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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 pre- 
liminary 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. 

Authoi"s were asked to address theiliselves 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 illus- 
trating the far-reaching influence of Darwin's work on the j)rogress 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 Oriffiu of 
Species quoted on page 71, 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. 

vi Preface 

In reading tlie essays in proof I have availed myself freely of the 
Avilling 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. Bougie'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 
Vortrdge iiher Descendenztheo7'ie which afterwards appeared (1904) 
in English mider the title The Evolution Theory. Copies of tliis 
plate were supplied by INIcssrs 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 funda- 

Preface vii 

mental 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 

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 progi*ess of 
research on lines which, though unkno^vn 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 difierent opinions of contributors. Whether 
Darwin's views on the modus ojyerandi of evolutionary forces receive 
further confirmation in the future, or whether they are materially 
modified, in no way afiects the truth of the statement that, by employ- 
ing 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 efibrts 
being overlaid and forgotten in the mass of new facts and new views 
which are daily turning up." In the onward I'ush, it is easy for students 
convinced of tlie 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 

He acted stiictly in accordance with his determination expressed 
in a letter to Lycll in 1044, "I shall keep out of controversy, and just 

viii Preface 

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 aiFords 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 


Botany School, Cambridge, 
March 20, 1909. 



L Introductory Letter to the Editor from Sir 

Joseph Dalton Hooker, O.M. . . . 1 

II. Darwin's Predecessors : 

J. Arthur Thomson, Professor of Natural History 

in the University of Aberdeen .... 3 

III. The Selection Theory : 

August Weismann, Professor of Zoology in the 

University of Freiburg (Baden) . . . 18 

IV. Variation : 

Hugo de Vries, Professor of Botany in the Uni- 
versity of Amsterdam 66 

V. Heredity and Variation in Modern Lights: 

W. Bateson, Professor of Biology in the University 

of Cambridge 85 

VI. The Minute Structure of Cells in Relation to 

Heredity : 

Eduard Strasburger, Professor of Botany in the 

University of Bonn 102 

VII. '« The Descent of Man " : 

G. SCHWALBE, Professor of Anatomy in the Uni- 
versity of Strassburg 112 

VIII. Charles Darwin as an Anthropologist: 

Ernst Haeckel, Proiessor of Zoology in the 

University of Jena ...... 137 

IX. Some Primitive Theories of the Origin of Man : 

J. G. Frazer, Fellow of Trinity College, Cambridge 152 



^/ X. Tlie Influence of Darwin on the Study of 

Animal Embryology: 

A. Sedgwick, Professor of Zoology and Compara- 
tive Anatomy in the University of Cambridge 

'^ XL The Palneontological Record. I. Animals: 

W. B, Scott, Professor of Geology in the Uni- 
versity of Princeton 

XII. The Palaeontological Record. II. Plants: 

D. H. Scott, President of the Linnean Society of 

XIII. The Influence of Environment on the Forms 
of Plants : 

Georg Klebs, Professor of Botany in the Uni- 
versity 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 : 

XIX. Darwin's work on the Movements of Plants: 
Francis Darwin 

XX. The Biology of Flowers : 

K. Goebel, Professor of Botany in the Uni- 
versity of Munich 

XXI. Mental Factors in Evolution : 

C. Lloyd Morgan, Professor of Psychology at 
University College, Bristol .... 
















XXII. Tlie Influence of the Conception of Evolu- 
tion on Modern Philosophy : 

XL HoFFDiNG, Professor of Philosophy in the 
University of Copenhagen .... 



^XXIII. Darwinism and Sociology : 

C. BouGL^, Professor of Social Philosophy in the 
University of Toulouse, and Deputy-Professor 
at the Sorbonne, Paris 465 

.^/XXIV. The Influence of Darwin upon Religious 

Rev. P. N. Waggett 

^ XXV. The Influence of Darwinism on the Study of 

Religions : 

Jane Ellen Hajirtson, Staff-Lecturer and some- 
time Fellow of Newnham College, Cambridge 

XXVI. Evolution and the Science of Language : 

P. Giles, Reader in Comparative Philology in 
the University of Cambridge 





Darwinism and History : 

J. B. Bury, Regius Professor of IModcrn History 
in the University of Cambridge . 

The Genesis of Double Stars : 

Sir George Darwin, Plumian Professor of As- 
tronomy and Experimental Philosophy in 
tlic University of Cambridge 







The Evolution of Matter : 

W. C. D. Whetham, Fellow of Trinity College, 

CaJ!i bridge 505 




FfiONTispiECE. Portrait of Cliarles Darwin (? 1854) from a photograph 
by Messrs Maull & Fox, previously reproduced in More Letters 
of Charles Dartcin and in the Annals of Botany, xiii. 1899, 
as the frontispiece of an article "The Botanical Work of Darwin," 
by Francis Darwin. 

Plate illustrating Anaea divina . . , Facing page 53 

Plate from Professor Weismann's Vortrdge uber Descendenztheorie, 
illustrating Mimicry in Butterflies . . Facing page 57 

The study at Down, from an etching by Mr Axel Haig 

Facing page 379 

Portrait of Charles Darwin (?1880) from a photograph by Messrs 
Elliott & Fry Facing page 493 


1809 Charles Darwin born at Shrewsbury, February 12. 

1817 "At 8i 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 loarnt 

absolutely nothing, except by amusing myself by reading and experimeutiug 
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 ISJS, and soon became acquainted 
with Professor Henslow.... Nothing could bo more simple, cordial and unpre- 
tending 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 iis the academical studies were concerned, aa 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.'.. .Tlie 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 

*' I gained a good place among the ol noXXol or crowd of men who do not go in 

f<jr honours." 
"1 am very busy,. ..and see a great deal of Henslow, whom I do not know 

whetlicr I love or respect most." 
Doc. 27. "Sidled from England on our circumnavigation," in 11. M.S. Beagle, a 

barque of 235 tons carrying G guns, under Capt. Fitzlloy. 
" There is indeed a tide in tlio aliairs of men." 

xiv Epitome of Charles Darwin's Life 

1836 Oct. 4. " Reached Shrowsbm-y after absence of 5 years and 2 days." 

" You cannot imagine liow gloriously delightful my first visit was at home ; it 

was worth the banishment." 
Dec. 13. Went to live at Cambridge (Fitzwnlliam 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 moutli 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, 1 happened to read for amusement ' Malthus on Population,' and 
being well prepared to appreciate the struggle for existence which every- 
where 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. 
" 1 marvel at my good fortune that she, so infinitely my suijerior 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 " [ Autobiogi-apliy]. 
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." 
Pulilished Joumial and Researches, being Vol. ill. of the Narratii-e of the 

Surveying Vayafje <>f H.M.S. Adrenhire and Beagle.... 
Publication of the Zoohgy of the Vmjage of H.M.S. Beagle, Part ii., Mam- 

malia, by G. K. Waterhouse, with a Notice of their habits and ratiges, 

by Charles Darwin. 

1840 Contributed Geological Introduction to Part I. (Fossil Mammalia) of the 
Zolngy of the Voyage of II. M.S. Beagle by Richard Owen. 

Epitome of Charles Darwin's Life xv 

1842 " In Jane 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 i." 
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 qf Coral Re^s ; 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 II.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-buildiug." 

1854 Publication of Monographs of the Balanidae and Verrucidae. 

" 1 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 1 had to discuss in the Origin of Species the principles ot" 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 

1856 " Flarly 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 
Avhich 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 Liunean 
Society by Sir Charles Lyell and Sir Joseph Hooker. 

"I was at first very unwilling to consent [to the communication of his MS. to 
tJio Society] as 1 thought Mr Wallace might consider my doing so unjustifi- 
able, for I did not then know how generous and noble was his disposition." 

"July 'JO to Aug. 12 at Sandown [Isle of Wight] began abstract of Species 

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 !...liut, alas, how frequent, how almost universal it is 
in an author io persuade himsclT of tljo trutii of iiis own dogmas. My only 
hope is that I certainly see many difficulties of gigantic stature." 

* The first draft of The Origin of Species, edited by Mr Francis Darwin, will bo 
pabliflhed this year (1909) by the Syndics of the Cambridge University Press. 

xvi Epitome of Charles Dai^win's Life 

1860 Publication of the second edition of the Origin (3000 copies). 
Publication of a Naturalisfs 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 1876.) 

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 

" 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 Tlie Descent of Man. 

"Although in the Origin of Sj)ecies 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 

1875 Publication of Insectivorous Plants. 

" I besin 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 oj Climbing Plants sls a separate book. 

1876 Wrote Autobiographical Sketch {Life and Letters, Vol. I., Chap. II.). 
I'uldication of The Effects <f Cross and Self fertilisation. 

"I now [IHSI] believe, however,, .that I ouglit to have insisted more strongly 

than 1 did on the many adaptations for self-fertilisation." 
Publication of the second edition of Observations on Volcanic Islands. 

Epitome of Charles Darwin's Life xvii 

1877 Publication of The Different Forms of Flowers on Plants of the game species. 
"I do not suppose that I shall publish any more books....! 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 Gross 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 Galtuu, Nov. 14, 1879.] 

1880 Publication of The Poicer of Movement in Plants. 

" It has always pleased me to exalt plants in the scale of organised beings." 
Publication of the second edition of Tfie Different Form^ 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 bo 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 IsaJic 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 Autobiogrnphy 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 Dancin: His life told in an Autobiographiciil Chapter, and in a selected 
series of his published Letters. Edited by his son, Francis Darwin, London, 1902. 

Miyre 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, 

"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 impor- 
tant 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 

Autobiography (1S81); The Life and Letters of Charles 
Darwin, Vol. i. p. 107. 

FROM Sir Joseph Dalton Hooker, 

CM., G.C.S.I., C.B., M.D., D.C.L., LL.D., F.R.S., BTO. 

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 congi-atulation to all students of Science. 

These Essays on the progi-ess of Science and Philosophy as 
aflPected 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 tlicorctical, which he set himself to solve and the stei)8 by M'hich 
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 lie regarded as models for those 
who were asked to address themselves primarily to the educated 
reader rather than to the expert. 

1 may add that by no one can the perusal of the Essays be more 
vividly upi)reciated than by the writer of these lines. It was my 
l»ri\ilege for forty years to [)ossess the intimate friendship of Charles 
u. 1 

2 Introductory Letter 

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 gi-atifying 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, 



By J. Arthur Thomson. 

Professor of Natural History in the University of Aberdeen. 

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

(I) As ever3'one 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 back- 
wards towards the literal " Protozoa ' and " Protophyta" about Avhich 
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 intelli- 
gence of the day, and he won wide-spread conviction by showing with 
consummate skill that it was an effective formula to work Avith, a key 
which no lock refused. In a scholarly, critical, and pre-eminently 
fair-minded way, admitting difficulties and removing them, fore- 
seeing 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 
Ixjdily 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 
Ixjfore Darwin's day, though no one [except Herbert Spencer in the 
psycliological domain (ir.55)] had come near him in precision and 
thoroughness of incjuiry. 

(HI) In the third place, Darwin contributed largely to a know- 
ledge of the factors in tlie evolution-process, especially by analysis 

1 — 2 

4 Darwin s Predecessors 

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 diiferent 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 ^Etiology 
but to Natural History in the widest sense, we rank the picture 
>vhich 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 naturalists like Christian Conrad Sprengel, 
Gilbert ^^^lite, 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 jjost urhem condUam 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\ 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 ijlants 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^." But the fundamental idea of one stage giving origin to 
another was absent. As the blue iEgean teemed with treasures of 
l>eauty 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. 

' Columbia University Biolonical Series, Vol. i. New York and London, 1894. We 
must auknowledge our great indebtedness to this fine piece of work. 
' op. cit. p. 41. 

Evolutionist Philosophers 5 

Aristotle's Tiews of Nature^ seem to have been more definitely 
evolutionist than those of his predecessors, in this sense, at least, that 
lie 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 degi'ees from lower to higher types." " Nature produces those 
things which, being continually moved by a certain principle con- 
tained 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", for difference of 
opinion as to how far he was an evolutionist in our sense of the 

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 seven- 
teenth centuries who had at least got beyond static formulae, but, as 
Professor Osborn points out^, " it is a very striking fact, that the basis 
of our modem 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 

Bacon seems to have been one of the first to think definitely about 

' See O. J. RomaneP, "Aristotle as a NatnraliBt," Contrmporary Bfview, Vol. lii. 
p. 276, 18'J1 ; G. Pouchet, La Biologic Aristottlique, Paris, iHMo ; E. Zeller, A History 
of Greek Philosophy, London, 1881, and " Ueber die griecbiechen Vorghnger Darwin's," 
Abhundl. Berlin Akad. 1878, pp. 111—124. 

' op. cit. p. 81. ^ op. cit. p. 87. 

6 Darwin's Predecessors 

the mutability of species, and he was far ahead of his age in his 
suggestion of wliat 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.' ij^iniilar 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, diflerentiated 
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^ 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 agree- 
ment of so many kinds of animals in a certain common plan of 
structure"... an "analogy of forms" which "strengthens the sup- 
position 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 con- 
tinuous 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 comprehen- 
sible, according to natural laws ordained by no intention." As Prof. 
Haeckel finely observes, Darwin rose up as Kant's Newton^. 

The scientific renaissance brought a wealth of fresh impressions 
and some freedom from the tyranny of tradition, and the twofold 
stinmlus stirred the speculative activity of a great variety of men 
from old Claude Duret of Moulins, of whose weird transformism 

' See Brook, "Die Stellung Kant's zur Deszendenztheorie," Biol. Centralbl. viii. 
1889, pp. GU — G48. I'ritz Schultze, Kant und Darwin, Jena, 1875. 

' Mr Alfred Kussel Wallace writes: "We claim for Darwin that he is the Newton of 
natural history, and that, juat 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 preserva- 
tion 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 " {Daripinism, London, 1880, p. 9). See also Prof. Karl 
Pearson's Grammar of Science (2nd edit.), London, 1900, p. 32. See Osborn, op. cit. p. 100. 

Erasmus Danchi 7 

(1609) Dr Henry de Varigny^ gives us a glimpse, to Lorenz Oken 
(1779 — 1851) whose writinprs are such mixtures of sense and nonsense 
that some regard liim 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 Pro- 
fessor 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 ^ 

The first naturalist to give a broad and concrete expression to 
the evolutionist doctrine of descent was Buflfon (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^, 
went the length of admitting (in 1762) that new species might 
arise by intercrossing. Bufibn'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 " I'enchaine- 
ment des etres." 

Erasmus Darwin (1731—1802), probably influenced by Buffon, 
was another firm evolutionist, and the outline of his argument in the 
Zoonomia* might serve in part at least to-day. " ^Yheu 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 pro- 
duced 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 commcuce- 

> Ezprrimental Evolution. London, 1892. Chap. x. p. 14. 

* See J. Arthur Thomson, The Science of Life. London, 1899. Chap. xvi. "Evolution 
of Evolution Theory." 

' See Caru.s Sterne (Ernat Krauso), Die allgemeine Weltnnnchauung in ihrer hintorischen 
Entwickelung. Stuttgart, 188'J. Chapter entitled " Beatiindigkeit oder Veranderlichkeit 
der Natorveson." 

* Zoonomia, or the Laiot of Organic Life, 2 vols. London, 1794 ; Osbom, op. eit. p. 145. 

8 Dancings Predecessors 

ment of the history of mankind, that all warm-blooded animals have 
arisen from one living filament?"...." This. idea of the gradual genera- 
tion 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 Trp&Tov d)6v, or first great egg, 
produced by night, that is, whose origin is involved in obscurity, and 
animated by "Epto?, that is, by Divine Love ; from whence proceeded 
all things which exist." 

Lamarck (1744 — 1829) seems to have become an evolutionist inde- 
pendently 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 Philo- 
sophie Zoologique as "the first connected and thoroughly logical 
exposition of the theory of descent \" 

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 Ti-eviranus 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 Geofii-oy 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 18551 

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 

' See AlpheuB 8. Packard, Lamarck, the Founder of Evolution, His Life and Work, 
xcith Translations of hit writings on Organic Evolution. London, 1901. 
' See Edward Clodd, Pioneers of Evolution, Loudon, p. 161, 1897. 

Pre-Darioinian Evolutionists 9 

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 Dar^vin 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 pedigi-ee of an organism, is often very intricate, and the 
evolution of the evolution-idea is bound up with the whole progi-ess 
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^; we have to realise 
liow the gi'owing 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 Avise 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 depart- 
ments 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 bio- 
logical 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 I'Sge mflr " — 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 cliange 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 — fjuite une(|ualled. Because, in the third place, he broke 

' See Chapter ix. "The Genetic View of Nature" in J. T. Merz's HUtory of European 
Thought in the Nineteenth Century, Vol. 2, Edinburph and London, 1903. 

10 Darwin's Predecessors 

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 

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 \ 

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-diSerentiating 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 varia- 

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 d force de forger quon 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^. 

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 

> See Prof. W. A. Locy'a Biology and its Makers. New York, 1908. Part il. "The 
Doctrine of Organic Evolution." 

* Presidential Address to the British Association meeting at Dublin in 1908. 

Pre- Darwinian Theories of Evolution 11 

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 
Buifonians — 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 Buffbn^ definitely suggested that environ- 
mental 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 AVTitings what extent 
of transformation he really believed in. Prof Osborn says of Bufibn : 
"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- : 

" Le cours ordinaire de la nature vivante, est en gen(5ral toujours 
constant, toujours le meme ; son mouvement, toujours r^gulier, roule 
sur deux points inebranlables : I'un, la fecondite sans bornes donnee 
h. toutes Ics esp^ces ; I'autre, les obstacles sans nombre qui reduisent 
cctte fccondit^ 5- une mesure determinee et ne laissent en tout temps 
qu'k peu pr6s la meme quantity d'individus de chaque esp6ce"..."Les 
esp^ces les moins parfaites, Ics plus delicates, les plus pesantes, les 
moins agissantes, les moins arm(ies, etc., ont dej^ disparu ou dis- 

Erasmus Darwin^ 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 

' See in particular Samuel Butler, Evolution Old and New, London, 1879; J. L. de 
Lanessan, "Buffon et Darwin," Revue Scientifique , pp. 385—391, 425—432, 188'J. 
' op. cii. p. 130. 
• See Eruet KrauHc and Charles Darwin, Eriumuu Darwin, Loudon, 1879. 

12 Darwin's Predecessors 

misses the connection between this struggle and the Survival of the 
Fittest \" 

Lamarck- (1744 — 1829) seems to have thought out his theory 
of evolution witliout 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 diftered from Buffon in not attaching 
importance, as far as animals are concerned, to the direct influence 
of the environment, "for environment can efiect 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), whom Huxley ranked beside Lamarck, 
was on the whole Buftbnian, attaching chief importance to the 
influence of a changeful environment both in modifying and in 
eliminating, but he was also Gocthian, 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), who knew Bufibn's work but not Lamarck's, 
is j)cculiarly interesting as one of the first to use the evolution-idea 
as a guiding hy})othesis, e.g. in the interpretation of vestigial structures 
in man, and to realise that organisms express an attempt to make a 
com})romise between specific inertia and individual change. He gave 

1 Osborn, op. cit. p. 142. 

- See: E. Perrier, La PhihsopJiie Zoologique avant Darwin, Paris, 1884; A. de 
Quatrefages, Darwin et set Pricursenrs Fran^ais, Paris, 1870; Packard, op. cit.; also 
ClauH, Lamarck ah Bcgriinder dcr Detcendenzlchre, Wien, 1888 ; Haeckel, Natural History 
of Creation, Edr. transl. London, 1879; Lang, Zur Charakteristik der Forschungswege 
von Lamarck und Darwin, Jena, 1889. 

' 8«e Hurley's article "Evolution in Wiolody ,'' Encrjdopaedia Britannica (9th edit), 
1878, pp. 744—751, and Sully's article, "Evolution in Philosophy," ibid. pp. 751—772. 

* Wee Haeckel, Die Naturaiuchauung von Darrein, Goethe und Lamarck, Jena, 1882. 

Goethe and other Pioneers of Evolution 13 

the finest expression that science has yet known — if it has known 
it — of the keniel-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 Buflfon, Erasmus Darwin, Lamarck, Treviranus, and 
Goethe, there were other "pioneers of evolution," whose views have 
been often discussed and appraised. Etienne Geoffi-oy Saint-Hilaire 
(1772 — 1844), whose work Goethe so much admired, was on the whole 
Buftbnian, 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 in- 
fluences. The complete history of evolution-theories will include 
many instances of guesses at truth which were afterwards sub- 
stantiated, thus the geographer von Buch (1773 — 1853) detected the 
im|)ortance 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 ^" Its author, Robert 
Chambers (1802 — 1871) was in part a Buftbnian — 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 enf^uiry, I happened to read for amusement 'Malthus 
on Ropulation,' and being well prepared to appreciate the struggle 
for existence which everywhere goes on from long-continued observa- 
tion of tlie habits of animals and i)lants, 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 fonnation of new species"^." 

Although Malthus gives no adumbration of the idea of Natural 

' Oriijin oj Specie* (Otli edit.), p. xvii. 

' The Life and Letlern of Charlet Darwin, Vol. i. p. 83. London, 1887. 

14 Danvin's Predecessors 

Selection in his exposition of the eliminative processes which go on 
in mankind, tlie suggestive vakie 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 \" 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 eflects 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 icoidd survive'^." 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 Avhich Darwin himself followed. It is interesting also to 
recall the fact that in 1852, when Herbert Spencer wi*ote 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 Avrote 
for The Westminster Rcvieiv another important essay, "A Theory 
of Population deduced from the General Law of Annual Fertility," 
towards the close of which he came M'ithin 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 [)roblem to a biological theory. There could be no 
bettor illustration, as l^i'of Patrick Geddcs has pointed out, of the 
Comtian thesis that science is a "social phenomenon." 

' A. II. Wallace, My Lije, A Record of Events and Opinions, London, 1905, Vol. i. p. 232. 
» Ibid. Vol. I. p. 361. 

Influence of Malthus 15 

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 theo- 
logical 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 \" It goes 
without saying that the idea suggested by JMalthus 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 afiected 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 
]>ublished 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 conmiunication, as Darwin said, "he observes, firstly, that all 
animals tend to vary in some degi-ee, 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'^."' 
Thus Wells had the clear idea of survival dependent upon a favourable 
variation, but he makes no more use of the idea and aj)plies it only 
to num. There is not in the paper the Icjwt liint that the author 
ever thought of generalising the remarkable sentence quoted alx)ve. 

Of Mr Patrick Matthew, who buried his treasure in an appendix 

' P. Oeddes, article "Biology," Chambers's Encyclopaedia. 
* Origin of Species (6th edit.) p. xv. 

16 Darwin's Predecessors 

to a work on Naval Timber and Arboriculture, Darwin said that 
" he clearly saw the full force of the principle of natural selection." 
In 18G0 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 \" 

De Quatrefages and De Variguy 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 diflferent 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 Geoffi-oy 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. Tlie 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 modifi- 
cations lead to injurious eftects, the animals which exhibit them perish 
and arc replaced by others of a somewhat different form, a form 
changed so as to be adapted to (-^ la convenance) the new environment." 

Prof. E. B. Poulton^ 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 (182G), 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 
subsecpicnt editions — the only ones that Darwin saw. Prof Poulton 

' Life and Letters, ii. p. 301. 

' 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. 

Pre'Darivinian Hints of Natural Selection 17 

finds in Prichard's work a recognition of the operation of Natural 
Selection. "After inquiring how it is that 'these varieties are de- 
veloped and preserved in connexion 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 dis- 
appear 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 " anticipa- 
tions" in More Letters of Charles Darwin, Vol. i. p. 43, and come to 
tlie conclusion that the evolutionary passages are entirely neutralised 
by others of an opposite trend. Tliere is the same difficulty with 

Hints of the idea of Natural Selection have been detected else- 
where. James Watt\ 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 tlie 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 tlie clue which IMalthus 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 tliat for a time he regtirded Natural Selection as almost the 
sole factor in evolution, variations being pre-supposed ; gi-adually, 
however, he came to recognise that there was some validity in the 
factors whicli 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, favour- 
able 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 verifi- 
cation, 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 interpre- 
tation it has advanced to the rank of a causal theory, the most 
convincing part oi which men will never cease to call Darwinism. 

' See Prof. Patrick Goddea'a article "Variation and Selection," Encyclopaedia 
Britattnica ptli edit.) IQSH. 

D 3 


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 Avould 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 8upi)ort 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 

Select ion 19 

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, M'hich 
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 under- 
gone 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, Avhen they 
Avished 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 oftspring and rejecting others? 
That was the problem that for a long time remained a riddle to 

Darwin himself relates how illumination suddenly came to him. 
Tie had been reading, for his own pleasure, JSIalthus' book on 
Population, and, as he had long knoA^Ti from numerous observa- 
tions, that every species gives rise to many more descendants than 
ever attain to maturity, and that, therefore, the gi-eater 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 wei'e 
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 iu a 
somewhat higher degree than the rest of the race. Some of the 
dcsceudants inherit this character, often in a still higher degree, and 
if tliis method be pursued throughout several generations, the race 
is tiiinsformed in res])ect of that particular character. 

Natural schct Ion depends on the same tinee factors as artificial 
selection: on variabiliti/, in/urifancc, and selection for breeding, but 
this last is here carried out not by a breeder but by what Darwin 
called the "struggle for existence." Tiiis last factor is one of the 


20 The Selectio7i Theory 

special features of the DarAnnian 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 at- 
tention 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 re- 
garded 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 
w^liich have the greatest power of resistance, while the others, less 
favourably constituted, perish earl}^ This struggle is so keen, that, 
within a limited area, where the conditions of life have long re- 
mained 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 gi-eat 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 Mhich survive, in the sense of living long enough to re- 

Thus the principle of natural selection is (lie selection of the 
best for reproduction, whether the " best " refers to the whole con- 
stitution, 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 genera- 
tions 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 

The Lamarckian Principle 21 

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 inter- 
vention 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 Avay 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 homo- 
geneity of primitive times into the infinite variety of the present, 
we should still be unable to infer fi-om this alone how each of the 
numberless forms adapted to particular conditions of life should have 
appeared precisely at tlie right moment in tJie 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 hunmiing-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 

There must therefore be an intrinsic connection between the 
conditions and the structural adaptations of the organism, and, 
since the conditions of life camiot he determined hy the animal 
itself the adaptations must be called forth by tJie 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. 

11. The Lamarckian Principle. 

Lamarck, as is well known, formulated a definite theory of evolu- 
tion at the l)egiiming of the nineteenth century, exactly fifty years 
V)cforc the Darwin-Wallace principle of selection w;us given to the 
world. Tliis brilliant investigator also endeavoured to support his 
theory by demonstrating forces which might have brought about the 
transfonnations of the organic world in the course of the ages. In 

22 The Selection Theory 

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 Lamarcldan ^9ri>iCi}9/e, as it is now 
generally called, as a factor in evolution, but he was not fully con- 
vinced 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 
princii)le 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 
pur])Osive variation ? 

To many this seems so improbable that they have urged a theory 
of evolution by leaps from species to species. Kolliker, in 1872, 
comi)ared the evolution of species with the processes which we can 
observe in tlie 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 
fonns 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 

Saltatory Evolution 23 

medusoid from a free-swimming animal to a mere brood-sac (gono- 
phore) 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 M'hich 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 slowiiess that makes it 
not directly perceptible, and I believe that this in itself justifies us 
in concluding that the same must he 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 repre- 
sent difierent 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 
mucli 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 Ixjcause 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, tlie oak 
with " fern-like leaves," certain garden-flowers, etc. But none of them 
Iiave persisted in free nature, or evolved into permanent types. 

On the other hand, wlierever 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 diint/rjf/tLsni, the first known cases of wliich exhibited 
marked difterences 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 diflerences between 

24 The Selection Theory 

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 v)hich are capable oj survival under the 
conditions of wild life. Experience has shown that in plants which 
have suddenly varied the power of persistence is diminished. Kor- 
schinksky attributes to them weaknesses of organisation in general ; 
" they bloom late, i-ipen few of their seeds, and shoAV gi'eat sensitive- 
ness 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 trans- 
formation 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, >vith strict inbreeding they are handed on pure to the next 
generation. I have elsewhere endeavoured to point out the weak- 
nesses of this theory^, and I am the less inclined to return to it here 
that it now appears^ that the far-reaching conclusions drawn by 
de Vries from his observations on the Evening Primrose, Oenothera 
lamarcMana, rest upon a very insecure foundation. The plant from 
which de Vries saw numerous "species" — his "mutations" — arise 
was not, as he assumed, a ivild species that had been introduced to 
Euroi)e 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 
actmilly imld species with which de Vries experimented showed no 
"mutations" but yielded only negative results. 

Thus we come to the conclusion that Darwin^ was right in regard- 
ing transformations as taking place by minute steps, which, if useful, 

* Vortrage Uher Descendenztheorie, Jena, 1904, ii. 2G9. Eng. Transl. London, 1904, ii. 
p. 317. 

* Ree Poulton, Etmyt on Evolution, Oxford, 1908, pp. xix — xxii. 

* Origin of Speeiet (6th edit.), pp. 176 et $eq. 

Importance of small differences 25 

are augmented in the course of innumerable generations, because 
their possessors more frequently siu'vive in the struggle for existence. 

(/S) Selection-valiie of the initial steps. 

Ts it possible that the insignificant 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 in- 
significant 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 be- 
ginnings 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, hut we 
cannot j)iove 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 thick- 
ness of the basin-shaped shell of the limpets that live among the 
breakers on the shore. Tliere 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 Avhich we 
must show to be convincing. 

For c'l 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 
mori)liological character with no biological significjince. But recent 
investigations have shown that these, too, have an adaptive signifi- 
cance (Hiicker). The sanje thing has been shown by Schiitt in regard 
to the lowly unicellular plants, the Peridineae, which abound alike 
on the surface of tlie ocean and in its deptha It has been shown 

26 The Selection Theory 

that the long skeletal processes which gi-ow 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^ 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 eftect 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 gi*eat 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 sufiicient to prevent too rapid sinking and consequent elimina- 
tion ? 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 

But even in organisms of more than microscopic size there must 
frequently be minute, even microscopic diflerences 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 raindrops. 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 ftict that, in many such trees, the leaves 
are drawn out into a beak-like prolongation (Stahl and Haberlandt) 
wliicli facilitates the rapid falling ott' of the rain water, and also 
troin the fact that the leaves, while they are still young, hang 
limply down in bunches which offer the least possible resistance to 
the rain. Tlius 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. 

* Chun, Reise der Valdivia, Leipzig, 1904. 

Useful Variations 27 

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 presmnptive 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 
gi*anted, we are confi'onted with the further question which I myself 
formulated many years ago: How does it happen that the necessar// 
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 bro^v^l ? How have the desert 
animals become yellow and the Arctic animals white? Why Avere 
the necessary variations always present ? How could the green locu^ 
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^ 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 can- 
not 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 happeiLS in 
caterpillars and locusts, lies in the fact that variations towards brown 
presented themselves, and so also did variations towards green : tlie 
hernel of the riddle lies in the varying, and for the present we can 
only say, that small variations in different directions present them- 
selves in every s[)ecies. Otherwise so many diflerent kinds of 
variations could not have arisen. I have endeavoured to explain 
tliis remarkable fact by means of the intimate processes that nuist 
take j)lace 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 

* riate, Selcktiotuprinzip u. Problenu der Artbilduug (3rd edit.), Leipzig, 1908. 

28 The Selection Theory 

prospect of its being preserved, notwithstanding its utility. Darwin 
at first believed, that even single variations might lead to trans- 
formation 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 
org-anisms, 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 gi'ass 
caterpillars, not oblique but longitudinal stripes, which are more 
effective for concealment among gi'ass 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 \ 

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 longi- 
tudinal 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, evolu- 
tion 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 Avay or another according to the require- 
ments 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 
i-aised them to the point of selection-value. I shall return to this in 
discussing germinal selection. But the case may be followed still 

> Studiftt zur Detcendenz-Theorie ii.,"Die Enstebung der Zeichnung bei den Schmetter- 
lingR-raupen," Leipzig, 1876. 

Initial Stages of Variation 29 

farther, and leads us to the same alternative on a still more secure 

Many years ago I observed in caterpillars of Smerlnthiis j^opuli 
(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 (Smerintkus tiliae) 
similar blood-red spots unite to form a line-like coloured seam in 
the last stage of larval life, while in S. occllata 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. jmpuH 
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 maij be evolved, if they are combined in this 
direction through the agency of natural selection. In S. popudi the 
spots are often small, but sometimes it seems as though several had 
united to form large spots. ^Vliether a process of selection in this 
direction will arise in S. 2>opnU 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 i)oplar 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 nmst already possess selection-value, or, as I said 
before : There iimst be some other reason for their cumtdative sian- 
mation. I should like to give one more example, in which we can 
infer, though we cannot directly observe, the initial stages. 

All the llolothurians or sea-cucumbers have in the skin calcareous 
bodies of ditlerent forms, usually thick and irregular, which make the 
skin tough and resistant. In a small gi'oup of them — the species of 
Synapta — the calcareous bodies occur in the form of delicate anchors 
of microscopic size (Figs. A, B). Up till 1897 these anchors, like 
many other delicate microscopic structures, were regjirded as 
curiosities, as natural marvels, liut a Swedish observer, Oestergren, 
haa recently sliown that they have a biological significance : they 


The Selection Theory 

serve tlie 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 

Fig. A. 

Anchor (a) and basal-plate {b) of Synapta lappa. Length of anchor = 0-35 mm. 
(After Oestergren, Zool. Anzeiger, xx. 1897.) 

Fig. B. 
Anchor (a) and basal-plate (6) in side-view (after Oestergren). 

of the tube-feet. Tlie anchors act automatically, sinking their tips 
towards the ground wlien the corresponding part of the body 
thickens, and returning to the original [)osition at an angle of 4.5° to 
the up[)cr surface when the part becomes thin again. The arms 
of the anchor do not lie in the same plane as the shaft, and thus 

Anchors of Holothurians 31 

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 contmcted 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 improve- 
ments, 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 adaj)ted to the 
rule 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 
anclior must have possessed selection-value. And that such minute 
changes of form fall within the si)here of fluctuating variations, that 
is to say, tluit theij occur is beyond all doubt. 

In many of the Synaj)tidae tlie ancliors are replaced by 
calcareous rods bent in the form of an 8, which are said to 
act in the same way. Others, such as those of the genus 
Ankyroderma, have ancliors which project considerably beyond the 
skin, and, according to Oestergren, serve "to cat<;h })lant-particles 
and other substances " and so mask the animal. Thus we see that 
in the Synaptidae iho thick and irregular calcareous bodies of the 

32 The Selection Theory 

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 tougluiess, 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 
gemi-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 gi-oup 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 ? 

(7) Coadaptation. 

DarAvin 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 ijrinciplc was greatly over-estimated, if the great 
changes Miiich 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 Avhich required not only a much stronger skull 
cap, but also greater strength of the sinews, nmscles, nerves and 
bones of the whole anterior half of the animal, if their mass was not 

Coadaptation 33 

to weigh down the animal altogether. It is inconceivable, he says, 
that 80 many processes of selection should take place simuUaneotisly, 
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 un- 
tenable, because it assumes the transmissihUity of functional mocli- 
fcations (so-caUed "acquired" characters), and this is not only 
undemonstrable, but is scarcely theoretically conceivable, for the 
secondary variations which accompany or follow the first as corre- 
lative variations, occur also in cases in which the animals concerned 
are sterile and therefore camiot transmit anything to their de- 
scendants. Tliis 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 
tlie 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 doew 
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 l)c (juestionablc whether selection could 
explain any adaptations whatever. In this particular caae — of worker 

D. 3 

34 The Selection Theory 

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 Lamarchian 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 progi*ess 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 receptacvlum 
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 rcceptacidum seminis, which 
can only have been disused as far as its glandular portion and its 
stalk are concerned, and also of the wings, tlie 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. 
Tliis 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 insur- 
mountable 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 

Harmonious Adajftatiou 35 

illustration to show how imposing the difl'erence 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\" 

Although the ant is a small animal as compared with man or with 
the Irish Elk, the "soldier" Avith its relatively enonnous 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 (co- 
adaptation) 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 shoiv thepoicer of cultural selectionV He explains his 
view by a simple but interesting illustration. Gardeners have pro- 
duced, by means of long continued artificial selection, a variety of 
Stock, which bears entirely double, and therefore infertile flowers^. 
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 difierence 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 i)reserved 
by artiticial selection on the part of the gardener, while the trans- 
formations that have taken place parallel with the sterility of the 
ants are useful, since they procure for the colony an advantage in 

> Origin oj Species (6th cHit.), p. '232. 

* Griffin of Species, p. 233 ; see also edit. 1, p. 242. • Jbid. p. 230. 


36 The Selection Theory 

the struggle for existence, and they are therefore preserved by- 
natural selection. Even the sterility itself in this case is not dis- 
advantageous, 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 
w orkers 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 pro- 
cesses, 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 fi-om 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 gi-anules, as the germ-siibstance 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 con- 
stituents 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, gi'ow, and 
multiply by division. Tliese determinants control the parts of the 
develoj)ing 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 biopJiors, 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 (lualitatively if the elemenls of which they are composed 

Germinal Selection 37 

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 Avill gi'ow 
more rapidly — become bigger, and divide more quickly, and, later, 
when the id concerned develops into an embryo, this sensory cell will 
bcKJome 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 h^-pothesis, favours 
the determinant N by chance, that is, for reasons unkno^vn 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 deter- 
minant 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 npivard movement, and attain a degree of 
strength from which there is no falling bach Then positive or 
negative selection sets in, favouring the variations which are ad- 
vantageous, setting aside those which are disadvantageous. 

In a similar manner a downward variation of the determinants 
may take i>lace, 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 corresj)onds to a ns(fnl 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- 
plaam, 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 oigan which has become tiseless, and 

38 The Selection Theory 

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 hy jyersonal selection, and 
therefore in their case alone can ive form any idea of how the 
pi'imary 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 iminfluenced by jyersonal 
selection, and, as experience shows, it sinks downwards ; that is, the 
organ that corresponds to it degenerates very slowly but uninter- 
ruptedly 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 equili- 
brium 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 camiot be proved mathemati- 
cally, since we cannot actually see the play of forces of the passive 
fluctuations and their causes. We cannot say how great these fluctua- 
tions are, and how quickly or slowly, how regularly or irregularly they 

Degeneration of disused parts 39 

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 varia- 
tions 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, fi'om 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 degenera- 
tion 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 Lamarclian 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 indifterent as far as the success and 
especially the functional capacity of the workers was concerned : 
wings, ovarian tubes, reaptaculum seminis, a number of the facets of 
the eye, perhaps even the whole eye. As to the ovarian tubes it 
is possible that tiieir degeneration was an advantage for the workers, 
in saving energy, and if so selection would favour tiie degeneration ; 
but how could the presence of eyes diminish the usefulness of the 
workers to the colony ? or the minute receptaculum seminis, or even 

40 The Selection Theory 

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 butter- 
flies, flies, and locusts, but in the larvae the imaginal discs of the 
wings are still laid dovra. With regard to the ovaries, degenera- 
tion has reached difierent levels in difierent 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 coadaptatlon 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 them- 
selves 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 interven- 
tion 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 
[)eriod8 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 i)rocess 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 

Organic Selection 41 

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 them- 
selves in an ascending direction, those less used in a descending 
direction, we must draw the conclusion that harmonious adaptation 
here comes about imthout the cooperation of the Lamarchian 
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 nou'here proved. We do not require it to explain the 
facts, and therefore ive 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 iruUvidual life, and so would be strengthened. The antlers 
can only have increased in size by very slow degi-ees, 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 in- 
creasing 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*. 

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 efiect complex harmonious adap- 
tations. 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 

^ Die EJfect oj External Injluencex upon Development, liomanea Lecture, Oxford, 

42 The Selection Theory 

convinced, in the course of years, that the LamarcMan 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 rudi- 
mentary, 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 

IV. Derivatives of the Theory of Selection. 

Tlie 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 


(a) Sexual Selection. 

Sexual selection goes hand in hand with natural selection. From 
the very first I have i-egarded sexual selection as aftbrding an ex- 
tremely 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 
ai)proaching 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 Seacual Selection, 

Sexual Selection 43 

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 gi-eater 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 atfect 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 cliief 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 inefjuality 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 

44 The Selection Theory 

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 
Avay 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 Aveapon. 

Among many animals, however, the females at first withdraw fi-om 
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 pre- 
liminary 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 re- 

In many cases the organ of smell shows a similar improvement. 

Sexual Selection 45 

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 
diflference 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 main- 
tenance 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 
tlic 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 Mould 
obtiiin 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 ITie 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 en- 
ticing, 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 tliis odour also served at first 

46 The Selection Theory 

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 Miiller found out that certain Brazilian butterflies 
gave off fragi-ance " 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 ofi* a delicate odour, 
which is agreeable even to man. The ethereal oil to which this 
fragi-ancc 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 recog- 
nisable as such by their form, but they must, nevertheless, give ofi* 
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 ofi", 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 fragi'ance, — that is to say, that excites them to the highest 
degi-ee. It is a pity that our organs of smell are not fine enough 
to examine the fi-agrance of male Lepidoptera in general, and to 
compare it with other perfumes which attract these insects \ As far 
as Ave can perceive them they resemble the fragrance of flowers, but 
there are Lepidoptera whose scent suggests musk. A smell of musk 
is also given oft" by several plants : it is a sexual excitant in the 
musk-deer, the musk-sheep, and the crocodile. 

As for as we know, then, it is perfumes similar to those of flowers 
tliat the male Lepidoptera give off" in order to entice their mates, 
and this is a further indication that animals, like plants, can to a 

' See Poulton, Eutai/'i on Evolution, 1908, pp. 316, 317. 

Decorative Colours 47 

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 con- 
nection, 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 ofi^ a smell unpleasant 
to us, but there is no case known to me in which this has been 

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 gi-eat 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 Ave 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 theiri 
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 
investigjitions ; we now know that the colours of flowers are there 
on account of the butterflies, as Sprengel fii-st 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 

48 The Selection Theory 

are many weighty arguments in favour of it, and these form a body 
of presumptive evidence so strong that it almost amounts to 

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 carni- 
vores, 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 dis- 
played before the female during courtship. I have elsewhere ^ 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 tlieir occurrence or absence in nearly related 
species, we may conclude that fragi'ance 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 deco- 
rative 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 Hpecies which brood on an exposed nest. In the parrots one can 
often observe that the general brilliant colouring of the male is found 

^ Hie Evolution Theory, London, 1901, i. p. 219. 

Natural Selection 49 

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 gi'oup 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 explain- 
ing the selection of distinctive coui'tship-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. ~ 

(y3) Natural Selection. 

An actual pi-oof 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 posses- 
sion 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 excite- 
ment caused in the female by agreeable perfumes, or by striking 
and l>eautiful colours. That these do make an imjjrcssion 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 tor>vurd any actual proof of the selection-value 
D. 4 

50 The Selection Theory 

of the initial stages, and the stages in the increase of variations, 
as has been akeady 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^ 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 °/^ of the pupae at Oxford were killed, 
chiefly by small birds, while at St Helens 68 °l^ perished. The experi- 
ments 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 "/„ ; on bark, 66 °l„ ; on 
walls, 54°/„; and among nettles, 57 7o« These interesting experi- 
ments 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 he 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, be- 
cause of our inability to demonstrate the selection- value of the initial 
stages and the individual stages of increase. We have therefore to 
faU back on presumptive evidence. This is to be found in the inter- 
pretative value of the theory. Let us consider this point in greater 

In the first place, it is necessary to emphasise what is often over- 
looked, 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. 

» RepoTl of the Britith Association (Bristol, 1898), London, 1899, pp. 906—909. 

Sympathetic Coloration 51 

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 j^itch. This conserving influence of natural 
selection is of gi*eat importance, and was early recognised by Darwin ; 
it follows naturally from the principle of the sui'vival 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 poAver 
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 
LamarcJcian 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 un- 
necessary to make the gi-atuitous assumption that many species are 
sensitive to the stimulus of cold and that others are not. The gi*eat 
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 fi-om 
as gi'eat 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 wliite famis, foxes, deer, etc. The whiteness, therefore, 
arises from internal causes, and only persists when it is useful. 
A gi'cat many animals living in a green environment have become 
clothed in gieen, especially insects, caterpillars, and Mantidae, both 
persecuted and persecutors. 

Tliat 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. 


52 The Selection Theory 

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 fi'om 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 diflBcult 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 browTi, a part 
remaining green. Wliether 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 Avhich are all gaily coloured on the upper 
surface, and on the reverse side exhibit the most delicate imitation 
of tlie colouring and pattern of a leaf, generally without any indica- 
tion 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 
si)lits 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 aflfect 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 


Fig. C. 
Anaea diviud (under side). 

Leaf-like Butterjlies 53 

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 semi- 
circular piece is of a clear, pale yellow colour, while the rest of the 
wing is of a strongly contrasted dark brown (Fig. C). 

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^ 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, wliile in others they are comparatively distinct. Tliis 
furnishes us with fresh evidence in favour of their origin tlnough 
processes of selection, for a botanically perfect picture could not 
arise in this Avay ; there could only be a fixing of such details as 
heiglitcncd the deceptive resemblance. 

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

1 I'roc. Ent. Soc, London, May 6, 1903. 

64 The Selection Theoi-y 

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 

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 ^, 
were thoroughly studied, the arguments which are still fi-equently 
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 ob- 
servations 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 arc 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 learning colours. If they were 
not thus recognisable easily and from a distance, they would fre- 
quently 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^ 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 hyi^othesis, but its foundations, — unpalatableness, and the 
liability of other butterflies to be eaten, — are certain, and its con- 
sequences — the existence of mimetic palatable forms — confirm it in 
the most convincing manner. Of the many cases now known I select 

» Eimy* on Evolutim, 1889—1907, Oxford, 1908, passim, e.g. p. 260. 
' The expression does not refer to all the enemiea of this butterdy ; against ichneumon* 
flies, (or instance, their unpleasant uniell usually gives no protection. 

Mimicry 55 

one, which is especially remarkable, and which has been thoroughly 
investigated, Papilio dardamis (inet'ope), a large, beautiful, diurnal 
butterfly which ranges from Abyssinia throughout the whole of Afiica 
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 diiFerent 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 difierent 
family the Danaids, which are among the Immune forms. In each 
region the females have thus copied two or three diiferent 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 poly- 
morphism in P. dardamis. 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 (pp. 3/3 — 3/5^). 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. dardamis, so that it probably 
represents the ancestor of this latter species. 

In face of such facts as these every attempt at another explana- 
tion 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 Avhich the male is also mimeti- 
cally coloured, it copies quite a differently coloured immune species 
fi-om the model followed by the female. This is quite intelligible 
when we consider that if there were too niany false immune types, 
the birds would soon discover that there were palatable individuals 

* Professor Poulton haa corrected some wrong descriptions wbich I had unfortunately 
overlooked in the Plates of my book Vortriige Uber Dacendciiztheorie, and which refer 
to Papilio dardanuB {merope). These mistakes are of no importance as far as an under- 
etandinp of the mimicry-theory is concerned, but I hope shortly to be able to correct 
them in a later edition. 

56 The Selection Theory 

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 
oi 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 we could 
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 sur- 
rounds 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 
Euplocine (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 



Fischer, .l<'i 

Mimicry 57 

not yet know ^Wth certainty what may be the biological significance 
of the gaily coloured upper surface. 

In general it may be said that mimetic butterflies are com- 
paratively rare species, but there are exceptions, for instance 
lAmenitis archippus in North America, of which the immune model 
(Danaida pkxipjn(s) 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. 

Figs. 1 — 4 represent a Mimicry-ring from Eastern Brazil composed of four immune 

species belonging to three difierent sub-families and four diflfereut genera. 
Fig. 1. Lycorea halia (Danainae). 
Fig. 2. Heliconius narcaea (eucrate) (Heliconinae). 
Fig. 3. Melinaea ethra (Ithomiinae). 
Fig. 4. Mechanitis lysimnia (Ithomiinae). 
Figs. 5, 6. Perrhybris pyrrha, male and female, S. American "Whites" (Pierinae). 

The female mimics immune Ithomiincs, while the male shows only an indication 

of the mimetic colouring on the under surface. 
Figs. 7, 8. Dismorphia astynome, male and female, also belonging to the family of 

S. American " whites," and mimicking immune Ithomiines ; a white ixatch on 

the posterior wing of the male and another on the corresponding surface of the 

under side of the upper wing, remain as traces of the original "white" coloration. 
Fig. 9. Elymnias phegea, W, Africa, of the sub-family of Satyrines, mimics the 

succeeding species (Fig. 10). 

Fig. 10. Planema epaea {gea), an immune West African species belonging to the 

Fig. 11. Danaida genutia, an immune Danaid from India, Burmah, etc. 

Fig. 12. Elymnias xaidalaris, female, one of the mimics of Fig. 11. 

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 hy degrees. We can recognise this 
in many cases, for even now the mimetic species show very varying 
degrees of resemblance to their imnmne model. If we compare, for 
instance, the many diftcrcnt imitators of Danaida chrysippus we find 
that, with tlieir brownish-yellow ground-colour, and the position and 
size, and more or less sharp limitation of their clear mai'ginal spot*^, 
they have reached very different degrees of nearness to their model. 
Or com[)are the female of Elymnias undularis (Fig. 12) with its 
model Daimida genutia (Fig. 11); there is a general resemblance, but 
the marking of the Danaida is very roughly imitiited in Flynuiias. 

68 The Selection Theory 

Another fact that bears out the theory of mimicry is, that even 
when the resemblance in colour-pattern is very great, the whig- 
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 entomo- 
logical 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 \ Thus the glass-like trans- 
parency of the M'ing of a certain Ithomiine (Methona) and its Pierine 
mimic (Dismorphia orlse) 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 (Oastnia linus var. 
heliconoides) the glass-like appearance of the wing is due neither to 
diminution nor to absence of scales, but to their absolute colour- 
lessness and transparency, and to the fact that they stand upright. 
In another moth mimic (Anthomyza) the arrangement of the trans- 
parent 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 favour- 
able variations that present themselves. The great faithfulness of 
the copy is astonishing in these cases, for it is not the whole whig 
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 other- 
wise 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 irreconcileable 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 Heli- 
conidae). 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 

» Joum. Linn. Soc. London {ZooL), Vol. xxvi. 1898, pp. 598—602. 

Mimicry 69 

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 (Figs. 1 — 4). 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 IMliller^, 
seventeen years after Bates, offered a solution to the riddle, when 
lie pohited out that young birds could not have an instinctive 
knoAvledge 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 
gi'eat 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 fi-om 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. The four Brazilian species are figured 
on the accompanying plate (Figs. 1 — 4) : Lycorea halia (Danainae), 
Heliconim narcaea (eiicrate) (Heliconinae), Melinaea ethra, and 
Mcchanitis lysimnia (Ithomiinae). 

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

In addition to the mimicry-rings first observed in South America, 
others have been descri]>ed from Tropical India by IMoore, and by 
Poulton and Dixey from Africa, and we may expect to learn many 
more interesting facts in this connection. Here again the i)reliminary 
postulates of the theory are satisfied. And how nmch more that 
would lead to the s;ime conclusion might be added ! 

1 In Kotmoi, 1879, p. 100. > Habit and Imtinct, London, 1896. 

60 The Selection Theory 

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 incon- 
spicuous 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, Promiba 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 difiiculty is solved as soon 
as Ave 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 ovm 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 Promiba 
yuccasella to processes of selection, which have gi-adually trans- 
formed 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, 

Importance of Selection 61 

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 Avhole 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 2^lienomena of evolution and adaptation must have a natural 
basis, and became it is the onlf/ possible eccplanation of thein\ 

Many people are willing to admit that selection explains adapta- 
tions, 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 cilbrt 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 everj^where in such enormous 
numbei*s, that it Mould be difficult in regard to any structure what- 
ever, 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 can- 
not 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 Avhole. But, 
it is asked, M'hat of the direct effect of external conditions, tempe- 
rature, nutrition, climate and the like ? Undoubtedly these can give 
rise to variations, but they too must pass through the door of selec- 
tion, 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 elfect of the cold of the Arctic regions was to make all the 
manunals become black ; the result would be that they would all 

* This has been dlBCusBed in mnny of my earlier workfl. See for instanco The All- 
Sufficiency of Natural Selection, a reply to Herbert Spencer, London, 1893. 

62 The Selection Theory 

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 estab- 
lishing 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 colour- 
ing 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 alivays 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 Avings, when at rest, in 
a perfectly definite position, which, in the leaf-butterfly, has the 
effect of bringing the two pieces on M^hich the marking occurs on 
the anterior and posterior ^ving 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 gi'ound-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 degi'ee 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-butter- 
flies, the holding of the wing was probably the primary character ; 
only after that was thoroughly established did the protective mark- 
ing 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 gi'eatly 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 inlo an almost 

Adaptation 63 

contrary instinct This moth does not fly away from danger, but 
"feigns death," that is, it draws antennae, legs and Avings 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 remark- 
able 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 \ 

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, do>vn 
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 difierent nutritive substances, and behaves in 
quite a diflerent 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 trans- 
formation of tlie 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 car-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 certtiin remarkable changes in the respiratory and 
circulatory organs which enable the animal to remain for a long time 

> The Evolution Theory, London, 1904, p. 144. 

64 The Selection Theory 

under water. I might have added many more, for the list of adapta- 
tions in the whale to aquatic life is by no means exhausted; they 
are found in the histological structure and in the minutest combina- 
tions in the nervous system. For it is obvious that a tail-fin must be 
used in quite a difierent 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 Avill require quite difierent refiex-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 %ip 
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 com- 
pared 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 Lamarcldan 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 Ave are only to call adaptation what 
has been acquired by the species we happen to be considering, there 

Adaptation 65 

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 persistence of the fundamental elements. 
Thus the feather, once acquired, persisted in all birds, and the 
vertebral column, once gained by adaptation in the lowest forms, 
has persisted in all the Vertebrates, from Amphioxus upwards, 
although with constant readaptation to the conditions of each par- 
ticular group. Thus everything we can see in animals is adaptation, 
whether of to-day, or of yesterday, or of ages long gone by ; every 
kind of cell, whether glandular, muscular, nervous, epidermic, or 
skeletal, is adapted to absolutely definite and specific functions, 
and every organ wliich is composed of these different kinds of cells 
contains them in the proper proportions, and in the particular 
arrangement which best serves the function of the organ ; it is thus 
adapted to its function. 

All parts of the organism are tuned to one another, that is, they 
are adapted to one another, and in the same way the organism as a 
whole is adapted to the conditions of its life, and it is so at every 
stage of its evolnfion. 

But all adaptations ca7i be referred to selection ; the only 
point that remains doubtful is whether they all must be referred 
to it. 

However that may be, whether the Lamarchian principle is 
a factor that has cooperated with selection in evolution, or whether 
it is altogether fallacious, the fact remains, that selection is the cause 
of a great part of the phyletic evolution of organisms on our earth. 
Tliose who agree with me in rejecting the Lamarch'an principle 
will regard selection as the only guiding factor in evolution, which 
creates what is new out of the transmissible variations, by ordering 
and arranging these, selecting them in relation to their number and 
size, as the architect does his building-stones so that a particular 
style must result ^ But the building-stones themselves, the variations, 
have their basis in tlie influences wliich cause variation in those vital 
unit*} which are handed on from one generation to anotlier, wliether, 
taken together they form the u'hole organism, as in Bacteria and 
other low forms of life, or only a germ-substance, as iu unicellular 
and multicelhihir organisms'. 

* Variation uudtr Domentication, 1875, ii. pp. 426, 427. 

* Tlio Author and Editor are iudebted to Professor Poulton for kindly assistiug in the 
revision of the proof of this Essay. 

D. 5 


By Hugo de Vries, 

Professor of Botany in the University of Amsterdam. 

Different hinds of variahihty. 

Before Darwin, little was known concerning the phenomena of 
variability. The fact, that hardly two leaves on a tree were exactly 
the same, could not escape observation : small deviations of the same 
kind were met with everywhere, among individuals as well as among 
the organs of the same plant. Larger aberrations, spoken of as 
monstrosities, were for a long time regarded as lying outside the 
range of ordinary phenomena. A special branch of inquiry, that of 
Teratology, was devoted to them, but it constituted a science by 
itself, sometimes connected with morphology, but having scarcely 
any bearing on the processes of evolution and heredity. 

Darwin was the first to take a broad survey of the whole range 
of variations in the animal and vegetable kingdoms. His theory of 
Natural Selection is based on the fact of variability. In order 
that this foundation should be as strong as possible he collected all 
the facts, scattered in the literature of his time, and tried to arrange 
them in a scientific way. He succeeded in showing that variations 
may be gi-ouped along a line of almost continuous gradations, 
beginning with simple difierences in size and ending with monstro- 
sities. He was struck by the fact that, as a rule, the smaller the 
deviations, the more frequently they appear, very abrupt breaks in 
cliaracters being of rare occurrence. 

