← catalogue

Darwin and Modern Science

by A. C. Seward · English · Gutenberg #1909 · 1,662,090 chars · public domain (US)

The Project Gutenberg eBook of Darwin and Modern Science
    
This eBook is for the use of anyone anywhere in the United States and
most other parts of the world at no cost and with almost no restrictions
whatsoever. You may copy it, give it away or re-use it under the terms
of the Project Gutenberg License included with this eBook or online
at www.gutenberg.org. If you are not located in the United States,
you will have to check the laws of the country where you are located
before using this eBook.

Title: Darwin and Modern Science

Author: A. C. Seward


        
Release date: September 1, 1999 [eBook #1909]
                Most recently updated: November 20, 2009

Language: English

Other information and formats: www.gutenberg.org/ebooks/1909

Credits: Produced by Sue Asscher, and David Widger


*** START OF THE PROJECT GUTENBERG EBOOK DARWIN AND MODERN SCIENCE ***




Produced by Sue Asscher





DARWIN AND MODERN SCIENCE

ESSAYS IN COMMEMORATION OF THE CENTENARY OF THE BIRTH OF CHARLES DARWIN
AND OF THE FIFTIETH ANNIVERSARY OF THE PUBLICATION OF "THE ORIGIN OF
SPECIES"


By A.C. Seward



"My success as a man of science, whatever this may have amounted to,
has been determined, as far as I can judge, by complex and diversified
mental qualities and conditions. Of these, the most important have
been--the love of science--unbounded patience in long reflecting over
any subject--industry in observing and collecting facts--and a fair
share of invention as well as of common sense. With such moderate
abilities as I possess, it is truly surprising that I should have
influenced to a considerable extent the belief of scientific men on some
important points."

Autobiography (1881); "The Life and Letters of Charles Darwin", Vol. 1.
page 107.




PREFACE

At the suggestion of the Cambridge Philosophical Society, the Syndics
of the University Press decided in March, 1908, to arrange for the
publication of a series of Essays in commemoration of the Centenary
of the birth of Charles Darwin and of the Fiftieth anniversary of the
publication of "The Origin of Species". The preliminary arrangements
were made by a committee consisting of the following representatives of
the Council of the Philosophical Society and of the Press Syndicate:
Dr H.K. Anderson, Prof. Bateson, Mr Francis Darwin, Dr Hobson, Dr Marr,
Prof. Sedgwick, Mr David Sharp, Mr Shipley, Prof. Sorley, Prof. Seward.
In the course of the preparation of the volume, the original scheme and
list of authors have been modified: a few of those invited to contribute
essays were, for various reasons, unable to do so, and some alterations
have been made in the titles of articles. For the selection of authors
and for the choice of subjects, the committee are mainly responsible,
but for such share of the work in the preparation of the volume as
usually falls to the lot of an editor I accept full responsibility.

Authors were asked to address themselves primarily to the educated
layman rather than to the expert. It was hoped that the publication
of the essays would serve the double purpose of illustrating the
far-reaching influence of Darwin's work on the progress of knowledge and
the present attitude of original investigators and thinkers towards the
views embodied in Darwin's works.

In regard to the interpretation of a passage in "The Origin of Species"
quoted by Hugo de Vries, it seemed advisable to add an editorial
footnote; but, with this exception, I have not felt it necessary to
record any opinion on views stated in the essays.

In reading the essays in proof I have availed myself freely of the
willing assistance of several Cambridge friends, among whom I wish more
especially to thank Mr Francis Darwin for the active interest he
has taken in the preparation of the volume. Mrs J.A. Thomson kindly
undertook the translation of the essays by Prof. Weismann and Prof.
Schwalbe; Mrs James Ward was good enough to assist me by translating
Prof. Bougle's article on Sociology, and to Mr McCabe I am indebted for
the translation of the essay by Prof. Haeckel. For the translation
of the botanical articles by Prof. Goebel, Prof. Klebs and Prof.
Strasburger, I am responsible; in the revision of the translation of
Prof. Strasburger's essay Madame Errera of Brussels rendered valuable
help. Mr Wright, the Secretary of the Press Syndicate, and Mr Waller,
the Assistant Secretary, have cordially cooperated with me in my
editorial work; nor can I omit to thank the readers of the University
Press for keeping watchful eyes on my shortcomings in the correction of
proofs.

The two portraits of Darwin are reproduced by permission of Messrs Maull
and Fox and Messrs Elliott and Fry. The photogravure of the study at
Down is reproduced from an etching by Mr Axel Haig, lent by Mr Francis
Darwin; the coloured plate illustrating Prof. Weismann's essay was
originally published by him in his "Vortrage uber Descendenztheorie"
which afterwards appeared (1904) in English under the title "The
Evolution Theory". Copies of this plate were supplied by Messrs Fischer
of Jena.

The Syndics of the University Press have agreed, in the event of
this volume being a financial success, to hand over the profits to a
University fund for the endowment of biological research.

It is clearly impossible to express adequately in a single volume of
Essays the influence of Darwin's contributions to knowledge on the
subsequent progress of scientific inquiry. As Huxley said in 1885:
"Whatever be the ultimate verdict of posterity upon this or that opinion
which Mr Darwin has propounded; whatever adumbrations or anticipations
of his doctrines may be found in the writings of his predecessors; the
broad fact remains that, since the publication and by reason of the
publication of "The Origin of Species" the fundamental conceptions
and the aims of the students of living Nature have been completely
changed... But the impulse thus given to scientific thought rapidly
spread beyond the ordinarily recognised limits of Biology. Psychology,
Ethics, Cosmology were stirred to their foundations, and 'The Origin of
Species' proved itself to be the fixed point which the general doctrine
needed in order to move the world."

In the contributions to this Memorial Volume, some of the authors
have more especially concerned themselves with the results achieved by
Darwin's own work, while others pass in review the progress of research
on lines which, though unknown or but little followed in his day, are
the direct outcome of his work.

The divergence of views among biologists in regard to the origin of
species and as to the most promising directions in which to seek for
truth is illustrated by the different opinions of contributors. Whether
Darwin's views on the modus operandi of evolutionary forces receive
further confirmation in the future, or whether they are materially
modified, in no way affects the truth of the statement that, by
employing his life "in adding a little to Natural Science," he
revolutionised the world of thought. Darwin wrote in 1872 to Alfred
Russel Wallace: "How grand is the onward rush of science: it is enough
to console us for the many errors which we have committed, and for our
efforts being overlaid and forgotten in the mass of new facts and new
views which are daily turning up." In the onward rush, it is easy for
students convinced of the correctness of their own views and equally
convinced of the falsity of those of their fellow-workers to forget the
lessons of Darwin's life. In his autobiographical sketch, he tells us,
"I have steadily endeavoured to keep my mind free so as to give up any
hypothesis, however much beloved...as soon as facts are shown to be
opposed to it." Writing to Mr J. Scott, he says, "It is a golden rule,
which I try to follow, to put every fact which is opposed to one's
preconceived opinion in the strongest light. Absolute accuracy is the
hardest merit to attain, and the highest merit. Any deviation is ruin."

He acted strictly in accordance with his determination expressed in a
letter to Lyell in 1844, "I shall keep out of controversy, and just
give my own facts." As was said of another son of Cambridge, Sir George
Stokes, "He would no more have thought of disputing about priority,
or the authorship of an idea, than of writing a report for a company
promoter." Darwin's life affords a striking confirmation of the truth
of Hazlitt's aphorism, "Where the pursuit of truth has been the habitual
study of any man's life, the love of truth will be his ruling passion."
Great as was the intellect of Darwin, his character, as Huxley wrote,
was even nobler than his intellect.

A.C. SEWARD.

Botany School, Cambridge, March 20, 1909.



CONTENTS
I. INTRODUCTORY LETTER TO THE EDITOR from SIR JOSEPH DALTON HOOKER, O.M.

II. DARWIN'S PREDECESSORS:  J. ARTHUR THOMSON, Professor of Natural
History in the University of Aberdeen.

III. THE SELECTION THEORY:  AUGUST WEISMANN, Professor of Zoology in the
University of Freiburg (Baden).

IV. VARIATION:  HUGO DE VRIES, Professor of Botany in the University of
Amsterdam.

V. HEREDITY AND VARIATION IN MODERN LIGHTS:  W. BATESON, Professor of
Biology in the University of Cambridge.

VI. THE MINUTE STRUCTURE OF CELLS IN RELATION TO HEREDITY:  EDUARD
STRASBURGER, Professor of Botany in the University of Bonn.

VII. "THE DESCENT OF MAN":  G. SCHWALBE, Professor of Anatomy in the
University of Strassburg.

VIII. CHARLES DARWIN AS AN ANTHROPOLOGIST:  ERNST HAECKEL, Professor of
Zoology in the University of Jena.

IX. SOME PRIMITIVE THEORIES OF THE ORIGIN OF MAN:  J.G. FRAZER, Fellow
of Trinity College, Cambridge.

X. THE INFLUENCE OF DARWIN ON THE STUDY OF ANIMAL EMBRYOLOGY:  A.
SEDGWICK, Professor of Zoology and Comparative Anatomy in the University
of Cambridge.

XI. THE PALAEONTOLOGICAL RECORD. I. ANIMALS:  W.B. SCOTT, Professor of
Geology in the University of Princeton.

XII. THE PALAEONTOLOGICAL RECORD. II. PLANTS:  D.H. SCOTT, President of
the Linnean Society of London.

XIII. THE INFLUENCE OF ENVIRONMENT ON THE FORMS OF PLANTS:  GEORG KLEBS,
Professor of Botany in the University of Heidelberg.

XIV. EXPERIMENTAL STUDY OF THE INFLUENCE OF ENVIRONMENT ON ANIMALS:
JACQUES LOEB, Professor of Physiology in the University of California.

XV. THE VALUE OF COLOUR IN THE STRUGGLE FOR LIFE:  E.B. POULTON, Hope
Professor of Zoology in the University of Oxford.

XVI. GEOGRAPHICAL DISTRIBUTION OF PLANTS:  SIR WILLIAM THISELTON-DYER.

XVII. GEOGRAPHICAL DISTRIBUTION OF ANIMALS:  HANS GADOW, Strickland
Curator and Lecturer on Zoology in the University of Cambridge.

XVIII. DARWIN AND GEOLOGY:  J.W. JUDD.

XIX. DARWIN'S WORK ON THE MOVEMENTS OF PLANTS:  FRANCIS DARWIN.

XX. THE BIOLOGY OF FLOWERS:  K. GOEBEL, Professor of Botany in the
University of Munich.

XXI. MENTAL FACTORS IN EVOLUTION:  C. LLOYD MORGAN, Professor of
Psychology at University College, Bristol.

XXII. THE INFLUENCE OF THE CONCEPTION OF EVOLUTION ON MODERN PHILOSOPHY:
H. HOFFDING, Professor of Philosophy in the University of Copenhagen.

XXIII. DARWINISM AND SOCIOLOGY:  C. BOUGLE, Professor of Social
Philosophy in the University of Toulouse, and Deputy-Professor at the
Sorbonne, Paris.

XXIV. THE INFLUENCE OF DARWIN UPON RELIGIOUS THOUGHT:  REV. P.N.
WAGGETT.

XXV. THE INFLUENCE OF DARWINISM ON THE STUDY OF RELIGIONS:  JANE ELLEN
HARRISON, Staff-Lecturer and sometime Fellow of Newnham College,
Cambridge.

XXVI. EVOLUTION AND THE SCIENCE OF LANGUAGE:  P. GILES, Reader in
Comparative Philology in the University of Cambridge.

XXVII. DARWINISM AND HISTORY:  J.B. BURY, Regius Professor of Modern
History in the University of Cambridge.

XXVIII. THE GENESIS OF DOUBLE STARS:  SIR GEORGE DARWIN, Plumian
Professor of Astronomy and Experimental Philosophy in the University of
Cambridge.

XXIX. THE EVOLUTION OF MATTER:  W.C.D. WHETHAM, Fellow of Trinity
College, Cambridge.

INDEX.




DATES OF THE PUBLICATION Of CHARLES DARWIN'S BOOKS AND OF THE PRINCIPAL
EVENTS IN HIS LIFE

1809:

Charles Darwin born at Shrewsbury, February 12.

1817:

"At 8 1/2 years old I went to Mr Case's school." (A day-school at
Shrewsbury kept by the Rev G. Case, Minister of the Unitarian Chapel.)

1818:

"I was at school at Shrewsbury under a great scholar, Dr Butler; I
learnt absolutely nothing, except by amusing myself by reading and
experimenting in Chemistry."

1825:

"As I was doing no good at school, my father wisely took me away at
a rather earlier age than usual, and sent me (Oct. 1825) to Edinburgh
University with my brother, where I stayed for two years."

1828:

Began residence at Christ's College, Cambridge.

"I went to Cambridge early in the year 1828, and soon became acquainted
with Professor Henslow...Nothing could be more simple, cordial and
unpretending than the encouragement which he afforded to all young
naturalists."

"During the three years which I spent at Cambridge my time was wasted,
as far as the academical studies were concerned, as completely as at
Edinburgh and at school."

"In order to pass the B.A. Examination, it was...necessary to get up
Paley's 'Evidences of Christianity,' and his 'Moral Philosophy'... The
careful study of these works, without attempting to learn any part by
rote, was the only part of the academical course which...was of the
least use to me in the education of my mind."

1831:

Passed the examination for the B.A. degree in January and kept the
following terms.

"I gained a good place among the oi polloi or crowd of men who do not go
in for honours."

"I am very busy,...and see a great deal of Henslow, whom I do not know
whether I love or respect most."

Dec. 27. "Sailed from England on our circumnavigation," in H.M.S.
"Beagle", a barque of 235 tons carrying 6 guns, under Capt. FitzRoy.

"There is indeed a tide in the affairs of men."

1836:

Oct. 4. "Reached Shrewsbury after absence of 5 years and 2 days."

"You cannot imagine how gloriously delightful my first visit was at
home; it was worth the banishment."

Dec. 13. Went to live at Cambridge (Fitzwilliam Street).

"The only evil I found in Cambridge was its being too pleasant."

1837:

"On my return home (in the 'Beagle') in the autumn of 1836 I immediately
began to prepare my journal for publication, and then saw how many facts
indicated the common descent of species... In July (1837) I opened my
first note-book for facts in relation to the Origin of Species, about
which I had long reflected, and never ceased working for the next twenty
years... Had been greatly struck from about the month of previous
March on character of South American fossils, and species on Galapagos
Archipelago. These facts (especially latter), origin of all my views."

"On March 7, 1837 I took lodgings in (36) Great Marlborough Street in
London, and remained there for nearly two years, until I was married."

1838:

"In October, that is fifteen months after I had begun my systematic
enquiry, I happened to read for amusement 'Malthus on Population,'
and being well prepared to appreciate the struggle for existence which
everywhere goes on from long-continued observation of the habits of
animals and plants, it at once struck me that under these circumstances
favourable variations would tend to be preserved, and unfavourable
ones to be destroyed. The result of this would be the formation of new
species. Here then I had at last got a theory by which to work; but I
was so anxious to avoid prejudice, that I determined not for some time
to write even the briefest sketch of it."

1839:

Married at Maer (Staffordshire) to his first cousin Emma Wedgwood,
daughter of Josiah Wedgwood.

"I marvel at my good fortune that she, so infinitely my superior in
every single moral quality, consented to be my wife. She has been my
wise adviser and cheerful comforter throughout life, which without
her would have been during a very long period a miserable one
from ill-health. She has earned the love of every soul near her"
(Autobiography).

Dec. 31. "Entered 12 Upper Gower street" (now 110 Gower street, London).
"There never was so good a house for me, and I devoutly trust you (his
future wife) will approve of it equally. The little garden is worth its
weight in gold."

Published "Journal and Researches", being Vol. III. of the "Narrative of
the Surveying Voyage of H.M.S. 'Adventure' and 'Beagle'"...

Publication of the "Zoology of the Voyage of H.M.S. 'Beagle'", Part
II., "Mammalia", by G.R. Waterhouse, with a "Notice of their habits and
ranges", by Charles Darwin.

1840:

Contributed Geological Introduction to Part I. ("Fossil Mammalia") of
the "Zoology of the Voyage of H.M.S. 'Beagle'" by Richard Owen.

1842:

"In June 1842 I first allowed myself the satisfaction of writing a very
brief abstract of my (species) theory in pencil in 35 pages; and this
was enlarged during the summer of 1844 into one of 230 pages, which I
had fairly copied out and still (1876) possess." (The first draft of
"The Origin of Species", edited by Mr Francis Darwin, will be published
this year (1909) by the Syndics of the Cambridge University Press.)

Sept. 14. Settled at the village of Down in Kent.

"I think I was never in a more perfectly quiet country."

Publication of "The Structure and Distribution of Coral Reefs"; being
Part I. of the "Geology of the Voyage of the Beagle".

1844:

Publication of "Geological Observations on the Volcanic Islands visited
during the Voyage of H.M.S. 'Beagle'"; being Part II. of the "Geology of
the Voyage of the 'Beagle'".

"I think much more highly of my book on Volcanic Islands since Mr Judd,
by far the best judge on the subject in England, has, as I hear, learnt
much from it." (Autobiography, 1876.)

1845:

Publication of the "Journal of Researches" as a separate book.

1846:

Publication of "Geological Observations on South America"; being Part
III. of the "Geology of the Voyage of the 'Beagle'".

1851:

Publication of a "Monograph of the Fossil Lepadidae" and of a "Monograph
of the sub-class Cirripedia".

"I fear the study of the Cirripedia will ever remain 'wholly unapplied,'
and yet I feel that such study is better than castle-building."

1854:

Publication of Monographs of the Balanidae and Verrucidae.

"I worked steadily on this subject for...eight years, and ultimately
published two thick volumes, describing all the known living
species, and two thin quartos on the extinct species... My work was of
considerable use to me, when I had to discuss in the "Origin of Species"
the principles of a natural classification. Nevertheless, I doubt
whether the work was worth the consumption of so much time."

"From September 1854 I devoted my whole time to arranging my huge
pile of notes, to observing, and to experimenting in relation to the
transmutation of species."

1856:

"Early in 1856 Lyell advised me to write out my views pretty fully, and
I began at once to do so on a scale three or four times as extensive as
that which was afterwards followed in my 'Origin of Species'."

1858:

Joint paper by Charles Darwin and Alfred Russel Wallace "On the Tendency
of Species to form Varieties; and on the perpetuation of Varieties and
Species by Natural Means of Selection," communicated to the Linnean
Society by Sir Charles Lyell and Sir Joseph Hooker.

"I was at first very unwilling to consent (to the communication of his
MS. to the Society) as I thought Mr Wallace might consider my doing so
unjustifiable, for I did not then know how generous and noble was his
disposition."

"July 20 to Aug. 12 at Sandown (Isle of Wight) began abstract of Species
book."

1859:

Nov. 24. Publication of "The Origin of Species" (1250 copies).

"Oh, good heavens, the relief to my head and body to banish the whole
subject from my mind!... But, alas, how frequent, how almost universal it
is in an author to persuade himself of the truth of his own dogmas.
My only hope is that I certainly see many difficulties of gigantic
stature."

1860:

Publication of the second edition of the "Origin" (3000 copies).

Publication of a "Naturalist's Voyage".

1861:

Publication of the third edition of the "Origin" (2000 copies).

"I am going to write a little book... on Orchids, and to-day I hate them
worse than everything."

1862:

Publication of the book "On the various contrivances by which Orchids
are fertilised by Insects".

1865:

Read paper before the Linnean Society "On the Movements and Habits of
Climbing plants". (Published as a book in 1875.)

1866:

Publication of the fourth edition of the "Origin" (1250 copies).

1868:

"I have sent the MS. of my big book, and horridly, disgustingly big it
will be, to the printers."

Publication of the "Variation of Animals and Plants under
Domestication".

"About my book, I will give you (Sir Joseph Hooker) a bit of advice.
Skip the whole of Vol. I, except the last chapter, (and that need only
be skimmed), and skip largely in the 2nd volume; and then you will say
it is a very good book."

"Towards the end of the work I give my well-abused hypothesis of
Pangenesis. An unverified hypothesis is of little or no value; but if
anyone should hereafter be led to make observations by which some such
hypothesis could be established, I shall have done good service, as an
astonishing number of isolated facts can be thus connected together and
rendered intelligible."

1869:

Publication of the fifth edition of the "Origin".

1871:

Publication of "The Descent of Man".

