active courage,
like that of the Englishman, or passive courage,
like that of the Jew.

As D. Dewar has said : In the struggle for
existence, "An ounce of good solid pug-
nacity is worth many pounds of protective
colouration."

It is of course possible for an animal to possess
too much courage. An excessive amount of
courage will often cause a creature to fight
unnecessary battles, which may lead to its pre-
mature death. This is perhaps the reason why
the pugnacious black form of the leopard is not
more numerous.

Under a good constitution we must include
the power of resisting the rigours of climate,
more especially damp, the ability to resist
disease, and the enjoyment of a good digestion.
When from any cause the normal food of a
species becomes scarce, the members of that
species will have to starve or supplement the
normal diet with food of an unusual nature ; and
those that are endowed with a good digestion
will be able to digest the new food and thus
survive, while those which cannot assimilate food

354

Attributes of Successful Species

to which they are unaccustomed will become
emaciated and perish. We see this in every hard
winter in England, when the redwing, which,
unlike other thrushes, cannot thrive on berries, is
the first to die. Most of the more successful
birds — the crows and gulls, for example — are
omnivorous — that is to say, they are able to
digest all manner of food.

Under mental capacity, we would include
cunning and sufficient intelligence to adapt one-
self to changed conditions. It is largely through
man's superior mental capacity that he has
become the dominant species. It is true that
he displays also courage and a good constitution,
being able to adapt himself to life under the most
diverse conditions ; but this is, of course, in part
due to his mental capacity, which enables him
to some extent to adapt his environment to
himself.

The advantages of prolificacy are so apparent
that it is unnecessary to dilate upon them.
Nearly as important as excessive fertility is the
ability on the part of the parents to look after their
young ones.

Every successful species possesses in a special
degree at least one of the above attributes. It
is interesting to take in turn the various species
which are most widely distributed and consider
to what extent they possess these several
qualities.

355

The Making of Species

Let us now consider a factor in evolution
which is nearly as important as natural selection
itself — we allude to the phenomenon of correlation.

CORRELATION

We may define correlation as the inter-
dependence of two or more characters. This
phenomenon is far more common than the
majority of naturalists seem to think. It very
frequently happens that one particular character
never appears in an organism without being
accompanied by some other character which we
should not expect to be in any way related to it.

Darwin called attention to this phenomenon.
"In monstrosities," he writes, on page 13 of the
Origin of Species (new edition), "the correlations
between quite different parts are very curious,
and many interesting instances are given in
Isidore Geoffroy St Hilaire's great work on this
subject. Breeders believe that long limbs are
almost always accompanied by an elongated head.
Some instances of correlation are quite whimsical :
thus cats which are entirely white and have blue
eyes are generally deaf; but it has been lately
stated by Mr Tait that this is confined to the
males.

" Colour and constitutional peculiarities go
together, of which many remarkable cases could
be given among animals and plants. From the

356

Correlation

facts collected by Heusinger, it appears that
white sheep and pigs are injured by certain
plants, whilst dark-coloured individuals escape.
Professor Wyman has recently communicated to
me a good illustration of this fact : on asking
some farmers in Virginia how it was that all
their pigs were black, they informed him that
the pigs ate the paint-root (Lachnanthes), which
coloured their bones pink, and which caused
the hoofs of all but the black varieties to drop
off; and one of the 'crackers' (i.e. Virginia
squatters) added, ' we select the black members
of a litter for raising, as they alone have a good
chance of living.'

" Hairless dogs have imperfect teeth ; long-
haired and coarse-haired animals are apt to
have, as is asserted, long or many horns ; pigeons
with feathered feet have skin between their outer
toes ; pigeons with short beaks have small feet,
and those with long beaks large feet.

" Hence, if man goes on selecting, and thus
augmenting, any peculiarity, he will almost cer-
tainly modify unintentionally other parts of the
structure, owing to the mysterious laws of the
correlation of growth."

The great importance of the principle of the
correlation of organs is, that natural selection
may indirectly cause the survival of unfavourable
variations, or of variations which are of no
utility to the organism, because they happen to

357

The Making of Species

be correlated with organs or structures that are
useful.

Physiologists insist more and more upon the
close interdependence of the various parts of the
organism. All recent researches tend to show
that each of the organs has, besides its primary
function, a number of subordinate duties to per-
form, and that the removal of one organ reacts
on all the others.

In face of these facts we should have expected
those zoologists who have followed Darwin to
have paid very close attention to the subject of
correlation. As a matter of fact, the phenomenon
seems to have been almost completely neglected.
This is an example of the manner in which the
superficial theories which to-day command wide
acceptance have tended to bar the way to
research.

There seems to be, in the case of some organ-
isms, at any rate, a distinct correlation between
their colouring and their constitution or mental
characters. For example, the black forms of the
cobra, the leopard, and the jaguar are notoriously
bad-tempered.

" There is," writes Col. Cunningham, on p.
344 of Some Indian Friends and Acquaintances,
" much variation in the temper of different
varieties of cobras, and, as is often so noticeable
among other sorts of animals, there would seem
to be a distinct correlation between darkness of

358

Correlation

colour and badness of temper. It is probably
in part owing to a recognition of this that the
cobras ordinarily seen in the hands of the so-
called snake charmers are of a very light colour,
although the choice may also be to some extent of
aesthetic origin, seeing that the paler varieties are
specially ornamental, due to the brilliancy of their
markings and the great development of their
hoods." It would thus appear that there is also
a correlation between the colour of the cobra and
the size of its hood.

Hesketh Pritchard informs us, in Through the
Heart of Patagonia, that the Gauchos assert that
a " picaso " colt — that is to say, a black one with
white points — is the reverse of docile. Similarly,
black mice are said to be very hard to tame.

We have already called attention to the im-
portance of courage and the power of resisting
the rigours of climate in the struggle for exist-
ence. It is apparently because black is so fre-
quently correlated with courage that it is seen
comparatively often in nature, in spite of the fact
that it is a very bad colour as regards protection
from enemies. Those birds and beasts which are
black are usually thriving species. The domi-
nance of the crow tribe is a case in point. Crows,
it is true, are not really courageous, but they are
dangerous owing to their gregarious habits, and
are dreaded by other creatures on account of
their power of combination. In Birds of the

359

The Making of Species

Plains, D. Dewar records an instance of a num-
ber of crows killing in revenge so powerful a
bird as the kite.

Since very many species seem to throw off
melanistic variations, it may perhaps be asked,
How is it that more black species do not exist ?

The reply is twofold. In the first place, it is
quite likely that in some organisms black varia-
tions are not correlated with courage or extreme
pugnacity, and when such is the case the melan-
istic varieties will be more likely to be exter-
minated by foes, on account of their conspicuous-
ness. It must be remembered that, other things
being equal, the inconspicuously coloured organ-
ism has a better chance of survival than the
showily coloured one. This is, of course, a very
different attitude from that which insists on the
all-importance to animals of protective coloura-
tion. Secondly, it is not difficult to see how too
much courage may be fatal to an animal in lead-
ing it to take risks which a more timid creature
would refrain from doing. This, as we have
already suggested, is probably the reason why
the black panther is so scarce. The black colour
is readily inherited, so there must be some cause
which tends to kill off the black varieties of the
panther.

Lest it be thought the idea that excessive
courage and pugnacity are harmful is mere fancy,
let us quote from the account of the nesting

360

Correlation

habits of the White-rumped Swallow ( Tachycineta
leiicorrhoa) given by Mr W. H. Hudson on p. 32
of Argentine Ornithology. He says that no
matter how many nesting sites are available,
there is always much fighting amongst these
birds for the best places. " Most vindictively,"
he writes, " do the little things clutch each other,
and fall to the earth twenty times an hour, where
they often remain struggling for a long time,
heedless of the screams of alarm their fellows set
up above them ; for often, while they thus lie on
the ground punishing each other, they fall an
easy prey to some wily pussy who has made her-
self acquainted with their habits."

We have already emphasised the importance
to many species of possessing the power of resist-
ing the effects of damp. In the case of some
organisms favourable variations in this direction
may possess a greater survival value than those
in the shape of greater speed or physical strength.

Now, if there be any correlation between the
power of resisting damp and the colour an animal
bears, it is quite probable that animals of this
colour, whether or no it be conspicuous, are likely
to survive in preference to those who are more
protectively coloured. There is some evidence
that in certain cases, at any rate, resistance to
climate is correlated with colour peculiarities.
For example, some fanciers assert that yellow-
legged poultry resist cold and damp better than

361

The Making of Species

those whose legs are not yellow. Fowls which
have yellow legs have also yellow skins. In this
connection the almost universal assumption of
orange feet by domestic guinea-fowls is sig-
nificant. Normally the feet of these birds are
black, and their natural African habitat is a dry
one.

A grey or white colour appears to be corre-
lated with resistance to cold. In birds this may
perhaps be explained by the fact that the feathers
in some light-coloured varieties are longer than
in those of normally-coloured ones. Thus mealy-
coloured canaries have longer feathers than
brightly-coloured ones.

The Arctic Skua, having no enemies to fear,
stands in no need of protective colouration. It
would therefore seem that the white-breasted
form of this bird becomes more numerous as it
nears the north pole, not because of the closer
assimilation of its plumage to the colour of the
snowy surroundings, but because the bird has to
resist the greater degree of cold the farther north
it finds itself. Similarly, in the region of the
south pole the albino form of the Giant Petrel
(Ossifraga gigantea) becomes common. Both
these birds are themselves predatory and not
liable to be preyed upon.