Among these numerous degrees of variability Darwin was always 
on the look out for those which might, with the greatest probability, 
be considered as affording material for natural selection to act ui)on 
in the development of new species. Neither of the extremes complied 
Avith his conceptions. He often ))ointod out, that there are a good 
many small fluctuations, which in this resi)ect must be absolutely 

Tendency to Vary 67 

useless. On the other hand, he strongly combated the belief, that 
great changes would be necessary to explain the origin of species. 
Some authors had propounded the idea that highly adapted organs, 
e.g. the wings of a bird, could not have been developed in any other 
way than by a comparatively sudden modification of a well defined 
and important kind. Such a conception would allow of great breaks 
or discontinuity in the evolution of highly differentiated animals and 
plants, shortening the time for the evolution of the whole organic 
kingdom and getting over numerous difficulties inherent in the 
theory of slow and gi-adual progress. It would, moreover, account 
for the genetic relation of the larger groups of both animals and 
plants. It would, in a word, undoubtedly affbrd an easy means of 
simplifying the problem of descent with modification. 

Darwin, however, considered such hypotheses as hardly belonging 
to the domain of science ; they belong, he said, to the realm of 
miracles. That species have a capacity for change is admitted 
by all evolutionists ; but there is no need to invoke modifications 
other than those represented by ordinary variability. It is mcU 
known that in artificial selection this tendency to vary has given rise 
to numerous distinct races, and there is no reason for denying that it 
can do the same in nature, by the aid of natural selection. On both 
lines an advance may be expected with equal probability. 

His main argument, however, is that the most striking and most 
highly adapted modifications may be acquired by successive varia- 
tions. Each of these may be slight, and they may affect different 
organs, gi-adually adapting them to the same purpose. The direction 
of the adaptations will be determined by the needs in the struggle for 
life, and natural selection will simply exclude all such changes as 
occur on opposite or deviating lines. In this way, it is not varia- 
bility itself which is called upon to explain beautiful adaptations, 
but it is quite sufficient to suppose that natural selection has operated 
during long periods in the same way. Eventually, all the acquired 
characters, being transmitted together, would appear to us, as if 
they had all been simultaneously developed. 

Correlations must play a large part in such special evolutions : 
when one part is modified, so will be other parts. The distri- 
bution of nourishment will come in as one of the causes, the 
leactions of different organs to tlie same external inffuences as 
another. But no doubt the more effective cause is that of the 
internal correlations, which, however, are still but dimly understood. 
Darwin repeatedly laid great stress on this view, although a definite 
proof of its correctness could not be given in his time. Sucli pioof 
requires the direct observation of a mutation, and it should be 
btuLed here tiiat even the firtst observations made in this direction 


68 Variation 

have clearly confirmed Darwin's ideas. The new evening primroses 
which have sprung in my garden from the old form of Oenothera 
Lamarckiana, and which have evidently been derived from it, in 
each case, by a single mutation, do not differ from their parent 
species in one character only, but in almost all their organs and 
qualities. Oenothera gigas, for example, has stouter stems and denser 
foliage; the leaves are larger and broader; its thick flower-buds 
produce gigantic flowers, but only small fruits with large seeds. 
Correlative changes of this kind are seen in all my new forms, and 
they lend support to the view that in the gradual development of 
higlily adapted structures, analogous correlations may have played a 
large part. They easily explain large deviations from an original 
type, without requiring the assumption of too many steps. 

Monstrosities, as their name implies, are widely different in 
character from natural species ; they cannot, therefore, be adduced 
as evidence in the investigation of the origin of species. There is 
no doubt that they may have much in common as regards their 
manner of origin, and that the origin of species, once understood, 
may lead to a better understanding of the monstrosities. But the 
reverse is not true, at least not as regards the main lines of develop- 
ment. Here, it is clear, monstrosities cannot have played a part 
of any significance. 

Reversions, or atavistic changes, would seem to give a better 
sui)port to the theory of descent through modifications. Tliese have 
been of paramount importance on many lines of evolution of the 
animal as well as of the vegetable kingdom. It is often assumed 
that monocotyledons are descended from some lower group of 
dicotyledons, probably allied to that which includes the buttercup 
family. On this view the monocotyledons must be assumed to have lost 
the cambium and all its influence on secondary growth, the differentia- 
tion of the flower into calyx and corolla, the second cotyledon or seed- 
leaf and several other characters. Losses of characters such as tliese 
may have been the result of abrupt changes, but this does not prove 
that the characters themselves have been produced with equal sudden- 
ness. On the contrary, Darwin shows very convincingly that a modi- 
fication may well be developed by a series of steps, and afterwards 
suddenly disapi)ear. Many monstrosities, such as those represented 
by twisted stems, furnish direct proofs in support of this view, since 
they are produced by the loss of one character and this loss implies 
secondary changes in a lai-gc number of other organs and qualities. 

Darwin criticises in detail the hypothesis of great and abrupt 
changes and conies to the conclusion that it does not give even a 
siiadow of an explanation of the origin of species. It is as improbable 
as it is unnecorisary. 

Polymorphic Sjjecies 60 

Sports and spontaneous variations must now be considered. It 
is well known that they have produced a large number of fine 
horticultural varieties. The cut-leaved maple and many other trees 
and shrubs with split leaves are known to have been produced 
at a single step ; this is true in the case of the single-leaf strawberry 
plant and of the laciniate variety of the greater celandine : many 
white flowers, Mhite or yellow berries and numerous other forms 
had a similar origin. But changes such as these do not come under 
the head of adaptations, as they consist for the most part in the loss 
of some quality or organ belonging to the species from which they were 
derived. Darwin thinks it impossible to attribute to this cause the 
innumerable structures, which are so well adapted to the habits of life 
of each species. At the present time we should say that such adapta- 
tions require progressive modifications, which are additions to the 
stock of qualities already possessed by the ancestors, and cannot, 
therefore, be explained on the ground of a supposed analogy with 
sports, which are for the most part of a retrogressive nature. 

Excluding all these more or less sudden changes, there remains 
a long series of gradations of variability, but all of these are not 
assumed by Darwin to be equally fit for the production of new 
species. In the first place, he disregards all mere temporary varia- 
tions, such as size, albinism, etc. ; further, he points out that very 
many species have almost certainly been produced by steps, not 
greater, and probably not very much smaller, than those separating 
closely related varieties. For varieties are only small species. Next 
comes the question of polymorphic species : their occurrence seems to 
have been a source of much doubt and difficulty in Darwin's mind, 
although at present it forms one of the main supports of the pre- 
vailing explanation of the origin of new species. Darwin simply states 
that this kind of variability seems to be of a peculiar nature ; since 
polymorphic species are now in a stable condition their occurrence 
gives no clue as to the mode of origin of new species. Polymorphic 
species are the expression of the result of previous variability acting 
on a large scale ; but they now simply consist of more or less numerous 
elementary species, which, as far as we know, do not at present exhibit 
a larger degree of variability than any other more miiform species. 
The vernal whitlow-grass {Drdha verna) and the Avild pansy are the 
best known examples; both have spread over almost the whole of 
Europe and are split up into hundreds of elementary forms. These 
sub-species show no signs of any extraordinary degree of variability, 
when cultivated under conditions necessary for the exclusion of inter- 
crossing. Hooker has shown, in the case of some ferns distributed 
over still wider areas, that the extinction of some of the intermediate 
forms in such groups would suffice to justify the elevation of the 

70 Variation 

remaining types to the rank of distinct species. Polymorphic species 
may now be regarded as the link which unites ordinary variability 
with the historical production of species. But it does not appear 
that they had this significance for Darwin ; and, in fact, they exhibit 
no phenomena which could explain the processes by which one 
species has been derived from another. By thus narrowing the limits 
of the species-producing variability Darwin was led to regard 
small deviations as the source from which natural selection derives 
material upon which to act. But even these are not all of the 
same type, and Darwin was well aware of the fact. 

It should here be pointed out that in order to be selected, a 
change must first have been produced. This proposition, which 
now seems self-evident, has, however, been a source of much differ- 
ence of opinion among Darwin's followers. The opinion that natural 
selection produces changes in useful directions has prevailed for a 
long time. In other words, it was assumed that natural selection, by 
the simple means of singling out, could induce small and useful changes 
to increase and to reach any desired degree of deviation from the 
original type. In my opinion this view was never actually held by 
Darmn. It is in contradiction with the acknowledged aim of all 
his work, — the explanation of the origin of species by means of 
natural forces and phenomena only. Natural selection acts as a 
sieve ; it does not single out the best variations, but it simply destroys 
the larger number of those which are, from some cause or another, 
unfit for their present environment. In this way it keeps the strains 
up to the required standard, and, in special circumstances, may even 
improve them. 

Returning to the variations which affbrd the material for the 
sieving-action of natural selection, we may distinguish two main 
kinds. It is true that the distinction between these was not clear 
at the time of Darwin, and that he was unable to draw a sharp line 
between them. Nevertheless, in many cases, he was able to separate 
them, and he often discussed the question which of the two would 
be the real source of the differentiation of species. Certain varia- 
tions constantly occur, especially such as are connected with size, 
weight, colour, etc. They are usually too small for natural selection 
to act upon, having hardly any influence in the struggle for life: 
others are more rare, occurring only from time to time, perhaps once 
or twice in a century, perhaps even only once in a thousand years. 
Moreover, these are of another type, not simply aflbcting size, number 
or weight, but bringing about something new, which may be useful 
or not. Whenever the variation is useful natural selection will take 
hold of it and preserve it; in other cases the variation may either 
persist or disappear. 

Two Types of Variation 71 

In his criticism of miscellaneous objections brought forward 
against the theory of natural selection after the publication of the 
first edition of Tlie Origin of Species, Darwin stated his view on 
this point very clearly: — "The doctrine of natural selection or the 
survival of the fittest, which implies that when variations or individual 
differences of a beneficial nature happen to arise, these will be 
preserved^" In this sentence the words '^happen to arise'' appear 
to me of prominent significance. They are evidently due to the 
same general conception which prevailed in Darwin's Pangenesis 

A distinction is indicated between ordinary fluctuations which are 
always present, and such variations as " happen to arise " from time 
to time^ The latter aiford the material for natural selection to act 
upon on the broad lines of organic development, but the first do 
not. Fortuitous variations are the species-producing kind, which the 
theory requires; continuous fluctuations constitute, in this respect, 
a useless type. 

Of late, the study of variability has returned to the recognition 
of this distinction. Darwin's variations, which from time to time 
happen to arise, are mutations, the opposite type being commonly 
designed fluctuations. A large mass of facts, collected during the 
last few decades, has confirmed this view, which in Darwin's 
time could only be expressed with much reserve, and everyone 

1 Origin of Species (6th edit.), P- 169, 1882. 

' Cf. de Vries, Intracellulare Pangenesis, p. 73, Jena, 1889, and Die Mutations theorie, 
1. p. 63. Leipzig, 1901. 

' [I think it right to point out that the interpretation of this passage from the Origin 
by Professor de Vries is not accepted as correct either by Mr Francis Darwin or by myself. 
We do not believe that Darwin intended to draw any distinction between two types of 
variation; the words "when variations or individual differences of a beneficial nature 
happen to arise " are not in our opinion meant to imply a dintinction between ordinary 
fluctuations and variations which "happen to arise," but we believe that "or" is here 
used in the sense of alias. With the permission of Professor de Vries, the following 
extract is quoted from a letter in which he replied to the objection raised to hia reading 
of the passage in question : 

"As to your remarks on the passage on page 6, I agree that it is now impossible to 
see clearly how far Darwin went in his distinction of the different kinds of variability. 
Distinctions were only dimly guessed at by him. But in our endeavour to arrive at a true 
conception of his view I think that the chapter on Pangenesis should be our leading guide, 
and that we should try to interpret the more difficult passages by that chapter. A careful 
and often repeated study of the Pangenesis hypothesis has convinced me that Darwin, 
when he wrote that chapter, was well aware that ordinary variability has nothing to do 
with evolution, but that other kinds of variation were necessary. In some chapters he 
comes nearer to a clear distinction than in others. To my mind the expression ' happen to 
arise' is the sharpest indication of his inclining in this direction. I am quite convinced 
that numerous expressions in his book become much clearer when looked at in this way." 

The statement in this pas.sago that "Darwin was well aware that ordinary variability 
has nothing to do with evolution, but that otlier kind.s of variation were necessary" ia 
contradicted by many passages in the Origin. A. C. 8.] 

72 Variation 

knows that Darwin was always very careful in statements of this 

From the same chapter I may here cite the following paragraph : 
"Tims as I am inclined to believe, morphological differences,... 
such as the arrangement of the leaves, the divisions of the flower or 
of the ovarium, the position of the ovules, etc. — first appeared in 
many cases as fluctuating variations, which sooner or later became 
constant through the nature of the organism and of the surrounding 
conditions... but not thrmigli natui'ctl selection^; for as these morpho- 
logical characters do not affect the welfare of the species, any slight 
deviation in them could not have been governed or accumulated 
through this latter agency^." We thus see that in Darwin's opinion, 
all small variations had not the same importance. In favourable 
circumstances some could become constant, but others could not. 

Since the appearance of the fii'st edition of The Origin of Species 
fluctuating variability has been thoroughly studied by Quetelet. He 
discovered the law, which governs all phenomena of organic life 
falling under this head. It is a very simple law, and states that 
individual variations follow the laws of probability. He proved it, 
in the first place, for the size of the human body, using the measure- 
ments published for Belgian recruits ; he then extended it to various 
other measurements of parts of the body, and finally concluded 
that it must be of universal validity for all organic beings. It must 
hold true for all characters in man, physical as well as intellectual 
and moral qualities; it must hold true for the plant kingdom as 
well as for the animal kingdom ; in short, it must include the whole 
living world. 

Quetelet's law may be most easily studied in those cases where 
the variability relates to measure, number and weight, and a vast 
number of facts have since confirmed its exactness and its validity 
for all kinds of organisms, organs and qualities. But if we examine 
it more closely, we find that it includes just those minute variations, 
which, as Darwin repeatedly pointed out, have often no significance 
for the origin of species. In the phenomena, described by Quetelet's 
law notliing "happens to arise"; all is governed by the common 
law, Avhich states that small deviations from the mean type are 
frequent, but that larger aberrations are rare, the rarer as they are 
larger. Any degree of variation will be found to occur, if only the 
number of individuals studied is large enough: it is even possible 
to calculate beforehand, how many specimens must be compared in 
order to find a previously fixed degree of deviation. 

The valuations, which from time to time happen to appear, are 
evidently not governed by this law. They cannot, as yet, be pro- 

1 The italics are mine (H. de V.). * Origin of Species (6tb edit.), p. 176. 

Fluctuations and Mutations 73 

duced at will : no sowings of thousands or even of millions of plants 
will induce them, although by such means the chance of their 
occurring will obviously be increased. But they are known to occur, 
and to occur suddenly and abruptly. They have been observed 
especially in horticulture, where they are ranged in the large and 
ill-defined group called sports. Korschinsky has collected all the 
evidence which horticultural literature affords on this points Several 
cases of the first appearance of a horticultural novelty have been 
recorded : this has always happened in the same way ; it appeared 
suddenly and unexpectedly without any definite relation to previously 
existing variability. Dwarf types are one of the commonest and 
most favourite varieties of flowering plants ; they are not originated 
by a repeated selection of the smallest specimens, but appear at 
once, without intermediates and without any previous indication. 
In many instances they are only about half the height of the original 
type, thus constituting obvious novelties. So it is in other cases 
described by Korschinsky : these sports or mutations are now recog- 
nised to be the main source of varieties of horticultural plants. 

As already stated, I do not pretend that the production of horti- 
cultural novelties is the prototype of the origin of new species in 
nature. I assume that they are, as a rule, derived from the parent 
species by the loss of some organ or quality, whereas the main lines 
of the evolution of the animal and vegetable kingdom are of course 
determined by progressive changes. Darwin himself has often pointed 
out this difference. But the saltatory origin of horticultural novelties 
is as yet the simplest parallel for natural mutations, since it relates to 
forms and phenomena, best known to the general student of evolution. 

The point which I wish to insist upon is this. The difference 
between small and ever present fluctuations and rare and more 
sudden vai-iations was clear to Darwin, although the facts known 
at his time were too meagre to enable a sharp line to be drawn 
between these two great classes of variability. Since Darwin's time 
evidence, which proves the correctness of his view, has accumulated 
with increasing rapidity. Fluctuations constitute one type; they 
are never absent and follow the law of chance, but they do not afford 
the material from which to build new species. Mutations, on the 
other hand, only happen to occur from time to time. They do not 
nccesstirily [)roduce greater changes than fluctuations, but such as may 
become, or rather are from their very nature, constant. It is this con- 
stancy which is the mark of specific characters, and on this basis every 
new specific character may be assumed to have arisen by nuitation. 

Some authors have tried to show that the theory of nnitation is 
opposed to Darwin's views. But this is erroneous. On the contrary, 

' S. Korpchinsky, " IJeterogenesia und Evolution," Flora, Vol. lxxxix. pp. 240—363, 1901. 

74 Valuation 

it is in fullest harmony A\ith the great principle laid down by 
Darwin. In order to be acted upon by that complex of environ- 
mental forces, which Darwin has called natural selection, the changes 
must obviously first be there. The manner in which they are pro- 
duced is of secondary importance and has hardly any bearing on the 
tlieory of descent with modification ^ 

A critical survey of all the fiicts of variability of plants in nature 
as well as under cultivation has led me to the conviction, that 
Darwin was right in stating that those rare beneficial variations, 
which from time to time happen to arise, — the now so-called muta- 
tions — are the real source of progress in the whole realm of the 
organic world. 


External and internal causes of variability. 

All phenomena of animal and plant life are governed by two sets 
of causes; one of these is external, the other internal. As a rule 
the internal causes determine the nature of a phenomenon — what an 
organism can do and what it cannot do. The external causes, on the 
other hand, decide when a certain variation will occur, and to what 
extent its features may be developed. 

As a very clear and wholly typical instance I cite the cocks-combs 
(Celosia). This race is distinguished from allied forms by its faculty of 
producing the well-known broad and much twisted combs. Every 
single individual possesses this power, but all individuals do not exhibit 
it in its most complete form. In some cases this faculty may not be 
exhibited at the top of the main stem, although developed in lateral 
branches: in others it begins too late for full development. Much 
depends upon nourishment and cultivation, but almost always the 
horticulturist has to single out the best individuals and to reject 
those which do not come up to the standard. 

The internal causes are of a historical nature. The external 
ones may be defined as nourishment and environment. In some 
cases nutrition is the main factor, as, for instance, in fluctuating 
vaiiability, but in natural selection environment usually plays the 
larger part. 

The inteiTial or historical causes are constant during the life-time 
of a species, using the term species in its most limited sense, as 
designating the so-called elementary species or the units out of 
which the ordinary species are built up. These historical causes are 
8imj)ly the specific characters, since in the origin of a species one or 
more of these must have been changed, thus producing the characters 
of the new type. These changes must, of course, also be due partly 
to internal and partly to external causes. 

1 Life mid Letter.i, u. 125. 



In contrast to these changes of the internal causes, the ordinary 
variability wliich is exhibited during the life-time of a species is 
called fluctuating variability. The name mutations or mutating 
variability is then given to the changes in the specific characters. 
It is desirable to consider these two main divisions of variability 

In the case of fluctuations the internal causes, as well as the 
extenial ones, are often apparent. The specific characters may be 
designated as the mean about which the observed forms vary. Almost 
every character may be developed to a greater or a less degree, but 
the variations of the single characters producing a small deviation 
from the mean are usually the commonest. The limits of these fluctua- 
tions may be called wide or narrow, according to the way we look at 
them, but in numerous cases the extreme on the favoured side 
hardly surpasses double the value of that on the other side. The 
degree of this development, for every individual and for every organ, 
is dependent mainly on nutrition. Better nourishment or an increased 
supply of food produces a higher development ; only it is not always 
easy to determine which direction is the fuller and which is the poorer 
one. Tlie differences among individuals grown from diiferent seeds are 
described as examples of individual variability, but those which may 
be observed on the same plant, or on cuttings, bulbs or roots derived 
from one individual are referred to as cases of partial variability. 
Partial variability, therefore, determines the differences among the 
flowers, fi-uits, leaves or branches of one individual : in the main, it 
follows the same laws as individual variability, but the position of a 
branch on a plant also determines its strength, and the part it may 
take in the nourishment of the whole. Composite flowers and umbels 
therefore have, as a rule, fewer rays on weak branches than on the 
strong main ones. The number of carpels in the fruits of poppies 
becomes very small on the weak lateral branches, which are pro- 
duced towards the autumn, as well as on crowded, and therefore on 
weakened individuals. Double flowers follow the same rule, and 
numerous other instances could easily be adduced. 

Mutating variability occurs along three main lines. Either a 
character may disappear, or, as we now say, become latent ; or a 
latent character may reappear, reproducing thereby a character 
which was once prominent in more or less remote anccstoiu The 
third and most interesting case is that of the production of quite 
new characters which never existed in the ancestors. Upon this 
progressive mutability the main development of the animal and 
vegetable kingdom evidently depends. In contrast to this, the two 
other cases are called retrogressive and degressive mutability. In 
nature retrogressive mutability plays a large j)art; in agriculture 

76 Variatiofi 

and in horticulture it gives rise to numerous varieties, which have in 
the i^ast been preserved, either on account of their usefulness or 
beauty, or simply as fancy-types. In fact the possession of numbers of 
varieties may be considered as the main character of domesticated 
animals and cultivated plants. 

In the case of retrogressive and degressive mutability the internal 
cause is at once apparent, for it is this which causes the disappear- 
ance or reappearance of some character. With progressive mutations 
the case is not so simple, since the new character must first be pro- 
duced and then displayed. These two processes are theoretically 
different, but they may occur together or after long intervals. 
The production of the new character I call premutation, and the 
displaying mutation. Both of course must have their external as 
well as their internal causes, as I have repeatedly pointed out in my 
Avork on the Mutation Theory \ 

It is probable that nutrition plays as important a part among the 
external causes of mutability as it does among those of fluctuating 
variability. Observations in support of this view, however, are too 
scanty to allow of a definite judgment. Darwin assumed an accumu- 
lative influence of external causes in the case of the production of new 
varieties or species. The accumulation might be limited to the 
life-time of a single hidividual, or embrace that of two or more 
generations. In the end a degree of instability in the equilibrium of 
one or more characters might be attained, great enough for a character 
to give way under a small shock produced by changed conditions of 
life. The character would then be thrown over from the old state 
of equilibrium into a new one. 

Characters which happen to be in this state of unstable equi- 
librium are called mutable. They may be either latent or active, 
being in the former case derived from old active ones or produced as 
new ones (by the process, designated premutation). They may be 
inherited in this mutable condition during a long series of genera- 
tions. I have shoAvn that in the case of the evening primrose of 
Lamarck this state of mutability must have existed for at least 
half a century, for this species was introduced from Texas into 
England about the year 18G0, and since then all the strains derived 
from its first distribution over the several countries of Europe show 
the same phenomena in producing new forms. The production of 
the dwarf evening primrose, or Oenothera nanella, is assumed to be 
due to one of the factors, which determines the tall stature of the 
parent form, becoming latent ; this would, therefore, aflbrd an example 
of retrogressive mutation. Most of the other types of my new 
mutants, on the other hand, seem to be due to progressive mutability. 

^ Die Mutatiottstheorie, 2 vols., Leipzig, 1901. 

Variability in Cereals 77 

The external causes of this curious period of mutability are as yet 
wholly unknown and can hardly be guessed at, since the origin of 
the Oenothera Laniarclciaua is veiled in mystery. The seeds, intro- 
duced into England about 1B60, were said to have come from Texas, 
but whether from wild or from cultivated plants we do not know. 
Nor has the species been recorded as having been observed in the 
wild condition. This, however, is nothing peculiar. The European 
types of Oenothera biennis and 0. muricata are in the same condition. 
The first is said to have been introduced from Virginia, and the 
second from Canada, but both probably from plants cultivated in the 
gardens of these countries. Whether the same elementary species 
are still growing on those spots is unknown, mainly because the 
different sub-species of the species mentioned have not been system- 
atically studied and distinguished. 

The origin of new species, which is in part the effect of mutability, 
is, however, due mainly to natural selection. Mutability provides the 
new characters and new elementary species. Natural selection, on 
the other hand, decides what is to live and what to die. Mutability 
seems to be free, and not restricted to previously determined lines. 
Selection, however, may take place along the same main lines in 
the coui-se of long geological epochs, thus directing the development 
of large branches of the animal and vegetable kingdom. In natural 
selection it is evident that nutrition and environment are the main 
factors. But it is probable that, while nutrition may be one of the 
main causes of mutability, environment may play the chief part in 
the decisions ascribed to natural selection. Relations to neighbour- 
ing plants and to injurious or useful animals, have been considered 
the most important determining factors ever since the time when 
Darwin pointed out their prevailing influence. 

From this discussion of the main causes of variability we may 
derive the proposition that the study of every phenomenon in the 
field of heredity, of variability, and of the origin of new species will 
have to be considered from two standpoints ; on one hand we have 
the internal causes, on the other the external ones. Sometimes the 
first are more easily detected, in other cases the latter are more 
accessible to investigation. But the complete elucidation of any 
phenomenon of life must always combine the study of the influence 
of internal with that of external causes. 


Polymorphic variahUity in cereals. 

One of the propositions of Darwin's theory of the struggle for life 
maintuins that the largest amount of life can be sui»ported on any 

78 Variation 

area, by great diversification or divergence in the structure and 
constitution of its inhabitants. Every meadow and every forest 
afibrds a proof of this thesis. The numerical proportion of the 
different species of the flora is always changing according to ex- 
ternal influences. Thus, in a given meadow, some species will flower 
abundantly in one year and then almost disappear, until, after a 
series of years, circumstances allow them again to multiply rapidly. 
Other species, which have taken their places, will then become rare. 
It follows from this principle, that notwithstanding the constantly 
changing conditions, a suitable selection from the constituents of a 
meadow will ensure a continued high production. But, although 
the principle is quite clear, artificial selection has, as yet, done very 
little towards reaching a really high standard. 

The same holds good for cereals. In ordinary circumstances a 
field will give a greater yield, if the crop grown consists of a 
number of sufficiently differing types. Hence it happens that almost 
all older varieties of wheat are mixtures of more or less diverging 
forms. In the same variety the numerical composition will vary 
fi-om year to year, and in oats this may, in bad years, go so far as to 
destroy more than half of the harvest, the wind-oats (Avena fatua), 
which scatter their grain to the winds as soon as it ripens, increasing 
so rapidly that they assume the dominant place. A severe winter, a 
cold spring and other extreme conditions of life will destroy one 
form more completely than another, and it is evident that great 
changes in the numerical composition of the mixture may thus be 
brought about. 

This mixed condition of the common varieties of cereals was 
well known to Darwin. For him it constituted one of the many 
types of variability. It is of that peculiar nature to which, in de- 
scribing other groups, he applies the term polymorphy. It does not 
imply that the single constituents of the varieties are at present 
really changing their characters. On the other hand, it does not 
exclude the possibility of such changes. It simply states that ob- 
servation shows the existence of different forms; how these have 
originated is a question which it does not deal with. In his well- 
known discussion of the variability of cereals, Darwin is mainly 
concerned with the question, whether under cultivation they have 
undergone great changes or only small ones. The decision ultimately 
depends on the question, how many forms have originally been taken 
into cultivation. Assuming five or six initial species, the variability 
must be assumed to have been very large, but on the assumption that 
there were between ten and fifteen types, the necessary range of 
variability is obviously much smaller. But in regard to this point, 
M'e are of course entirely without historical data. 

Breeding of Cereals 79 

Few of the varieties of wheat show conspicuous differences, 
although their number is great. If we compare the differentiating 
characters of the smaller types of cereals with those of ordinary 
wild species, even within the same genus or family, they are obviously 
much less marked. All these small characters, however, are strictly 
inherited, and this fact makes it very probable that the less obvious 
constituents of the mixtures in ordinary fields must be constant and 
pure as long as they do not intercross. Natural crossing is in most 
cereals a plienomenon of rare occurrence, common enough to admit of 
the production of all possible hybrid combinations, but requiring the 
lapse of a long series of years to reach its full effect. 

Darwin laid gi*eat stress on this high amount of variability in the 
plants of the same variety, and illustrated it by the experience of 
Colonel Lc Couteur^ on his farm on the isle of Jersey, who cultivated 
upwards of 150 varieties of wheat, which he claimed were as pure as 
those of any other agriculturalist. But Professor La Gasca of Madrid, 
who visited him, drew attention to aberrant ears, and pointed out, 
that some of them might be better yielders than the majority 
of plants in the crop, whilst others might be poor types. Thence 
he concluded that the isolation of the better ones might be a 
means of increasing his crops. Le Couteur seems to have con- 
sidered the constancy of such smaller types after isolation as 
absolutely probable, since he did not even discuss the possibility 
of their being variable or of their yielding a changeable or mixed 
progeny. This curious fact proves that he considered the types, dis- 
covered in his fields by La Gasca to be of the same kind as his other 
varieties, which until that time he had relied upon as being pure and 
uniform. Thus we see, that for him, the variability of cereals was 
what we now call polymorpliy. He looked through his fields for useful 
aberrations, and collected twenty-three new types of wheat. He was, 
moreover, clear about one point, which, on being rediscovered after 
half a century, has become the starting-point for the new Swedish 
principle of selecting agricultural plants. It was the princii)le of 
single-ear sowing, instead of mixing the grains of all the selected 
ears together. By sowing each ear on a separate plot he intended 
not only to multiply them, but also to compare their value. Iln's 
comparison ultimately led him to the choice of some few valuable 
sorts, one of which, the "Bcllevue de Talavera,'' still holds its place 
among the prominent sorts of wheat cultivated in France. This 
variety seems to be really a uniform type, a quality very useful under 
favourable conditions of cultivation, but which seems to have de- 
stroyed its capacity for further improvement by selection. 

Tlic princii)le of single-ear sowing, with a view to obtain pure and 

* On the Varietici, Propertiei, and Cltfsification oj Wheat, JerBcy, 1837. 

80 Variation 

uniform strains without further selection, has, until a few years ago, 
been almost entirely lost sight of. Only a very few agriculturists 
have applied it : among these are Patrick ShirrefF^ in Scotland and 
Willet M. Hays^ in Minnesota. Patrick Shirreff observed the fact, 
that in large fields of cereals, single plants may from time to time 
be found with larger ears, which justify the expectation of a far 
greater yield. In the course of about twenty-five years he isolated in 
this way tAvo varieties of wheat and two of oats. He simply multiplied 
them as fast as possible, without any selection, and put them on the 

Hays was struck by the fact that the yield of wheat in Minnesota 
was far beneath that in the neighbouring States. The local varieties 
were Fife and Blue Stem. They gave him, on inspection, some better 
specimens, "phenomenal yielders" as he called them. These were 
simply isolated and propagated, and, after comparison with the 
parent- variety and with some other selected strains of less value, were 
judged to be of sufficient importance to be tested by cultivation 
all over the State of Minnesota. They have since almost supplanted 
the original types, at least in most parts of the State, with the result 
that the total yield of wheat in Minnesota is said to have been 
increased by about a million dollars yearly. 

Definite progress in the method of single-ear sowing has, however, 
been made only recently. It had been foreshadowed by Patrick 
Shirreft', who after the production of the four varieties already 
mentioned, tried to carry out his work on a larger scale, by in- 
cluding numerous minor deviations from the main type. He found 
by doing so that the chances of obtaining a better form were 
sufficiently increased to justify the trial. But it was Nilsson who 
discovered the almost inexhaustible polymorphy of cereals and other 
agi'icultural crops and made it the starting-point for a new and 
entirely trustworthy method of the highest utility. By this means 
he has produced during the last fifteen years a number of new and 
valuable races, which have already supplanted the old types on 
numerous farms in Sweden and which are now being introduced on 
a large scale into Germany and other European countries. 

It is now twenty years since the station at Svalof was founded. 
During the first period of its work, embracing about five years, 
selection was practised on the principle which was then generally 
used in Germany. In order to improve a race a sample of the best 
ears was carefully selected from the best fields of the variety. These 
cars were considered as representatives of the type under cultivation, 

' Die Verbesserung der Getreide-Arten, translated by R. Hesse, Halle, 1880. 
' Wheat, varieties, hreeding, cultivation, Univ. Minnesota, Agricultural Experiment 
Station, Bull. no. 02, 1899. 

Breeding of Cereals 81 

and it was assumed that by sowing their grains on a small plot 
a family could be obtained, which could afterwards be improved by 
a continuous selection. Differences between the collected ears were 
either not observed or disregarded- At Svalof this method of 
selection was practised on a far larger scale than on any German 
farm, and the result was, broadly speaking, the same. This may be 
stated in the following words : improvement in a few cases, failure in 
all the others. Some few varieties could be improved and yielded 
excellent new types, some of which have since been introduced into 
Swedish agriculture and are now prominent races in the southern 
and middle parts of that country. But the station had definite aims, 
and among them was the improvement of the Chevalier barley. This, 
in Middle Sweden, is a fine brewer's barley, but liable to failure 
during unfavourable summers on account of its slender stems. It 
was selected with a view of giving it stiffer stems, but in spite of all 
the care and work bestowed upon it no satisfactory result was obtained. 

Tliis experience, combined with a number of analogous failures, 
could not fail to throw doubt upon the whole method. It was 
evident that good results were only exceptions, and that in most 
cases the principle was not one that could be relied upon. The 
exceptions might be due to unknown causes, and not to the validity 
of the method ; it became therefore of much more interest to search 
for the causes than to continue the work along these lines. 

In the year 1892 a number of different varieties of cereals were 
cultivated on a large scale and a selection was again made from them. 
About two hundred samples of ears were chosen, each apparently con- 
stituting a diflerent type. Their seeds were so>vn on separate plots 
and manured and treated as much as possible in the same manner. 
The plots were small and arranged in rows so as to facilitate the 
comparison of allied types. During the whole period of growth and 
during the ripening of the ears the plots were carefully studied and 
compared : they were harvested separately ; ears and kernels were 
counted and weighed, and notes >vere made concerning layering, 
rust and other cereal pests. 

The result of this experiment was, in the main, no distinct 
imi)rovement. Nilsson was especially struck by the fact that the 
plots, which should represent distinct types, Avere far from uniform. 
Many of them were as multiform as the fields from which the parent- 
ears were taken. Others showed variability in a less degree, but in 
almost all of them it was clear that a pure race had not been 
obtained. The experiment was a fair one, inasmuch as it demon- 
strated the polymorphic variability of cereals beyond all doubt and 
in a degree hitherto iniHuspected; but from the standpoint of the 
selectionist it was u failure. Fortunately there were, however, one 

D. 6 

82 Variation 

or two exceptions. A few lots showed a perfect uniformity in regard 
to all the stalks and ears: these were small families. This fact 
suggested the idea that each might have been derived from a single 
ear. During the selection in the previous summer, Nilsson had tried 
to find as many ears as possible of each new type which he recognised 
in his fields. But the variability of his crops was so great, that 
he was rarely able to include more than two or three ears in the 
same gi'oup, and, in a few cases, he found only one representative 
of the supposed type. It might, therefore, be possible that those 
smaU uniform plots were the direct progeny of ears, the grains of 
which had not been mixed with those from other ears before sowing. 
Exact records had, of course, been kept of the chosen samples, 
and the number of ears had been noted in each case. It was, there- 
fore, possible to answer the question and it was found that those 
plots alone were uniform on which the kernels of one single ear 
only had been sown. Nilsson concluded that the mixture of two or 
more ears in a single sowing might be the cause of the lack of uni- 
formity in the progeny. Apparently similar ears might be different 
in their progeny. 

Once discovered, this fact was elevated to the rank of a leading 
principle and tested on as large a scale as possible. The fields were 
again carefully investigated and every single ear, which showed a 
distinct divergence from the main type in one character or another, 
was selected. A thousand samples were chosen, but this time 
each sample consisted of one ear only. Next year, the result 
corresponded to the expectation. Uniformity prevailed almost every- 
where ; only a few lots showed a discrepancy, which might be 
ascribed to the accidental selection of hybrid ears. It was now clear 
that the progeny of single ears was, as a rule, pure, whereas that of 
mixed ears Avas impure. The single-ear selection or single-ear sowing, 
which had fallen into discredit in Germany and elsewhere in Europe, 
was rediscovered. It proved to be the only trustworthy principle of 
selection. Once isolated, such single-parent races are constant 
from seed and remain true to their type. No further selection is 
needed ; they have simply to be multiplied and their real value 

Patrick ShirrefiF, in his early experiments, Le Couteur, Hays and 
others had observed the rare occurrence of exceptionally good 
yielders and the value of their isolation to the agriculturist. The 
possibility of error in the choice of such striking specimens and the 
necessity of judging their value by their progeny were also known to 
these investigators, but they had not the slightest idea of all the 
possibilities suggested by their principle. Nilsson, who is a botanist 
as Mcll as an agriculturist, discovered that, besides these exception- 

Breeding of Cereals 83 

ably good yieMers, every variety of a cereal consists of hundreds of 
different types, which find the best conditions for success when 
grown together, but which, after isolation, prove to be constant. 
Their preference for mixed growth is so definite, that once isolated, 
their claims on manure and treatment are found to be much higher 
than those of the original mixed variety. Moreover, the greatest 
care is necessary to enable them to retain their purity, and as soon as 
they are left to themselves they begin to deteriorate through acci- 
dental crosses and admixtures and rapidly return to the mixed 

Reverting now to Darwin's discussion of the variability of cereals, 
we may conclude that subsequent investigation has proved it to be 
exactly of the kind Avhich he describes. The only difference is that 
in reality it reaches a degree, quite unexpected by Darwin and his 
contemporaries. But it is polymorphic variability in the strictest 
sense of the word. How the single constituents of a variety originate 
we do not see. We may assume, and there can hardly be a doubt 
about the truth of the assumption, that a new character, once pro- 
duced, will slowly but surely be combined through accidental crosses 
with a large number of previously existing types, and so will tend to 
double the number of the constituents of the variety. But whether 
it first appears suddenly or whether it is only slowly evolved we 
cannot determine. It would, of course, be impossible to observe either 
process in such a mixture. Only cultures of pure races, of single- 
parent races as we have called them, can afford an opportunity 
for this kind of observation. In the fields of Svalof new and un- 
expected qualities have recently been seen, from time to time, to 
appear suddenly. These characters are as distinct as the older ones 
and appear to be constant from the moment of their origin. 

Darwin has repeatedly insisted that man does not cause variability, 
lie simply selects the variations given to him by the hand of nature, 
lie may repeat this process in order to accumulate different new 
characters in the same family, thus producing varieties of a 
higher order. This process of accumulation would, if continued for 
a longer time, lead to the augmentation of the slight differences 
characteristic of varieties into the greater differences characteristic 
of species and genera. It is in this way that horticultural and 
agricultural experience contribute to the problem of the conversion 
of varieties into s[)ecies, and to the explanation of the admirable 
a(lai)tations of eacli organism to its complex conditions of life. In 
tiie long run new forms, distinguished from their allies by quite 
a number of new characters, would, by the extermination of the 
older intermediateH, become distinct sj)ecies. 

llius we see that the theory of the origin of species by means of 


84 • Variation 

iiatui-al selection is quite independent of the question, how the 
variations to be selected arise. They may arise slowly, fi'om simple 
fluctuations, or suddenly, by mutations ; in both cases natural 
selection will take hold of them, will multiply them if they are 
beneficial, and in the course of time accumulate them, so as to 
produce that great diversity of organic life, which we so highly 

Darwin has left the decision of this difficult and obviously sub- 
ordinate point to his followers. But in his Pangenesis hypothesis 
he has given us the clue for a close study and ultimate elucidation 
of the subject under discussion. 


By W. Bateson, MA., RRS. 

Professor of Biology in the University of Cambridge. 

Darwin's work has the property of gi*eatness in tliat it may be 
admired fiom more aspects than one. For some the perception of 
the principle of Natural Selection stands out as his most wonderful 
achievement to which all the rest is subordinate. Others, among 
whom I would range myself, look up to him rather as the first who 
plainly disthiguished, collected, and comprehensively studied that 
new class of evidence fi-om which hereafter a true understanding of 
the process of Evolution may be developed. We each prefer our 
own standpoint of admiration ; but I think that it will be in their 
wider aspect that his labours will most command the veneration of 

A treatise written to advance knowledge may be read in two 
moods. Tlie reader may keep his mind passive, willing merely to 
receive the impress of the writer's thought ; or he may read ^\ith his 
attention strained and alert, asking at every instant how the new know- 
ledge can be used in a further advance, watching continually for 
fresh footholds by which to climb higher still. Of Shelley it has been 
said that he was a poet for poets : so Darwin was a naturalist for 
naturalists. It is when his Avritings are used in the critical and more 
exacting spirit with which we test the outfit for our own enterprise 
that we learn their full value and strength. A\liether we glance back 
and compare his performance with the efforts of his predecessors, or 
look forward along the course which modern research is disclosing, we 
shall honour most in him not the rounded merit of finite accomplish- 
ment, but the creative power by Avhich he inaugurated a line of 
discovery endless in variety and extension. Let ua attempt thus to 
see his work in true perspective between the past from which it grew, 
and the i)rcsent which is its consc(iuence. Darwin attacked the 
problem of Evolution by reference to facts of three classes : Varia- 

86 Heredity and Variation in Modern Lights 

tion ; Heredity ; Natural Selection. His work was not as the laity 
suppose, a sudden and unheralded revelation, but the first fruit of a 
long and hitherto barren controversy. The occurrence of variation 
from type, and the hereditary transmission of such variation had of 
course been long familiar to practical men, and inferences as to the 
possible bearing of those phenomena on the nature of specific 
difference had been from time to time drawn by naturalists. Mau- 
pertuis, for example, MTote : " Ce qui nous reste ^ examiner, c'est 
comment d'un seul individu, il a pu naitre tant d'esp^ces si difi'^rentes." 
And again : " La Nature contient le fonds de toutes ces vari^t(^s : 
mais le hasard ou I'art les mettent en oeuvre. C'est ainsi que ceux 
dont I'industrie s'applique ^ satisfaire le goftt des curieux, sont, pour 
ainsi dire, createurs d'esp^ces nouvelles\" 

Such passages, of which many (though few so emphatic) can be 
found in eighteenth century writers, indicate a true perception of the 
mode of Evolution. Tlie speculations hinted at by Bufibn^, developed 
by Erasmus Darwin, and independently proclaimed above all by 
Lamarck, gave to the doctrine of descent a wide renown. The uni- 
formitarian teaching which Lyell deduced from geological observation 
had gained acceptance. The facts of geographical distribution^ had 
been shown to be obviously inconsistent with the Mosaic legend. 
Prichard, and Lawrence, following the example of Blumenbach, had 
successfully demonstrated that the races of Man could be regarded 
as different forms of one species, contrary to the opinion up till then 
received. These treatises all begin, it is true, with a profound 
obeisance to the sons of Noah, but that performed, they continue on 
strictly modern lines. The question of the mutability of species was 
thus prominently raised. 

Those who rate Lamarck no higher than did Huxley in his con- 
temptuous phrase " buccinator tantum,^' will scarcely deny that the 
sound of the trumpet had carried far, or that its note was clear. If 
then there were few who had already turned to evolution with 
positive conviction, all scientific men must at least have known that 

^ Venus Physique, contenant deux Dissertations, Vune sur Vorigine des Hommes et des 
Animaux: Et Vautre sur Vorigine des Noirs, La Haye, 1746, pp. 124 and 129. For an 
introduction to the writings of Maupertuis I am indebted to an article by Professor 
Lovejoy in Popular Sci. Monthly, 1902. 

" For the fullest account of the views of these pioneers of Evolution, see the works of 
Samuel Butler, especially Evolution, Old and New (2nd edit.) 1882. Butler's claims on 
behalf of Buffon have met with some acceptance ; but after reading what Butler has said, 
and a considerable part of Bulfon's own works, the word "hinted" seems to me a 
sufficiently correct description of the part he played. It is interesting to note that in 
the chapter on the Ass, which contains some of his evolutionary passages, there is a 
reference to "plusieurs idees tres-elevees sur la generation" contained in the Letters of 

» See especially W. Lawrence, Lectures on Physiology, London, 1823, pp. 213 f. 

Why Darwin succeeded 87 

such views had been promulgated ; and many must, as Huxley says, 
have taken up his own position of " critical expectancy \" 

Why, then, was it, that Darwin succeeded where the rest had 
failed ? The cause of that success was two-fold. First, and obviously, 
in the principle of Natural Selection he had a suggestion which would 
work. It might not go the whole way, but it was true as far as it 
went. Evolution could thus in gi-eat measure be fairly represented as 
a consequence of demonstrable processes. Darwin seldom endangers 
the mechanism he devised by putting on it strains much greater than 
it can bear. He at least was under no illusion as to the omnipotence 
of Selection ; and he introduces none of the forced pleading which in 
recent years has threatened to discredit that principle. 

For example, in the latest text of the Origin^ we find him saying: 
" But as my conclusions have lately been much misrepresented, 
and it has been stated that I attribute the modification of species 
exclusively to natural selection, I may be permitted to remark 
that in the first edition of this work, and subsequently, I placed 
in a most conspicuous position — namely, at the close of the 
Introduction — the following words : ' I am convinced that natural 
selection has been the main but not the exclusive means of 
modification.' " 

' See the chapter contribated to the Life and Letters of Charles Darwin, n. p. 195. I do 
not clearly understand the sense in which Darwin wrote (Autobiography, ibid. i. p. 87) : 
'•It has sometimes been said that the success of the Origin proved 'that the subject was in 
the air,' or ' that men's minds were prepared for it.' I do not think that this is strictly 
true, for I occasionally sounded not a few naturalists, and never happened to come across 
a single one who seemed to doubt about the permanence of species." This experience may 
perhaps have been an accident due to Darwin's isolation. The literature of the period 
abounds with indications of "critical expectancy." A most interesting expression of that 
feeling is given in the charming account of the "Early Days of Darwinism" by Alfred 
Newton, Macmillan's Magazine, lvii. 1888, p. 241. He tells how in 1858 when spending a 
dreary summer in Iceland, he and his friend, the ornithologist John WoUey, in default of 
active occupation, spent their days in discussion. "Both of us taking a keen interest in 
Natural History, it was but reasonable that a question, which in those days was always 
coming up wherever two or more naturalists were gathered together, should be continually 
recurring. That question was, 'What is a species?' and connected therewith was the 
other question, ' How did a species begin ? '...Now we were of course fairly well acquainted 
with what had been published on these subjects." He then enumerates some of these 
publications, mentioning among others T. Vernon Wollaston's Variatioji of Species — 
ft work which has in my opinion never been adequately appreciated. He proceeds: ''Of 
course we never arrived at anything like a solution of these problems, general or special, 
bat we felt very strongly that a solution ought to be found, and that quickly, if the study 
of Botany and Zoology waH to make any great advance." He then describes how on 
his return home be received the famous number of the Linnean Journal on a certain 
evening. "I sat up late that night to read it ; and never shall I forget the impression it 
made upon me. Herein was contained a perfectly simple solution of all the diflicultiea 
which had been troubling me for months past. ...I went to bed satisfied that a solution 
had been found." 

» Origin, 6th edit. (1882), p. 421. 

38 Heredity and Variation in Modern Lights 

But apart from the invention of this reasonable hypothesis, which 
may well, as Huxley estimated, "be the guide of biological and 
psychological speculation for the next three or four generations," 
Darwin made a more significant and imperishable contribution. Not 
for a few generations, but through all ages he should be remem- 
bered as the first who showed clearly that the problems of Heredity 
and Variation are soluble by observation, and laid down the course 
by which we must proceed to their solution ^ The moment of in- 
spiration did not come with the reading of Malthus, but with the 
opening of the "first note-book on Transmutation of Species^." Evolu- 
tion is a process of Variation and Heredity. The older writers, 
though they had some vague idea that it must be so, did not study 
Variation and Heredity. Darwin did, and so begat not a theory, but 
a science. 

The extent to which this is true, the scientific world is only be- 
ginning to realise. So little was the fact appreciated in Darmn's 
own time that the success of his writings was followed by an almost 
total cessation of work in that special field. Of the causes which 
led to this remarkable consequence I have spoken elsewhere. They 
proceeded from circumstances peculiar to the time ; but whatever 
the causes there is no doubt that this statement of the result is 
historically exact, and those who make it their business to collect 
facts elucidating the physiology of Heredity and Variation are well 
aware that they will find little to reward their quest in the leading 
scientific Journals of the Darwinian epoch. 

In those thirty years the original stock of evidence current and 
in circulation even underwent a process of attrition. As in the story 
of the Eastern sage who first wrote the collected learning of the 
universe for his sons in a thousand volumes, and by successive com- 
pression and burning reduced them to one, and from this by further 
burning distilled the single ejaculation of the Faith, "There is no 
god but God and Mohamed is the Prophet of God," which was all his 
maturer wisdom deemed essential : — so in the books of that period do 
we find the corpus of genetic knowledge dwindle to a few prerogative 
instances, and these at last to the brief formula of an unquestioned 

* Whatever be our estimate of the importance of Natural Selection, in this we all agree. 
Samuel Butler, the most brilliant, and by far the most interesting of Darwin's 
opponents — whose works are at length emerging from oblivion — in his Preface (1882) to 
the 2nd edition of Evolution, Old and New, repeats his earlier expression of homage to 
one whom he had come to regard as an enemy: "To the end of time, if the question be 
asked, 'Who taught people to believe in Evolution?' the answer must be that it was 
Mr. Darwin. This is true, and it is hard to see what palm of higher praise can be 
awarded to any philosopher." 

2 Life and Letters, i. pp. 276 and 83. 

Weismann's Challenge 89 

And yet in all else that concerns biological science this period 
was, in very truth, our Golden Age, when the natural history of the 
earth was explored as never before ; morphology and embryology were 
exhaustively ransacked ; the physiology of plants and animals began 
to rival chemistry and physics in precision of method and in the 
rapidity of its advances ; and the foundations of pathology were laid. 

In contrast with this immense activity elsewhere the neglect 
which befel the special physiology of Descent, or Genetics as we now 
call it, is astonishing. This may of course be interpreted as meaning 
that the favoured studies seemed to promise a quicker return for 
effort, but it would be more true to say that those who chose these 
other pursuits did so without making any such comparison ; for the 
idea that the physiology of Heredity and Variation was a coherent 
science, offering possibilities of extraordinary discovery, was not 
present to their minds at all. In a word, the existence of such a 
science was well nigh forgotten. It is true that in ancillary periodicals, 
as for example those that treat of entomology or horticulture, or in 
the writings of the already isolated systematists \ observations with 
this special bearing were from time to time related, but the class of 
fact on which Darwin built his conceptions of Heredity and Variation 
was not seen in the highways of biology. It formed no part of the 
official curriculum of biological students, and found no place among 
the subjects which their teachers were investigating. 

During this period nevertheless one distinct advance was made, 
that with which Weismann's name is prominently connected. In 
Darwin's genetic scheme the hereditary transmission of parental 
experience and its consequences played a considerable role. Exactly 
how great that role was supposed to be, he with his habitual caution 
refrained from specifying, for the sufficient reason that he did not 
know. Nevertheless much of the process of Evolution, especially 
that by which organs have become degenerate and rudimentary, was 
certainly attributed by Darwin to such inheritance, though since 
belief in the inheritance of acquired characters fell into disrepute, 
the fact has been a good deal overlooked. The Origin without " use 

1 This isolation of the systematists is the one most melancholy sequela of Darwinism. It 
seems an irony that we should read in the peroration to the Origin that when the Darwinian 
view is accepted "Systematists will be able to pursue their labours as at present; but they 
will not be incessantly haunted by the shadowy doubt whether this or that form be a true 
species. This, I feel sure, and I speak after experience, will be no slight relief. The endless 
disputes whether or not some fifty species of British brambles are good species will cease." 
Origin, Cth edit. (1882), p. 425. True they have ceased to attract the attention of those 
who lead opinion, but anyone who will turn to the literature of systcmatics will fiud that 
they have not ceased in any other sense. Should there not be somethinR disquieting in the 
fact that among the workers who come most into contact with specific difTorences, are 
to be found the only men who have failed to bo persuaded of the unreality of those 
differences ? 

90 Heredity and Variation in Modern Lights 

and disuse " would be a materially different book. A certain vacillation 
is discernible in Darwin's utterances on this question, and the fact 
gave to the astute Butler an opportunity for his most telling attack. 
The discussion which best illustrates the genetic views of the period 
arose in regard to the production of the rudimentary condition of the 
wings of many beetles in the Madeira group of islands, and by com- 
paring passages from the Origin^ Butler convicts Darwin of saying 
firet that this condition was in the main the result of Selection, with 
disuse aiding, and in another place that the main cause of degenera- 
tion was disuse, but that Selection had aided. To Darwin however 
I think the point would have seemed one of dialectics merely. To 
him the one paramount purpose was to show that somehow an 
Evolution by means of Variation and Heredity might have brought 
about the facts observed, and whether they had come to pass in the 
one way or the other was a matter of subordinate concern. 

To us moderns the question at issue has a diminished significance. 
For over all such debates a change has been brought by Weismann's 
challenge for evidence that use and disuse have any transmitted 
effects at all. Hitherto the transmission of many acquired charac- 
teristics had seemed to most naturalists so obvious as not to call for 
demonstration^. Weismann's demand for facts in support of the 
main proposition revealed at once that none having real cogency 
could be produced. Tlie time-honoured examples were easily shown 
to be capable of different explanations. A few certainly remain 
which cannot be so summarily dismissed, but — though it is manifestly 
impossible here to do justice to such a subject — I think no one will 
dispute that these residual and doubtful phenomena, whatever be 
their true nature, are not of a kind to help us much in the inter- 
pretation of any of those complex cases of adaptation which on the 
hypothesis of unguided Natural Selection are especially difficult to 
understand. Use and disuse were invoked expressly to help us over 
these hard places ; but whatever changes can be induced in offspring 
by direct treatment of the parents, they are not of a kind to en- 
courage hope of real assistance from that quarter. It is not to be 
denied that through the collapse of this second line of argument the 
Selection hypothesis has had to take an increased and perilous 
burden. Various ways of meeting the difficulty have been proposed, 

' Cth edit. pp. 109 and 401. See Butler, Essays on Life, Art, and Science, p. 265, 
reprinted 1908, and Evolution, Old and New, chap. xxii. (2nd edit.), 1882. 

'^ W. Lawrence was one of the few who consistently maintained the contrary opinion. 
Prichard, who previonsly had expressed himself in tlie same sense, docs not, I believe, 
repeat these views in his later writings, and there are sifjns that he came to believe in the 
transmission of acquired habits. See Lawrence, Lect. Physiol. 1823, pp. 436 — 437, 447 
Prichard, Edin. Inaag. Disp. 1808 [not seen by me], quoted ibid, and Nat. Hist. Man, 
1843, pp. 34 f. 

Cytology and Heredity 91 

but these mostly resolve themselves into improbable attempts to 
expand or magnify the powers of Natural Selection. 

Weismann's interpellation, though negative in purpose, has had a 
lasting and beneficial effect, for through his thorough demolition of 
the old loose and distracting notions of inherited experience, the 
ground has been cleared for the construction of a true knowledge of 
heredity based on experimental fact. 

In another way he made a contribution of a more positive 
character, for his elaborate speculations as to the genetic meaning of 
cytological appearances have led to a minute investigation of the 
visible phenomena occurring in those cell-divisions by which germ- 
cells arise. Though the particular views he advocated have very 
largely proved incompatible with the observed facts of heredity, yet we 
must acknowledge that it was chiefly through the stimulus of Weis- 
mann's ideas that those advances in cytology were made ; and though 
the doctrine of the continuity of germ-plasm cannot be maintained 
in the form originally propounded, it is in the main true and illu- 
minating \ Nevertheless in the present state of knowledge we are 
still as a rule quite unable to connect cytological appearances Avith 
any genetic consequence and save in one respect (obviously of extreme 
importance — to be spoken of later) the two sets of phenomena might, 
for all we can see, be entirely distinct. 