"Although in the 'Origin of Species' the derivation of any particular
species is never discussed, yet I thought it best, in order that no
honourable man should accuse me of concealing my views, to add that by
the work 'light would be thrown on the origin of man and his history'."

1872:

Publication of the sixth edition of the "Origin".

Publication of "The Expression of the Emotions in Man and Animals".

1874:

Publication of the second edition of "The Descent of Man".

"The new edition of the "Descent" has turned out an awful job. It took
me ten days merely to glance over letters and reviews with criticisms
and new facts. It is a devil of a job."

Publication of the second edition of "The Structure and Distribution of
Coral Reefs".

1875:

Publication of "Insectivorous Plants".

"I begin to think that every one who publishes a book is a fool."

Publication of the second edition of "Variation in Animals and Plants".

Publication of "The Movements and Habits of Climbing Plants" as a
separate book.

1876:

Wrote Autobiographical Sketch ("Life and Letters", Vol. I., Chap II.).

Publication of "The Effects of Cross and Self fertilisation".

"I now (1881) believe, however,...that I ought to have insisted more
strongly than I did on the many adaptations for self-fertilisation."

Publication of the second edition of "Observations on Volcanic Islands".

1877:

Publication of "The Different Forms of Flowers on Plants of the same
species".

"I do not suppose that I shall publish any more books... I cannot endure
being idle, but heaven knows whether I am capable of any more good
work."

Publication of the second edition of the Orchid book.

1878:

Publication of the second edition of "The Effects of Cross and Self
fertilisation".

1879:

Publication of an English translation of Ernst Krause's "Erasmus
Darwin", with a notice by Charles Darwin. "I am EXTREMELY glad that
you approve of the little 'Life' of our Grandfather, for I have been
repenting that I ever undertook it, as the work was quite beyond my
tether." (To Mr Francis Galton, Nov. 14, 1879.)

1880:

Publication of "The Power of Movement in Plants".

"It has always pleased me to exalt plants in the scale of organised
beings."

Publication of the second edition of "The Different Forms of Flowers".

1881:

Wrote a continuation of the Autobiography.

Publication of "The Formation of Vegetable Mould, through the Action of
Worms".

"It is the completion of a short paper read before the Geological
Society more than forty years ago, and has revived old geological
thoughts... As far as I can judge it will be a curious little book."

1882:

Charles Darwin died at Down, April 19, and was buried in Westminster
Abbey, April 26, in the north aisle of the Nave a few feet from the
grave of Sir Isaac Newton.

"As for myself, I believe that I have acted rightly in steadily
following and devoting my life to Science. I feel no remorse from having
committed any great sin, but have often and often regretted that I have
not done more direct good to my fellow creatures."

The quotations in the above Epitome are taken from the Autobiography and
published Letters:--

"The Life and Letters of Charles Darwin", including an Autobiographical
Chapter. Edited by his son, Francis Darwin, 3 Vols., London, 1887.

"Charles Darwin": His life told in an Autobiographical Chapter, and in
a selected series of his published Letters. Edited by his son, Francis
Darwin, London, 1902.

"More Letters of Charles Darwin". A record of his work in a series of
hitherto unpublished Letters. Edited by Francis Darwin and A.C. Seward,
2 Vols., London, 1903.




I. INTRODUCTORY LETTER From Sir Joseph Dalton Hooker, O.M., G.C.S.I.,
C.B., M.D., D.C.L., LL.D., F.R.S., ETC.


The Camp,

near Sunningdale,

January 15, 1909.

Dear Professor Seward,

The publication of a Series of Essays in Commemoration of the century
of the birth of Charles Darwin and of the fiftieth anniversary of the
publication of "The Origin of Species" is assuredly welcome and is a
subject of congratulation to all students of Science.

These Essays on the progress of Science and Philosophy as affected by
Darwin's labours have been written by men known for their ability to
discuss the problems which he so successfully worked to solve. They
cannot but prove to be of enduring value, whether for the information of
the general reader or as guides to investigators occupied with problems
similar to those which engaged the attention of Darwin.

The essayists have been fortunate in having for reference the five
published volumes of Charles Darwin's Life and Correspondence. For there
is set forth in his own words the inception in his mind of the problems,
geological, zoological and botanical, hypothetical and theoretical,
which he set himself to solve and the steps by which he proceeded to
investigate them with the view of correlating the phenomena of life with
the evolution of living things. In his letters he expressed himself in
language so lucid and so little burthened with technical terms that they
may be regarded as models for those who were asked to address themselves
primarily to the educated reader rather than to the expert.

I may add that by no one can the perusal of the Essays be more vividly
appreciated than by the writer of these lines. It was my privilege for
forty years to possess the intimate friendship of Charles Darwin and to
be his companion during many of his working hours in Study, Laboratory,
and Garden. I was the recipient of letters from him, relating mainly to
the progress of his researches, the copies of which (the originals are
now in the possession of his family) cover upwards of a thousand pages
of foolscap, each page containing, on an average, three hundred words.

That the editorship of these Essays has been entrusted to a Cambridge
Professor of Botany must be gratifying to all concerned in their
production and in their perusal, recalling as it does the fact that
Charles Darwin's instructor in scientific methods was his lifelong
friend the late Rev. J.S. Henslow at that time Professor of Botany in
the University. It was owing to his recommendation that his pupil was
appointed Naturalist to H.M.S. "Beagle", a service which Darwin himself
regarded as marking the dawn of his scientific career.

Very sincerely yours,

J.D. HOOKER.




II. DARWIN'S PREDECESSORS. By J. Arthur Thomson.

Professor of Natural History in the University of Aberdeen.


In seeking to discover Darwin's relation to his predecessors it is
useful to distinguish the various services which he rendered to the
theory of organic evolution.

(I) As everyone knows, the general idea of the Doctrine of Descent
is that the plants and animals of the present-day are the lineal
descendants of ancestors on the whole somewhat simpler, that these again
are descended from yet simpler forms, and so on backwards towards the
literal "Protozoa" and "Protophyta" about which we unfortunately know
nothing. Now no one supposes that Darwin originated this idea, which in
rudiment at least is as old as Aristotle. What Darwin did was to make
it current intellectual coin. He gave it a form that commended itself
to the scientific and public intelligence of the day, and he won
wide-spread conviction by showing with consummate skill that it was
an effective formula to work with, a key which no lock refused. In
a scholarly, critical, and pre-eminently fair-minded way, admitting
difficulties and removing them, foreseeing objections and forestalling
them, he showed that the doctrine of descent supplied a modal
interpretation of how our present-day fauna and flora have come to be.

(II) In the second place, Darwin applied the evolution-idea to
particular problems, such as the descent of man, and showed what a
powerful organon it is, introducing order into masses of uncorrelated
facts, interpreting enigmas both of structure and function, both
bodily and mental, and, best of all, stimulating and guiding further
investigation. But here again it cannot be claimed that Darwin was
original. The problem of the descent or ascent of man, and other
particular cases of evolution, had attracted not a few naturalists
before Darwin's day, though no one (except Herbert Spencer in the
psychological domain (1855)) had come near him in precision and
thoroughness of inquiry.

(III) In the third place, Darwin contributed largely to a knowledge of
the factors in the evolution-process, especially by his analysis of what
occurs in the case of domestic animals and cultivated plants, and by
his elaboration of the theory of Natural Selection, which Alfred Russel
Wallace independently stated at the same time, and of which there had
been a few previous suggestions of a more or less vague description.
It was here that Darwin's originality was greatest, for he revealed to
naturalists the many different forms--often very subtle--which natural
selection takes, and with the insight of a disciplined scientific
imagination he realised what a mighty engine of progress it has been and
is.

(IV) As an epoch-marking contribution, not only to Aetiology but to
Natural History in the widest sense, we rank the picture which
Darwin gave to the world of the web of life, that is to say, of
the inter-relations and linkages in Nature. For the Biology of the
individual--if that be not a contradiction in terms--no idea is more
fundamental than that of the correlation of organs, but Darwin's most
characteristic contribution was not less fundamental,--it was the idea
of the correlation of organisms. This, again, was not novel; we find
it in the works of naturalist like Christian Conrad Sprengel, Gilbert
White, and Alexander von Humboldt, but the realisation of its full
import was distinctively Darwinian.

AS REGARDS THE GENERAL IDEA OF ORGANIC EVOLUTION.

While it is true, as Prof. H.F. Osborn puts it, that "'Before and after
Darwin' will always be the ante et post urbem conditam of biological
history," it is also true that the general idea of organic evolution
is very ancient. In his admirable sketch "From the Greeks to Darwin"
("Columbia University Biological Series", Vol. I. New York and London,
1894. We must acknowledge our great indebtness to this fine piece of
work.), Prof. Osborn has shown that several of the ancient philosophers
looked upon Nature as a gradual development and as still in process of
change. In the suggestions of Empedocles, to take the best instance,
there were "four sparks of truth,--first, that the development of life
was a gradual process; second, that plants were evolved before animals;
third, that imperfect forms were gradually replaced (not succeeded)
by perfect forms; fourth, that the natural cause of the production of
perfect forms was the extinction of the imperfect." (Op. cit. page
41.) But the fundamental idea of one stage giving origin to another was
absent. As the blue Aegean teemed with treasures of beauty and threw
many upon its shores, so did Nature produce like a fertile artist what
had to be rejected as well as what was able to survive, but the idea of
one species emerging out of another was not yet conceived.

Aristotle's views of Nature (See G.J. Romanes, "Aristotle as a
Naturalist", "Contemporary Review", Vol. LIX. page 275, 1891; G. Pouchet
"La Biologie Aristotelique", Paris, 1885; E. Zeller, "A History of
Greek Philosophy", London, 1881, and "Ueber die griechischen Vorganger
Darwin's", "Abhandl. Berlin Akad." 1878, pages 111-124.) seem to have
been more definitely evolutionist than those of his predecessors, in
this sense, at least, that he recognised not only an ascending scale,
but a genetic series from polyp to man and an age-long movement towards
perfection. "It is due to the resistance of matter to form that Nature
can only rise by degrees from lower to higher types." "Nature produces
those things which, being continually moved by a certain principle
contained in themselves, arrive at a certain end."

To discern the outcrop of evolution-doctrine in the long interval
between Aristotle and Bacon seems to be very difficult, and some of
the instances that have been cited strike one as forced. Epicurus and
Lucretius, often called poets of evolution, both pictured animals as
arising directly out of the earth, very much as Milton's lion long
afterwards pawed its way out. Even when we come to Bruno who wrote that
"to the sound of the harp of the Universal Apollo (the World Spirit),
the lower organisms are called by stages to higher, and the lower stages
are connected by intermediate forms with the higher," there is great
room, as Prof. Osborn points out (op. cit. page 81.), for difference of
opinion as to how far he was an evolutionist in our sense of the term.

The awakening of natural science in the sixteenth century brought the
possibility of a concrete evolution theory nearer, and in the early
seventeenth century we find evidences of a new spirit--in the embryology
of Harvey and the classifications of Ray. Besides sober naturalists
there were speculative dreamers in the sixteenth and seventeenth
centuries who had at least got beyond static formulae, but, as Professor
Osborn points out (op. cit. page 87.), "it is a very striking fact, that
the basis of our modern methods of studying the Evolution problem was
established not by the early naturalists nor by the speculative writers,
but by the Philosophers." He refers to Bacon, Descartes, Leibnitz, Hume,
Kant, Lessing, Herder, and Schelling. "They alone were upon the main
track of modern thought. It is evident that they were groping in the
dark for a working theory of the Evolution of life, and it is remarkable
that they clearly perceived from the outset that the point to which
observation should be directed was not the past but the present
mutability of species, and further, that this mutability was simply the
variation of individuals on an extended scale."

Bacon seems to have been one of the first to think definitely about the
mutability of species, and he was far ahead of his age in his suggestion
of what we now call a Station of Experimental Evolution. Leibnitz
discusses in so many words how the species of animals may be changed
and how intermediate species may once have linked those that now seem
discontinuous. "All natural orders of beings present but a single
chain"... "All advances by degrees in Nature, and nothing by leaps."
Similar evolutionist statements are to be found in the works of the
other "philosophers," to whom Prof. Osborn refers, who were, indeed,
more scientific than the naturalists of their day. It must be borne in
mind that the general idea of organic evolution--that the present is
the child of the past--is in great part just the idea of human history
projected upon the natural world, differentiated by the qualification
that the continuous "Becoming" has been wrought out by forces inherent
in the organisms themselves and in their environment.

A reference to Kant (See Brock, "Die Stellung Kant's zur
Deszendenztheorie," "Biol. Centralbl." VIII. 1889, pages 641-648. Fritz
Schultze, "Kant und Darwin", Jena, 1875.) should come in historical
order after Buffon, with whose writings he was acquainted, but he seems,
along with Herder and Schelling, to be best regarded as the culmination
of the evolutionist philosophers--of those at least who interested
themselves in scientific problems. In a famous passage he speaks of
"the agreement of so many kinds of animals in a certain common plan of
structure"... an "analogy of forms" which "strengthens the supposition
that they have an actual blood-relationship, due to derivation from a
common parent." He speaks of "the great Family of creatures, for as
a Family we must conceive it, if the above-mentioned continuous and
connected relationship has a real foundation." Prof. Osborn alludes to
the scientific caution which led Kant, biology being what it was, to
refuse to entertain the hope "that a Newton may one day arise even to
make the production of a blade of grass comprehensible, according
to natural laws ordained by no intention." As Prof. Haeckel finely
observes, Darwin rose up as Kant's Newton. (Mr Alfred Russel Wallace
writes: "We claim for Darwin that he is the Newton of natural history,
and that, just so surely as that the discovery and demonstration by
Newton of the law of gravitation established order in place of chaos and
laid a sure foundation for all future study of the starry heavens, so
surely has Darwin, by his discovery of the law of natural selection and
his demonstration of the great principle of the preservation of useful
variations in the struggle for life, not only thrown a flood of light
on the process of development of the whole organic world, but
also established a firm foundation for all future study of nature."
("Darwinism", London, 1889, page 9). See also Prof. Karl Pearson's
"Grammar of Science" (2nd edition), London, 1900, page 32. See Osborn,
op. cit. Page 100.))

The scientific renaissance brought a wealth of fresh impressions and
some freedom from the tyranny of tradition, and the twofold stimulus
stirred the speculative activity of a great variety of men from old
Claude Duret of Moulins, of whose weird transformism (1609) Dr Henry
de Varigny ("Experimental Evolution". London, 1892. Chap. 1. page 14.)
gives us a glimpse, to Lorenz Oken (1799-1851) whose writings are such
mixtures of sense and nonsense that some regard him as a
far-seeing prophet and others as a fatuous follower of intellectual
will-o'-the-wisps. Similarly, for De Maillet, Maupertuis, Diderot,
Bonnet, and others, we must agree with Professor Osborn that they were
not actually in the main Evolution movement. Some have been included in
the roll of honour on very slender evidence, Robinet for instance, whose
evolutionism seems to us extremely dubious. (See J. Arthur Thomson,
"The Science of Life". London, 1899. Chap. XVI. "Evolution of Evolution
Theory".)

The first naturalist to give a broad and concrete expression to the
evolutionist doctrine of descent was Buffon (1707-1788), but it
is interesting to recall the fact that his contemporary Linnaeus
(1707-1778), protagonist of the counter-doctrine of the fixity
of species (See Carus Sterne (Ernest Krause), "Die allgemeine
Weltanschauung in ihrer historischen Entwickelung". Stuttgart, 1889.
Chapter entitled "Bestandigkeit oder Veranderlichkeit der Naturwesen".),
went the length of admitting (in 1762) that new species might arise
by intercrossing. Buffon's position among the pioneers of the
evolution-doctrine is weakened by his habit of vacillating between his
own conclusions and the orthodoxy of the Sorbonne, but there is no doubt
that he had a firm grasp of the general idea of "l'enchainement des
etres."

Erasmus Darwin (1731-1802), probably influenced by Buffon, was another
firm evolutionist, and the outline of his argument in the "Zoonomia"
("Zoonomia, or the Laws of Organic Life", 2 vols. London, 1794; Osborn
op. cit. page 145.) might serve in part at least to-day. "When we
revolve in our minds the metamorphoses of animals, as from the tadpole
to the frog; secondly, the changes produced by artificial cultivation,
as in the breeds of horses, dogs, and sheep; thirdly, the changes
produced by conditions of climate and of season, as in the sheep of
warm climates being covered with hair instead of wool, and the hares and
partridges of northern climates becoming white in winter: when,
further, we observe the changes of structure produced by habit, as seen
especially in men of different occupations; or the changes produced by
artificial mutilation and prenatal influences, as in the crossing
of species and production of monsters; fourth, when we observe the
essential unity of plan in all warm-blooded animals,--we are led to
conclude that they have been alike produced from a similar living
filament"... "From thus meditating upon the minute portion of time in
which many of the above changes have been produced, would it be too bold
to imagine, in the great length of time since the earth began to exist,
perhaps millions of years before the commencement of the history of
mankind, that all warm-blooded animals have arisen from one living
filament?"... "This idea of the gradual generation of all things seems to
have been as familiar to the ancient philosophers as to the modern
ones, and to have given rise to the beautiful hieroglyphic figure of the
proton oon, or first great egg, produced by night, that is, whose origin
is involved in obscurity, and animated by Eros, that is, by Divine Love;
from whence proceeded all things which exist."

Lamarck (1744-1829) seems to have become an evolutionist independently
of Erasmus Darwin's influence, though the parallelism between them is
striking. He probably owed something to Buffon, but he developed his
theory along a different line. Whatever view be held in regard to that
theory there is no doubt that Lamarck was a thorough-going evolutionist.
Professor Haeckel speaks of the "Philosophie Zoologique" as "the first
connected and thoroughly logical exposition of the theory of descent."
(See Alpheus S. Packard, "Lamarck, the Founder of Evolution, His Life
and Work, with Translations of his writings on Organic Evolution".
London, 1901.)

Besides the three old masters, as we may call them, Buffon, Erasmus
Darwin, and Lamarck, there were other quite convinced pre-Darwinian
evolutionists. The historian of the theory of descent must take account
of Treviranus whose "Biology or Philosophy of Animate Nature" is full of
evolutionary suggestions; of Etienne Geoffroy St Hilaire, who in
1830, before the French Academy of Sciences, fought with Cuvier, the
fellow-worker of his youth, an intellectual duel on the question of
descent; of Goethe, one of the founders of morphology and the greatest
poet of Evolution--who, in his eighty-first year, heard the tidings
of Geoffroy St Hilaire's defeat with an interest which transcended the
political anxieties of the time; and of many others who had gained with
more or less confidence and clearness a new outlook on Nature. It
will be remembered that Darwin refers to thirty-four more or less
evolutionist authors in his Historical Sketch, and the list might be
added to. Especially when we come near to 1858 do the numbers increase,
and one of the most remarkable, as also most independent champions of
the evolution-idea before that date was Herbert Spencer, who not only
marshalled the arguments in a very forcible way in 1852, but applied the
formula in detail in his "Principles of Psychology" in 1855. (See Edward
Clodd, "Pioneers of Evolution", London, page 161, 1897.)

It is right and proper that we should shake ourselves free from all
creationist appreciations of Darwin, and that we should recognise the
services of pre-Darwinian evolutionists who helped to make the time
ripe, yet one cannot help feeling that the citation of them is apt to
suggest two fallacies. It may suggest that Darwin simply entered into
the labours of his predecessors, whereas, as a matter of fact, he knew
very little about them till after he had been for years at work. To
write, as Samuel Butler did, "Buffon planted, Erasmus Darwin and Lamarck
watered, but it was Mr Darwin who said 'That fruit is ripe,' and shook
it into his lap"... seems to us a quite misleading version of the facts
of the case. The second fallacy which the historical citation is
a little apt to suggest is that the filiation of ideas is a simple
problem. On the contrary, the history of an idea, like the pedigree
of an organism, is often very intricate, and the evolution of the
evolution-idea is bound up with the whole progress of the world. Thus
in order to interpret Darwin's clear formulation of the idea of organic
evolution and his convincing presentation of it, we have to do more than
go back to his immediate predecessors, such as Buffon, Erasmus Darwin,
and Lamarck; we have to inquire into the acceptance of evolutionary
conceptions in regard to other orders of facts, such as the earth and
the solar system (See Chapter IX. "The Genetic View of Nature" in J.T.
Merz's "History of European Thought in the Nineteenth Century", Vol. 2,
Edinburgh and London, 1903.); we have to realise how the growing success
of scientific interpretation along other lines gave confidence to those
who refused to admit that there was any domain from which science could
be excluded as a trespasser; we have to take account of the development
of philosophical thought, and even of theological and religious
movements; we should also, if we are wise enough, consider social
changes. In short, we must abandon the idea that we can understand
the history of any science as such, without reference to contemporary
evolution in other departments of activity.