The curious china-white legs of some desert
birds — as, for example, coursers and larks — would
seem to indicate a power of resisting the hot rays

362

Correlation

radiating from the sand on which these creatures
dwell.

White quills do not wear well either in
domestic birds or in wild albinos. This may
explain why it is that when a white wild species
of bird has any black in its plumage the black is
almost invariably on the tips of the wings.

White quill-feathers are one of the commonest
variations observed in domesticated birds, never-
theless they are as rare as complete whiteness
among birds in their natural state.

A chestnut or bay colour in mammals appears
to be correlated with a high rate of speed, as in
the thoroughbred horse. This perhaps explains
why so many of the swiftest species of antelope,
such as the hartebeests and sassaby (Damaliscus
lunatus], are chestnut bay in colour. It is further
a remarkable fact that in the Black-buck (Antilope
cervicapra] and the Nilgai (Boselaphus trago-
camelus] the females, which are faster than the
males, are not black or grey like their respective
males, but reddish.

Wild turkeys are bronze ; tame ones are black
more often than any other colour. This may be
due to the fact that in them nigritude is cor-
related with the power to resist damp. Among
human beings those races which live in very
swampy districts are often intensely black.

It is a significant fact that those domestic
animals which are bred for speed or for fighting

363

The Making of Species

purposes do not assume all the varied hues that
characterise those that are allowed to breed in-
discriminately. Racehorses, greyhounds, and
homing pigeons furnish examples of this. Even
more remarkable is the case of the Indian Aseel
or game-cock. This is bred purely for fighting
purposes, and is required to display extraordinary
powers of endurance, since the spurs are cut off
in order to prolong the fight. Thus it is that
this Indian race of game-cocks shows little varia-
tion when compared with the English breed,
which fights in a more natural manner. The
hens of the Indian form seem never to show the
colouration of the wild jungle fowl, although the
cocks may do so. It would appear that hens
having the colouration of their wild ancestors
cannot breed cocks possessed of the requisite
courage. The Aseel is said to be of the highest
courage only when the legs, beak and iris are
white.

There is, we believe, not the least doubt that
many other connections between colour and
various characteristics have yet to be discovered.
It is high time that competent naturalists paid
attention to this subject. A study of the question
will almost certainly throw much light upon many
phenomena of animal colouration which hitherto
have not been satisfactorily explained. It is
quite likely that the sandy hue displayed by
birds and beasts which frequent desert regions

364

Correlation

may be due to a correlation with the power of
withstanding intense dry heat rather than to its
rendering them inconspicuous to their foes.

As other examples of correlation we may cite
the correlation which seems to obtain between
short canine teeth and the absence of a hairy
covering to the body. This phenomenon is
observed both in men and pigs. Hairless dogs
almost invariably have their teeth but poorly
developed.

Darwin called attention to the connection
between a short beak and small feet in pigeons ;
we see the same phenomenon in the dwarf breed
of ducks known as call-ducks.

A curious correlation exists between fowls'
eggs with brown shells and the incubating habit.
Fanciers have long tried in vain to produce a
hen that lays brown eggs without becoming
" broody" at certain seasons.

Among fowls, long legs are invariably cor-
related with a short tail, as is well seen in the
Malay breed. This correlation may explain the
short tails of wading birds. Short-legged fowls,
like Japanese bantams, have long tails, and it is
significant that the short-legged Weka Rails
(Ocydromus) of New Zealand have unusually
long tails for the family. In this connection we
may say that the tail-like plumes of the cranes
are not tail-feathers, but the tertiary feathers of
the wings. As egrets also have long trains of

365

The Making of Species

plumes growing from the back, it cannot be said
that the short tail of the vast majority of the
waders is due to the fact that these birds would
be at a disadvantage were their caudal feathers
long.

ISOLATION

Isolation is a most important factor in the
making of species. It is a factor to which
Darwin failed to attach sufficient importance,
and one which has been to a large extent
neglected by Wallaceians.

We have seen how a species can be improved
or changed by natural selection. All those in-
dividuals which have varied in a favourable
direction have been preserved, and allowed to
leave behind them offspring that inherit their
peculiarities, while those which have not so
varied have perished without leaving behind
any descendants. Thus the nature of the species
has changed. The old type has given place to
a new one. Instead of species A, species B
exists. This is what Romanes has called mono-
typic evolution — the transformation of one species
into another species. But any theory of the
origin of species must be able to answer the
question, Why have species multiplied ? How is
it that species A has given rise to species B, C,
and D, or, while itself continuing to exist, has
thrown off sister species B and C ? How is it

366

Divergence of Character

that in the course of evolution, species have
not been transmuted in linear series instead of
ramifying into branches ? This ramification of
a species into branches has been termed by
Romanes polytypic evolution. It is easy to see
how natural selection can bring about monotypic
evolution, but how can it have effected polytypic
evolution ? To use Darwin's phraseology, how
is it that divergence of character has come about ?
Darwin's reply to this question is (Origin of
Species, p. 1 36), "from the simple circumstance that
the more diversified the descendants from any
one species become in structure, constitution, and
habits, by so much will they be better enabled to
seize on many and widely diversified places in the
polity of nature, and so be enabled to increase in
numbers.

" We can clearly discern this in the case of
animals with simple habits. Take the case of a
carnivorous quadruped, of which the number that
can be supported in any country has long ago
arrived at its full average. If its natural power
of increase be allowed to act, it can succeed in
increasing (the country not undergoing any
change in its conditions) only by its varying
descendants seizing on places at present occupied
by other animals : some of them, for instance,
being enabled to feed on new kinds of prey,
either dead or alive ; some inhabiting new
stations, climbing trees, frequenting water, and

367

The Making of Species

some perhaps becoming less carnivorous. The
more diversified in habits and structure the
descendants of our carnivorous animal become,
the more places they will be enabled to occupy.
What applies to one animal will apply throughout
all time to all animals — that is, if they vary — for
otherwise natural selection can effect nothing."
Darwin was, therefore, of opinion that natural
selection is able to bring about polytypic evolu-
tion. Darwin tacitly assumes, in the illustration
he gives, that the various races of the carnivorous
animal are in some way prevented from inter-
crossing ; for if they interbreed indiscriminately,
these races will tend to be obliterated.

" That perfectly free intercrossing," writes
Professor Lloyd Morgan (on p. 98 of Animal
Life and Intelligence), " between any or all of the
individuals of a given group of animals is, so
long as the characters of the parents are blended
in the offspring, fatal to divergence of character,
is undeniable. Through the elimination of less
favourable variations, the swiftness, strength,
and cunning of a race may be gradually im-
proved. But no form of elimination can possibly
differentiate the group into swift, strong, and
cunning varieties, distinct from each other, so
long as all three varieties freely interbreed, and
the characters of the parents blend with the
offspring. Elimination may and does give rise
to progress in any given group, as a group ; it

368

Isolation

does not and cannot give rise to differentia-
tion and divergence, so long as interbreeding
with consequent interblending of characters be
freely permitted. Whence it inevitably follows,
as a matter of simple logic, that where diver-
gence has occurred, intercrossing and interbreed-
ing must in some way have been lessened or
prevented.

Thus a new factor is introduced, that of
isolation or segregation. And there is no ques-
tioning the fact that it is of great importance,
Its importance, indeed, can only be denied by
denying the swamping effects of intercrossing,
and such denial implies the tacit assumption that
interbreeding and interblending are held in check
by some form of segregation. The isolation
explicitly denied is implicitly assumed."

This is very sound criticism, and is not very
materially affected by the fact that the inter-
crossing of varieties does not necessarily imply
a blending of their characters in the offspring ;
for, as we have seen, some characters do not
blend. No matter what form inheritance takes,
in order that natural selection may cause poly-
typic evolution it must be assisted by isolation
in some form or other.

Thus isolation is an important factor in evolu-
tion, though probably not so important as its
more extreme advocates would have us believe.
Wagner, Romanes, and Gulick have, in insisting
2 A 369

The Making of Species

upon the importance of the principle of isolation,
rendered valuable service to biological science,
but, in common with most men having a new
theory, they have pushed their conclusions to
absurd lengths.

As Romanes has pointed out, isolation may
be discriminate or indiscriminate. " If," he
writes, on p. 5 of vol. iii. of Darwin and after
Darwin, "a shepherd divides a flock of sheep
without regard to their characters, he is isolating
one section from the other indiscriminately ; but
if he places all the white sheep in one field, and
all the black sheep in another field, he is isolating
one section from the other discriminately. Or, if
geological subsidence divides a species into two
parts, the isolation will be indiscriminate ; but if
the separation be due to one of the sections
developing, for example, a change of instinct
determining migration to another area, or occu-
pation of a different habitat on the same area,
then the isolation will be discriminate, so far as
the resemblance of instinct is concerned."

Other names for indiscriminate isolation are
separate breeding and apogamy. Discriminate
isolation is also called segregate breeding and
homogamy. The human breeder resorts to
discriminate isolation in that he separates all
those creatures from which he seeks to breed,
from those from which he does not wish to
breed. Natural selection itself is, therefore, a

Discriminate Isolation

kind of discriminate isolator, since it isolates the
fit by destroying all the unfit, and, inasmuch as
it kills off all those creatures which it fails to
isolate, it differs from other forms of isolation
in preventing the inter-breeding of the unisolated
forms and their giving rise to a different race.
Thus it is clear that natural selection, unless
aided by some other form of isolation, can give
effect to only monotypic evolution. This is a
point on which Romanes rightly insists strongly.