I cannot avoid attaching importance to this want of connection 
between the nuclear phenomena and the features of bodily organisa- 
tion. All attempts to investigate Heredity by cytological means lie 
under the disadvantage that it is the nuclear changes which can 
alone be effectively observed. Important as they must surely be, 
I have never been persuaded that the rest of the cell counts for 
nothing. What we know of the behaviour and variability of chromo- 
somes seems in my opinion quite incompatible with the belief that 
they alone govern form, and are the sole agents responsible in 

* It is interesting to see liow nearly Butler was led by natural penetration, and from 
absolutely opposite conclusiona, back to this underlying truth : " So that each ovum when 
impregnate should be considered not as descended from its ancestors, but as being a 
continuation of the personality of every ovum in the chain of its ancestry, which every 
ovum tf actually is quite as truly as the octogenarian is the same identity with the ovum 
from which he has been developed. This process cannot stop short of the primordial cell, 
which again will probably turn out to be but a brief resting-place. We therefore prove each 
one of us to he actualbj the primordinl cell which never died nor dies, but has differentiated 
itself into the life of the world, all living beings whatever, being one with it and members 
one of another," Life and Ilahit, 1878, p. 86. 

' This view is no doubt contrary to the received opinion. I am however interested to 
see it lately maintained by Driescli (Science and I'hiUifophy oj the Organimn, hondon, 1907, 
p. 233), and from the recent observations of Godlewski it baa received distinct experi- 
mental support. 

92 Heredity and Variation in Modern Lights 

If, then, progress was to be made in Genetics, work of a different 
kind was required. To learn the laws of Heredity and Variation 
there is no other way than that which Darwin himself followed, the 
direct examination of the phenomena. A beginning could be made 
by collecting fortuitous observations of this class, which have often 
throMii a suggestive light, but such evidence can be at best but 
superficial and some more penetrating instrument of research is 
required. This can only be provided by actual experiments in 

The truth of these general considerations was becoming gi-adually 
clear to many of us when in 1900 Mendel's work was rediscovered. 
Segregation, a phenomenon of the utmost novelty, was thus revealed. 
From that moment not only in the problem of th.e origin of species, 
but in all the great problems of biology a new era began. So un- 
expected was the discovery that many naturalists were convinced it 
was untrue, and at once proclaimed Mendel's conclusions as either 
altogether mistaken, or if true, of very limited application. Many 
fantastic notions about the workings of Heredity had been asserted 
as general principles before : this was probably only another fancy of 
the same class. 

Nevertheless those who had a preliminary acquaintance with the 
facts of Variation were not wholly unprepared for some such revela- 
tion. The essential deduction from the discovery of segregation was 
that the characters of living things are dependent on the presence of 
definite elements or factors, which are treated as units in the pro- 
cesses of Heredity. These factors can thus be recombined in various 
ways. They act sometimes separately, and sometimes they interact 
in conjunction with each other, producing their various effects. All 
this indicates a definiteness and specific order in heredity, and there- 
fore in variation. This order cannot by the nature of the case be 
dependent on Natural Selection for its existence, but must be a con- 
sequence of the fundamental chemical and physical nature of living 
things. The study of Variation had from the first shown that an 
orderliness of this kind was present. The bodies and the properties 
of living tilings are cosmic, not chaotic. No matter how low in the 
scale we go, never do we find the slightest hint of a diminution in 
that all-pervading orderliness, nor can we conceive an organism 
existing for a moment in any other state. Moreover not only does 
this order prevail in normal forms, but again and again it is to be 
seen in newly-sprung varieties, which by general consent cannot have 
been subjected to a prolonged Selection. The discovery of Mendelian 
elements admirably coincided with and at once gave a rationale of 
these facts. Genetic Variation is then primarily the consequence of 
additions to, or omissions from, the stock of elements which the 

MendeVs Discovery 93 

species contains. The further investigation of the species-problem 
must thus proceed by the analytical method which breeding experi- 
ments provide. 

In the nine years which have elapsed since Mendel's clue became 
generally known, progi'ess has been rapid. We now understand the 
process by which a polymorphic race maintains its polymorphism. 
When a family consists of dissimilar members, given the numerical 
proportions in which these members are occurring, we can represent 
their composition symbolically and state what t}^es can be trans- 
mitted by the various members. The diflficulty of the "swamping 
effects of intercrossing" is practically at an end. Even the famous 
puzzle of sex-limited inheritance is solved, at all events in its more 
regular manifestations, and we know now how it is brought about 
that the normal sisters of a colour-blind man can transmit the 
colour-blindness while his normal brothers cannot transmit it. 

We are still only on the fringe of the inquiry. It can be seen 
extending and ramifying in many directions. To enumerate these 
here would be impossible. A whole new range of possibilities is 
being brought into view by study of the interrelations between the 
simple factors. By following up the evidence as to segi*egation, 
indications have been obtained which can only be interpreted as 
meaning that when many factors are being simultaneously redis- 
tributed among the germ-cells, certain of them exert M'hat must be 
described as a repulsion upon other factors. We cannot surmise 
whither this discovery may lead. 

In the new light all the old problems wear a fresh aspect Upon 
the question of the nature of Sex, for example, the bearing of 
Mendelian evidence is close. Elsewhere I have shown that from 
several sets of parallel experiments the conclusion is almost forced 
upon us that, in the types investigated, of the two sexes the female 
is to be regarded as heterozygous in sex, containing one unpaired 
dominant element, while the male is similarly homozygous in the 
absence of that element \ It is not a little remarkable that on this 
point — which is the only one where observations of the nuclear pro- 
cesses of gameto-genesis have yet been brought into relation with the 
visible characteristics of the organisms themselves — there should be 
diametrical opposition between the results of breeding experiments 
and those derived from cytology. 

Those who liave followed the researches of the American school 
will be aware that, after it had been found in certain insects that the 
«l)crinatozoa were of two kinds according as they contained or did 
not conbiin the accessory chromosome, E. B. Wilson succeeded in 

* In other words, the ova are each either female, or male (i.e. non-female), but the 
Bp«rm8 are all non- female. 

94 Heredity and Variation m Modern Lights 

proving that the sperms possessing this accessory body were destined 
to form females on fertilisation, while sperms without it form males, 
the eggs being apparently indifferent. Perhaps the most striking of 
all this series of observations is that lately made by T. H. Morgan ^ 
since confirmed by von Baehr, that in a Phylloxeran two kinds of 
spermatids are formed, respectively with and without an accessory 
(in this case, double) chromosoma Of these, only those possessing the 
accessory body become functional spet'matozoa, the others degene- 
rating. We have thus an elucidation of the puzzling fact that in 
these forms fertilisation results in the formation of females only. 
How the males are formed — for of course males are eventually 
produced by the parthenogenetic females — we do not know. 

If the accessory body is really to be regarded as bearing the factor 
for femaleness, then in Mendelian terms female is DD and male is 
DR. The eggs are indifferent and the spermatozoa are each male, 
or female. But according to the evidence derived from a study of 
the sex-limited descent of certain features in other animals the 
conclusion seems equally clear that in them female must be regarded 
as DR and male as RR. The eggs are thus each either male or 
female and the spermatozoa are indifferent. How this contradictory 
evidence is to be reconciled we do not yet know. The breeding work 
concerns fowls, canaries, and the Currant moth {Abraxas grossu- 
lariata). The accessory chromosome has been now observed in most 
of the great divisions of insects^ except, as it happens, Lepidoptera. 
At first sight it seems difficult to suppose that a feature apparently 
so fundamental as sex should be differently constituted in different 
animals, but that seems at present the least improbable inference. 
I mention these two groups of facts as illustrating the nature and 
methods of modern genetic work. We must proceed by minute and 
specific analytical investigation. Wherever we look we find traces 
of the operation of precise and specific rules. 

In the light of present knowledge it is evident that before we can 
attack the Species-problem with any hope of success there are vast 
arrears to be made up. He would be a bold man who would now 
assert that there was no sense in which the term Species might not 
have a strict and concrete meaning in contradistinction to the term 
Variety. We have been taught to regard the difference between 
species and variety as one of degree. I think it unlikely that this 

^ Morgan, Proc. Soc. Exp. Biol. Med. v. 1908, and von Baehr, Zool. Anz. zxxii. p. 507) 

^ As Wilson has proved, the unpaired body is not a universal feature even in those 
orders in which it has been observed. Nearly allied types may differ. In some it is 
altogether unpaired. In others it is paired with a body of much smaller size, and by 
selection of various types all gradations can be demonstrated ranging to the condition 
in which the members of the pair are indistinguishable from each other. 

What is a Variation? 95 

conclusion will bear the test of further research. To Darwin the 
question, What is a variation? presented no difficulties. Any difference 
between parent and offspring was a variation. Now we have to be 
more precise. First we must, as de Vries has shown, distinguish real, 
genetic, variation from fliictuatioual variations, due to environmental 
and other accidents, which cannot be transmitted. Having excluded 
these sources of error the variations observed must be expressed in 
terms of the factors to which they are due before their significance 
can be understood. For example, numbers of the variations seen 
under domestication, and not a few witnessed in nature, are simply 
the consequence of some ingi-cdient being in an imknown way omitted 
from the composition of the varying individual. The variation may 
on the contrary be due to the addition of some new clement, but to 
prove that it is so is by no means an easy matter. Casual observation is 
useless, for though these latter variations will always be dominants, yet 
many dominant characteristics may arise from another cause, namely 
the meeting of complementary factors, and special study of each case 
in two generations at least is needed before these two phenomena can 
be distinguished. 

^Vlien such considerations are fully appreciated it will be realised 
that medleys of most dissimilar occurrences are all confused together 
under the term Variation. One of the first objects of genetic analysis 
is to disentangle this mass of confusion. 

To those who have made no study of heredity it sometimes 
appears that the question of the effect of conditions in causing 
variation is one which we should immediately investigate, but a little 
thought will show that before any critical inquiry into such possi- 
bilities can be attempted, a knowledge of the working of heredity 
under conditions as far as possible uniform must be obtained. At 
the time when Darwin was writing, if a plant brought into cultivation 
gave ofi* an albino variety, such an event was without hesitation 
ascribed to the change of life. Kow we see that albino gametes, 
germs, that is to say, which are destitute of the pigment-forming 
factor, may have been originally produced by individuals standing an 
indefinite number of generations back in the ancestry of the actual 
albino, and it is indeed almost certain that the variation to which the 
appearance of the albino is due cannot have taken place in a genera- 
tion later than that of the grandparents. It is true that when a new 
dominant api)oar8 we should feel greater confidence that we were 
witnessing the original variation, but such events are of extreme 
rarity, and no such case has come under the notice of an experi- 
menter in modern times, as far as I am aware. That they must have 
appeared is clear enougli. Nothing corresijonding to the Brown- 
breasted Game fowl is known wild, yet that colour is a most definite 

96 Heredity and Variation in Modern Lights 

dominant, and at some moment since Galliis hanlciva was domesticated, 
the element on which that special colour depends must have at least 
once been formed in the germ-cell of a fowl ; but we need harder 
evidence than any which has yet been produced before we can declare 
that this novelty came through over-feeding, or change of climate, or 
any other disturbance consequent on domestication. When we reflect 
on the intricacies of genetic problems as we must now conceive them 
there come moments when we feel almost thankful that the Mendelian 
principles were unkno>vn to Darwin. The time called for a bold 
pronouncement, and he made it, to our lasting profit and delight. 
AVith fuller knowledge we pass once more into a period of cautious 
expectation and reserve. 

In every arduous enterprise it is pleasanter to look back at 
difficulties overcome than forward to those which still seem insur- 
mountable, but in the next stage there is nothing to be gained by 
disguising the fact that the attributes of living things are not what 
we used to suppose. If they are more complex in the sense that the 
properties they display are throughout so regular^ that the Selection 
of minute random variations is an unacceptable account of the origin 
of their diversity, yet by virtue of that very regularity the problem is 
limited in scope and thus simplified. 

To begin with, we must relegate Selection to its proper place. 
Selection permits the viable to continue and decides that the non- 
viable shall perish ; just as the temperature of our atmosphere 
decides that no liquid carbon shall be found on the face of the earth : 
but we do not suppose that the form of the diamond has been 
gradually achieved by a process of Selection. So again, as the 
course of descent branches in the successive generations. Selection 
determines along which branch Evolution shall proceed, but it does 
not decide what novelties that branch shall bring forth. "Zra Nature 
coutient Ic fonds de toutes ces varietes, mats le hazard ou I art les 
mettent en oeuvre," as Maupertuis most truly said. 

Not till knowledge of the genetic properties of organisms has 
attained to far greater completeness can evolutionary speculations 
have more than a suggestive value. By genetic experiment, cytology 
and physiological chemistry aiding, we may hope to acquire such 
knowledge. In 1872 Nathusius wrote- : "Das Gesetz der Vererbung 
ist noch nicht erkannt ; der Apfel ist noch niclit vom Baum der 
Erkcnntniss gefallen, welcher, der Sage nach, Newton auf den 

^ I have in view, for example, the marvellous and specific phenomena of regeneration, 
and those discovered by the students of " Entwicklungamechanik." The circumstances of 
its occurrence here preclude any suggestion that this regularity has been brought about by 
the workings of Selection. The attempts thus to represent the phenomena have resulted iu 
mere parodies of scientific reasoning. 

' Vortriige uber Viehzucht und Rasscnerkenntnisi, p. 120, Berlin, 1872. 

Sterility of Hybrids 97 

rechten Weg zur Ergriindiing der Gravitationsgesetze fiihrte." We 
cannot pretend that the words are not still true, but iu Mendeliau 
analysis the seeds of that apple-tree at last are sown. 

If we were asked what discovery would do most to forward our 
inquiry, what one bit of knowledge would more than any other 
illuminate the problem, I think we may give the answer without 
hesitation. The greatest advance that we can foresee will be made 
when it is found possible to connect the geometrical phenomena 
of development with the chemical. The geometrical symmetry of 
living things is the key to a knowledge of their regularity, and 
the forces which cause it In the synmietry of the dividing cell 
the basis of that resemblance we call Heredity is contained. To 
imitate the morphological phenomena of life we have to devise a 
system which can divide. It must be able to divide, and to segment 
as — gi'ossly — a vibrating plate or rod does, or as an icicle can do as it 
becomes ribbed in a continuous stream of water ; but with this dis- 
tinction, that the distribution of chemical differences and properties 
must simultaneously be decided and disposed in orderly relation to 
the pattern of the segmentation. Even if a model which would do 
this could be constructed it might prove to be a useful beginning. 

This may be looking too far ahead. If we had to choose some one 
piece of more proximate knowledge which we would more especially 
like to acquire, I suppose we should ask for the secret of interracial 
sterility. Nothing has yet been discovered to remove the grave 
diflBculty, by which Huxley in particular was so much oppressed, that 
among the many varieties produced under domestication — which we 
all regard as analogous to the species seen in nature — no clear case 
of interracial sterility has been demonstrated. The phenomenon is 
probably the only one to which the domesticated products seem to 
afford no parallel. No solution of the difficulty can be offered which 
has positive value, but it is perhaps worth considering the facts in 
the light of modern ideas. It should be observed that we are not 
discussing incompatibility of two species to produce offspring (a totally 
distinct phenomenon), but the sterility of the offspring which many 
of them do produce. 

When two species, both perfectly fertile severally, produce on 
crossing a sterile progeny, there is a presumption that the sterility 
ia due to the development in the hybrid of some substance which can 
only be formed by the meeting of two complementary factors. That 
some such account is correct in essence may be inferred from the 
well-known observation that if the hybrid is not totally sterile but 
only partially so, and thus is able to form some good germ-cells 
which develop inlo new individuals, the sLcrilily of these daughter- 
individuals is sensibly reduced or may be entirely absent. The 

D. 7 

98 Heredity mid Variation in Modern Lights 

fertility once re-established, the sterility does not return in the later 
progeny, a fact strongly suggestive of segi-egation. Now if the sterility 
of the cross-bred be really the consequence of the meeting of two 
complementary factors, we see that the phenomenon could only be 
produced among the divergent offspring of one species by the acquisi- 
tion of at least two new factors ; for if the acquisition of a single 
factor caused sterility the line would then end. Moreover each factor 
must be separately acquired by distinct individuals, for if both were 
present together, the possessors would by hypothesis be sterile. And 
in order to imitate the case of species each of these factors must be 
acquired by distinct breeds. Tlie factors need not, and probably would 
not, produce any other percei)tible effects ; they might, like the colour- 
factors present in white flowers, make no difference in the form or 
other characters. Not till the cross was actually made between the 
two complementary individuals would either factor come into play, 
and the effects even then might be unobserved until an attempt was 
made to breed from the cross-bred. 

Next, if the factors responsible for stei-ility were acquired, they 
would in all probability be peculiar to certain individuals and would 
not readily be distributed to the whole breed. Any member of the 
breed also into which both the factors were introduced would drop 
out of the pedigi'ee by virtue of its sterility. Hence the evidence 
that the various domesticated breeds say of dogs or fowls can when 
mated together produce fertile offspring, is beside the mark. The 
real question is. Do they ever produce sterile offspring ? I think the 
evidence is clearly that sometimes they do, oftener perhaps than is 
commonly supposed. These suggestions are quite amenable to ex- 
perimental tests. The most obvious way to begin is to get a pair of 
parents which are known to have had any sterile offspring, and to 
find the proportions in which these steriles were produced. If, as I 
anticipate, these proportions are found to be definite, the rest is 

In passing, certain other considerations may be referred to. First, 
that there are observations favouring the view that the production of 
totally sterile cross-breds is seldom a universal property of two species, 
and that it may be a matter of individuals, which is just what on the 
view here proposed would be expected. Moreover, as Ave all know 
now, though incompatibility may be dependent to some extent on 
the degree to which the species are dissimilar, no such principle can 
be demonstrated to determine sterility or fertility in general. For 
example, though all our Finches can breed together, the hybrids are 
all sterile. Of Ducks some species can breed together without pro- 
ducing the slightest sterility ; others have totally sterile offspring, and 
so on. The hybrids between several getiera of Orchids are perfectly 

Definite Variation 99 

fertile on the female side, and some on the male side also, but the 
hybrids produced between the Turnip (Brassica napns) and the 
Swede (Brassica campestris), which, according to our estimates of 
affinity, should be nearly allied forms, are totally sterile \ Lastly, it 
may be recalled that in sterility we are almost certainly considering a 
meristic phenomenon. Failure to divide is, we may feel fairly sure, 
the immediate " cause " of the sterility. Now, though we know very 
little about the heredity of meristic differences, all that we do know 
points to the conclusion that the less-divided is dominant to the 
more-divided, and we are thus justified in supposing that there are 
factors which can arrest or prevent cell-division. My conjecture 
therefore is that in the case of sterility of cross-breds we see the 
effect produced by a complementary pair of such factors. This and 
many similar problems are now open to our analysis. 

The question is sometimes asked. Do the new lights on Variation 
and Heredity make the process of Evolution easier to understand? 
On the whole the answer may be given that they do. There is some 
appearance of loss of simplicity, but the gain is real. As was said 
above, the time is not ripe for the discussion of the origin of species. 
With faith in Evolution unshaken — if indeed the word faith can be 
used in application to that which is certain — we look on the manner 
and causation of adapted differentiation as still wholly mysterious. 
As Samuel Butler so truly said : " To me it seems that the ' Origin of 
Variation,' whatever it is, is the only true 'Origin of Species'"^, and 
of that Origin not one of us knows anything. But given Variation — 
and it is given : assuming further that the variations are not guided 
into paths of adaptation — and both to the Darwinian and to the 
modern school this hypothesis appears to be sound if unproven — an 
evolution of species proceeding by definite steps is more, rather than 
less, easy to imagine than an evolution proceeding by the accumulation 
of indefinite and insensible steps. Those who have lost themselves in 
contemplating the miracles of Adaptation (whether real or spurious) 
have not unnaturally fixed their hopes rather on the indefinite than 
on the definite changes. Tlie reasons are obvious. By suggesting 
that the steps through which an adaptative mechanism arose were 
indefinite and insensible, all further trouble is spared. \Vhile it 
could be said that species arise by an insensible and imperceptible 
process of variation, there was clearly no use in tiring ourselves by 
trying to perceive that i)rocess. This labour-saving counsel found 
i^reat favour. All that had to be done to develop evolution-theory 
was to discover the good in everything, a task which, in the complete 
absence of any control or test whereby to check the truth of the 

' See Sutton, A. W., Journ. Linn. Soc. xxxviii. p. 341, 190S. 
» Life and Habit, T,nndon, p. 2G3, 1878. 

100 Heredity and Variation in Modern Lights 

discovery, is not very onerous. Tlie doctrine ^'que tout est au mieux" 
was therefore preached with fresh vigour, and examples of that 
illuminating principle were discovered with a facility that Pangloss 
himself might have envied, till at last even the spectators wearied of 
such dazzling performances. 

But in all seriousness, why should indefinite and unlimited 
variation have been regarded as a more probable account of the 
origin of Adaptation ? Only, I think, because the obstacle was shifted 
one plane back, and so looked rather less prominent. The abundance 
of Adaptation, we all grant, is an immense, almost an unsurpassable 
difficulty in all non-Lamarckian views of Evolution ; but if the steps 
by which that adaptation arose were fortuitous, to imagine them 
insensible is assuredly no help. In one most important respect 
indeed, as has often been observed, it is a multiplication of troubles. 
For the smaller the steps, the less could Natural Selection act 
upon theuL Definite variations — and of the occurrence of definite 
variations in abundance we have now the most convincing proof — 
have at least the obvious merit that they can make and often do 
make a real difterence in the chances of life. 

There is another aspect of the Adaptation problem to which I 
can only allude very briefly. May not our present ideas of the 
universality and precision of Adaptation be greatly exaggerated? 
The fit of organism to its environment is not after all so very close — 
a proposition unwelcome perhaps, but one which could be illustrated 
by very copious evidence. Natural Selection is stern, but she has 
her tolerant moods. 

We have now most certain and irrefragable proof that much 
definiteness exists in living things apart fi'om Selection, and also much 
that may very well have been preserved and so in a sense constituted 
by Selection. Here the matter is likely to rest. There is a passage 
in the sixth edition of the Origin which has I think been overlooked. 
On page 70 Darwin says " The tuft of hair on the breast of the wild 
turkey-cock cannot be of any use, and it is doubtful whether it can 
be ornamental in the eyes of the female bird." This tuft of hair is a 
most definite and unusual structure, and I am afraid that the remark 
that it "cannot be of any use" may have been made inadvertently; 
but it may have been intended, for in the first edition the usual 
qualification was given and must therefore have been deliberately 
excised. Anyhow I should like to think that Darwin did throw over 
that tuft of hair, and that he felt relief when he had done so. 
AVliether however we have his great authority for such a course or 
not, I feel quite sure that we shall be rightly interpreting the facts 
of nature if we cease to expect to find purposefulness wherever we 
meet with definite structures or patterns. Such things are, as often 

Definite Variation 101 

as not, I suspect rather of the nature of tool-marks, mere incidents 
of manufacture, benefiting their possessor not more than the wire- 
marks in a sheet of paper, or the ribbing on the bottom of an oriental 
plate renders those objects more attractive in our eyes. 

If Variation may be in any way definite, the question once more 
arises, may it not be definite in direction ? The belief that it is has 
had many supporters, from Lamarck onwards, who held that it was 
guided by need, and others who, like Nageli, while laying no emphasis 
on need, yet were convinced that there was guidance of some kind. 
The latter view under the name of "Orthogenesis," devised I believe 
by Eimer, at the present day commends itself to some naturalists. 
The objection to such a suggestion is of course that no fragment of 
real evidence can be produced in its support. On the other hand, 
with the experimental proof that variation consists largely in the 
unpacking and repacking of an original complexity, it is not so certain 
as we might like to think that the order of these events is not 
pre-determined. For instance the original "pack" may have been 
made in such a way that at the nth. division of the germ-cells of a 
Sweet Pea a colour-factor might be dropped, and that at the n + n' 
division the hooded variety be given off, and so on. I see no ground 
whatever for holding such a view, but in fairness the possibility should 
not be forgotten, and in the light of modern research it scarcely looks 
so absurdly improbable as before. 

No one can survey the work of recent years without perceiving 
that evolutionary orthodoxy developed too fast, and that a gi-eat deal 
has got to come down ; but this satisfaction at least remains, that in 
the experimental methods which Mendel inaugurated, we have 
means of reaching certainty in regard to the physiology of Heredity 
and Variation upon which a more lasting structure may be built. 



By Eduard Strasburger, 

Professor of Botany in the University of Bonn. 

Since 1875 an unexpected insight has been gained into the 
internal structure of cells. Those who are familiar with the results 
of investigations in this branch of Science are convinced that any 
modern theory of heredity must rest on a basis of cytology and 
cannot be at variance with cytological facts. Many histological 
discoveries, both such as have been proved correct and others which 
may be accepted as probably well founded, have acquired a funda- 
mental importance from the point of view of the problems of heredity. 

My aim is to describe the present position of our knowledge of 
Cytology. The account must be confined to essentials and cannot 
deal with far-reaching and controversial questions. In cases where 
difference of opinion exists, I adopt my own view for which I hold 
myself responsible. I hope to succeed in making myself intelligible 
even without the aid of illustrations : in order to convey to the 
uninitiated an adequate idea of the phenomena connected with the 
life of a cell, a greater number of figures would be required than 
could be included within the scope of this article. 

So long as the most eminent investigators^ believed that the 
nucleus of a cell was destroyed in the course of each division and 
that the nuclei of the daughter-cells were produced de novo, theories 
of heredity were able to dispense with the nucleus. If they sought, 
as did Charles Darwin, who showed a correct grasp of the problem 
in the enunciation of his Pangenesis hypothesis, for histological con- 
necting links, their hypotheses, or at least the best of them, had 
reference to the cell as a whole. It was known to Darwin that 
the cell multiplied by division and was derived from a similar pre- 
existing cell. Towards 1870 it was first demonstrated that cell-nuclei 
do not arise de novo, but are invariably the result of division of pre- 

^ As for example the illustrious Wilhelm Hofmeister in his Lehre von der Pjlunzenzelle 

Nuclear Division 103 

existing nuclei. Better methods of investigation rendered possible 
a deeper insight into the phenomena accompanying cell and nuclear 
divisions and at the same time disclosed the existence of remarkable 
structures. The work of 0. Biitschli, O. Hertwig, W. Flemming, 
H. Fol and of the author of this article \ have furnished conclusive 
evidence in favour of these facts. It was found that when the 
reticular framework of a nucleus prepares to divide, it separates into 
single segments. These then become thicker and denser, taking up 
with avidity certain stains, Avhich are used as aids to investigation, 
and finally form longer or shorter, variously bent, rodlets of uniform 
thickness. In these organs which, on account of their special 
property of absorbing certain stains, were styled Chromosomes^ 
there may usually be recognised a separation into thicker and thinner 
discs ; the former are often termed Chromomeres^. In the course 
of division of the nucleus, the single rows of chromomeres in the 
chromosomes are doubled and this produces a band-like flattening 
and leads to the longitudinal splitting by which each chromosome 
is divided into two exactly equal halves. The nuclear membrane 
then disappears and fibrillar cell-plasma or cytoplasm invades the 
nuclear area. In animal cells these fibrillae in the cytoplasm centre 
on definite bodies*, which it is customary to speak of as Centro- 
somes. Radiating lines in the adjacent cell-plasma suggest that these 
bodies constitute centres of force. The cells of the higher plants 
do not possess such individualised centres ; they have probably 
disappeared in the course of phylogenetic development : in spite 
of this, however, in the nuclear division-figures the fibrillae of the 
cell-plasma are seen to radiate from two opposite poles. In both 
animal and plant cells a fibrillar bipolar spindle is formed, the fibrillae 
of which grasp the longitudinally divided chromosomes from two 
opposite sides and arrange them on the equatorial plane of the 
spindle as the so-called nuclear or equatorial plate. Each half- 
chromosome is connected with one of the spindle poles only and is 
then drawn towards that pole^ 

The formation of the daughter-nuclei is then effected. The 
changes which the daughter-chromosomes undergo in the process 
of producing tlie daughter-nuclei repeat in the reverse order the 
changes which they went through in the course of their pro- 

' For further reference to literature, Bee my article on " Die Ontogenie der Zelle aeit 
1875," in the Progrestm Rei Botanicae, Vol. i. p. 1, Jena, 1907. 

* By W. Waldeyer in 1888. 

» DiBCovered by W. Pfitzn-r iu 1880. 

* Their eiiatcnce and tbcir multiplication by fission were demonstrated by E. van 
Beneden and Th. Boveri in 1887. 

* These important factrf, suspected by W. FlemminR in 1882, were demonstrated by 
E. Heaser, L. Ouignard, E. van Beneden, M. Nusobaum, and C. liabl. 

104 Cell Structure in Relation to Heredity 

gressive differentiation from the mother-nucleus. The division of 
the cell-body is completed midway between the two daughter-nuclei. 
In animal cells, which possess no chemically differentiated membrane, 
separation is effected by simple constriction, while in the case of 
plant cells provided with a definite wall, the process begins with the 
iormation of a cytoplasmic separating layer. 

The phenomena observed in the course of the division of the 
nucleus show beyond doubt that an exact halving of its substance is 
of the greatest importance ^ Compared with the method of division 
of the nucleus, that of the cytoplasm appears to be very simple. 
This led to the conception that the cell-nucleus must be the chief if 
not the sole carrier of hereditary characters in the organism. It is 
for this reason that the detailed investigation of fertilisation phe- 
nomena immediately followed researches into the nucleus. The 
fundamental discovery of the union of two nuclei in the sexual 
act was then made^ and this afforded a new support for the correct 
conception of the nuclear functions. The minute study of the 
behaviour of the other constituents of sexual cells during fertilisation 
led to the result, that the nucleus alone is concerned with handing 
on hereditary characters^ fi'om one generation to another. Especially 
important, fi'om the point of view of this conclusion, is the study of 
fertilisation in Angiosperms (Flowering plants); in these plants the 
male sexual cells lose their cell-body in the pollen-tube and the 
nucleus only — the sperm-nucleus — reaches the egg. The cytoplasm 
of the male sexual cell is therefore not necessary to ensure a trans- 
ference of hereditary characters from parents to offspring. I lay stress 
on the case of the Angiosperms because researches recently repeated 
with the help of the latest methods failed to obtain different results. 
As regards the descendants of angiospermous plants, the same laws 
of heredity hold good as for other sexually differentiated organisms ; 
we may, therefore, extend to the latter what the Angiosperms so 
clearly teach us. 

The next advance in the hitherto rapid progress in our know- 
ledge of nuclear division was delayed, because it was not at once 
recognised that there are two absolutely different methods of nuclear 
division. All such nuclear divisions were united under the head of 
indirect or mitotic divisions ; these were also spoken of as karyo- 
kinesis, and were distinguished from the direct or amitotic divisions 
which are characterised by a simple constriction of the nuclear body. 
So long as the two kinds of indirect nuclear division were not clearly 

' First shown by W. Eoux in 1883. 
' By 0. Hertwig in 1875. 

' Thig was done by 0. Hertwig and the author of this essay simultaneously in 

Homotypic Nuclear Division 105 

distinguished, their correct interpretation was impossible. This was 
accomplished after long and laborious research, which has recently 
been carried out and with results which should, perhaps, be regarded 
as provisional. 

Soon after the new study of the nucleus began, investigators 
were struck by the fact that the course of nuclear division in the 
mother-cells, or more correctly in the grandmother-cells, of spores, 
pollen-grains, and embryo-sacs of the more highly organised plants 
and in the spermatozoids and eggs of the higher animals, exhibits 
similar phenomena, distinct from those which occur in the somatic 

In the nuclei of all those cells which we may group together as 
gonotokonts^ (i.e. cells concerned in reproduction) there are fewer 
chromosomes than in the adjacent body-cells (somatic cells). It was 
noticed also that there is a peculiarity characteristic of the gono- 
tokonts, namely the occurrence of two nuclear divisions rapidly 
succeeding one another. It was afterwards recognised that in the 
first stage of nuclear division in the gonotokonts the chromosomes 
unite in pairs : it is these chromosome-pairs, and not the two longi- 
tudinal halves of single chromosomes, which form the nuclear plate 
in the equatorial plane of the nuclear spindle. It has been proposed 
to call these pairs gemini^. In the course of this division the spindle- 
fibrillae attach themselves to the gemini, i.e. to entire chromosomes 
and direct them to the points where the new daughter-nuclei are 
formed, that is to those positions towards which the longitudinal 
halves of the chromosomes travel in ordinary nuclear divisions. It is 
clear that in this way the number of chromosomes which the daughter- 
nuclei contain, as the result of the first stage in division in the 
gonotokonts, will be reduced by one half, while in ordinary divisions 
the number of chromosomes always remains the same. The first 
stage in the division of the nucleus in the gonotokonts has therefore 
been termed the reduction division ^ This stage in division deter- 
mines the conditions for the second division which rapidly ensues. 
Each of the paired chromosomes of the mother-nucleus has already, 
as in an ordinary nuclear division, completed the longitudinal fission, 
but in this case it is not succeeded by the immediate separation of 
the longitudinal halves and their allotment to diflerent nuclei. Each 
chromosome, therefore, takes its two longitudinal halves into the 
same daughter-nucleus. Thus, in each daughter-nucleus the longi- 
tudinal halves of the chromosomes are present ready for the next 

' At the anggeetion of J. P. Lotny in 1904. 

^ J. E. 8. Mooro and A. L. EmbletoD, Froc. Roy. Soc. London, Vol. lxzvii. p. 665, 1CJ6; 
V. Or6goiro, 1907. 

» In 18b7 W. Flcmming termed thiB the heterotypic form of nuclear diviflion. 

106 Cell Structure in Helation to Heredity 

stage in the division ; they only require to be arranged in the 
nuclear plate and then distributed among the granddaughter-nuclei. 
This method of division, which takes place with chromosomes already 
split, and which have only to provide for the distribution of their 
longitudinal halves to the next nuclear generation, has been called 
homotypic nuclear di vision \ 

Reduction division and homotypic nuclear division are included 
together under the term allotypic nuclear division and are dis- 
tinguished from the ordinary or typical nuclear division. The 
name Meiosis- has also been proposed for these two allotypic nuclear 
divisions. The typical divisions are often spoken of as somatic. 

Observers who were actively engaged in this branch of recent 
histological research soon noticed that the chromosomes of a given 
organism are differentiated in definite numbers from the nuclear 
network in the course of division. This is especially striking in the 
gonotokonts, but it applies also to the somatic tissues. In the latter, 
one usually finds twice as many chromosomes as in the gonotokonts. 
Thus the conclusion was gradually reached that the doubling of 
chromosomes, which necessarily accompanies fertilisation, is main- 
tained in the product of fertilisation, to be again reduced to one half 
in the gonotokonts at the stage of reduction-division. This enabled 
us to form a conception as to the essence of true alternation of 
generations, in which generations containing single and double 
chromosomes alternate with one another. 

The single-chromosome generation, which I will call the lia^yloid, 
must have been the primitive generation in all organisms ; it might 
also persist as the only generation. Every sexual differentiation 
in organisms, which occurred in the course of phylogenetic develop- 
ment, was followed by fertilisation and therefore by the creation of a 
diploid or double-chromosome product. So long as the germina- 
tion of the product of fertilisation, the zygote, began with a reducing 
j)roccss, a special diploid generation was not represented. This, 
however, appeared later as a product of the further evolution of the 
zygote, and the reduction division was correspondingly postponed. 
In animals, as in plants, the diploid generation attained the higher 
development and gradually assumed the dominant position. The 
haploid generation suffered a proportional reduction, until it finally 
ceased to have an independent existence and became restricted 
to the role of producing the sexual products within the body 
of the diploid generation. Those who do not possess the necessary 
special knowledge are unable to realise what remains of the first 

' The name was proposed by W. Flemming in 1887 ; the nature of thia type of 
division wan, however, not explained until later. 

* By J. Bretland Famier and J. E. S. Moore in 1905. 

Nuclei as Carriers of Hereditary Characters 107 

haploid generation in a phanerogamic plant or in a vertebrate 
animal. In Angiosperms this is actually represented only by the 
short developmental stages which extend from the pollen mother- 
cells to the sperm-nucleus of the pollen-tube, and from the embryo- 
sac mother-cell to the egg and the endosperm tissue. The embryo- 
sac remains enclosed in the diploid ovule, and within this from the 
fertilised egg is formed the embryo which introduces the new diploid 
generation. On the full development of the diploid embryo of the 
next generation, the diploid ovule of the preceding diploid genera- 
tion is separated from the latter as a ripe seed. The uninitiated 
sees in the more highly organised plants only a succession of diploid 
generations. Similarly all the higher animals appear to us as in- 
dependent organisms with diploid nuclei only. The haploid genera- 
tion is confined in them to the cells produced as the result of the 
reduction division of the gonotokonts ; the development of these 
is completed with the homotypic stage of division which succeeds the 
reduction division and produces the sexual products. 

The constancy of the numbers in which the chromosomes 
separate themselves from the nuclear network during division gave 
rise to the conception that, in a certain degree, chromosomes possess 
individuality. Indeed the most careful investigations^ have shown 
that the segments of the nuclear network, wliich separate from one 
another and condense so as to produce chromosomes for a new 
division, correspond to the segments produced from the chromo- 
somes of the preceding division. The behaviour of such nuclei as 
possess chromosomes of unequal size affords confirmatory evidence 
of the permanence of individual chromosomes in corresponding 
sections of an apparently uniform nuclear network. Moreover at 
each stage in division chromosomes with the same differences in size 
reappear. Other cases are known in which thicker portions occur in 
the substance of the resting nucleus, and these agree in number 
with the chromosomes. In this network, therefore, the individual 
chromosomes must have retained their original position. But the 
chromosomes cannot be regarded as the ultimate hereditary units in 
the nuclei, as their number is too small. Moreover, related species 
not infrequently show a difference in the number of their chromo- 
somes, whereas the number of hereditary units must approximately 
agree. We thus picture to ourselves the carriers of hereditary 
characters as enclosed in the chromosomes ; the transmitted fixed 
number of chromosomes is for us only the visible expression of the 
conception that the number of hereditary units which the chromo- 
somes carry must be also constant. The ultimate hereditary unit« 

* Particulurly those of V. Ordgoire and his pupils. 

108 Cell Structure in Relation to Heredity 

may, like the chromosomes themselves, retain a definite position 
in the resting nucleus. Further, it may be assumed that during 
the separation of the chromosomes from one another and during 
their assumption of the rod-like form, the hereditary units become 
aggregated in the chromomeres and that these are characterised 
by a constant order of succession. The hereditary units then grow, 
divide into two and are uniformly distributed by the fission of the 
chromosomes between their longitudinal halves. 

As the contraction and rod-like separation of the chromosomes 
serve to insure the transmission of all hereditary units in the pro- 
ducts of division of a nucleus, so, on the other hand, the reticular 
distension of each chromosome in the so-called resting nucleus may 
effect a separation of the carriers of hereditary units from each 
other and facilitate the specific activity of each of them. 

In the stages preliminary to their division, the chromosomes 
become denser and take up a substance which increases their 
staining capacity ; this is called chromatin. This substance collects 
in the chromomeres and may form the nutritive material for the 
carriers of hereditary units which we now believe to be enclosed in 
them. The chromatin cannot itself be the hereditary substance, as 
it afterwards leaves the chromosomes, and the amount of it is sub- 
ject to considerable variation in the nucleus, according to its stage 
of development. Conjointly with the materials which take part in 
the formation of the nuclear spindle and other processes in the 
cell, the chromatin accumidates in the resting nucleus to form the 

Naturally connected with the conclusion that the nuclei are 
the carriers of hereditary characters in the organism, is the question 
whether enucleate organisms can also exist. Phylogenetic considera- 
tions give an affirmative answer to this question. The diffierentia- 
tion into nucleus and cytoplasm represents a division of labour in 
the protoplast. A study of organisms which belong to the lowest 
class of the organic world teaches us how this was accomplished. 
Instead of well-defined nuclei, scattered granules have been described 
in the protoplasm of several of these organisms \ characterised by 
the same reactions as nuclear material, provided also with a nuclear 
network, but without a limiting membrane*. Thus the carriers 
of hereditary characters may originally have been distributed in 
tlie common protoplasm, afterwards coming together and eventually 
assuming a definite form as special organs of the cell. It may be also 
assumed that in tlie protoplasm and in the primitive types of nucleus, 

' Bacteria, Cyanophyceae, Protozoa. 

* This is the result of the work of R. Hertwig and of the most recently publiehed 

Chromosome Pairs 109 

the carriers of the same hereditary unit were represented in consider- 
able quantity ; they became gradually differentiated to an extent 
commensurate with newly acquired characters. It was also neces- 
sary that, in proportion as this happened, the mechanism of nuclear 
division must be refined. At first processes resembling a simple con- 
striction would suffice to provide for the distribution of all hereditary 
units to each of the products of division, but eventually in both 
organic kingdoms nuclear division, which alone insured the quali- 
tative identity of the products of division, became a more marked 
feature in the course of cell-multiplication. 

Where direct nuclear division occurs by constriction in the 
higher organisms, it does not result in the halving of hereditary 
units. So far as my observations go, direct nuclear division occurs 
in the more highly organised plants only in cells which have lost 
their specific functions. Such cells are no longer capable of specific 
reproduction. An interesting case in this connection is afibrded by 
the interuodal cells of the Characeae, which possess only vegetative 
functions. These cells grow vigorously and their cytoplasm increases, 
their growth being accompanied by a correspondingly direct multipli- 
cation of the nuclei. They serve chiefly to nourish the plant, but, 
unlike the other cells, they are incapable of producing any oftspring. 
This is a very instructive case, because it clearly shows that the 
nuclei are not only carriers of hereditary characters, but that they 
also play a definite part in the metabolism of the protoplasts. 

Attention was drawn to the fact that during the reducing 
division of nuclei which contain chromosomes of unequal size, 
gemini arc constantly produced by the pairing of chromosomes of 
the same size. This led to the conclusion that the pairing chromo- 
somes are homologous, and that one comes from the father, the other 
from the mother ^ This evidently applies also to the pairing of 
cliromosomes in those reduction-divisions in which diflerences in 
size do not enable us to distinguish the individual chromosomes. In 
this case also each pair would be formed by two homologous chro- 
mosomes, the one of paternal, the other of maternal origin. When 
the separation of these chromosomes and their distribution to both 
daughter-nuclei occur a chromosome of each kind is provided for each 
of these nuclei. It would seem that the components of each pair 
might pass to either pole of the nuclear spindle, so that the paternal 
and maternal chromosomes would be distributed in varying pro- 
portion between the daughter-nuclei ; and it is not impossible that 
one daughter-nucleus might occasionally contain paternal chromo- 
somes only and its sister-nucleus exclusively maternal chromosomes. 

1 First stated by T. H. Montgomery in liiUl and by W. b. Button in 1902. 

110 Cell Structure in Relation to Heredity 

The fact that in nuclei containing chromosomes of various sizes, 
the chromosomes which pair together in reduction-division are always 
of equal size, constitutes a further and more important proof of their 
qualitative difference. This is supported also by ingenious experi- 
ments which led to an unequal distribution of chromosomes in the 
products of division of a sea-urchin's egg, with the result that a 
difference was induced in their further developments 

The recently discovered fact that in diploid nuclei the chromo- 
somes are arranged in pairs affords additional evidence in favour of 
the unequal value of the chromosomes. This is still more striking in 
the case of chromosomes of different sizes. It has been shown that 
in the first division-figure in the nucleus of the fertilised egg the 
chromosomes of corresponding size form pairs. They appear with 
this arrangement in all subsequent nuclear divisions in the diploid 
generation. The longitudinal fissions of the chromosomes provide 
for the unaltered preservation of this condition. In the reduction 
nucleus of the gonotokouts the homologous chromosomes being near 
together need not seek out one another ; they are ready to form 
gemini. The next stage is their separation to the haploid daughter- 
nuclei, which have resulted from the reduction process. 

Peculiar phenomena in the reduction nucleus accompany the 
formation of gemini in both organic kingdoms^. Probably for the 
purpose of entering into most intimate relation, the pairs are 
stretched to long threads in which the chromomeres come to lie 
opposite one another ^ It seems probable that these are homo- 
logous chromomeres, and that the pairs afterwards unite for a short 
time, so that an exchange of hereditary units is rendered possible*. 
This cannot be actually seen, but certain facts of heredity point 
to the conclusion that this occurs. It follows from these phenomena 
that any exchange which may be effected must be one of homologous 
carriers of hereditary units only. These units continue to form 
exchangeable segments after they have undergone unequal changes ; 
they then constitute allelotropic pairs. We may thus calculate what 
sum of possible combinations the exchange of homologous hereditary 
units between the pairing chromosomes provides for before the 
reduction division and the subsequent distribution of paternal and 
maternal chromosomes in the haploid daughter-nuclei. These nuclei 
then transmit their characters to the sexual cells, the conjugation of 

' Demonstrated by Th. Boveri in 1902. 

' This has been shown more particularly by the work of L. Guignard, M. Mottier, 
J. B. Farmer, C. B. Wilson, V. Hacker and more recently by V. Gr6goire and his 
pupil C. A. Allen, by the researches conducted in the Bonn Botanical Institute, and by 
A. and K. E. Schreiner. 

» C. A. Allen, A. and K. E. Schreiner, and Strasbuiger. 
' * H. de Vries and Strasburger. 

Pangenesis 111 

which in fertilization again produces the most varied combinations \ 
In this way all the cooperations which the carriers of hereditary 
characters are capable of in a species are produced ; this must give 
it an appreciable advantage in the struggle for life. 

The admirers of Charles Darwin must deeply regret that he did 
not live to see the results achieved by the new Cytology. ^Vhat 
service would they have been to him in the presentation of his 
hypothesis of Pangenesis ; what an outlook into the future would 
they have given to his active mind ! 

The Darwinian hypothesis of Pangenesis rests on the conception 
that all inheritable properties are represented in the cells by small 
invisible particles or gemnniles and that these gemmules increase by 
division. Cytology began to develop on new lines some years after 
the publication in 1868 of Charles Darwin's Provisional hypothesis 
of Pangenesis-, and when he died in 1882 it was still in its infancy. 
Darwin would have soon suggested the substitution of the nuclei 
for his gemmules. At least the great majority of present-day 
investigators in the domain of cytology have been led to the con- 
clusion that the nucleus is the carrier of hereditary characters, and 
they also believe that hereditary characters are represented in the 
nucleus as distinct units. Such would be DarAvin's gemmules, which in 
conformity with the name of his hypothesis may be called pangens^ : 
these pangens multiply by division. All recently adopted views may 
be thus linked on to this part of Darwin's hypothesis. It is otherwise 
with Darwin's conception to which Pangenesis owes its name, namely 
the view that all cells continually give off gemmules, which migrate 
to other places in the organism, where they unite to form repro- 
ductive cells. "NVhen Darwin foresaw this possibility, the continuity 
of the germinal substance was still unkno^vn*, a fact which excludes 
a transference of gemmules. 

But even Charles Darwin's genius was confined within finite 
boundaries by the state of science in his day. 

It is not my province to deal with other theories of development 
which followed from Darwin's Pangenesis, or to discuss their histo- 
logical probabilities. We can, however, affirm that Charles Darwin's 
idea that invisible gemmules are the carriers of hereditary characters 
and that they multiply by division has been removed from the 
position of a provisional hypothesis to that of a well-founded theory. 
It is suj)ported by histology, and the results of experimental work in 
heredity, which arc now assuming extraordinary prominence, are in 
close agreement with it. 

' A. Weinniann gave the impulKe to these ideas in his theory on Amphimixis. 

' Animals and Plant* under Domestication, London, 1808, Chapter xxvii. 

" So called by H. do Vries in 18H9. 

* Demonstrated by Nu.s.-.baum in 1880, by Sachs in 1882, and by Weismnun in 1885. 


By G. Schwalbe. 

Professor of Anatomy in the University of Strasshurg. 

The problem of the origin of the human race, of the descent of 
man, is ranked by Huxley in his epoch-making book Man's Place in 
Nature, as the deepest with which biology has to concern itself, " the 
question of questions," — the problem which underlies all others. In 
the same brilliant and lucid exposition, which appeared in 1863, soon 
after the publication of Darwin's Origin of Species, Huxley stated his 
own views in regard to this great problem. He tells us how the idea 
of a natural descent of man gradually grew up in his mind. It was 
especially the assertions of Owen in regard to the total difference 
between the human and the simian brain that called forth strong 
dissent from the great anatomist Huxley, and he easily succeeded in 
showing that Owen's supposed differences had no real existence ; he 
even established, on the basis of his own anatomical investigations, 
the proposition that the anatomical differences between the Marmoset 
and the Chimpanzee are much greater than those between the 
Chimpanzee and Man. 

But why do we thus introduce the study of Darwin's Descent of 
Man, which is to occupy us here, by insisting on the fact that Huxley 
had taken the field in defence of the descent of man in 1863, while 
Darwin's book on the subject did not appear till 1871? It is in order 
that we may clearly understand how it happened that from this time 
onwards Darwin and Huxley followed the same great aim in the most 
intimate association. 

Huxley and Darwin working at the same Prohlema maximuml 
Huxley fiery, impetuous, eager for battle, contemptuous of the 
resistance of a dull world, or energetically triumphing over it. Darwin 
calm, weighing every problem slowly, letting it mature thoroughly, — 
not a fighter, yet having the gi-eater and more lasting influence by virtue 
of his immense mass of critically sifted proofs. Darwin's friend, Huxley, 
was the first to do him justice, to understand his nature, and to find 
in it the reason why the detailed and carefully considered book 

''The Origin of Species'' ' 113 

on the descent of man made its appearance so late. Huxley, always 
generous, never thought of claiming priority for himself. In enthu- 
siastic language he tells how Darwin's immortal work, The Origin 
of Species, first shed light for him on the problem of the descent of 
man ; the recognition of a vera causa in the transformation of species 
illuminated his thoughts as with a flash. He was now content to 
leave what perplexed him, what he could not yet solve, as he says 
himself, "in the mighty hands of Darwin." Happy in the bustle of 
strife against old and deep-rooted prejudices, against intolerance and 
superstition, he wielded his sharp weapons on Darwin's behalf; Avearing 
Darwin's armour he joyously overthrew adversary after adversary. 
Darwin spoke of Huxley as his "general agent \" Huxley says of 
himself "I am Darwin's bulldog^." 

Thus Huxley openly acknowledged that it was Darwin's Origin of 
Species that first set the problem of the descent of man in its true 
light, that made the question of the origin of the human race a 
I)ressing one. That this was the logical consequence of his book 
Darwin himself had long felt. He had been reproached with inten- 
tionally shirking the application of his theory to Man. Let us hear 
what he says on this point in his autobiography : " As soon as I had 
become, in the year 1837 or 1838, convinced that species were mutable 
productions, I could not avoid the belief that man must come under 
the same law. Accordingly I collected notes on the subject for my oAvn 
satisfaction, and not for a long time with any intention of publishing. 
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 slwuld accuse me of concealing my views^, to add 
that by the work * light would be throAvn on the origin of man and his 
history.' It would have been useless and injurious to the success of 
tlie book to have paraded, without giving any evidence, my conviction 
with respect to his origin*." 

In a letter written in January, 18G0, to the Rev. Ij. Blomefield, 
Darwin expresses himself in similar terms. " With respect to man, I 
am very far from wishing to obtrude my belief; but I thought it 
dishonest to quite conceal my opinion\" 

The brief allusion in the Origin of Species is so far from prominent 
and so incidental that it was excusable to assume that Darwin had not 
touched upon the descent of man in this work. It was solely the 
desire to have his mass of evidence sufficiently complete, solely 

' lAfe ami T.etteTt of Thomas Henry Huxley, Vol. i. p. 171, London, 1900. 
» Ibid. p. 363. 

* No italics in original. 

* Liff and Letlfm of CharUi Darwin, Vol. I. p. 93. 

* Ibid. Vol. 11. p. 2G3. 

D. 8 

114 ' '' The Descent of Man'' 

Darwin's great characteristic of never publishing till he had carefully 
weighed all aspects of his subject for years, solely, in short, his most 
fastidious scientific conscience that restrained him from challenging 
the world in 1859 with a book in which the theory of the descent 
of man was fully set forth. Three years, frequently interrupted 
by ill-health, were needed for the actual writing of the book^: the 
first edition, which appeared in 1871, was followed in 1874 by a much 
improved second edition, the preparation of which he very reluctantly 

This, briefly, is the history of the work, which, with the Origin 
of Species, marks an epoch in the history of biological sciences — the 
work with which the cautious, peace-loving investigator ventured 
forth fi-om his contemplative life into the arena of strife and unrest, 
and laid himself open to all the annoyances that deep-rooted belief 
and prejudice, and the prevailing tendency of scientific thought at 
the time could devise. 

Darwin did not take this step lightly. Of great interest in this 
connection is a letter written to Wallace on Dec. 22, 1857^ in which 
he says, " You ask whether I shall discuss ' man.' I think I shall avoid 
the whole subject, as so surrounded with prejudices; though I fully 
admit that it is the highest and most interesting problem for the 
naturalist." But his conscientiousness compelled him to state briefly 
his opinion on the subject in the Origin of Species in 1859. Never- 
theless he did not escape reproaches for having been so reticent. 
This is unmistakably apparent from a letter to Fritz Miiller dated 
Feb. 22 [1809?], in which he says: "I am thinking of writing a little 
essay on the Origin of Mankind, as I have been taunted with con- 
cealing my opinions*." 

It might be thought that Darwin behaved thus hesitatingly, and 
was so slow in deciding on the full publication of his collected 
material in regard to the descent of man, because he had religious 
difiiculties to overcome. 

But this was not the case, as we can see from his admirable 
confession of faith, the publication of which Ave owe to his son 
Francis ^ Whoever wishes really to understand the lofty character 
of this great man should read these immortal lines in which he unfolds 
to us in simple and straightforward words the development of his 
conception of the universe. He describes how, though he was still 
quite orthodox during his voyage round the world on board the 
Beagle, he came gradually to see, shortly afterwards (1836— -1839) 
that the Old Testament was no more to be trusted than the Sacred 

J Life and Letters, Vol. i. p. <J4. 2 Ibid. Vol. in. p. 175. 

» Ibid. Vol. II. p. 109. ■• Ibid. Vol. ni. p. 112. 

» Ibid. Vol. I. pp. 304—317. 

Sexual Selection 115 

Books of the Hindoos; the miracles by which Christianity is sup- 
ported, the discrepancies between the accounts in the different 
Gospels, gi'adually led him to disbelieve in Christianity as a divine 
revelation. "Thus," he writes \ "disbelief crept over me at a very 
slow rate, but was at last complete. The rate was so slow that I felt 
no distress." But Darwin was too modest to presume to go beyond 
the limits laid down by science. He wanted nothing more than to be 
able to go, freely and unhampered by belief in authority or in the 
Bible, as far as human knowledge could lead him. We learn this 
from the concluding words of his chapter on religion : " The mystery 
of the beginning of all things is insoluble by us; and I for one must 
be content to remain an Agnostic-." 

Darwin was always very unwilling to give publicity to his views in 
regard to religion. In a letter to Asa Gray on INIay 22, 1860^, he 
declares that it is always painful to him to have to enter into 
discussion of religious problems. He had, he said, no intention of 
writing atheistical 1 v. 

Finally, let us cite one characteristic sentence from a letter from 
Darwin to C. Ridley* (Nov. 28, 1878). A clergyman, Dr Pusey, had 
asserted that Darwin had written the Origin of S2yecies with some 
relation to theology. Darwin writes emphatically, " Many years ago, 
when I was collecting facts for the 'Origin,' my belief in what is 
called a personal God was as firm as that of Dr Pusey himself, and 
as to the eternity of matter I never troubled myself about such 
insoluble questions." The expression "many years ago" refers to 
the time of his voyage round the Avorld, as has already been pointed 
out. Darwin means by this utterance that the views which had 
gradually developed in his mind in regard to the origin of species 
were quite compatible with the faith of the Church. 

If we consider all these utterances of Darwin in regard to religion 
and to his outlook on life (Weltanschauung), we shall see at least so 
much, that religious reflection could in no way have influenced him 
in regard to the writing and publishing of his book on The Descent 
of Alan. Darwin had early won for himself freedom of thought, and 
to this freedom he remained true to the end of his life, uninfluenced 
by the customs and opinions of the world around him. 

Darwin Mas thus inwardly fortified and armed against the host of 
calumnies, accusations, and attacks called forth by the publication of 
the Origin of Species, and to an even greater extent by the appearance 
of the Descent of Man. But in his defence he could rely on the aid 
of a band of distinguished auxiliaries of the rarest ability. His 

" Life and Lettert, Vol. i. y. 309. * Loc. cit. p. 313. » IbiA. Vol. ii. p. 310. 

* Ibid. Vol. III. p. 236. ["C. Ridley," Mr Iruncia Daisvin points out to me, should be 
U. N. Uidlt-y. A.C.S.] 