While there were many evolutionists before Darwin, few of them were
expert naturalists and few were known outside a small circle; what
was of much more importance was that the genetic view of nature was
insinuating itself in regard to other than biological orders of facts,
here a little and there a little, and that the scientific spirit had
ripened since the days when Cuvier laughed Lamarck out of court. How was
it that Darwin succeeded where others had failed? Because, in the first
place, he had clear visions--"pensees de la jeunesse, executees par
l'age mur"--which a University curriculum had not made impossible, which
the "Beagle" voyage made vivid, which an unrivalled British doggedness
made real--visions of the web of life, of the fountain of change within
the organism, of the struggle for existence and its winnowing, and of
the spreading genealogical tree. Because, in the second place, he put
so much grit into the verification of his visions, putting them to the
proof in an argument which is of its kind--direct demonstration being
out of the question--quite unequalled. Because, in the third place,
he broke down the opposition which the most scientific had felt to
the seductive modal formula of evolution by bringing forward a more
plausible theory of the process than had been previously suggested.
Nor can one forget, since questions of this magnitude are human and not
merely academic, that he wrote so that all men could understand.

AS REGARDS THE FACTORS OF EVOLUTION.

It is admitted by all who are acquainted with the history of biology
that the general idea of organic evolution as expressed in the Doctrine
of Descent was quite familiar to Darwin's grandfather, and to others
before and after him, as we have briefly indicated. It must also be
admitted that some of these pioneers of evolutionism did more than apply
the evolution-idea as a modal formula of becoming, they began to inquire
into the factors in the process. Thus there were pre-Darwinian theories
of evolution, and to these we must now briefly refer. (See Prof. W.A.
Locy's "Biology and its Makers". New York, 1908. Part II. "The Doctrine
of Organic Evolution".)

In all biological thinking we have to work with the categories
Organism--Function--Environment, and theories of evolution may be
classified in relation to these. To some it has always seemed that the
fundamental fact is the living organism,--a creative agent, a striving
will, a changeful Proteus, selecting its environment, adjusting
itself to it, self-differentiating and self-adaptive. The necessity of
recognising the importance of the organism is admitted by all Darwinians
who start with inborn variations, but it is open to question whether the
whole truth of what we might call the Goethian position is exhausted in
the postulate of inherent variability.

To others it has always seemed that the emphasis should be laid on
Function,--on use and disuse, on doing and not doing. Practice makes
perfect; c'est a force de forger qu'on devient forgeron. This is one of
the fundamental ideas of Lamarckism; to some extent it met with Darwin's
approval; and it finds many supporters to-day. One of the ablest
of these--Mr Francis Darwin--has recently given strong reasons for
combining a modernised Lamarckism with what we usually regard as sound
Darwinism. (Presidential Address to the British Association meeting at
Dublin in 1908.)

To others it has always seemed that the emphasis should be laid on the
Environment, which wakes the organism to action, prompts it to change,
makes dints upon it, moulds it, prunes it, and finally, perhaps, kills
it. It is again impossible to doubt that there is truth in this
view, for even if environmentally induced "modifications" be not
transmissible, environmentally induced "variations" are; and even if
the direct influence of the environment be less important than
many enthusiastic supporters of this view--may we call them
Buffonians--think, there remains the indirect influence which Darwinians
in part rely on,--the eliminative process. Even if the extreme view
be held that the only form of discriminate elimination that counts is
inter-organismal competition, this might be included under the rubric of
the animate environment.

In many passages Buffon (See in particular Samuel Butler, "Evolution
Old and New", London, 1879; J.L. de Lanessan, "Buffon et Darwin",
"Revue Scientifique", XLIII. pages 385-391, 425-432, 1889.) definitely
suggested that environmental influences--especially of climate and
food--were directly productive of changes in organisms, but he did not
discuss the question of the transmissibility of the modifications so
induced, and it is difficult to gather from his inconsistent writings
what extent of transformation he really believed in. Prof. Osborn
says of Buffon: "The struggle for existence, the elimination of the
least-perfected species, the contest between the fecundity of certain
species and their constant destruction, are all clearly expressed in
various passages." He quotes two of these (op. cit. page 136.):

"Le cours ordinaire de la nature vivante, est en general toujours
constant, toujours le meme; son mouvement, toujours regulier, roule
sur deux points inebranlables: l'un, la fecondite sans bornes donnee
a toutes les especes; l'autre, les obstacles sans nombre qui reduisent
cette fecondite a une mesure determinee et ne laissent en tout temps
qu'a peu pres la meme quantite d'individus de chaque espece"... "Les
especes les moins parfaites, les plus delicates, les plus pesantes,
les moins agissantes, les moins armees, etc., ont deja disparu ou
disparaitront."

Erasmus Darwin (See Ernst Krause and Charles Darwin, "Erasmus Darwin",
London, 1879.) had a firm grip of the "idea of the gradual formation and
improvement of the Animal world," and he had his theory of the process.
No sentence is more characteristic than this: "All animals undergo
transformations which are in part produced by their own exertions, in
response to pleasures and pains, and many of these acquired forms or
propensities are transmitted to their posterity." This is Lamarckism
before Lamarck, as his grandson pointed out. His central idea is that
wants stimulate efforts and that these result in improvements, which
subsequent generations make better still. He realised something of the
struggle for existence and even pointed out that this advantageously
checks the rapid multiplication. "As Dr Krause points out, Darwin just
misses the connection between this struggle and the Survival of the
Fittest." (Osborn op. cit. page 142.)

Lamarck (1744-1829) (See E. Perrier "La Philosophie Zoologique avant
Darwin", Paris, 1884; A. de Quatrefages, "Darwin et ses Precurseurs
Francais", Paris, 1870; Packard op. cit.; also Claus, "Lamarck als
Begrunder der Descendenzlehre", Wien, 1888; Haeckel, "Natural History
of Creation", English translation London, 1879; Lang "Zur Charakteristik
der Forschungswege von Lamarck und Darwin", Jena, 1889.) seems to have
thought out his theory of evolution without any knowledge of Erasmus
Darwin's which it closely resembled. The central idea of his theory
was the cumulative inheritance of functional modifications. "Changes
in environment bring about changes in the habits of animals. Changes in
their wants necessarily bring about parallel changes in their habits. If
new wants become constant or very lasting, they form new habits, the new
habits involve the use of new parts, or a different use of old
parts, which results finally in the production of new organs and the
modification of old ones." He differed from Buffon in not attaching
importance, as far as animals are concerned, to the direct influence of
the environment, "for environment can effect no direct change whatever
upon the organisation of animals," but in regard to plants he agreed
with Buffon that external conditions directly moulded them.

Treviranus (1776-1837) (See Huxley's article "Evolution in Biology",
"Encyclopaedia Britannica" (9th edit.), 1878, pages 744-751, and Sully's
article, "Evolution in Philosophy", ibid. pages 751-772.), whom Huxley
ranked beside Lamarck, was on the whole Buffonian, attaching chief
importance to the influence of a changeful environment both in modifying
and in eliminating, but he was also Goethian, for instance in his idea
that species like individuals pass through periods of growth, full
bloom, and decline. "Thus, it is not only the great catastrophes of
Nature which have caused extinction, but the completion of cycles
of existence, out of which new cycles have begun." A characteristic
sentence is quoted by Prof. Osborn: "In every living being there exists
a capability of an endless variety of form-assumption; each possesses
the power to adapt its organisation to the changes of the outer world,
and it is this power, put into action by the change of the universe,
that has raised the simple zoophytes of the primitive world to
continually higher stages of organisation, and has introduced a
countless variety of species into animate Nature."

Goethe (1749-1832) (See Haeckel, "Die Naturanschauung von Darwin, Goethe
und Lamarck", Jena, 1882.), who knew Buffon's work but not Lamarck's, is
peculiarly interesting as one of the first to use the evolution-idea as
a guiding hypothesis, e.g. in the interpretation of vestigial structures
in man, and to realise that organisms express an attempt to make a
compromise between specific inertia and individual change. He gave the
finest expression that science has yet known--if it has known it--of
the kernel-idea of what is called "bathmism," the idea of an "inherent
growth-force"--and at the same time he held that "the way of life
powerfully reacts upon all form" and that the orderly growth of form
"yields to change from externally acting causes."

Besides Buffon, Erasmus Darwin, Lamarck, Treviranus, and Goethe,
there were other "pioneers of evolution," whose views have been often
discussed and appraised. Etienne Geoffroy Saint-Hilaire (1772-1844),
whose work Goethe so much admired, was on the whole Buffonian,
emphasising the direct action of the changeful milieu. "Species
vary with their environment, and existing species have descended by
modification from earlier and somewhat simpler species." He had a
glimpse of the selection idea, and believed in mutations or sudden
leaps--induced in the embryonic condition by external influences. The
complete history of evolution-theories will include many instances
of guesses at truth which were afterwards substantiated, thus the
geographer von Buch (1773-1853) detected the importance of the Isolation
factor on which Wagner, Romanes, Gulick and others have laid great
stress, but we must content ourselves with recalling one other pioneer,
the author of the "Vestiges of Creation" (1844), a work which passed
through ten editions in nine years and certainly helped to harrow the
soil for Darwin's sowing. As Darwin said, "it did excellent service in
this country in calling attention to the subject, in removing prejudice,
and in thus preparing the ground for the reception of analogous views."
("Origin of Species" (6th edition), page xvii.) Its author, Robert
Chambers (1802-1871) was in part a Buffonian--maintaining
that environment moulded organisms adaptively, and in part a
Goethian--believing in an inherent progressive impulse which lifted
organisms from one grade of organisation to another.

AS REGARDS NATURAL SELECTION.

The only thinker to whom Darwin was directly indebted, so far as the
theory of Natural Selection is concerned, was Malthus, and we may once
more quote the well-known passage in the Autobiography: "In October,
1838, that is, fifteen months after I had begun my systematic enquiry,
I happened to read for amusement 'Malthus on Population', and being well
prepared to appreciate the struggle for existence which everywhere goes
on from long-continued observation of the habits of animals and
plants, it at once struck me that under these circumstances favourable
variations would tend to be preserved, and unfavourable ones to be
destroyed. The result of this would be the formation of new species."
("The Life and Letters of Charles Darwin", Vol. 1. page 83. London,
1887.)

Although Malthus gives no adumbration of the idea of Natural Selection
in his exposition of the eliminative processes which go on in mankind,
the suggestive value of his essay is undeniable, as is strikingly
borne out by the fact that it gave to Alfred Russel Wallace also "the
long-sought clue to the effective agent in the evolution of organic
species." (A.R. Wallace, "My Life, A Record of Events and Opinions",
London, 1905, Vol. 1. page 232.) One day in Ternate when he was resting
between fits of fever, something brought to his recollection the work of
Malthus which he had read twelve years before. "I thought of his clear
exposition of 'the positive checks to increase'--disease, accidents,
war, and famine--which keep down the population of savage races to
so much lower an average than that of more civilized peoples. It then
occurred to me that these causes or their equivalents are continually
acting in the case of animals also; and as animals usually breed much
more rapidly than does mankind, the destruction every year from these
causes must be enormous in order to keep down the numbers of each
species, since they evidently do not increase regularly from year to
year, as otherwise the world would long ago have been densely crowded
with those that breed most quickly. Vaguely thinking over the enormous
and constant destruction which this implied, it occurred to me to ask
the question, Why do some die and some live? And the answer was clearly,
that on the whole the best fitted live. From the effects of disease the
most healthy escaped; from enemies the strongest, the swiftest, or
the most cunning; from famine the best hunters or those with the
best digestion; and so on. Then it suddenly flashed upon me that this
self-acting process would necessarily IMPROVE THE RACE, because in every
generation the inferior would inevitably be killed off and the superior
would remain--that is, THE FITTEST WOULD SURVIVE." (Ibid. Vol. 1. page
361.) We need not apologise for this long quotation, it is a tribute
to Darwin's magnanimous colleague, the Nestor of the evolutionist
camp,--and it probably indicates the line of thought which Darwin
himself followed. It is interesting also to recall the fact that in
1852, when Herbert Spencer wrote his famous "Leader" article on "The
Development Hypothesis" in which he argued powerfully for the thesis
that the whole animate world is the result of an age-long process of
natural transformation, he wrote for "The Westminster Review" another
important essay, "A Theory of Population deduced from the General Law of
Animal Fertility", towards the close of which he came within an ace
of recognising that the struggle for existence was a factor in organic
evolution. At a time when pressure of population was practically
interesting men's minds, Darwin, Wallace, and Spencer were being
independently led from a social problem to a biological theory. There
could be no better illustration, as Prof. Patrick Geddes has pointed
out, of the Comtian thesis that science is a "social phenomenon."

Therefore, as far more important than any further ferreting out of vague
hints of Natural Selection in books which Darwin never read, we would
indicate by a quotation the view that the central idea in Darwinism
is correlated with contemporary social evolution. "The substitution
of Darwin for Paley as the chief interpreter of the order of nature is
currently regarded as the displacement of an anthropomorphic view by a
purely scientific one: a little reflection, however, will show that
what has actually happened has been merely the replacement of the
anthropomorphism of the eighteenth century by that of the nineteenth.
For the place vacated by Paley's theological and metaphysical
explanation has simply been occupied by that suggested to Darwin and
Wallace by Malthus in terms of the prevalent severity of industrial
competition, and those phenomena of the struggle for existence which the
light of contemporary economic theory has enabled us to discern, have
thus come to be temporarily exalted into a complete explanation
of organic progress." (P. Geddes, article "Biology", "Chambers's
Encyclopaedia".) It goes without saying that the idea suggested by
Malthus was developed by Darwin into a biological theory which was then
painstakingly verified by being used as an interpretative formula, and
that the validity of a theory so established is not affected by what
suggested it, but the practical question which this line of thought
raises in the mind is this: if Biology did thus borrow with such
splendid results from social theory, why should we not more deliberately
repeat the experiment?

Darwin was characteristically frank and generous in admitting that the
principle of Natural Selection had been independently recognised by
Dr W.C. Wells in 1813 and by Mr Patrick Matthew in 1831, but he had no
knowledge of these anticipations when he published the first edition
of "The Origin of Species". Wells, whose "Essay on Dew" is still
remembered, read in 1813 before the Royal Society a short paper entitled
"An account of a White Female, part of whose skin resembles that of a
Negro" (published in 1818). In this communication, as Darwin said, "he
observes, firstly, that all animals tend to vary in some degree, and,
secondly, that agriculturists improve their domesticated animals by
selection; and then, he adds, but what is done in this latter case
'by art, seems to be done with equal efficacy, though more slowly, by
nature, in the formation of varieties of mankind, fitted for the country
which they inhabit.'" ("Origin of Species" (6th edition) page xv.)
Thus Wells had the clear idea of survival dependent upon a favourable
variation, but he makes no more use of the idea and applies it only
to man. There is not in the paper the least hint that the author ever
thought of generalising the remarkable sentence quoted above.

Of Mr Patrick Matthew, who buried his treasure in an appendix to a work
on "Naval Timber and Arboriculture", Darwin said that "he clearly saw
the full force of the principle of natural selection." In 1860 Darwin
wrote--very characteristically--about this to Lyell: "Mr Patrick
Matthew publishes a long extract from his work on "Naval Timber and
Arboriculture", published in 1831, in which he briefly but completely
anticipates the theory of Natural Selection. I have ordered the book,
as some passages are rather obscure, but it is certainly, I think, a
complete but not developed anticipation. Erasmus always said that surely
this would be shown to be the case some day. Anyhow, one may be excused
in not having discovered the fact in a work on Naval Timber." ("Life and
Letters" II. page 301.)

De Quatrefages and De Varigny have maintained that the botanist Naudin
stated the theory of evolution by natural selection in 1852. He explains
very clearly the process of artificial selection, and says that in the
garden we are following Nature's method. "We do not think that Nature
has made her species in a different fashion from that in which we
proceed ourselves in order to make our variations." But, as Darwin said,
"he does not show how selection acts under nature." Similarly it must
be noted in regard to several pre-Darwinian pictures of the struggle
for existence (such as Herder's, who wrote in 1790 "All is in
struggle... each one for himself" and so on), that a recognition of this
is only the first step in Darwinism.

Profs. E. Perrier and H.F. Osborn have called attention to a remarkable
anticipation of the selection-idea which is to be found in the
speculations of Etienne Geoffroy St Hilaire (1825-1828) on the evolution
of modern Crocodilians from the ancient Teleosaurs. Changing environment
induced changes in the respiratory system and far-reaching consequences
followed. The atmosphere, acting upon the pulmonary cells, brings about
"modifications which are favourable or destructive ('funestes'); these
are inherited, and they influence all the rest of the organisation of
the animal because if these modifications lead to injurious effects,
the animals which exhibit them perish and are replaced by others of a
somewhat different form, a form changed so as to be adapted to (a la
convenance) the new environment."

Prof. E.B. Poulton ("Science Progress", New Series, Vol. I. 1897. "A
Remarkable Anticipation of Modern Views on Evolution". See also
Chap. VI. in "Essays on Evolution", Oxford, 1908.) has shown that the
anthropologist James Cowles Prichard (1786-1848) must be included, even
in spite of himself, among the precursors of Darwin. In some passages
of the second edition of his "Researches into the Physical History of
Mankind" (1826), he certainly talks evolution and anticipates Prof.
Weismann in denying the transmission of acquired characters. He is,
however, sadly self-contradictory and his evolutionism weakens in
subsequent editions--the only ones that Darwin saw. Prof. Poulton finds
in Prichard's work a recognition of the operation of Natural Selection.
"After enquiring how it is that 'these varieties are developed and
preserved in connection with particular climates and differences of
local situation,' he gives the following very significant answer: 'One
cause which tends to maintain this relation is obvious. Individuals and
families, and even whole colonies, perish and disappear in climates for
which they are, by peculiarity of constitution, not adapted. Of this
fact proofs have been already mentioned.'" Mr Francis Darwin and Prof.
A.C. Seward discuss Prichard's "anticipations" in "More Letters of
Charles Darwin", Vol. I. page 43, and come to the conclusion that the
evolutionary passages are entirely neutralised by others of an opposite
trend. There is the same difficulty with Buffon.

Hints of the idea of Natural Selection have been detected elsewhere.
James Watt (See Prof. Patrick Geddes's article "Variation and
Selection", "Encyclopaedia Britannica (9th edition) 1888.), for
instance, has been reported as one of the anticipators (1851). But we
need not prolong the inquiry further, since Darwin did not know of any
anticipations until after he had published the immortal work of 1859,
and since none of those who got hold of the idea made any use of it.
What Darwin did was to follow the clue which Malthus gave him, to
realise, first by genius and afterwards by patience, how the complex
and subtle struggle for existence works out a natural selection of
those organisms which vary in the direction of fitter adaptation to the
conditions of their life. So much success attended his application of
the Selection-formula that for a time he regarded Natural Selection
as almost the sole factor in evolution, variations being pre-supposed;
gradually, however, he came to recognise that there was some validity in
the factors which had been emphasized by Lamarck and by Buffon, and in
his well-known summing up in the sixth edition of the "Origin" he
says of the transformation of species: "This has been effected chiefly
through the natural selection of numerous successive, slight, favourable
variations; aided in an important manner by the inherited effects of
the use and disuse of parts; and in an unimportant manner, that is, in
relation to adaptive structures, whether past or present, by the direct
action of external conditions, and by variations which seem to us in our
ignorance to arise spontaneously."

To sum up: the idea of organic evolution, older than Aristotle, slowly
developed from the stage of suggestion to the stage of verification, and
the first convincing verification was Darwin's; from being an a priori
anticipation it has become an interpretation of nature, and Darwin is
still the chief interpreter; from being a modal interpretation it has
advanced to the rank of a causal theory, the most convincing part of
which men will never cease to call Darwinism.




III. THE SELECTION THEORY, By August Weismann.

Professor of Zoology in the University of Freiburg (Baden).