There are several other forms of discriminate
isolation. Sexual selection would be one of
these. Suppose, for example, that in any
species there are large and small varieties
formed, and like tends to breed with like, then
the small individuals will breed with other
small individuals, while large ones will mate
with large ones ; thus two races — a large one
and a small one — will be evolved side by side,
provided, of course, natural selection does not
step in and destroy one of them.

Another kind of discriminate isolation may be
due to the fact that one variety is ready to pair
before the other ; thus two races are likely to
arise which breed at different seasons. It is un-
necessary for us to discourse further on the
subject of discriminate isolation ; those interested
in the subject should read vol. iii. of Darwin
and after Darwin, by Romanes.

It is impossible to deny the importance of

The Making of Species

discriminate isolation as a factor in evolution.
On this there can be no room for disagreement
among biologists. It is when we come to the
subject of indiscriminate isolation that we enter
a region of zoological strife.

Is indiscriminate isolation per se a factor of
evolution ? Romanes, Gulick, and Wagner
assert that it is, Wallace and his adherents
assert that it is not.

As the burden of proof is on the former, they
are entitled to the first hearing.

" We may well be disposed, at first sight,"
writes Romanes (Darwin and after Darwin,
p. 10), " to conclude that this kind of isolation
can count for nothing in the process of evolution.
For if the fundamental importance of isolation in
the production of organic forms be due to its
segregation of like with like, does it not follow
that any form of isolation which is indiscriminate
must fail to supply the very condition on which
all the forms of discriminate isolation depend for
their efficacy in the causing of organic evolution?
Or, to return to one's concrete example, is it not
self-evident that the farmer who separated his
flock into two or more parts indiscriminately,
would not effect any more change in his stock
than if he had left them all to breed together ?
Well, although at first sight this seems self-
evident, it is, in fact, untrue. For, unless the
individuals which are indiscriminately isolated

37*

Indiscriminate Isolation

happen to be a very large number, sooner or
later their progeny will come to differ from that
of the parent type, or unisolated portion of the
parent stock. And, of course, as soon as this
change of type begins, the isolation ceases to be
indiscriminate ; the previous apogamy has been
converted into homogamy, with the usual result
of causing a divergence of type. The reason
why progeny of an indiscriminately isolated
section of an originally uniform stock — e.g. of a
species — will eventually deviate from the original
type is, to quote Mr Gulick, as follows : — ' No
two portions of a species possess exactly the
same average character, and the initial differ-
ences are for ever reacting on the environment
and on each other, in such a way as to ensure
increasing divergence as long as the individuals
of the two groups are kept from inter-
generating.' '

The words of Mr Gulick require close scrutiny.
We may admit that " no two portions of a species
possess exactly the same average character," but
why should the two, if prevented from inter-
breeding yet subjected to similar climatic and
other conditions, present the phenomenon of
" increasing divergence ? " The reason assigned
by Romanes is the " Law " of Delbceuf, which
runs: — UA constant cause of variation, however
insignificant it may be, changes the uniformity of
type little by little, and diversifies it ad in-

373

The Making of Species

finitum" From this "Law" it follows, says
Romanes, on p. 13 of vol. iii. Darwin and after
Darwin, that " no matter how infinitesimally
small the difference may be between the average
qualities of an isolated section of a species com-
pared with the average qualities of the rest of
that species, if the isolation continues sufficiently
long, differentiation of specific type is necessarily
bound to ensue."

This deduction involves two important assump-
tions. The first is, that in each of the separated
portions of the given species there is a constant
cause of variation operating in one direction in
the case of one portion and in another direction
in the case of the other. This assumption is,
unfortunately, not founded on fact. If we were
to take one hundred race-horses and shut them
up in one park and one hundred cart-horses and
shut them up in another park, and prevent the
interbreeding of the two stocks, we should, if
Romanes's tacit assumption be true, see the two
types diverge more and more from one another.
We know that as a matter of fact they will tend,
generation after generation, to become more like
one another. Galton's Law of Regression, of
which we have already spoken, and which is
supported by ample evidence, clearly negatives
this tacit assumption made by Romanes and
Gulick. The second assumption upon which
their reasoning is based is that there is no limit

374

Mollusca of Sandwich Isles

to the amount of change which can be effected
by the accumulation of fluctuating variations ;
but, as we have already seen (on p. 70), there
is a very definite limit and this limit is quickly
reached.

Thus the arguments of Romanes and Gulick
are fundamentally unsound.

But the fact remains, and has to be accounted
for, that, as a general rule, when two portions of
a species are separated, so that they are pre-
vented from interbreeding, they begin to diverge
in character, and the longer they remain thus
separated the greater becomes that divergence.
This is an observed fact which cannot be
gainsaid.

It was the observance of this fact which led
Gulick to insist with such emphasis on the im-
portance of geographical isolation as a factor in
evolution. He discovered that the land mollusca
of the Sandwich Islands fall into a great number
of varieties.

These islands are very hilly, and Gulick found
that each of the varieties is confined not merely
to one island, but to one valley. " More-
over," writes Romanes, on p. 16 of Darwin
and after Darwin, "on tracing this fauna from
valley to valley, it is apparent that a slight
variation in the occupants of valley 2, as com-
pared with those of the adjacent valley i,
becomes more pronounced in the next, valley 3,

375

The Making of Species

still more so in 4, etc., etc. Thus it was possible,
as Mr Gulick says, roughly to estimate the
amount of divergence between the occupants of
any two given valleys by measuring the number
of miles between them. . . . The variations
which affect scores of species, and themselves
eventually run into fully specific distinctions, are
all more or less finely graduated as they pass
from one isolated region to the next ; and they
have reference to changes of form or colour,
which in no one case presents any appearance
of utility."

Hitherto three different attempts have been
made to explain this and allied phenomena :—

1. That it is the result of isolation.

2. That it is the result of natural selection.

3. That it is the result of the action of the

environment on the organism.

Let us consider these in inverse order.

In the case of some organisms, more especially
plants, invertebrates, and fish, the environment
does exert a direct influence on their colouration.
But, as we have seen, the changes in colour, etc.,
thus induced appear never to be transmitted to
the offspring of the organisms so affected. They
disappear when the offspring are removed to
other surroundings.

On the other hand, local races or species—
as, for example, the white-cheeked variety of
sparrow found in India — usually retain their

376

Mollusca of Sandwich Isles

external appearance when the environment is
changed. In the one case the peculiarity is not
inherited ; in the other it is inherited.

The Wallaceian explanation is, of course, that
the phenomenon is the result of natural selection.
There must, say Wallace and his followers, be
some differences in the environment, differences
which we poor human beings cannot perceive,
that have caused the divergence between the
various isolated sections of the species. In the
case of some local species this explanation is
probably the correct one, but we have no hesita-
tion in saying that natural selection is unable
to offer a satisfactory explanation in a con-
siderable number of instances. Take, for
example, the case of the land mollusca of the
Sandwich Islands. Mr Gulick worked for fifteen
years at them, and states that so far as he is able
to ascertain the environment in the fifteen valleys
is essentially the same. " To argue," writes
Romanes, on p. 17 of vol. iii. of Darwin and
after Darwin, " that every one of some twenty
contiguous valleys in the area of the same small
island must necessarily present such differences
of environment that all the shells in each are
differently modified thereby, while in no one
out of the hundreds of cases of modification in
minute respects of form and colour can any
human being suggest an adaptive reason therefor
— to argue thus is merely to affirm an intrinsic-

377

The Making of Species

ally improbable dogma in the presence of a great
and consistent array of opposing facts."

Men of science not infrequently charge the
clergy with adhering to dogma in face of oppos-
ing facts ; it seems to us that many of the
apostles of science are in this respect worse
offenders than the most orthodox of Churchmen.

The example of the mollusca of the Sandwich
Islands is by no means a solitary one. D.
Dewar cited some interesting cases in a paper
recently read before the Royal Society of Arts
(p. 103 of vol. Ivii. of the Society's Journal) :

" The Indian robins present even greater
difficulties to those who profess to pin their faith
to the all-sufficiency of natural selection. Robins
are found in nearly all parts of India, and fall
into two species, the brown-backed (Thamnobia
cambaiensis] and the black-backed Indian Robin
(Thamnobia fulicata). The former occurs only
in Northern India, and the latter is confined to
the southern portion of the peninsula. The hen
of each species is a sandy brown bird with a
patch of brick-red feathers under the tail, so that
we cannot tell by merely looking at a hen to
which of the two species she belongs. The
cock of the South Indian form is, in winter, a
glossy black bird, with a white bar in the wing,
and the characteristic red patch under the tail.
The cock of the northern species, as his name
implies, has a sandy-brown back, which contrasts

378

Local Species

strongly with the glossy black of his head, neck,
and under parts. In summer the cocks of the
two species grow more like one another owing to
the wearing away of the outer edges of their
feathers ; but it is always possible to distinguish
between them at a glance. The two species
meet at about the latitude of Bombay. Gates
states that in a certain zone, from Ahmednagar
to the mouth of the Godaveri valley, both
species occur, and they do not appear to
interbreed.

It seems impossible to maintain that natural
selection, acting on minute variations, has
brought about the divergence between these
two species. Even if it be asserted that the
difference in the colour of the feathers of the
back of the two cocks is in some way correlated
with adaptability to their particular environment,
how are we to explain the fact that in a certain
zone both species flourish ?