116 '' The Descent of Man" 

faithful confederate, Huxley, was joined by the botanist Hooker, and, 
after longer resistance, by the famous geologist Lyell, whose 
"conversion" aiforded Darwin peculiar satisfaction. All three took 
the field with enthusiasm in defence of the natural descent of man. 
From Walhice, on the other hand, though he shared vAih him the 
idea of natural selection, Darwin got no support in this matter. 
Wallace expressed himself in a strange manner. He admitted every- 
thing in regard to the morphological descent of man, but maintained, 
in a mystic way, that something else, something of a spiritual nature 
nmst have been added to what man inherited from his animal 
ancestors. Darwin, whose esteem for Wallace was extraordinarily 
high, could not understand how he could give utterance to such a 
mystical view in regard to man; the idea seemed to him so " incredibly 
strange " that he thought some one else must have added these 
sentences to Wallace's paper. 

Even now there are thinkers who, like Wallace, shrink from 
applying to man the ultimate consequences of the theory of descent. 
The idea that man is derived from ape-like forms is to them un- 
pleasant and humiliating. 

So far I have been depicting the development of Darwin's work 
on the descent of man. In what follows I shall endeavour to give a 
condensed survey of the contents of the book. 

It must at once be said that the contents of Darwin's work fall 
into two parts, dealing with entirely diflferent subjects. The Descent 
of Man includes a very detailed investigation in regard to secondary 
sexual characters in the animal series, and on this investigation 
Darwin founded a new theory, that of sexual selection. With as- 
tonishing patience he gathered together an immense mass of material, 
and showed, in regard to Arthropods and Vertebrates, the wide 
distribution of secondary characters, which develop almost exclusively 
in the male, and which enable him, on the one hand, to get the better 
of his rivals in the struggle for the female by the greater perfection of 
his weapons, and, on the other hand, to offer greater allurements to 
the female through the higher development of decorative characters, 
of song, or of scent-producing glands. The best equipped males will 
thus crowd out the less well-equipped in the matter of reproduction, 
and thus the relevant characters will be increased and perfected 
through sexual selection. It is, of course, a necessary assumption 
that these secondary sexual characters may be transmitted to the 
female, although perhaps in rudimentary form. 

As we have said, this theory of sexual selection takes up a gi-eat 
deal of space in Darwin's book, and it need only be considered here 
in 80 far as Darwin applied it to the descent of man. To this latter 
problem the whole of Part I is devoted, while Part III contains a 

Man and the Lower Animals 117 

discussion of sexual selection in relation to man, and a general 
summary. Part II treats of sexual selection in general, and may be 
disregarded in our present study. Moreover, many interesting details 
must necessarily be passed over in what follows, for want of space. 

The first part of the Descent of Man begins with an enumeration 
of the proofs of the animal descent of man taken from the structure 
of the human body. Darwin chiefly emphasises the fact that the 
Imman body consists of the same organs and of the same tissues as 
those of the other mammals ; he shows also that man is subject to the 
same diseases and tormented by the same parasites as the apes. He 
further dwells on the general agreement exhibited by young, em- 
bryonic forms, and he illustrates this by two figures placed one 
above the other, one representing a human embryo, after Ecker, the 
other a dog embryo, after Bischofl'^ 

Darwin finds further proofs of the animal origin of man in the 
reduced structures, in themselves extremely variable, which are 
either absolutely useless to their possessors, or of so little use that 
they could never have developed under existing conditions. Of such 
vestiges he enumerates : the defective development of the panniculus 
carnosus (muscle of the skin) so widely distributed among mammals, 
the ear-muscles, the occasional persistence of the animal ear-point in 
man, the rudimentary nictitating membrane {plica semilunaris) in 
the human eye, the slight development of the organ of smell, the 
general hairiness of the human body, the frequently defective develop- 
ment or entire absence of the third molar (the Avisdom tooth), the 
vermiform appendix, the occasional reappearance of a bony canal 
{foramen supraconihjloidcum) at the lower end of the humerus, the 
rudimentary tail of man (the so-called taillessness), and so on. Of 
these rudimentary structures the occasional occurrence of the animal 
ear-point in man is most fully discussed. Darwin's attention was 
called to this interesting structure by the sculptor Woolner. He 
figures such a case observed in man, and also the head of an 
alleged orang-foetus, the photogi-aph of which he received from 

Darwin's interpretation of Woolner's case as having arisen through 
a folding over of the free edge of a pointed ear has been fully borne 
out by my investigations on the external ear-. In particular, it was 
established by these investigations that the human foetus, about the 
middle of its embryonic life, possesses a pointed car somewhat 
siiiiihir to that of the monkey genus Macacus. One of Darwin's 
statements in regard to the head of the orang-foetus must be 

» Deicent of Man (Popular Edit., 1901), fip. 1, p. 14. 

"^ G. Schwalbe, " Das DarwinVche Spitzohr beim menschlichen Embryo," Anatom. 
Anzeiger, 1889, pp. 176—189, and other papers. 

118 " The Descent of Man'* 

corrected. A large ear with a point is shown in the photograph \ 
but it can easily be demonstrated — and Deniker has ah-eady pointed 
this out — that the figure is not that of an orang-foetus at all, for that 
form has much smaller ears with no point ; nor can it be a gibbon- 
foetus, as Deniker supposes, for the gibbon ear is also without a 
point. I myself regard it as that of a Macacus-embryo. But this 
mistake, which is due to Nitsche, in no way afiects the fact recognised 
by Darwin, that ear-forms showing the point characteristic of the 
animal ear occur in man with extraordinary frequency. 

Finally, there is a discussion of those rudimentary structures 
which occur only in one sex, such as the rudimentary mammary glands 
in the male, the veslcula prostatica, w^hich corresponds to the uterus 
of the female, and others. All these facts tell in favour of the 
common descent of man and all other vertebrates. The conclusion 
of this section is characteristic : " It is only our natural j^rejudicef 
and that arrogance which made our forefathers declare that they 
were descended from demi-gods, which leads us to demur to this 
conclusion. But the time will before long come, when it ivill be 
thought wonderful that naturalists, who were ivell acquainted ivith 
tJie comparative structure and development of man, and other 
mammals, shoidd have believed that each was the work of a separate 
act of creationV 

In the second chapter there is a more detailed discussion, again 
based upon an extraordinary wealth of facts, of the problem as to 
the manner in which, and the causes through which, man evolved 
from a lower form. Precisely the same causes are here suggested for 
the origin of man, as for the origin of species in general. Variability, 
which is a necessary assumption in regard to all transformations, 
occurs in man to a high degree. Aloreover, the rapid multiplication 
of the human race creates conditions which necessitate an energetic 
struggle for existence, and thus afford scope for the intervention of 
natural selection. Of the exercise of artificial selection in the 
human race, there is nothing to be said, unless we cite such cases as 
the grenadiers of Frederick William I, or the population of ancient 
Sparta. In the passages already referred to and in those which 
follow, the transmission of acquired characters, upon which Darwin 
does not dwell, is taken for gi-anted. In man, direct effects of 
changed conditions can be demonstrated (for instance in regard 
to bodily size), and there are also proofs of the influence exerted 
on his physical constitution by increased use or disuse. Reference is 
here made to the fact, established by Forbes, that the Quechua- 
Indiana of the high plateaus of Peru show a striking development 

1 Descent of Man, fig. 3, p. 24. » Ibid. p. 86. 

Man's Erect Position 119 

of lungs and thorax, as a result of living constantly at high al- 

Such special forms of variation as arrests of development (micro- 
cephalism) and reversion to lower forms are next discussed. Darwin 
himself felt^ that these subjects are so nearly related to the cases 
mentioned in the first chapter, that many of them might as well have 
been dealt with there. It seems to me that it would have been better 
so, for the citation of additional instances of reversion at this place 
rather disturbs the logical sequence of his ideas as to the conditions 
which have brought about the evolution of man from lower forms. 
The instances of reversion here discussed are microcephalism, which 
Darwin wrongly interpreted as atavistic, supernumerary mammae, 
supernumerary digits, bicornuate uterus, the development of ab- 
normal muscles, and so on. Brief mention is also made of correlative 
variations observed in man. 

Darwin next discusses the question as to the manner in which 
man attained to the erect position from the state of a climbing 
quadruped. Here again he puts the influence of Natural Selection in 
the first rank. The immediate progenitors of man had to maintain a 
struggle for existence in which success was to the more intelligent, 
and to those with social instincts. TTie hand of these climbing 
ancestors, which had little skill and served mainly for locomotion, 
could only undergo further development when some early member of 
the Primate series came to live more on the ground and less among 

A bipedal existence thus became possible, and with it the 
liberation of the hand from locomotion, and the one-sided develop- 
ment of the human foot. The upright position brought about 
correlated variations in the bodily structure; with the free use of 
the hand it became possible to manufacture weapons and to use 
them; and this again resulted in a degeneration of the powerful 
canine teeth and the jaws, which were then no longer necessary for 
defence. Above all, however, the intelligence immediately increased, 
and with it skull and brain. The nakedness of man, and the absence 
of a tail (rudimcntariness of the tail vertebrae) are next discussed. 
Darwin is inclined to attribute the nakedness of man, not to the 
action of natural selection on ancestors who originally inhabited 
a tropical land, but to sexual selection, which, for aesthetic reasons, 
brought about the loss of the hairy covering in man, or primarily in 
woman. An interesting discussion of the loss of the tail, which, 
however, man shares with the anthropoid apes, some other monkeys and 
lemurs, forms the conclusion of the ahnost superabundant material 
which Darwin worked up in the second chapter. His object was to 

' JDetcent of Alan, p. 54. 

120 " The Descent of Man'' 

show that some of the most distinctive human characters are in all 
probability directly or indirectly due to natural selection. With 
characteristic modesty he adds^: "Hence, if I have erred in giving 
to natural selection great power, which I am very far fi'om ad- 
mitting, or in having exaggerated its power, which is in itself 
probable, I have at least, as I hope, done good service in aiding to 
overthrow the dogma of separate creations." At the end of the 
chapter he touches upon the objection as to man's helpless and 
defenceless condition. Against this he urges his intelligence and 
social instincts. 

The two following chapters contain a detailed discussion of the 
objections draAvn from the supposed great differences between the 
mental powers of men and animals. Darwin at once admits that the 
differences are enormous, but not that any fundamental difference 
between the two can be found. Very characteristic of him is the 
following passage : " In what manner the mental powers were first 
developed in the lowest organisms, is as hopeless an enquiry as how 
life itself first originated. These are problems for the distant future, 
if they are ever to be solved by man^." 

After some brief observations on instinct and intelligence, Darwin 
brings forward evidence to show that the greater number of the 
emotional states, such as pleasure and pain, happiness and misery, 
love and hate are common to man and the higher animals. He goes 
on to give various examples showing that wonder and curiosity, 
imitation, attention, memory and imagination (dreams of animals), 
can also be observed in the higher mammals, especially in apes. In 
regard even to reason there are no sharply defined limits. A certain 
faculty of deliberation is characteristic of some animals, and the more 
thoroughly we know an animal the more intelligence we are inclined 
to credit it with. Examples are brought forward of the intelligent 
and deliberate actions of apes, dogs and elephants. But although no 
sharply defined dififerences exist between man and animals, there is, 
nevertheless, a series of other mental powers which are characteristics 
usually regarded as absolutely peculiar to man. Some of these charac- 
teristics are examined in detail, and it is shown that the arguments 
drawn from them are not conclusive. Man alone is said to be capable 
of progi-essive improvement ; but against this must be placed as some- 
thing analogous in animals, the fact that they learn cunning and 
caution through long continued persecution. Even the use of tools is 
not in itself peculiar to man (monkeys use sticks, stones and twigs), 
but man alone fashions and uses implements designed for a special 
purpose. In this connection the remarks taken from Lubbock in 
regard to the origin and gradual development of the earliest flint 

Descent of Man, p. 92. ' Ibid. p. 100. 

Intellectual and Moral Faculties 121 

implements will be read with interest; these are similar to the 
observations on modern eoliths, and their bearing on the develop- 
ment of the stone-industry. It is interesting to learn from a letter 
to Hooker \ that Darwin himself at first doubted whether the stone 
implements discovered by Boucher de Perthes were really of the 
nature of tools. With the relentless candour as to himself which 
characterised him, he writes four years later in a letter to Lyell in 
regard to this view of Boucher de Perthes' discoveries: "I know 
something about his errors, and looked at his book many years ago, 
and am ashamed to think that I concluded the whole was rubbish ! 
Yet he has done for man something like what Agassiz did for 

To return to Darwin's further comparisons between the higher 
mental powers of man and animals. He takes much of the force 
from the argument that man alone is capable of abstraction and 
self-consciousness by his own observations on dogs. One of the 
main differences between man and animals, speech, receives detailed 
treatment. He points out that various animals (birds, monkeys, 
dogs) have a large number of different sounds for different emotions, 
that, further, man produces in common with animals a whole series 
of inarticulate cries combined with gestures, and that dogs learn to 
understand whole sentences of human speech. In regard to human 
language, Darwin expresses a view contrary to that held by Max 
.Miiller^: '* I cannot doubt that language owes its origin to the 
imitation and modification of various natural sounds, the voices of 
other animals, and man's own instinctive cries, aided by signs and 
gestures." The development of actual language presupposes a 
higher degree of intelligence than is found in any kind of ape. 
Darwin remarks on this point*: "The fact of the higher apes not 
using their vocal organs for speech no doubt depends on their 
intelligence not having been sufficiently advanced." 

The sense of beauty, too, has been alleged to be peculiar to man. 
In refutation of this assertion Darwin points to the decorative colours 
of birds, which are used for display. And to the last objection, that 
man alone has religion, that he alone has a belief in God, it is 
answered "that numerous races have existed, and still exist, who 
have no idea of one or more gods, and who have no >vords in their 
languages to express such an idea^" 

The result of the investigations recorded in this chapter is to 
show that, gi'eat as the difierence in mental powers between man and 

' TAff and Letters, Vol. ii. p. 101, June 22, 1S59. 

' Ibid. Vol. III. p. 15, March 17, 18G3. 

» Dencent of Man, p. 132. * Ibid. pp. ISR, 1^7. 

' Ibid. p. 143. 

122 " The Descent of Man " 

the higher animals may be, it is undoubtedly only a difference "of 
degree and not of kind\" 

In the fourth chapter Darwin deals with the moral sense or 
conscience, which is the most important of all differences between 
man and animals. It is a result of social instincts, which lead to 
sympathy for other members of the same society, to non-egoistic 
actions for the good of others. Darwin shows that social tendencies 
are found among many animals, and that among these love and kin- 
sympathy exist, and he gives examples of animals (especially dogs) 
which may exhibit characters that we should call moral in man 
(e.g. disinterested self-sacrifice for the sake of others). The early 
ape-like progenitors of the human race were undoubtedly social. 
With the increase of intelligence the moral sense develops farther ; 
with the acquisition of speech public opinion arises, and finally, 
moral sense becomes habit. The rest of Darmn's detailed discussions 
on moral philosophy may be passed over. 

The fifth chapter may be very briefly summarised. In it Darwin 
shows that the intellectual and moral faculties are perfected through 
natural selection. He inquires how it can come about that a tribe at 
a low level of evolution attains to a higher, although the best and 
bravest among them often pay for their fidelity and courage with 
their lives without leaving any descendants. In this case it is the 
sentiment of glory, praise and blame, the admiration of others, 
which bring about the increase of the better members of the tribe. 
Property, fixed dwellings, and the association of families into a 
community are also indispensable requirements for civilisation. In 
the longer second section of the fifth chapter Darwin acts mainly as 
recorder. On the basis of numerous investigations, especially those 
of Greg, Wallace, and Galton, he inquires how far the influence of 
natural selection can be demonstrated in regard to civilised nations. 
In the final section, which deals with the proofs that all civilised 
nations were once barbarians, Darwin again uses the results gained 
by other investigators, such as Lubbock and Tylor. Tliere are two 
sets of facts which prove the proposition in question. In the first 
place, we find traces of a former lower state in the customs and 
beliefs of all civilised nations, and in the second place, there are 
proofs to show that savage races are independently able to raise 
themselves a few steps in the scale of civilisation, and that they have 
thus raised themselves. 

In the sixth chapter of the work. Morphology comes into the 
foreground once more. Darwin first goes back, however, to the 
argument based on the great difference between the mental powers 
of the highest animals and those of man. That this is only quanti- 

* Descent of Man, p. 193. 

Genealogy of 3fan 123 

tative, not qualitative, he has already shown. Very instructive in 
this connection is the reference to the enormous difference in mental 
powers in another class. No one would draw from the fact that the 
cochineal insect (Coccus) and the ant exhibit enormous differences in 
their mental powers, the conclusion that the ant should therefore 
be regarded as something quite distinct, and withdrawn from the 
class of insects altogether. 

Darwin next attempts to establish the sj)ecJJic genealogical tree of 
man, and carefully weighs the differences and resemblances between 
the different families of the Primates. The erect position of man is 
an adaptive character, just as are the various characters referable to 
aquatic life in the seals, which, notwithstanding these, are ranked as 
a mere family of the Carnivores. The following utterance is very 
characteristic of Darwin ^- "If man had not been his own classifier, 
he would never have thought of founding a separate order for his 
own reception." In numerous characters not mentioned in systematic 
works, in the features of the face, in the form of the nose, in the 
structure of the external ear, man resembles the apes. The arrange- 
ment of the hair in man has also much in common with the apes ; as 
also the occurrence of hair on the forehead of the human embryo, 
the beard, the convergence of the hair of the upper and under arm 
towards the elbow, which occurs not only in the anthropoid apes, 
but also in some American monkeys. Darwin here adopts Wallace's 
explanation of the origin of the ascending direction of the hair in the 
forearm of the orang, — that it has arisen through the habit of holding 
the hands over the head in rain. But this explanation cannot be 
maintained when M-e consider that this disposition of the hair is widely 
distributed among the most different mammals, being found in the 
dog, in the sloth, and in many of the lower monkeys. 

After further careful analysis of the anatomical characters Darwin 
reaches the conclusion that the New World monkej-s (Platyrrhine) 
may be excluded from the genealogical tree altogether, but that man 
is an offshoot from the Old World monkeys (Catarrhine) whose 
progenitors existed as far back as the Miocene period. Among these 
Old World monkeys the forms to which man shows the greatest 
resemblance arc the anthropoid apes, which, like him, possess neither 
tail nor ischial callosities. Tlie platyrrhine and catarrhine monkeys 
have their primitive ancestor among extinct forms of the Lenmridae. 
Darwin also touches on the question of the original home of the 
human race and supposes that it may have been in Africa, because 
it is there that man's nearest relatives, the gorilla and the chimi)anzee, 
are found, lint he regards speculation on this point as useless. It is 
remarkable that, in this connection, Darwin regards the loss of the 

^ Descent of ilan, p. 231. 

124 " The Descent of Man'' 

hair-covering in man as having some relation to a warm climate, 
while elsewhere he is inclined to make sexual selection responsible 
for it. Darwin recognises the great gap between man and his nearest 
relatives, but similar gaps exist at other parts of the mammalian 
genealogical tree : the allied forms have become extinct. After the 
extermination of the lower races of mankind, on the one hand, and of 
the anthropoid apes on the other, which will undoubtedly take place, 
the gulf will be greater than ever, since the baboons Avill then bound 
it on the one side, and the white races on the other. Little weight need 
be attached to the lack of fossil remains to fill up this gap, since the 
discovery of these depends upon chance. The last part of the chapter 
is devoted to a discussion of the earlier stages in the genealogy of 
man. Here Darwin accepts in the main the genealogical tree, which 
had meantime been published by Haeckel, who traces the pedigree 
back through Monotremes, Reptiles, Amphibians, and Fishes, to 

Then follows an attempt to reconstruct, from the atavistic 
characters, a picture of our primitive ancestor who was undoubtedly 
an arboreal animal. The occurrence of rudiments of parts in one 
sex which only come to full development in the other is next 
discussed. This state of things Darwin regards as derived from an 
original hermaphroditism. In regard to the mammary glands of the 
male he does not accept the theory that they are vestigial, but 
considers them rather as not fully developed. 

The last chapter of Part I deals with the question whether the 
different races of man are to be regarded as different species, or as 
sub-species of a race of monophyletic origin. The striking differences 
between the races are first emphasised, and the question of the 
fertility or infertility of hybrids is discussed. That fertility is the 
more usual is shown by the excessive fertility of the hybrid popula- 
tion of Brazil. This, and the great variability of the distinguishing 
characters of the different races, as well as the fact that all grades 
of transition stages are found between these, while considerable 
general agi*eemcnt exists, tell in favour of the unity of the races 
and lead to the conclusion that they all had a common primitive 

Darwin therefore classifies all the different races as sub-species of 
one and the same species. Then follows an interesting inquiry into 
the reasons for the extinction of human races. He recognises as the 
ultimate reason the injurious effects of a change of the conditions of 
life, which may bring about an increase in infantile mortality, and a 
diminished fertility. It is precisely the reproductive system, among 
animals also, which is most susceptible to changes in the environ- 

" The Descent of Man " 125 

The final section of this chapter deals mth the formation of the 
races of mankind. DarAvin discusses the question how far the direct 
effect of different conditions of life, or the inherited effects of in- 
creased use or disuse may have brought about the characteristic 
differences between the different races. Even in regard to the origin 
of the colour of the skin he rejects the transmitted effects of an 
original difference of climate as an explanation. In so doing he is 
folIo^ving his tendency to exclude Lamarckian explanations as far as 
possible. But here he makes gratuitous difiiculties from which, since 
natural selection fails, there is no escape except by bringing in the 
principle of sexual selection, to which, he regarded it as possible, 
skin-colouring, arrangement of hair, and form of features might 
be traced. But with his characteristic conscientiousness he guards 
himself thus : " I do not intend to assert that sexual selection will 
account for all the differences between the races \" 

I may be permitted a remark as to Darwin's attitude towards 
Lamarck. \\Tiile, at an earlier stage, when he was engaged in the 
preliminary laboui^s for his immortal work, The Origin of Species, 
Darwin expresses himself very forcibly against the views of Lamarck, 
speaking of Lamarckian " nonsense ^" and of Lamarck's "absurd, 
though clever work^" and expressly declaring, "I attribute very 
little to the direct action of climate, etc.*" yet in later life he 
became more and more convinced of the influence of external con- 
ditions. In 1876, that is, two years after the appearance of the 
second edition of The Descent of Man, he writes with his usual 
candid honesty : " In my opinion the greatest error which I have 
committed, has been not allowing sufficient weight to the direct 
action of the environment, i.e. food, climate, etc. independently of 
natural selection^" It is certain from this change of opinion that, 
if he had been able to make up his mind to issue a third edition of 
The Descent of Man, he would have ascribed a much greater in- 
fluence to the effect of external conditions in explaining the different 
characters of the races of man than he did in the second edition. 
He would also undoubtedly have attributed less influence to sexual 
selection as a factor in tlic origin of the different bodily characteristics, 
if iiideed he would not have excluded it altogether. 

In Part III of the Descent two additional chapters are devoted to 
the discussion of sexual selection in relation to man. These may be 
very briefly referred to. Darwin here seeks to show that sexual 
selection has been operative on man and his i)riniitive progenitor. 
Space fails me to follow out his interesting arguments. I can only 
mention that he is inclined to trace back hairlessness, the development 

' Detcent of Mun, p. 308. ' Life and Letlert, Vol. ir. p. 23. 

» Loc. cit. p. 3'J. * Loc. cit. (185G), p. 82. » Ibid. Vol. iii. p. 150. 

126 ''The Descent of Man'' 

of the beard in man, and the characteristic colour of the different 
human races to sexual selection. Since bareness of the skin could be 
no advantage, but rather a disadvantage, this character cannot have 
been brought about by natural selection. Darwin also rejected a 
direct influence of climate as a cause of the origin of the skin-colour. 
I have already expressed the opinion, based on the development of 
his views as shown in his letters, that in a third edition Darwin would 
probably have laid more stress on the influence of external environ- 
ment. He himself feels that there are gaps in his proofs here, and 
says in self-criticism : " The views here advanced, on the part which 
sexual selection has played in the history of man, want scientific 
precision \" I need here only point out that it is impossible to 
explain the graduated stages of skin-colour by sexual selection, since 
it would have produced races sharply defined by their colour and not 
united to other races by transition stages, and this, it is well known, 
is not the case. Moreover, the fact established by me^, that in all 
races the ventral side of the trunk is paler than the dorsal side, and 
the inner surface of the extremities paler than the outer side, cannot 
be explained by sexual selection in the Darwinian sense. 

With this I conclude my brief survey of the rich contents of 
Darwin's book. I may be permitted to conclude by quoting the 
magnificent final words of The Descent of Man: "We must, however, 
acknoAvledge, as it seems to me, that man, with all his noble qualities, 
with sympathy which feels for the most debased, with benevolence 
which extends not only to other men but to the humblest living 
creature, with his god-like intellect which has penetrated into the 
movements and constitution of the solar system — with all these 
exalted powers — Man still bears in his bodily frame the indelible 
stamp of his lowly origin^" 

AVhat has been the fate of Darwin's doctrines since his great 
achievement ? How have they been received and followed up by the 
scientific and lay Avorld ? And what do the successors of the mighty 
hero and genius think now in regard to the origin of the human 

At the present time we are incomparably more favourably placed 
than Darwin was for answering this question of all questions. We 
have at our command an incomparably greater wealth of material 
than he had at his disposal. And we are more fortunate than he in 
this respect, that we now know transition-forms which help to fill up 
the gap, still great, between the lowest human races and the highest 

^ Descent of Man, p. 924. 

' " Die Ilautfarbe ties Menschen," Mitteilungen der Anthropologisclien QeselUchaft in 
Wlcn, Vol. XXXIV. pp. 331—362. 
» Ibid. p. 047. 

Fossil Monkeys 127 

apes. Let us consider for a little the more essential additions to our 
knowledge since the publication of The Descefit of Man. 

Since that time our knowledge of animal embryos has increased 
enormously. Wliile Darwin was obliged to content himself with 
comparing a human embryo with that of a dog, there are now avail- 
able the youngest embryos of monkeys of all possible groups (Orang, 
Gibbon, Semnopithecus, Macacus), thanks to Selenka's most successful 
tour in the East Indies in search of such material. We can now compare 
corresponding stages of the lower monkeys and of the Anthropoid 
apes with human embryos, and convince ourselves of their great 
resemblance to one another, thus strengthening enormously the 
armour prepared by Darwin in defence of his view on man's nearest 
relatives. It may be said that Selenka's material fills up the blanks 
in Darwin's array of proofs in the most satisfactory manner. 

The deepening of our knowledge of comparative anatomy also 
gives us much surer foundations than those on which Darwin was 
obliged to build. Just of late there have been many workers in the 
domain of the anatomy of apes and lemurs, and their investigations 
extend to the most ditFerent organs. Our knowledge of fossil apes 
and lemurs has also become much wider and more exact since 
Darwin's time : the fossil lemurs have been especially w^orked up 
by Cope, Forsyth Major, Ameghino, and others. Darwin knew very 
little about fossil monkeys. He mentions two or three anthropoid apes 
as occurring in the Miocene of Europe^ but only names Dryoj^ithecus, 
the largest form from the I\Iiocene of France. It was erroneously 
supposed that this form was related to Hylohates. We now know 
not only a form that actually stands near to the gibbon (Pliopi- 
themis), and remains of other anthropoids (Pliohi/lobates and the 
fossil chimpanzee, Palaeoplthecus), but also several lower catarrhine 
monkeys, of which Mcsopithccus, a form nearly related to the modern 
Sacred Monkeys (a species of SeniuojntJiccus) and found in strata of the 
Miocene period in Greece, is the most important. Quite recently, too, 
Ameghino's investigations have made us acquainted with fossil monkeys 
from South America (Anthrojwps, Homaticuliis), which, according to 
their discoverer, are to be regarded as in the line of human descent. 

What Darwin missed most of all — intermediate forms between 
apes and man — has l)cen recently furnished. E. Dubois, as is well 
known, discovered in 1893, near Trinil in Java, in the alhivial 
deposits of the river Bengawan, an imjjortant form represented by 
a HkuU-cap, some molars, and a femur. His opinion — much disputed 
juj it has been — that in this form, which he named Fithcctinthropus, 
he has found a long-desired transition-form is shared by the present 
writer. And although the geological age of these fossils, which, 

1 Descent of Man, p. 240. 

128 ''The Descent of Man" 

according to Dubois, belong to the uppermost Tertiary series, the 
Pliocene, has recently been fixed at a later date (the older Diluvium), 
the morphological value of these interesting remains, that is, the inter- 
mediate position of Pithecanthropus, still holds good. Volz says with 
justice \ that even if Pithecanthropus is not the missing link, it is 
undoubtedly a missing link. 

As on the one hand there has been found in Pithecanthropus a 
form which, though intermediate between apes and man, is never- 
theless more closely allied to the apes, so on the other hand, much 
progress has been made since Darwin's day in the discovery and 
description of the oldest human remains. Since the famous roof of 
a skull and the bones of the extremities belonging to it were found 
in 1856 in the Neandertal near Dusseldorf, the most varied judgments 
have been expressed in regard to the significance of the remains and 
of the skull in particular. In Darwin's Descent of Man there is only 
a passing allusion to them' in connection with the discussion of the 
skull-capacity, although the investigations of SchaalFhausen, King, 
and Huxley were then knoAvn. I believe I have shown, in a series of 
papers, that the skull in question belongs to a form dififerent from 
any of the races of man now living, and, with King and Cope, I regard 
it as at least a dift'erent species from living man, and have therefore 
designated it Homo primigcnius. The form unquestionably belongs to 
the older Diluvium, and in the later Diluvium human forms already 
appear, which agree in all essential points with existing human races. 

As far back as 1886 the value of the Neandertal skull was greatly 
enhanced by Fraipont's discovery of two skulls and skeletons from 
Spy in Belgium. These are excellently described by their discoverer^, 
and are regarded as belonging to the same group of forms as the 
Neandertal remains. In 1899 and the following years came the 
discovery by Gorjanovic-Kramberger of different skeletal parts of at 
least ten individuals in a cave near Krapina in Croatia*. It is in 
particular the form of the lower jaw which is different from that of 
all recent races of man, and which clearly indicates the lowly position 
of Homo primigcnius, while, on the other hand, the long-known skull 
from Gibraltar, which P have referred to Homo j^t'imigenius, and 
which has lately been examined in detail by Sollas^, has made us 

1 "Das geologische Alter der Pithecauthropus-Schichten bei Trinil, Ost-Java." Neues 
Jahrb. f. Mineralogie. Festband, 1907. 

* Descent of Man, p. 82. 

3 "La race humaine de Neanderthal ou de Canstatt en Belgique." Arch, de Biologic, 
Yii. 1887. 

* GorjanoviC-Kramberger. Der diluviale Mensch von Krapina in Kroatien, 1906. 
' Stiidien zur Vorgeschichte des Menschen, 1906, pp. 154 fl. 

* "On the cranial and facial characters of the Neandertal Race." Trans. R. Soc. 
London, vol. 199, 1908, p. 281. 

Post-Daricinian Discoveries 129 

acquainted with the surprising shape of the eye-orbit, of the nose, 
and of the whole upper part of the face. Isolated lower jaws found 
at La Naulette in Belgium, and at Malarnaud in France, increase 
our material which is now as abundant as could be desired. The 
most recent discovery of all is that of a skull dug up in August of 
this year [1908] by Klaatsch and Hauser in the lower grotto of the 
Le Moustier in Southern France, but this skull has not yet been fully 
described. Thus Homo primiffenim must also be regarded as 
occupying a position in the gap existing between the highest apes 
and the lowest human races, Pithecanthropus, standing in the lower 
part of it, and Homo j^rimigenms in the higher, near man. In order 
to prevent misunderstanding, I should like here to emphasise that in 
arranging this structural series — anthropoid apes, Pithecanthropus, 
Homo primigenius, Homo sapiens — I have no intention of estab- 
lishing it as a direct genealogical series. I shall have something to 
say in regard to the genetic relations of these forms, one to another, 
when discussing the diflferent theories of descent current at the 
present day\ 

In quite a different domain from that of morphological relation- 
ship, namely in the physiological study of the blood, results have 
recently been gained which are of the highest importance to the 
doctrine of descent. Uhlenhuth, Nuttall, and others have established 
the fact that the blood-serum of a rabbit which has previously had 
human blood injected into it, forms a precipitate mth human blood. 
This biological reaction was tried with a great variety of mammalian 
species, and it was found that those far removed from man gave no 
precipitate under these conditions. But as in other cases among 
mammals all nearly related forms yield an almost equally marked 
precipitate, so the serum of a rabbit treated with human blood and 
then added to the blood of an anthropoid ape gives almost as marked 
a precipitate as in human blood ; the reaction to the blood of the 
lower Eastern monkeys is weaker, that to the Western monkeys 
weaker still ; indeed in this last case there is only a slight clouding 
after a considerable time and no actual precipitate. The blood 
of the Lenmridae (Nuttall) gives no reaction or an extremely weak 
one, that of the other mammals none whatever. We have in this not 
only a proof of the literal blood-relationship between man and apes, 
but the degi-ee of rchitionshii) with the different main groups of apes 
can be detennined beyond possibility of mistake. 

' [Since this essay was written Schoetensack has discovered near Heidelberg and briefly 
described an esceedingly interesting? lower jaw from rocks between the Pliocene and 
Diluvial beds. This exhibits interesting dififerenccs from the forms of lower jaw of 
Hoiiw primifjeniui. (SchoetenBack, Der Unterkie/er da Homo heidelbergensis. Leipzig, 
1908.) O. S.] 

D. 9 

130 " The Descent of Man'' 

Finally, it must be briefly mentioned that in regard to remains 
of human handicraft also, the material at our disposal has greatly 
increased of late years, that, as a result of this, the opinions of 
archaeologists have undergone many changes, and that, in particular, 
their views in regard to the age of the human race have been greatly 
influenced. There is a tendency at the present time to refer the 
origin of man back to Tertiary times. It is true that no remains 
of Tertiary man have been found, but flints have been discovered 
which, according to the opinion of most investigators, bear traces 
either of use, or of very primitive workmanship. Since Rutot's time, 
following Mortillet's example, investigators have called these "eoliths," 
and they have been traced back by Verworn to the Miocene of the 
Auvergne, and by Rutot even to the upper Oligocene. Although 
these eoliths are even nowadays the subject of many dififerent views, 
the preoccupation with them has kept the problem of the age of the 
human race continually before us. 

Geology, too, has made great progress since the days of Darwin 
and Lyell, and has endeavoured with satisfactory results to arrange 
the human remains of the Diluvial period in chronological order 
(Penck). I do not intend to enter upon the question of the 
primitive home of the human race ; since the space at my dis- 
posal will not allow of my touching even very briefly upon all the 
departments of science which are concerned in the problem of 
the descent of man. How Darwin would have rejoiced over 
each of the discoveries here briefly outlined ! What use he 
would have made of the new and precious material, which would 
have prevented the discouragement fi'om which he sufiered when 
preparing the second edition of The Descent of Man ! But it was 
not granted to him to see this progress towards filling up the gaps 
in his edifice of which he was so painfully conscious. 

He did, however, have the satisfaction of seeing his ideas steadily 
gaining ground, notwithstanding much hostility and deep-rooted 
prejudice. Even in the years between the appearance of The Origin 
of Sjyecies and of the first edition of the Descent, the idea of a 
natural descent of man, Avhich was only briefly indicated in the work 
of 1859, had been eagerly welcomed in some quarters. It has been 
already pointed out how brilliantly Huxley contributed to the de- 
fence and diffusion of Darwin's doctrines, and how in 3Ian's Place 
in Nature he has given us a classic work as a foundation for the 
doctrine of the descent of man. As Huxley was Darwin's champion 
in England, so in Germany Carl Vogt, in particular, made himself 
master of the Darwinian ideas. But above all it was Haeckel who, 
in energy, eagerness for battle, and knowledge may be placed side by 
side with Huxley, who took over the leadership in the controversy 

Genealogical Trees 131 

over the new conception of the universe. As far back as 1866, in his 
Generelle Morphologie, he had inquired minutely into the question of 
the descent of man, and not content with urging merely the general 
theory of descent from lower animal forms, he drew up for the first 
time genealogical trees showing the close structural relationships of 
the different animal groups ; the last of these illustrated the relation- 
ships of Mammals, and among them of all gi'oups of the Primates, 
including man. It was Haeckel's genealogical trees that formed the 
basis of the special discussion of the relationships of man, in the 
sixth chapter of Darwin's Descent of Man. 

In the last section of this essay I shall return to Haeckel's con- 
ception of the special descent of man, the main features of which he 
still upholds, and rightly so. Haeckel has contributed more than any 
(»ne else to the spread of the Darwinian doctrine. 

I can only allow myself a few words as to the spread of the theory 
of the natural descent of man in other countries. The Parisian 
anthropological school, founded and guided by the genius of Broca, 
took up the idea of the descent of man, and made many notable 
contributions to it (Broca, Manouvrier, Mahoudeau, Deniker and 
others). In England itself Darwin's work did not die. Huxley took 
care of that, for he, with his lofty and unprejudiced mind, dominated 
and inspired English biology until his death on June 29, 1895. He 
had the satisfaction shortly before his death of learning of Dubois' 
discovery, which he illustrated by a humorous sketch \ But there 
are still many followers in Darwin's footsteps in England. Keane 
has worked at the special genealogical tree of the Primates ; Keith 
has inquired which of the anthropoid apes has the greatest number 
of characters in common with man ; Morris concerns himself with the 
evolution of man in general, especially with his acquisition of the 
erect position. The recent discoveries of Plthecanthropits and Homo 
primigenms are being vigorously discussed ; but the present writer 
is not in a position to fomi an opinion of the extent to Avhich the 
idea of descent has penetrated throughout England generally. 

In Italy independent work in the domain of the descent of man is 
being produced, especially by Morselli ; with him are associated, in 
the investigation of related problems, Sergi and Giuffrida-Ruggeri. 
From the ranks of American investigators we may single out in 
particular the eminent geologist Cope, who championed with much 
decision the idea of the specific diflercnce of Homo iieandertalensis 
{prim'njenins) and maintained a more direct descent of man from the 
fossil Lemuridae. In South America too, in Argentina, new life is 
stirring in this department of science. Ameghino in Buenos Ayres 
has awakened the fossil primates of the Pampas formation to new 

' Life and Letters of 'I'homas Henry Huxley, Vol. ii. p. 301. 


132 " The Descent of Man " 

life ; lie even believes that in his Tetraprothomo, represented by a 
femur, he has discovered a direct ancestor of man. Lehmann-Nitsche 
is working at the other side of the gulf between apes and men, and 
he describes a remarkable first cervical vertebra (atlas) from Monte 
Hermoso as belonging to a form which may bear the same relation 
to Homo sapiens in South America as Homo prmiigenius does in 
the Old World. After a minute investigation he establishes a human 
species Homo iieogaeus, while Ameghino ascribes this atlas vertebra 
to his Tetraprothomo. 

Thus throughout the whole scientific world there is arising a 
new life, an eager endeavour to get nearer to Huxley's problema 
maximMm, to penetrate more deeply into the origin of the human 
race. There are to-day very few experts in anatomy and zoology 
who deny the animal descent of man in general. Religious con- 
siderations, old prejudices, the reluctance to accept man, who so far 
surpasses mentally all other creatures, as descended from " soulless " 
animals, prevent a few investigators from giving full adlierence to 
the doctrine. But there are very few of these who still postulate 
a special act of creation for man. Although the majority of experts 
in anatomy and zoology accept unconditionally the descent of man 
from lower forms, there is much diversity of opinion among them in 
regard to the special line of descent. 

In trying to establish any special hypothesis of descent, whether 
by the graphic method of di'awing up genealogical trees or otherwise, 
let us always bear in mind Darwin's words ^ and use them as a critical 
guiding line : " As we have no record of the lines of descent, the 
pedigree can be discovered only by observing the degrees of re- 
semblance between the beings which are to be classed." Darwin 
carries this further by stating "that resemblances in several 
unimportant structures, in useless and rudimentary organs, or 
not now functionally active, or in an embryological condition, are 
by far the most serviceable for classification^." It has also to be 
remembered that numerous separate points of agreement are of 
much greater importance than the amount of similarity or dis- 
similarity in a few points. 

The hypotheses as to descent current at the present day may be 
divided into two main gi-oups. The first group seeks for the roots 
of the human race not among any of the families of the apes — the 
anatomically nearest forms — nor among their very similar but less 
specialised ancestral forms, the fossil representatives of which 
we can know only in i)art, but, setting the monkeys on one side, 
it seeks for them lower down among the fossil Eocene Pseudo- 
lemuridae or Lemuridae (Cope), or even among the primitive 

* Descent of Man, p. 229. ' Loc. cit. 

Man and MonTceys 133 

pentadactylous Eocene forms, which may either have led directly 
to the evolution of man (Adloff ), or have given rise to an ancestral 
form common to apes and men (Klaatsch\ Giuffrida-Ruggeri). Tlie 
common ancestral form, from which man and apes are thus supposed 
to have arisen independently, may explain the numerous resemblances 
which actually exist between them. That is to say, all the characters 
upon which the great structural resemblance between apes and 
man depends must have been present in their common ancestor. 
Ijet us take an example of such a common character. The bony 
external ear-passage is in general as highly developed in the lower 
Eastern monkeys and the anthropoid apes as in man. This character 
must, therefore, have already been present in the common primitive 
form. In that case it is not easy to understand why the Western 
monkeys have not also inherited the character, instead of possessing 
only a tympanic ring. But it becomes more intelligible if we assume 
that forms with a primitive tympanic ring were the original type, and 
that from these were evolved, on the one hand, the existing New 
World monkeys with persistent tympanic ring, and on the other an 
ancestral form common to the lower Old World monkeys, the anthro- 
poid apes and man. For man shares with these the character in 
question, and it is also one of the "unimportant" characters required 
by Darwin. Thus we have two divergent lines arising from the 
ancestral form, the Western monkeys (Platyrrhine) on the one hand, 
and an ancestral form common to the lower Eastern monkeys, the 
anthropoid apes, and man, on the other. But considerations similar 
to those which showed it to be impossible that man should have 
developed fiom an ancestor common to him and the monkeys, yet 
outside of and parallel with these, may be urged also against the 
likelihood of a parallel evolution of the lower Eastern monkeys, the 
aiitlnopoid apes, and man. The anthropoid apes have in common 
with man many characters which are not present in the lower Old 
World monkeys. These characters must therefore have been present 
in the ancestral form common to the three groups. But here, again, 
it is difficult to understand why the lower Eastern monkeys should 
not also have inhei-ited these characters. As this is not the case, 
there remains no alternative but to assume divergent evolution from 
an indifJerent form. The lower Eastern monkeys are carrying on 
the evolution in one direction — I might almost say towards a blind 
alley — while anthropoids and men have struck out a progressive 
path, at first in common, which ex[)lains the many points of re- 
semblaiice between them, without regarding man as derived directly 
froM) tlie anthropoids. Their many striking points of agreement 

' Klaatach in his last publications spenlts in the main only of an ancestral form 
common to men and anthropoid apes. 

134 " The Descent of Man " 

indicate a common descent, and cannot be explained as phenomena 
of convergence. 

I believe 1 have shown in the above sketch that a theory which 
derives man directly from lower forms without regarding apes as 
transition-types leads ad absurdum. The close structural relation- 
ship between man and monkeys can only be understood if both are 
brought into the same line of evolution. To trace man's line of 
descent directly back to the old Eocene mammals, alongside of, but 
with no relation to these very similar forms, is to abandon the method 
of exact comparison, which, as Darwin rightly recognised, alone 
justifies us in drawing up genealogical trees on the basis of resem- 
blances and difterences. The farther down we go the more does the 
ground slip fi-om beneath our feet. Even the Lemuridae show very 
numerous divergent conditions, much more so the Eocene mammals 
(Creodonta, Condylarthra), the chief resemblance of which to man 
consists in the possession of pentadactylous hands and feet ! Thus 
the farther course of the line of descent disappears in the darkness 
of the ancestry of the mammals. With just as much reason we might 
pass by the Vertebrates altogether, and go back to the lower Inverte- 
brates, but in that case it would be much easier to say that man 
has arisen independently, and has evolved, without relation to any 
animals, from the lowest primitive form to his present isolated and 
dominant position. But this would be to deny all value to classifica- 
tion, which must after all be the ultimate basis of a genealogical tree. 
We can, as Darwin rightly observed, only infer the line of descent 
from the degree of resemblance between single forms. If we 
regard man as directly derived from primitive forms very far back, 
we have no way of explaining the many points of agreement between 
him and the monkeys in general, and the anthropoid apes in par- 
ticular. Tiiese must remain an inexplicable marvel. 

I have thus, I trust, shown that the first class of special theories 
of descent, which assumes that man has developed, parallel with the 
monkeys, but without relation to them, from very low primitive forms 
cannot be upheld, because it fails to take into account the close 
structural afiinity of man and monkeys. I cannot but regard this hypo- 
thesis as lamentably retrograde, for it makes impossible any application 
of the facts that have been discovered in the course of the anatomical 
and embryological study of man and monkeys, and indeed prejudges 
investigations of that class as pointless. The whole method is per- 
verted; an unjustifiable theory of descent is first formulated with the 
aid of the imagination, and then we are asked to declare that all 
structural relations between man and monkeys, and between the 
different groups of the latter, are valueless, — the fact being that they 
are the only true basis on which a genealogical tree can be constructed 

Man and Monkeys 135 

So much for this most modern method of classification, which 
has probably found adherents because it would deliver us from the 
relationship to apes which many people so much dislike. In contrast to 
it we have the second class of special hypotheses of descent, which keeps 
strictly to the nearest structural relationships. This is the only basis 
that justifies the drawing up of a special hypothesis of descent. If 
this fundamental proposition be recognised, it will be admitted that 
the doctrine of special descent upheld by Haeckel, and set forth in 
Darwin's Descent of Man, is still valid to-day. In the genealogical 
tree, man's place is quite close to the anthropoid apes ; these again 
have as their nearest relatives the lower Old World monkeys, and 
their progenitors must be sought among the less differentiated 
Platyrrhine monkeys, whose most important characters have been 
handed on to the present day New World monkeys. How the 
different genera are to be arranged within the general scheme in- 
dicated depends in the main on the classificatory value attributed 
to individual characters. This is particularly true in regard to 
PitJtecanthropus, which I consider as the root of a branch which 
has sprung ft'om the anthropoid ape root and has led up to man ; 
the latter I have designated the family of the Hominidae. 

For the rest, there are, as we have said, various possible ways of 
constructing the narrower genealogy within the limits of this bmnch 
including men and apes, and these methods will probably continue 
to change with the accumulation of new facts. Haeckel himself has 
modified his genealogical tree of the Primates iu certain details since 
the publication of his Generelle Morphologie in 1866, but its general 
basis remains the same^ All the special genealogical trees drawn 
up on the lines laid down by Haeckel and Darwin — and that of 
Dubois may be specially mentioned — are based, in general, on the 
close relationship of monkeys and men, although they may vary in 
detail. Various hypotheses have been formulated on these lines, 
with special reference to the evolution of man. Pithecauthropus 
is regarded by some authorities as the direct ancestor of man, by 
others as a side-track failure in the attempt at the evolution of man. 
The problem of the monophyletic or polyphyletic origin of the human 
race has also been much discussed. Sergi^ inclines towards the 
assumption of a polyphyletic origin of the three main races of man, 
the African primitive form of which has given rise also to the gorilla 
and chimpanzee, the Asiatic to the Orang, the Gibbon, and Pithecan- 
throDus. Kollmann regards existing human races as derived from 
small primitive races (pigmies), and considers that Homo primi- 
genius must have arisen in a secondary and degenerative manner, 

' Haeckel's latest genealogical tree in to be found in liis most recent work, Unnere 
Ahnenreilie. Jena, 1908. 

« Seryi, O. Europa, 1908. 

136 " The Descent of Man'' 

But this is not the place, nor have I the space to criticise the 
various special theories of descent. One, however, must receive par- 
ticular notice. According to Ameghino, the South American monkeys 
(PithecnUtes)from the oldest Tertiary of the Pampas are the forms from 
which have arisen the existing American monkeys on the one hand, 
and on the other, the extinct South American Homunculidae, which 
are also small forms. From these last, anthropoid apes and man 
have, he believes, been evolved. Among the progenitors of man, 
Ameghino reckons the form discovered by him (Tetraprothomo), 
from which a South American primitive man, Homo pampaeus, might 
be directly evolved, while on the other hand all the lower Old World 
monkeys may have arisen from older fossil South American forms 
(Clenialitidae), the distribution of which may be explained by the 
bridge formerly existing between South America and Africa, as may 
be the derivation of all existing human races from Homo pampaeus^. 
The fossil forms discovered by Ameghino deserve the most minute 
investigation, as does also the fossil man from South America of 
which Lehmann-Nitsche^ has made a thorough study. 

It is obvious that, notwithstanding the necessity for fitting man's 
line of descent into the genealogical tree of the Primates, especially 
the apes, opinions in regard to it differ greatly in detail. This could 
not be otherwise, since the different Primate forms, especially the 
fossil forms, are still far from being exhaustively known. But one 
thing remains certain, — the idea of the close relationship between 
man and monkeys set forth in Darwin's Descent of Man. Only 
those who deny the many points of agreement, the sole basis of 
classification, and thus of a natural genealogical tree, can look upon 
the position of Darwin and Haeckel as antiquated, or as standing 
on an insufficient foundation. For such a genealogical tree is nothing 
more than a summarised representation of what is known in regard 
to the degree of resemblance between the different forms. 

Darwin's work in regard to the descent of man has not been 
surpassed ; the more we immerse ourselves in the study of the 
structural relationships between apes and man, the more is our path 
illumined by the clear light radiating from him, and through his 
calm and deliberate investigation, based on a mass of material in 
the accumulation of which he has never had an equal. Darwin's 
fame will be bound up for all time with the unprejudiced investiga- 
tion of the (juestion of all questions, the descent of the human race. 

^ See Ameghino's latest paper, "Notas preliminares sobre el Tetraprothomo argentinus," 
etc. Analcs del Museo nacional de Buenos Aires, xvi. pp. 107 — 242, 1907. 

* "Nouvellesrecherches eur la formation pamp6enne et rhomme fossile de laR^publique 
Argentine." Rivista del Museo de la Plata, T. xiv. pp. 193 — 488. 



By Ernst Haeckel. 
Professor of Zoology in the University of Jena. 

The great advance that anthropology has made in the second half of 
the nineteenth century is due, in the first place, to Darwin's discovery 
of the origin of man. No other problem in the whole field of 
research is so momentous as that of " Man's place in nature," which 
was justly described by Huxley (1863) as the most fundamental of 
all questions. Yet the scientific solution of this problem was im- 
possible until the theory of descent had been established. 

It is now a hundred years since the great French biologist 
Jean Lamarck published his PhiloscypMe Zoologique. By a re- 
markable coincidence the year in which that work was issued, 1809, 
was the year of the birth of his most distinguished successor, Charles 
Darwin. Lamarck had already recognised that the descent of man 
from a series of other Vertebrates — that is, from a series of Ape-like 
Primates — was essentially involved in the general theory of trans- 
formation which he had erected on a broad inductive basis ; and he 
had sufficient penetration to detect the agencies that had been at 
work in the evolution of the erect bimanous man from the arboreal 
and quadrumanous ape. He had, however, few empirical arguments 
to advance in support of his hypothesis, and it could not be established 
until the further development of the biological sciences — the found- 
ing of comparative embryology by Baer (1828) and of the cell-theory 
by Schleiden and Schwann (1838), the advance of physiology under 
Johannes Midler (1833), and tlie enormous progiess of palaeontolog>' 
and comparative anatomy between 1820 and 18G0 — provided this 
necessary foundation. Darwin was the first to coordinate the ample 
results of these lines of research. With no less comprehensiveness 
than discrimination he consolidated them as a basis of a modified 
theory of descent, and associated with tliem his t)wn theory of natural 
selection, wliich we tiike to be distinctive of "Darwinism" in the 

138 Darwin as an AntJwopologist 

stricter sense. The illuminating truth of these cumulative arguments 
was so great in every branch of biology that, in spite of the most 
vehement opposition, the battle was won within a single decade, and 
Darwin secured the general admiration and recognition that had 
been denied to his forerunner, Lamarck, up to the hour of his death 

Before, however, we consider the momentous influence that 
Darwinism has had in anthropology, we shall find it useful to glance 
at its history in the course of the last half century, and notice the 
various theories that have contributed to its advance. The first 
attempt to give extensive expression to the reform of biology by 
Darwin's work will be found in my Generelle Morphologie (1866)^ 
which was followed by a more popular treatment of the subject in 
my Natiirliche Schopfungsgeschichte (1868)^ a compilation from the 
earlier work. In the first volume of the Generelle Morphologie 
I endeavoured to show the great importance of evolution in settling 
the fundamental questions of biological philosophy, especially in 
regard to comparative anatomy. In the second volume I dealt 
broadly with the principle of evolution, distinguishing ontogeny and 
phylogeny as its two coordinate main branches, and associating the 
two in the Biogenetic Law. The Law may be formulated thus : 
"Ontogeny (embryology or the development of the individual) is 
a concise and compressed recapitulation of phylogeny (the palae- 
ontological or genealogical series) conditioned by laws of heredity 
and adaptation." The " Systematic introduction to general evo- 
lution," with which the second volume of the Generelle MorjyJio- 
logie opens, was the first attempt to draw up a natural system of 
organisms (in harmony with the principles of Lamarck and Darwin) 
in the form of a hypothetical pedigree, and was provisionally set 
forth in eight genealogical tables. 

In the nineteenth chapter of the Generelle Mor2)hologie — a part 
of which has been republished, without any alteration, after a lapse 
of forty years — I made a critical study of Lamarck's theory of descent 
and of Darwin's theory of selection, and endeavoured to bring the 
complex phenomena of heredity and adaptation under definite laws 
for the first time. Heredity I divided into conservative and pro- 
gi-essive : adaptation into indirect (or potential) and direct (or actual). 
I then found it possible to give some explanation of the correlation of 
the two physiological functions in the struggle for life (selection), and 
to indicate the important laws of divergence (or difibrentiation) 
and complexity (or division of labour), which are the direct and 
inevitable outcome of selection. Finally, I marked ofl" dysteleology 

> Generelle Morphologic der Organismen, 2 vols., Berlin, 1866. 
^ Eng. transl.; The History of Creation, London, 1876. 

Heredity 139 

as the science of the aimless (vestigial, abortive, atrophied, and 
useless) organs and parts of the body. In all this I worked from 
a strictly monistic standpoint, and sought to explain all biological 
phenomena on the mechanical and naturalistic lines that had long 
been recognised in the study of inorganic nature. Then (1866), as 
now, being convinced of the unity of nature, the fundamental identity 
of the agencies at work in the inorganic and the organic worlds, 
I discarded vitalism, teleology, and all hypotheses of a mystic 

It was clear from the first that it was essential, in the monistic 
conception of evolution, to distinguish between the laws of con- 
servative and progi'essive heredity. Conservative heredity maintains 
from generation to generation the enduring characters of the species. 
Each organism transmits to its descendants a part of the morpho- 
logical and physiological qualities that it has received from its 
parents and ancestors. On the other hand, progressive heredity 
brings new characters to the species — characters that were not found 
in preceding generations. Each organism may transmit to its off- 
spring a part of the morphological and physiological features that 
it has itself acquired, by adaptation, in the course of its individual 
career, through the use or disuse of particular organs, the influence 
of environment, climate, nutrition, etc. At that time I gave the 
name of "progressive heredity" to this inheritance of acquired 
characters, as a short and convenient expression, but have since 
changed the term to " transformative heredity " (as distinguished from 
conservative). Tliis term is preferable, as inherited regressive modi- 
ficatioas (degeneration, retrograde metamorphosis, etc.) come under 
the same head. 

Transformative heredity— or the transmission of acquired charac- 
ters — is one of the most important principles in evolutionary science. 
Unless we admit it most of the facts of comparative anatomy and 
physiology are inexplicable. That was the conviction of Darwin no 
less tlian of Lamarck, of Spencer as well as Virchow, of Huxley as well 
as Gcgenbaur, indeed of the great majority of speculative biologists. 
This fundamental principle waa for the first time called in question 
and assailed in 1885 by August Weismann of Freiburg, the eminent 
zoologist to whom the theory of evolution owes a great deal ol 
valuable support, and who has attained distinction by his extension 
of the theory of selection. In explanation of the phenomena of 
heredity he introduced a new theory, the " theory of the continuity 
of the germ-plasm." According to him the living substance in all 
organisms consists of two (juite distinct kinds of plasm, somatic and 
genniiial. The permanent genn-plasm, or the active substance of 
the two germ -cells (egg-cell and sperm-cell), passes unchanged 

140 Darwin as an Anthropologist 

through a series of generations, and is not affected by enyiron- 
mental influences. The environment modifies only the soraa-plasm, 
the organs and tissues of the body. The modifications that these 
parts undergo through the influence of the environment or their own 
activity (use and habit), do not aflect the germ-plasm, and cannot 
therefore be transmitted. 