I. THE IDEA OF SELECTION.

Many and diverse were the discoveries made by Charles Darwin in the
course of a long and strenuous life, but none of them has had so
far-reaching an influence on the science and thought of his time as the
theory of selection. I do not believe that the theory of evolution would
have made its way so easily and so quickly after Darwin took up the
cudgels in favour of it, if he had not been able to support it by a
principle which was capable of solving, in a simple manner, the greatest
riddle that living nature presents to us,--I mean the purposiveness
of every living form relative to the conditions of its life and its
marvellously exact adaptation to these.

Everyone knows that Darwin was not alone in discovering the principle
of selection, and that the same idea occurred simultaneously and
independently to Alfred Russel Wallace. At the memorable meeting of the
Linnean Society on 1st July, 1858, two papers were read (communicated by
Lyell and Hooker) both setting forth the same idea of selection. One
was written by Charles Darwin in Kent, the other by Alfred Wallace
in Ternate, in the Malay Archipelago. It was a splendid proof of
the magnanimity of these two investigators, that they thus, in all
friendliness and without envy, united in laying their ideas before a
scientific tribunal: their names will always shine side by side as two
of the brightest stars in the scientific sky.

But it is with Charles Darwin that I am here chiefly concerned, since
this paper is intended to aid in the commemoration of the hundredth
anniversary of his birth.

The idea of selection set forth by the two naturalists was at the time
absolutely new, but it was also so simple that Huxley could say of it
later, "How extremely stupid not to have thought of that." As Darwin was
led to the general doctrine of descent, not through the labours of
his predecessors in the early years of the century, but by his own
observations, so it was in regard to the principle of selection. He was
struck by the innumerable cases of adaptation, as, for instance, that
of the woodpeckers and tree-frogs to climbing, or the hooks and
feather-like appendages of seeds, which aid in the distribution of
plants, and he said to himself that an explanation of adaptations was
the first thing to be sought for in attempting to formulate a theory of
evolution.

But since adaptations point to CHANGES which have been undergone by the
ancestral forms of existing species, it is necessary, first of all, to
inquire how far species in general are VARIABLE. Thus Darwin's attention
was directed in the first place to the phenomenon of variability, and
the use man has made of this, from very early times, in the breeding of
his domesticated animals and cultivated plants. He inquired carefully
how breeders set to work, when they wished to modify the structure and
appearance of a species to their own ends, and it was soon clear to him
that SELECTION FOR BREEDING PURPOSES played the chief part.

But how was it possible that such processes should occur in free
nature? Who is here the breeder, making the selection, choosing out one
individual to bring forth offspring and rejecting others? That was the
problem that for a long time remained a riddle to him.

Darwin himself relates how illumination suddenly came to him. He had
been reading, for his own pleasure, Malthus' book on Population, and, as
he had long known from numerous observations, that every species gives
rise to many more descendants than ever attain to maturity, and that,
therefore, the greater number of the descendants of a species perish
without reproducing, the idea came to him that the decision as to which
member of a species was to perish, and which was to attain to maturity
and reproduction might not be a matter of chance, but might be
determined by the constitution of the individuals themselves, according
as they were more or less fitted for survival. With this idea the
foundation of the theory of selection was laid.

In ARTIFICIAL SELECTION the breeder chooses out for pairing only such
individuals as possess the character desired by him in a somewhat higher
degree than the rest of the race. Some of the descendants inherit this
character, often in a still higher degree, and if this method be pursued
throughout several generations, the race is transformed in respect of
that particular character.

NATURAL SELECTION depends on the same three factors as ARTIFICIAL
SELECTION: on VARIABILITY, INHERITANCE, and SELECTION FOR BREEDING, but
this last is here carried out not by a breeder but by what Darwin called
the "struggle for existence." This last factor is one of the special
features of the Darwinian conception of nature. That there are
carnivorous animals which take heavy toll in every generation of the
progeny of the animals on which they prey, and that there are herbivores
which decimate the plants in every generation had long been known, but
it is only since Darwin's time that sufficient attention has been paid
to the facts that, in addition to this regular destruction, there exists
between the members of a species a keen competition for space and food,
which limits multiplication, and that numerous individuals of each
species perish because of unfavourable climatic conditions. The
"struggle for existence," which Darwin regarded as taking the place
of the human breeder in free nature, is not a direct struggle between
carnivores and their prey, but is the assumed competition for survival
between individuals OF THE SAME species, of which, on an average, only
those survive to reproduce which have the greatest power of resistance,
while the others, less favourably constituted, perish early. This
struggle is so keen, that, within a limited area, where the conditions
of life have long remained unchanged, of every species, whatever be the
degree of fertility, only two, ON AN AVERAGE, of the descendants of each
pair survive; the others succumb either to enemies, or to disadvantages
of climate, or to accident. A high degree of fertility is thus not an
indication of the special success of a species, but of the numerous
dangers that have attended its evolution. Of the six young brought forth
by a pair of elephants in the course of their lives only two survive in
a given area; similarly, of the millions of eggs which two thread-worms
leave behind them only two survive. It is thus possible to estimate the
dangers which threaten a species by its ratio of elimination, or, since
this cannot be done directly, by its fertility.

Although a great number of the descendants of each generation fall
victims to accident, among those that remain it is still the greater
or lesser fitness of the organism that determines the "selection
for breeding purposes," and it would be incomprehensible if, in this
competition, it were not ultimately, that is, on an average, the best
equipped which survive, in the sense of living long enough to reproduce.

Thus the principle of natural selection is THE SELECTION OF THE BEST FOR
REPRODUCTION, whether the "best" refers to the whole constitution,
to one or more parts of the organism, or to one or more stages of
development. Every organ, every part, every character of an animal,
fertility and intelligence included, must be improved in this manner,
and be gradually brought up in the course of generations to its highest
attainable state of perfection. And not only may improvement of parts
be brought about in this way, but new parts and organs may arise,
since, through the slow and minute steps of individual or "fluctuating"
variations, a part may be added here or dropped out there, and thus
something new is produced.

The principle of selection solved the riddle as to how what was
purposive could conceivably be brought about without the intervention
of a directing power, the riddle which animate nature presents to our
intelligence at every turn, and in face of which the mind of a Kant
could find no way out, for he regarded a solution of it as not to be
hoped for. For, even if we were to assume an evolutionary force that is
continually transforming the most primitive and the simplest forms of
life into ever higher forms, and the homogeneity of primitive times into
the infinite variety of the present, we should still be unable to infer
from this alone how each of the numberless forms adapted to particular
conditions of life should have appeared PRECISELY AT THE RIGHT MOMENT
IN THE HISTORY OF THE EARTH to which their adaptations were appropriate,
and precisely at the proper place in which all the conditions of life to
which they were adapted occurred: the humming-birds at the same time as
the flowers; the trichina at the same time as the pig; the bark-coloured
moth at the same time as the oak, and the wasp-like moth at the same
time as the wasp which protects it. Without processes of selection we
should be obliged to assume a "pre-established harmony" after the famous
Leibnitzian model, by means of which the clock of the evolution of
organisms is so regulated as to strike in exact synchronism with that of
the history of the earth! All forms of life are strictly adapted to the
conditions of their life, and can persist under these conditions alone.

There must therefore be an intrinsic connection between the conditions
and the structural adaptations of the organism, and, SINCE THE
CONDITIONS OF LIFE CANNOT BE DETERMINED BY THE ANIMAL ITSELF, THE
ADAPTATIONS MUST BE CALLED FORTH BY THE CONDITIONS.

The selection theory teaches us how this is conceivable, since it
enables us to understand that there is a continual production of what is
non-purposive as well as of what is purposive, but the purposive alone
survives, while the non-purposive perishes in the very act of arising.
This is the old wisdom taught long ago by Empedocles.

II. THE LAMARCKIAN PRINCIPLE.

Lamarck, as is well known, formulated a definite theory of evolution at
the beginning of the nineteenth century, exactly fifty years before
the Darwin-Wallace principle of selection was given to the world.
This brilliant investigator also endeavoured to support his theory by
demonstrating forces which might have brought about the transformations
of the organic world in the course of the ages. In addition to other
factors, he laid special emphasis on the increased or diminished use
of the parts of the body, assuming that the strengthening or weakening
which takes place from this cause during the individual life, could be
handed on to the offspring, and thus intensified and raised to the rank
of a specific character. Darwin also regarded this LAMARCKIAN PRINCIPLE,
as it is now generally called, as a factor in evolution, but he was not
fully convinced of the transmissibility of acquired characters.

As I have here to deal only with the theory of selection, I need not
discuss the Lamarckian hypothesis, but I must express my opinion that
there is room for much doubt as to the cooperation of this principle in
evolution. Not only is it difficult to imagine how the transmission of
functional modifications could take place, but, up to the present time,
notwithstanding the endeavours of many excellent investigators, not
a single actual proof of such inheritance has been brought forward.
Semon's experiments on plants are, according to the botanist Pfeffer,
not to be relied on, and even the recent, beautiful experiments made
by Dr Kammerer on salamanders, cannot, as I hope to show elsewhere,
be regarded as proof, if only because they do not deal at all with
functional modifications, that is, with modifications brought about by
use, and it is to these ALONE that the Lamarckian principle refers.

III. OBJECTIONS TO THE THEORY OF SELECTION.

(a) Saltatory evolution.

The Darwinian doctrine of evolution depends essentially on THE
CUMULATIVE AUGMENTATION of minute variations in the direction of
utility. But can such minute variations, which are undoubtedly
continually appearing among the individuals of the same species,
possess any selection-value; can they determine which individuals are
to survive, and which are to succumb; can they be increased by natural
selection till they attain to the highest development of a purposive
variation?

To many this seems so improbable that they have urged a theory of
evolution by leaps from species to species. Kolliker, in 1872, compared
the evolution of species with the processes which we can observe in the
individual life in cases of alternation of generations. But a polyp only
gives rise to a medusa because it has itself arisen from one, and there
can be no question of a medusa ever having arisen suddenly and de
novo from a polyp-bud, if only because both forms are adapted in their
structure as a whole, and in every detail to the conditions of their
life. A sudden origin, in a natural way, of numerous adaptations is
inconceivable. Even the degeneration of a medusoid from a free-swimming
animal to a mere brood-sac (gonophore) is not sudden and saltatory, but
occurs by imperceptible modifications throughout hundreds of years, as
we can learn from the numerous stages of the process of degeneration
persisting at the same time in different species.

If, then, the degeneration to a simple brood-sac takes place only by
very slow transitions, each stage of which may last for centuries, how
could the much more complex ASCENDING evolution possibly have taken
place by sudden leaps? I regard this argument as capable of further
extension, for wherever in nature we come upon degeneration, it is
taking place by minute steps and with a slowness that makes it not
directly perceptible, and I believe that this in itself justifies us in
concluding that THE SAME MUST BE TRUE OF ASCENDING evolution. But in the
latter case the goal can seldom be distinctly recognised while in cases
of degeneration the starting-point of the process can often be inferred,
because several nearly related species may represent different stages.

In recent years Bateson in particular has championed the idea of
saltatory, or so-called discontinuous evolution, and has collected a
number of cases in which more or less marked variations have suddenly
appeared. These are taken for the most part from among domesticated
animals which have been bred and crossed for a long time, and it is
hardly to be wondered at that their much mixed and much influenced
germ-plasm should, under certain conditions, give rise to remarkable
phenomena, often indeed producing forms which are strongly suggestive of
monstrosities, and which would undoubtedly not survive in free nature,
unprotected by man. I should regard such cases as due to an intensified
germinal selection--though this is to anticipate a little--and from this
point of view it cannot be denied that they have a special interest. But
they seem to me to have no significance as far as the transformation
of species is concerned, if only because of the extreme rarity of their
occurrence.

There are, however, many variations which have appeared in a sudden and
saltatory manner, and some of these Darwin pointed out and discussed
in detail: the copper beech, the weeping trees, the oak with "fern-like
leaves," certain garden-flowers, etc. But none of them have persisted in
free nature, or evolved into permanent types.

On the other hand, wherever enduring types have arisen, we find traces
of a gradual origin by successive stages, even if, at first sight, their
origin may appear to have been sudden. This is the case with SEASONAL
DIMORPHISM, the first known cases of which exhibited marked differences
between the two generations, the winter and the summer brood. Take
for instance the much discussed and studied form Vanessa (Araschnia)
levana-prorsa. Here the differences between the two forms are so great
and so apparently disconnected, that one might almost believe it to be
a sudden mutation, were it not that old transition-stages can be called
forth by particular temperatures, and we know other butterflies, as for
instance our Garden Whites, in which the differences between the
two generations are not nearly so marked; indeed, they are so little
apparent that they are scarcely likely to be noticed except by experts.
Thus here again there are small initial steps, some of which, indeed,
must be regarded as adaptations, such as the green-sprinkled or lightly
tinted under-surface which gives them a deceptive resemblance to parsley
or to Cardamine leaves.

Even if saltatory variations do occur, we cannot assume that these HAVE
EVER LED TO FORMS WHICH ARE CAPABLE OF SURVIVAL UNDER THE CONDITIONS
OF WILD LIFE. Experience has shown that in plants which have suddenly
varied the power of persistence is diminished. Korschinksky attributes
to them weaknesses of organisation in general; "they bloom late, ripen
few of their seeds, and show great sensitiveness to cold." These are not
the characters which make for success in the struggle for existence.

We must briefly refer here to the views--much discussed in the last
decade--of H. de Vries, who believes that the roots of transformation
must be sought for in SALTATORY VARIATIONS ARISING FROM INTERNAL CAUSES,
and distinguishes such MUTATIONS, as he has called them, from ordinary
individual variations, in that they breed true, that is, with strict
inbreeding they are handed on pure to the next generation. I have
elsewhere endeavoured to point out the weaknesses of this theory
("Vortrage uber Descendenztheorie", Jena, 1904, II. 269. English
Translation London, 1904, II. page 317.), and I am the less inclined
to return to it here that it now appears (See Poulton, "Essays on
Evolution", Oxford, 1908, pages xix-xxii.) that the far-reaching
conclusions drawn by de Vries from his observations on the Evening
Primrose, Oenothera lamarckiana, rest upon a very insecure
foundation. The plant from which de Vries saw numerous "species"--his
"mutations"--arise was not, as he assumed, a WILD SPECIES that had been
introduced to Europe from America, but was probably a hybrid form which
was first discovered in the Jardin des Plantes in Paris, and which does
not appear to exist anywhere in America as a wild species.

This gives a severe shock to the "Mutation theory," for the other
ACTUALLY WILD species with which de Vries experimented showed no
"mutations" but yielded only negative results.

Thus we come to the conclusion that Darwin ("Origin of Species" (6th
edition), pages 176 et seq.) was right in regarding transformations as
taking place by minute steps, which, if useful, are augmented in
the course of innumerable generations, because their possessors more
frequently survive in the struggle for existence.

(b) SELECTION-VALUE OF THE INITIAL STEPS.

Is it possible that the significant deviations which we know as
"individual variations" can form the beginning of a process of
selection? Can they decide which is to perish and which to survive? To
use a phrase of Romanes, can they have SELECTION-VALUE?

Darwin himself answered this question, and brought together many
excellent examples to show that differences, apparently insignificant
because very small, might be of decisive importance for the life of the
possessor. But it is by no means enough to bring forward cases of this
kind, for the question is not merely whether finished adaptations have
selection-value, but whether the first beginnings of these, and whether
the small, I might almost say minimal increments, which have led up
from these beginnings to the perfect adaptation, have also had
selection-value. To this question even one who, like myself, has been
for many years a convinced adherent of the theory of selection, can only
reply: WE MUST ASSUME SO, BUT WE CANNOT PROVE IT IN ANY CASE. It is not
upon demonstrative evidence that we rely when we champion the doctrine
of selection as a scientific truth; we base our argument on quite other
grounds. Undoubtedly there are many apparently insignificant features,
which can nevertheless be shown to be adaptations--for instance, the
thickness of the basin-shaped shell of the limpets that live among the
breakers on the shore. There can be no doubt that the thickness of these
shells, combined with their flat form, protects the animals from the
force of the waves breaking upon them,--but how have they become so
thick? What proportion of thickness was sufficient to decide that of two
variants of a limpet one should survive, the other be eliminated? We can
say nothing more than that we infer from the present state of the shell,
that it must have varied in regard to differences in shell-thickness,
and that these differences must have had selection-value,--no proof
therefore, but an assumption which we must show to be convincing.

For a long time the marvellously complex RADIATE and LATTICE-WORK
skeletons of Radiolarians were regarded as a mere outflow of "Nature's
infinite wealth of form," as an instance of a purely morphological
character with no biological significance. But recent investigations
have shown that these, too, have an adaptive significance (Hacker). The
same thing has been shown by Schutt in regard to the lowly unicellular
plants, the Peridineae, which abound alike on the surface of the ocean
and in its depths. It has been shown that the long skeletal processes
which grow out from these organisms have significance not merely as a
supporting skeleton, but also as an extension of the superficial area,
which increases the contact with the water-particles, and prevents
the floating organisms from sinking. It has been established that the
processes are considerably shorter in the colder layers of the ocean,
and that they may be twelve times as long (Chun, "Reise der Valdivia",
Leipzig, 1904.) in the warmer layers, thus corresponding to the greater
or smaller amount of friction which takes place in the denser and less
dense layers of the water.

The Peridineae of the warmer ocean layers have thus become long-rayed,
those of the colder layers short-rayed, not through the direct effect
of friction on the protoplasm, but through processes of selection, which
favoured the longer rays in warm water, since they kept the organism
afloat, while those with short rays sank and were eliminated. If we put
the question as to selection-value in this case, and ask how great
the variations in the length of processes must be in order to possess
selection-value; what can we answer except that these variations must
have been minimal, and yet sufficient to prevent too rapid sinking
and consequent elimination? Yet this very case would give the
ideal opportunity for a mathematical calculation of the minimal
selection-value, although of course it is not feasible from lack of data
to carry out the actual calculation.

But even in organisms of more than microscopic size there must
frequently be minute, even microscopic differences which set going the
process of selection, and regulate its progress to the highest possible
perfection.

Many tropical trees possess thick, leathery leaves, as a protection
against the force of the tropical rain drops. The DIRECT influence
of the rain cannot be the cause of this power of resistance, for the
leaves, while they were still thin, would simply have been torn to
pieces. Their toughness must therefore be referred to selection, which
would favour the trees with slightly thicker leaves, though we cannot
calculate with any exactness how great the first stages of increase in
thickness must have been. Our hypothesis receives further support from
the fact that, in many such trees, the leaves are drawn out into a
beak-like prolongation (Stahl and Haberlandt) which facilitates the
rapid falling off of the rain water, and also from the fact that the
leaves, while they are still young, hang limply down in bunches which
offer the least possible resistance to the rain. Thus there are here
three adaptations which can only be interpreted as due to selection.
The initial stages of these adaptations must undoubtedly have had
selection-value.

But even in regard to this case we are reasoning in a circle, not giving
"proofs," and no one who does not wish to believe in the selection-value
of the initial stages can be forced to do so. Among the many pieces of
presumptive evidence a particularly weighty one seems to me to be THE
SMALLNESS OF THE STEPS OF PROGRESS which we can observe in certain
cases, as for instance in leaf-imitation among butterflies, and
in mimicry generally. The resemblance to a leaf, for instance of a
particular Kallima, seems to us so close as to be deceptive, and yet we
find in another individual, or it may be in many others, a spot added
which increases the resemblance, and which could not have become fixed
unless the increased deceptiveness so produced had frequently led to
the overlooking of its much persecuted possessor. But if we take the
selection-value of the initial stages for granted, we are confronted
with the further question which I myself formulated many years ago: How
does it happen THAT THE NECESSARY BEGINNINGS OF A USEFUL VARIATION ARE
ALWAYS PRESENT? How could insects which live upon or among green leaves
become all green, while those that live on bark become brown? How have
the desert animals become yellow and the Arctic animals white? Why were
the necessary variations always present? How could the green locust lay
brown eggs, or the privet caterpillar develop white and lilac-coloured
lines on its green skin?

It is of no use answering to this that the question is wrongly
formulated (Plate, "Selektionsprinzip u. Probleme der Artbildung" (3rd
edition), Leipzig, 1908.) and that it is the converse that is true; that
the process of selection takes place in accordance with the variations
that present themselves. This proposition is undeniably true, but so
also is another, which apparently negatives it: the variation required
has in the majority of cases actually presented itself. Selection cannot
solve this contradiction; it does not call forth the useful variation,
but simply works upon it. The ultimate reason why one and the same
insect should occur in green and in brown, as often happens in
caterpillars and locusts, lies in the fact that variations towards brown
presented themselves, and so also did variations towards green: THE
KERNEL OF THE RIDDLE LIES IN THE VARYING, and for the present we
can only say, that small variations in different directions present
themselves in every species. Otherwise so many different kinds of
variations could not have arisen. I have endeavoured to explain this
remarkable fact by means of the intimate processes that must take place
within the germ-plasm, and I shall return to the problem when dealing
with "germinal selection."