" A similar phenomenon is furnished by the
red-vented bulbul. This genus falls into several
species, each corresponding to a definite locality
and differing only in details from the allied
species, as, for example, the distance down the
neck to which the black of the head extends.
There is a Punjab Red-vented Bulbul (Molpastes
intermedius], a Bengal {Molpastes bengalensis), a
Burmese {Molpastes burmanicus], and a Madras
(Molpastes hcemorrhous) species.

379

The Making of Species

"It does not seem possible to maintain the
contention that these various species are the
products of natural selection, for that would
mean if the black of the head of the Punjab
species extended further into the neck the bird
could not live in that country."

Thus, natural selection clearly is unable to
explain some cases of divergence of character
due to geographical isolation.

There remains the third explanation, that the
divergence is the result of the simple fact of
isolation.

We have already shown how insuperable are
the objections to the view held by Romanes and
Gulick.

It seems to us that explanation must lie in the
fact that mutations occur every now and again in
some species. If two portions of a species are
separated and a mutation occurs in one portion
and not in the other, and if the mutating form
succeeds in supplanting the parent form in that
isolated portion of the species in which it has
appeared, we should have the phenomenon of
two races or species differing in appearance
although subjected to what appear to be identical
environment.

This, of course, is pure conjecture. All that
can be said of it at present is that it is not
opposed to observed facts. That mutations do
occur must be admitted. At present we are

380

Cormorants

totally in the dark as to what causes them.
They arise at the most unexpected times.

In favour of the explanation based on " muta-
tion " there is the interesting fact that geographi-
cal isolation does not by any means always cause
divergence of character. This Romanes, with
great fairness, freely admits. " There are/' he
writes, on p. 133 of vol. iii. of Darwin and
after Darwin, " four species of butterflies, belong-
ing to three genera (Lyccena donzelii, L.pheretes,
Argynnis pales, Erebia manto\ which are iden-
tical in the polar regions and the Alps, notwith-
standing that the sparse Alpine populations have
been presumably separated from their parent
stocks since the glacial period." Again, there
are "certain species of fresh- water crustaceans
(Apus), the representatives of which are com-
pelled habitually to form small isolated colonies
in widely separated ponds, and nevertheless
exhibit no divergence of character, although
apogamy has probably lasted for centuries."

To these examples we may add that of the
cormorants. These birds have an almost world-
wide range. One species — our Cormorant
(Pkalacrocorax carbo] — occurs in every imagin-
able kind of environment. Isolation has not
effected any changes in the appearance of this
species. Yet in New Zealand there exist no
fewer than fourteen other species of cormorant.
New Zealand is a country where climatic con-

381

The Making of Species

ditions are comparatively uniform, nevertheless
it boasts of no fewer than fifteen out of the thirty-
seven known species of cormorant. A possible
explanation of this phenomenon may be found
in the comparatively easy conditions under which
cormorants live in New Zealand.1 Under such
circumstances mutants may be permitted by
natural selection to survive, whereas in other
parts of the world such mutants have not been
able to hold their own.

Prof. Bateson has likened natural selection
to a competitive examination to which every
organism must submit. The penalty for failure
is immediate death. The standard of the ex-
amination may vary with the locality.

Isolation, then, is a very important factor in
the making of species, for without it, in some
form, the multiplication of species is impossible.

Let us, in conclusion, briefly summarise what
we now know of the method in which new species
are made. We have studied the various factors
of evolution — variation and correlation, heredity,
natural selection, sexual selection, and the other
kinds of isolation. How do these combine to bring
new species into being, and to establish the same ?

Let us first consider the factor known as
natural selection, since this is the one on which

1 Hutton and Drummond record other examples of this in the
valuable work entitled The Animals of New Zealand.

382

Natural Selection

Darwin laid such great stress. Natural selection,
although a most important factor in evolution, is
not an indispensable one. Evolution is possible
without natural selection.

Let us suppose that there is no such thing as
natural selection ; that the numbers of existing
species are kept constant by the elimination of
all individuals born in excess of the number
required to maintain the species at the existing
figure, and that the elimination of the surplus is
effected, not by natural selection, but by chance,
by the drawing of lots. Under such circum-
stances there may be evolution, existing species
may undergo change, but the evolution will be
determined solely by the lines along which
variations occur.

If mutations take place along certain fixed
lines, and tend to accumulate in the given
directions, evolution will proceed along these
lines quite independently of the utility to the
organism of the mutations that occur. An un-
favourable mutation will have precisely the same
chance of survival as a favourable one.

If, on the other hand, mutations occur in-
discriminately on all sides of the mean, then
those mutations which happen to occur most
frequently will have the best chance of survival,
and they will mark the lines of evolution. But
suppose that no mutation occurs more frequently
than the others. Under such circumstances there

383

The Making of Species

will be no evolution, unless, by some cause or
other, portions of the species are isolated, because
in the long run the mutations will neutralise one
another.

Let us now suppose that natural selection
comes into play. The old method of determining
by lot which forms shall persist is replaced by
selection on the fixed principle that the fittest
shall survive. The mutations appear as before,
and as before, of the large number that occur,
only a few are permitted to survive. But now
the survivors, instead of being a motley crowd,
are a selected band, composed of individuals
having many characteristics in common — a
homogeneous company. Thus one result of
natural selection is to accelerate evolution, by
weeding out certain classes of individuals and
preventing them breeding with those it has
selected. On the other hand, natural selection
will tend to diminish the number of species which
have arisen through mutation, inasmuch as it
weeds out many mutants which would have
perished had their survival been determined by
lot

From this the kind of work performed by
natural selection should be obvious. Natural
selection does not make new species. These
make themselves, or, rather, originate in accord-
ance with the laws of variation.

"You can," runs an old proverb, " bring a
384

Natural Selection

horse to the drinking fountain, but you cannot
make him drink." You may be able to bring a
child into the world, but you cannot secure its
survival. Variation brings into being mutants,
which are incipient species, but variation cannot
determine their survival. It is at this stage that
natural selection steps in.

But because natural selection allows certain
mutations to persist, it is not correct to say that
natural selection has caused these mutations or
made or originated the species to which they give
rise.

The Civil Service Commissioners do not make
Indian civil servants : they merely determine
which of a number of ready-made men shall
become civil servants. Similarly, natural selec-
tion does not make new species, it simply decides
which of a number of ready-made organisms shall
survive and establish themselves as new species.
Nor does natural selection always do as much as
this ; for it is not the only determinant of survival.
Its position is sometimes comparable to that of
the Medical Board which inspects and rejects
the physically unfit of the candidates which have
already been selected by some other authority.

The examination conducted by natural selec-
tion may be compared to a competitive one. A
separate, independent examination is held for
each particular locality ; consequently the severity
of the competition will vary with the locality.
2B 385

The Making of Species

In each competition some candidates pass with
ease : they gain an unnecessarily high total of
marks. So in nature do certain organisms, as,
for example, the Leaf-butterflies (Kallimas),
appear to be over-adapted to their environment.
Other candidates manage to pass only by a very
narrow margin : these are paralleled in nature by
those species which are barely able to maintain
themselves, which become extinct the moment
the competition increases in severity.

The great bulk of the candidates fail to obtain
sufficient marks to gain a place among the chosen
few ; these unsuccessful candidates correspond to
the mutating forms which perish in the struggle
for existence, to those individuals which happen
to have mutated in unfavourable directions.

Even as many candidates have acquired know-
ledge of subjects in which they are not examined,
so do many organisms possess characteristics
which are of no utility to them in the struggle
for existence.

Wallaceians expend much time and energy in
misguided attempts to explain the existence of
such characters in terms of natural selection.

Nature's examination, like that held for en-
trance to the Indian Civil Service, is a liberal
one, so that the qualifications of the successful
candidates vary considerably. Provided a can-
didate is able to gain more marks than the other
candidates for a vacancy, it matters not in what

386

Origin of the Fittest

subjects the marks are gained. So is it in nature.
Natural selection takes an organism as a whole.
One species may have established itself because
of its fleetness, a second because of its courage,
a third because it has a strong constitution, a
fourth because it is protectively coloured, a fifth
because it has good digestive powers, and so on.

We thus perceive the part played by natural
selection and other forms of isolation in the
making of species. It is obvious that these
do not make species any more than the Civil
Service Commissioners manufacture Indian civil
servants.

The real makers of species are the inherent
properties of protoplasm and the laws of variation
and heredity. These determine the nature of the
organism ; natural selection and the like factors
merely decide for each particular organism whether
it shall survive and give rise to a species.

The way in which natural selection does its
work is comparatively easy to understand. But
this is only the fringe of the territory which we
call evolution.

We seem to be tolerably near a solution of
the problem of the causes of the survival of
any particular mutation. This, however, is
merely a side issue. The real problem is the
cause of variations and mutations, or, in other
words, how species originate. At present our
knowledge of the causes of variation and muta-

387

The Making of Species

tion is practically nil. We do not even know
along what particular lines mutations occur.

We have yet to discover whether one mutation
invariably leads to another along the same lines
— in other words, whether mutating organisms
behave as though they had behind them a force
acting in a definite direction. The solution of
these problems seems afar off. The hope of
solving them lies, not in the speculations in
which biologists of to-day are so fond of in-
dulging, but in observation and experiment,
especially the last.

The future of biology is largely in the hands
of the practical breeder.