This theory of the continuity of the germ-plasm has been ex- 
pounded by Weismann during the last twenty-four years in a number 
of able volumes, and is regarded by many biologists, such as 
Mr Francis Galton, Sir E. Ray Lankester, and Professor J. Arthur 
Thomson (who has recently made a thoroughgoing defence of 
it in his important work HeredityY, as the most striking advance in 
evolutionary science. On the other hand, the theory has been rejected 
by Herbert Spencer, Sir W. Turner, Gegenbaur, Kblliker, Hertwig, 
and many others. For my part I have, with all respect for the 
distinguished Darwinian, contested the theory fi-om the first, because 
its whole foundation seems to me erroneous, and its deductions do 
not seem to be in accord with the main facts of comparative mor- 
phology and physiology. Weismann's theory in its entirety is a 
finely conceived molecular hypothesis, but it is devoid of empirical 
basis. The notion of the absolute and permanent independence of 
the germ-plasm, as distinguished fi-om the soma-plasm, is purely 
speculative ; as is also the theory of germinal selection. The 
determinants, ids, and idants, are purely hypothetical elements. 
The experiments that have been devised to demonstrate their 
existence really prove nothing. 

It seems to me quite improper to describe this hypothetical 
structure as " Neodarwinism." Darwin was just as convinced as 
Lamarck of the transmission of acquired characters and its great 
importance in the scheme of evolution. I had the good fortune to 
visit Darwin at Down three times and discuss with him the main 
principles of his system, and on each occasion we were fully agreed 
as to the incalculable importance of what I call transformative 
inheritance. It is only proper to point out that Weismann's theory 
of the germ-plasm is in express contradiction to the fundamental 
principles of Darwin and Lamarck. Nor is it more acceptable in 
Avhat one may call its " ultradarwinism " — the idea that the theory 
of selection explains everything in the evolution of the organic 
world. This belief in the " omnipotence of natural selection " was 
not shared by Darwin himself. Assuredly, I regard it as of the 
utmost value, as the process of natural selection through the struggle 
for life aflV)rds an explanation of the mechanical origin of the 
adapted organisation. It solves the gi*eat problem : how could the 

1 London, 1908. 

DancirCs Successors 141 

finely adapted structure of the animal or plant body be formed 
unless it was built on a preconceived plan? It thus enables us to 
dispense with the teleology of the metaphysician and the dualist, 
and to set aside the old mythological and poetic legends of creation. 
The idea had occurred in vague form to the gi-eat Empedocles 
2000 years before the time of Darwin, but it was reserved for modern 
research to give it ample expression. Nevertheless, natural selection 
does not of itself give the solution of all our evolutionary problems. 
It has to be taken in conjunction with the transformism of Lamarck, 
with which it is in complete harmony. 

The monumental greatness of Charles Darwin, who surpasses 
every other student of science in the nineteenth century by the 
loftiness of his monistic conception of nature and the progressive 
influence of his ideas, is perhaps best seen in the fact that not one of 
his many successors has succeeded in modifying his theory of descent 
in any essential point or in discovering an entirely new standpoint 
in the interpretation of the organic world. Neither Nageli nor 
Weismann, neither De Vries nor Roux, has done this. Nageli, in his 
Mcchanisch-Physiologische Theorie der Abstammiaigsl€hie\ which 
is to a gi-eat extent in agi-eement with Weismann, constructed 
a theory of the idioplasm, that represents it (like the germ-plasm) as 
developing continuously in a definite direction from internal causes. 
But his internal " principle of progi-ess " is at the bottom just as 
teleological as the vital force of the Vitalists, and the micellar 
structure of the idioplasm is just as hypothetical as the " dominant " 
structure of the germ-plasm. In 1889 Moritz Wagner sought to 
explain the origin of species by migration and isolation, and on that 
basis constructed a special " migi-ation-theory." This, however, is 
not out of harmony with the theory of selection. It merely elevates 
one single factor in the theory to a predominant position. Isolation 
is only a si)ecial case of selection, as I had pohited out in the fifteenth 
chapter of my Natural history of creation. The " mutation-theory " 
of De Vries ^ that would explain the origin of species by sudden and 
saltatory variations rather than by gradual modification, is regarded 
by many botanists as a great step in advance, but it is generally 
rejected by zoologists. It aftords no explanation of the facts of 
a<hiptation, and has no causal value. 

Much more important than these theories is that of Wilhelm 
Iloux^ of "the struggle of parts within the organism, a supple- 
mentation of the theory of mechanical adaptation." lie explains 
the functional autoformation of the purposive structure by a 
combination of Darwin's principle of selection with Lamarck's idea 

1 Munich, 1884. ' Die MutatiomUieorie, Leipzig, 1903. 

» Der Kampfder Theile im Organismut, Leipzig, 1881. 

142 Darwin as an Atithrojyologist 

of transformative heredity, and applies the two in conjunction to the 
facts of liistology. He lays stress on the significance of functional 
adaptation, which I had described in 1866, under the head of cumu- 
lative adaptation, as the most important factor in evolution. Pointing 
out its influence in the cell-life of the tissues, he puts "cellular 
selection" above "personal selection," and shows how the finest 
conceivable adaptations in the structure of the tissue may be brought 
about quite mechanically, without preconceived plan. Tliis "me- 
chanical teleology" is a valuable extension of Darwin's monistic 
principle of selection to the whole field of cellular physiology and 
histology, and is wholly destructive of dualistic vitalism. 

The most important advance that evolution has made since 
Darwin and the most valuable amplification of his theory of selec- 
tion is, in my opinion, the work of Richard Semon: Die Mneme 
als erhaltendes Primip im Wechsel des organischen Geschehens^. 
He ofl'ers a psychological explanation of the facts of heredity by 
reducing them to a process of (unconscious) memory. The physio- 
logist Ewald Bering had shown in 1870 that memory must be 
regarded as a general function of organic matter, and that we are 
quite unable to explain the chief vital phenomena, especially those 
of reproduction and inheritance, unless we admit this unconscious 
memory. In my essay Die Perigenesis der Plasfidide^ I elabo- 
rated this far-reaching idea, and applied the physical principle of 
transmitted motion to the plastidules, or active molecules of plasm. 
I concluded that "heredity is the memory of the plastidules, and 
variability their power of comprehension." This "provisional attempt 
to give a mechanical explanation of the elementary processes of 
evolution" I afterwards extended by showing that sensitiveness is 
(as Carl Nageli, Ernst Mach, and Albrecht Rau express it) a general 
quality of matter. This form of panpsychism finds its simplest 
expression in the "trinity of substance." 

To the two fundamental attributes that Spinoza ascribed to 
substance — Extension (matter as occupying space) -and Cogitation 
(energy, force) — we now add the third fundamental quality of 
Psychoma (sensitiveness, soul). I further elaborated this trinitarian 
conception of substance in the nineteenth chapter of my Die 
Lehenswimdcr (1904)^, and it seems to me well calculated to aflbrd a 
monistic solution of many of the antitheses of philosophy. 

This important Mneme-theory of Semon and the luminous 
physiological experiments and observations associated with it not 
only throw considerable light on transformative inheritance, but 
provide a sound physiological foundation for the biogenetic law. 

1 Leipzig', 1904. 2 Berlin, 1876. 

* Wonders of Life, London, 1904. 

Embryology 143 

I had endeavoured to show in 1874, in the first chapter of my 
Anthropogenie^, that this fundamental law of organic evolution 
holds good generally, and that there is everywhere a direct causal 
connection between ontogeny and phylogeny. "Phylogenesis is 
the mechanical cause of ontogenesis " ; in other words, " The 
evolution of the stem or race is — in accordance with the laws of 
heredity and adaptation — the real cause of all the changes that 
appear, in a condensed form, in the development of the individual 
organism from the ovum, in either the embryo or the larva." 

It is now fifty years since Charles Darwin pointed out, in the 
thirteenth chapter of his epoch-making Origin of Species, the 
fundamental importance of embryology in connection with his theory 
of descent : 

"The leading facts in embryology, which are second to none in 
importance, are explained on the principle of variations in the many 
descendants from some one ancient progenitor, having appeared at 
a not very early period of life, and having been inherited at a 
corresponding period^." 

He then shows that the striking resemblance of the embryos and 
larvae of closely related animals, which in the mature stage belong to 
widely different species and genera, can only be explained by their 
descent from a common progenitor. Fritz Miiller made a closer 
study of these important phenomena in the instructive instance of 
the Crustacean larva, as given in his able work Fiir Darwin^ (1864). 
I then, in 1872, extended the range so as to include all animals (with 
the exception of the unicellular Protozoa) and showed, by means of 
the theory of the Gastraea, that all multicellular, tissue-forming 
animals — all the Metazoa — develop in essentially the same way from 
the primary germ-layers. I conceived the embryonic form, in which 
the whole structure consists of only two layers of cells, and is 
known as the gastrula, to be the ontogenetic recapitulation, main- 
tained by tenacious heredity, of a primitive common progenitor of 
all the Metazoa, the Gastraea. At a later date (1895) Monticelli 
discovered that this conjectural ancestral form is still preserved in 
certain primitive Coelenterata — Pemmatodiscus, Kunstleria, and the 
ncai-ly-related Orthonectida. 

The general apj>lication of the biogenetic law to all classes 
of animals and plants has been proved in my Sf/stematische 
PJn/logenie*. It has, however, been frequently challenged, both by 
botanists and zoologists, chiefly owing to the fact that many have 
failed to distinguish its two essential elements, palingenesis and 

' EnK. tranKl.; The F.voUttion uf Man, 2 vols., London, 1879 and 1905. 

» Ori<jin of Specif. i (Gtli edit.), p. ^^^^^>. 

' Eng. trannl. ; Facts and Arguments for Daricin, London, 1869. 

* 3 vols., Berlin, 1894-96. 

144 Darivin as an Anthropologist 

cenogenesis. As early as 18/4 I had emphasised, in the first chapter 
of my Evolution of Man, the importance of discriminating carefully 
between these two sets of phenomena : 

" In the evolutionary appreciation of the facts of embryology we 
must take particular care to distinguish sharply and clearly between 
the primary, palingenetic evolutionary processes and the secondary, 
cenogenetic processes. The palingenetic phenomena, or embryonic 
recapitulations, are due to heredity, to the transmission of characters 
from one generation to another. They enable us to draw direct 
inferences in regard to corresponding structures in the development 
of the species (e.g. the chorda or the branchial arches in all vertebrate 
embryos). The cenogenetic phenomena, on the other hand, or the 
embryonic variations, cannot be traced to inheritance fi'om a mature 
ancestor, but are due to the adaption of the embryo or the larva to 
certain conditions of its individual development (e.g. the amnion, the 
allantois, and the vitelline arteries in the embryos of the higher 
vertebrates). These cenogenetic phenomena are later additions ; we 
must not infer from them that there were corresponding processes in 
the ancestral history, and hence they are apt to mislead." 

The fundamental importance of these facts of comparative anatomy, 
atavism, and the rudimentary organs, was pointed out by Darwin in 
the first part of his classic work. The Descent of Man and Selection 
in Relation to Sex (1871)^ In the "General summary and con- 
clusion " (chap. XXI.) he was able to say, with perfect justice : " He 
who is not content to look, like a savage, at the phenomena of nature 
as disconnected, cannot any longer believe that man is the work of a 
separate act of creation. He will be forced to admit that the close 
resemblance of the embryo of man to that, for instance, of a dog — 
the construction of his skull, limbs, and whole fi'ame on the same 
plan with that of other mammals, independently of the uses to which 
the parts may be put — the occasional reappearance of various struc- 
tures, for instance of several muscles, which man does not normally 
possess, but which are common to the Quadrumana — and a crowd of 
analogous facts — all point in the plainest manner to the conclusion 
that man is the co-descendant with other mammals of a common 

These few lines of Darwin's have a greater scientific value than 
hundreds of those so-caUed "anthropological treatises," which give 
detailed descriptions of single organs, or mathematical tables with 
series of numbers and what are claimed to be " exact analyses," but 
are devoid of synoptic conclusions and a philosophical spirit. 

Charles Darwin is not generally recognised as a great anthro- 
pologist, nor does the school of modern anthropologists regard him 

1 Descent of Man (Popular Edit.), p. ^27. 

Vir chow's opposition to Dane in 145 

as a leadings authority. In Germany, especially, the great majority 
of the members of the anthropological societies took up an attitude 
of hostility to him from tiie very beginning of the controversy in 
1800. The Descent of Man was not merely rejected, but even the 
discussion of it was forbidden on the gi'ound that it was "unscientific." 

The centre of this inveterate hostility for thirty years — especially 
after 1877 — was Rudolph Virchow of Bci-lin, the leading investigator 
in pathological anatomy, who did so much for the reform of medicine 
by his establishment of cellular pathology in 1858. As a prominent 
representative of "exact" or "descriptive" anthropology, and lacking 
a broad equipment in comparative anatomy and ontogeny, he was 
unable to accept the theory of descent. In earlier years, and 
especially during his splendid period of activity at Wurzburg (1848 — 
1856), he had been a consistent fi*ee-thinker, and had in a number of 
able articles (collected in his Gesammelte Abhandlu7igeny upheld 
the unity of human nature, the inseparability of body and spirit. 
In later years at Berlin, where he was more occupied with political 
work and sociology (especially after 18GG), he abandoned the positive 
monistic position for one of agnosticism and scepticism, and made 
concessions to the dualistic dogma of a spiritual world apart from 
the material frame. 

In the course of a Scientific Congress at Munich in 1877 the 
conflict of these antithetic views of nature came into sharp relief. 
At this memorable Congress I had undertaken to deliver the first 
address (September 18th) on the subject of "Modern evolution in 
relation to the whole of science." I maintained that Darwin's theory 
not only solved the great problem of the origin of species, but that 
its implications, especially in regard to the nature of man, threw 
considerable light on the whole of science, and on anthropology in 
particular. The discovery of the real origin of man by evolution 
from a long series of mammal ancestors threw light on his place in 
nature in every aspect, as Huxley had already shown in his excellent 
lectures of 180:5. Just as all the organs and tissues of the human 
body had originated from those of the nearest related mammals, 
certain ape-like forms, so we were bound to conclude that his mental 
(lualities also had been derived from those of his extinct primate 

This monistic view of the origin and nature of man, which is now 
adiiiittcd by nearly all who have the rc(|uisite acquaintance with 
biology, and approach the subject without prejudice, encountered a 
sharp ojjposition at that time. The opposition found its strongest 
cxjjression in an address that Virchow delivered at Munich four 
days afterwards (September 22nd), on "The freedom of science in 

' Gesammelte Abhandtungen zur wisseiucha/tlichen Medizin, Berlin, 18J)6. 
D. 10 

146 Darwin as an Anthrojjologist 

the modern State." He spoke of the theory of evohition as an 
unproved hypothesis, and declared that it ought not to be taught 
in the schools, because it was dangerous to the State. "We must 
not," he said, " teach that man has descended fi'om the ape or any 
other animal." When Dai'win, usually so lenient in his judgment, 
read the English translation of Virchow's speech, he expressed 
his disapproval in strong terms. But the great authority that 
Virchow had — an authority well founded in pathology and 
sociology — and his prestige as President of the German Anthro- 
pological Society, had the effect of preventing any member of 
the Society fi'om raising serious opposition to him for thirty 
years. Numbers of journals and treatises repeated his dogmatic 
statement: "It is quite certain that man has descended neither 
fi'om the ape nor from any other animal." In this he persisted till 
his death in 1902. Since that time the whole position of German 
anthropology has changed. The question is no longer whether man 
was created by a distinct supernatural act or evolved fi'om other 
mammals, but to which line of the animal hierarchy we must look 
for the actual series of ancestors. The interested reader will 
find an account of this "battle of Munich" (1877) in my three 
Berlin lectures (April, 1905), Der Kampf um die Entwickeluugs- 

The main points in our genealogical tree were clearly recognised 
by Darwin in the sixth chapter of the Descent of 3Ian. Lowly 
organised fishes, like the lancelet (Amphioxus), are descended from 
lower invertebrates resembling the larvae of an existing Tunicate 
(Appendicularia). From these primitive fishes were evolved higher 
fishes of the ganoid type and others of the type of Lepidosiren 
(Dipneusta). It is a very small step from these to the Amphibia : 

"In the class of mammals the steps are not difficult to conceive 
which led from the ancient Monotremata to the ancient Marsupials ; 
and from these to the early progenitors of the placental mammals. 
We may thus ascend to the Lemuridae ; and the interval is not very 
wide from these to the Simiadae. The Simiadae then branched ofi" 
into two gi-eat stems, the New World and Old World monkeys ; and 
from the latter, at a remote period, Man, the wonder and glory of the 
Universe, proceeded^." 

In these few lines Darwin clearly indicated the way in which we 
were to conceive our ancestral series within the vertebrates. It is 
fully confirmed by all the arguments of comparative anatomy and 
embiyology, of palaeontology and physiology ; and all the research of 
the subseifuent forty years has gone to establish it. The deep interest 

' Eng. transl. ; Last Words on Evolution, London, 1906, 
■■' Descent of Man (Pojjular Edit.), p. 255. 

" The Descent of Man'' U7 

in geology which Darwin maintained throughout his life and his 
complete Icnowledge of palaeontology enabled him to grasp the funda- 
mental importance of the palaeontological record more clearly than 
anthropologists and zoologists usually do. 

There has been much debate in subsequent decades whether 
Darwin liimself maintained that man was descended from the ape, 
and many writers have sought to deny it. But the lines I have 
quoted verbatim from the conclusion of the sixth chapter of the 
Descent of Man (1871) leave no doubt that he was as firmly con- 
vinced of it as was his gi-eat precursor Jean Lamarck in 1809. 
Moreover, Darwin adds, with particular explicitness, in the "general 
summary and conclusion" (chap, xxi.) of that standard work^: 

" By considering the embryological structure of man — the homo- 
logies which he presents with the lower animals, — the rudiments 
which he retains, — and the reversions to which he is liable, we can 
partly recall in imagination the former condition of our early pro- 
genitors ; and can approximately place them in their proper place in 
the zoological series. We thus learn that man is descended from a 
hairy, tailed quadruped, probably arboreal in its habits, and an 
inhabitant of the Old World. This creature, if its whole structure 
had been examined by a naturalist, would have been classed amongst 
the Quadrumana, as surely as the still more ancient progenitor of the 
Old and New World monkeys." 

These clear and definite lines leave no doubt that Darwin — so 
critical and cautious in regard to important conclusions — was quite 
as firmly convinced of the descent of man from the apes (the Catar- 
rhinae, in particular) as Lamarck was in 1809 and Huxley in 18G3. 

It is to be noted particularly that, in these and other observations 
on the subject, Darwin decidedly assumes the monophyletic origin of 
the mammals, including man. It is my own conviction that this is of 
the greatest importance. A number of difficult questions in regard 
to the development of man, in respect of anatomy, physiology, psy- 
chology, and embryology, are easily settled if we do not merely 
extend our progonotaxis to our nearest relatives, the anthropoid 
apes and the tailed monkeys from which these have descended, 
but go further back and find an ancestor in the group of the 
Lcniuridae, and still further back to tlie Marsupials and Monotre- 
mata. The essential identity of all the Manmiuls in point of ana- 
tomical structure and embryonic development — in sj)ite of their 
it-jtoninhiug difiercnces in external apj)earancc and habits of life — is 
so palpably significant that modern zoologists are agreed in the 
hypothesis that they have all sprung from a common root, and that 
tliis root may be sought in the earlier Palaeozoic Amphibia. 

* DitceiU oj Man, p. 930. 


148 Darwin as an Antfu-opologist 

The fundamental importance of this comparative morphology of 
the Manmials, as a sound basis of scientific anthropology, was re- 
cognised just before the beginning of the nineteenth century, when 
Lamarck first emphasised (1794) the division of the animal kingdom 
into Vertebrates and Invertebrates. Even thirteen years earlier 
(1781), when Goethe made a close study of the mammal skeleton 
in the Anatomical Institute at Jena, he was intensely interested to 
find that the composition of the skull was the same in man as in the 
other mammals. His discovery of the os intermaxillare in man (1 784), 
which was contradicted by most of the anatomists of the time, and 
his ingenious " vertebral theory of the skull," were the splendid fi'uit 
of his morphological studies. They remind us how Germany's greatest 
philosopher and poet was for many years ardently absorbed in the 
comparative anatomy of man and the mammals, and how he divined 
that their wonderful identity in structure was no mere superficial 
resemblance, but pointed to a deep internal connection. In my 
Gefierelle Morphohgie (18C6), in which I published the first attempts 
to construct phylogenetic trees, I have given a number of remarkable 
theses of Goethe, which may be called "phyletic prophecies." They 
justify us in regarding him as a precursor of Darwin. 

In the ensuing forty years I have made many conscientious efibrts 
to penetrate further along that line of anthropological research that 
was opened up by Goethe, Lamarck, and Darwin. I have brought 
together the many valuable results that have constantly been reached 
in comparative anatomy, physiology, ontogeny, and palaeontology, and 
maintained the effort to reform the classification of animals and 
plants in an evolutionary sense. The first rough drafts of pedigrees 
that were published in the Generelle Morphohgie have been improved 
time after time in the ten editions of my Natiirliche Schop/ungs- 
geschichte (1868 — 1902)\ A sounder basis for my phyletic hypotheses, 
derived from a discriminating combination of the three great records — 
morphology, ontogeny, and palaeontology — was provided in the three 
volumes of my Systematische Phylogenie^ (1894 Protists and Plants, 
1895 Vertebrates, 1896 Invertebrates). In my Anthropogenie^ I 
endeavoured to employ all the kno^vn facts of comparative ontogeny 
(embryology) for the purpose of completing my scheme of human 
phylogcny (evolution). I attempted to sketch the historical develop- 
ment of each organ of the body, beginning with the most elemen- 
tary structures in the germ-layers of the Gastraea. At the same time 
I drew up a corrected statement of the most important steps in the 
line of our ancestral series. 

1 Eng. transl. ; The History of Creation, London, 1876. '^ Berlin, 1894—96. 

' Leipzig, 1874, 5th edit. 1905. Eng. transl.; The Evolution of Man, London, 

Man's Place in Nature 149 

At the fourth International Congress of Zoology at Cambridge 
(August 26th, 1898) I delivered an address on "Our present knowledge 
of the Descent of Man." It was translated into English, enriched 
with many valuable notes and additions, by my friend and pupil in 
earlier days Dr Hans Gadow (Cambridge), and published under the 
title : The Last Link ; our present hnoivlcdgc of the Descent of 
Man\ The determination of the chief animal forms that occur in 
the line of our ancestry is there restricted to thirty types, and these 
are distributed in six main groups. 

The first half of tliis " Progonotaxis hominis," which has no 
support from fossil evidence, comprises three groups : (i) Protista 
(unicellular organisms, 1 — 5) : (ii) Invertebrate Metazoa (Coelenteria 
6 — 8, Vermalia 9 — 11): (iii) Monorrhine Vertebrates (Acrania 12 — 
13, Cyclostoma 14 — 15). The second half, which is based on fossil 
records, also comprises three gi-oups : (iv) Palaeozoic cold-blooded 
Craniota (Fishes 16 — 18, Amphibia 19, Reptiles 20) : (v) Mcsozoic 
Mammals (Monotrema 21, Marsupialia 22, Mallotheria 23): (vi) Ce- 
nozoic Primates (Lemuridae 24 — 25, Tailed Apes 26 — 27, Anthropo- 
morpha 28 — 30). An improved and enlarged edition of this hypothetic 
"Progonotaxis hominis" was published in 1908, in my essay Unsere 

If I have succeeded in furthering, in some degi*ee, by these an- 
thropological works, the solution of the great problem of Man's place 
in nature, and particularly in helping to trace the definite stages in 
our ancestral series, I owe the success, not merely to the vast progress 
that biology has made in the last half century, but largely to the 
luminous example of the great investigators who have applied them- 
selves to the problem, M'ith so much assiduity and genius, for a 
century and a quarter — I mean Goethe and Lamarck, Gegcnbaur and 
Huxley, but, above all, Charles Darwin. It was the great genius of 
Darwin that first brought together the scattered material of biology 
and shaped it into that symmetrical temple of scientific knowledge, 
the theory of descent. It was Darwin who put the crown on tlie 
edifice by his theory of natural selection. Not until this broad in- 
ductive law was firmly established was it possible to vindicate the 
special conclusion, the descent of man from a series of other Verte- 
brates. By his illuminating discovery Darwin did more for anthro- 
j)ology than thousands of those ^vriters, who are more specifically 
titled anthropologists, have done by their technical treatises. We 
may. indeed, say that it is not merely as an exact observer and ingenious 
experimenter, but as a distinguished anthropologist and lar-seeing 

' Loiulon, 1898. 

' FesUchri/t zur S50-jtihrigen Jubelfeier der ThUringer Universitdt Jena. Jena, 

150 Darwin as an Anthropologist 

thinker, that Darwin takes his place among the greatest men of science 
of the nineteenth century. 

To appreciate fully the immortal merit of Darwin in connection 
with anthropology, we must remember that not only did his chief 
work, The Origin of SiJecies, which opened up a new era in natural 
history in 1859, sustain the most virulent and widespread opposition 
for a lengthy period, but even thirty years later, when its principles 
were generally recognised and adopted, the application of them to 
man was energetically contested by many high scientific authorities. 
Even Alfi-ed Russel Wallace, who discovered the principle of natural 
selection independently in 1858, did not concede that it was applicable 
to the higher mental and moral qualities of man. Dr Wallace still 
holds a spiritualist and dualist view of the nature of man, contending 
that he is composed of a material frame (descended fi-om the apes) 
and an immortal immaterial soul (infused by a higher power). This 
dual conception, moreover, is still predominant in the wide circles of 
modern theology and metaphysics, and has the general and influential 
adherence of the more conservative classes of society. 

In strict contradiction to this mystical dualism, which is generally 
connected with teleology and vitalism, Darwin always maintained the 
complete unity of human nature, and showed convincingly that the 
psychological side of man was developed, in the same way as the body, 
from the less advanced soul of the anthropoid ape, and, at a still more 
remote period, from the cerebral functions of the older vertebrates. 
The eighth chapter of the Origin of Species, which is devoted to 
instinct, contains weighty evidence that the instincts of animals are 
subject, like all other vital processes, to the general laws of historic 
development. The special instincts of particular species were formed 
by adaptation, and the modifications thus acquired were handed on 
to posterity by heredity ; in their formation and preservation natural 
selection plays the same part as in the transformation of every other 
physiological function. The higher moral qualities of civilised man 
have been derived from the lower mental functions of the un- 
cultivated barbarians and savages, and these in turn from the social 
instincts of the mammals. This natural and monistic psychology of 
Darwin's was afterwards more fully developed by his friend George 
Romanes in his excellent works Mental Evolution in Animals and 
Mental Evolution in Man^. 

Many valuable and most interesting contributions to this monistic 
I)sychology of man were made by Darwin in his fine work on The 
Descent of Man and Selection in Relation to Sex, and again in his sup- 
plementary work, The Expression of the Emotions in Man and A nimals. 
To understand the historical development of Darwin's anthropology one 

1 London, 1885; 1888. 

Darivin's views on the Descent of Man 151 

must read his life and the introduction to The Descent of Man. From 
the moment that he was convinced of the truth of the principle of 
descent — that is to say, from his thirtieth year, in 1838 — he recognised 
clearly that man could not be excluded from its range. He recognised 
as a logical necessity the important conclusion that "man is the co- 
descendant with other species of some ancient, lower, and extinct 
form." For many years he gathered notes and argimients in support 
of this thesis, and for the purpose of showing the probable line of 
man's ancestry. But in the first edition of The Origin of Species 
(1859) he restricted himself to the single line, that by this work 
" light would be thrown on the origin of man and his history." In 
the fifty years that have elapsed since that time the science of the 
origin and nature of man has made astonishing progress, and we are 
now fairly agi'eed in a monistic conception of nature that regards the 
whole universe, including man, as a Avonderful unity, governed by 
unalterable and eternal laws. In my philosophical book Die 
Weltriitsel (1899)^ and in the supplementary volume Die Lehens- 
umnder (1904)^ I have endeavoured to show that this i)ure 
monism is securely established, and that the admission of the all- 
powerful rule of the same principle of evolution throughout the 
universe compels us to formulate a single supreme law — the all-em- 
bracing " Law of Substance," or the united laws of the constancy of 
matter and the conservation of energy. We should never have 
reached this supreme general conception if Charles Darwin — a "mo- 
nistic philosopher" in the true sense of the word — had not prepared 
the way by his theory of descent by natural selection, and crowned 
the gi-eat work of his life by the association of this theory with a 
naturalistic anthropology. 

* The Riddle of the Universe, London, 1900. 
« The Wonders of Life, London, 1904. 




By J. G. Frazer. 

Fellow of Trinity College, Cambridge. 

On a bright day in late autumn a good many years ago I had 
ascended the hill of Panopeus in Phocis to examine the ancient Greek 
fortifications which crest its brow. It was the first of November, but 
the weather was very hot ; and when my work among the ruins was 
done, I was glad to rest under the shade of a clump of fine holly-oaks, 
to inhale the sweet refreshing perfume of the wild thyme which 
scented all the air, and to enjoy the distant prospects, rich in natural 
beauty, rich too in memories of the legendary and historic past. 
To the south the finely-cut peak of Helicon peered over the low 
intervening hills. In the west loomed the mighty mass of Parnassus, 
its middle slopes darkened by pine-woods like shadows of clouds 
brooding on the mountain-side ; while at its skirts nestled the ivy- 
mantled walls of Daulis overhanging the deep glen, whose romantic 
beauty accords so well with the loves and sorrows of Procne and 
Philomela, which Greek tradition associated with the spot. North- 
wards, across the broad plain to which the hill of Panopeus descends, 
steep and bare, the eye rested on the gap in the hills through which 
the Cephissus winds his tortuous way to flow under grey willows, at 
the foot of barren stony hills, till his turbid waters lose themselves, no 
longer in the vast reedy swamps of the now vanished Copaic Lake, 
but in the darkness of a cavern in the limestone rock. Eastward, 
clinging to the slopes of the bleak range of which the hill of Panopeus 
forms part, were the ruins of Chaeronea, the birthplace of Plutarch ; 
and out there in the plain was fought the disastrous battle which laid 
Greece at the feet of Macedonia. There, too, in a later age East and 
West met in deadly conflict, when the Roman armies under Sulla 
defeated the Asiatic hosts of Mithridates. Such was the landscape 
spread out before me on one of those farewell autumn days of almost 
pathetic splendour, when the departing summer seems to linger 
fondly, as if loth to resign to winter the enchanted mountains ot 

Creation of Man out of Clay 153 

Greece. Next day the scene had changed : summer was gone. A 
grey November mist hung low on the hills wliich only yesterday had 
shone resplendent in the sun, and under its melancholy curtain the 
dead flat of the Chaeronean plain, a wide treeless expanse shut in by 
desolate slopes, wore an aspect of chilly sadness befitting the battle- 
field where a nation's freedom was lost. 

But crowded as the prospect fi-om Panopeus is ^vith memories of the 
past, the place itself, now so still and deserted, was once the scene of an 
event even more ancient and memorable, if Greek story-tellers can be 
trusted. For here, they say, the sage Prometheus created our first 
parents by fashioning them, like a potter, out of clay^ The very spot 
where he did so can still be seen. It is a forlorn little glen or rather 
hollow behind the hill of Panopeus, below the ruined but still stately 
walls and towers which crown the grey rocks of the summit. The glen, 
when I visited it that hot day after the long drought of summer, was 
quite dry ; no water trickled down its bushy sides, but in the bottom 
I found a reddish crumbling earth, a relic perhaps of the clay out of 
which the potter Prometheus moulded the Greek Adam and Eve. In 
a volume dedicated to the honour of one who has done more than any 
other in modern times to shape the ideas of mankind as to their 
origin it may not be out of place to recall this crude Greek notion of 
the creation of the human race, and to compare or contrast it with 
other rudimentary speculations of primitive peoples on the same 
subject, if only for the sake of marking the interval which divides 
the childhood from the maturity of science. 

The simple notion that the first man and woman were modelled 
out of clay by a god or other superhuman being is found in the 
traditions of many peoples. This is the Hebrew belief recorded in 
Genesis : "The Lord God formed man of the dust of the ground, and 
breathed into his nostrils the breath of life ; and man became a living 
soul-." To the Hebrews this derivation of our species suggested itself 
all the more naturally because in their language the word for 
"ground" {adamali) is in form the feminine of the word for man 

' Pausanias, x. 4. 4. Compare ApoUodorus, Bihliotheca, i. 7. 1 ; Ovid, Metamorph. 
I. 82 sg. ; Juvenal, Sat. xiv. 35. According to another verbiou of the tale, this creation of 
mankind took place not at Panopeus, but at Iconium in Lycaonia. After the original race 
of mankind had been destroyed in the great flood of Deucalion, the Greek Noah, Zeus 
commanded Promethcua and Athena to create men afresh by moulding images out of clay, 
breathing the winds into them, and making them live. See Ktymologicum Magnum, s.v. 
'iKiviof, PI'. '170 nq. It is said that Prometheus fashioned the animals as well as men, giving 
to each kind of beast its proper nature. See Philemon, quoted by Stobaeus, Florilegium, 
n. 27. The creation of man by Prometheus is figured on ancient works of art. See 
J. Toutain, Etudes dc Mythologie et d' Histoire des lieliijion* Antiques (Pp.ria, 1909), p. 190. 
According to Hcsiod [W'orku nnd Days, GO iqq.) it was Hephaestus who at the bidding 
of Zeus moulded the first woman out of moist earth. 

' Genesis ii. 7. 

154 Primitive Theories of the Origin of Man 

(adam)\ From various allusions in Babylonian literature it would 
seem that the Babylonians also conceived man to have been moulded 
out of clay I According to Berosus, the Babylonian priest whose 
account of creation has been preserved in a Greek version, the god 
Bel cut off his own head, and the other gods caught the flowing blood, 
mixed it with earth, and fashioned men out of the bloody paste ; and 
that, they said, is why men are so wise, because their mortal clay is 
tempered with divine bloods In Egyptian mythology Khnoumou, 
the Father of the gods, is said to have moulded men out of clay*. 
We cannot doubt that such crude conceptions of the origin of our 
race were handed down to the civilised peoples of antiquity by their 
savage or barbarous forefathers. Certainly stories of the same sort 
are known to be current among savages and barbarians. 

Thus the Australian blacks in the neighbourhood of Melbourne 
said that Pund-jel, the creator, cut three large sheets of bark with his 
big knife. On one of these he placed some clay and worked it up 
with his knife into a proper consistence. He then laid a portion 
of the clay on one of the other pieces of bark and shaped it into 
a human form ; first he made the feet, then the legs, then the trunk, 
the arms, and the head. Thus he made a clay man on each of the 
two pieces of bark ; and being well pleased with them he danced 
round them for joy. Next he took stringy bark fi'om the Eucalyptus 
tree, made hair of it, and stuck it on the heads of his clay men. Then 
he looked at them again, was pleased with his work, and again danced 
round them for joy. He then lay down on them, blew his breath 
hard into their mouths, their noses, and their navels ; and presently 
they stirred, spoke, and rose up as full-grown men^ The Maoris 
of New Zealand say that Tiki made man after his own image. He 
took red clay, kneaded it, like the Babylonian Bel, with his own blood, 
fashioned it in human form, and gave the image breath. As he had 
made man in his own likeness he called him Tiki-ahua or Tiki's like- 
ness^ A very generally received tradition in Tahiti was that the 
first human pair was made by Taaroa, the chief god. They say that 

^ S. E. Driver and W. H. Bennett, in their commentaries on Genesis ii. 7. 

* H. Zimmern, in E. Schrader'e Die Keilinschriften und das Altc Testament'^ (Berlin, 
1902), p. 506. 

2 Eusebius, Chronicon, ed. A. Schoenc, Vol. i. (Berlin, 1875), col. 16. 

* G. Maspero, Histoire Ancienne des Peuples de VOricnt Classique, i. (Paris, 1895), 
p. 128. 

" B. Brough Smyth, The Aborigines of Victoria (Melbourne, 1878), i. 424. This and 
many of the following legends of creation have been already cited by me in a note on 
Pausanias, x. 4. 4 [Pausanias^s Discription of Greece, translated with a Covimentary 
(London, 1898), Vol. v. pp. 220 sq.\ 

« R. Taylor, Te Ika A Maui, or New Zealand and its Inhabitants, Second Edition 
(London, 1870), p. 117. Compare E. Shortland, Maori Religion and Mythology (London, 
1882), pp. 21 $q. 

Creation of Man out of Clay 155 

after he had formed the world he created man out of red earth, which 
was also the food of mankind until bread-fruit was produced. Further, 
some say that one day Taaroa called for the man by name, and when he 
came he made him fall asleep. As he slept, the creator took out one 
of his bones (^Vi) and made a woman of it, whom he gave to the man 
to be his wife, and the pair became the progenitors of mankind. This 
narrative was taken down from the lips of the natives in the early 
years of tlie mission to Tahiti. The missionary who records it observes : 
"This always appeared to me a mere recital of the IMosaic account of 
creation, which they had heard from some European, and I never 
placed any reliance on it, although they have repeatedly told me it 
was a tradition among them before any foreigner arrived. Some have 
also stated that the woman's name was Ivi, which would be by them 
pronounced as if written Eve. Ivi is an aboriginal word, and not 
only signifies a bone, but also a widow, and a victim slain in war. 
Notwithstanding the assertion of the natives, I am disposed to think 
that Ivi, or Eve, is the only aboriginal part of the story, as far as it 
respects the mother of the human race^." However, the same tradi- 
tion has been recorded in other parts of Polynesia besides Taliiti. 
Tlius the natives of Fakaofo or Bowditch Island say that the first 
man was produced out of a stone. After a time he bethought him of 
making a woman. So he gathered earth and moulded the figure of a 
woman out of it, and having done so he took a rib out of his left side 
and thrust it into the earthen figure, which thereupon started up a live 
woman. He called her Ivi (Eevee) or " rib " and took her to Avife, and 
the whole human race sprang from this pair^. The Maoris also are 
reported to believe that the first woman was made out of the first 
man's ribs^. Tliis wide difiiision of the story in Polynesia raises a 
doubt whether it is merely, as Ellis thought, a repetition of the 
Biblical narrative learned from Europeans. In Nui, or Netherland 
Island, it was the god Aulialia who made earthen models of a man 
and woman, raised them up, and made them live. He called the man 
Tepapa and the woman Tetata*. 

In the Pelew Islands they say that a brother and sister made 
men out of clay kneaded with tlic blood of various animals, and 
that the characters of these first men and of their descendants 
were determined by the characters of the animals whose blood 
had been kneaded with the priujordial clay ; for instance, men who 
have rat's blood in them are thieves, men who have serpent's blood 

' W. Ellis, Polynetian Jictearches, Second Edition (London, 1832), i. 110 sq. Ivi 
or iwi is the regular word for "bone" in the various Polynesian lan^iuages. See E. Tre(.;car, 
Thf Maori- I'ohjnrtian Comparative Dictionary (Wellington, New Zealand, 1891), p. 109. 

' O. Turner, Samoa (London, 1HS4), pp. 207 sq. 

•"" .1. L. Nicholas, Narrative of a Voyage to New Zealand (London, 1817), i. 59, who 
writcB "and to add still more to this strange coincidence, the general tt-nn for bone is Ilevee." 

* G. Turner, Samoa, pp. 3U0 tq. 

156 Frimitive Theories of the Origin of Man 

in them are sneaks, and men who have cock's blood in them are 
brave \ According to a Melanesian legend, told in Mota, one of the 
Banks Islands, the hero Qat moulded men of clay, the red clay fi-om 
the marshy river-side at Vanua Lava. At first he made men and pigs 
just alike, but his brothers remonstrated with him, so he beat down 
the pigs to go on all fours and made men walk upright. Qat fashioned 
the first woman out of supple twigs, and when she smiled he knew she 
was a living woman 2. A somewhat difierent version of the Melanesian 
story is told at Lakona, in Santa Maria. There they say that Qat and 
another spirit {via) called Marawa both made men. Qat made them 
out of the wood of dracaena-trees. Six days he worked at them, 
carving their limbs and fitting them together. Then he allowed them 
six days to come to life. Three days he hid them away, and three 
days more he worked to make them live. He set them up and 
danced to them and beat his drum, and little by little they stirred, till 
at last they could stand all by themselves. Then Qat divided them 
into pairs and called each pair husband and wife. Marawa also made 
men out of a tree, but it was a different tree, the tavisoviso. He 
likewise worked at them six days, beat his drum, and made them live, 
just as Qat did. But when he saw them move, he dug a pit and buried 
them in it for six days, and then, when he scraped away the earth to 
see what they were doing, he found them all rotten and stinking. 
Tliat was the origin of deaths 

The inhabitants of Noo-hoo-roa, in the Kei Islands say that their 
ancestors were fashioned out of clay by the supreme god, Dooad- 
lera, who breathed life into the clay figures*. The aborigines of 
Minahassa, in the north of Celebes, say that two beings called 
Wailan Wangko and Wangi were alone on an island, on which grew 
a cocoa-nut tree. Said Wailan Wangko to Wangi, "Remain on 
earth while I climb up the tree." Said Wangi to Wailan Wangko, 
"Good." But then a thought occurred to Wangi and he climbed up 
the tree to ask Wailan Wangko why he, Wangi, should remain down 
there all alone. Said Wailan Wangko to Wangi, "Return and take 
earth and make two images, a man and a woman." Wangi did so, and 
both images were men who could move but could not speak. So Wangi 
climbed up the tree to ask Wailan Wangko, " How now ? The two 
images are made, but they cannot speak." Said Wailan Wangko to 
Wangi, "Take this ginger and go and blow it on the skulls and the 
ears of these two images, that they may be able to speak ; call the man 

' J. Knbary, "Die Eeligion der Pelauer," in A. Bastian's Allerlei aut Volks- und 
M<'iuchenhunde (Berlin, 1888), i. 3, 56. 

2 11. H. Coihington, The Melanesians (Oxford, 1891), p. 158. 

' 11. H. Codrington, op. cit., pp. 157 nq. 

* C. M. Pleyte, " Ethnographische BeHchrijving der KeiEilanden," Tijdschrift vanhet 
Nederlandfch Aardrijkshundiy Gcnootschap, Tweede Serie, x. (1893), p. 664. 

Creation of Man out of Clay 157 

Adam and the woman Ewa\" In this narrative the names of tlie man 
and woman betray European influence, but the rest of the story may 
be aboriginal. The Dyaks of Sakarran in British Borneo say that 
the first man was made by two large birds. At first they tried to 
make men out of trees, but in vain. Then they hewed them out 
of rocks, but the figures could not speak. Then they moulded a man 
out of damp earth and infused into his veins the red gum of the 
kumpang-tree. After that they called to him and he answered ; they 
cut him and blood flowed from his wounds'^. 

The Kumis of South-Eastern India related to Captain Lewin, the 
Deputy Commissioner of Hill Tracts, the following tradition of the 
creation of man. "God made the world and the trees and the creeping 
things first, and after that he set to work to make one man and one 
woman, forming their bodies of clay ; but each night, on the com- 
pletion of his work, there came a great snake, which, while God was 
sleeping, devoured the two images. This happened twice or thrice, 
and God was at his wit's end, for he had to work all day, and could 
not finisli the pair in less than twelve hours; besides, if he did not 
sleep, he would be no good," said Captain Lewin's informant. "If 
he were not obliged to sleep, there would be no death, nor would 
mankind be afllicted with illness. It is when he rests that the snake 
carries us off" to this day. Well, he was at his wit's end, so at last he 
got up early one morning and first made a dog and put life into it, 
and tliat night, when he had finished the images, he set the dog to 
watch them, and Avhen the snake came, the dog barked and frightened 
it away. This is the reason at this day that when a man is dying the 
dogs begin to howl ; but I suppose God sleeps heavily now-a-days, or 
the snake is bolder, for men die all the same^" The Khasis of Assam 
tell a similar tale\ 

Tlic Ewe-speaking tribes of Togo-land, in West Africa, think that 
God still makes men out of clay. When a little of the water with 
which he moistens the clay remains over, he pours it on the ground 
and out of that he makes the bad and disobedient people. When he 
wishes to make a good man he makes him out of good clay ; but 
when he wishes to make a bad man, he employs only bad clay for the 
purpose. In the beginning God fashioned a man and set him on tlie 
earth; after that he fashioned a woman. The two looked at each 

1 N. Graafland, De Minahaixa (Rotterdam, 18G'J), i. pp. 96 sq. 

' HoiBburi^h, (luoted by H. Ling Roth, The Natives of Sarauak and of Uritinh North 
Borneo (London, IH'.iC), i. pp. 299 sq. Compare The Lord Bishop of Labtmn, "On the Wild 
Tribes of the North-WcHt Coast of Borneo," Transactions of tlie Ethnological Society of 
London, New Series, n. (IBCi:}), p. 27. 

» Capi. T. H. Lewin, Wild Races of South-Kustcrn India (London, 1870), pp. 224—26. 

♦ A. liiistian, Volkerstfimme am Braltmnpntra und verwandtschaftUche Ntichbarn (Berlin, 
1883), p. 8; Major P. R. T. Gurdon, The Khasis (London, 1907), p. 106. 

158 Primitive Theories of the Origin of Man 

other and began to laugh, whereupon God sent them into the worlds 
Tlie Innuit or Esquimaux of Point Barrow, in Alaska, tell of a time 
when there was no man in the land, till a spirit named d se lu, 
who resided at Point Barrow, made a clay man, set liira up on 
the shore to dry, breathed into him and gave him life^. Other 
Esquimaux of Alaska relate how the Raven made the first woman 
out of clay to be a companion to the first man ; he fastened water- 
grass to the back of the head to be hair, flapped his wings over the 
clay figure, and it arose, a beautiful young woman ^ The Acagchemem 
Indians of California said that a powerful being called Chinigchinich 
created man out of clay which he found on the banks of a lake ; male 
and female created he them, and the Indians of the present day are 
their descendants*. A priest of the Natchez Indians in Louisiana 
told Du Pratz "that God had kneaded some clay, such as that 
which potters use and had made it into a little man ; and that after 
examining it, and finding it well formed, he blew up his work, and 
forthwith that little man had life, grew, acted, walked, and found 
himself a man perfectly well shaped." As to the mode in which 
the first woman was created, the priest had no information, but 
thought she was probably made in the same way as the first 
man; so Du Pratz corrected his imperfect notions by reference to 
Scripture^. The Michoacans of Mexico said that the great god 
Tucapacha first made man and woman out of clay, but that when the 
couple went to bathe in a river they absorbed so much water that 
the clay of which they were composed all fell to pieces. Then the 
creator went to work again and moulded them afresh out of ashes, 
and after that he essayed a third time and made them of metal. 
This last attempt succeeded. The metal man and woman bathed in 
the river without falling to pieces, and by their union they became 
the progenitors of mankind*^. 

According to a legend of the Peruvian Indians, which was told to 
a Spanish priest in Cuzco about half a century after the conquest, 
it Avas in Tiahuanaco that man was first created, or at least was 
created afresh after the deluge. "There (in Tiahuanaco)," so runs 

^ J. Spieth, Die Ewe-Stdmme, Material zur Kunde des Ewe-Volkes in Deiitsch-Togo 
(Berlin, 1900), pp. 828, 840. 

^ Report of the International Expedition to Point Barrow (Washington, 1885), p. 47. 

3 E. W. Nelson, "The Eskimo about Bering Strait," Eighteenth Annual Report of 
the Bureau of American Ethnology, Part i. (Washington, 1899), p. 454. 

* Friar Geronimo Boscaua, "Chinigchinich," appended to [A, Kobinson's] Life in 
California (New York, 1846), p. 247. 

* M. Le Page Du Pratz, Tfie History of Louisiana (London, 1774), p. 330. 

" A. de Ilerrera, General History of the vast Continent and Islands of America, trans- 
lated into English by Capt. J. Stevens (London, 1725, 1720), in. 2o4 ; Brasseur de Bour- 
bourg, Histoire des Nations Civilisees du Mexique et de VAmerique-Centrale (Paris, 1857 — 
1859), HI. 80 sq. ; compare id. i. 54 sq. 

Kinship of Man with Animals 159 

the legend, "the Creator began to raise up the people and nations 
that are in that region, making one of each nation of clay, and 
painting the dresses that each one was to wear ; those that were to 
wear their hair, with hair, and those that were to be shorn, with hair 
cut. And to each nation was given the language, that was to be 
spoken, and the songs to be sung, and the seeds and food that they 
were to sow. ^Vhen the Creator had finished painting and making 
the said nations and figures of clay, he gave life and soul to each 
one, as well men as women, and ordered that they should pass under 
the earth. Thence each nation came up in the places to which he 
ordered them to go\" 

These examples suffice to prove that the theory of the creation of 
man out of dust or clay has been current among savages in many 
parts of the world. But it is by no means the only explanation which 
the savage philosopher has given of the beginnings of human life on 
earth- Struck by the resemblances which may be traced between 
himself and the beasts, he has often supposed, like Dar\nn himself, 
that mankind has been developed out of lower forms of animal life. 
For the simple savage has none of that high notion of the transcendant 
dignity of man which makes so many superior persons shrink with 
horror from the suggestion that they are distant cousins of the 
brutes. He on the contrary is not too proud to own his humble 
relations; indeed his difficulty often is to perceive the distinction 
between him and them. Questioned by a missionary, a Bushman of 
more than average intelligence "could not state any difference 
between a man and a brute — he did not know but a bufllilo might 
shoot with bows and arrows as well as a man, if it had them'l" ^Mien 
the Russians first landed on one of the Alaskan islands, the natives 
took them for cuttle-fish " on account of the buttons on their clothes^" 
Tlie Giliaks of the Amoor think that the outward form and size of an 
animal are only apparent; in substance every beast is a real man, 
just like a Giliak himself, only endowed with an intelligence and 
strength, which often surpass those of mere ordinary human beings \ 
The Borororos, an Indian tribe of Brazil, will have it that they are 
parrots of a gorgeous red plumage which live in their native forests. 
Accordingly they treat the birds as their fellow-tribesmen, keeping 
them in captivity, refusing to eat their flesh, and mourning for them 
when they die^ 

' E. J. Payne, History of the New World called America, i. (Oxford, 1892), p. 4G2. 

* Rev. John Campbell, Travels in South Africa (London, 1822), ii. p. 34. 

' I. Petroff, Report on the Population, Industries, ami Jlesources of Alaska, p. 145. 

* L. Sternberg, "Die Religion der (Jiljiikcn," Arrhiv filr Ili'lii/iutisu-isseruichaft, viii. 
(I'M-,), p. 248. 

* K. von den Steinen, Unter den Naturvblkern Zentrul-Urasiliens (Berlin, 18'J4), 
pp. 352 >q., 512. 

160 Prwiitive Theories of the Origin of Man 

Tliis sense of the close relationship of man to the lower creation 
is the essence of totemism, that curious system of superstition which 
unites by a mystic bond a group of human kinsfolk to a species of 
animals or plants. Wliere that system exists in full force, the mem- 
bers of a totem clan identify themselves with their totem animals in 
a way and to an extent which we find it hard even to imagine. For 
example, men of the Cassowary clan in Mabuiag think that cassowaries 
are men or nearly so. "Cassowary, he all same as relation, he belong 
same family," is the account they give of their relationship with the 
long-legged bird. Conversely they hold that they themselves are 
cassowaries for all practical purposes. They pi-ide themselves on 
having long thin legs like a cassowary. This reflection affords them 
peculiar satisfaction when they go out to fight, or to run away, as 
the case may be ; for at such times a Cassowary man will say to himself, 
" My leg is long and thin, I can run and not feel tired ; my legs will 
go quickly and the grass will not entangle them." JMembers of the 
Cassowary clan are reputed to be pugnacious, because the cassowary 
is a bird of very uncertain temper and can kick with extreme 
violence \ So among the Ojibways men of the Bear clan are 
reputed to be surly and pugnacious like bears, and men of the 
Crane clan to have clear ringing voices like cranes^. Hence the 
savage will often speak of his totem animal as his father or his 
brother, and will neither kill it himself nor allow others to do so, 
if he can help it. For example, if somebody were to kill a bird 
in the presence of a native Australian who had the bird for his 
totem, the black might say, " What for you kill that fellow ? that 
my father ! " or " That brother belonging to me you have killed ; why 
did you do it?^" Bechuanas of the Porcupine clan are greatly 
afilicted if anybody hurts or kills a porcupine in their presence. 
They say, "They have killed our brother, our master, one of our- 
selves, him whom we sing of"; and so saying they piously gather 
the quills of their murdered brother, spit on them, and rub their 
eyebrows with them. They think they would die if they touched its 
flesh. In like manner Bechuanas of the Crocodile clan call the 
crocodile one of themselves, their master, their brother; and they 
mark the ears of their cattle with a long slit like a crocodile's mouth 
by May of a family crest. Similarly Bechuanas of the Lion clan 
would not, like the members of other clans, partake of lion's flesh ; 
for how, say they, could they eat their grandfather? If they are 

1 A. C. Haddon, "The Ethnography of the Wef9tern Tribe of Torres Straits," Journal 
of the Anthropological Imtitule, xix. (1890), p. 393 ; Rejiorts of the Cambridge Anthropolo- 
gical Expedition to Torres Straits, v. (Cambridge, 1901), pp. 166, 184. 

' W. W. Warren, "History of the Ojibways," Collections of the Minnesota Historical 
Society, v. (Saint Paul, Miun. 1885), pp. 47, 19. 

* E. Palmer, "Notes on some Australian Tribes," Journal of the Anthropological 
Institute, xiii. (1884), p. 300. 

Kinship of Man tvith Animals 161 

forced in self-defence to kill a lion, they do so with great regret and 
rub their eyes carefully Avith its skin, fearing to lose their sight if 
they neglected this precaution \ A ]\landingo porter has been knoMii 
to offer the whole of his month's pay to save the life of a python, be- 
cause the python was his totem and he therefore regarded the reptile 
as his relation ; he thought that if he allowed the creature to be killed, 
the whole of his own family would perish, probably through the venge- 
ance to be taken by the reptile kinsfolk of the murdered serpent'. 

Sometimes, indeed, the savage goes further and identifies the 
revered animal not merely with a kinsman but with himself; he 
imagines that one of his own more or less numerous souls, or at all 
events that a vital part of himself, is in the beast, so that if it is 
killed he must die. Thus, the Balong tribe of the Cameroons, in 
Wcat Africa, think that every man has several souls, of which one is 
lodged in an elephant, a wild boar, a leopard, or what not. ^Vhen 
any one comes home, feels ill, and says, " I shall soon die," and is as 
good as his word, his friends are of opinion that one of his souls has 
been shot by a himter in a Avild boar or a leopard, for example, and 
that that is the real cause of his deaths A Catholic missionary, 
sleeping in the hut of a chief of the Fan negroes, awoke in the 
middle of the night to see a huge black serpent of the most dangerous 
sort in the act of darting at him. He was about to shoot it when the 
chief stopped him, saying, " In killing that serpent, it is me that you 
would have killed. Fear nothing, the serpent is my elangela\" 
At Calabar there used to be some years ago a huge old crocodile 
which was well known to contain the spirit of a chief who resided in 
the flesh at Duke Town. Sporting Vice-Consuls, with a reckless 
disregard of human life, from time to time made determined attempts 
to injure the animal, and once a peculiarly active officer succeeded in 
hitting it. The chief was immediately laid up with a wound in his 
leg. He said that a dog had bitten him, but few peoi)le perhaps were 
deceived by so flimsy a pretexts Once when Mr Partridge's canoe- 

^ T. Arbousset et F. Daumas, Relation d'un Voyage d' Exploration au Nord-Est de la 
Colonie du Cap de Bonne-Eapirance (Paris, 1842), pp. 319 «g., 422 — 24. 

^ M. le Docteur Tautain, "Notes sur les Croyanoes et Pratiques Eeligieuses des 
Banmanas," Revue d'Ethnographie, in. (1885), pp. 396 sq. ; A. Eancjon, Dam la Ilaute- 
Qambie, Voyage d'Exploration Scientifique (Paris, 1894), p. 44.5. 

* J, Keller, "Ueber das Land uud Volk der Balong," Deutsches Kolonialblatt, 
1 Oktober, 1895, p. 484. 

* Father Trilles, "Chez Jes Fang, leurs Moeurs, leur Langue, leur Religion," Les 
iliuioTis Catholiqucs, xxx. (1898), p. 322. 