We have, however, to make still greater demands on variation, for it
is not enough that the necessary variation should occur in isolated
individuals, because in that case there would be small prospect of its
being preserved, notwithstanding its utility. Darwin at first believed,
that even single variations might lead to transformation of the species,
but later he became convinced that this was impossible, at least
without the cooperation of other factors, such as isolation and sexual
selection.

In the case of the GREEN CATERPILLARS WITH BRIGHT LONGITUDINAL STRIPES,
numerous individuals exhibiting this useful variation must have been
produced to start with. In all higher, that is, multicellular organisms,
the germ-substance is the source of all transmissible variations, and
this germ-plasm is not a simple substance but is made up of many primary
constituents. The question can therefore be more precisely stated thus:
How does it come about that in so many cases the useful variations
present themselves in numbers just where they are required, the white
oblique lines in the leaf-caterpillar on the under surface of the body,
the accompanying coloured stripes just above them? And, further, how has
it come about that in grass caterpillars, not oblique but longitudinal
stripes, which are more effective for concealment among grass and
plants, have been evolved? And finally, how is it that the same
Hawk-moth caterpillars, which to-day show oblique stripes, possessed
longitudinal stripes in Tertiary times? We can read this fact from the
history of their development, and I have before attempted to show
the biological significance of this change of colour. ("Studien
zur Descendenz-Theorie" II., "Die Enstehung der Zeichnung bei den
Schmetterlings-raupen," Leipzig, 1876.)

For the present I need only draw the conclusion that one and the same
caterpillar may exhibit the initial stages of both, and that it depends
on the manner in which these marking elements are INTENSIFIED and
COMBINED by natural selection whether whitish longitudinal or oblique
stripes should result. In this case then the "useful variations"
were actually "always there," and we see that in the same group of
Lepidoptera, e.g. species of Sphingidae, evolution has occurred in both
directions according to whether the form lived among grass or on broad
leaves with oblique lateral veins, and we can observe even now that the
species with oblique stripes have longitudinal stripes when young, that
is to say, while the stripes have no biological significance. The white
places in the skin which gave rise, probably first as small spots,
to this protective marking could be combined in one way or another
according to the requirements of the species. They must therefore either
have possessed selection-value from the first, or, if this was not
the case at their earliest occurrence, there must have been SOME OTHER
FACTORS which raised them to the point of selection-value. I shall
return to this in discussing germinal selection. But the case may be
followed still farther, and leads us to the same alternative on a still
more secure basis.

Many years ago I observed in caterpillars of Smerinthus populi (the
poplar hawk-moth), which also possess white oblique stripes, that
certain individuals showed RED SPOTS above these stripes; these spots
occurred only on certain segments, and never flowed together to form
continuous stripes. In another species (Smerinthus tiliae) similar
blood-red spots unite to form a line-like coloured seam in the last
stage of larval life, while in S. ocellata rust-red spots appear in
individual caterpillars, but more rarely than in S. Populi, and they
show no tendency to flow together.

Thus we have here the origin of a new character, arising from small
beginnings, at least in S. tiliae, in which species the coloured stripes
are a normal specific character. In the other species, S. populi and
S. ocellata, we find the beginnings of the same variation, in one more
rarely than in the other, and we can imagine that, in the course of
time, in these two species, coloured lines over the oblique stripes will
arise. In any case these spots are the elements of variation, out
of which coloured lines MAY be evolved, if they are combined in this
direction through the agency of natural selection. In S. populi the
spots are often small, but sometimes it seems as though several had
united to form large spots. Whether a process of selection in this
direction will arise in S. populi and S. ocellata, or whether it is
now going on cannot be determined, since we cannot tell in advance what
biological value the marking might have for these two species. It is
conceivable that the spots may have no selection-value as far as these
species are concerned, and may therefore disappear again in the course
of phylogeny, or, on the other hand, that they may be changed in another
direction, for instance towards imitation of the rust-red fungoid
patches on poplar and willow leaves. In any case we may regard the
smallest spots as the initial stages of variation, the larger as a
cumulative summation of these. Therefore either these initial stages
must already possess selection-value, or, as I said before: THERE MUST
BE SOME OTHER REASON FOR THEIR CUMULATIVE SUMMATION. I should like to
give one more example, in which we can infer, though we cannot directly
observe, the initial stages.

All the Holothurians or sea-cucumbers have in the skin calcareous bodies
of different forms, usually thick and irregular, which make the
skin tough and resistant. In a small group of them--the species of
Synapta--the calcareous bodies occur in the form of delicate anchors of
microscopic size. Up till 1897 these anchors, like many other delicate
microscopic structures, were regarded as curiosities, as natural
marvels. But a Swedish observer, Oestergren, has recently shown that
they have a biological significance: they serve the footless Synapta as
auxiliary organs of locomotion, since, when the body swells up in the
act of creeping, they press firmly with their tips, which are embedded
in the skin, against the substratum on which the animal creeps, and thus
prevent slipping backwards. In other Holothurians this slipping is
made impossible by the fixing of the tube-feet. The anchors act
automatically, sinking their tips towards the ground when the
corresponding part of the body thickens, and returning to the original
position at an angle of 45 degrees to the upper surface when the part
becomes thin again. The arms of the anchor do not lie in the same plane
as the shaft, and thus the curve of the arms forms the outermost part
of the anchor, and offers no further resistance to the gliding of the
animal. Every detail of the anchor, the curved portion, the little teeth
at the head, the arms, etc., can be interpreted in the most beautiful
way, above all the form of the anchor itself, for the two arms prevent
it from swaying round to the side. The position of the anchors, too, is
definite and significant; they lie obliquely to the longitudinal axis of
the animal, and therefore they act alike whether the animal is creeping
backwards or forwards. Moreover, the tips would pierce through the skin
if the anchors lay in the longitudinal direction. Synapta burrows in the
sand; it first pushes in the thin anterior end, and thickens this again,
thus enlarging the hole, then the anterior tentacles displace more sand,
the body is worked in a little farther, and the process begins anew. In
the first act the anchors are passive, but they begin to take an
active share in the forward movement when the body is contracted again.
Frequently the animal retains only the posterior end buried in the sand,
and then the anchors keep it in position, and make rapid withdrawal
possible.

Thus we have in these apparently random forms of the calcareous bodies,
complex adaptations in which every little detail as to direction, curve,
and pointing is exactly determined. That they have selection-value in
their present perfected form is beyond all doubt, since the animals
are enabled by means of them to bore rapidly into the ground and so to
escape from enemies. We do not know what the initial stages were, but we
cannot doubt that the little improvements, which occurred as variations
of the originally simple slimy bodies of the Holothurians, were
preserved because they already possessed selection-value for the
Synaptidae. For such minute microscopic structures whose form is so
delicately adapted to the role they have to play in the life of the
animal, cannot have arisen suddenly and as a whole, and every new
variation of the anchor, that is, in the direction of the development
of the two arms, and every curving of the shaft which prevented the tips
from projecting at the wrong time, in short, every little adaptation
in the modelling of the anchor must have possessed selection-value. And
that such minute changes of form fall within the sphere of fluctuating
variations, that is to say, THAT THEY OCCUR is beyond all doubt.

In many of the Synaptidae the anchors are replaced by calcareous rods
bent in the form of an S, which are said to act in the same way. Others,
such as those of the genus Ankyroderma, have anchors which project
considerably beyond the skin, and, according to Oestergren, serve "to
catch plant-particles and other substances" and so mask the animal. Thus
we see that in the Synaptidae the thick and irregular calcareous bodies
of the Holothurians have been modified and transformed in various ways
in adaptation to the footlessness of these animals, and to the peculiar
conditions of their life, and we must conclude that the earlier stages
of these changes presented themselves to the processes of selection in
the form of microscopic variations. For it is as impossible to think of
any origin other than through selection in this case as in the case of
the toughness, and the "drip-tips" of tropical leaves. And as these
last could not have been produced directly by the beating of the heavy
rain-drops upon them, so the calcareous anchors of Synapta cannot have
been produced directly by the friction of the sand and mud at the bottom
of the sea, and, since they are parts whose function is PASSIVE the
Lamarckian factor of use and disuse does not come into question. The
conclusion is unavoidable, that the microscopically small variations of
the calcareous bodies in the ancestral forms have been intensified
and accumulated in a particular direction, till they have led to the
formation of the anchor. Whether this has taken place by the action
of natural selection alone, or whether the laws of variation and the
intimate processes within the germ-plasm have cooperated will become
clear in the discussion of germinal selection. This whole process of
adaptation has obviously taken place within the time that has
elapsed since this group of sea-cucumbers lost their tube-feet, those
characteristic organs of locomotion which occur in no group except the
Echinoderms, and yet have totally disappeared in the Synaptidae.
And after all what would animals that live in sand and mud do with
tube-feet?

(c) COADAPTATION.

Darwin pointed out that one of the essential differences between
artificial and natural selection lies in the fact that the former can
modify only a few characters, usually only one at a time, while Nature
preserves in the struggle for existence all the variations of a species,
at the same time and in a purely mechanical way, if they possess
selection-value.

Herbert Spencer, though himself an adherent of the theory of selection,
declared in the beginning of the nineties that in his opinion the range
of this principle was greatly over-estimated, if the great changes which
have taken place in so many organisms in the course of ages are to
be interpreted as due to this process of selection alone, since no
transformation of any importance can be evolved by itself; it is always
accompanied by a host of secondary changes. He gives the familiar
example of the Giant Stag of the Irish peat, the enormous antlers of
which required not only a much stronger skull cap, but also greater
strength of the sinews, muscles, nerves and bones of the whole anterior
half of the animal, if their mass was not to weigh down the animal
altogether. It is inconceivable, he says, that so many processes of
selection should take place SIMULTANEOUSLY, and we are therefore
forced to fall back on the Lamarckian factor of the use and disuse of
functional parts. And how, he asks, could natural selection follow two
opposite directions of evolution in different parts of the body at the
same time, as for instance in the case of the kangaroo, in which the
forelegs must have become shorter, while the hind legs and the tail were
becoming longer and stronger?

Spencer's main object was to substantiate the validity of the Lamarckian
principle, the cooperation of which with selection had been doubted
by many. And it does seem as though this principle, if it operates
in nature at all, offers a ready and simple explanation of all such
secondary variations. Not only muscles, but nerves, bones, sinews,
in short all tissues which function actively, increase in strength
in proportion as they are used, and conversely they decrease when the
claims on them diminish. All the parts, therefore, which depend on the
part that varied first, as for instance the enlarged antlers of the
Irish Elk, must have been increased or decreased in strength, in exact
proportion to the claims made upon them,--just as is actually the case.

But beautiful as this explanation would be, I regard it as untenable,
because it assumes the TRANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS
(so-called "acquired" characters), and this is not only undemonstrable,
but is scarcely theoretically conceivable, for the secondary variations
which accompany or follow the first as correlative variations, occur
also in cases in which the animals concerned are sterile and THEREFORE
CANNOT TRANSMIT ANYTHING TO THEIR DESCENDANTS. This is true of WORKER
BEES, and particularly of ANTS, and I shall here give a brief survey of
the present state of the problem as it appears to me.

Much has been written on both sides of this question since the published
controversy on the subject in the nineties between Herbert Spencer and
myself. I should like to return to the matter in detail, if the space
at my disposal permitted, because it seems to me that the arguments I
advanced at that time are equally cogent to-day, notwithstanding all the
objections that have since been urged against them. Moreover, the matter
is by no means one of subordinate interest; it is the very kernel of the
whole question of the reality and value of the principle of selection.
For if selection alone does not suffice to explain "HARMONIOUS
ADAPTATION" as I have called Spencer's COADAPTATION, and if we require
to call in the aid of the Lamarckian factor it would be questionable
whether selection could explain any adaptations whatever. In this
particular case--of worker bees--the Lamarckian factor may be excluded
altogether, for it can be demonstrated that here at any rate the effects
of use and disuse cannot be transmitted.

But if it be asked why we are unwilling to admit the cooperation of
the Darwinian factor of selection and the Lamarckian factor, since this
would afford us an easy and satisfactory explanation of the phenomena,
I answer: BECAUSE THE LAMARCKIAN PRINCIPLE IS FALLACIOUS, AND BECAUSE BY
ACCEPTING IT WE CLOSE THE WAY TOWARDS DEEPER INSIGHT. It is not a spirit
of combativeness or a desire for self-vindication that induces me to
take the field once more against the Lamarckian principle, it is the
conviction that the progress of our knowledge is being obstructed by the
acceptance of this fallacious principle, since the facile explanation it
apparently affords prevents our seeking after a truer explanation and a
deeper analysis.

The workers in the various species of ants are sterile, that is to say,
they take no regular part in the reproduction of the species, although
individuals among them may occasionally lay eggs. In addition to this
they have lost the wings, and the receptaculum seminis, and their
compound eyes have degenerated to a few facets. How could this last
change have come about through disuse, since the eyes of workers are
exposed to light in the same way as are those of the sexual insects and
thus in this particular case are not liable to "disuse" at all? The same
is true of the receptaculum seminis, which can only have been disused
as far as its glandular portion and its stalk are concerned, and also
of the wings, the nerves tracheae and epidermal cells of which could
not cease to function until the whole wing had degenerated, for the
chitinous skeleton of the wing does not function at all in the active
sense.

But, on the other hand, the workers in all species have undergone
modifications in a positive direction, as, for instance, the greater
development of brain. In many species large workers have evolved,--the
so-called SOLDIERS, with enormous jaws and teeth, which defend the
colony,--and in others there are SMALL workers which have taken over
other special functions, such as the rearing of the young Aphides. This
kind of division of the workers into two castes occurs among several
tropical species of ants, but it is also present in the Italian species,
Colobopsis truncata. Beautifully as the size of the jaws could be
explained as due to the increased use made of them by the "soldiers," or
the enlarged brain as due to the mental activities of the workers, the
fact of the infertility of these forms is an insurmountable obstacle
to accepting such an explanation. Neither jaws nor brain can have been
evolved on the Lamarckian principle.

The problem of coadaptation is no easier in the case of the ant than in
the case of the Giant Stag. Darwin himself gave a pretty illustration to
show how imposing the difference between the two kinds of workers in one
species would seem if we translated it into human terms. In regard to
the Driver ants (Anomma) we must picture to ourselves a piece of work,
"for instance the building of a house, being carried on by two kinds of
workers, of which one group was five feet four inches high, the other
sixteen feet high." ("Origin of Species" (6th edition), page 232.)

Although the ant is a small animal as compared with man or with the
Irish Elk, the "soldier" with its relatively enormous jaws is hardly
less heavily burdened than the Elk with its antlers, and in the ant's
case, too, a strengthening of the skeleton, of the muscles, the nerves
of the head, and of the legs must have taken place parallel with the
enlargement of the jaws. HARMONIOUS ADAPTATION (coadaptation) has here
been active in a high degree, and yet these "soldiers" are sterile!
There thus remains nothing for it but to refer all their adaptations,
positive and negative alike, to processes of selection which have taken
place in the rudiments of the workers within the egg and sperm-cells
of their parents. There is no way out of the difficulty except the one
Darwin pointed out. He himself did not find the solution of the riddle
at once. At first he believed that the case of the workers among social
insects presented "the most serious special difficulty" in the way of
his theory of natural selection; and it was only after it had become
clear to him, that it was not the sterile insects themselves but their
parents that were selected, according as they produced more or less
well adapted workers, that he was able to refer to this very case of the
conditions among ants "IN ORDER TO SHOW THE POWER OF NATURAL SELECTION"
("Origin of Species", page 233; see also edition 1, page 242.). He
explains his view by a simple but interesting illustration. Gardeners
have produced, by means of long continued artificial selection, a
variety of Stock, which bears entirely double, and therefore infertile
flowers (Ibid. page 230.). Nevertheless the variety continues to be
reproduced from seed, because in addition to the double and infertile
flowers, the seeds always produce a certain number of single, fertile
blossoms, and these are used to reproduce the double variety. These
single and fertile plants correspond "to the males and females of an
ant-colony, the infertile plants, which are regularly produced in large
numbers, to the neuter workers of the colony."

This illustration is entirely apt, the only difference between the two
cases consisting in the fact that the variation in the flower is not
a useful, but a disadvantageous one, which can only be preserved
by artificial selection on the part of the gardener, while the
transformations that have taken place parallel with the sterility of the
ants are useful, since they procure for the colony an advantage in the
struggle for existence, and they are therefore preserved by
natural selection. Even the sterility itself in this case is not
disadvantageous, since the fertility of the true females has at the same
time considerably increased. We may therefore regard the sterile forms
of ants, which have gradually been adapted in several directions to
varying functions, AS A CERTAIN PROOF that selection really takes place
in the germ-cells of the fathers and mothers of the workers, and that
SPECIAL COMPLEXES OF PRIMORDIA (IDS) are present in the workers and in
the males and females, and these complexes contain the primordia of the
individual parts (DETERMINANTS). But since all living entities vary, the
determinants must also vary, now in a favourable, now in an unfavourable
direction. If a female produces eggs, which contain favourably varying
determinants in the worker-ids, then these eggs will give rise to
workers modified in the favourable direction, and if this happens with
many females, the colony concerned will contain a better kind of worker
than other colonies.

I digress here in order to give an account of the intimate processes,
which, according to my view, take place within the germ-plasm, and which
I have called "GERMINAL SELECTION." These processes are of importance
since they form the roots of variation, which in its turn is the root
of natural selection. I cannot here do more than give a brief outline of
the theory in order to show how the Darwin-Wallace theory of selection
has gained support from it.

With others, I regard the minimal amount of substance which is contained
within the nucleus of the germ-cells, in the form of rods, bands, or
granules, as the GERM-SUBSTANCE or GERM-PLASM, and I call the individual
granules IDS. There is always a multiplicity of such ids present in the
nucleus, either occurring individually, or united in the form of rods
or bands (chromosomes). Each id contains the primary constituents of a
WHOLE individual, so that several ids are concerned in the development
of a new individual.

In every being of complex structure thousands of primary constituents
must go to make up a single id; these I call DETERMINANTS, and I mean
by this name very small individual particles, far below the limits of
microscopic visibility, vital units which feed, grow, and multiply
by division. These determinants control the parts of the developing
embryo,--in what manner need not here concern us. The determinants
differ among themselves, those of a muscle are differently constituted
from those of a nerve-cell or a glandular cell, etc., and every
determinant is in its turn made up of minute vital units, which I
call BIOPHORS, or the bearers of life. According to my view, these
determinants not only assimilate, like every other living unit, but they
VARY in the course of their growth, as every living unit does; they may
vary qualitatively if the elements of which they are composed vary, they
may grow and divide more or less rapidly, and their variations give rise
to CORRESPONDING variations of the organ, cell, or cell-group which they
determine. That they are undergoing ceaseless fluctuations in regard to
size and quality seems to me the inevitable consequence of their unequal
nutrition; for although the germ-cell as a whole usually receives
sufficient nutriment, minute fluctuations in the amount carried to
different parts within the germ-plasm cannot fail to occur.

Now, if a determinant, for instance of a sensory cell, receives for a
considerable time more abundant nutriment than before, it will grow more
rapidly--become bigger, and divide more quickly, and, later, when the
id concerned develops into an embryo, this sensory cell will become
stronger than in the parents, possibly even twice as strong. This is an
instance of a HEREDITARY INDIVIDUAL VARIATION, arising from the germ.

The nutritive stream which, according to our hypothesis, favours the
determinant N by chance, that is, for reasons unknown to us, may remain
strong for a considerable time, or may decrease again; but even in
the latter case it is conceivable that the ascending movement of the
determinant may continue, because the strengthened determinant now
ACTIVELY nourishes itself more abundantly,--that is to say, it attracts
the nutriment to itself, and to a certain extent withdraws it from its
fellow-determinants. In this way, it may--as it seems to me--get into
PERMANENT UPWARD MOVEMENT, AND ATTAIN A DEGREE OF STRENGTH FROM WHICH
THERE IS NO FALLING BACK. Then positive or negative selection sets in,
favouring the variations which are advantageous, setting aside those
which are disadvantageous.