388

INDEX

ACCENTOR, i

Accipitcr cooperi, 243

Acorn, 49

Acquired characters, 10, 14, 15, 18-
24, 60, 107-10

Acrceidce, 175, 215, 228

j&gilops speltceformiS) 118

j&githina tiphia, 244

^Esthetic sense in birds, 306

"African Nature Notes and Re-
miniscences," 192, 195, 199

Aggressive resemblance, 173

Aguara-guazu, 181

Aitken, E. H., 64

"Albany Review, The," 43, 48,
195, 204

Albinism, 64, 65, 99, 283, 284, 362

Alcedo ispida, 289

Alcock, Col., 216, 217

Alcohol, 152, 153

Alexander, 181

Allen, Grant, 66

Allotrophy, 159

Alternating characters, 143

Alternative inheritance, 127

Amadavat, 311

Amandina crythrocephala, 122

A.fasciata, 122

" Amazement," 93

Amazon parrot, 103

Amazonian dolphin, 99

Ammonites, 67

Ammonium sulphate, 151

Amoeba, 35

Auiphidasys betularia, 101

Anas boscas, 123, 334

A. obscura, 334

A. pacilorhyncha, 315, 334

A. superciliosa, 315, 334

A. undulata, 334

Anastomus oscitans, 282

Ancon sheep, 95

Anemone magellanica, 118

A. sylvestris, 118

Anemophilous flowers, 261

"Animal Colouration," 194, 205,

211, 213, 2l8, 222

" Animal Life and Intelligence,"

368

"Animals of New Zealand," 382

Anous, 278

Anser cygnoides, 1 14

Anseranas melanoleucus ', 281

Antarctic fauna, 191

Antelope, 48, 199, 334

Anthracoceros, 220

Anthropoides paradisea, 279

A. virgo, 279

Antilope cervicapra, 363

Ape, 101

Apogamy, 370

Appenzeller, 340

t 381

Archiv fiir Entwicklungs-
mechanik der Organismen,"

32S» 330

Arctic fauna, 173, 174, 190, 19^
Arctic regions, 173, 189
Ardea asha, 317, 318
A. gularis, 318
Ardeola grayii, 250, 254
Argali, 120, 130, 131
" Argentine Ornithology," 361
Argynnis pales, 381
A. paphia, 103
Aristotle, I

Artcmia iiiilhausenii, 156
A. salina, 156
Aseel, 364

Asexual reproduction, 135
Asiatic, 140
Ass, 117, 127, 128, 140
Astur badius, 235
Atavism, 136, 293
Athene chiaradic£y 97
A. noctua, 97
Atoms, biological, 158
"Auk, The," 190
Aularches militaris, 216
Avebury, Lord, 205, 260
" Avicultural Magazine, The," 98
Avocet, 80

BABBLER, 244
Bactrian camel, 1 21
Bailey, 88
Baillon's crake, 251

Balanced characters, 143
389

The Making of Species

Balearica chrysopelargus, 105

B. regulorum, 105

Bassaris astuta, 242

Batesian mimicry, 177

Bateson, 26, 72, 73, 74, 75, 76,

102, 103, 302
Bats, 42

Bear, 101, 119, 190, 216, 282
Beddard, 180, 188, 194, 205, 21 1
Bee, 178, 179, 214, 221, 263, 264,

269

Beech, purple, 87
Bee-eater, 220, 278
Beetroots, 71
Belt, 216
Beluga, 190
Bentham, 260
Bestiary, 125
Bicheno's finch, 105
Bilateral symmetry, 252, 253, 257
Bingham, Col. C. T., 239
Biological atoms, 158-69, 280
Biological molecules, 157-69, 280,

285, 291, 293, 294, 295, 344
Biological radicles, 158-69
Biophors, 153
"Bird Book, the," 207
"Birds of the Plains," 233, 303,

309, 359
Bison, 119, 126
Blackcock, 129, 131, 249, 278
Blackberry, 118
Blackbird, 201, 203, 207
Black-buck, 363
Blakiston, 181
Bloodsucker, 220
Blue-bellied waxbill, 104
Blyth, 115, 251
Boisier, 263
Bombyx arrindia, 125
B. cynthia, 124
Bonhote, 126, 288, 289, 290, 291,

292, 293, 337
Bontebock, 196

Boselaphus tragocamehts, 357, 363
Bos frontatts, 126
Boulenger, 88
Bower-bird, 306
Brain-fever bird, 235, 236, 248
Bramble, 261
BranchipuS) 156
Brannam, 92
Brent, Mr, 307

British Museum, 129, 130, 187

BubovirginiamiS) 221

Bubulcus coromandus, 254

Budgerigars, 101

Buffalo, 120, 199

Buffon, 2

Buff Orpingtons, 65

Buff-tip moth, 215

Bufo melanostictus, 219

Bulbul, 123, 220, 221, 244, 245,
255, 256, 279

Bull, 119

Bungarus ccerulcus, 217, 247

Bunting, reed, 98, 190, 289

Buphus corotnandus, 3i7> 318

Burbank, 118

Burnet moth, 102

Bush-buck, 196

Butcher-bird, 241, 253

Buttercups, 70, 267, 274

Butterfly, 45, 47, 102, 103, 196, 197,
203, 204, 209, 212, 216. 238,
239, 240, 250, 264, 280, 306, 381

Buzzard, 262

CACOMISTLE, 242

Cairina moschata, 127, 245

Californian currant, 119

Catenas nicobarica, 65

Calotes versicolor, 22O

Camel, 120, 357

Campophaga, 248

Canary, 100, 101, 102, 117, 120,

127, 280, 338, 362
Canis jubatus, 181
Capercailzie, 129, 131
Capuchin monkey, 216
Carbon, 153
Carduelis caniceps, 255
C. carduelis, 255
Carnation, 85, 86
Carnivores, 67
Carp, 102
Carrion crow, 123
Carrot, 71, 269, 270
Casarca cana, 129
C. tadornoides, 129
" Cassell's Book of the Horse," 69
Castle, 149

Castration, effects of, 335, 344
Cat, 61, 98, 99, loo, 206, 282, 283,

339, 350, 356, 361
Cat-rabbit, 125

390

Index

Cataloe, 119
Cataract, 340
Caterpillars, 155, 175, 205, 21 1, 21$,

221, 350

Cattle, 94, 95, 115

Centropus sinensis, 22O, 244

Ccphalophus dorite, 243

Cephalopyrus flammiccps, 244

Cervulus muntjac, 101

C. reevcsii, 114

C. vaginalis, 114

Cervus paludosus, 180

C. sika, 120

Ceryle rztdis, 202

Chaffinch, 289

Chamba monaul, 104

" Champion Ladybird," 91, 92, 93

Change of function, theory of, 36,

37

Chen nivalis, 282
C. rossi, 282

Chenatopex cegyptiaca, 316
Chenonetta jubata, 316
Chinese goose, 99, 114, 121, 130
Chinese pheasant, 123
Chloephaga dispar, 105
C. magellanica, 105, 334
C. rubidiceps, 105, 334
Chromosomes, 145-7
Chryscena victor, 333
Chrysolophus anther stice^ 121
C, obscurus, 97
C.pictus, ,97, 121,337
Chrysomitris colombiana, 244
Chrysalis <zstiva, 103
Ciconia alba, 282
C. boyciana, 282
Cinnabar moth, 227
Cissopis leveriana, 281
Civil Service Commissioners, 385,

387

Cleistogamous flowers, 260
Climate as check on multiplication,

349, 350

Clouded-yellow butterfly, 103
Clover, 69, 274
Clytus arietis, 178, 229
Cobra, 224, 225, 226, 358, 359
Colias edusa, 103
Colour-blindness, 340
Colouration of Flowers, Law of

Progressive, 66
of Organisms, 170-296

Columbidse, 331, 333

Concealing colouration, 184-7

Congenital characters, 1 8, 19

Conn, 47

"Contemporary Review," 26

Cope, 15, 67

Copsychus saularis, 281

Coracias affinis, 123, 255

C. indica, 123, 220, 255

Cordon-bleu, 104

Cormorant, 190, 191, 277, 381, 382

Corn, Indian, 81

Correlation, 39, 40, 117, 162, 167,

223, 339, 34°, 344, 356-65
Corvus corone, 123, 255
C. comix, 123, 255
C. splendens, 353
"Country-Side, The," 261, 265,

266, 273, 304, 311, 313
Courser, 362
Court-bee, 72
Cow, 119, 120, 126
Crab, 155

Crane, 105, 247, 248, 279, 282, 292
Crateropus bicolor^ 242
C, canorus, 179
Crax globicera, 104, 304
C. grayi, 104
C. hecki, 104, 304
Crested newt, 124
Cretaceous reptiles, 67
Crinoids, 67
Crocodile, 187

Cross-fertilisation, 69, 258-60
Crotalus, 223
Crow, 47, 123, 206, 220, 247, 255,

281, 353, 355, 359, 361
" Crow-pheasant," 220
Cryptic colouring, 173
Cuckoo, 220, 233, 235, 236, 243,

244, 247, 248, 289

shrike, 248

Cuculus eanoriiS) 289

Cuenot, 149

Cunningham, Col., 225, 226, 358

J. T., 15, 19, 20, 324, 325, 329,

331, 332, 333, 336
Cupples, Mr, 308
Curassow, 104, 304
Currant, 119
Cut-throat finch, 122
Cypselus affinis, 243
Cytisus adami) 119

391

The Making of Species

DAFILA ACUTA, 122

Dahlia, 86

Daisy, 266, 274

Daltonism, 340

Damaliscus tunatus, 363

Damp as a check to multiplication
of species, 350, 351

Danaidce, 175, 179, 215, 216, 226,
228

Danais chrysippus> 179, 250

Danger signal, 183, 214, 253, 254

Darter, 277

Darwin, I-I2, 14, 25-27, 31, 35,42,
S2, 54-7, 59, 60-3, 68, 83, 96,
112, 114-7, "9, 123, 127, 130,
151, 171, 175, 182, 184,233,259,
299, 301-8, 316, 319-21, 325,
326, 347