» MisB Mary H. Kini^Hley, Travelt in West Africa (London, 1897), pp. 638 sq. As 
to the external or bush souls of human beings, which in this part of Africa are supposed to be 
lodged in the bodies of animals, sec Miss Mary H. Kingsley, op. cit. pp. 459 — 4G1 ; R. Hen- 
Bhaw, "Notes on the Efik belief in 'bush soul,'" 3/um, vi. (19U6), pp. 121*^.; J. Parkinson, 
"Notes on the Asalia people (Ibos) of the Niger," Journal of the Anthropological Institute, 
XXXVI. (190C), pp. 314 117. 

O. 11 

162 Primitive Theories of the Origin of Man 

men were about to catch fish near an Assiga town in Southern 
Nigeria, the natives of the town objected, saying, " Our souls live in 
those fish, and if you kill them we shall die^." On another occasion, 
in the same region, an Englishman shot a hippopotamus near a native 
village. The same night a woman died in the village, and her friends 
demanded and obtained from the marksman five pounds as compensa- 
tion for the murder of the woman, whose soul or second self had been 
in that hippopotamus^. Similarly at Ndolo, in the Congo region, we 
hear of a chief whose life was bound up with a hippopotamus, but he 
prudently suffered no one to fire at the animaP. 

Amongst people who thus fail to perceive any sharp line of 
distinction between beasts and men it is not surprising to meet with 
the belief that human beings are directly descended from animals. 
Such a belief is often found among totemic tribes wlio imagine that 
their ancestors sprang from their totemic animals or plants ; but it is 
by no means confined to them. Thus, to take instances, some of the 
Californian Indians, in whose mythology the coyote or prairie-wolf is 
a leading personage, think that they are descended from coyotes. At 
first they Avalked on all fours ; then they began to have some 
members of the human body, one finger, one toe, one eye, one ear, 
and so on ; then they got two fingers, two toes, two eyes, two ears, 
and so forth ; till at last, progressing from period to period, 
they became perfect human beings. The loss of their tails, 
which they still deplore, was produced by the habit of sitting upright*. 
Similarly Darwin thought that " the tail has disappeared in man and 
the anthropomorphous apes, owing to the terminal portion having 
been injured by friction during a long lapse of time ; the basal and 
embedded portion having been reduced and modified, so as to 
become suitable to the erect or semi-erect position ^" The Turtle 
clan of the Iroquois think that they are descended from real 
mud turtles which used to live in a pool. One hot summer the 
pool dried up, and the mud turtles set out to find another. A very 
fat turtle, waddling after the rest in the heat, was much incommoded 
by the weight of his shell, till by a great effort he heaved it off" 
altogether. After that he gradually developed into a man and 
became the progenitor of the Turtle clan^. The Crawfish band of the 

^ Charles Partridge, Cross River Natives (London, 1905), pp. 225 sq. 

* C. H. Robinson, Ilausaland (London, 1896), pp. 36 sq. 

^ Notes Anahjtiques sur les Collections Ethnographiques dii Musee du Congo, i. 
(Brussels, 1902—00), p. 150. 

* H. R. Schoolcraft, Indian Tribes of the United States, iv. (Philadelphia, 1856), 
pp. 224 sq. ; compare id. v. p. 217. Tlie descent of some, not all, Indians from co3'otes 
is mentioned also by Friar Boscana, in [A. Robinson's] Life in California (New York, 
1840), p. 299. 

•> Charles Darwin, The Descent of Man, Second Edition (London, 1879), p. 60. 
' E. A. Smith, "Myths of the Iroquois," Second Annual Report of the Bureau of 
Ethnology (Washingtou, 1883), p. 77. 

Descent of Man from Animals 163 

Choctaws are in like manner descended from real crawfish, which 
used to live under ground, only coming up occasionally through the 
mud to the surface. Once a party of Choctaws smoked them out, 
taught them the Choctaw language, taught them to walk on two legs, 
made them cut off their toe nails and pluck the hair from their bodies, 
after which they adopted them into the tribe. But the rest of their 
kindred, the craAvfish, are crawfish under ground to this day\ The 
Osage Indians universally believed that they were descended from 
a male snail and a female beaver. A flood swept the snail down to 
the Missouri and left him high and dry on the bank, where the sun 
ripened him into a man. He met and married a beaver maid, and 
from the pair the tribe of the Osages is descended. For a long time 
these Indians retained a pious reverence for their animal ancestors 
and refrained from hunting beavers, because in killing a beaver they 
killed a brother of the Osages. But when white men came among 
them and ofiered high prices for beaver skins, the Osages yielded to 
the temptation and took the lives of their furry brethren"^. The Carp 
clan of the Ootawak Indians are descended from the eggs of a carp 
which had been deposited by the fish on the banks of a stream and 
warmed by the sun^. The Crane clan of the Ojibways are sprung 
originally from a pair of cranes, which after long wanderings settled 
on the rapids at the outlet of Lake Superior, where they were changed 
by the Great Spirit into a man and woman*. The members of two 
Omaha clans were originally bufialoes and lived, oddly enough, under 
water, which they splashed about, making it muddy. And at death 
all the members of these clans went back to their ancestors the 
bufialoes. So when one of them lay adying, his friends used to wrap 
him up in a bufialo skin with the hair outside and say to him, " You 
came hither from the animals and you are going back thither. Do 
not face this way again. When you go, continue walking^." The 
Haida Indians of Queen Charlotte Islands believe that long ago the 
raven, who is the chief figure in the mythology of North-West 
America, took a cockle from the beach and married it ; the cockle 
gave birth to a female child, whom the raven took to wife, and from 
their union the Indians were produced^ The Delaware Indians 
called the rattle-snake their grandfather and would on no account 

' Geo. Catlin, North American Indians* (London, 1844), ii. p. 128. 

* Lewis and Clarke, Travels to the Source of the Missouri Bivcr (London, 1815), i. 12 
(Vol. I. pp. 44 sq. of the London reprint, I'JO.'j). 

* Lettres Edijiantes et Curieuses, Nouvcllo Elition, vi. (Paris, 1781), p. 171. 

* L. II. Morgan, Ancient Society (London, 1877), j). 180. 

* J. Owen Dorscy, "Omaha SocioloK.v," Third Annual Report of the llureau of 
Ethnology (Washington, 1884), pp. 22'J, 233. 

* O. M. Dawson, Heport on the Queen Charlotte Inlands (Montreal, 1880), pp. 149 8*7. 
(Qeolvj/ical Surrey of Canada) ; V. Poole, Queen Charlotte Islands, p. I'M]. 


164 Primitive Theories of the Origin of Man 

destroy one of these reptiles, believing that were they to do so the 
whole race of rattle-snakes would rise up and bite them. Under the 
influence of the white man, however, their respect for their grand- 
father the rattle-snake gradually died away, till at last they killed 
him without compunction or ceremony whenever they met him. 
The writer who records the old custom observes that he had often 
reflected on the curious connection which appears to subsist in the 
mind of an Indian between man and the brute creation ; " all 
animated nature," says he, "in whatever degree, is in their eyes a 
great whole, from which they have not yet ventured to separate 

Some of the Indians of Peru boasted of being descended from the 
puma or American lion ; hence they adored the lion as a god and 
appeared at festivals like Hercules dressed in the skins of lions with 
the heads of the beasts fixed over their own. Others claimed to be 
sprung from condors and attired themselves in great black and white 
wings, like that enormous bird^. The Wanika of East Africa look 
upon the hyaena as one of their ancestors or as associated in some 
way with their origin and destiny. The deatli of a hyaena is mourned 
by the whole people, and the greatest funeral ceremonies which they 
perform are performed for this brute. The wake held over a chief 
is as nothing compared to the wake held over a hyaena ; one 
tribe only mourns the death of its chief, but all the tribes unite 
to celebrate the obsequies of a h^^aena^ Some Malagasy families 
claim to be descended from the babacoote {Liclianotus hrevi- 
ccmdatus), a large lemur of grave appearance and staid demeanour, 
which lives in the depth of the forest. When they find one of 
these creatures dead, his human descendants bury it solemnly, 
digging a grave for it, wrapping it in a shroud, and weeping and 
lamenting over its carcase. A doctor who had shot a babacoote was 
accused by the inhabitants of a Betsimisaraka village of having killed 
"one of their grandfathers in the forest," and to appease their 
indignation he had to promise not to skin the animal in the village 
but in a solitary place where nobody could see him^ Many of the 

^ Eev. John Heckewelder, "An Account of the History, Manners, and Customs, of the 
Indian Nations, who once inhabited Pennsylvania and the Neighbouring States," Trans- 
actions of the Ilutorical and Literary Committee of the American Philosophical Society, r. 
(Philadelphia, 1819), pp. 245, 217, 248. 

^ Garcilaffso de la Vega, Fiist Part of the Royal Commentaries of the Yncas, Vol. r. 
p. 323, Vol. II. p. 156 (Maikham's translation). 

' Charles New, Life, Wanderinys, and Labours in Eastern Africa (London, 1873), p. 122. 

* Father Abiiial, "Croyances fabuleuses des Malj:;aches," Lcs Missions Catholiqucs, xir. 
(1880), p. 526; G. H. Smith, "Some Betsimisaraka superstitions," The Antananarivo 
Annual and Madagascar Magazine, No. 10 (Antananarivo, 1886), p. 239 ; H. W. Little, 
Madagascar, its History and People (London, 1884), pp. 321 sq. ; A. van Gennep, Tabou et 
Totfviisme a Madagascar (Paris, 1904), pp. 214 sqq. 

Descent of Man from Animals 165 

Betsimisaraka believe that the curious nocturnal animal called the 
aye-aye (Cheiromi/s madagascariensis) "is the embodiment of 
their forefathers, and hence will not touch it, much less do it an 
injury. It is said that when one is discovered dead in the forest, 
these people make a tomb for it and bury it with all the forms of 
a funeral. They think that if they attempt to entrap it, they will 
surely die in consequence V Some Malagasy tribes believe themselves 
descended ft-om crocodiles and accordingly they deem the formidable 
reptiles their brothers. If one of these scaly brothers so far forgets 
the ties of kinship as to devour a man, the chief of the tribe, or in his 
absence an old man familiar with the tribal customs, repairs at the 
head of the people to the edge of the water, and summons the family 
of the culprit to deliver him up to the arm of justice. A hook is 
then baited and cast into the river or lake. Next day the guilty 
brother or one of his family is dragged ashore, formally tried, 
sentenced to death, and executed. The claims of justice being thus 
satisfied, the dead animal is lamented and buried like a kinsman ; a 
mound is raised over his grave and a stone marks the place of his 

Amongst the Tshi-spcaking tribes of the Gold Coast in West 
Africa the Horse-mackerel family traces its descent from a real horse- 
mackerel whom an ancestor of theirs once took to wife. She lived M'ith 
him happily in human shape on shore till one day a second wife, 
whom the man had married, cruelly taunted her with being nothing 
but a fish. That hurt her so much that bidding her husband farewell 
she returned to her old home in the sea, with her youngest child in 
her arms, and never came back again. But ever since the Horse- 
mackerel people have refrained from eating horse-mackerels, because 
the lost wife and mother was a fish of that sort^ Some of the Land 
Dyaks of Borneo tell a similar tale to explain a similar custom. 
"There is a fish which is taken in their rivers called a,puttln, which 
they would on no account touch, under the idea that if they did 
they would be eating their relations. The tradition respecting it is, 
that a solitary old man went out fishing and caught aiputtm, which 
he dragged out of the water and laid down in his boat. On turning 
round, he found it had changed into a very pretty little girl. Con- 
ceiving tlie idea she would make, what he had long wislicd for, a 

^ G. A. Shaw, "The Aye-aye," AnUinaiiarivo Annual and Madafinscar Magazine, 
Vol. II. (Aiitaniiuarivo, 1896), i)p. 201, 203 (Reprint of the Second four Numbers). Com- 
pare A. van Genncp, Tahou et Totdmisme a Madagascar, pp. 'I'l'isq. 

^ Father Abinal, "Croyance.s fahuleuBCs des MalgacheH," Lc» Mixsions Catholiqurs, sir. 
(1880), p. 527 ; A. van Gennep, Tahvu ct Tolcnii.smc il Madagascar, pp. 281 sq. 

* A. B. Ellis, The Tnhinpeaking Pcopli's of the Gold Coast of Wcxt Africa (London, 
1887), pp. 20m — 11. A similar tale in told byannthir fiBh family who ahstain from eating the 
fish (apijei) (rem wliich thoy take their name (A. B. Ellis, oj). cit. pp. 211 eq.). 

166 Primitive Theories of the Origin of Man 

charming wife for his son, he took her home and educated her until 
she was fit to be married. She consented to be the son's wife 
cautioning her husband to use her well. Some time after their 
marriage, however, being out of temper, he struck her, when she 
screamed, and rushed away into the water ; but not without leaving 
behind her a beautiful daughter, who became afterwards the mother 
of the race\" 

Members of a clan in Mandailing, on the west coast of Sumatra, 
assert that they are descended from a tiger, and at the present day, 
when a tiger is shot, the women of the clan are bound to offer betel 
to the dead beast. "SVlien members of this clan come upon tlie tracks 
of a tiger, they must, as a mark of homage, enclose them with 
three little sticks. Further, it is believed that the tiger will not 
attack or lacerate his kinsmen, the members of the clan^ The 
Battas of Central Sumatra are divided into a number of clans which 
have for their totems white buffaloes, goats, wild turtle-doves, dogs, 
cats, apes, tigers, and so forth; and one of the explanations which 
they give of their totems is that these creatures were their ancestors, 
and that their own souls after death can transmigrate into the 
animals^ In Amboyna and the neighbouring islands the inhabitants 
of some villages aver that they are descended from trees, such as 
the Cajjcllenia moluccana, which had been fertilised by the Pandion 
Haliaetus. Others claim to be sprung from pigs, octopuses, croco- 
diles, sharks, and eels. People will not burn the wood of the trees 
from which they trace their descent, nor eat the flesh of the animals 
which they regard as their ancestors. Sicknesses of all sorts are 
believed to result from disregarding these taboos^ Similarly in 
Ceram persons who think they are descended from crocodiles, 
serpents, iguanas, and sharks will not eat the flesh of these animals ^ 

1 The Lord Bishop of Labuan, "On the Wild Tribes of the North- West Coast of 
Borneo," Transactions of the Ethnological Society of London, New Series, ii. (London, 
1863), pp. 2(3 sq. Such stories conform to a well-known type which may be called the 
Swan-Maiden type of story, or Beauty and the Beast, or Cupid and Psyche. The occurrence 
of stories of this type among totemic peoples, such as the Tshi-speaking negroes of the Gold 
Coast, who tell them to explain their totemic taboos, suggests that all such tales may have 
originated in totemism. I shall deal with this question elsewhere. 

- H. Eis, "De Onderafdeeling Klein Mandailing Oeloe en Pahantan en hare Bevolking 
met uitzondering van de Oeloes," Bijdragen tot de Taal- Land- en Volkenkunde van Neder- 
landsch-Indie, xlvi. (1896), p. 473. 

* J. B. Neumann, "Het Pane en Bila-stroomgebied op heteiland Sumatra," Tijdschrift 
van het Nederhindsck Aardrijkskundig Genootschap, Tweede Serie, in. Afdeeliug, Meer 
uitgebreide Artikelen, No. 2 (Amsterdam, 1886), pp. 311 sq. ; id. ib. Tweede Serie, iv. 
Afdeeling, Meer uitgebreide Artikelen, No. 1 (Amsterdam, 1887), pp. 8 sq. 

* J. G. F. Riedel, De sluik- en kroesharige rassen tusschen Selebes en Papua (The Hague, 
1880), pp. 32, 61 ; G. W. W. C. Baron van Hoevell, Ambon en meer bepaaldelijk de Oeliasers 
(Dordrecht, 1875), p. 152. 

« J. G. F. liiedel, op. cit. p. 122. 

Descent of Man from Animals 167 

Many other peoples of the Mohicca Islands entertain similar beliefs 
and observe similar taboos \ Again, in Ponape, one of the Caroline 
Islands, "the different families suppose themselves to stand in a 
certain relation to animals, and especially to fishes, and believe in 
their descent from them. They actually name these animals 
* mothers ' ; the creatures are sacred to the family and may not 
be injured. Great dances, accompanied with the offering of prayers, 
are performed in their honour. Any person who killed such an 
animal would expose himself to contempt and punishment, certainly 
also to the vengeance of the insulted deity." Blindness is commonly 
supposed to be the consequence of such a sacrilege-. 

Some of the aborigines of Western Australia believe that their 
ancestors were swans, ducks, or various other species of water-fowl 
before they were transformed into men^ The Dieri tribe of Central 
Australia, who are divided into totemic clans, explain their origin by 
the following legend. They say that in the beginning the earth 
opened in the midst of Perigundi Lake, and the totems (murdiis or 
madas) came trooping out one after the other. Out came the crow, 
and the shell parakeet, and the emu, and aU the rest. Being as yet 
imperfectly formed and without members or organs of sense, they 
laid themselves do^vn on the sandhills which surrounded the lake 
then just as they do now. It was a bright day and the totems lay 
basking in the sunshine, till at last, refreshed and invigorated by it, 
they stood up as human beings and dispersed in all directions. That 
is why people of the same totem are now scattered all over the 
country. You may still see the island in the lake out of which the 
totems came trooping long ago*. Another Dieri legend relates how 
Paralina, one of the Mura-3Iuras or mythical predecessors of the 
Dieri, perfected mankind. He was out hunting kangaroos, when he 
saw four incomplete beings cowering together. So he went up to 
them, smoothed their bodies, stretched out their limbs, slit up their 
fingers and toes, formed their mouths, noses, and eyes, stuck ears 
on them, and blew into their ears in order that they might hear. 
UavJDg perfected their organs and so produced mankind out of these 
rudimentary beings, he went about making men everywhere^ Yet 
another Dieri tradition sets forth how the 3Tura-3Iura produced the 
race of man out of a species of small black lizards, which may still be 

> J. G. F. Riedel, De sluik- en kroesharige rassen tusschen Selebe$ en Papua (The 
Hague, 188G), pp. 253, 334, 341, 318, 412, 414, 4.3-2. 

* Dr Ilabl, "Mitthcilungeu iiber Sittcn uud rechtlicho Verliiiltuisao auf Ponape," 
EthnologUches Notizblatt, Vol. ii. Heft 2 (Berlin, 1901), p. 10. 

- Captain O. Grey, .( Vnrnhnhinj of the Dialects of South Wettern Australia, Second 
Edition (London, 1840), pp. 29, 37, 01, 63, tjf,, 71. 

* A. W. Howitt, Native Tribe* of South- Eait Auitralia (Loudon, 1901), pp. 470, 779 <g. 
» A. W. Howitt, op. cit., pj). 470, IHOiiq. 

168 Pi'imitive Theories of the Origin of Man 

met with under dry bark. To do this he divided the feet of the 
lizards into fingers and toes, and, applying his forefinger to the middle 
of their faces, created a nose ; likeAvise he gave them human eyes, 
mouths and ears. He next set one of them upright, but it fell down 
again because of its tail ; so he cut ofi" its tail and the lizard then 
walked on its hind legs. Tliat is the origin of mankind \ 

The Arunta tribe of Central Australia similarly tell how in the be- 
ginning mankind was developed out of various rudimentary forms of 
animal life. They say that in those days two beings called Ungamhi- 
Tcula, that is, " out of nothing," or " self-existing," dwelt in the western 
sky. From their lofty abode they could see, far away to the east, 
a number of inapertwa creatures, that is, rudimentary human beings 
or incomplete men, whom it was their mission to make into real men 
and women. For at that time there were no real men and women ; 
the rudimentary creatures (inapertwa) were of various shapes and 
dwelt in groups along the shore of the salt water which covered the 
country. These embryos, as we may call them, had no distinct limbs 
or organs of sight, hearing, and smell ; they did not eat food, and 
they presented the appearance of human beings all doubled up into 
a rounded mass, in which only the outline of the different parts 
of the body could be vaguely perceived. Coming down from their 
home in the western sky, armed with great stone knives, the Ungam- 
bikida took hold of the embryos, one after the other. First of all 
they released the arms from the bodies, then making four clefts at 
the end of each arm they fashioned hands and fingers ; afterwards 
legs, feet, and toes were added in the same way. The figure could 
now stand ; a nose was then moulded and tlie nostrils bored with the 
fingers. A cut with the knife made the mouth, which Avas pulled 
open several times to render it flexible. A slit on each side of the 
face separated the upper and lower eye-lids, disclosing the eyes, 
which already existed behind them ; and a few strokes more com- 
pleted the body. Thus out of the rudimentary creatures were 
formed men and women. These rudimentary creatures or embryos, 
we are told, " were in reality stages in the transformation of various 
animals and plants into human beings, and thus they were naturally, 
when made into human beings, intimately associated with the par- 
ticular animal or plant, as the case may be, of which they were the 
transformations — in other words, each individual of necessity belonged 
to a totem, the name of which was of course that of the animal 

' S. Gason, "The Manners and Customs of the Dieyerie tribe of Australian 
Aborigines," Native Tribes of South Australia (Adelaide, 1879), p. 260. This writer 
ffll into the mistake of regarding the Mura-Mura (Mooramoora) as a Good-Spirit instead 
of as one of the mythical but more or less human jiredecessors of the Dieri in the 
country. See A. W. Howitt, Native Tribes of South -East Australia, pp. 475 sqq. 

Arunta Theory of Evolution 169 

or plant of which he or she was a transformation." However, it is 
not said that all the totemic clans of the Arunta were thus developed ; 
no such tradition, for example, is told to explain the origin of the 
important Witchetty Grub clan. The clans which are positivel}" 
known, or at least said, to have originated out of embryos in the way 
described are the Plum Tree, the Grass Seed, the Large Lizard, the 
Small Lizard, the Alexandra Parakeet, and the Small Rat clans. 
AAlien the Ungamhikida had thus fashioned people of these totems, 
they circumcised them all, except the Plum Tree men, by means 
of a fire-stick. After tliat, having done the work of creation or 
evolution, the TJngambikula turned themselves into little lizards 
which bear a name meaning "snappers-up of flies\" 

This Arunta tradition of the origin of man, as Messrs Spencer and 
Gillen, who have recorded it, justly observe, " is of considerable 
interest ; it is in the first place evidently a crude attempt to describe 
the origin of human beings out of non-human creatures who were of 
various forms ; some of them were representatives of animals, others 
of plants, but in all cases they are to be regarded as intermediate 
stages in the transition of an animal or plant ancestor into a human 
individual who bore its name as that of his or her totem-." In a sense 
these speculations of the Arunta on their own origin may be said to 
combine the theory of creation with the theory of evolution ; for 
Avhile they represent men as developed out of much simpler forms of 
life, they at the same time assume that this development was effected 
by the agency of two powerful beings, whom so far we may call 
creators. It is well kno^Mi that at a far higher stage of culture 
a crude form of the evolutionary hypothesis was propounded by the 
Greek philosopher Empedocles. He imagined that shapeless lumps of 
earth and water, thrown up by the subterranean fires, developed into 
monstrous animals, bulls with the heads of men, men M'ith the heads 
of bulls, and so forth ; till at last, these hybrid forms being gradually 
eliminated, the various existing species of animals and men were 
evolved^. The theory of the civilised Greek of Sicily may be set 
beside the similar theory of the savage Arunta of Central Australia. 
Both represent gropings of the human mind in the dark abyss of the 
past ; both were in a measure grotesque anticipations of the modern 
tlieory of evolution. 

In this essay I have made no attempt to illustrate all the many 

* Baldwin Spencer and F. J. Gillen, Nutive Tribes of Central Australia (London, 1899), 
pp. 888 »g.; coinpare id.. Northern Trihes of Central Australia (London, 1901). j). 150. 

- Baldwin Spencer and F. J. Gillen, Native 'Tribes of Central Australia, pp. 391 sq. 

3 E. Zeller, Die Philosophie der Griechen, \* (Leipsic, 1876), pp. 718 sq. ; H. Hitter et 
L. I'reller, llintoria I'liilosophiae Graecae et liomanae ex fontium loci* contexta'', pp. 102 sq. ; 
H. Diela, Die Fragmente der Vorsokratiker", i. (13t»rliu, 190G), pp. 190 «yg. Compare 
Lucretius, De rerum vatura, v. 837 »qq. 

170 Primitive Theories of the Origin of Man 

various and divergent views which primitive man has taken of his 
own origin. I have confined myself to collecting examples of two 
radically different views, which may be distinguished as the theory of 
creation and the theory of evolution. According to the one, man was 
fashioned in his existing shape by a god or other powerful being ; 
according to the other he was evolved by a natural process out of 
lower forms of animal life. Roughly speaking, these two theories 
still divide the civilised world between them. The partisans of each 
can appeal in support of their view to a large consensus of opinion ; 
and if truth were to be decided by weighing the one consensus 
against the other, with Genesis in the one scale and The Origin of 
Species in the other, it might perhaps be found, when the scales 
were finally trimmed, that the balance hung very even between 
creation and evolution- 



By a. Sedgwick, M.A., F.R.S. 

Professor of Zoology and Comparative Anatomy in the 
University of Cambridge. 

The publication of The Origin of Species ushered in a new era in i 
the study of Embryology. Wliereas, before the year 1859 the facts of I 
anatomy and development were loosely held together by the theory 
of types, which owed its origin to the great anatomists of the pre- 
ceding generation, to Cuvier, L. Agassiz, J. Miiller, and R. Owen, 
they were now combined together into one organic whole by the 
theory of descent and by the hypothesis of recapitulation which was 
deduced from that theory. The view^ that a knowledge of embryonic 
and larval histories would lay bare the secrets of race-history and 
^enable the coui'se of evolution to be traced, and so lead to the 
discovery of the natural system of classification, gave a powerful 
stimulus to morphological study in general and to embryological 
investigation in particular. In Darwin's words: "Embryology rises 
"greatly in interest, when we look at the embryo as a picture, 
more or less obscured, of the progenitor, either in its adult or larval 
state, of all the members of the same great class 2." In the period 
under consideration the output of embryological work has been 
enormous. No group of the animal kingdom has escaped exhaustive 
examination and no eflfort has been spared to obtain the embryos of 
isolated and out of the way forms, the development of which might 
have an important bearing upon questions of phylogeny and classifi- 
cation. Marine zoological stations have been established, expeditions 
have been sent to distant countries, and the methods of investigation 
have been greatly improved. The result of this activity has been 
that the main features of the developmental history of all the most 
important animals are now known and the curiosity as to develop- ) 
mental processes, so greatly excited by the j>rumu]i;ati<)n of the I 
Darwinian theory, has to a considerable extent been satisfied. ! 

' First clearly enunciated liy Fritz Miiller in Lis well-known work, Filr Dancin, 
Leipzig, 1804 ; (English Edition, Pac(» for Darwin, 1869). 
« Origin (Rth edit.), p. 396. 


172 Dm'win and Umbryology 

To what extent have the results of this vast activity fulfilled the 
expectations of the m orkers who have achieved them ? The Darwin 
centenary is a fitting moment at which to take stock of our position. 
In this inquiry we shall leave out of consideration the immense and 
intensely interesting additions to our knowledge of Natural History. 
These may be said to constitute a capital fund upon which philo- 
sophers, poets and men of science will draw for many generations. 
The interest of Natural History existed long before Darwinian 
evolution was thought of and will endure without any reference to 
philosophic speculations. She is a mistress in whose face are beauties 
and in whose arms are delights elsewhere unattainable. She is and 
always has been pursued for her own sake without any reference to 
philosophy, science, or utility. 

Darwin's own views of the bearing of the facts of embryology 
upon questions of wide scientific interest are perfectly clear. He 

" On the other hand it is highly probable that with many animals 
the embryonic or larval stages show us, more or less completely, the 
condition of the progenitor of the whole group in its adult state. In 
the great class of the Crustacea, forms wonderfully distinct from each 
other, namely, suctorial parasites, cirripedes, cntomostraca, and even 
the malacostraca, appear at first as larvae under the nauplius-form ; 
and as these larvae live and feed in the open sea, and are not adapted 
for any peculiar habits of life, and from other reasons assigned by 
Fritz Miiller, it is probable that at some very remote period an 
independent adult animal, resembling the Nauplius, existed, and 
subsequently produced, along several divergent lines of descent, the 
above-named great Crustacean groups. So again it is probable, 
from M'hat we know of the embryos of mammals, birds, fishes, and 
reptiles, that these animals are the modified descendants of some 
ancient progenitor, which was furnished in its adult state with 
branchiae, a swim-bladder, four fin-like limbs, and a long tail, all 
fitted for an aquatic life. 

" As all the organic beings, extinct and recent, which have ever 
lived, can be arranged within a few great classes ; and as all within 
each class have, according to our theory, been connected together by 
fine gradations, the best, and, if our collections were nearly perfect, 
the only possible arrangement, would be genealogical ; descent being 
the hidden bond of connexion which naturalists have been seeking 
under tlie term of the Natural System. On this view >ve can under- 
stand how it is that, in the eyes of most naturalists, the structure of 
the embryo is even more important for classification than that of the 
adult. In two or more groups of animals, however much they may 

1 Oiiyin (6tb edit.), P- 300. 

Embryology and Phylogeny 173 

differ from each other in structure and habits in their adult condition, 
if they pass through closely similar embryonic stages, we may feel 
assured that they all are descended from one parent-form, and are 
therefore closely related. JThus^ community in embryonic structure 
reveals community of descent; but dissimilarity in embryonic develop- 
liTent does not prove discommunity of descent, for in one of tAvo 
gi'oups the developmental stages may have been suppressed, or may 
have been so greatly modified through adaptation to new habits of 
life, as to be no longer recognisable. Even in groups, in which the 
adults have been modified to an extreme degree, community of origin 
is often revealed by the structure of the larvae; we have seen, for 
instance, that cirripedes, though externally so like shell-fish, are at 
once known by their larvae to belong to the great class of crustaceans. 
As the embryo often shows us more or less plainly the structure of 
the less modified and ancient progenitor of the group, we can see why 
ancient and extinct forms so often resemble in their adult state the 
embryos of existing species of the same class. Agassiz believes this 
to be a universal law of nature ; and we may hope hereafter to see 
the law proved true. It can, however, be proved true only in those 
cases in which the ancient state of the progenitor of the group has 
not been wholly obliterated, either by successive variations having 
supervened at a very early period of growth, or by such variations 
having been inherited at an earlier stage than that at which they first 
appeared. It should also be borne in mind, that the law may be 
true, but yet, owing to the geological record not extending far 
enough back in time, may remain for a long period, or for ever, 
incapable of demonstration. The law will not strictly hold good in 
those cases in which an ancient form became adapted in its larval 
state to some special line of life, and transmitted the same larval 
state to a whole group of descendants; for such larvae will not 
resemble any still more ancient form in its adult state." 

As this passage shows, Darwin held that embryology was of 
interest because of the light it seems to throw upon ancestral history 
(phylogeny) and because of the help it would give in enabling us to 
arrive at a natural system of classification. With regard to the 
latter point, he ([uotes with approval the opinion that "the structure 
of the embryo is even more important for classification than that of 
the adult." AV'hat justification is there for this view? The phase of 
life chosen for the ordinary anatomical and physiological studies, 
namely, the adult i)hase, is merely one of the large number of stages 
of structure through which the organism ptisses. By far the greater 
numl>er of these are iiicliidod in what is specially called the develop- 
mental or (if we iucliide larvae with embryos) embryonic period, for 
the developmental changes are more numerous and take place with 

174 Darwin and Embryology 

greater rapidity at the beginning of life than in its later periods. As 
each of these stages is equal in value, for our present purpose, to the 
adult phase, it clearly follows that if there is anything in the view 
that the anatomical study of organisms is of importance in deter- 
mining their mutual relations, the study of the organism in its 
various embryonic (and larval) stages must have a greater importance 
than the study of the single and arbitrarily selected stage of life called 
the adult. 

But a deeper reason than this has been assigned for the im- 
portance of embryology in classification. It has been asserted, and is 
imjjlied by Darwin in the passage quoted, that the ancestral history is 
repeated in a condensed form in the embryonic, and that a study of 
the latter enables us to form a picture of the stages of structure 
through which the organism has passed in its evolution. It enables 
us on this view to reconstruct the pedigrees of animals and so to 
form a genealogical tree which shall be the true expression of their 
^ natural relations. 
I The real question which we have to consider is to what extent the 
embryological studies of the last 50 years have confirmed or rendered 
probable this "theory of recapitulation." In the first place it must 
be noted that the recapitulation theory is itself a deduction from 
the theory of evolution. The facts of embryology, particularly of 
vertebrate embryology, and of larval history receive, it is argued, an 
explanation on the view that the successive stages of development 
are, on the whole, records of adult stages of structure which the 
species has passed through in its evolution. AVliether this statement 
will bear a critical verbal examination I will not now pause to inquire, 
for it is more important to determine whether any independent facts 
can be alleged in favour of the theory. If it could be shown, as was 
stated to be the case by L. Agassiz, that ancient and extinct forms of 
life present features of structure now only found in embryos, we should 
have a body of facts of the greatest importance in the present 
discussion. But as Huxley^ has shown and as the whole course of 
palaeontological and embryological investigation has demonstrated, 
no such statement can be made. The extinct forms of life are very 
similar to those now existing and there is nothing specially embryonic 
about them. So that the facts, as we know them, lend no sujjport to 

But there is another class of facts which have been alleged in 
favour of the theory, viz. the facts which have been included in the 

^ See Huxley's Scientific Memoirs, London, 1898, Vol. i. p. 303 : " There is no real 
parallel between the successive forms assumed in the development of the life of the 
individual at present, and those which have appeared at diflerent epochs in the past." 
See also his Address to the Geological Society of London (18C2) ' On the Palaeontological 
Evidence of Evolution,' ibid. Vol. ii. p. 512. 

Theory of Recapitulation 175 

generalisation known as the Law of v. Baer. Tlie law asserts that 
embryos of diflferent species of animals of the same group are more 
alike than the adults and that, the younger the embryo, the greater 
are the resemblances. If this law could be established it would 
undoubtedly be a strong argument in favour of the "recapitu- 
lation" explanation of the facts of embryology. But its truth has 
been seriously di8i)uted. If it were true we should expect to find 
that the embryos of closely similar species would be indistinguishable 
from one another, but this is notoriously not the case. It is more 
difficult to meet the assertion when it is made in the form given 
above, for here we are dealing with matters of opinion. For instance, 
no one would deny that the embryo of a dogfish is different from the 
embryo of a rabbit, but there is room for dift'erence of opinion when 
it is asserted that the diiSerence is less than the difference between an 
adult dogfish and an adult rabbit. It would be perfectly true to say 
that the ditferences between the embryos concern other organs more 
than do the differences between the adults, but who is prepared to 
affirm that the presence of a cephalic coelom and of cranial segments, 
of external gills, of six gill slits, of the kidney tubes opening into the 
muscle-plate coelom, of an enormous yolk-sac, of a neurenteric canal, 
and the absence of any trace of an anmion, of an allantois and of a 
primitive streak are not morphological facts of as high an import as 
those implied by the differences between the adults ? The generalisa- 
tion undoubtedly had its origin in the fact that there is what may be 
called a family resemblance between embryos and larvae, but this 
resemblance, which is by no means exact, is largely superficial and "T 
does not extend to anatomical detail. 

It is useless to say, as Weismann has stated \ that "it cannot 
be disputed that the rudiments [vestiges his translator means] of 
gill-arches and gill-clefts, which are peculiar to one stage of human 
ontogeny, give us every ground for concluding that we possessed fish- 
like ancestors." The (juestion at issue is : did the pharyngeal arches 
and clefts of mammalian embryos ever discharge a branchial function 
in an adult ancestor of the mammalia ? We cannot therefore, without 
beggiug the question at issue in the grossest manner, apply to them 
the terms "gill-arches" and "gill-clefts." That they are homologous 
with the "gill-arches" and "gill-clefts" of fishes is true; but there is 
no evidence to show that they ever discharged a branchial function. 
Until such evidence is forthcoming, it is beside the point to say that 
it "cannot be disputed" that they are evidence of a i)iscine ancestry. 

It must, therefore, be adiiiitted that one outcome of the progress 
of embryological and palaeontological research for the last 50 years 

* The Evolution Theory, by A. Weismann, Eugliah Translation, Vol. ii. p. 176, 
London, 1904. 

176 Darioin and Embryology 

is negative. The recapitulation theory originated as a deduction 
ft'om the evohition theory and as a deduction it still remains. 

Let us before leaving the subject apply another test. If the 
evolution theory and the recapitulation theory are both true, how 
is it that living birds are not only without teeth but have no rudiments 
of teeth at any stage of their existence ? How is it that the missing 
digits in birds and mammals, the missing or reduced limb of snakes 
and whales, the reduced mandibulo-hyoid cleft of elasmobranch fishes 
are not present or relatively more highly developed in the embryo 
than in the adult? How is it that when a marked variation, such 
as an extra digit, or a reduced limb, or an extra segment, makes its 
appearance, it is not confined to the adult but can be seen all through 
the development ? All the clear evidence we can get tends to show 
that marked variations, whether of reduction or increase, of organs 
are manifest during the whole of the development of the organ and 
do not merely aftect the adult. And on reflection we see that it could 
hardly be otherwise. All such evidence is distinctly at variance with 
the theory of recapitulation, at least as applied to embryos. In the 
case of larvae of course the case will be diiferent, for in them the 
organs are functional, and reduction in the adult will not be accom- 
panied by reduction in the larva unless a change in the conditions 
of life of the larva enables it to occur. 

If after 50 years of research and close examination of the facts 
of embryology the recapitulation theory is still without satisfactory 
proof, it seems desirable to take a wider sweep and to inquire whether 
the facts of embryology cannot be included in a larger category. 

As has been pointed out by Huxley, development and life are 
co-extensive, and it is impossible to point to any period in the life of 
an organism when the developmental changes cease. It is true that 
these changes take place more rapidly at the commencement of life, 
but they are never wholly absent, and those which occur in the later 
or so-called adult stages of life do not differ in their essence, however 
much they may differ in their degree, from those which occur dm-ing 
the embryonic and larval periods. This consideration at once brings 
the changes of the embryonic period into the same category as those 
of the adult and suggests that an explanation which will account for 
the one will account for the other. What then is the problem we are 
dealing with ? Surely it is this : Why does an organism as soon as it 
is established at the fertilisation of the ovum enter upon a cycle of 
transformations which never cease until death puts an end to them ? 
In other words what is the meaning of that cycle of changes which all 
organisms present in a greater or less degi-ee and which constitute the 
very essence of life? It is impossible to give an answer to this question 
so long as we remain within the precincts of Biology — and it is not 

Reaction and Environment 177 

my present purpose to penetrate beyond those precincts into the 
realms of philosophy. We have to do with an ultimate biological fact, 
with a fundamental property of living matter, which governs and 
includes all its other properties. How may this property be stated ? 
Thus : it is a property of living matter to react in a remarkable way 
to external forces without undergoing destruction. The life-cycle, 
of which the embryonic and larval periods are a part, consists of the 
orderly interaction between the organism and its environment. The 
action of the environment produces certain morphological changes 
in the organism. These changes enable the organism to come into 
relation with new external forces, to move into what is pmctically 
a new environment, which in its turn produces further structural 
changes in the organism. These in their turn enable, indeed necessi- 
tate, the organism to move again into a new environment, and so the 
process continues until the structural changes are of such a nature 
that the organism is unable to adapt itself to the environment in 
which it finds itself. The essential condition of success in this process 
is that the organism should always shift into the environment to which 
its new structure is suited — any failure in this leading to the impair- 
ment of the organism. In most cases the shifting of the environment 
is a very gradual process (wliether consisting in the very slight and 
gi'adual alteration in the relation of the embryo as a whole to the 
egg-sliell or uterine wall, or in the relations of its parts to each other, 
or in the successive phases of adult life), and the morphological 
changes in connection with each step of it are but slight. But in 
some cases jumps are made such as we find in the phenomena known 
as hatching, birth, and metamorphosis. 

This property of reacting to the environment mthout undergoing 
destruction is, as has been stated, a fundamental property of organisms. 
It is impossible to conceive of any matter, to which the term living could 
be ajiplied, being without it. And with this property of reacting to the 
environment goes the further property of undergoing a change which 
alters the relation of the organism to the old environment and places 
it in a new environment. If this reasoning is correct, it necessarily 
follows that this property must have been possessed by living matter 
at its first appearance on the eartli. In other words living matter 
muHt always have presented a life-cycle, and the question arises what 
kind of modification has that cycle undergone? Has it increased or 
diininiHhc'd in duration and complexity since organisms first appeared 
on the earth ? The current view is that the cycle was at first very 
short and that it has increased in length by the evolutionary creation 
of new adult phases, that these new phases are in addition to those 
already existing and that each of them as it apj)cars takes over from 
the preceding adult i)hase the functional condition of the reproductive 

D. 12 

178 Darwin and Embryology 

organs. According to the same view the old adult phases are not 
obliterated but persist in a more or less modified form as larval stages. 
It is further supposed that as the life-history lengthens at one end by 
the addition of noAv adult phases, it is shortened at the other by the 
abbreviation of embryonic development and by the absorption of 
some of the early larval stages into the embryonic period ; but on the 
whole the lengthening process has exceeded that of shortening, so 
that the whole life-history has, with the progress of evolution, become 
longer and more complicated. 

Now there can be no doubt that the life-history of organisms has 
been shortened in the way above suggested, for cases are known in 
which this can practically be seen to occur at the present day. 
But the process of lengthening by the creation of new stages 
at the other end of the life-cycle is more difficult to conceive 
and moreover there is no evidence for its having occurred. This, 
indeed, may have occurred, as is suggested below, but the evidence 
we have seems to indicate that evolutionary modification has pro- 
ceeded by altering and not by superseding : that is to say that each 
stage in the life-history, as we see it to-day, has proceeded from a 
corresponding stage in a former era by the modification of that stage 
and not by the creation of a new one. Let me, at the risk of repeti- 
tion, explain my meaning more fully by taking a concrete illustration. 
The mandibulo-hyoid cleft (spiracle) of the elasmobranch fishes, the 
lateral digits of the pig's foot, the hind-limbs of whales, the enlarged 
digit of the ostrich's foot are supposed to be organs which have been 
recently modified. This modification is not confined to the final adult 
stage of the life-history but characterises them throughout the whole 
of their development. A stage with a reduced spiracle does not 
proceed in development from a preceding stage in which the spiracle 
shows no reduction : it is reduced at its first appearance. The same 
statement may be made of organs which have entirely disappeared 
in the adult, such as bird's teeth and snake's fore-limbs : the adult 
stage in which they have disappeared is not preceded by embryonic 
stages in which the teeth and limbs or rudiments of them are present. 
In fact the evidence indicates that adult variations of any part are 
accompanied by precedent variations in the same direction in the 
embryo. The evidence seems to show, not that a stage is added on 
at the end of the life-history, but only that some of the stages in the 
life-history are modified. Indeed, on the wider view of development 
taken in this essay, a view which makes it coincident Avith life, one 
would not expect often to find, even if new stages are added in the 
course of evolution, that they are added at the end of the series when 
the organism has passed through its reproductive period. It is 
possible of course that new stages have been intercalated in the 

Ch'oivth Variations 179 

course of the life-history, though it is difficult to see how this 
has occurred. It is much more likely, if we may judge from 
available evidence, that every stage has had its counterpart in the 
ancestral form from which it has been derived by descent with 
modification. Just as the adult phase of the living form diflers, 
owing to evolutionary modification, fi'om the adult phase of the 
ancestor from which it has proceeded, so each larval phase will difier 
for the same reason from the corresponding larval phase in the life- 
history of the ancestor. Inasmuch as the organism is variable at 
every stage of its independent existence and is exposed to the action 
of natural selection there is no reason why it should escape modifica- 
tion at any stage. 

If there is any truth in these considerations it would seem to 
follow that at the dawn of life the life-cycle must have been, either 
in posse or iu esse, at least as long as it is at the present time, and 
that the peculiarity of passing through a series of stages in which new 
chai-acters are successively evolved is a primordial quality of living 

Before leaving this part of the subject, it is necessary to touch 
upon another aspect of it. What are these variations in structure 
which succeed one another in the life-history of an organism ? I am 
conscious that I am here on the threshold of a chamber which 
contains the clue to some of our difficulties, and that I cannot enter 
it. Looked at from one point of view they belong to the class of 
genetic variations, which depend upon the structure or constitution 
of the protoplasm; but instead of appearing in different zygotes \ 
they are present in the same zygote though at different times in its 
life-history. They are of the same order as the mutational variations 
of the modern biologist upon which the appearance of a new character 
depends. \\'liat is a genetic or nmtational variation? It is a genetic 
character whicli was not present in either of the parents. But these 
"growth variations" were present in the parents, and in this they 
differ from nmtational variations. But what are genetic characters ? 
They are characters Avhich must appear if any development occurs. 
They are usually contrasted with "acquired characters," using the 
ex[)ressi()n "ac(iuired character" in the Lamarckian sense. But 
strictly speaking tlicy cire acquired characters, for the zygote at first 
has none of the characters which it subsequently acquires, but only 
the power of ac(|uiriiig tlie/n in response to the action of the envir(»n- 
nieiit. But the characters so acquired are not what we technically 
understand and what Lamarck meant by "acquired characters." 
Tliey are genetic characters, as defiiRMl above. AVliat then are 

' A zygote is a fertilised ovum, i.e. u uew organism resultiug from the fusion of an 
OTum and a epermatozoon, 


180 Darwin and Embryology 

Lamarck's "acquired characters"? They are variations in genetic 
characters caused in a particular way. There are, in fact, two kinds 
of variation in genetic characters depending on tlie mode of causa- 
tion. Firstly, there are those variations consequent upon a variation 
in the constitution of the protoplasm of a particular zygote, and 
independent of the environment in which the organism develops, 
save in so far as this simply calls them forth : these are the 
so-called genetic or mutational variations. Secondly, there are 
those variations which occur in zygotes of similar germinal con- 
stitution and which are caused solely by difl'erences in the environ- 
ment to Avhicli the individuals are respectively exposed : these are 
the "acquired characters" of Lamarck and of authors generally. 
In consequence of this double sense in which the term "acquired 
characters" may be used, great confusion may and does occur. If 
the protoplasm be compared to a machine, and the external con- 
ditions to the hand that works the machine, then it may be said that, 
as the machine can only work in one way, it can only produce one 
kind of result (genetic character), but the particular form or quality 
(Lamarckian " acquired character ") of the result will depend upon 
the hand that works the machine (environment), just as the quality 
of the sound produced by a fiddle depends entirely upon the hand 
Avhich plays upon it. It would be improper to apply the term 
" mutation " to those genetic characters which are not new characters 
or new variants of old characters, but such genetic characters are of 
the same nature as those characters to which the term mutation has 
been applied. It may be noticed in passing that it is very questionable 
if the modern biologist has acted in the real interests of science in ap- 
plying the term mutation in the sense in which he has applied it. The 
genetic characters of organisms come from one of two sources : either 
they are old characters and are due to the action of what we call in- 
heritance or they are new and are due to what we call variation. If 
the term mutation is applied to the actual alteration of the machinery 
of the protoplasm, no objection can be felt to its use; but if it be 
applied, as it is, to the product of the action of the altered machine, 
viz, to the new genetic character, it leads to confusion. Inheritance 
is the persistence of the structure of the machine; characters are 
the products of the working of the machine; variation in genetic 
characters is due to the alteration (nmtation) in the arrangement 
of the machinery, while variation in acquired characters (Lamarckian) 
is due to differences in the mode of working the machinery. The 
machinery M'hen it starts (in the new zygote) has the power of 
gi-inding out certain results, which we call the characters of the 
organism. These appear at successive intervals of time, and the 
orderly manifestation of them is what we call the life-history of the 

Sexual Maturity 181 

organism. This brings us back to the question with which we started 
this discussion, viz. what is the relation of these variations in struc- 
ture, which successively appear in an organism and constitute its 
life-history, to the mutational variations which appear in different 
organisms of the same brood or species. The question is brought 
liome to us when we ask what is a bud-sport, such as a nectarine 
appearing on a peach-tree? From one point of view, it is simply 
a mutation appearing in asexual reproduction; from another it is 
one of these successional characters ("groAvth variations") which 
constitute the life-history of the zygote, for it appears in the same 
zygote which first produces a peach. Here our analogy of a machine 
which only Morks in one way seems to fail us, for these bud-sports 
do not appear in all parts of the organism, only in certain buds or 
parts of it, so that one part of the zygotic machine would appear to 
work differently to another. To discuss this question further would 
take us too far from our subject. Suffice it to say that we cannot 
answer it, any more than we can this further question of burning- 
interest at the present day, viz. to what extent and in what manner 
is the machine itself altered by the particular way in which it is 
worked. In connection with this question we can only submit one 
consideration: the zygotic machine can, by its nature, only work 
once, so that any alteration in it can only be ascertained by studying 
the replicas of it M'hich are produced in the reproductive organs. 

It is a peculiarity that the result which we call the ripening of the 
generative organs nearly always appears among the final products 
of the action of the zygotic machine. It is remarkable that this 
should be the case. What is the reason of it? The late appear- 
ance of functional reproductive organs is almost a universal law, 
and the explanation of it is suggested by expressing the law in 
another way, viz. that the machine is almost always so constituted 
that it ceases to work efficiently soon after the reproductive organs 
have sufficiently discharged their function. Why this should occur 
we cannot explain: it is an ultimate fact of nature, and cannot be 
included in any wider category. The period during which the 
reproductive organs can act may be short as in ephcmerids or long 
a.s in man and trees, and there is no reason to suppose that their 
action (lainagc.s the vital machinery, though sometimes, as in the case 
of aniuiiil jdants (Metschnikoff), it may incidentally do so; but, long 
or short, the cessation of their actions is always a prelude to the end. 
When they and their action are impaired, the organism ceases to 
react with jH-ecision to the environment, and the organism as a wliole 
iiiidergoes retrogressive changes. 

it has been pointed out above that there is reason to believe that 
at the dawn of life the lile-cycle was, cither in esse or in posse, at 

182 Darwin and Embryology 

least as long as it is at the present time. The qualification implied 
by the words in italics is necessary, for it is clearly possible that the 
external conditions then existing were not suitable for the production 
of all the stages of the potential life-history, and that what we call 
organic evolution has consisted in a gradual evolution of new en- 
vironments to which the organism's innate capacity of change has 
enabled it to adapt itself. We have warrant for this possibility in 
the case of the Axolotl and in otlier similar cases of neoteny. And 
these cases further bring home to us the fact, to which I have already 
referred, that the full development of the functional reproductive 
organs is nearly always associated with the final stages of the life- 

On this view of the succession of characters in the life-history of 
organisms, how shall we explain the undoubted fact that the develop- 
ment of buds hardly ever presents any phenomena corresponding to 
the embryonic and larval changes ? The reason is clearly this, that 
budding usually occurs after the embryonic stage is past; when the 
characters of embryonic life have been worked out by the machine. 
When it takes place at an early stage in embryonic life, as it does in 
cases of so-called embryonic fission, the product shows, either partly 
or entirely, phenomena similar to those of embryonic development. 
The only case known to me in which budding by the adult is 
accompanied by morphological features similar to those displayed 
by embryos is furnished by the budding of the medusiform spore-sacs 
of hydrozoon polyps. But this case is exceptional, for here we have 
to do with an attempt, which fails, to fomi a free-swimming organism, 
the medusa; and the vestiges which appear in the buds are the 
umbrella-cavity, marginal tentacles, circular canal, etc., of the medusa 
arrested in development. 

But the question still remains, are there no cases in which, as 
implied by the recapitulation theory, variations in any organ are 
confined to the period in which the organ is functional and do not 
afiect it in the embryonic stages ? The teeth of the whalebone whales 
may be cited as a case in which this is said to occur; but here the 
teeth are only imperfectly developed in the embryo and are soon 
absorbed. They have been afi'ected by the change Mhich has 
produced their disappearance in the adult, but not to complete 
extinction. Nor are they now likely to be extinguished, for having 
become exclusively embryonic they are largely protected from the 
action of natural selection. This consideration brings up a most 
important aspect of the question, so far as disappearing organs are 
concerned. Kvery organ is laid doMii at a certain period in the 
embryo and undergoes a certain course of growth until it obtains 
full functional development. When for any cause reduction begins, 

Emhryonic Vestiges 183 

it is affected at all stages of its growth, unless it has functional 
importance in the larva, and in some cases its life is shortened at one 
or both ends. In cases, as in that of the whale's teeth, in which it 
entirely disappears in the adult, the latter part of its life is cut off; 
in others, the beginning of its life may be deferred. This happens, for 
instance, with the spiracle of many Elasmobranchs, which makes its 
appearance after the hyobranchial cleft, not before it as it should do, 
being anterior to it in position, and as it does in the Amniota in which 
it shows no reduction in size as compared with the other pharyngeal 
clefts. In those Elasmobranchs in which it is absent in the adult but 
present in the embryo (e.g. Carcharias) its life is shortened at both 
ends. Many more instances of organs, of which the beginning and 
end have been cut off, might be mentioned; e.g. the muscle-plate 
coelom of Aves, the primitive streak and the ncurenteric canal of 
amniote blastoderms. In yet other cases in which the reduced 
organ is almost on the verge of disappearance, it may appear for a 
moment and disappear more than once in the course of develop- 
ment. As an instance of this striking phenomenon I may mention 
the neurenteric canal of avine embryos, and the anterior neuropore 
of Ascidians. Lastly the reduced organ may disappear in the 
developing stages before it docs so in the adult. As an instance 
of this may be mentioned the mandibular palp of those Crustacea 
with zoaea larvae. This structure disappears in the larva only to 
reappear in a reduced forai in later stages. In all these cases 
we are dealing with an organ which, we imagine, attained a fuller 
functional development at some previous stage in race-history, but in 
most of them we have no proof that it did so. It may be, and the 
possibility must not be lost sight of, that these organs never were 
anything else than functionless and that though they have been got 
rid of in the adult by elimination in the course of time, they have 
been able to persist in embryonic stages which are protected from 
the full action of natural selection. There is no reason to suppose 
that living matter at its first appearance diirered from non-living 
matter in possessing only properties conducive to its well-being 
and prolonged existence. No one thinlcs that the properties of the 
various forms of inorganic matter are all strictly related to external 
conditions. Of what use to the diamond is its high specific gravity 
and high refrangibility, and to gold of its yellow colour and great 
weight? These substances continue to exist in virtue of other 
pro{)crties than these. It is impossible to suppose that the properties 
of living matter at its fii-st appearance were all useful to it, for even 
now after aeons ol* elimination we find that it i)ossesses many useless 
organs and that many of its relations to the external world are 
capable of considerable improvement. 

184 Darwin and Embryology 

In writing this essay I have purposely refrained from taking a 
definite position with regard to the problems touched. My desire 
has been to write a chapter showing the influence of Darwin's work 
so far as Embryology is concerned, and the various points which come 
up for consideration in discussing his views. Darwin was the last 
man who would have claimed finality for any of his doctrines, but he 
might fairly have claimed to have set going a process of intellectual 
fermentation which is still very far from completion. 



By W. B. Scott. 

Professor of Geology in the University of Princeton, U.S.A. 

To no branch of science did the publication of T?ie Origin of \ 
Species prove to be a more vivifying and transforming influence than 1 
to Palaeontology. This science had sutiered, and to some extent, still ) 
suffers from its rather anomalous position between geology and 
biology, each of which makes claim to its territory, and it was held 
in strict bondage to the Linnean and Cuvierian dogma that species 
were immutable entities. There is, however, reason to maintain that 
this strict bondage to a dogma now abandoned, Avas not Avithout its 
good side, and served the purpose of keeping the infant science in 
leading-strings until it was able to Avalk alone, and preventing a flood 
of premature generalisations and speculations. 

As Zittel has said : " Two directions were fi'om the first apparent 
in palaeontological research — a stratigi-aphical and a biological. 
Stratigraphers wished from palaeontology mainly confirmation re- 
garding the true order or relative age of zones of rock-deposits 
in the field. Biologists had, theoretically at least, the more genuine 
interest in fossil organisms as individual forms of life\" The geo- 
logical or stratigraphical direction of the science was given by the 
work of William Smith, "the father of historical geology," in the 
closing decade of the eighteenth century. Smith was the first to 
make a systematic use of fossils in determining the order of suc- 
cession of the rocks which make up the accessible crust of the earth, 
and this use has continued, without essential change, to the present 
day. It is true that the theory of evolution has greatly modified our 
conceptions concerning the introduction of new 8j)ecics and tlio 
manner in which palaeontological dat<i are to be interpreted in terms 
of stratigraphy, but, broadly speaking, the method remains funda- 
mentally the HJime as that introduced by Smith. 