In a similar manner a DOWNWARD variation of the determinants may take
place, if its progress be started by a diminished flow of nutriment. The
determinants which are weakened by this diminished flow will have less
affinity for attracting nutriment because of their diminished strength,
and they will assimilate more feebly and grow more slowly, unless chance
streams of nutriment help them to recover themselves. But, as will
presently be shown, a change of direction cannot take place at EVERY
stage of the degenerative process. If a certain critical stage of
downward progress be passed, even favourable conditions of food-supply
will no longer suffice permanently to change the direction of
the variation. Only two cases are conceivable; if the determinant
corresponds to a USEFUL organ, only its removal can bring back the
germ-plasm to its former level; therefore personal selection removes the
id in question, with its determinants, from the germ-plasm, by causing
the elimination of the individual in the struggle for existence. But
there is another conceivable case; the determinants concerned may be
those of an organ which has become USELESS, and they will then continue
unobstructed, but with exceeding slowness, along the downward path,
until the organ becomes vestigial, and finally disappears altogether.

The fluctuations of the determinants hither and thither may thus be
transformed into a lasting ascending or descending movement; and THIS IS
THE CRUCIAL POINT OF THESE GERMINAL PROCESSES.

This is not a fantastic assumption; we can read it in the fact of the
degeneration of disused parts. USELESS ORGANS ARE THE ONLY ONES WHICH
ARE NOT HELPED TO ASCEND AGAIN BY PERSONAL SELECTION, AND THEREFORE IN
THEIR CASE ALONE CAN WE FORM ANY IDEA OF HOW THE PRIMARY CONSTITUENTS
BEHAVE, WHEN THEY ARE SUBJECT SOLELY TO INTRA-GERMINAL FORCES.

The whole determinant system of an id, as I conceive it, is in a state
of continual fluctuation upwards and downwards. In most cases the
fluctuations will counteract one another, because the passive streams of
nutriment soon change, but in many cases the limit from which a return
is possible will be passed, and then the determinants concerned will
continue to vary in the same direction, till they attain positive or
negative selection-value. At this stage personal selection intervenes
and sets aside the variation if it is disadvantageous, or favours--that
is to say, preserves--it if it is advantageous. Only THE DETERMINANT
OF A USELESS ORGAN IS UNINFLUENCED BY PERSONAL SELECTION, and,
as experience shows, it sinks downwards; that is, the organ that
corresponds to it degenerates very slowly but uninterruptedly till,
after what must obviously be an immense stretch of time, it disappears
from the germ-plasm altogether.

Thus we find in the fact of the degeneration of disused parts the proof
that not all the fluctuations of a determinant return to equilibrium
again, but that, when the movement has attained to a certain strength,
it continues IN THE SAME DIRECTION. We have entire certainty in regard
to this as far as the downward progress is concerned, and we must
assume it also in regard to ascending variations, as the phenomena of
artificial selection certainly justify us in doing. If the Japanese
breeders were able to lengthen the tail feathers of the cock to
six feet, it can only have been because the determinants of the
tail-feathers in the germ-plasm had already struck out a path of
ascending variation, and this movement was taken advantage of by the
breeder, who continually selected for reproduction the individuals in
which the ascending variation was most marked. For all breeding depends
upon the unconscious selection of germinal variations.

Of course these germinal processes cannot be proved mathematically,
since we cannot actually see the play of forces of the passive
fluctuations and their causes. We cannot say how great these
fluctuations are, and how quickly or slowly, how regularly or
irregularly they change. Nor do we know how far a determinant must be
strengthened by the passive flow of the nutritive stream if it is to
be beyond the danger of unfavourable variations, or how far it must be
weakened passively before it loses the power of recovering itself by its
own strength. It is no more possible to bring forward actual proofs in
this case than it was in regard to the selection-value of the initial
stages of an adaptation. But if we consider that all heritable
variations must have their roots in the germ-plasm, and further, that
when personal selection does not intervene, that is to say, in the case
of parts which have become useless, a degeneration of the part, and
therefore also of its determinant must inevitably take place; then we
must conclude that processes such as I have assumed are running their
course within the germ-plasm, and we can do this with as much certainty
as we were able to infer, from the phenomena of adaptation, the
selection-value of their initial stages. The fact of the degeneration
of disused parts seems to me to afford irrefutable proof that the
fluctuations within the germ-plasm ARE THE REAL ROOT OF ALL HEREDITARY
VARIATION, and the preliminary condition for the occurrence of the
Darwin-Wallace factor of selection. Germinal selection supplies the
stones out of which personal selection builds her temples and
palaces: ADAPTATIONS. The importance for the theory of the process of
degeneration of disused parts cannot be over-estimated, especially when
it occurs in sterile animal forms, where we are free from the doubt as
to the alleged LAMARCKIAN FACTOR which is apt to confuse our ideas in
regard to other cases.

If we regard the variation of the many determinants concerned in the
transformation of the female into the sterile worker as having come
about through the gradual transformation of the ids into worker-ids,
we shall see that the germ-plasm of the sexual ants must contain three
kinds of ids, male, female, and worker ids, or if the workers have
diverged into soldiers and nest-builders, then four kinds. We understand
that the worker-ids arose because their determinants struck out a useful
path of variation, whether upward or downward, and that they continued
in this path until the highest attainable degree of utility of the parts
determined was reached. But in addition to the organs of positive or
negative selection-value, there were some which were indifferent as far
as the success and especially the functional capacity of the workers was
concerned: wings, ovarian tubes, receptaculum seminis, a number of the
facets of the eye, perhaps even the whole eye. As to the ovarian tubes
it is possible that their degeneration was an advantage for the workers,
in saving energy, and if so selection would favour the degeneration; but
how could the presence of eyes diminish the usefulness of the workers to
the colony? or the minute receptaculum seminis, or even the wings? These
parts have therefore degenerated BECAUSE THEY WERE OF NO FURTHER VALUE
TO THE INSECT. But if selection did not influence the setting aside of
these parts because they were neither of advantage nor of disadvantage
to the species, then the Darwinian factor of selection is here
confronted with a puzzle which it cannot solve alone, but which at once
becomes clear when germinal selection is added. For the determinants
of organs that have no further value for the organism, must, as we have
already explained, embark on a gradual course of retrograde development.

In ants the degeneration has gone so far that there are no
wing-rudiments present in ANY species, as is the case with so many
butterflies, flies, and locusts, but in the larvae the imaginal discs of
the wings are still laid down. With regard to the ovaries, degeneration
has reached different levels in different species of ants, as has been
shown by the researches of my former pupil, Elizabeth Bickford. In many
species there are twelve ovarian tubes, and they decrease from that
number to one; indeed, in one species no ovarian tube at all is present.
So much at least is certain from what has been said, that in this
case EVERYTHING depends on the fluctuations of the elements of the
germ-plasm. Germinal selection, here as elsewhere, presents the
variations of the determinants, and personal selection favours or
rejects these, or,--if it be a question of organs which have become
useless,--it does not come into play at all, and allows the descending
variation free course.

It is obvious that even the problem of COADAPTATION IN STERILE
ANIMALS can thus be satisfactorily explained. If the determinants are
oscillating upwards and downwards in continual fluctuation, and
varying more pronouncedly now in one direction now in the other, useful
variations of every determinant will continually present themselves
anew, and may, in the course of generations, be combined with one
another in various ways. But there is one character of the determinants
that greatly facilitates this complex process of selection, that,
after a certain limit has been reached, they go on varying in the same
direction. From this it follows that development along a path once
struck out may proceed without the continual intervention of personal
selection. This factor only operates, so to speak, at the beginning,
when it selects the determinants which are varying in the right
direction, and again at the end, when it is necessary to put a check
upon further variation. In addition to this, enormously long periods
have been available for all these adaptations, as the very gradual
transition stages between females and workers in many species plainly
show, and thus this process of transformation loses the marvellous and
mysterious character that seemed at the first glance to invest it,
and takes rank, without any straining, among the other processes of
selection. It seems to me that, from the facts that sterile animal forms
can adapt themselves to new vital functions, their superfluous parts
degenerate, and the parts more used adapt themselves in an ascending
direction, those less used in a descending direction, we must draw
the conclusion that harmonious adaptation here comes about WITHOUT
THE COOPERATION OF THE LAMARCKIAN PRINCIPLE. This conclusion once
established, however, we have no reason to refer the thousands of cases
of harmonious adaptation, which occur in exactly the same way among
other animals or plants, to a principle, the ACTIVE INTERVENTION OF
WHICH IN THE TRANSFORMATION OF SPECIES IS NOWHERE PROVED. WE DO NOT
REQUIRE IT TO EXPLAIN THE FACTS, AND THEREFORE WE MUST NOT ASSUME IT.

The fact of coadaptation, which was supposed to furnish the strongest
argument against the principle of selection, in reality yields the
clearest evidence in favour of it. We MUST assume it, BECAUSE NO OTHER
POSSIBILITY OF EXPLANATION IS OPEN TO US, AND BECAUSE THESE ADAPTATIONS
ACTUALLY EXIST, THAT IS TO SAY, HAVE REALLY TAKEN PLACE. With this
conviction I attempted, as far back as 1894, when the idea of germinal
selection had not yet occurred to me, to make "harmonious adaptation"
(coadaptation) more easily intelligible in some way or other, and so
I was led to the idea, which was subsequently expounded in detail by
Baldwin, and Lloyd Morgan, and also by Osborn, and Gulick as ORGANIC
SELECTION. It seemed to me that it was not necessary that all the
germinal variations required for secondary variations should have
occurred SIMULTANEOUSLY, since, for instance, in the case of the
stag, the bones, muscles, sinews, and nerves would be incited by
the increasing heaviness of the antlers to greater activity in THE
INDIVIDUAL LIFE, and so would be strengthened. The antlers can only have
increased in size by very slow degrees, so that the muscles and bones
may have been able to keep pace with their growth in the individual
life, until the requisite germinal variations presented themselves. In
this way a disharmony between the increasing weight of the antlers and
the parts which support and move them would be avoided, since time would
be given for the appropriate germinal variations to occur, and so to set
agoing the HEREDITARY variation of the muscles, sinews, and bones.
("The Effect of External Influences upon Development", Romanes Lecture,
Oxford, 1894.)

I still regard this idea as correct, but I attribute less importance
to "organic selection" than I did at that time, in so far that I do
not believe that it ALONE could effect complex harmonious adaptations.
Germinal selection now seems to me to play the chief part in bringing
about such adaptations. Something the same is true of the principle
I have called "Panmixia". As I became more and more convinced, in the
course of years, that the LAMARCKIAN PRINCIPLE ought not to be called in
to explain the dwindling of disused parts, I believed that this process
might be simply explained as due to the cessation of the conservative
effect of natural selection. I said to myself that, from the moment in
which a part ceases to be of use, natural selection withdraws its
hand from it, and then it must inevitably fall from the height of its
adaptiveness, because inferior variants would have as good a chance of
persisting as better ones, since all grades of fitness of the part in
question would be mingled with one another indiscriminately. This is
undoubtedly true, as Romanes pointed out ten years before I did, and
this mingling of the bad with the good probably does bring about a
deterioration of the part concerned. But it cannot account for the
steady diminution, which always occurs when a part is in process of
becoming rudimentary, and which goes on until it ultimately disappears
altogether. The process of dwindling cannot therefore be explained as
due to panmixia alone; we can only find a sufficient explanation in
germinal selection.

IV. DERIVATIVES OF THE THEORY OF SELECTION.

The impetus in all directions given by Darwin through his theory of
selection has been an immeasurable one, and its influence is still felt.
It falls within the province of the historian of science to enumerate
all the ideas which, in the last quarter of the nineteenth century, grew
out of Darwin's theories, in the endeavour to penetrate more deeply into
the problem of the evolution of the organic world. Within the narrow
limits to which this paper is restricted, I cannot attempt to discuss
any of these.

V. ARGUMENTS FOR THE REALITY OF THE PROCESSES OF SELECTION.

(a) SEXUAL SELECTION.

Sexual selection goes hand in hand with natural selection. From the
very first I have regarded sexual selection as affording an extremely
important and interesting corroboration of natural selection, but,
singularly enough, it is precisely against this theory that an adverse
judgment has been pronounced in so many quarters, and it is only quite
recently, and probably in proportion as the wealth of facts in proof of
it penetrates into a wider circle, that we seem to be approaching a
more general recognition of this side of the problem of adaptation. Thus
Darwin's words in his preface to the second edition (1874) of his book,
"The Descent of Man and Sexual Selection", are being justified: "My
conviction as to the operation of natural selection remains unshaken,"
and further, "If naturalists were to become more familiar with the idea
of sexual selection, it would, I think, be accepted to a much greater
extent, and already it is fully and favourably accepted by many
competent judges." Darwin was able to speak thus because he was already
acquainted with an immense mass of facts, which, taken together,
yield overwhelming evidence of the validity of the principle of sexual
selection.

NATURAL SELECTION chooses out for reproduction the individuals that are
best equipped for the struggle for existence, and it does so at every
stage of development; it thus improves the species in all its stages and
forms. SEXUAL SELECTION operates only on individuals that are already
capable of reproduction, and does so only in relation to the attainment
of reproduction. It arises from the rivalry of one sex, usually the
male, for the possession of the other, usually the female. Its influence
can therefore only DIRECTLY affect one sex, in that it equips it
better for attaining possession of the other. But the effect may
extend indirectly to the female sex, and thus the whole species may be
modified, without, however, becoming any more capable of resistance
in the struggle for existence, for sexual selection only gives rise to
adaptations which are likely to give their possessor the victory over
rivals in the struggle for possession of the female, and which are
therefore peculiar to the wooing sex: the manifold "secondary sexual
characters." The diversity of these characters is so great that I cannot
here attempt to give anything approaching a complete treatment of them,
but I should like to give a sufficient number of examples to make the
principle itself, in its various modes of expression, quite clear.

One of the chief preliminary postulates of sexual selection is the
unequal number of individuals in the two sexes, for if every male
immediately finds his mate there can be no competition for the
possession of the female. Darwin has shown that, for the most part, the
inequality between the sexes is due simply to the fact that there are
more males than females, and therefore the males must take some pains
to secure a mate. But the inequality does not always depend on the
numerical preponderance of the males, it is often due to polygamy; for,
if one male claims several females, the number of females in proportion
to the rest of the males will be reduced. Since it is almost always
the males that are the wooers, we must expect to find the occurrence
of secondary sexual characters chiefly among them, and to find it
especially frequent in polygamous species. And this is actually the
case.

If we were to try to guess--without knowing the facts--what means the
male animals make use of to overcome their rivals in the struggle for
the possession of the female, we might name many kinds of means, but it
would be difficult to suggest any which is not actually employed in some
animal group or other. I begin with the mere difference in strength,
through which the male of many animals is so sharply distinguished from
the female, as, for instance, the lion, walrus, "sea-elephant," and
others. Among these the males fight violently for the possession of the
female, who falls to the victor in the combat. In this simple case no
one can doubt the operation of selection, and there is just as little
room for doubt as to the selection-value of the initial stages of the
variation. Differences in bodily strength are apparent even among human
beings, although in their case the struggle for the possession of the
female is no longer decided by bodily strength alone.

Combats between male animals are often violent and obstinate, and the
employment of the natural weapons of the species in this way has led
to perfecting of these, e.g. the tusks of the boar, the antlers of the
stag, and the enormous, antler-like jaws of the stag-beetle. Here again
it is impossible to doubt that variations in these organs presented
themselves, and that these were considerable enough to be decisive in
combat, and so to lead to the improvement of the weapon.

Among many animals, however, the females at first withdraw from the
males; they are coy, and have to be sought out, and sometimes held by
force. This tracking and grasping of the females by the males has given
rise to many different characters in the latter, as, for instance,
the larger eyes of the male bee, and especially of the males of the
Ephemerids (May-flies), some species of which show, in addition to the
usual compound eyes, large, so-called turban-eyes, so that the whole
head is covered with seeing surfaces. In these species the females are
very greatly in the minority (1-100), and it is easy to understand that
a keen competition for them must take place, and that, when the insects
of both sexes are floating freely in the air, an unusually wide range
of vision will carry with it a decided advantage. Here again the actual
adaptations are in accordance with the preliminary postulates of the
theory. We do not know the stages through which the eye has passed
to its present perfected state, but, since the number of simple eyes
(facets) has become very much greater in the male than in the female,
we may assume that their increase is due to a gradual duplication of
the determinants of the ommatidium in the germ-plasm, as I have already
indicated in regard to sense-organs in general. In this case, again,
the selection-value of the initial stages hardly admits of doubt; better
vision DIRECTLY secures reproduction.

In many cases THE ORGAN OF SMELL shows a similar improvement. Many lower
Crustaceans (Daphnidae) have better developed organs of smell in the
male sex. The difference is often slight and amounts only to one or two
olfactory filaments, but certain species show a difference of nearly
a hundred of these filaments (Leptodora). The same thing occurs among
insects.

We must briefly consider the clasping or grasping organs which have
developed in the males among many lower Crustaceans, but here natural
selection plays its part along with sexual selection, for the union
of the sexes is an indispensable condition for the maintenance of the
species, and as Darwin himself pointed out, in many cases the two forms
of selection merge into each other. This fact has always seemed to me to
be a proof of natural selection, for, in regard to sexual selection,
it is quite obvious that the victory of the best-equipped could have
brought about the improvement only of the organs concerned, the factors
in the struggle, such as the eye and the olfactory organ.

We come now to the EXCITANTS; that is, to the group of sexual characters
whose origin through processes of selection has been most frequently
called in question. We may cite the LOVE-CALLS produced by many male
insects, such as crickets and cicadas. These could only have arisen in
animal groups in which the female did not rapidly flee from the male,
but was inclined to accept his wooing from the first. Thus, notes like
the chirping of the male cricket serve to entice the females. At first
they were merely the signal which showed the presence of a male in the
neighbourhood, and the female was gradually enticed nearer and nearer
by the continued chirping. The male that could make himself heard to the
greatest distance would obtain the largest following, and would transmit
the beginnings, and, later, the improvement of his voice to the greatest
number of descendants. But sexual excitement in the female
became associated with the hearing of the love-call, and then the
sound-producing organ of the male began to improve, until it attained to
the emission of the long-drawn-out soft notes of the mole-cricket or
the maenad-like cry of the cicadas. I cannot here follow the process
of development in detail, but will call attention to the fact that the
original purpose of the voice, the announcing of the male's presence,
became subsidiary, and the exciting of the female became the chief goal
to be aimed at. The loudest singers awakened the strongest excitement,
and the improvement resulted as a matter of course. I conceive of the
origin of bird-song in a somewhat similar manner, first as a means of
enticing, then of exciting the female.

One more kind of secondary sexual character must here be mentioned: the
odour which emanates from so many animals at the breeding season. It is
possible that this odour also served at first merely to give notice
of the presence of individuals of the other sex, but it soon became an
excitant, and as the individuals which caused the greatest degree of
excitement were preferred, it reached as high a pitch of perfection as
was possible to it. I shall confine myself here to the comparatively
recently discovered fragrance of butterflies. Since Fritz Muller found
out that certain Brazilian butterflies gave off fragrance "like a
flower," we have become acquainted with many such cases, and we now know
that in all lands, not only many diurnal Lepidoptera but nocturnal ones
also give off a delicate odour, which is agreeable even to man.
The ethereal oil to which this fragrance is due is secreted by the
skin-cells, usually of the wing, as I showed soon after the discovery
of the SCENT-SCALES. This is the case in the males; the females have no
SPECIAL scent-scales recognisable as such by their form, but they must,
nevertheless, give off an extremely delicate fragrance, although our
imperfect organ of smell cannot perceive it, for the males become aware
of the presence of a female, even at night, from a long distance off,
and gather round her. We may therefore conclude, that both sexes have
long given forth a very delicate perfume, which announced their presence
to others of the same species, and that in many species (NOT IN ALL)
these small beginnings became, in the males, particularly strong
scent-scales of characteristic form (lute, brush, or lyre-shaped). At
first these scales were scattered over the surface of the wing, but
gradually they concentrated themselves, and formed broad, velvety bands,
or strong, prominent brushes, and they attained their highest pitch of
evolution when they became enclosed within pits or folds of the skin,
which could be opened to let the delicious fragrance stream forth
suddenly towards the female. Thus in this case also we see that
characters, the original use of which was to bring the sexes together,
and so to maintain the species, have been evolved in the males into
means for exciting the female. And we can hardly doubt, that the females
are most readily enticed to yield to the butterfly that sends out the
strongest fragrance,--that is to say, that excites them to the highest
degree. It is a pity that our organs of smell are not fine enough to
examine the fragrance of male Lepidoptera in general, and to compare it
with other perfumes which attract these insects. (See Poulton, "Essays
on Evolution", 1908, pages 316, 317.) As far as we can perceive them
they resemble the fragrance of flowers, but there are Lepidoptera
whose scent suggests musk. A smell of musk is also given off by several
plants: it is a sexual excitant in the musk-deer, the musk-sheep, and
the crocodile.