"Darwin and after Darwin," 370-

5, 377, 38i
Darwinian theory, 3, 5-8, n, 13,

27,28,35,42,45,52,75, in, 171
Darwinism, I, 7, 8, n, 14, 26
"Darwinism," 40, 53, 112, 117,

178, 207, 213, 228, 322, 323
"Darwinism To-day," 16, 45, 67
Dasyurus, 283
De Candolle, 86
Decorative plumage, 40
Deer, 101, 120, 180, 298
Deerhound, 304, 308
Deer-ponies, 125
Degeneration, 168
Dejerine, 340
Delage, 33, 147
Delbceuf, Law of, 373
Delias eucharis, 2 1 6, 220, 221
Demicgrttta, 100
Demoiselle crane, 277
" Descent of Man," 234, 299, 301,

302, 304, 305, 319, 320, 326
Determination of sex, 165
"Development and Heredity," 17
De Vries, 26, 66, 69-72, 75-8, 82-9,

95, 105, 118, 151
Dewar, D., 43, 44, 47, 48, 195, 204,

206, 208, 210, 225, 233, 236, 303,

308, 309, 354, 360, 378
Dewar, G. A. B., 196, 197
Dicrurus ater, 179, 233
Didtlphys nurina, 243
Dimorphism, sexual, 51, 200, 201
Dipsacus, 58

Disease as a check to multiplication

of species, 351

Dt 'ssenntrus paradiseus, 179, 220
Divergence of character, 367
D°g» 59, 68, 99, 100, 125, 225, 226,

282, 283, 304, 308, 352, 357, 364,

365

Dog-rose, 261
Dolphin, 99

Dominant characters, 142
Donald, Mr D., 256
Dragon-fly, 216, 264
Driesh, 136
Drongo cuckoo, 233
Drongo-shrikes, 179, 220
Drummond, 382
Duck, 51, 60, 68, 97, 99, 100, 122,

126-8, 190, 247, 249, 282, 292,

3.14, 315, 334, 337, 338, 365
Duiker-buck, 243
Dyer, Sir William Thistleton, 26

EAGLE, 65, 190, 350

Eagle-owl, 221

East, M. E., 79

Echis carinatct) 224

" Eclipse," 69

" Edinburgh Review, The," 38

Eel, 102

Eggs, colours of birds', 206-9

Egret, 100, 206, 254, 365

Eider-duck, 249

Eimer, 15, 16, 33

Eisig, 222

Elanoidesfurcatus, 282

Elaps, 197, 198

Elder, 49

Elementary species, 77, 78, 87, 88, 89

Elk, Irish, 67

Emberiza citrinella, 289

E. pyrrhuloides, 98

E. schceniclus, 98

Entom oph ila p icata, 281

Entomophilous flowers, 261

Epenthesisfolleata, 103

Epilobias, 260

Equus, 41

Erebia manto, 381

Erythrura prasina> 1 02

"Essays on Evolution," n, 173,
177, 181, 184, 213, 223, 226,
227, 229, 230, 231, 234, 237,
238, 239

392

Index

Estrelda cyanogastra, 104
E. phcenicotis, 104
Ether, 152, 153
Eucheliajacobacce, 227
Eurasian, 140
European, 140
Euxenura maguari, 282
Evening primrose, 84, 85, 88
"Evolution of Sex, The," 306
Existence, struggle for, 31, 32
Eye-colour in human beings, 310
Eyesight of birds, 21 1, 237-41

insects, 264

Eyton, 15

"FAERY YEAR, THE," 196

Falcon, 204, 246, 250

Falco peregrinator, 25 1

F. severus, 251

False mimicry, 243

Faults in poultry, 64

Ferrets, 100, 119

Finch, 117, 120

Bicheno's, 105

chestnut-breasted, 98

cut-throat, 122

Gouldian, 98

Nonpareil, 102

red-headed, 142

ringed, 104

saffron, 244

yellow-rumped, 98

Finn, 99, 102, 115, 131, 179,216,
219, 220, 235, 241, 255, 304,
309, 310, 313, 315, 316, 358

Fittest, survival of the, 32

Flowers, 65, 66

Flowers, colours of, 258-75

Fly-catchers, 44, 45, 47, 285, 338

Flying squirrel, 243

"Fortnightly Review, The," 37, 38

Foul-brood, 353

Fowl, 56, 58, 61, 64, 65, 99, 101,
125, 127, 128, 282, 301, 302,
307, 3H, 330, 336, 338, 339,
361, 362, 364, 365

Fowl-ducks, 125

Foxes, 101, 131, 190, 191

Fox-terrier, 19

Franqueiro cattle, 95

Francolinus pondtcerianus, 337

Friar-bird, 249

Fringella coelebs^ 209
Fritillary butterfly, 103
Frog, 325

Fruits, colours of, 258, 275
Fiiligula marila, 290
Fulmar petrel, 190
Function, change of, 36, 37
Fungi, 263

GADOW, Dr, 197, 245

Gadwall, 126, 315

Galton, 81, 82, 374

"Game Birds and Wild Fowl of

India," 131

Gametes, segregation of, 143-5
Gannet, 282
Gayal, 126
Gauchos, 359
Gecko, 210
Geddes, 306, 326
Gemmules, 151
"Genesis of Species," 7, 61
Geographical isolation, 375
Geological record, imperfection of,

40-2, 94
Geranium, 260

Germ-plasm, continuity of the, 25
Germinal variations, 106-10
Geum urbanum, 263
Gibbon ape, 101
Giraffe, 17, 18, 192, 196
Globicera, 104
Glutton, 190
Goat, 283
Goethe, 2
Golden pheasant, 97, 129, 149,

337, 338

Golden tench, 101
Goldfinch, 127, 255
Goldfish, 101, 102
Goose, 99, 100, 105, 115, 121, 130,

190, 281, 316, 334, 339
Gordon's currant, 119
Goshawk, 247
Gouldian Finch, 99
Graba, 58
Gradation of colour, principle of,

185

Graculipica meZanoptera, 244
" Grammar of Science, The," 309
Grass, 273
Grasshopper, 185
Greenfinch, 122

393

The Making of Species

Greyhound, 364
Grosbeak, 281, 284
Groundsel, 260
Grouse, red, 125
Growth-force, 15, 16, 68
Grus leucogeramis, 282
Guillemot, 58, 190, 245
Guinea-fowl, 100, 127, 128, 279,

362

Guinea-pig, 95, 101, 129, 283
Gulick, 369, 372-7, 380
Gull, 190, 191, 207, 247, 290, 355
Gygis, 278
Gyrfalcon, 190

HAECKEL, 15, 24

Haemophilia, 340

Halcyon smyrnensis, 2O2

Halicetus albicilla, 65

Hare, 131, 185, 200

Harrier, 101

Hartebeeste, 363

Hawk-cuckoo, 235, 236

Hawk-eagle, 101

Hawks, 222, 235, 236, 247, 277

Heckiy 104

Helice, 103

Heliconida:, 175, 215, 216, 228

Heloderm, 217

Henslow, 15, 22, 23, 47, 48, 259

Heredity," 103, 145, 166, 340
"Heredity of Acquired Characters

in Plants," 22, 48
" Heredity of Sexual Characters

in relation to Hormones," 19, 330
Heron, 250, 317
Herring, 193
Hertwig, 151
Heusinger, 357
Hewitt, Mr, 307
Hierococcyx varius, 235, 248
Hilversum, 84
Himalayan argali, 120
Hinny, 127, 136, 140, 162
Hipparchia, semele, 205
Hippotragus equinus> 334
H. niger, 334
Hirundo riistica, 251
H. tytleri, 251
" History of Creation," 24
Hobby, 250, 251
Homogamy, 370
Honeyeater, 281

Hormones, 335, 338

Hornbill, 65, 220

Homer, 340

Horse, 61, 68, 69, 95, 96, 100, 101,
117, 127, 128, 140, 266, 267, 268,
272, 283, 322, 389, 363, 364, 374

Horse, genealogy of, 41

Houghton, 91

Howard, 315, 332

Hubrecht, 26

Hume, 131

Humming-bird, 328

Hutton, 3

Hutton, Captain, 115, 382

Huxley, 3, 6, n, 40, 100, in

Hyaena, 353

Hybridism, 111-32, 292, 293

Hydra, 21

Hydrogen, 152, 153

Hydrophasianus chirurgus, 250

Hyla, 245

Hypertely, 237, 240

Hypolimnas misippus, 179, 180

" IBIS, THE," 255, 256

Icterus vulgariS) 244, 281, 284

Impeyan pheasant, 104

Indian Civil Service, 385, 386, 387

Indian corn, 8 1

Inheritance, 133-69

alternative, 127

blended, 140, 148

definition of, 138

of acquired characters, 10, 14,

15, 18-24, 60, 107-10

particulate, 140

unilateral, 139, 140, 162

Insectivores, 67

Intercrossing, swamping effects of,

42, 83

Intimidating attitudes, 224, 225
lora, 244
Iridescence, 186
Irish elk, 67, 168
Isolation, 366-82, 387
Isomerism, biological, 154-8

chemical, 152-4, 157

Ithomiime, 228, 246
Ivy, 261

JACANA, 250
Jackdaw, 51, 306
Jaeger, 86

394

Index

Jaguar, 45, 358

Japanese greenfinch, 122

- pheasant, 122, 124, 129

Jardin des plantes, 88

Java sparrow, 99, 100

Jelly-fish, 192

Jesse, W., 255

Johnston, 92

"Journal of the Bombay Natural

History Society," 209
"Journal of the Royal Society of

Arts," 236, 324, 378
Jungle-babbler, 179
Jungle fowl, 332

, 47, 209, 212, 235, 386
Kellog, 16, 26, 45, 47, 67
Kingfisher, 202, 203, 206
Kite, 282