The biological direction of palaeontology Wius due to (*uvier and 
his associates, who first sliowi-d that fossils were not nioroly varieties 

* Zittel, Hiitory of Geology and I'alaeontology, p. 3(53, London, 1901. 

186 The Pdlaeontological Record. I. Animals 

of existing organisms, but belonged to extinct species and genera, an 
altogether revolutionary conception, which startled the scientific 
world. Cuvier made careful studies, especially of fossil vertebrates, 
from the standpoint of zoology and was thus the founder of 
palaeontology as a biological science. His great work on Ossements 
Fossiles (Paris, 1821) has never been surpassed as a masterpiece 
of the comparative method of anatomical investigation, and has 
furnished to the palaeontologist the indispensable implements of 

On the other hand, Cuvier's theoretical views regarding the 
history of the earth and its successive faunas and floras are such 
as no one believes to-day. He held that the earth had been re- 
peatedly devastated by great cataclysms, which destroyed every 
living thing, necessitating an entirely new creation, thus regarding 
the geological periods as sharply demarcated and strictly contem- 
poraneous for the whole earth, and each species of animal and plant 
as confined to a single period. Cuvier's immense authority and his 
commanding personality dominated scientific thought for more than 
a generation and marked out the line which the development of 
palaeontology was to follow. The work was enthusiastically taken 
up by many very able men in the various European countries and 
in the United States, but, controlled as it was by the belief in the 
fixity of species, it remained almost entirely descriptive and consisted 
in the description and classification of the different groups of fossil 
organisms. As already intimated, this narrowness of view had its 
compensations, for it deferred generalisations until some adequate 
foundations for these had been laid. 

Dominant as it was, Cuvier's authority was slowly undermined 
by the progress of knowledge and the way was prepared for the 
introduction of more rational conceptions. The theory of "Cata- 
strophism" was attacked by several geologists, most effectively by 
Sir Charles Lyell, who greatly amplified the principles enunciated 
by Hutton and Playfair in the preceding century, and inaugurated 
a new era in geology. Lycll's uniforniitarian views of the earth's 
history and of the agencies which had wrought its changes, had 
undoubted effect in educating men's minds for the acceptance of 
essentially similar views regarding the organic world. In palaeontology 
too the doctrine of the immutability of species, though vehemently 
maintained and reasserted, was gradually weakening. In reviewing 
long series of fossils, relations were observed which pointed to genetic 
connections and yet were interpreted as purely ideal. Agassiz, for 
example, who never accepted the evolutionary theory, drew attention 
to facts which could be satisfactorily interpreted only in terms of 
that theory. Among the fossils he indicated "progressive," "syn- 

" The Origin of Species " 187 

thetic," "prophetic," and "embryonic" types, and pointed out the 
parallelism which obtains between the geological succession of ancient 
animals and the ontogenetic development of recent forms. In 
Darwin's words : "This view accords admirably well with our theory ^" 
Of similar import were Owen's views on "generalised types" and 

The appearance of The Origin, of Species in 1859 revolutionised J 
all the biological sciences. From the very nature of the case, Darwin 
was compelled to give careful consideration to the palaeontological 
evidence ; indeed, it was the palaeontology and modern distribution 
of animals in South America which first led him to reflect upon the 
great problem. In his o\vn words : " I had been deeply impressed 
by discovering in the Pampcan formation great fossil animals covered 
with armour like that on tlie existing armadillos ; secondly, by the 
manner in which closely allied animals replace one another in pro- 
ceeding southward over the Continent ; and thirdly, by the South 
American character of most of the productions of the Galapagos 
archipelago, and more especially by the manner in which they differ 
slightly on each island of the group-." In the famous tenth and 
eleventh chapters of the Origin, tlic palaeontological evidence is 
examined at length and the imperfection of the geological record 
is strongly emphasised. The conclusion is reached, that, in view of 
this extreme imperfection, palaeontology could not reasonably be 
expected to yield complete and convincing proof of the evolutionary 
theory. " I look at the geological record as a history of the world 
imperfectly kept, and written in a changing dialect ; of this history 
we possess the last volume alone, relating only to two or three 
countries. Of tliis volume, only here and there a short chapter has 
been preserved ; and of each page, only here and there a few lines ^" 
Yet, aside from these inevitable difficulties, he concludes, that "the 
other great leading facts in palaeontology agree admirably with tlie 
theory of descent M'ith modification through variation and natural 

Darwin's theory gave an entirely new significance and importance 
to palaeontology. Cuvier's conception of the science had been a 
limited, though a lofty one. " How glorious it would be if we could 
arrange the organised i)roduct3 of the universe in tlieir chronological 
order!... The chronological succession of organised forms, the exact 
detcniiination of those types which appeared first, the sinnil- 
taneouH origin of certain species and their gradual decay, would 
perhaps teach us as much about the mysteries of organisation aa 

' Oriitin of Species {6th edit.), p. 310. 

■ Life and Letters of Charles Darwin, i. p. 82. 

• Origin of Species, p. 289. « Ibid. p. 313. 

188 The Palaeontological Record. I. Animals 

we can possibly learn tliroiigh experiments with living organisms^." 
This, however, was rather the expression of a hope for the distant 
future than an account of what was attainable, and in practice the 
science remained almost purely descriptive, until Darwin gave it a 
new standpoint, new problems and an altogether fresh interest and 
charm. The revolution thus accomplished is comparable only to that 
produced by the Copernican astronomy. 

From the first it was obvious that one of the most searching 
tests of the evolutionary theory would be given by the advance of 
palaeontological discovery. However imperfect the geological record 
might be, its ascertained facts would necessarily be consistent, under 
any reasonable interpretation, vnt\\ the demands of a true theory; 
otherwise the theory would eventually be overwhelmed by the mass 
of irreconcilable data. A very great stimulus was thus given to 
geological investigation and to the exploration of new lands. In the 
last forty years, the examination of North and South America, of 
Africa and Asia has brought to light many chapters in the history 
of life, which are astonishingly full and complete. The flood of new 
material continues to accumulate at such a rate that it is impossible 
to keep abreast of it, and the very wealth of the collections is a source 
of difficulty and embarrassment. In modern palaeontology phylo- 
genetic questions and problems occupy a foremost place and, as a 
result of the labours of many eminent investigators in many lands, 
it may be said that this science has proved to be one of the most 
solid supports of Darwin's theory. Ti'ue, there are very many un- 
solved problems, and the discouraged worker is often tempted to 
believe that the fossils raise more questions than they answer. Yet, 
on the other hand, the whole trend of the evidence is so strongly in 
^ favour of the evolutionary doctrine, that no other interpretation 
^ seems at all rational. 

To present any adequate account of the palaeontological record 
from the evolutionary standpoint, would require a large volume and 
a singularly unequal, broken and disjointed history it would be. 
Here the record is scanty, interrupted, even unintelligible, while 
there it is crowded with embarrassing wealth of material, but too 
often these full chapters are separated by such stretches of unrecorded 
time, that it is difficult to connect them. It will be more profitable 
to present a few illustrative examples than to attempt an outline of 
the whole history. 

At the outset, the reader should be cautioned not to expect too 
nmch, for the task of determining phylogenies fairly bristles with 
difficulties and encounters many unanswered ([ucstions. Even when 
the evidence seems to be as copious and as complete as could be 

1 Zitttl, op. cit. p. 140. 

Fossil Mammals 189 

wished, different observers will put diflercnt interpretations upon 
it, as in the notorious case of the Steinheim shells \ The ludicrous 
discrepancies which often appear between the phylogenetic "trees" 
of various writers have cast an undue discredit upon the science and 
have led many zoologists to ignore palaeontology altogether as un- 
worthy of serious attention. One principal cause of these discrepant 
and often contradictory results is our ignorance concerning the exact 
modes of developmental change. What one writer postulates as 
almost axiomatic, another will reject as impossible and absurd. Few 
will be found to agree as to how far a given resemblance is offset by 
a given unlikeness, and so long as the question is one of weighing 
evidence and balancing probabilities, complete harmony is not to 
be looked for. These formidable difficulties confront us even in 
attempting to work out from abundant material a brief chapter 
in the ph} logenetic history of some small and clearly limited group, 
and they become disproportionately greater, when we extend our 
view over vast periods of time and undertake to determine the 
mutual relationships of classes and types. If the evidence were 
complete and available, we should hardly be able to unravel its 
infinite complexity, or to find a clue through the mazes of the 
labyrintL " Our ideas of the course of descent must of necessity be 

Some of the most complete and convincing examples of descent 
with modification are to be found among the mammals, and nowhere 
more abundantly than in North America, where the series of con- 
tinental formations, running through the whole Tertiary period, is 
remarkably full. Most of these formations contain a marvellous 
wealth of mammalian remains and in an unusual state of preserva- 
tion. The oldest Eocene (Palcocene) has yielded a mammalian fauna 
which is still of prevailingly Mesozoic character, and contains but 
few forms which can be regarded as ancestral to those of later times. 
The succeeding fauna of the lower Eocene proper (Wasatch stage) 
is radically different and, while a few forms continue over from the 
Paleocene, the majority are evidently recent immigrants from some 
region not yet identified. From the Wasatch onward, the develop- 
ment of many phyla may be traced in almost unbroken continuity, 
though from time to time the record is somewhat obscured by 
migrations from the Old World and South America. As a rule, 
however, it is easy to distinguish between the inunigrant and tlio 
indigenous elements of the faunju 

' In tlic Miocene beds of Steinheim, Wiirtembcrp, occur countlo^sB fresh-wftter sholU, 
wliich show niimerouH lines of moditication, but those have been very dillerently inter- 
preted by different writers. 

* 1). H. Scott, Studie$ in Fostil Botany, p. 524. London, 1000. 

190 The Palaeoiitological Record. I. Animals 

From their gregarious habits and individual abundance, the 
histor}^ of many hoofed animals is preserved with especial clearness. 
So well known as to have become a commonplace, is the phylogeny 
of the horses, which, contrary to all that Avould have been expected, 
ran the greater part of its course in North America. So far as it has 
yet been traced, the line begins in the lower Eocene with the genus 
Eohi2)piis, a little creature not much larger than a cat, which has 
a short neck, relatively short limbs, and, in particular, short feet, 
with four functional digits and a splint-like rudiment in the fore-foot, 
three functional digits and a rudiment in the hind-foot. The fore- 
arm bones (ulna and radius) are complete and separate, as are also 
the bones of the lower leg (fibula and tibia). The skull has a short 
face, with the orbit, or eye-socket, incompletely enclosed with bone, 
and the brain-case is slender and of small capacity. The teeth are 
short-crowned, the incisors without "mark," or enamel pit, on the 
cutting edge ; the premolars are all smaller and simpler than the 
molars. The pattern of the upper molars is so entirely difterent 
from that seen in the modern horses that, without the intermediate 
connecting steps, no one would have ventured to derive the later 
from the earlier plan. This pattern is quadritubercular, with four 
principal, conical cusps arranged in two transverse pairs, forming 
a square, and two minute cuspules between each transverse pair, 
a tooth wliich is much more pig-like than horse-like. In the lower 
molars the cusps have already united to form two crescents, one 
behind the other, forming a pattern which is extremely common 
in the early representatives of many difterent families, both of the 
Perissodactyla and the Artiodactyla. In spite of the manifold 
diflerences in all parts of the skeleton between Eohippiis and the 
recent horses, the former has stamped upon it an equine character 
which is unmistakable, though it can hardly be expressed in words. 

Each one of the difibrent Eocene and Oligocene horizons has its 
characteristic genus of horses, showing a slow, steady progress in 
a definite direction, all parts of the structure participating in the 
advance. It is not necessary to follow each of these successive steps 
of change, but it should be emphasised that the changes are gradual 
and uninterrupted. The genus Mesohipp^is, of the middle Oligocene, 
may be selected as a kind of half-way stage in tlic long progression. 
Conq)aring Mesohippus with Eohippiis, we observe that the former 
is mucli larger, some species attaining the size of a sheej), and has 
a relatively longer neck, longer limbs and much more elongate feet, 
which are tridactyl, and the middle toe is so enlarged that it bears 
most of the weight, while the lateral digits are very much more 
slender. The fore-arm bones have begun to co-ossify and the ulna 
is greatly reduced, while the fibula, though still complete, is liardly 

Evolution of the Hones 191 

more than a thread of bone. The skull has a longer face and a nearly 
enclosed orbit, and the brain-case is fuller and more capacious, the 
internal cast of Avhich shows that the brain was richly convoluted. 
The teeth are still very short-crowned, but the upper incisors plainly 
show the beginning of the " mark " ; the premolars have assumed the 
molar form, and the upper molars, though plainly derived from those 
of Eohippus, have made a long stride toward the horse pattern, in 
that the separate cusps have united to form a continuous outer wall 
and two transverse crests. 

In the lower Miocene the interesting genus Desmatippns shows 
a further advance in the development of the teeth, which are beginning 
to assume the long-crowned shape, delaying the formation of roots ; 
a thin layer of cement covers the crowns, and the transverse crests 
of the upper grinding teeth display an incipient degree of their 
modern complexity. This tooth-pattern is strictly intermediate 
between the recent type and the ancient type seen in Mesohippns 
and its predecessors. The upper Miocene genera, Protohqjpiis and 
Hipparimi are, to all intents and purposes, modern in character, but 
their smaller size, tridactyl feet and somewhat shorter-crowned teeth 
are reminiscences of their ancestry. 

From time to time, when a land-connection between Xorth 
America and Eurasia was established, some of the successive equine 
genera migrated to the Old World, but they do not seem to have 
gained a i)ermancnt footing there until the end of the Miocene or 
beginning of the Pliocene, eventually diversifying into the horses, 
asses, and zebras of Africa, Asia and Europe. At about the same 
period, the family extended its range to South America and there 
gave rise to a number of species and genera, some of them extremely 
peculiar. For some unknown reason, all the horse tribe had become 
extinct in the western hemisphere before the European discovery, but 
not until after the native race of man had peopled the continents. 

In addition to the main stem of equine descent, briefly considered 
in the foregoing paragraphs, several side-branches were given oil" at 
successive levels of the stem. Most of these branches were short- 
lived, but some of them flourished for a considerable period and 
ramified into many species. 

Apparently related to the horses and derived from the same 
root-stock is the family of the Palaeothcrcs, confined to the Eocene 
and Oligocene of lOnrope, dying out without descendants. In tiie 
earlier attempts to work out the history of the horses, as in the 
famous essay of Kowalevsky\ the I'alaeotheres were i)laced in the 
direct line, because the number of adcijuately known Eocene mam- 

* " Snr VAnchitherium aurelianense Cuv. ot Bur riiiBtoirf> paliontologiquedee Chevaux,'' 
ilim. de VAcad. Imp. det Sc. de St Piterthourg, xx. no. 6, 1873. 

192 The Palaeontological Record. I. Animals 

mals was then so small, that Cuvier's types were forced into various 
incongruous positions, to serve as ancestors for unrelated series. 

The American family of the Titanotheres may also be distantly 
related to the horses, but passed through an entirely different course 
of development. From the lower Eocene to the lower sub-stage of 
the middle Oligocene the series is complete, beginning with small and 
rather lightly built animals. Gradually the stature and massiveness 
increase, a transverse pair of nasal horns make their appearance and, 
as these increase in size, the canine tusks and incisors diminish 
correspondingly. Already in the oldest known genus the number 
of digits had been reduced to four in the fore-foot and three in the 
hind, but there the reduction stops, for the increasing body-weight 
made necessary the development of broad and heavy feet. The final 
members of the series comprise only large, almost elephantine animals, 
with immensely developed and very various nasal horns, huge and 
massive heads, and altogether a grotesque appearance. The growth 
of the brain did not at all keep pace with the increase of the head 
and body, and the ludicrously small brain may well have been one of 
the factors which determined the startlingly sudden disappearance 
and extinction of the group. 

Less completely known, but of unusual interest, is the genealogy 
of the rhinoceros family, which probably, though not certainly, was 
likewise of American origin. The group in North America at least, 
comprised three divisions, or sub-families, of very different pro- 
portions, appearance and habits, representing three divergent lines 
from the same stem. Though the relationship between the three 
lines seems hardly open to question, yet the form ancestral to all 
of them has not yet been identified. This is because of our still very 
incomplete knowledge of several perissodactyl genera of the Eocene, 
any one of which may eventually prove to be the ancestor sought for. 

The first sub-family is the entirely extinct group of Hyracodonfcs, 
which may be traced in successive modifications through the upper 
Eocene, lower and middle Oligocene, then disappearing altogether. 
As yet, the hyracodonts have been found only in North America, and 
the last genus of the series, Hyracodon, was a cursorial animal. 
Very briefly stated, the modifications consist in a gradual increase 
in size, with greater slenderness of proportions, accompanied by 
elongation of the neck, limbs, and feet, which become tridactyl and 
very narrow. The grinding teeth have assumed the rhinoceros-like 
pattern and the premolars resemble the molars in form ; on the 
other hand, the front teeth, incisors and canines, have become very 
small and arc useless as weapons. As the animal had no horns, it (|uite delenceless and must have found its safety in its swift 
running, for H yracodon displays many superficial resemblances to 

Rhinoceroses, Camels, and Llamas 193 

the contemporary Oligocene horses, and was evidently adapted for 
speed. It may well have been the competition of the horses which 
led to the extinction of these cursorial rhinoceroses. 

The second sub-family, that of the AmjTiodonts, followed a 
totally different course of development, becoming short-legged and 
short-footed, massive animals, the proportions of which suggest 
aquatic habits; they retained four digits in the front foot. The 
animal was well provided with weapons in the large canine tusks, 
but was without horns. Some members of this group extended 
their range to the Old World, but they all died out in the middle 
Oligocene, leaving no successors. 

The sub-family of the true rhinoceroses cannot yet be certainly 
traced farther back than to the base of the middle Oligocene, though 
some fragmentary remains found in the lower Oligocene are probably 
also referable to it. The most ancient and most primitive member of 
this series yet discovered, the genus Trigonias, is unmistakably a 
rhinoceros, yet much less massive, having more the proportions of a 
tapir ; it had four toes in the front foot, three in the hind, and had a 
full complement of teeth, except for the lower canines, though the 
upper canines are about to disappear, and the peculiar modification 
of the incisors, characteristic of the true rhinoceroses, is already 
apparent ; the skull is hornless. Representatives of this sub-family 
continue through the Oligocene and Miocene of North America, 
becoming rare and localised in the Pliocene and then disappearing 
altogether. In the Old World, on the other hand, where the line 
appeared almost as early as it did in America, this group underwent 
a gi'eat expansion and ramification, giving rise not only to the 
Asiatic and African forms, but also to several extinct series. 

Turning now to the Artiodactyla, we find still another group of 
mammals, that of the camels and llamas, which has long vanished 
from North America, yet took its rise and ran the greater part of its 
course in that continent. From the lower Eocene onward the history 
of this series is substantially complete, though much remains to be 
learned concerning the earlier members of the family. The story is 
very like that of the horses, to which in many respects it runs 
curiously parallel. Beginning with very small, five-toed animals, we 
observe in the successive genera a gradual transformation in all parts 
of the skeleton, an elongation of the neck, limbs and feet, a reduction 
of the digits from five to two, and eventually the coalescence of the 
remaining two digits into a " cannon-bone." The grinding teeth, by 
e«iually gradual steps, take on the ruminant pattern. In the upper 
Miocene the line divides into the two branclies of the camels and 
llamas, the former migrating to Eurasia and the latter to Houth 
America, though representatives of both lines persisted in North 

D. 13 

194 The Palaeontologicdl Record. I, Animals 

America until a very late period. Interesting side-branches of this 
line have also been found, one of which ended in the upper Miocene 
in animals which had almost the proportions of the giraffes and must 
have resembled them in appearance. 

The American Tertiary has yielded several other groups of 
ruminant-like animals, some of which form beautifully complete 
evolutionary series, but space forbids more than this passing mention 
of them. 

It was in Europe that the Artiodactyla had their principal 
development, and the upper Eocene, Oligocene and Miocene are 
crowded with such an overwhelming number and variety of forms 
that it is hardly possible to marshal them in orderly array and 
determine their mutual relationships. Yet in this chaotic exuberance 
of life, certain important facts stand out clearly, among these none is 
of greater interest and importance than the genealogy of the true 
Ruminants, or Pecora, which may be traced from the upper Eocene 
onward. The steps of modification and change are very similar to 
those through which the camel phylum passed in North America, 
but it is instructive to note that, despite their many resemblances, 
the two series can be connected only in their far distant beginnings. 
The pecoran stock became vastly more expanded and diversified than 
did the camel line and was evidently more plastic and adaptable, 
spreading eventually over all the continents except Australia, and 
forming to-day one of the dominant types of mammals, while the 
camels are on the decline and not far from extinction. The Pecora 
successively ramified into the deer, antelopes, sheep, goats and oxen, 
and did not reach North America till the Miocene, when they were 
already far advanced in specialisation. To this invasion of the 
Pecora, or true ruminants, it seems probable that the decline and 
eventual disappearance of the camels is to be ascribed. 

Recent discoveries in Egypt have thrown much light upon a 
problem which long baffled the palaeontologist, namely, the origin of 
the elephants^. Early representatives of this order, Mastodons, had 
appeared almost simultaneously (in the geological sense of that word) 
in the upper Miocene of Europe and North America, but in neither 
continent was any more ancient type known which could plausibly be 
regarded as ancestral to them. Evidently, these problematical animals 
had reached the northern continents by migrating from some other 
region, but no one could say where that region lay. The Eocene and 
Oligocene beds of the Fayoum show us that the region sought for is 
Africa, and that the elephants form just such a series of gradual 
modifications as we have found among other hoofed animals. The 

1 C, W. Andrews. "On the Evolution of the Proboscidea," Phil. Trans, Roy. Soc. 
London, Vol. 196, 1<J04, p. 99. 

The Origin of Whales and Carnivores 195 

later steps of the tranfjformation, by which the mastodons lost their 
lower tusks, and their relatively small and simple grinding teeth 
acquired the gi*eat size and highly complex structure of the true 
elephants, may be followed in the uppermost Miocene and Pliocene 
fossils of India and southern Europe. 

Egypt has also of late furnished some very welcome material 
which contributes to the solution of another unsolved problem which 
had quite eluded research, the origin of the whales. The toothed- 
whales may be traced back in several more or less parallel lines as 
far as the lower Miocene, but their predecessors in the Oligocene are 
still so incompletely known that safe conclusions can hardly be dra>vn 
from them. In the middle Eocene of Egypt, however, has been 
found a small, whale-like animal (Protocetus), which shows what 
the ancestml toothed-whale was like, and at the same time seems 
to connect these thoroughly marine mammals with land-animals. 
Though already entirely adapted to an aquatic mode of life, the 
teeth, skull and backbone of Frotocetus display so many differences 
from tliose of the later whales and so many approximations to those 
of primitive, carnivorous land-mammals, as, in a large degree, to 
bridge over the gap between the two groups. Thus one of the most 
puzzling of palaeontological questions is in a fair way to receive a 
satisfactory answer. The origin of the whalebone-whales and their 
relations to the toothed-whales cannot yet be determined, since the 
necessary fossils have not been discovered. 

Among the carnivorous mammals, phylogenetic series are not so 
clear and distinct as among the hoofed animals, chiefly because the 
carnivores are individually much less abundant, and well-preserved 
skeletons are among the prizes of the collector. Nevertheless, much 
has already been learned concerning the mutual relations of the 
carnivorous families, and several phylogenetic series, notably that of 
the dogs, are quite complete. It has been made extremely probable 
that the piimitive dogs of the Eocene represent the central stock, 
from wliicli nearly or quite all the otlier families branched off, though 
the origin and descent of the cats have not yet been determined. 

It should be clearly understood tliat the foregoing account of 
mammalian descent is merely a selection of a few representative 
cases and might be almost indefinitely extended. Nothing has been 
said, for exam[)le, of the wonderful museum of ancient mannnalian 
life wliicli is entoiiibed in the rocks of South America, csjtocially of 
Patagonia, and wliicli opens a world so entirely dillcrent from that of 
the northern continents, yet exemplilying the sjime laws of "descent 
with modification." Very beautiful phylogenetic series have already 
been established among these most interesting and marvellously 
l)reserved fossils, but lack of space forbids a consideration of them. 


196 The Palaeontological Record. I. Animals 

The origin of the mammalia, as a class, offers a problem of which 
palaeontology can as yet present no definitive solution. Many 
morphologists regard the early amphibia as the ancestral group from 
which the mammals were derived, while most palaeontologists believe 
that the mammals are descended from the reptiles. The most ancient 
known manunals, those from the upper Triassic of Europe and North 
America, are so extremely rare and so very imperfectly known, that 
they give little help in determining the descent of the class, but, on 
the other hand, certain reptilian orders of the Permian period, 
especially well represented in South Africa, display so many and such 
close approximations to mammalian structure, as strongly to suggest 
a genetic relationship. It is difficult to believe that all those like- 
nesses should have been independently acquired and are without 
phylogenetic significance. 

Birds are comparatively rare as fossils and we should therefore 
look in vain among them for any such long and closely knit series as 
the mammals display in abundance. Nevertheless, a few extremely 
fortunate discoveries have made it practically certain that birds are 
descended from reptiles, of which they represent a highly specialised 
branch. The most ancient representative of this class is the extra- 
ordinary genus Archaeopteryx from the upper Jurassic of Bavaria, 
which, though an unmistakable bird, retains so many reptilian 
structures and characteristics as to make its derivation plain. Not 
to linger over anatomical minutiae, it may suffice to mention the 
absence of a horny beak, which is replaced by numerous true teeth, 
and the long lizard-like tail, which is made up of numerous distinct 
vertebrae, each with a pair of quill-like feathers attached to it. Birds 
with teeth are also found in the Cretaceous, though in most other 
respects the birds of that period had attained a substantially modern 
structure. Concerning the interrelations of the various orders and 
families of birds, palaeontology has as yet little to tell us. 

The life of the Mesozoic era was characterised by an astonishing 
number and variety of reptiles, which were adapted to every mode of 
life, and dominated the air, the sea and the land, and many of which 
were of colossal proportions. Owing to the conditions of preserva- 
tion which obtained during the Mesozoic period, the history of the 
reptiles is a broken and interrupted one, so that we can make out 
many short series, rather than any one of considerable length. 
While the relations of several reptilian orders can be satisfactorily 
determined, others still baffle us entirely, making their first known 
ai)pearance in a fully differentiated state. We can trace the descent 
of the sea-dragons, the Ichthyosaurs and Plesiosaurs, from terrestrial 
ancestors, but the most ancient turtles yet discovered show us no 
closer approximation to any other order than do the recent turtles ; 

The Descent of the Aimnonltes 197 

and the oldest known Pterosaurs, the fljing dragons of the Jurassic, 
are ah-eady fully ditferentiated. There is, however, no ground for 
discouragement in this, for the progress of discovery has been so 
rapid of late years, and our knowledge of Mesozoic life has increased 
with such leaps and bounds, that there is every reason to expect a 
solution of many of the outstanding problems in the near future. 

Passing over the lower vertebrates, for lack of space to give them 
any adequate consideration, we may briefly take up the record of 
invertebrate life. From the overwhelming mass of material it is 
difficult to make a representative selection and even more difficult 
to state the facts intelligibly Avithout the use of unduly technical 
language and without the aid of illustrations. 

Several groups of the Mollusca, or shell-fish, yield very full and 
convincing evidence of their descent from earlier and simpler forms, 
and of these none is of greater interest than the Ammonites, an 
extinct order of the cephalopoda. The nearest living ally of the 
ammonites is the pearly nautilus, the other existing cephalopods, 
such as the squids, cuttle-fish, octopus, etc., are much more distantly 
related. Like the nautilus, the ammonites all possess a coiled and 
chambered shell, but their especial characteristic is the complexity 
of the " sutures." By sutures is meant the edges of the transverse 
partitions, or septa, where these join the shell-wall, and their 
complexity in the fully developed genera is extraordinary, forming 
patterns like the most elaborate oak-leaf embroidery, while in the 
nautiloids the sutures form simple curves. In the rocks of the 
Mesozoic era, wherever conditions of preservation are favourable, 
these beautiful shells are stored in countless multitudes, of an 
incredible variety of form, size and ornamentation, as is shown by 
the fact that nearly 5000 species have already been described The 
ammonites are particularly well adapted for phylogenetic studies, 
because, by removing the successive Mliorls of the coiled shell, the 
individual development may be followed back in inverse order, to 
the microscopic " i)rotoconch," or embryonic shell, which lies con- 
cealed in the middle of the coil. Thus the valuable aid of embryology 
is obtained in determining relationships. 

The descent of the annnonites, taken as a gi'oup, is simple and 
clear ; they arose as a branch of the nautiloids in the lower Devonian, 
the shells known as goniatites liaving zigzag, angulated sutures. 
Late in the succeeding Carboniferous period appear shells with a 
truly ainmonoid coiii[)le\ity of sutures, and in the Permian their 
numl)er and variety cause them to form a striking element of the 
marine ijunias. It is in the Mesozoic era, however, that these shells 
attain their full develojjment; incrciusing enormously in the Triassic, 
they culminate in the Jurassic in the number of families, genera and 

198 The Palaeontological Record. I. Animals 

species, in the complexity of the sutures, and in the variety of shell- 
ornamentation. A slow decline begins in the Cretaceous, ending in 
the complete extinction of the whole group at the end of that period. 
As a final phase in the history of the ammonites, there appear many 
so-called " abnormal " genera, in which the shell is irregularly coiled, 
or more or less uncoiled, in some forms becoming actually straight. 
It is interesting to observe that some of these genera are not natural 
groups, but are " poly phyle tic," i.e. are each derived from several 
distinct ancestral genera, which have undergone a similar kind of 

In the huge assembly of ammonites it is not yet possible to 
arrange all the forms in a truly natural classification, which shall 
express the various interrelations of the genera, yet several beautiful 
series have already been determined. In these series the individual 
development of the later genera shows transitory stages which are 
permanent in antecedent genera. To give a mere catalogue of names 
without figures would not make these series more intelligible. 

The Brachiopoda, or " lamp-shells," are a phylum of which com- 
paratively few survive to the present day ; their shells have a 
superficial likeness to those of the bivalved RloUusca, but are not 
homologous with the latter, and the phylum is really very distinct 
from the molluscs. Wliile greatly reduced now, these animals were 
incredibly abundant throughout the Palaeozoic era, great masses of 
limestone being often composed almost exclusively of their shells, 
and their variety is in keeping with their individual abundance. As 
in the case of the ammonites, the problem is to arrange this great 
multitude of forms in an orderly array that shall express the 
ramifications of the group according to a genetic system. For many 
brachiopods, both recent and fossil, the individual development, or 
ontogeny, has been worked out and has proved to be of great 
assistance in the problems of classification and phylogeny. Already 
very encouraging progress has been made in the solution of these 
problems. All brachiopods form first a tiny, embryonic shell, called 
the protegulum, which is believed to represent the ancestral form of 
the whole group, and in the more advanced genera the developmental 
stages clearly indicate the ancestral genera of the series, the suc- 
cession of adult forms in time corresponding to the order of the 
ontogenetic stages. The transformation of the delicate calcareous 
supports of the arms, often exquisitely preserved, are extremely 
interesting. Many of the Palaeozoic genera had these supports 
coiled like a pair of spiral springs, and it has been shown that these 
genera were derived from types in Avhich the supports were simply 
shelly loops. 

The long extinct class of Crustacea known as the Trilobites 

Trilohites anid Echinoderms 199 

are likewise very favourable subjects for phylogenetic studies. 
So far as the known record can inform us, the trilobites are 
exclusively Palaeozoic in distribution, but their course must have 
begun long before that era, as is shown by the number of distinct 
types among the genera of the lower Cambrian. The group reached 
the acme of abundance and relative importance in the Cambrian and 
Ordovician; then followed a long, slow decline, ending in complete 
and final disappearance before the end of the Permian. The newly- 
hatched and tiny trilobite larva, known as the protaspis, is very near 
to the primitive larval form of all the Crustacea. By the aid of the 
correlated ontogenetic stages and the succession of the adult forma 
in the rocks, many phylogenetic series have been established and a 
basis for the natural arrangement of the whole class has been laid. 

Very instructive series may also be observed among the Echino- 
derms and, what is very rare, we are able in this sub-kingdom to 
demonstrate the derivation of one class from another. Indeed, there 
is much reason to believe that the extinct class Cystidea of the 
Cambrian is the ancestral group, from which all the other Echino- 
derms, star-fishes, brittle-stars, sea-urchins, feather-stars, etc., are 

The foregoing sketch of the palaeontological record is, of necessity, 
extremely meagre, and does not represent even an outline of the 
evidence, but merely a few illustrative examples, selected almost at 
random from an immense body of material. However, it will perhaps 
suffice to show that the geological record is not so hopelessly incom- 
plete as Darwin believed it to be. Since The Origin of Species was 
written, our knowledge of that record has been enormously extended 
and we now possess, no complete volumes, it is true, but some 
remarkably full and illuminating chapters. The main significance of 
the whole lies in the fact, that just in pro2)ortion to the completeness 
of the record is the unequivocal character of its testimony to the 
truth of the evolutionary theory. 

The test of a true, as distinguished from a false, theory is the 
manner in which newly discovered and unanticipated facts arrange 
themselves under it. No more striking illustration of this can be 
found than in the contrasted fates of Cuvier's theory and of that of 
Darwin. Even before Cuvier's death his views had been undermined 
and the progress of discovery soon laid them in irreparable ruin, 
while the activity of half-a-century in many different lines of inquiry 
has established the theory of evolution upon a foundation of ever 
growing solidity. It is Darwin's imperishable glory that he prescribed 
the lines along whicli all the biological sciences were to advance to 
conquests not dreamed of when he wrote. 



By D. H. Scott, F.RS. 
President of the Linnean Society. 

There are several points of view from which the subject of the 
present essay may be regarded. We may consider the fossil record 
of plants in its bearing : I. on the truth of the doctrine of Evolution ; 
II. on Phylogeny, or the course of Evolution ; III. on the theory of 
Natural Selection. The remarks which follow, illustrating certain 
aspects only of an extensive subject, may conveniently be grouped 
under these three headings. 

I. The Truth of Evolution. 

When The Origin of Species was written, it was necessary to 
show that the Geological Record Avas favourable to, or at least 
consistent with, the Theory of Descent. The point is argued, closely 
and fuUy, in Chapter x. "On the Imperfection of the Geological 
Record," and Chapter xi. " On the Geological Succession of Organic 
Beings"; there is, however, little about plants in these chapters. 
At the present time the truth of Evolution is no longer seriously 
disputed, though there are writers, like Reinke, who insist, and 
rightly so, that the doctrine is still only a belief, rather than an 
established fact of science \ Evidently, then, however little the 
Theory of Descent may be questioned in our oAvn day, it is desirable 
to assure ourselves how the case stands, and in particular how far the 
evidence from fossil plants has grown stronger Mith time. 

As regards direct evidence for the derivation of one species from 
another, there has probably been little advance since Darmn wrote, 
at least so we must infer from the emphasis laid on the discontinuity 
of successive fossil species by great systematic authorities like 
Grand'Eury and Zeiller in their most recent wi-itings. We must 
either adopt the mutationist views of those authors (referred to in 

' J. lieinke, " Kritieche kh&\xag&\&hxe,''Wiesner-FestschriJt, p. 11, Vienna, 1908. 

The Truth of Evolution 201 

the last section of this essay) or must still rely on Darwin's explana- 
tion of the absence of numerous intermediate varieties. The attempts 
which have been made to trace, in the Tertiary rocks, the evolution 
of recent species, cannot, owing to the imperfect character of the 
evidence, be regarded as wholly satisfactory. 

When we come to groups of a somewhat higher order we have 
an interesting history of the evolution of a recent family in the 
work, not yet completed, of Kidston and Gwynne-Vaughan on the 
fossil Osmundaceae\ The authors are able, mainly on anatomical 
evidence, to trace back this now limited group of Ferns, through the 
Tertiary and jMesozoic to the Permian, and to show, with great 
probability, how their structure has been derived from that of early 
Palaeozoic types. 

The history of the Ginkgoaceae, now represented only by the 
isolated maidenhair tree, scarcely known in a wild state, offers 
another strildng example of a family which can be traced with 
certainty to the older Mesozoic and perhaps further back still"^. 

On the wider question of the derivation of the great groups 
of plants, a very considerable advance has been made, and, so far 
as the higher jilants are concerned, we are now able to form a far 
better conception than before of the probable course of evolution. 
This is a matter of phylogeny, and the facts will be considered under 
that head; our immediate point is that the new knowledge of the 
relations between the classes of plants in question materially 
strengthens the case for the theory of descent. The discoveries 
of the last few years throw light especially on the relation of the 
Angiosperms to the Gymnosperms, on that of the Seed-plants gener- 
ally to the Ferns, and on the interrelations between the various 
classes of the higher Cryptogams. 

That the fossil record has not done still more for Evolution is due 
to the fact that it begins too late — a point on which Darwin laid 
stress^ and which has more recently been elaborated by Poulton*. 
An immense proportion of the whole evolutionary history lies behind 
the lowest fossiliferous rocks, and the case is worse for plants than 
for animals, as the record for the former begins, for all practical 
purposes, much higher up in the rocks. 

It may be well here to call attention to a question, often over- 
looked, which has lately been revived by Reinke^ As all admit, 

1 Tram. Royal Soc. Edinburgh, Vol. 45, Pt. in. 1907, Vol, 46, Pt. ii. 1908, Vol. 46, 
rt. ni. 1909. 

* See Seward and Gowan, "The Maidenhair Tree {Ginkgo biloba)," AnnaU of Botany, 
Vol. XIV. 1900, p. 109 ; also A. Sprccher, Le Ginkgo biloba L., Geneva, 1907. 

* Origin of Species (6th edit.), p. 286. 

* Essays on Evolution, pp. 46 et hcq,, Oxford, 1903. 

* Rcinke, loc. cit. p. 13. 

202 The Palaeontologkal Record. II. Plants 

we know nothing of the origin of life ; consequently, for all we 
can tell, it is as probable that life began, on this planet, with 
many living things, as with one. If the first organic beings were 
many, they may have been heterogeneous, or at least exposed to 
different conditions, from their origin ; in either case there would 
have been a number of distinct series from the beginning, and if so 
we should not be justified in assuming that all organisms are related 
to one another. There may conceivably be several of the original 
lines of descent still surviving, or represented among extinct forms— 
to reverse the remark of a distinguished botanist, there may be 
several Vegetable Kingdoms ! However improbable this may sound, 
the possibility is one to be borne in mind. 

That all vascular plants really belong to one stock seems certain, 
and here the palaeontological record has materially strengthened the 
case for a mouophyletic history. The Bryophyta are not likely to be 
absolutely distinct, for their sexual organs, and the stomata of the 
Mosses strongly suggest community of descent with the higher plants ; 
if this be so it no doubt establishes a certain presumption in favour 
of a common origin for plants generally, for the gap between " Mosses 
and Ferns " has been regarded as the widest in the Vegetable King- 
dom. The direct evidence of consanguinity is however much weaker 
when we come to the Algae, and it is conceivable (even if improbable) 
that the higher plants may have had a distinct ancestry (now wholly 
lost) from the beginning. The question had been raised in Darwin's 
time, and he referred to it in these words : " No doubt it is possible, 
as Mr G. H. Lewes has urged, that at the first commencement of life 
many different forms were evolved ; but if so, we may conclude that 
only a very few have left modified descendants \" This question, 
though it deserves attention, does not immediately affect the subject 
of the palaeontological record of plants, for there can be no reasonable 
doubt as to the interrelationship of those groups on which the record 
at present throws light. 

The past history of plants by no means shows a regular pro- 
gi'ession from the simple to the complex, but often the contrary. 
This apparent anomaly is due to two causes. 

1. The palaeobotanical record is essentially the story of the 
successive ascendancy of a series of dominant families, each of which 
attained its maximum, in organisation as well as in extent, and then 
sank into comparative obscurity, giving place to other families, which 
under new conditions were better able to take a leading place. As 
each family ran its downward course, either its members underwent an 
actual reduction in structure as they became relegated to herbaceous 
or perhaps aquatic life (this may have happened with the Horsetails 

* Origin of Species, p. 425. 

From the Complex to the Simple 203 

and with Isoctes if derived from Lepidodendreae), or the higher 
branches of the family were crowded out altogether and only the 
"poor relations" were able to maintain their position by evading 
the competition of the ascendant races ; this is also illustrated by 
the history of the Lycopod phylum. In either case there would result 
a lowering of the type of organisation within the group. 

2. The course of real progress is often from the complex to the 
simple. If, as we shaU find some grounds for believing, the Angio- 
sperms came from a type with a flower resembling in its complexity 
that of Mesozoic " Cycads," almost the whole evolution of the flower 
in the highest plants has been a process of reduction. Tlie stamen, 
in particular, has undoubtedly become extremely simplified during 
evolution ; in the most primitive known seed-plants it was a highly 
compound leaf or pinna ; its reduction has gone on in the Conifers 
and modern Cycads, as well as in the Angiosperms, though in diflerent 
ways and to a varying extent. 

The seed ofl'ers another striking example; the Palaeozoic seeds 
(if we leave the seed-like organs of certain Lycopods out of conside- 
ration) were always, so far as we know, highly complex structures, 
with an elaborate vascular system, a pollen-chamber, and often a 
much-diflerentiated testa. In the present day such seeds exist only 
in a few Gymnosperms which retain their ancient characters — in all 
the higher Spermophytes the structure is very much simplified, and 
this holds good even in the Coniferae, where there is no counter- 
vailing complication of ovary and stigma. 

Reduction, in fact, is not always, or even generally, the same 
thing as degeneration. Simplification of parts is one of the most 
usual means of advance for the organism as a whole. A large pro- 
portion of the higher plants are microphyllous in comparison with 
the highly megaphyllous fern-like forms from which they appear to 
have been derived. 

Darwin treated the general question of advance in organisation 
with much caution, saying: "The geological record... does not extend 
far enough back, to show with unmistakeable clearness that within 
the known history of the world organisation has largely advanced \" 
Further on'^ he gives two standards by which advance may be 
measured: "We ought not solely to compare the highest members 
of a class at any two periods... but we ought to compare all the 
members, high and low, at the two periods." Judged by either 
standard the Horsetails and Club Mosses of the Carboniferous were 
higher than those of our own day, and the same is true of the Meso- 
zoic Cycads. There is a general advance in the succession of classes, 
but not witliin each class. 

1 Origin of Species, p. 303. » Ibid. p. 309. 

204 The Palaeontological Record. II. Plants 

Darwin's argument that "the inhabitants of the world at each 
successive period in its history have beaten their predecessors in the 
race for life, and are, in so far, higher in the scale ^ " is unanswerable, 
but we must remember that "higher in the scale" only means "better 
adapted to the existing conditions." Darwin points out^ that species 
have remained unchanged for long periods, probably longer than the 
periods of modification, and only underwent change when the con- 
ditions of their life were altered. Higher organisation, judged by 
the test of success, is thus purely relative to the changing conditions, 
a fact of which we have a striking illustration in the sudden in- 
coming of the Angiosperms with all their Avonderful floral adaptations 
to fertilisation by the higher families of Insects. 

XL Phylooeny. 

The question of phylogeny is really inseparable fi-om that of the 
truth of the doctrine of evolution, for we cannot have historical 
evidence that evolution has actually taken place without at the same 
time having evidence of the course it has followed. 

As already pointed out, the progress hitherto made has been 
rather in the way of joining up the great classes of plants than in 
tracing the descent of particular species or genera of the recent flora. 
There appears to be a difierence in this respect from the Animal 
record, which tells us so much about the descent of living species, 
such as the elephant or the horse. The reason for this difference is 
no doubt to be found in the fact that the later part of the palaeonto- 
logical record is the most satisfactory in the case of animals and the 
least so in the case of plants. The Tertiary plant-remains, in the 
great majority of instances, are impressions of leaves, the conclusions 
to be drawn from which are highly precarious ; until the whole 
subject of Angiospermous paleobotany has been reinvestigated, it 
would be rash to venture on any statements as to the descent of the 
families of Dicotyledons or Monocotyledons. 

Our attention will be concentrated on the following questions, all 
relating to the phylogeny of main groups of plants : i. The Origin of 
the Angiosperms. ii. Tlie Origin of the Seed-plants, iii. The Origin 
of the different classes of the Higher Cryptogamia. 

i. The Origin of tJie Angiosperms. 

The first of these questions has long been the great crux of 
botanical phylogeny, and until quite recently no light had been 
thrown upon the difficulty. The Angiosperms are the Flowering 
Plants, par excellence, and form, beyond comparison, tlie dominant 

J Origin of Species, p. 315, " Ibid. p. 279. 

Origin of Angiosperms 205 

sub-kingdom in the flora of our own age, including, apart from a few 
Conifers and Ferns, all the most familiar plants of our fields and 
gardens, and practically all plants of service to man. All recent 
work has tended to separate the Angiosperms more widely from the 
other seed-plants now living, the Gymnosperms. Vast as is the 
range of organisation presented by the great modern sub-kingdom, 
embracing forms adapted to every environment, there is yet a marked 
uniformity in certain points of structure, as in the development of 
the embryo-sac and its contents, the pollination through the inter- 
vention of a stigma, the strange phenomenon of double fertilisation \ 
the structure of the stamens, and the arrangement of the parts of 
the flower. All these points are common to Monocotyledons and 
Dicotyledons, and separate the Angiosperms collectively from all 
other plants. 

In geological history the Angiosperms first appear in the Lower 
Cretaceous, and by Upper Cretaceous times had already swamped 
all other vegetation and seized the dominant position which they 
still hold. Thus they are isolated structurally from the rest of the 
Vegetable Kingdom, while historically they suddenly appear, almost 
in full force, and apparently without intermediaries with other groups. 
To quote Darwin's vigorous words i " The rapid development, as far 
as we can judge, of all the higher plants within recent geological 
times is an abominable mystery"^." A couple of years later he made 
a bold suggestion (which he only called an " idle thought ") to meet 
this difiiculty. He says : " I have been so astonished at the appa- 
rently sudden coming in of the higher phanerogams, that I have 
sometimes fancied that development might have slowly gone on for 
an immense period in some isolated continent or large island, perhaps 
near the South Pole^." This idea of an Angiospermous invasion from 
some lost southern land has sometimes been revived since, but has 
not, so far as the writer is aware, been supported by evidence. Light 
on the problem has come from a difierent direction. 

The immense development of plants with the habit of Cycads, 
during the Mesozoic Period up to the Lower Cretaceous, has long 
been knoMu. Tlie existing Order Cycadaceae is a small family, with 
9 genera and perhaps 100 species, occurring in the tropical and 
sub-tropical zones of both the Old and New World, but nowhere 
forming a dominant feature in the vegetation. Some few attain the 
stature of small trees, while in the majority the stem is short, though 
often living to a gi-eat age. The large pinnate or rarely bipinnate 

^ One Bperm fertilising the egg, while the other unites with the embryo-sac nucleus, 
itself the product of a nuclear fusion, to give rise to a nutritive tissue, the endosperm. 
■•' More Letters of Charles Darwin, Vol. ii. p. 20, letter to J. D. Hooker, 1879. 
» Ibid. p. 26, letter to Hooker, 1881. 

206 The Palaeontological Record. II. Plants 

leaves give the Cycads a superficial resemblance in habit to Palms. 
Recent C3 cads are dioecious ; throughout the family the male fructifi- 
cation is in the form of a cone, each scale of the cone representing 
a stamen, and bearing on its lower surface numerous pollen-sacs, 
grouped in sori like the sporangia of Ferns. In all the genera, except 
Cycas itself, the female fructifications are likewise cones, each carpel 
bearing two ovules on its margin. In Cycas, however, no female 
cone is produced, but the leaf-like carpels, bearing from two to six 
ovules each, are borne directly on the main stem of the plant in 
rosettes alternating with those of the ordinary leaves — the most 
primitive arrangement known in any living seed-plant. The whole 
Order is relatively primitive, as shown most strikingly in its crypto- 
gamic mode of fertilisation, by means of spermatozoids, which it shares 
with the maidenhair tree alone, among recent seed-plants. 

In all the older Mesozoic rocks, from the Trias to the Lower 
Cretaceous, plants of the Cycad class (Cycadophyta, to use Nathorst's 
comprehensive name) are extraordinarily abundant in all parts of the 
world ; in fact they were almost as prominent in the flora of those 
ages as the Dicotyledons are in that of our own day. In habit 
and to a great extent in anatomy, the Mesozoic Cycadophyta for the 
most part much resemble the recent Cycadaceae. But, strange to 
say, it is only in the rarest cases that the fructification has proved 
to be of the simple type characteristic of the recent family ; the vast 
majority of the abundant fertile specimens yielded by the Mesozoic 
rocks possess a type of reproductive apparatus far more elaborate 
than anything known in Cycadaceae or other Gymnosi^erms. The 
predominant Mesozoic family, characterised by this advanced repro- 
ductive organisation, is known as the Bennettiteae ; in habit these 
plants resembled the more stunted Cycads of the recent flora, but 
diftered from them in the presence of numerous lateral fructifi- 
cations, like large buds, borne on the stem among the crowded bases 
of the leaves. The organisation of these fructifications was first 
worked out on European specimens by Carruthers, Solms-Laubacli, 
Lignier and others, but these observers had only more or less ripe 
fruits to deal with; the complete structure of the flower has only 
been elucidated within the last few years by the researches of 
Wieland on the magnificent American material, derived from the 
Upper Jurassic and Lower Cretaceous beds of Maryland, Dakota and 
Wyoming \ The word "flowci-" is used deliberately, for reasons 
wliich will be apparent from the following brief description, based 
on Wieland's observations. 

The friictificati-on is attached to the stem by a thick stalk, 
which, in its upper part, bears a large number of spirally arranged 

' G. R. Wieland, American Fossil Cycads, Carnegie Institution, Washington, 1906. 

Origin of Angiosjyerms 207 

bracts, forming collectively a kind of perianth and completely en- 
closing the essential organs of reproduction. The latter consist of 
a whorl of stamens, of extremely elaborate structure, surrounding a 
central cone or receptacle bearing numerous ovules. The stamens 
resemble the fertile fronds of a fern ; they are of a compound, 
pinnate form, and bear very large numbers of pollen-sacs, each of 
which is itself a compound structure consisting of a number of com- 
partments in which the pollen was formed. In their lower part the 
stamens are fused together by their stalks, like the "monadelphous" 
stamens of a mallow. The numerous ovules borne on the central 
receptacle are stalked, and are intermixed v, ith sterile scales ; the 
latter are expanded at their outer ends, which are united to form a 
kind of pericarp or ovary-wall, only interrupted by the protruding 
micropyles of the ovules. There is thus an approach to the closed 
pistil of an Angiosperm, but it is evident that the ovules received 
the pollen directly. The whole fructification is of large size ; in the 
case of Cycadeoidea dacoteusis, one of the species investigated by 
Wieland, the total length, in the bud condition, is about 12 cm., 
half of which belongs to the peduncle. 

The general arrangement of the organs is manifestly the same 
as in a typical Angiospermous flo%ver, with a central pistil, a sur- 
rounding whorl of stamens and an enveloping perianth ; there is, 
as we have seen, some approach to the closed ovary of an Angio- 
sperm ; another point, first discovered nearly 20 years ago by Solms- 
Laubach in his investigation of a British species, is that the seed 
was practically " exalbuminous," its cavity being filled by the large, 
dicotyledonous embryo, whereas in all known Gymnosperms a large 
part of the sac is occupied by a nutritive tissue, the prothallus or 
endosperm ; here also we have a condition only met with elsewhere 
among the higher Flowering Plants. 

Taking all the characters into account, the indications of affinity 
between the Mesozoic Cycadophyta and the Angiosperms appear 
extremely significant, as was recognised by Wieland Avhen he first 
discovered the hermaphrodite nature of the Bennettitean flower. 
The Angiosperm with which he specially compared the fossil type 
was the Tulip tree (Liriodendron) and certainly there is a remarkable 
analogy with the Magnoliaceous flowers, and with those of related 
orders such as Ranunculaceae and the Water-lilies. It cannot, of 
course, be maintained that the Bcnnettiteae, or any other Mesozoic 
('ycadophyta at present known, were on the direct line of descent 
of the Angiosperms, for there are some important points of difference, 
as, for example, in the great complexity of the stamens, and in the 
fact that the ovary-wall or pericarp was not formed by the carpels 
themselves, but by the accompanying sterile scale-leaves. Botanists, 

208 The Palaeontological Record. II. Plants 

since the discovery of the bisexual flowers of the Beimettiteae, 
have expressed diflferent views as to the nearness of their relation 
to the higher Flowering Plants, but the points of agreement are 
so many that it is difficult to resist the conviction that a real 
relation exists, and that the ancestry of the Angiosperms, so long 
shrouded in complete obscurity, is to be sought among the great 
plexus of Cycad-like plants which dominated the flora of the world 
in Mesozoic times ^ 

The great complexity of the Bennettitean flower, the earliest 
known fructification to which the word "flower" can be applied 
without forcing the sense, renders it probable, as Wieland and 
others have pointed out, that the evolution of the flower in 
Angiosperms has consisted essentially in a process of reduction, 
and that the simplest forms of flower are not to be regarded as the 
most primitive. The older morphologists generally took the view 
that such simple flowers were to be explained as reductions from 
a more perfect type, and this opinion, though abandoned by many 
later writers, appears likely to be true when we consider the elabora- 
tion of floral structure attained among the Mesozoic Cycadophyta, 
which preceded the Angiosperms in evolution. 

If, as now seems probable, the Angiosperms were derived from 
ancestors allied to the Cycads, it would naturally follow that the 
Dicotyledons were first evolved, for their structure has most in 
common with that of the Cycadophyta. We should then have to 
regard the Monocotyledons as a side-line, diverging probably at a 
very early stage from the main dicotyledonous stock, a view which 
many botanists have maintained, of late, on other grounds l So far, 
however, as the palaeontological record shows, the Monocotyledons 
were little if at all later in their appearance than the Dicotyledons, 
though always subordinate in numbers. The typical and beautifully 
preserved Palm-wood from Cretaceous rocks is striking evidence 
of the early evolution of a characteristic monocotyledonous family. 
It must be admitted that the whole question of the evolution of 
Monocotyledons remains to be solved. 

Accepting, provisionally, the theory of the cycadophytic origin 
of Angiosperms, it is interesting to see to what further conclusions 
we are led. Tlie Bennettiteae, at any rate, were still at the gym- 
nospermous level as regards their pollination, for the exposed 

1 On this subject see, in addition to Wieland's great work above cited, F. W. Oliver, 
" Pteridosperms and Angiosperms," New Pliytologist, Vol. v. 1906; D. H. Scott, "The 
Flowering Plants of the Mesozoic Age in the Light of Recent Discoveries," Journal R. 
Microscop. Soc. 1907, and especially E. A. N. Arber and J. Parkin, "On the Origin of Angio- 
sperms," Journal Linn. Soc. (Bot.) Vol. xxxviii. p. 29, 1907. 

' See especially Ethel Sargant, " The Reconstruction of a Race of Primitive Angio- 
sperms," Aniiali of Botany, Vol. xxu. p. 121, 1908. 

Origin of Seed-plants 209 

micropyles of the ovules were in a position to receive the pollen 
directly, without the intervention of a stigma. It is thus indicated 
that the Angiosperms sprang from a gymnospermous source, and 
that the two great phyla of Seed-plants have not been distinct 
from the first, though no doubt the great majority of known 
Gymnosperms, especially the Coniferae, represent branch-lines of 
their own. 

The stamens of the Bennettiteae are arranged precisely as in 
an angiospermous flower, but in form and structure they are like 
the fertile fronds of a Fern, in fact the compound pollen-sacs, or 
synangia as they are technically called, almost exactly agree with 
the spore-sacs of a particular family of Ferns — the Marattiaceae, a 
limited group, now mainly tropical, which was probably more promi- 
nent in the later Palaeozoic times than at present. The scaly hairs, 
or ramenta, which clothe every part of the plant, are also like those 
of Ferns. 

It is not likely that the characters in which the Bennettiteae 
resemble the Ferns came to them directly from ancestors belonging 
to that class ; an extensive gi-oup of Seed-plants, the Pteridospermeae, 
existed in Palaeozoic times and bear evident marks of affinity with 
the Fern phylum. The fern-like characters so remarkably persistent 
in the highly organised Cycadophyta of the Mesozoic were in all 
likelihood derived through the Pteridosperms, plants which show an 
unmistakable approach to the cycadophytic type. 

The family Bennettiteae thus presents an extraordinary association 
of characters, exhibiting, side by side, features which belong to the 
Angiosperms, the Gymnosperms and the Ferns. 

ii. Origin of Seed-2)lants. 