As far as we know, then, it is perfumes similar to those of flowers that
the male Lepidoptera give off in order to entice their mates, and this
is a further indication that animals, like plants, can to a large extent
meet the claims made upon them by life, and produce the adaptations
which are most purposive,--a further proof, too, of my proposition
that the useful variations, so to speak, are ALWAYS THERE. The flowers
developed the perfumes which entice their visitors, and the male
Lepidoptera developed the perfumes which entice and excite their mates.

There are many pretty little problems to be solved in this connection,
for there are insects, such as some flies, that are attracted by smells
which are unpleasant to us, like those from decaying flesh and carrion.
But there are also certain flowers, some orchids for instance, which
give forth no very agreeable odour, but one which is to us repulsive
and disgusting; and we should therefore expect that the males of such
insects would give off a smell unpleasant to us, but there is no case
known to me in which this has been demonstrated.

In cases such as we have discussed, it is obvious that there is no
possible explanation except through selection. This brings us to the
last kind of secondary sexual characters, and the one in regard to
which doubt has been most frequently expressed,--decorative colours
and decorative forms, the brilliant plumage of the male pheasant, the
humming-birds, and the bird of Paradise, as well as the bright colours
of many species of butterfly, from the beautiful blue of our little
Lycaenidae to the magnificent azure of the large Morphinae of Brazil. In
a great many cases, though not by any means in all, the male butterflies
are "more beautiful" than the females, and in the Tropics in particular
they shine and glow in the most superb colours. I really see no reason
why we should doubt the power of sexual selection, and I myself stand
wholly on Darwin's side. Even though we certainly cannot assume that
the females exercise a conscious choice of the "handsomest" mate, and
deliberate like the judges in a court of justice over the perfections
of their wooers, we have no reason to doubt that distinctive forms
(decorative feathers) and colours have a particularly exciting effect
upon the female, just as certain odours have among animals of so many
different groups, including the butterflies. The doubts which existed
for a considerable time, as a result of fallacious experiments, as to
whether the colours of flowers really had any influence in attracting
butterflies have now been set at rest through a series of more careful
investigations; we now know that the colours of flowers are there on
account of the butterflies, as Sprengel first showed, and that the
blossoms of Phanerogams are selected in relation to them, as Darwin
pointed out.

Certainly it is not possible to bring forward any convincing proof of
the origin of decorative colours through sexual selection, but there
are many weighty arguments in favour of it, and these form a body of
presumptive evidence so strong that it almost amounts to certainty.

In the first place, there is the analogy with other secondary sexual
characters. If the song of birds and the chirping of the cricket have
been evolved through sexual selection, if the penetrating odours of male
animals,--the crocodile, the musk-deer, the beaver, the carnivores, and,
finally, the flower-like fragrances of the butterflies have been evolved
to their present pitch in this way, why should decorative colours
have arisen in some other way? Why should the eye be less sensitive
to SPECIFICALLY MALE colours and other VISIBLE signs ENTICING TO THE
FEMALE, than the olfactory sense to specifically male odours, or the
sense of hearing to specifically male sounds? Moreover, the decorative
feathers of birds are almost always spread out and displayed before
the female during courtship. I have elsewhere ("The Evolution Theory",
London, 1904, I. page 219.) pointed out that decorative colouring and
sweet-scentedness may replace one another in Lepidoptera as well as
in flowers, for just as some modestly coloured flowers (mignonette and
violet) have often a strong perfume, while strikingly coloured ones are
sometimes quite devoid of fragrance, so we find that the most beautiful
and gaily-coloured of our native Lepidoptera, the species of Vanessa,
have no scent-scales, while these are often markedly developed in grey
nocturnal Lepidoptera. Both attractions may, however, be combined in
butterflies, just as in flowers. Of course, we cannot explain why both
means of attraction should exist in one genus, and only one of them in
another, since we do not know the minutest details of the conditions
of life of the genera concerned. But from the sporadic distribution of
scent-scales in Lepidoptera, and from their occurrence or absence in
nearly related species, we may conclude that fragrance is a relatively
MODERN acquirement, more recent than brilliant colouring.

One thing in particular that stamps decorative colouring as a product of
selection is ITS GRADUAL INTENSIFICATION by the addition of new spots,
which we can quite well observe, because in many cases the colours have
been first acquired by the males, and later transmitted to the females
by inheritance. The scent-scales are never thus transmitted, probably
for the same reason that the decorative colours of many birds are often
not transmitted to the females: because with these they would be exposed
to too great elimination by enemies. Wallace was the first to point out
that in species with concealed nests the beautiful feathers of the male
occurred in the female also, as in the parrots, for instance, but
this is not the case in species which brood on an exposed nest. In the
parrots one can often observe that the general brilliant colouring of
the male is found in the female, but that certain spots of colour are
absent, and these have probably been acquired comparatively recently by
the male and have not yet been transmitted to the female.

Isolation of the group of individuals which is in process of varying
is undoubtedly of great value in sexual selection, for even a solitary
conspicuous variation will become dominant much sooner in a small
isolated colony, than among a large number of members of a species.

Anyone who agrees with me in deriving variations from germinal selection
will regard that process as an essential aid towards explaining the
selection of distinctive courtship-characters, such as coloured spots,
decorative feathers, horny outgrowths in birds and reptiles, combs,
feather-tufts, and the like, since the beginnings of these would
be presented with relative frequency in the struggle between the
determinants within the germ-plasm. The process of transmission of
decorative feathers to the female results, as Darwin pointed out and
illustrated by interesting examples, in the COLOUR-TRANSFORMATION OF A
WHOLE SPECIES, and this process, as the phyletically older colouring
of young birds shows, must, in the course of thousands of years, have
repeated itself several times in a line of descent.

If we survey the wealth of phenomena presented to us by secondary sexual
characters, we can hardly fail to be convinced of the truth of the
principle of sexual selection. And certainly no one who has accepted
natural selection should reject sexual selection, for, not only do the
two processes rest upon the same basis, but they merge into one another,
so that it is often impossible to say how much of a particular character
depends on one and how much on the other form of selection.

(b) NATURAL SELECTION.

An actual proof of the theory of sexual selection is out of the
question, if only because we cannot tell when a variation attains to
selection-value. It is certain that a delicate sense of smell is of
value to the male moth in his search for the female, but whether the
possession of one additional olfactory hair, or of ten, or of twenty
additional hairs leads to the success of its possessor we are unable
to tell. And we are groping even more in the dark when we discuss the
excitement caused in the female by agreeable perfumes, or by striking
and beautiful colours. That these do make an impression is beyond doubt;
but we can only assume that slight intensifications of them give any
advantage, and we MUST assume this SINCE OTHERWISE SECONDARY SEXUAL
CHARACTERS REMAIN INEXPLICABLE.

The same thing is true in regard to natural selection. It is not
possible to bring forward any actual proof of the selection-value of
the initial stages, and the stages in the increase of variations, as has
been already shown. But the selection-value of a finished adaptation can
in many cases be statistically determined. Cesnola and Poulton have made
valuable experiments in this direction. The former attached forty-five
individuals of the green, and sixty-five of the brown variety of the
praying mantis (Mantis religiosa), by a silk thread to plants, and
watched them for seventeen days. The insects which were on a surface of
a colour similar to their own remained uneaten, while twenty-five green
insects on brown parts of plants had all disappeared in eleven days.

The experiments of Poulton and Sanders ("Report of the British
Association" (Bristol, 1898), London, 1899, pages 906-909.) were made
with 600 pupae of Vanessa urticae, the "tortoise-shell butterfly." The
pupae were artificially attached to nettles, tree-trunks, fences, walls,
and to the ground, some at Oxford, some at St Helens in the Isle of
Wight. In the course of a month 93 per cent of the pupae at Oxford were
killed, chiefly by small birds, while at St Helens 68 per cent perished.
The experiments showed very clearly that the colour and character of the
surface on which the pupa rests--and thus its own conspicuousness--are
of the greatest importance. At Oxford only the four pupae which were
fastened to nettles emerged; all the rest--on bark, stones and the
like--perished. At St Helens the elimination was as follows: on fences
where the pupae were conspicuous, 92 per cent; on bark, 66 per cent; on
walls, 54 per cent; and among nettles, 57 per cent. These interesting
experiments confirm our views as to protective coloration, and show
further, THAT THE RATIO OF ELIMINATION IN THE SPECIES IS A VERY HIGH
ONE, AND THAT THEREFORE SELECTION MUST BE VERY KEEN.

We may say that the process of selection follows as a logical necessity
from the fulfilment of the three preliminary postulates of the theory:
variability, heredity, and the struggle for existence, with its enormous
ratio of elimination in all species. To this we must add a fourth
factor, the INTENSIFICATION of variations which Darwin established as
a fact, and which we are now able to account for theoretically on
the basis of germinal selection. It may be objected that there is
considerable uncertainty about this LOGICAL proof, because of our
inability to demonstrate the selection-value of the initial stages and
the individual stages of increase. We have therefore to fall back on
PRESUMPTIVE EVIDENCE. This is to be found in THE INTERPRETATIVE VALUE OF
THE THEORY. Let us consider this point in greater detail.

In the first place, it is necessary to emphasise what is often
overlooked, namely, that the theory not only explains the
TRANSFORMATIONS of species, it also explains THEIR REMAINING THE SAME;
in addition to the principle of varying, it contains within itself that
of PERSISTING. It is part of the essence of selection, that it not
only causes a part to VARY till it has reached its highest pitch of
adaptation, but that it MAINTAINS IT AT THIS PITCH. THIS CONSERVING
INFLUENCE OF NATURAL SELECTION is of great importance, and was early
recognised by Darwin; it follows naturally from the principle of the
survival of the fittest.

We understand from this how it is that a species which has become
fully adapted to certain conditions of life ceases to vary, but remains
"constant," as long as the conditions of life FOR IT remain unchanged,
whether this be for thousands of years, or for whole geological epochs.
But the most convincing proof of the power of the principle of selection
lies in the innumerable multitude of phenomena which cannot be explained
in any other way. To this category belong all structures which are only
PASSIVELY of advantage to the organism, because none of these can have
arisen by the alleged LAMARCKIAN PRINCIPLE. These have been so often
discussed that we need do no more than indicate them here. Until quite
recently the sympathetic coloration of animals--for instance, the
whiteness of Arctic animals--was referred, at least in part, to
the DIRECT influence of external factors, but the facts can best be
explained by referring them to the processes of selection, for then it
is unnecessary to make the gratuitous assumption that many species are
sensitive to the stimulus of cold and that others are not. The great
majority of Arctic land-animals, mammals and birds, are white, and this
proves that they were all able to present the variation which was most
useful for them. The sable is brown, but it lives in trees, where
the brown colouring protects and conceals it more effectively. The
musk-sheep (Ovibos moschatus) is also brown, and contrasts sharply
with the ice and snow, but it is protected from beasts of prey by its
gregarious habit, and therefore it is of advantage to be visible from
as great a distance as possible. That so many species have been able to
give rise to white varieties does not depend on a special sensitiveness
of the skin to the influence of cold, but to the fact that Mammals and
Birds have a general tendency to vary towards white. Even with us, many
birds--starlings, blackbirds, swallows, etc.--occasionally produce white
individuals, but the white variety does not persist, because it readily
falls a victim to the carnivores. This is true of white fawns, foxes,
deer, etc. The whiteness, therefore, arises from internal causes, and
only persists when it is useful. A great many animals living in a
GREEN ENVIRONMENT have become clothed in green, especially insects,
caterpillars, and Mantidae, both persecuted and persecutors.

That it is not the direct effect of the environment which calls forth
the green colour is shown by the many kinds of caterpillar which rest on
leaves and feed on them, but are nevertheless brown. These feed by night
and betake themselves through the day to the trunk of the tree, and hide
in the furrows of the bark. We cannot, however, conclude from this that
they were UNABLE to vary towards green, for there are Arctic animals
which are white only in winter and brown in summer (Alpine hare, and
the ptarmigan of the Alps), and there are also green leaf-insects which
remain green only while they are young and difficult to see on the leaf,
but which become brown again in the last stage of larval life, when they
have outgrown the leaf. They then conceal themselves by day, sometimes
only among withered leaves on the ground, sometimes in the earth itself.
It is interesting that in one genus, Chaerocampa, one species is brown
in the last stage of larval life, another becomes brown earlier, and in
many species the last stage is not wholly brown, a part remaining green.
Whether this is a case of a double adaptation, or whether the green is
being gradually crowded out by the brown, the fact remains that the same
species, even the same individual, can exhibit both variations. The case
is the same with many of the leaf-like Orthoptera, as, for instance, the
praying mantis (Mantis religiosa) which we have already mentioned.

But the best proofs are furnished by those often-cited cases in which
the insect bears a deceptive resemblance to another object. We now know
many such cases, such as the numerous imitations of green or withered
leaves, which are brought about in the most diverse ways, sometimes by
mere variations in the form of the insect and in its colour, sometimes
by an elaborate marking, like that which occurs in the Indian
leaf-butterflies, Kallima inachis. In the single butterfly-genus Anaea,
in the woods of South America, there are about a hundred species which
are all gaily coloured on the upper surface, and on the reverse side
exhibit the most delicate imitation of the colouring and pattern of a
leaf, generally without any indication of the leaf-ribs, but extremely
deceptive nevertheless. Anyone who has seen only one such butterfly
may doubt whether many of the insignificant details of the marking can
really be of advantage to the insect. Such details are for instance the
apparent holes and splits in the apparently dry or half-rotten leaf,
which are usually due to the fact that the scales are absent on a
circular or oval patch so that the colourless wing-membrane lies bare,
and one can look through the spot as through a window. Whether the
bird which is seeking or pursuing the butterflies takes these holes for
dewdrops, or for the work of a devouring insect, does not affect
the question; the mirror-like spot undoubtedly increases the general
deceptiveness, for the same thing occurs in many leaf-butterflies,
though not in all, and in some cases it is replaced in quite a peculiar
manner. In one species of Anaea (A. divina), the resting butterfly looks
exactly like a leaf out of the outer edge of which a large semicircular
piece has been eaten, possibly by a caterpillar; but if we look more
closely it is obvious that there is no part of the wing absent, and that
the semicircular piece is of a clear, pale yellow colour, while the rest
of the wing is of a strongly contrasted dark brown.

But the deceptive resemblance may be caused in quite a different manner.
I have often speculated as to what advantage the brilliant white C
could give to the otherwise dusky-coloured "Comma butterfly" (Grapta C.
album). Poulton's recent observations ("Proc. Ent. Soc"., London, May 6,
1903.) have shown that this represents the imitation of a crack such as
is often seen in dry leaves, and is very conspicuous because the light
shines through it.

The utility obviously lies in presenting to the bird the very familiar
picture of a broken leaf with a clear shining slit, and we may conclude,
from the imitation of such small details, that the birds are very sharp
observers and that the smallest deviation from the usual arrests their
attention and incites them to closer investigation. It is obvious that
such detailed--we might almost say such subtle--deceptive resemblances
could only have come about in the course of long ages through the
acquirement from time to time of something new which heightened the
already existing resemblance.

In face of facts like these there can be no question of chance, and no
one has succeeded so far in finding any other explanation to replace
that by selection. For the rest, the apparent leaves are by no means
perfect copies of a leaf; many of them only represent the torn or
broken piece, or the half or two-thirds of a leaf, but then the leaves
themselves frequently do not present themselves to the eye as a whole,
but partially concealed among other leaves. Even those butterflies
which, like the species of Kallima and Anaea, represent the whole of
a leaf with stalk, ribs, apex, and the whole breadth, are not actual
copies which would satisfy a botanist; there is often much wanting.
In Kallima the lateral ribs of the leaf are never all included in the
markings; there are only two or three on the left side and at most four
or five on the right, and in many individuals these are rather obscure,
while in others they are comparatively distinct. This furnishes us with
fresh evidence in favour of their origin through processes of selection,
for a botanically perfect picture could not arise in this way; there
could only be a fixing of such details as heightened the deceptive
resemblance.

Our postulate of origin through selection also enables us to understand
why the leaf-imitation is on the lower surface of the wing in the
diurnal Lepidoptera, and on the upper surface in the nocturnal forms,
corresponding to the attitude of the wings in the resting position of
the two groups.

The strongest of all proofs of the theory, however, is afforded by
cases of true "mimicry," those adaptations discovered by Bates in 1861,
consisting in the imitation of one species by another, which becomes
more and more like its model. The model is always a species that enjoys
some special protection from enemies, whether because it is unpleasant
to taste, or because it is in some way dangerous.

It is chiefly among insects and especially among butterflies that we
find the greatest number of such cases. Several of these have been
minutely studied, and every detail has been investigated, so that it is
difficult to understand how there can still be disbelief in regard
to them. If the many and exact observations which have been carefully
collected and critically discussed, for instance by Poulton ("Essays
on Evolution", 1889-1907, Oxford, 1908, passim, e.g. page 269.) were
thoroughly studied, the arguments which are still frequently urged
against mimicry would be found untenable; we can hardly hope to find
more convincing proof of the actuality of the processes of selection
than these cases put into our hands. The preliminary postulates of
the theory of mimicry have been disputed, for instance, that diurnal
butterflies are persecuted and eaten by birds, but observations
specially directed towards this point in India, Africa, America and
Europe have placed it beyond all doubt. If it were necessary I could
myself furnish an account of my own observations on this point.

In the same way it has been established by experiment and observation
in the field that in all the great regions of distribution there
are butterflies which are rejected by birds and lizards, their
chief enemies, on account of their unpleasant smell or taste. These
butterflies are usually gaily and conspicuously coloured and thus--as
Wallace first interpreted it--are furnished with an easily recognisable
sign: a sign of unpalatableness or WARNING COLOURS. If they were not
thus recognisable easily and from a distance, they would frequently be
pecked at by birds, and then rejected because of their unpleasant taste;
but as it is, the insect-eaters recognise them at once as unpalatable
booty and ignore them. Such IMMUNE (The expression does not refer to all
the enemies of this butterfly; against ichneumon-flies, for instance,
their unpleasant smell usually gives no protection.) species, wherever
they occur, are imitated by other palatable species, which thus acquire
a certain degree of protection.

It is true that this explanation of the bright, conspicuous colours
is only a hypothesis, but its foundations,--unpalatableness, and the
liability of other butterflies to be eaten,--are certain, and its
consequences--the existence of mimetic palatable forms--confirm it in
the most convincing manner. Of the many cases now known I select
one, which is especially remarkable, and which has been thoroughly
investigated, Papilio dardanus (merope), a large, beautiful, diurnal
butterfly which ranges from Abyssinia throughout the whole of Africa to
the south coast of Cape Colony.

The males of this form are everywhere ALMOST the same in colour and in
form of wings, save for a few variations in the sparse black markings on
the pale yellow ground. But the females occur in several quite different
forms and colourings, and one of these only, the Abyssinian form, is
like the male, while the other three or four are MIMETIC, that is to
say, they copy a butterfly of quite a different family the Danaids,
which are among the IMMUNE forms. In each region the females have thus
copied two or three different immune species. There is much that is
interesting to be said in regard to these species, but it would be out
of keeping with the general tenor of this paper to give details of this
very complicated case of polymorphism in P. dardanus. Anyone who is
interested in the matter will find a full and exact statement of the
case in as far as we know it, in Poulton's "Essays on Evolution" (pages
373-375). (Professor Poulton has corrected some wrong descriptions which
I had unfortunately overlooked in the Plates of my book "Vortrage uber
Descendenztheorie", and which refer to Papilio dardanus (merope).
These mistakes are of no importance as far as and understanding of the
mimicry-theory is concerned, but I hope shortly to be able to correct
them in a later edition.) I need only add that three different mimetic
female forms have been reared from the eggs of a single female in South
Africa. The resemblance of these forms to their immune models goes so
far that even the details of the LOCAL forms of the models are copied by
the mimetic species.