"Knowledge," 171, 198, 277
Korchinsky, 15, 33
Krait, 216, 247
Kuppa, 224

LABERNUM, 119
LachnantheS) 357
Ladybird, 213, 214
Lamarck, 2, 14, 17, 52
Lamarckism, 16, 24, 25
Lambert, Edward, 341
Lankester, Sir E. Ray, 13, 25
Lapwing, 207
Lark, 185, 362
Larus ridibundus, 290
Latent characters, 149
Law of battle, 301, 302, 321
Leaf-butterfly, 45, 47, 209, 235,

386

Lemming, 190
Lemur, 242, 243
Lemur catta, 242
Leopard, black, 101, 354, 358
Leucopternis, 282
Ligurinus stnicus, 122
Lily, 146

Linaria vulgaris peloria, 86
Linden, Grafin von, 155
Links, missing, 41, 42
Linnaeus, 65, 115
Linnet, 212, 338
" Linus I.," 95, 96
Lion, 192, 334, 349, 352
Liothrix luteus, 179

Lizard, 64, 207, 210, 212, 216, 217,

220, 223, 269, 350
Loddigesia mirabilis, 328
Loeb, 147

Lophophorus chambanus, 104
L. impeyanuS) 104
Lucerne, 118
Lung, 36, 37
Lutinism, 102
Lycfcna donzelli, 381
L. pheretes, 381
Lycodon aulicus> 247
Lyell, 3

MACKEREL, 193

Madingly, 102

Mania typica, 221

Magnus, 86

Magpie, 281

Magpie colouring, 66, 67, 280, 281

Magrath, 256

Male-fern, 49

Mallard, 65, 97, 122, 126, 132,

293, 313, 3I5. 334, 337

Malthus, 31

Malva, 260

Manchester School, 27

Mannikin, 104

Marbled newt, 124, 245

Marshall, 28

Mr G. A. K., 239

Milnes, 37, 174

Marsupials, 67

Masters, 86

" Materials for the Study of Varia-
tion," 73, 103

Mauchamp sheep, 95

Mayer, 228

" Mechanischphysiologische The-
orie der Abstammungslehre," 15

Medicago media., 1 1 8

Megascops asio, 44

Melanism, 64, 101, 360

Mclopsittacus undulatus, IOI

Mendel, 42, 74, 136, 141, 142, 144,

145

Mendel's Law, 145, 149, 150, 161
Mendelism, 145
Mesohippus, 41
Micellse, 151

Micropus melanoleucus, 245
" Mikado, The," 237
Mildew, 49

395

The Making of Species

Mimicry, conditions of, 178
Mimicry, protective, 45, 50, 51,

173, 177-82, 226-51, 275, 293,

294

Mink, 243
Miohippus, 41
Missing links, 41, 42
Missouri currant, 119
Mivart, Dr St George, 7, 61
Mole, 1 80
Molge blasii, 124
M. cristatci, 124
M. marmorata, 124
M. vulgartS) 221
Mollusca, 49
of Sandwich Islands, 375,

378

Molpastes, 123, 255
Molpastes bengalensis, 256, 379
M. burmanicus, 379
M. hcemorrhous, 255? 379
M. intermedius, 256, 379
M. leucogenys, 256
Monaul, 104
Monkey, 64, 213
Monotypic evolution, 366
Monstrosities, 56, 57, 358
Morgan, Prof. LI., 368

T. H., 26

Morse, 190

Moseley, Prof., 311

Motacilla lugubris^ 122

M. mclanopc, 122

Moth, 101, 102, 124, 209, 215, 227,

238, 240
Mouse, 64, 105, 139, 141, 146, 149,

150, 180, 185, 282, 359
Mule, 127, 136, 140, 160, 162
Miiller, Fritz, 81, 180
Mlillerian mimicry, 177, 181, 182
Munia atricapilla, 104
M. castaneithorax, 98
M. flaviprymna,) 98
M. malacca, 104

Muscovy duck, 99, 127, 128, 281
Musk ox, 190, 192
Mustela sarmatica, 243
Mutations, 41, 43, 66, 69, 72, 75-

105, 124, 127, 134, 159, 160,

169, 223, 280, 281, 284, 292,

295, 339, 34i, 342-4, 38o-8
Mutations, theory of, 26, 38, 75,

76, 95

Myna, 244
Myristicivora, 282

NAEGELI, 15, 16, 151

Nahrwal, 190

Natural selection, theory of, stated,

31, 32

"Nature," 184
Nautili, 67
Nectar of flowers, 262, 264, 265,

268, 270, 271
Neo-Darwinians, 13, 14, 25, 173,

174, 176, 188, 214, 218, 222,

233, 238, 242, 263, 264
Neo-Darwinism, 51, 172, 234, 235,

264, 275, 276, 297
Neo-Lamarckians, 13, 14, 15
Neophron, 282
Nepheronia hippia, 179
Nettium albigtilare, 179
New organs, beginnings of, 36, 73
Newman, 126
Newt, 124, 221, 222
Niata cattle, 95
Nicobar pigeon, 65
Nilgai, 337
Nitrogen, 153
Noddy, 62, 279
Nonpareil finch, 102
Nyroca africana, 337

GATES, 255, 379

Obliterative colouration, 184-7

Ocydromus, 365

(Enis, 205

(Enopopelia tranquebarica, 122,
123, 324, 333

(Enothera lamarckiana, 84, 85 , 87, 88

Ononis repens, 23

0. spinosa, 22

Opossum, 243

Orchid, 268, 269, 270, 272

Orgyia antiqua, 215

"Origin of Species, The, "7, 9, n,
3i, 53, 57, 63, 114, 170, 194,
347, 348, 356, 367

Oriole, 244, 249, 284, 304

Oriolus galbula, 282

O. kundoo, 282

O. melanocephalus, 244, 284

"Ornithological and Other Oddi-
ties," 255

Orohippus, 41

396

Index

Orr, 15-7

Orthogenesis, 15, 16, 34
Ossifraga gigantea, 99, 362
Otidiphaps insularis, 244
Ovis ammon, 120
O. vignei, 120
Owen, Sir Richard, 7
Owl, 247, 277, 289

little, 97, 98

scops, 101

snowy, 190

Ox, 146, 352
Oxygen, 152, 153, 263

PADDY BIRD, 254

Paint-root, 357

Palaornis torquatus^ IO2, 325

Pallas, 115

Pansy, 260

Panther, 360

Papilio, 228, 246

P. aristolochicc, 179, 216, 22O, 221

P. polites, 179

Paradise, bird of, 62, 249

Paradise flycatcher, 47, 202, 298,

303, 316, 324, 338
Paradisea apoda, 249
Paraguay cattle, 94
Parnassius apollo, 155
Paroquet, 102, 121, 325
Parrot, 103

Parthenogenesis, 135, 138
Partridge, 185, 315, 337
Partis leticopterus, 245
Passer domesticus^ 289, 342
P. montanus, 342
P. swainsoni, 342
Pasteur, 5

Pavo nigripennis, 96
Pavoncella pugnax, 343
Pea, sweet, 74, 75, 81, 141
Pear, 72

Pearson, Karl, 309, 310
Peckham, 308
Pekin robin, 179
Pelagic animals, 173, 192-4
Penguin, 191
Pennant's parakeet, 121
Petaurus breviceps, 243
Petrel, 44, 190, 191, 277, 337
Pfeffer, 33

Phalacrocorax carbo, 381
Phalanger, 243

Phalarope, 327

Phasianidce, 125, 330

Phasianus colchicus, 114, 123

P. torquatuS) 114, 123

P. vtrsicolor, 114, 123, 124

Pheasant, 97, 104, 114, 121, 123,
128-30, 141, 315, 336, 338

Pictet, 155, 156

Pieris napi, 155

Piezorhynckus, 285

Pig, 57, 283, 357, 365

Pigeon, 61, 62, 65, 68, 71, 72, 91,
92, 93, 98, 101, 109, 126, 127,
244, 277, 282, 353, 357, 364, 365