It remains to be said that in Madagascar a butterfly, Papilio meriones,
occurs, of which both sexes are very similar in form and markings to
the non-mimetic male of P. dardanus, so that it probably represents the
ancestor of this latter species.

In face of such facts as these every attempt at another explanation must
fail. Similarly all the other details of the case fulfil the preliminary
postulates of selection, and leave no room for any other interpretation.
That the males do not take on the protective colouring is easily
explained, because they are in general more numerous, and the females
are more important for the preservation of the species, and must also
live longer in order to deposit their eggs. We find the same state of
things in many other species, and in one case (Elymnias undularis)
in which the male is also mimetically coloured, it copies quite a
differently coloured immune species from the model followed by the
female. This is quite intelligible when we consider that if there were
TOO MANY false immune types, the birds would soon discover that there
were palatable individuals among those with unpalatable warning colours.
Hence the imitation of different immune species by Papilio dardanus!

I regret that lack of space prevents my bringing forward more examples
of mimicry and discussing them fully. But from the case of Papilio
dardanus alone there is much to be learnt which is of the highest
importance for our understanding of transformations. It shows us chiefly
what I once called, somewhat strongly perhaps, THE OMNIPOTENCE OF
NATURAL SELECTION in answer to an opponent who had spoken of its
"inadequacy." We here see that one and the same species is capable of
producing four or five different patterns of colouring and marking;
thus the colouring and marking are not, as has often been supposed,
a necessary outcome of the specific nature of the species, but a
true adaptation, which cannot arise as a direct effect of climatic
conditions, but solely through what I may call the sorting out of the
variations produced by the species, according to their utility. That
caterpillars may be either green or brown is already something more than
could have been expected according to the old conception of species, but
that one and the same butterfly should be now pale yellow, with black;
now red with black and pure white; now deep black with large, pure white
spots; and again black with a large ochreous-yellow spot, and many small
white and yellow spots; that in one sub-species it may be tailed like
the ancestral form, and in another tailless like its Danaid model,--all
this shows a far-reaching capacity for variation and adaptation that
wide never have expected if we did not see the facts before us. How
it is possible that the primary colour-variations should thus be
intensified and combined remains a puzzle even now; we are reminded of
the modern three-colour printing,--perhaps similar combinations of the
primary colours take place in this case; in any case the direction of
these primary variations is determined by the artist whom we know as
natural selection, for there is no other conceivable way in which the
model could affect the butterfly that is becoming more and more like it.
The same climate surrounds all four forms of female; they are subject
to the same conditions of nutrition. Moreover, Papilio dardanus is by
no means the only species of butterfly which exhibits different kinds of
colour-pattern on its wings. Many species of the Asiatic genus Elymnias
have on the upper surface a very good imitation of an immune Euploeine
(Danainae), often with a steel-blue ground-colour, while the under
surface is well concealed when the butterfly is at rest,--thus there are
two kinds of protective coloration each with a different meaning! The
same thing may be observed in many non-mimetic butterflies, for
instance in all our species of Vanessa, in which the under side shows
a grey-brown or brownish-black protective coloration, but we do not yet
know with certainty what may be the biological significance of the gaily
coloured upper surface.

In general it may be said that mimetic butterflies are comparatively
rare species, but there are exceptions, for instance Limenitis archippus
in North America, of which the immune model (Danaida plexippus) also
occurs in enormous numbers.

In another mimicry-category the imitators are often more numerous than
the models, namely in the case of the imitation of DANGEROUS INSECTS by
harmless species. Bees and wasps are dreaded for their sting, and they
are copied by harmless flies of the genera Eristalis and Syrphus, and
these mimics often occur in swarms about flowering plants without damage
to themselves or to their models; they are feared and are therefore left
unmolested.

In regard also to the FAITHFULNESS OF THE COPY the facts are quite in
harmony with the theory, according to which the resemblance must have
arisen and increased BY DEGREES. We can recognise this in many
cases, for even now the mimetic species show very VARYING DEGREES OF
RESEMBLANCE to their immune model. If we compare, for instance, the
many different imitators of Danaida chrysippus we find that, with their
brownish-yellow ground-colour, and the position and size, and more or
less sharp limitation of their clear marginal spots, they have reached
very different degrees of nearness to their model. Or compare the female
of Elymnias undularis with its model Danaida genutia; there is a general
resemblance, but the marking of the Danaida is very roughly imitated in
Elymnias.

Another fact that bears out the theory of mimicry is, that even when the
resemblance in colour-pattern is very great, the WING-VENATION, which is
so constant, and so important in determining the systematic position
of butterflies, is never affected by the variation. The pursuers of the
butterfly have no time to trouble about entomological intricacies.

I must not pass over a discovery of Poulton's which is of great
theoretical importance--that mimetic butterflies may reach the same
effect by very different means. ("Journ. Linn. Soc. London (Zool.)",
Vol. XXVI. 1898, pages 598-602.) Thus the glass-like transparency of the
wing of a certain Ithomiine (Methona) and its Pierine mimic (Dismorphia
orise) depends on a diminution in the size of the scales; in the Danaine
genus Ituna it is due to the fewness of the scales, and in a third
imitator, a moth (Castnia linus var. heliconoides) the glass-like
appearance of the wing is due neither to diminution nor to absence of
scales, but to their absolute colourlessness and transparency, and to
the fact that they stand upright. In another moth mimic (Anthomyza) the
arrangement of the transparent scales is normal. Thus it is not some
unknown external influence that has brought about the transparency of
the wing in these five forms, as has sometimes been supposed. Nor is it
a hypothetical INTERNAL evolutionary tendency, for all three vary in a
different manner. The cause of this agreement can only lie in selection,
which preserves and intensifies in each species the favourable
variations that present themselves. The great faithfulness of the copy
is astonishing in these cases, for it is not THE WHOLE wing which is
transparent; certain markings are black in colour, and these contrast
sharply with the glass-like ground. It is obvious that the pursuers
of these butterflies must be very sharp-sighted, for otherwise the
agreement between the species could never have been pushed so far. The
less the enemies see and observe, the more defective must the imitation
be, and if they had been blind, no visible resemblance between the
species which required protection could ever have arisen.

A seemingly irreconcilable contradiction to the mimicry theory is
presented in the following cases, which were known to Bates, who,
however, never succeeded in bringing them into line with the principle
of mimicry.

In South America there are, as we have already said, many mimics of the
immune Ithomiinae (or as Bates called them Heliconidae). Among these
there occur not merely species which are edible, and thus require the
protection of a disguise, but others which are rejected on account of
their unpalatableness. How could the Ithomiine dress have developed in
their case, and of what use is it, since the species would in any case
be immune? In Eastern Brazil, for instance, there are four butterflies,
which bear a most confusing resemblance to one another in colour,
marking, and form of wing, and all four are unpalatable to birds. They
belong to four different genera and three sub-families, and we have to
inquire: Whence came this resemblance and what end does it serve? For
a long time no satisfactory answer could be found, but Fritz Muller
(In "Kosmos", 1879, page 100.), seventeen years after Bates, offered a
solution to the riddle, when he pointed out that young birds could not
have an instinctive knowledge of the unpalatableness of the Ithomiines,
but must learn by experience which species were edible and which
inedible. Thus each young bird must have tasted at least one individual
of each inedible species and discovered its unpalatability, before it
learnt to avoid, and thus to spare the species. But if the four species
resemble each other very closely the bird will regard them all as of
the same kind, and avoid them all. Thus there developed a process
of selection which resulted in the survival of the Ithomiine-like
individuals, and in so great an increase of resemblance between the four
species, that they are difficult to distinguish one from another even in
a collection. The advantage for the four species, living side by side
as they do e.g. in Bahia, lies in the fact that only one individual
from the MIMICRY-RING ("inedible association") need be tasted by a young
bird, instead of at least four individuals, as would otherwise be the
case. As the number of young birds is great, this makes a considerable
difference in the ratio of elimination.

These interesting mimicry-rings (trusts), which have much significance
for the theory, have been the subject of numerous and careful
investigations, and at least their essential features are now fully
established. Muller took for granted, without making any investigations,
that young birds only learn by experience to distinguish between
different kinds of victims. But Lloyd Morgan's ("Habit and Instinct",
London, 1896.) experiments with young birds proved that this is really
the case, and at the same time furnished an additional argument against
the LAMARCKIAN PRINCIPLE.

In addition to the mimicry-rings first observed in South America, others
have been described from Tropical India by Moore, and by Poulton and
Dixey from Africa, and we may expect to learn many more interesting
facts in this connection. Here again the preliminary postulates of the
theory are satisfied. And how much more that would lead to the same
conclusion might be added!

As in the case of mimicry many species have come to resemble one another
through processes of selection, so we know whole classes of phenomena
in which plants and animals have become adapted to one another, and have
thus been modified to a considerable degree. I refer particularly to the
relation between flowers and insects; but as there is an article on "The
Biology of Flowers" in this volume, I need not discuss the subject, but
will confine myself to pointing out the significance of these remarkable
cases for the theory of selection. Darwin has shown that the originally
inconspicuous blossoms of the phanerogams were transformed into flowers
through the visits of insects, and that, conversely, several large
orders of insects have been gradually modified by their association
with flowers, especially as regards the parts of their body actively
concerned. Bees and butterflies in particular have become what they
are through their relation to flowers. In this case again all that is
apparently contradictory to the theory can, on closer investigation, be
beautifully interpreted in corroboration of it. Selection can give rise
only to what is of use to the organism actually concerned, never to what
is of use to some other organism, and we must therefore expect to find
that in flowers only characters of use to THEMSELVES have arisen, never
characters which are of use to insects only, and conversely that in the
insects characters useful to them and not merely to the plants would
have originated. For a long time it seemed as if an exception to this
rule existed in the case of the fertilisation of the yucca blossoms by
a little moth, Pronuba yuccasella. This little moth has a sickle-shaped
appendage to its mouth-parts which occurs in no other Lepidopteron,
and which is used for pushing the yellow pollen into the opening of
the pistil, thus fertilising the flower. Thus it appears as if a new
structure, which is useful only to the plant, has arisen in the insect.
But the difficulty is solved as soon as we learn that the moth lays
its eggs in the fruit-buds of the Yucca, and that the larvae, when they
emerge, feed on the developing seeds. In effecting the fertilisation
of the flower the moth is at the same time making provision for its own
offspring, since it is only after fertilisation that the seeds begin to
develop. There is thus nothing to prevent our referring this structural
adaptation in Pronuba yuccasella to processes of selection, which
have gradually transformed the maxillary palps of the female into the
sickle-shaped instrument for collecting the pollen, and which have at
the same time developed in the insect the instinct to press the pollen
into the pistil.

In this domain, then, the theory of selection finds nothing but
corroboration, and it would be impossible to substitute for it any
other explanation, which, now that the facts are so well known, could
be regarded as a serious rival to it. That selection is a factor, and
a very powerful factor in the evolution of organisms, can no longer be
doubted. Even although we cannot bring forward formal proofs of it IN
DETAIL, cannot calculate definitely the size of the variations which
present themselves, and their selection-value, cannot, in short,
reduce the whole process to a mathematical formula, yet we must assume
selection, because it is the only possible explanation applicable to
whole classes of phenomena, and because, on the other hand, it is made
up of factors which we know can be proved actually to exist, and
which, IF they exist, must of logical necessity cooperate in the manner
required by the theory. WE MUST ACCEPT IT BECAUSE THE PHENOMENA OF
EVOLUTION AND ADAPTATION MUST HAVE A NATURAL BASIS, AND BECAUSE IT IS
THE ONLY POSSIBLE EXPLANATION OF THEM. (This has been discussed in many
of my earlier works. See for instance "The All-Sufficiency of Natural
Selection, a reply to Herbert Spencer", London, 1893.)

Many people are willing to admit that selection explains adaptations,
but they maintain that only a part of the phenomena are thus explained,
because everything does not depend upon adaptation. They regard
adaptation as, so to speak, a special effort on the part of Nature,
which she keeps in readiness to meet particularly difficult claims
of the external world on organisms. But if we look at the matter more
carefully we shall find that adaptations are by no means exceptional,
but that they are present everywhere in such enormous numbers, that it
would be difficult in regard to any structure whatever, to prove that
adaptation had NOT played a part in its evolution.

How often has the senseless objection been urged against selection that
it can create nothing, it can only reject. It is true that it cannot
create either the living substance or the variations of it; both must be
given. But in rejecting one thing it preserves another, intensifies
it, combines it, and in this way CREATES what is new. EVERYTHING in
organisms depends on adaptation; that is to say, everything must be
admitted through the narrow door of selection, otherwise it can take
no part in the building up of the whole. But, it is asked, what of the
direct effect of external conditions, temperature, nutrition, climate
and the like? Undoubtedly these can give rise to variations, but they
too must pass through the door of selection, and if they cannot do this
they are rejected, eliminated from the constitution of the species.

It may, perhaps, be objected that such external influences are often of
a compelling power, and that every animal MUST submit to them, and that
thus selection has no choice and can neither select nor reject. There
may be such cases; let us assume for instance that the effect of the
cold of the Arctic regions was to make all the mammals become black; the
result would be that they would all be eliminated by selection, and
that no mammals would be able to live there at all. But in most cases a
certain percentage of animals resists these strong influences, and
thus selection secures a foothold on which to work, eliminating the
unfavourable variation, and establishing a useful colouring, consistent
with what is required for the maintenance of the species.

Everything depends upon adaptation! We have spoken much of adaptation
in colouring, in connection with the examples brought into prominence by
Darwin, because these are conspicuous, easily verified, and at the same
time convincing for the theory of selection. But is it only desert and
polar animals whose colouring is determined through adaptation? Or the
leaf-butterflies, and the mimetic species, or the terrifying markings,
and "warning-colours" and a thousand other kinds of sympathetic
colouring? It is, indeed, never the colouring alone which makes up
the adaptation; the structure of the animal plays a part, often a very
essential part, in the protective disguise, and thus MANY variations may
cooperate towards ONE common end. And it is to be noted that it is by
no means only external parts that are changed; internal parts are ALWAYS
modified at the same time--for instance, the delicate elements of the
nervous system on which depend the INSTINCT of the insect to hold its
wings, when at rest, in a perfectly definite position, which, in the
leaf-butterfly, has the effect of bringing the two pieces on which
the marking occurs on the anterior and posterior wing into the same
direction, and thus displaying as a whole the fine curve of the midrib
on the seeming leaf. But the wing-holding instinct is not regulated in
the same way in all leaf-butterflies; even our indigenous species
of Vanessa, with their protective ground-colouring, have quite a
distinctive way of holding their wings so that the greater part of the
anterior wing is covered by the posterior when the butterfly is at rest.
But the protective colouring appears on the posterior wing and on the
tip of the anterior, TO PRECISELY THE DISTANCE TO WHICH IT IS LEFT
UNCOVERED. This occurs, as Standfuss has shown, in different degree in
our two most nearly allied species, the uncovered portion being
smaller in V. urticae than in V. polychloros. In this case, as in most
leaf-butterflies, the holding of the wing was probably the primary
character; only after that was thoroughly established did the protective
marking develop. In any case, the instinctive manner of holding the
wings is associated with the protective colouring, and must remain as it
is if the latter is to be effective. How greatly instincts may change,
that is to say, may be adapted, is shown by the case of the Noctuid
"shark" moth, Xylina vetusta. This form bears a most deceptive
resemblance to a piece of rotten wood, and the appearance is greatly
increased by the modification of the innate impulse to flight common to
so many animals, which has here been transformed into an almost contrary
instinct. This moth does not fly away from danger, but "feigns death,"
that is, it draws antennae, legs and wings close to the body, and
remains perfectly motionless. It may be touched, picked up, and thrown
down again, and still it does not move. This remarkable instinct must
surely have developed simultaneously with the wood-colouring; at all
events, both cooperating variations are now present, and prove that both
the external and the most minute internal structure have undergone a
process of adaptation.

The case is the same with all structural variations of animal parts,
which are not absolutely insignificant. When the insects acquired wings
they must also have acquired the mechanism with which to move them--the
musculature, and the nervous apparatus necessary for its automatic
regulation. All instincts depend upon compound reflex mechanisms and are
just as indispensable as the parts they have to set in motion, and all
may have arisen through processes of selection if the reasons which I
have elsewhere given for this view are correct. ("The Evolution Theory",
London, 1904, page 144.)

Thus there is no lack of adaptations within the organism, and
particularly in its most important and complicated parts, so that we may
say that there is no actively functional organ that has not undergone a
process of adaptation relative to its function and the requirements of
the organism. Not only is every gland structurally adapted, down to the
very minutest histological details, to its function, but the function
is equally minutely adapted to the needs of the body. Every cell in the
mucous lining of the intestine is exactly regulated in its relation to
the different nutritive substances, and behaves in quite a different way
towards the fats, and towards nitrogenous substances, or peptones.

I have elsewhere called attention to the many adaptations of the whale
to the surrounding medium, and have pointed out--what has long been
known, but is not universally admitted, even now--that in it a great
number of important organs have been transformed in adaptation to the
peculiar conditions of aquatic life, although the ancestors of the whale
must have lived, like other hair-covered mammals, on land. I cited a
number of these transformations--the fish-like form of the body, the
hairlessness of the skin, the transformation of the fore-limbs to fins,
the disappearance of the hind-limbs and the development of a tail fin,
the layer of blubber under the skin, which affords the protection
from cold necessary to a warm-blooded animal, the disappearance of the
ear-muscles and the auditory passages, the displacement of the external
nares to the forehead for the greater security of the breathing-hole
during the brief appearance at the surface, and certain remarkable
changes in the respiratory and circulatory organs which enable the
animal to remain for a long time under water. I might have added many
more, for the list of adaptations in the whale to aquatic life is by no
means exhausted; they are found in the histological structure and in the
minutest combinations in the nervous system. For it is obvious that a
tail-fin must be used in quite a different way from a tail, which serves
as a fly-brush in hoofed animals, or as an aid to springing in the
kangaroo or as a climbing organ; it will require quite different
reflex-mechanisms and nerve-combinations in the motor centres.

I used this example in order to show how unnecessary it is to assume a
special internal evolutionary power for the phylogenesis of species, for
this whole order of whales is, so to speak, MADE UP OF ADAPTATIONS; it
deviates in many essential respects from the usual mammalian type, and
all the deviations are adaptations to aquatic life. But if precisely the
most essential features of the organisation thus depend upon adaptation,
what is left for a phyletic force to do, since it is these essential
features of the structure it would have to determine? There are few
people now who believe in a phyletic evolutionary power, which is not
made up of the forces known to us--adaptation and heredity--but the
conviction that EVERY part of an organism depends upon adaptation has
not yet gained a firm footing. Nevertheless, I must continue to regard
this conception as the correct one, as I have long done.

I may be permitted one more example. The feather of a bird is a
marvellous structure, and no one will deny that as a whole it depends
upon adaptation. But what part of it DOES NOT depend upon adaptation?
The hollow quill, the shaft with its hard, thin, light cortex, and the
spongy substance within it, its square section compared with the round
section of the quill, the flat barbs, their short, hooked barbules
which, in the flight-feathers, hook into one another with just
sufficient firmness to resist the pressure of the air at each wing-beat,
the lightness and firmness of the whole apparatus, the elasticity of
the vane, and so on. And yet all this belongs to an organ which is only
passively functional, and therefore can have nothing to do with the
LAMARCKIAN PRINCIPLE. Nor can the feather have arisen through some
magical effect of temperature, moisture, electricity, or specific
nutrition, and thus selection is again our only anchor of safety.

But--it will be objected--the substance of which the feather consists,
this peculiar kind of horny substance, did not first arise through
selection in the course of the evolution of the birds, for it formed the
covering of the scales of their reptilian ancestors. It is quite true
that a similar substance covered the scales of the Reptiles, but why
should it not have arisen among them through selection? Or in what other
way could it have arisen, since scales are also passively useful parts?
It is true that if we are only to call adaptation what has been acquired
by the species we happen to be considering, there would remain a great
deal that could not be referred to selection; but we are postulating an
evolution which has stretched back through aeons, and in the course of
which innumerable adaptations took place, which had not merely ephemeral
persistence in a genus, a family or a class, but which was continued
into whole Phyla of animals, with continual fresh adaptations to
the special conditions of each species, family, or class, yet with
pers

Showing first 200,000 characters. Full text: gutenberg.org/ebooks/1909