Pigment, massing of, 256

Pike, 102, 222

Pimpernel, 261

Pintail duck, 130, 132, 293, 337

Pintailed nonpareil finch, IO2

"Plant Breeding, "87

Plasomes, 151

Plastidules, 151

Platycercus elegant, 1 21

P. erythropepluS) 121

P. eximius, 121

Pliohippus, 41

Plover, 207

Plumage, decorative, 40

Pochard, 126, 337

Poecilomeres, 288-95

Poephila mirabilis, 99

Polar bear, 119, 130

Polar bodies, 135

Polecat, 119

Polytypic evolution, 367

Poppy, 82, 261

Porzana bailloni^ 251

P. pusilla, 251

Post-nuptial display, 316

Potentilla tormentilla^ 263

Poulton, II, 25, 26, 171, 173, 177,

l8l, 184, 210, 213, 217, 221, 223-

5, 229-35, 238-42

Precis artexia, 203, 204, 212

Preferential mating among human
beings, 309, 310

Prepotency, 136

Prickly pear, 274

Primrose, evening, 84, 85, 88

Pritchard, Hesketh, 359

" Proceedings of the Fourth In-
ternational Ornithological Con-
gress," 288, 337

397

The Making of Species

"Proceedings of the Linnaean So-
ciety," 288

" Proceedings of the Natural His-
tory Society of Brunn," 141

ProtohippuS) 37

Pseudoclytia pentata^ 103

Pseudo-sematic colours, 173

Pseudotantalus cinereus, 282

Ptarmigan, 190

Pteroclurus exustus^ 204

Puffin, 191

Pugnacity of animals, 206, 360

Puma, 45

Purple beech, 87

Pycraft, W. P., 277

Pycnorhampus affinis, 284

P. icteroides, 284

Pygcera bucephala> 215

QUAIL, 185
Quatrefages, de, 124
Quelea quelea, 98
Q. russi, 98

Querquedula crecca, 290
Quetelet's Law, 77

RABBIT, 99, 100, 105, 183, 253,

283, 35o» 352
Racehorse, 69
Radicles, biological, 159
Rallus aqtiaticuS) 251
R. indicus, 251
Ranuncuhis bulbosus, 70
Rappia, 245
Raspberry, 118
Rat, 74, 282

water, 101

Raven, 190
Razorbill, 190
Recessive characters, 142
Recognition colours, 251-7* 275

marks, 124

Red-mantled parakeet, 121
Redpole, 207
Redwing, 354
Reed bunting, 98
Reeves' pheasant, 129
Regression, Law of, 82, 374
Reid, Archdale, 5
Reindeer, 190
Rest-harrow, 22
Reversion, 64, 65, 129, 293
Rhinosciurtis tupaioides, 180

Rhodocera rhamnt, 155
Rhododendron Jerrtigineum, 1 1 8
R. hirsutuniy Il8
Rhynchcea, 327
Ricardo, 28
Ringed finch, 104
Robin, 281, 378
Robin, Indian, 202
Robinson, Dr H., 171, 198

E. K., 261, 264, 265, 266,

268, 270, 272-4
Rodents, 67
Rogeron, 126
Roller, 123, 220, 255
Romanes, 366-81
Rook, 51, 187
Rose, 61, 267
Rosella parakeet, 121
Rous, Admiral, 69
Roux, 136
Ruff, 343

SABLE, 190
Saffron finch, 244
Sainfoin, 267

Salamander, 217, 219, 221
Salix alba, 118
S. pentandra, 118
Sandgrouse, 204, 351
Sandpipers, 185, 190
Sassaby, 363
Satyridcc, 205
Scatliff, H. P., 91-3
Scatliff strain, 91
Scaup, 290
Schmankewitsch, 156
" Science," 166
Sciuroptcrus volucella, 243
Scops giu, 101
Scops owl, American, 44

, Indian, 101

Scoter, 249

Seal, 190, 191

Sea-urchin, 149

Seaweed, 263

Sebright, Sir John, 63

Secondary sexual characters, 298

Segregation, 369

of gametes, 143-5

Selous, Edmund, 308

F. C., 192, 195, 197, 203

Sematic colours, 173
Sesiafuciformis, 178

398

Index

Sexual dimorphism, 51, 297-344

Sexual selection, theory of, 299-321

Shaheen, 251

Shamrock, 274

Sheathbill, 191

Sheep, 95, 266, 267, 283, 357, 372

Sheldrake, 109, 129

Shikra, 235, 236

Shoveler, 290

Shrew, 180, 216

Sidgwick, 28

Sidney, 5, 49

Sika deer, 120

Silver- washed fritillary butterfly, 103

Siskin, 127, 244

Skua, Arctic, 44, 362

Skua-gull, 191

Skunk, 1 86, 217, 221

Skylark, 315

Slug, 49, 185

Smith, Adam, 28

Snake, 185, 197, 198, 217, 220, 223-
6, 247, 356

Snap-dragon, 268, 272

Snipe, 69, 327

Sodium sulphate, 151

Somatic variations, 106-10.

" Some Indian Friends and Ac-
quaintances," 225, 358

Sorrel, 274

Sparrow, 213, 241, 341, 342

Java, 99, 100

Sparrow-hawk, 2359 243

Spatula clypeata, 290

Spavin, 332

" Species and Varieties," 69, 77, 84,
87, 118

Species, definition of, 89

Species, elementary, 77, 78, 87-9

Spencer, 3, 15, 16, 28, 38, 151

Spider, 269, 272

Sporaginthiis amandava, 311

Sports, 41, 43, 66, 75, 85, 135

Squirrel, 101, 186, 243

Stag, 325

Irish, 67

Standfuss, 155

Stanley crane, 248, 279

St Hilaire, T. G., 2, 356

Stick insect, 209

Stictoptera annulosa, 104

Stoat, 119, 190, 290

Stolzmann, 327-9, 342, 343

Stonechat, 353
Stork, 247, 282
"Strand Magazine," 64
Strix flammea, 289
Struggle for existence, 31, 32, 48
for nourishment, 167

Suchetet, A., 126, 130

Sula capensis, 282

S. serrator, 282

Sunbird, 324

Surniculus lugubris, 235, 243

Survival of the fittest, 32

Survival value, 33, 34

Swallow, 250, 251, 279, 361

Swallow-shrike, 281

Swallow-tail butterfly, 179

Swan, 100

Swift, 243, 250

Swimming bladder of fishes, 36, 37

Sycalis flaveola, 244

Syrphidct) 178

TACHYCINETA LEUCORRHOA, 361

Tadorna cornuta, 129

T. tadornoideS) 129

Tails, 62, 64

Tait, Mr, 356

Tanager, 281

Tapir, 42

Tasmanian devil, 282

Teal, 290, 316

Teasel, fuller's, 58

Teeth, molar, 105

Tegetmeier, Mr, 307

Tern, 62, 278

Terpsiphone paradisi, 202, 298, 304,

3i6, 324
Tetraogallus, 337
Tetraonida, 125
Tetrapteryx paradisea^ 249
Tetrao tetrix, 129
T. urogallus, 129
Thamnobia cambayensis, 202, 275
T.fulicata, 202, 378
Thayer, Mr Abbot, 184-7
Thompson, Seton, 354
Thomson, 103, 136, 14$, 166, 306,

326, 340

Throat disease, 353
"Through Southern Mexico," 197,

245
" Through the Heart of Patagonia,"

359

399

The Making of Species

Thrush, 203, 207, 355

Tiger, 334

Tit, 245

Toad, 210, 219, 241

Toad-flax, 56

Tortoise. 222

Trefoil, 274

Trochilium, 229

Trogon, 62

Tropidonotus piscator, 22O

Troupial, 244, 281, 284

Tsetse-fly, 352

Tupaia, 180, 216

T. el Hot i, 216

Turbit, 72, 91-3

"Turbit, The Modern," 91

Turkey, 95, 363

Turnspit dog, 59

Turtur cambayensis ', 333

T. suratemis, 333

T. risorius, 33, 123, 126

Tylor, Mr Alfred, 287

UNGULATES, 67
Unilateral transmission, 341
Unit characters, 148-52
Uriagrylle^ 245
U. lacrymanS) 58
Urial, 120, 130, 131
Urodynamis tritensis, 243

VALEZINA, 103
Vanessa levana, 154
V. prorsa, 154
Vapourer moth, 215
Variation, 52-110

cause of, 59-60

continuous, 56, 69, 76, 105

definite, 55

determinate, 55

discontinuous, 43, 56, 72, 73,

76, 78, 79, 87, 105, 106, 133,

159, 295

germinal, 106-10, 133

indefinite, 55, 59

somatic,

Viola, 260
V. tricolor, 260
Volckamer, 86
Vulture, 282

WAGGETT, 12
Wagner, 369, 372
Wagtail, 122, 203

Wallace, 3, 10, 13, 14, 25, 26, 35-
42, 53, 112, 114, 116, 117, 171,
175, 177, 183, 184, 207, 213,
228, 230, 251, 253, 256, 287,
296, 308, 321-7, 343, 372, 377

Wallaceian school of biologists, 14,
24, 25, 47, 192, 210, 251, 346,
347, 3.66, 377

Wallaceism, 172, 202

Walrus, 190

Warblers, British, 315, 332

Warning colours, 173, 176, 198,
212-26

Wasp, 174, 178, 179, 214, 227

Wasp-beetle, 229

Water-rail, 251

Waxbill, blue-bellied, 104

Weasel, 190

Weaver, red-billed, 98

Weber, 86

Weir, Mr Jenner, 299

Weismann, 25, 106, 107, 151, 154

Weka rail, 365

"Westminster Review," 112

Weston, G. E,, 127

Whale, 42, 185, 190, 193

Wheatear, 253

Whinchat, 253

Wiesner, 151

Wilson, Prof. E. B., 166

Winter coat, 188

Wolf, 48, 130, 185, 192

Wonder horse, 95, 96

Woodpecker, 102

Wright, Mr, 304

Wymau, Professor, 357

X-ELEMENT, 165

YAK, 120

Yarrow, 268

"Year-book of the Smithsonian

Institution," 184
Yerbury, Col., 239
Youatt, 63

ZEBRA, 196

Zebu, 1 20

Zocher & Co., 56

Zoological Gardens, Lahore, 309

, London, 104, 119, 126, 130,

206, 304, 316

Zoological Society of London, 330
Zygcena fi lipendultz, 102

400

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