The general relation of the gymnospermous Seed-plants to the 
Higher Cryptogamia was cleared up, independently of fossil evidence, 
by the brilliant researches of Hofineister, dating fi-om the middle 
of the past century ^ He showed that "the embryo-sac of the 
Coniferae may be looked upon as a spore remaining enclosed in 
its sporangium ; the prothallium which it forms does not come to 
the light ^." He thus determined the homologies on the female side. 
Recognising, as some previous observers had already done, that the 
microspores of those Cryptogams in which two kinds of spore are 
developed, are equivalent to the pollen-grains of the higher plants, 
he further pointed out that fertilisation "in the Rhizocarpeae and 

' W. Hofmeister, On the Germination, Development and Fructijication of the Higher 
Crijptuijamia, Eay Society, London, 1862. The original German treatise appeared in 

' Ibid. p. 438. 

D. U 

210 The Palaeontological Record. II. Plants 

Selaginellae takes place by free spermatozoa, and in the Coniferae 
by a pollen-tube, in the interior of which spermatozoa are probably 
fomied" — a remarkable instance of prescience, for though sperma- 
tozoids have not been found in the Conifers proper, they were 
demonstrated in the allied groups Cycadaceae and Ginkgo, in 1896, 
by the Japanese botanists Ikeno and Hirase. A new link was thus 
established between the Gymnosperms and the Cryptogams. 

It remained uncertain, however, from which line of Cryptogams 
the gymnospermous Seed-plants had sprung. The great point of 
morphological comparison was the presence of two kinds of spore, 
and this was known to occur in the recent Lycopods and Water-ferns 
(Rhizocarpeae) and was also found in fossil representatives of the 
tliird phylum, that of the Horsetails. As a matter of fact all the 
three great Cryptogamic classes have found champions to maintain 
their claim to the ancestry of the Seed-plants, and in every case 
fossil evidence Mas called in. For a long time the Lycopods were 
the favourites, while the Ferns found the least support. The writer 
remembers, however, in the year 1881, hearing the late Prof Sachs 
maintain, in a lecture to his class, that the descent of the Cycads 
could be traced, not merely from Ferns, but from a definite family of 
Ferns, the Marattiaceae, a view which, though in a somewhat crude 
form, anticipated more modern ideas. 

Williamson appears to have been the first to recognise the 
presence, in the Carboniferous flora, of plants combining the charac- 
ters of Ferns and Cycads \ This conclusion was first reached in the 
case of the genera Heterangium and Lyginodendron, plants, which 
with a wholly fern-like habit, were found to unite an anatomical 
structure holding the balance between that of Ferns and Cycads, 
Heterangium inclining more to the former and Lyginodendron to the 
latter. Later researches placed Williamson's original suggestion on 
a firmer basis, and clearly proved the intermediate nature of these 
genera, and of a number of others, so far as their vegetative organs 
were concerned. This stage in our knowledge was marked by the 
institution of the class Cycadofilices by Potoni^ in 1897. 

Nothing, however, was known of the organs of reproduction of 
the Cycadofilices, until F. W. Oliver, in 1903, identified a fossil 
seed, Lagenostoma Lomaxi, as belonging to Lyginodendron, the 
identification depending, in the first instance, on the recognition 
of an identical form of gland, of very characteristic structure, on the 
vegetative organs of Lyginodendron and on the cupule enveloping 
the seed. This evidence was supported by the discovery of a close 
anatomical agreement in other respects, as well as by constant 

^ See especially his "Organisation of the Fossil Plants of the Coal-Measures," Part xiii. 
Phil. Trans. Royal Soc. 1887, b. p. 299. 

Pteridospenneae 211 

association between the seed and the plants The structure of the 
seed of Lyginodendron, proved to be of the same general type as 
that of the Cycads, as shown especially by the presence of a pollen- 
chamber or special cavity for the reception of the pollen-gi-ains, an 
organ only known in the Cycads and Ginkgo among recent plants. 

Within a few months after the discovery of the seed of Lygino- 
dendron, Kidston found the large, nut-like seed of a Neuropteris, 
another fern-like Carboniferous plant, in actual connection with the 
pinnules of the ft-ond, and since then seeds have been observed on 
the frond in species of Aneimites and Pecopteris, and a vast body 
of evidence, direct or indirect, has accumulated, showing that a large 
proportion of the Palaeozoic plants formerly classed as Ferns were in 
reality reproduced by seeds of the same type as those of recent 
Cycadaceae^ At the same time, the anatomical structure, where it 
is open to investigation, confirms the suggestion given by the habit, 
and shows that these early seed-bearing plants had a real affinity 
with Ferns. This conclusion received strong corroboration when 
Kidston, in 1905, discovered the male organs of Lyginodendron, and 
showed that they were identical with a fructification of the genus 
Crossotheca, hitherto regarded as belonging to Marattiaceous Ferns ^ 

The general conclusion which follows from the various obser- 
vations alluded to, is that in Palaeozoic times there was a great 
body of plants (including, as it appears, a large majority of the 
fossils previously regarded as Ferns) which had attained the rank of 
Spermophyta, bearing seeds of a Cycadean type on fi-onds scarcely 
difiering from the vegetative foliage, and in other respects, namely 
anatomy, habit and the structure of the pollen-bearing organs, re- 
taining many of the characters of Ferns. From this extensive class 
of plants, to which the name Pteridospermeae has been given, it 
can scarcely be doubted that the abundant Cycadophyta, of the 
succeeding Mesozoic period, were derived. This conclusion is of 
far-reaching significance, for we have already found reason to think 
that the Angiosperms themselves sprang, in later times, from the 
Cycadophytic stock ; it thus appears that the Fern-phylum, taken in 
a broad sense, ultimately represents the source fi'om which the main 
line of descent of the Phanerogams took its rise. 

It must further be borne in mind that in the Palaeozoic period 
there existed another gi-oup of seed-bearing plants, the Cordaiteae, 

' F. W. Oliver and D. H. Scott, "On the Structure of the Palaeozoic Seed, Lagenostoma 
Lomnxi, etc." rhil. 'Trans, noyal Soc. Vol. 197, b. 1'J04. 

* A summary of the evidence will be found in the writer's article "On the present 
position of Palaeozoic Botany," Progressus liei Botunicae, 1907, p. 130, and Studies in 
Fossil Botany, Vol. ii. (2nd edit.) London, 11109. 

* Kidston, " On the Microsporangia of the Pteridospermeae, etc." Fhil. Trans, Eoyal 
Soc. Vol. 198, u. 1906. 


212 The Palaeojitological Record. II. Plants 

far more advanced than the Pteridospermeae, and in many respects 
approaching the Coniferae, which themselves begin to appear in the 
latest Palaeozoic rocks. The Cordaiteae, while wholly diiFerent in 
habit from the contemporary fern-like Seed-plants, show unmis- 
takable signs of a common origin with them. Not only is there 
a whole series of forms connecting the anatomical structure of the 
Cordaiteae with that of the Lyginodendi'eae among Pteridosperms, 
but a still more important point is that the seeds of tlie Cordaiteae, 
which have long been known, are of the same Cycadean type as those 
of the Pteridosperms, so that it is not always possible, as yet, to 
discriminate between the seeds of the two groups. These facts 
indicate that the same fern-like stock which gave rise to the Cycado- 
phyta and through them, as appears j)robable, to the Angiosperms, 
was also the source of the Cordaiteae, which in their turn show 
manifest affinity with some at least of the Coniferae. Unless the 
latter are an artificial group, a view which does not commend itself 
to the writer, it would appear probable that the Gymnosperms 
generally, as well as the Angiosperms, were derived from an ancient 
race of Cryptogams, most nearly related to the Ferns \ 

It may be mentioned here that the small gymnospermous 
group Gnetales (including the extraordinary West African plant 
Welwitschia) which were formerly regarded by some authorities 
as akin to the Equisetales, have recently been referred, on better 
grounds, to a common origin with the Angiosperms, from the 
Mesozoic Cycadophyta, 

The tendency, therefore, of modern work on the palaeontological 
record of the Seed-plants has been to exalt the importance of the 
Fern-phylum, which, on present evidence, appears to be that from 
which the great majority, possibly the whole, of the Spermophyta 
have been derived. 

One word of caution, however, is necessary. The Seed-plants 
are of enormous antiquity ; both the Pteridosperms and the more 
highly organised family Cordaiteae, go back as far in geological 
history (namely to the Devonian) as the Ferns themselves or any 
other Vascular Cryptogams. It must therefore be understood that 
in speaking of the derivation of the Spermophyta from the Fern- 
phylum, we refer to that phylum at a very early stage, probably 
earlier than the most ancient period to which our record of land- 
plants extends. The affinity between the oldest Seed-plants and the 
Ferns, in the widest sense, seems established, but the common stock 
from which they actually arose is still unknoAvn ; though no doubt 

' Some botanists, however, believe that the Coniferae, or some of them, are probably 
more nearly related to the Lycopoda. See Seward and Ford, " The Araucarieae, Recent 
and Extinct," Fhil. Trans. Royal Soc. Vol. 198, b. 1006. 

Early History of Ferns 218 

nearer to the Ferns than to any other group, it must have differed 
widely from the Ferns as we now know them, or perhaps even from 
any which the fossil record has yet revealed to us. 

iii. Tlie Origin of the Higher Cryptogamia. 

The Sub-kingdom of the higher Spore-plants, the Cryptogamia 
possessing a vascular system, was more prominent in early geological 
periods than at present. It is true that the dominance of the Pteri- 
dophyta in Palaeozoic times has been much exaggerated owing to 
the assumption that everything which looked like a Fern really was 
a Fern. But, allowing for the fact, now established, that most of the 
Palaeozoic fern-like plants were already Spermophyta, there remains 
a vast mass of Cryptogamic forms of that period, and the familiar 
statement that they formed the main constituent of the Coal-forests 
still holds good. The three classes, Ferns (Filicales), Horsetails 
(Equisetales) and Club-mosses (Lycopodiales), under which we now 
group the Vascular Cryptogams, all extend back in geological history 
as far as we have any record of the flora of the land ; in the Palaeo- 
zoic, however, a fourth class, the Sphenophyllales, was present. 

As regards the early history of the Ferns, which are of special 
interest from their relation to the Seed-plants, it is impossible to 
speak quite positively, OAving to the difficulty of discriminating 
between true fossil Ferns and the Pteridosperms Avhich so closely 
simulated them. The difficulty especially affects the question of the 
position of Marattiaceous Ferns in the Palaeozoic Floras. This 
family, now so restricted, was until recently believed to have been 
one of the most important groups of Palaeozoic plants, especially 
during later Carboniferous and Permian times. Evidence both from 
anatomy and from sporangial characters appeared to establish this 
conclusion. Of late, however, doubts have arisen, owing to the 
discovery that some supposed members of the IMarattiaceae bore 
seeds, and that a form of fructification previously referred to that 
family (Crossotheca) was really the pollen-bearing apparatus of a 
Pteridosperm (Lyginodendron). The question presents much diffi- 
culty ; though it seems certain that our ideas of the extent of the 
family in Palaeozoic times will have to be restricted, there is still a 
decided balance of evidence in favour of the view that a considerable 
body of Marattiaceous Ferns actually existed. The plants in (juestion 
were of large size (often arborescent) and highly organised — they 
represent, in fact, one of the highest developments of the Fern-stock, 
rather than a primitive type of the class. 

There Avas, however, in the Palaeozoic period, a considerable 
group of comparatively simple Ferns (for which Arber has proposed 

214 The Palaeontological Record. II. Plants 

the collective name Primofilices) ; the best known of these are 
referred to the family Botryopterideae, consisting of plants of small 
or moderate dimensions, with, on the whole, a simple anatomical 
structure, in certain cases actually simpler than that of any recent 
Ferns. On the other hand the sporangia of these plants were usually 
borne on special fertile fronds, a mark of rather high differentiation. 
This group goes back to the Devonian and includes some of the 
earliest types of Fern with which we are acquainted. It is probable 
that the Primofilices (though not the particular family Botryopte- 
rideae) represent the stock from which the various families of modern 
Ferns, already developed in the Mesozoic period, may have sprung. 

None of the early Ferns show any clear approach to other classes 
of Vascular Cryptogams ; so far as the fossil record affords any 
evidence. Ferns have always been plants with relatively large and 
usually compound leaves. There is no indication of their derivation 
from a microphyllous ancestry, though, as we shall see, there is some 
slight evidence for the converse hypothesis. Whatever the origin of 
the Ferns may have been it is hidden in the older rocks. 

It has, however, been held that certain other Cryptogamic phyla 
had a common origin with the Ferns. The Equisetales are at present 
a well-defined group ; even in the rich Palaeozoic floras the habit, 
anatomy and reproductive characters usually render the members of 
this class unmistakable, in spite of the gi-eat development and stature 
which they then attained. It is interesting, however, to find that in 
the oldest known representatives of the Equisetales the leaves were 
highly developed and dichotomously divided, thus differing greatly 
from the mere scale-leaves of the recent Horsetails, or even from the 
simple linear leaves of the later Calamites. The early members of 
the class, in their forked leaves, and in anatomical characters, show 
an approximation to the Sphenophyllales, which are chiefly repre- 
sented by the large genus Sphenophyllum, ranging through the 
Palaeozoic from the Middle Devonian omvards. These were plants 
with rather slender, ribbed stems, bearing whorls of wedge-shaped 
or deeply forked leaves, six being the typical number in each whorl. 
From their weak habit it has been conjectured, with much proba- 
bility, that they may have been climbing plants, like the scrambling 
Bedstraws of our hedgerows. The anatomy of the stem is simple and 
root-like ; the cones are remarkable for the fact that each scale or 
sporoi)hyll is a double structure, consisting of a lower, usually sterile 
lobe and one or more upper lobes bearing the sporangia ; in one 
species both parts of the sporophyll were fertile. Sphenophyllum 
was evidently nmch specialised ; the only other known genus is based 
on an isolated cone, Cheirostrobus, of Lower Carboniferous age, with 
an extraordinarily complex structure. In this genus especially, but 

Early History of Lycopods 215 

also in the entire group, there is an evident relation to the Equisetales ; 
hence it is of great interest that Nathorst has described, from the 
Devonian of Bear Island in the Arctic regions, a new genus Pseudo- 
bornia, consisting of large plants, remarkable for their highly com- 
pound leaves which, when found detached, were taken for the fronds 
of a Fern. The whorled arrangement of the leaves, and the habit 
of the plant, suggest affinities either with the Equisetales or the 
Sphenophyllales ; Nathorst makes the genus the type of a new class, 
the Pseudoborniales^ 

The available data, though still very fragmentary, certainly suggest 
that both Equisetales and Sphenophyllales may have sprung from a 
common stock having certain fern-like characters. On the other hand 
the Sphenophylls, and especially the peculiar genus Cheirostrobus, 
have in their anatomy a good deal in common with the Lycopods, 
and of late years they have been regarded as the derivatives of 
a stock common to that class and the Equisetales. At any rate the 
characters of the Sphenophyllales and of the new group Pseudo- 
borniales suggest the existence, at a very early period, of a synthetic 
race of plants, combining the characters of various phyla of the Vascular 
Cryptogams. It may further be mentioned that the Psilotaceae, an 
isolated epiphytic family hitherto referred to the Lycopods, have 
been regarded by several recent authors as the last survivors of the 
Sphenophyllales, which they resemble both in their anatomy and in 
the position of their sporangia. 

The Lycopods, so far as their early history is known, are remark- 
able rather for their high development in Palaeozoic times than for 
any indications of a more primitive ancestry. In the recent Flora, 
two of the four living genera^ (Selaginella and Isoetes) have spores 
of two kinds, while the other two (Lycopodium and Phylloglossum) 
are homosporous. Curiously enough, no certain instance of a homo- 
sporous Palaeozoic Lycopod has yet been discovered, though well- 
preserved fructifications are numerous. Wherever the facts have 
been definitely ascertained, we find two kinds of spore, differentiated 
quite as sharply as in any living members of the group. Some of 
the Palaeozoic Lycopods, in fact, went further, and produced bodies 
of the nature of seeds, some of which were actually regarded, for 
many years, as the seeds of Gyinnosperms. This specially advanced 
form of fructification goes back at least as far as the Lower Carboni- 
ferous, while the oldest known genus of Lycopods, Bothrodendron, 
which is found in the Devonian, though not seed-bearing, was typically 
heterosporous, if we may judge from the Coal-measure species. No 

1 A. G, Nathorst, " Zur Oberclevonischcn Flora der Baren-Insel," Kovgl. Svenska 
Vntejiskiips-Akadcmieiii HamUingar, Bd. 36, No. 3, Stockholm, 1902. 
'^ Excluding Psilotaceae. 

216 The Palaeontological Record. 11. Plants 

doubt homosporous Lycopods existed, but the great prevalence of 
the higher mode of reproduction in days which to us appear ancient, 
shows how long a course of evolution must have already been passed 
through before the oldest known members of the gi'oup came into 
being. The other characters of the Palaeozoic Lycopods tell the 
same tale ; most of them attained the stature of trees, with a 
corresponding elaboration of anatomical structure, and even the 
herbaceous forms show no special simplicity. It appears from recent 
work that herbaceous Lycopods, indistinguishable from our recent 
Selaginellas, already existed in the time of the Coal-measures, while 
one herbaceous form (Miadesmia) is known to have borne seeds. 

The utmost that can be said for primitiveness of character in 
Palaeozoic Lycopods is that the anatomy of the stem, in its primary 
ground-plan, as distinguished from its secondary growth, was simpler 
than that of most Lycopodiums and Selaginellas at the present 
day. There are also some peculiarities in the underground organs 
(Stigmaria) which suggest the possibility of a somewhat imperfect 
differentiation between root and stem, but precisely parallel difficulties 
are met with in the case of the living Selaginellas, and in some degree 
in species of Lycopodium. 

In spite of their high development in past ages the Lycopods, 
recent and fossil, constitute, on the whole, a homogeneous group, 
and there is little at present to connect them with other phyla. 
Anatomically some relation to the Sphenophylls is indicated, and 
perhaps the recent Psilotaceae give some support to this connection, 
for while their nearest alliance appears to be with the Sphenophylls, 
they approach the Lycopods in anatomy, habit, and mode of branching. 

The typically microphyllous character of the Lycopods, and the 
simple relation between sporangium and sporophyU which obtains 
throughout the class, have led various botanists to regard them as 
the most primitive phylum of the Vascular Cryptogams. There is 
nothing in the fossil record to disprove this view, but neither is there 
anything to support it, for this class so far as we know is no more 
ancient than the megaphyllous Cryptogams, and its earliest repre- 
sentatives show no special simplicity. If the indications of affinity 
with Sphenophylls are of any value the Lycopods are open to sus- 
picion of reduction from a megaphyllous ancestry, but there is no 
direct palaeontological evidence for such a history. 

The general conclusions to which we are led by a consideration 
of the fossil record of the Vascular Cryptogams are still very hypo- 
thetical, but may be provisionally stated as follows : 

The Ferns go back to the earliest known period. In Mesozoic 
times practically all the existing families had appeared ; in the 
Palaeozoic the class was less extensive than formerly believed, a 

Natural Selection 217 

majority of the supposed Ferns of that age having proved to be seed- 
bearing plants. The oldest authentic representatives of the Ferns 
were megaphyllous plants, broadly speaking, of the same type as 
those of later epochs, though differing much in detail. As far back 
as the record extends they show no sign of becoming merged with 
other phyla in any synthetic group. 

The Equisetales likewise have a long history, and manifestly 
attained their greatest development in Palaeozoic times. Their 
oldest forms show an approach to the extinct class Sphenophyllales, 
which connects them to some extent, by anatomical characters, with 
the Lycopods. At the same time the oldest Equisetales show a 
someM'hat megaphyllous character, which was more marked in the 
Devonian Pseudoborniales. Some remote affinity mth the Ferns 
(which has also been upheld on other grounds) may thus be indicated. 
It is possible that in the Sphenophyllales we may have the much- 
modified representatives of a very ancient synthetic group. 

The Lycopods likewise attained their maximum in the Palaeozoic, 
and show, on the whole, a greater elaboration of structure in their 
early forms than at any later period, while at the same time maintain- 
ing a considerable degree of uniformity in morphological characters 
throughout their history. The Sphenophyllales are the only other 
class with wliich they show any relation ; if such a connection existed, 
the common point of origin must lie exceedingly far back. 

The fossil record, as at present known, cannot, in the nature of 
things, throw any direct light on what is perhaps the most disputed 
question in the morphology of plants — the origin of the alternating 
generations of the higher Cryptogams and the Spermophyta. At the 
earliest period to which terrestrial plants have been traced back all 
the groups of Vascular Cryptogams were in a highly advanced stage 
of evolution, while innumerable Seed-plants — presumably the descend- 
ants of Cryptogamic ancestors — were already flourishing. On the 
other hand we know practically nothing of Palaeozoic Bryophyta, 
and the evidence even for their existence at that period cannot be 
termed conclusive. AVliile there are thus no palaeontological gi-ounds 
for the hypothesis that the Vascular plants came of a Bryophytic 
stock, the question of their actual origin remains unsolved. 

III. Natural Selection. 

Hitherto we have considered the palaeontological record of 
plants in relation to Evolution. The question remains, whether 
the record throws any light on the theory of Avliich Darwin and 
AVallace were the authors — that of Natural Selection. The subject 
is clearly one which must be investigated by other methods than 

218 The Palaeontological Record. II. Plants 

those of the palaeontologist ; still there are certain important points 
involved, on which the palaeontological record appears to bear. 

One of these points is the supposed distinction between morpho- 
logical and adaptive characters, on which Nageli, in particular, laid 
so much stress. The question is a difficult one ; it was discussed by 
Darwin \ who, while showing that the apparent distinction is in part 
to be explained by our imperfect knowledge of function, recognised 
the existence of important morphological characters which are not 
adaptations. The following passage expresses his conclusion. "Thus, 
as I am inclined to believe, morphological differences, which we 
consider as important — such as the arrangement of the leaves, the 
divisions of the flower or of the ovarium, the position of the ovules, 
etc. — first appeared in many cases as fluctuating variations, which 
sooner or later became constant through the nature of the organism 
and of the surrounding conditions, as well as through the inter- 
crossing of distinct individuals, but not through natural selection; 
for as these morphological characters do not affect the welfare of the 
species, any slight deviations in them could not have been governed 
or accumulated through this latter agency^" 

This is a sufficiently liberal concession ; Nageli, however, went 
much further when he said: "I do not know among plants a morpho- 
logical modification which can be explained on utilitarian principles^" 
If this were true the field of Natural Selection would be so seriously 
restricted, as to leave the theory only a very limited importance. 

It can be shown, as the writer believes, that many typical 
"morphological characters," on which the distinction between great 
classes of plants is based, were adaptive in origin, and even that 
their constancy is due to their functional importance. Only one 
or two cases will be mentioned, where the fossil evidence affects the 

The pollen-tube is one of the most important morphological 
characters of the Spermophyta as now existing — in fact the name 
Siphonogama is used by Engler in his classification, as expressing 
a peculiarly constant character of the Seed-plants. Yet the pollen- 
tube is a manifest adaptation, following on the adoption of the 
seed-habit, and serving first to bring the spermatozoids with greater 
precision to their goal, and ultimately to relieve them of the necessity 
for independent movement. The pollen-tube is constant because it 
has proved to be indispensable. 

In the Palaeozoic Seed-plants there are a number of instances 
in which the pollen-grains, contained in the pollen-chamber of a 
seed, are so beautifully preserved that the presence of a group of 

» Origin of Species (6th edit.), pp. 170—176. » Ihid. p. 176. 

' See More Letters, Vol. ii. p. 375 (footuote). 

Morphological Characters 219 

cells within the grain can be demonstrated ; sometimes we can even 
see how the cell-walls broke do^vn to emit the sperms, and quite 
lately it is said that the sperms themselves have been recognised K 
In no case, however, is there as yet any satisfactory evidence for the 
formation of a pollen-tube ; it is probable that in these early Seed- 
plants the pollen-grains remained at about the evolutionary level 
of the microspores in Pilularia or Selaginella, and discharged their 
spermatozoids directly, leaving them to find their own way to the 
female cells. It thus appears that there were once Spermophyta 
without pollen-tubes. The pollen-tube method ultimately prevailed, 
becoming a constant "morphological character," for no other 
reason than because, under the new conditions, it provided a more 
perfect mechanism for the accomplishment of the act of fertilisation. 
We have still, in the Cycads and Ginkgo, the transitional case, where 
the tube remains short, serves mainly as an anchor and water- 
reservoir, but yet is able, by its slight growth, to give the spermato- 
zoids a "lift" in the right direction. In other Seed-plants the sperms 
are mere passengers, carried all the way by the poUen-tube ; this 
fact has alone rendered the Angiospermous method of fertilisation 
through a stigma possible. 

We may next take the seed itself — the very type of a morphological 
character. Our fossil record does not go far enough back to tell us 
the origin of the seed in the Cycadophyta and Pteridosperms (the 
main line of its development) but some interesting sidelights may 
be obtained from the Lycopod phylum. In two Palaeozoic genera, 
as we have seen, seed-like organs are known to have been developed, 
resembling true seeds in the presence of an integument and of a 
single functional embryo-sac, as well as in some other points. We 
will call these organs "seeds" for the sake of shortness. In one 
genus (Lepidocarpon) the seeds were borne on a cone indistinguish- 
able from that of the ordinary cryptogamic Lepidodendreae, the 
typical Lycopods of the period, while the seed itself retained much 
of the detailed structure of the sporangium of that family. In the 
second genus, Miadesmia, the seed-bearing plant was herbaceous, 
and much like a recent Selaginella^. The seeds of the two genera 
arc differently constructed, and evidently had an independent origin. 
Here, then, we have seeds arising casually, as it were, at diflerent 
points among plants which otherwise retain all the characters of their 
cryptogamic fellows; the seed is not yet a morphological character 
of importance. To suppose that in these isolated cases the seed 

* F. W. Oliver, "On PIn/sostoma elegans, an arcliaic type of seed from tlio Palaeozoio 
Rocku," Annals of Botauij, January, I'JO'J. See also the earlier papers there cited. 

'^ See Margaret Benson, "Miadesmia membranarea, a new Palaeozoic LycopoJ with a 
seed-like structure," Fhil. Tram. Royal Soc. Vol. VJ'J, b. 1008. 

220 The Pcdaeoiitological Record. II. Plants 

sprang into being in obedience to a Law of Advance ("Vervollkom- 
mungsprincip"), from which other contemporary Lycopods were ex- 
empt, involves us in unnecessary mysticism. On the other hand it 
is not difficult to see how these seeds may have arisen, as adaptive 
structures, under the influence of Natural Selection. The seed-like 
structure afforded protection to the prothallus, and may have enabled 
the embryo to be launched on the world in gi-eater security. There 
was further, as we may suppose, a gain in certainty of fertilisation. 
As the writer has pointed out elsewhere, the chances against the 
necessary association of the small male with the large female spores 
must have been enormously great when the cones were borne high 
up on tall trees. The same difficulty may have existed in the case 
of the herbaceous Miadesmia, if, as Miss Benson conjectures, it was 
an epiphyte. One way of solving the problem was for pollination 
to take place while the megaspore was still on the parent plant, and 
this is just what the formation of an ovule or seed was likely to 

The seeds of the Pteridosperms, unlike those of the Lycopod 
stock, have not yet been found in statu nascendi — in all known 
cases they were already highly developed organs and far removed 
from the crytogamic sporangium. But in two respects we find that 
these seeds, or some of them, had not yet realised their possibilities. 
In the seed of Lyginodendron and other cases the micropyle, or 
orifice of the integument, was not the passage through which the 
pollen entered ; the open neck of the pollen-chamber protruded 
through the micropyle and itself received the pollen. We have met 
with an analogous case, at a more advanced stage of evolution, in 
the Bennettiteae (p. 208), where the Avail of the gynaecium, though 
otherwise closed, did not provide a stigma to catch the pollen, but 
allowed the micropyles of the ovules to protrude and receive the 
pollen in the old gymnospermous fashion. The integument in the 
one case and the pistil in the other had not yet assumed all the 
functions to which the organ ultimately became adapted. Again, 
no Palaeozoic seed has yet been found to contain an embryo, though 
the preservation is often good enough for it to have been recognised 
if present. It is probable that the lun-sing of the embryo had not 
yet come to be one of the functions of the seed, and that the whole 
embryonic development was relegated to the germination stage. 

In these two points, the reception of the pollen by the micropyle 
and the imrsing of the embryo, it appears that many Palaeozoic seeds 
were imperfect, as compared with the typical seeds of later times. 
As evolution went on, one function was superadded on another, and 
it ai)pears impossible to resist the conclusion that the whole difleren- 
tiation of the seed was a process of adaptation, and consequently 

Mutations 221 

governed by Natural Selection, just as much as the specialisation of 
the rostellum in an Orchid, or of the pappus in a Composite. 

Did space allow, other examples might be added. We may 
venture to maintain that the glimpses which the fossil record allows 
us into early stages in the evolution of organs now of high systematic 
importance, by no means justify the belief in any essential distinction 
between morphological and adaptive characters. 

Another point, closely connected with Darwin's theory, on which 
the fossil history of plants has been supposed to have some bearing, 
is the question of Mutation, as opposed to indefinite variation. 
Arber and Parkin, in their interesting memoir on the Origin of 
Angiosperms, have suggested calling in Mutation to explain the ap- 
parently sudden transition from the cycadean to the angiospermous 
type of foliage, in late Mesozoic times, though they express themselves 
with much caution, and point out *' a distinct danger that Mutation 
may become the last resort of the phylogenetically destitute " ! 

The distinguished French palaeobotanists,Grand'Eury ^and Zeiller-, 
are of opinion, to quote the words of the latter writer, that the facts 
of fossil Botany are in agreement with the sudden appearance of 
new forms, differing by marked characters from those that have given 
them birth ; he adds that these results give more amplitude to this 
idea of IMutation, extending it to groups of a higher order, and even 
revealing the existence of discontinuous series between the suc- 
cessive terms of which we yet recognise bonds of filiation ^ 

If Zeiller's opinion should be confirmed, it would no doubt be a 
serious blow to the Darwinian theory. As Darwin said : " Under a 
scientific point of view, and as leading to further investigation, but 
little advantage is gained by believing that new forms are suddenly 
developed in an inexplicable manner from old and widely different 
fonns, over the old belief in the creation of species from the dust of 
the earth*." 

It must however be pointed out, that such mutations as Zeillei-, 
and to some extent Arber and Parkin, appear to have in view, bridging 
the gulf between different Orders and Classes, bear no relation to 
any mutations which have been actually observed, such as the com- 
paratively small changes, of sub-specific value, described by De Yries 
in the type-case of Oenothera Lamarckiana. The results of palaeo- 
botanical research have undoubtedly tended to fill up gaps in the 
Natural System of plants — that many such gaps still persist is not 

^ C. Grand'Eury, "Sur lea mutations de quelqnes Plantes fossiles du Terrain houiller." 
Comptes Rendus, cxi.ii. p. 25, 1000. 

* R. Zoiller, "Lea Vc'tjolaux fossiles et leurs Enchainements,'' Revue du Mois, iii. 
February, 1907. 

' loc. cit. p. 23. * Origin of Species, p. 424. 

222 The Palaeoiitological Record. II. Plants 

surprising ; their presence may well serve as an incentive to further 
research but does not, as it seems to the writer, justify the assump- 
tion of changes in the past, wholly without analogy among living 

As regards the succession of species, there are no gi-eater au- 
thorities than Grand'Eury and Zeiller, and gi'eat weight must be 
attached to their opinion that the evidence from continuous deposits 
favours a somewhat sudden change from one specific form to another. 
At the same time it will be well to bear in mind that the subject of the 
"absence of numerous intermediate varieties in any single formation" 
was fully discussed by Darwin^; the explanation which he gave may 
go a long way to account for the facts which recent writers have 
regarded as favouring the theory of saltatory mutatioa 

The rapid sketch given in the present essay can do no more than 
call attention to a few salient points, in which the palaeontological 
records of plants has an evident bearing on the Darwinian theory. 
At the present day the whole subject of palaeobotany is a study in 
evolution, and derives its chief inspiration from the ideas of Darwin 
and Wallace. In return it contributes something to the verification of 
their teaching ; the recent progress of the subject, in spite of the 
immense difficulties which still remain, has added fresh force to 
DarMin's statement that "the great leading facts in palaeontology 
agree admirably with the theory of descent with modification through 
variation and natural selection^." 

1 Origin of Species, pp. 275—282, and p. 312. = Ibid. p. S13. 




By Georg Klebs, Ph.D. 

Professor of Botany in the University of Heidelberg. 

The dependence of plants on their environment became the object 
of scientific research wlien the phenomena of life were first investi- 
gated and physiology took its place as a special branch of science. 
This occurred in the course of the eighteenth century as the result 
of the pioneer M^ork of Hales, Duhamel, Ingenhousz, Senebier and 
others. In the nineteenth century, particularly in the second half, 
physiology experienced an unprecedented development in that it 
began to concern itself with the experimental study of nutrition 
and groMth, and with the phenomena associated with stimulus and 
movement ; on the other hand, physiology neglected phenomena 
connected with the production of form, a department of knowledge 
which Mas the province of morphology, a purely descriptive science. 
It Avas in the middle of the last century that the growth of com- 
parative morphology and the study of phases of development reached 
their highest point. 

The forms of plants appeared to be the expression of their in- 
scrutable inner nature ; the stages passed through in the development 
of the individual were regarded as the outcome of purely internal 
and hidden laws. The feasibility of experimental inquiry seemed 
therefore remote. Meanwhile, the recognition of the great im- 
portance of such a causal morphology emerged from the researches 
of the physiologists of that time, more especially from those of 
Hoftneister', and afterwards from the work of Sachs ^. Hofmeister, 
in speaking of this line of inquiry, described it as " the most pressing 
and immediate aim of the investigator to discover to Mhat extent 
external forces acting on the organism arc of importance in dcter- 
miiiing its form." This advance was the outcome of the influence of 

^ Hofmeister, Allpcmeine Morphologic, Leipzig, 18C8, p. 579. 

- Sachs, Stnjf unci Form der PJlanzenorgune, Vol. i. 1880; Vol. ii. 1882. Gesanimelte 
Ahhaiidluvgen ilber VJlanzen-Physiologie, n. Leipzig, 1893. 

224 Influence of E^ivironment on Plants 

that potent force in biology which was created by Darmn's Origin 
of Species (1859). 

The significance of the splendid conception of the transformation 
of species was first recognised and discussed by Lamarck (1809); as 
an explanation of transformation he at once seized upon the idea — an 
intelligible view — that the external world is the determining factor. 
Lamarck^ endeavoured, more especially, to demonstrate from the 
behaviour of plants that changes in environment induce change 
in form which eventually leads to the production of new species. 
In the case of animals, Lamarck adopted the teleological view that 
alterations in the environment first lead to alterations in the needs 
of the organisms, which, as tlie result of a kind of conscious effort 
of will, induce useful modifications and even the development of new 
organs. His work has not exercised any influence on the progress 
of science : Darwin himself confessed in regard to Lamarck's work 
— " I got not a fact or idea from it^" 

On a mass of incomparably richer and more essential data Darwin 
based his view of the descent of organisms and gained for it general 
acceptance ; as an explanation of modification he elaborated the 
ingeniously conceived selection theory. The question of special 
interest in this connection, namely what is the importance of the 
influence of the environment, Darwin always answered with some 
hesitation and caution, indeed with a certain amount of indecision. 

The fundamental principle underlying his theory is that of general 
variability as a whole, the nature and extent of which, especially in 
cultivated organisms, are fully dealt with in his well-known book^ In 
regard to the question as to the cause of variability Darwin adopts a 
consistently mechanical view. He says : "These several considerations 
alone render it probable that variability of every kind is directly or 
indirectly caused by changed conditions of life. Or, to put the case 
under another point of view, if it were possible to expose all the 
individuals of a species during many generations to absolutely 
uniform conditions of life, there would be no variability*." Darwin 
did not draw further conclusions from this general principle. 

Variations produced in organisms by the environment are dis- 
tinguished by Darwin as "the definite" and "the indefinite ^" The 
first occur " when all or nearly all the offspring of an individual 
exi)osed to certain conditions during several generations are modified 
in tlie same manner." Indefinite variation is much more general and a 

^ Lamarck, Philosophic zoologique, pp. 223 — 227. Paris, 1809. 
" Life and Letters, Vol. ii. p. 215. 

5 Darwin, The variation of Animals and Plants under domestication, 2 vols., edit. 1, 
18G8; edit. 2, 1875; popular edit. 1905. 

•• The variation of Animals and Plants (2nd edit.), Vol. ii. p. 212. 
<> Ibid. II. p. 2G0. See also Origin of Species (6th edit.), p. 0. 

Variability 225 

more important factor in the production of new species ; as a result 
of this, single individuals are distinguished from one another by 
"slight" diflerences, first in one then in another character. There 
may also occur, though this is very rare, more marked modifications, 
"variations which seem to us in our ignorance to arise spon- 
taneously \" The selection theory demands the further postulate 
that such changes, " Avhether extremely slight or strongly marked," 
are inherited. Darwin was no nearer to an experimental proof of 
this assumption than to the discovery of the actual cause of varia- 
bility. It was not until the later years of his life that Darwin was 
occupied with the "perplexing problem... what causes almost every 
cultivated plant to vary^": he began to make experiments on the 
influence of the soil, but these were soon given up. 

In the course of the violent controversy which was the outcome of 
Darwin's work the fundamental principles of his teaching were not 
advanced by any decisive observations. Among the supporters and 
opponents, Nageli^ was one of the few who sought to obtain proofs 
by experimental methods. Ilis extensive cultural experiments with 
alpine Hieracia led him to form the opinion that the changes which 
are induced by an alteration in the food-supply, in climate or in 
habitat, are not inherited and are therefore of no importance from 
the point of view of the production of species. And yet Nageli did 
attribute an important influence to the external world ; he believed 
that adaptations of plants arise as reactions to continuous stimuli, 
which supply a need and are therefore useful. These opinions, which 
recall the teleological aspect of Lamarckism, are entirely unsupported 
by proof While other far-reaching attempts at an explanation of the 
theory of descent were formulated both inNageli's time and afterwards, 
some in support of, others in opposition to Darwin, the necessity 
of investigating, from different standpoints, the underlying causes, 
variabilityand heredity, was more and more realised. To this category 
belong the statistical investigations undertaken by Quetelet and 
Galton, the researches into hybridisation, to which an impetus was 
given by the re-discovery of the Mendclian law of segregation, as 
also by the culture experiments on mutating species following the 
work of de Vrics, and lastly the consideration of the question how 
far variation and heredity are governed by external influences. 
These latter problems, which are concerned in general with the 
causes of form-production and form-modification, may be treated in 
a short summary which falls under two heads, one having reference 
to the conditions of form-production in single species, the other 

* Origin of Species (0th edit.), p. 421. 
■ Life and Letters, Vol. iii. p. 342. 

• Nageli, Theorie der Abstammuugslehre, Munich, 1884; cf. Chapter in. 

D 15 

226 Influence of Environment on Plants 

being concerned with the conditions governing the transformation 
of species. 

I. The influence of external conditions on form-production 


Tlie members of plants, which we express by the terms stem, leaf, 
flower, etc. are capable of modification within certain limits; since 
Lamarck's time this power of modification has been brought more or 
less into relation with the environment. We are concerned not only 
with the question of experimental demonstration of this relationship, 
but, more generally, with an examination of the origin of forms, 
the sequences of stages in development that are governed by re- 
cognisable causes. We have to consider the general problem ; to 
study the conditions of all typical as well as of atypic forms, in other 
words, to found a physiology of form. 

If we survey the endless variety of plant-forms and consider the 
highly complex and still little known processes in the interior of cells, 
and if we remember that the whole of this branch of investigation 
came into existence only a few decades ago, we are able to grasp the 
fact that a satisfactory explanation of the factors determining form 
cannot be discovered all at once. The goal is still far away. We are 
not concerned now with the controversial question, whether, on the 
whole, the fundamental processes in the development of form can 
be recognised by physiological means. A belief in the possibility of 
this can in any case do no harm. What we may and must attempt is 
this — to discover points of attack on one side or another, which may 
enable us by means of experimental methods to come into closer 
touch with these elusive and difiicult problems. While we are forced 
to admit that there is at present much that is insoluble there 
remains an inexhaustible supply of problems capable of solution. 

The object of our investigations is the species ; but as regards the 
question, what is a species, science of to-day takes up a position 
different from that of Darwin. For him it was the Linnean species 
which illustrates variation: we now know, thanks to the work of 
Jordan, de Bary, and particularly to that of de Vries^ that the 
Linnean species consists of a large or small number of entities, 
elementary species. In experimental investigation it is essential that 
observations be made on a pure species, or, as Johaunsen^ says, 
on a pure "line." What has long been recognised as necessary in 
the investigation of fungi, bacteria and algae must also be in- 
sisted on in the case of flowering plants; we must start with a 
single individual which is reproduced vegetatively or by strict self- 

1 lie VricB, Die Mutationstheorie, Leipzig, 1901, Vol. i. p. 33. 

* Johannsen, Ueber Erblichkeit m Populatioiien und reinen Linien, Jeua, 1903. 

Sjjecijlc Structure 227 

fertilisation. In dioecious plants we must aim at the reproduction of 
brothers and sisters. 

We may at the outset take it for granted that a pure species 
remains the same under similar external conditions; it varies as 
these vary. It is characteristic of a species that it always exhibits 
a constant relation to a particular environment. In the case of two 
different species, e.g. the hay and anthrax bacilli or two varieties of 
Campanula with blue and white flowers respectively, a similar environ- 
ment produces a constant difference. The cause of this is a mystery. 

According to the modern standpoint, the living cell is a complex 
chemico-physical system which is regarded as a dynamical system of 
equilibrium, a conception suggested by Herbert Spencer and which 
has acquired a constantly increasing importance in the light of 
modem developments in physical chemistry. The various chemical 
compounds, proteids, carbohydrates, fats, the whole series of different 
ferments, etc. occur in the cell in a definite physical arrangement. 
The two systems of two species must as a matter of fact possess a 
constant difference, which it is necessary to define by a special term. 
We say, therefore, that the specific structure is different. 

By way of illustrating this provisionally, we may assume that 
the proteids of the two species possess a constant chemical difference. 
This conception of specific structure is specially important in its 
bearing on a further treatment of the subject. In the original cell, 
eventually also in every cell of a plant, the characters which after- 
wards become apparent must exist somewhere ; they are integral 
parts of the capabilities or potentialities of specific structure. Thus 
not only the characters which are exhibited under ordinary conditions 
in nature, but also many others which become apparent only under 
special conditions^ are to be included as such potentialities in cells; 
the conception of specific structure includes the whole of the imten- 
tialities of a species ; specific structure comprises that which we 
must always assume without being able to explain it. 

A relatively simple substance, such as oxalate of lime, is known 
under a great number of different crystalline forms belonging to 
different systems^; these may occur as single crystals, concretions or 
as concentric sphaerites. The power to assume this variety of form 
is in some way inherent in the molecular structure, though we cannot, 
even in this case, explain the necessary connection between structure 

' In this connection I leave out of account, as before, the idea of material carriers of 
heredity which since the publication of Darwin's Pangenesis hypothesis has been frequently 
suggested. See my remarks in " Variationen der Bliitcn," Pringshcim's Jahrh. Wiss. Dot. 
1905, p. 298; also Detto, Biol. Centralhl. 19U7, p. 81, "Die Erklarbarkeit der Ontogenese 
durch materielle Anlagen."' 

" Coin|)are Kohl's work on Anatomisch-pltya. Unterstichungen ilbcr Kalksalze, etc. 
Marburg, 1889. 


228 Influence of Environment on Plants 

and crystalline form. These potentialities can only become operative 
under the influence of external conditions; their stimulation into 
activity depends on the degree of concentration of the various solu- 
tions, on the nature of the particular calcium salt, on the acid or 
alkaline reactions. Broadly speaking, the plant cell behaves in a 
similar way. The manifestation of each form, which is inherent as 
a potentiality in the specific structure, is ultimately to be referred to 
external conditions. 

An insight into this connection is, however, rendered exceedingly 
diihcult, often quite impossible, because the environment never 
directly calls into action the potentialities. Its influence is exerted 
on Avhat we may call the inner world of the organism, the importance 
of which increases with the degree of differentiation. The production 
of form in every plant depends upon processes in the interior of 
the cells, and the nature of these determines which among the possible 
characters is to be brought to light. In no single case are we 
acquainted with the internal process responsible for the production 
of a particular form. All possible factors may play a part, such as 
osmotic pressure, permeability of the protoplasm, the degree of 
concentration of the various chemical substances, etc. ; all these 
factors should be included in the category of internal conditions. 
This inner world appears the more hidden from our ken because 
it is always represented by a certain definite state, whether we are 
dealing with a single cell or with a small group of cells. These have 
been produced from pre-existing cells and they in turn from others ; 
the problem is constantly pushed back through a succession of gene- 
rations until it becomes identified with that of the origin of species. 

A way, however, is opened for investigation ; experience teaches 
us that this inner world is not a constant factor : on the contrary, 
it appears to be very variable. The dependence of vm^lahle internal 
on variable external conditions gives us the key with which research 
may open the door. In the lower plants this dependence is at once 
apparent, each cell is directly subject to external influences. In 
the higher plants with their different organs, these influences were 
transmitted to cells in course of development along exceedingly 
complex lines. In the case of the growing-point of a bud, which 
is capable of producing a complete plant, direct influences play 
a much less important part than those exerted through other 
organs, particularly through the roots and leaves, which are 
essential in nutrition. These correlations, as we may call them, 
are of the greatest importance as aids to an understanding of form- 
production. When a bud is produced on a particular part of a 
plant, it undergoes definite internal modifications induced by the 
influence of other organs, the activity of which is governed by the 

Relation between External Influences and Development 229 

environment, and as the result of this it develops along a certain 
direction ; it may, for example, become a flower. The particular 
direction of development is determined before the rudiment is 
differentiated and is exerted so strongly that further development 
ensues ^Wthout interruption, even though the external conditions 
vary considerably and exert a positively inimical influence : this 
produces the impression that development proceeds entirely inde- 
pendently of the outer world. The widespread belief that such 
independence exists is very premature and at all events unproven. 

The state of the young rudiment is the outcome of previous 
influences of the external world communicated through other organs. 
Experiments show that in certain cases, if the efficiency of roots and 
leaves as organs concerned with nutrition is interfered with, the 
production of flowers is affected, and their characters, which are 
normally very constant, undergo far-reaching modifications. To find 
the right moment at which to make the necessary alteration in the 
environment is indeed difficult and in many cases not yet possible. 
This is especially the case with fertilised eggs, which in a higher 
degree than buds have acquired, through parental influences, an 
apparently fixed internal organisation, and this seems to have pre- 
determined their development. It is, however, highly probable 
that it will be possible, by influencing the parents, to alter the 
internal organisation and to switch off development on to other 

Having made these general observations I will now cite a few of 
the many facts at our disposal, in order to illustrate the methods and 
aim of the experimental methods of research. As a matter of con- 
venience I will deal separately with modification of development and 
with modification of single organs. 

i. Effect of environment upon the course of development. 

Every plant, whether an alga or a flowering plant passes, under 
natural conditions, through a series of developmental stages charac- 
teristic of each species, and these consist in a regular sequence of 
definite forms. It is impossible to form an opinion from mere obser- 
vation and description as to what inner changes are essential for the 
production of the several forms. We must endeavour to influence 
the inner factors by known external conditions in such a way that the 
individual stages in development are separately controlled and the 
order of their sequence determined at will by experimental treat- 
ment. Such control over the course of development may be gained 
with specifd certainty in the case of the lower organisms. 

Witli tliese it is practicable to control the principal conditions of 
cultivation and to vary them in various ways. By this means it has 

230 Influence of Environment on Plants 

been demonstrated that each developmental stage depends upon 
special external conditions, and in cases where our knowledge is 
sufficient, a particular stage may be obtained at will. In the Green 
Algae \ as in the case of Fungi, we may classify the stages of develop- 
ment into purely vegetative growth (growth, cell-division, branching), 
asexual reproduction (formation of zoospores, conidia) and sexual 
processes (formation of male and female sexual organs). By modify- 
ing the external conditions it is possible to induce algae or fungi 
(Vaucheria, Saprolegnia) to grow continuously for several years or, 
in the course of a few days, to die after an enormous production of 
asexual or sexual cells. In some instances even an almost complete 
stoppage of growth may be caused, reproductive cells being scarcely 
formed before the organism is again compelled to resort to repro- 
duction. Thus the sequence of the different stages in development 
can be modified as we may desire. 

The result of a more thorough investigation of the determining 
conditions appears to produce at first sight a confused impression of 
all sorts of possibilities. Even closely allied species exhibit differ- 
ences in regard to the connection between their development and 
external conditions. It is especially noteworthy that the same form 
in development may be produced as the result of very different 
alterations in the environment. At the same time we can un- 
doubtedly detect a certain unity in the multiplicity of the individual 

If we compare the factors essential for the different stages in de- 
velopment, we see that the question always resolves itself into one 
of modification of similar conditions common to all life-processes. We 
should rather have inferred that there exist specific external stimuli 
for each developmental stage, for instance, certain chemical agencies. 
Experiments hitherto made support the conclusion that quantitative 
alterations in the general conditions of life produce different types 
of development. An alga or a fungus grows so long as all the con- 
ditions of nutrition remain at a certain optimum for growth. In 
order to bring about asexual reproduction, e.g. the formation of zoo- 
spores, it is sometimes necessary to increase the degree of intensity 
of external factors ; sometimes, on the other hand, these must be 
reduced in intensity. In the case of many algae a decrease in light- 
intensity or in the amount of salts in the culture solution, or in the 
temperature, induces asexual reproduction, while in others, on the 
contrary, an increase in regard to each of these factors is required to 
produce the same result. This holds good for the quantitative vari- 
ations which induce sexual reproduction in algae. The controlling 

> See Klebs, Die Bedingung der Fortpftanzung..., Jena, 1896; alBoJahrb.filr Wiss.Bot. 
1808 and 1900; "Probleme der Entwickelung, m." Biol. Centralbl. 1904, p. 452. 

Quantitative alteration of External Conditions 231 

factor is found to be a reduction in the supply of nutritive salts and 
the exposure of the plants to prolonged illumination or, better still, 
an increase in the intensity of the light, the efficiency of illumination 
depending on the consequent formation of organic substances such as 

The quantitative alterations of external conditions may be spoken 
of as releasing stimuli. They produce, in the complex equilibrium of 
the cell, quantitative modifications in the arrangement and distri- 
bution of mass, by means of which other chemical processes are at 
once set in motion, and finally a new condition of equilibrium is 
attained. But the commonly expressed view that the environment 
can as a rule act only as a releasing agent is incorrect, because it 
overlooks an essential point. The power of a cell to receive stimuli 
is only acquired as the result of previous nutrition, which has pro- 
duced a definite condition of concentration of different substances. 
Quantities are in this case the determining factors. The distribution 
of quantities is especially important in the sexual reproduction of 
algae, for which a vigorous production of the materials formed during 
carbon-assimilation appears to be essential. 

In the Flowering plants, on the other hand, for reasons already 
mentioned, the whole problem is more complicated. Investigations 
on changes in the course of development of fertilised eggs have 
hitherto been unsuccessful; the difficulty of influencing egg-cells 
deeply immersed in tissue constitutes a serious obstacle. Other 
parts of plants are, however, convenient objects of experiment; 
e.g. the growing apices of buds which serve as cuttings for repro- 
ductive purposes, or buds on tubers, runners, rhizomes, etc. A grow- 
ing apex consists of cells capable of division in which, as in egg-cells, 
a complete series of latent possibilities of development is embodied. 
Wliich of these possibilities becomes effective depends upon the 
action of the outer world transmitted by organs concerned with 

Of the different stages which a flowering plant passes through in 
the course of its development we will deal only with one in order 
to show that, in spite of its great complexity, the problem is, in 
essentials, equally open to attack in the higher plants and in the 
simplest organisms. The most important stage in the life of a 
flowering plant is the transition from purely vegetative growth to 
sexual reproduction — that is, the production of flowers. In certain 
cases it can be demonstrated that there is no internal cause, de- 
pendent simply on the specific structure, which compels a plant to 
produce its flowers after a definite period of vegetative growth \ 

1 Kleba, Willkiirliche Entwickelungsdnderungen, Jena 1903 ; see also " Probleme der 
Entwickelung, i. ir." Biol. Centralbl. 1901. 

232 Influence of JiJnvironment on Plants 

One extreme case, that of exceptionally early flowering, has been 
observed in nature and more often in cultivation. A number of plants 
under certain conditions are able to flower soon after germination \ 
This shortening of the period of development is exhibited in the 
most striking form in trees, as in the oak'^, flowering seedlings of 
which have been observed from one to three years old, whereas 
normally the tree does not flower until it is sixty or eighty years old. 

Another extreme case is represented by prolonged vegetative 
growth leading to the complete suppression of flower-production. 
This result may be obtained with several plants, such as Glechoma, 
the sugar beet, Digitalis, and others, if they are kept during the 
winter in a warm, damp atmosphere, and in rich soil ; in the following 
spring or summer they fail to flower^ Theoretically, however, experi- 
ments are of greater importance in which the production of flowers is 
inliibited by very favourable conditions of nutrition* occurring at the 
normal flowering period. Even in the case of plants of Sempervivum 
several years old, which, as is shown by control experiments on 
precisely similar plants, are on the point of flowering, flowering is 
rendered impossible if they are forced to very vigorous growth by an 
abundant supply of water and salts in the spring. Flowering, how- 
ever, occurs, if such plants are cultivated in relatively dry sandy soil 
and in the presence of strong hght. Careful researches into the 
conditions of gi-owth have led, in the case of Sempervivum, to the 
following results: (1) With a strong light and vigorous carbon- 
assimilation a considerably increased supply of water and nutritive 
salts produces active vegetative growth. (2) With a vigorous carbon- 
assimilation in strong light, and a decrease in the supply of water and 
salts active flower-production is induced. (3) If an average supply 
of water and salts is given both processes are possible ; the intensity 
of carbon-assimilation determines which of the two is manifested. 
A diminution in the production of organic substances, particularly of 
carbohydrates, induces vegetative growth. This can be eflected by 
culture in feeble light or in light deprived of the yellow-red rays: 
on the other hand, flower-production follows an increase in light- 
intensity. These results are essentially in agreement with well- 
known observations on cultivated plants, according to which, the 
application of much moisture, after a plentiful supply of manure 
composed of inorganic salts, hinders the flower-production of many 
vegetables, while a decrease in the supply of water and salts favours 

* Cf. numerous records of this kind by Diels, Jugendformen nnd Blilten, Berlin, 1906. 
" Mobius, Beitriige zur Lehre von der Fortpjianzung, Jena, 181)7, p. 89. 

■' Klebs, WillkiirUche Aenderungen, etc. Jena, 1903, p. 130. 

* Klebs, Veher kUnstUche Metamorphosen, Stuttgart, 1906, p. 115 {Abh. Naturf. Ges. 
Halle, XXV.). 

Influence of Environinent on Plant-organs 233 

ii. Influence of the environment on the form of single organs'^. 

If we look closely into the development of a flowering plant, we 
notice that in a given species differently formed organs occur in 
definite positions. In a potato plant colourless runners are formed 
from the base of the main stem which grow underground and pro- 
duce tubers at their tips: from a higher level foliage shoots arise 
nearer the apex. External appearances suggest that both the place 
of origin and the form of these organs were predetermined in the 
egg-cell or in the tuber. But it was shown experimentally by the 
well-known investigator Knight^ that tubers may be developed 
on the aerial stem in place of foliage shoots. These observations 
were considerably extended by Vochting^ In one kind of potato, 
germinating tubers were induced to form foliage shoots under the 
hifluence of a higher temperature ; at a lower temperature they formed 
tuber-bearing shoots. Many other examples of the conversion of 
foliage-shoots into runners and rhizomes, or vice versa, have been 
described by Goebel and others. As in the asexual reproduction 
of algae quantitative alteration in the amount of moisture, light, 
temperature, etc. determines whether this or that form of shoot is 
produced. If the primordia of these organs are exposed to altered 
conditions of nutrition at a sufficiently early stage a complete sub- 
stitution of one organ for another is effected. If the rudiment has 
reached a certain stage in development before it is exposed to these 
influences, extraordinary intermediate forms are obtained, bearing 
the characters of both organs. 

The study of regeneration follo^ving injury is of greater import- 
ance as regards the problem of the development and place of origin 
of organs*. Only in relatively very rare cases is there a complete 
re-formation of the injured organ itself, as e.g. in the growing-apex. 
Much more commonly injury leads to the development of comple- 
mentary formations, it may be the rejuvenescence of a hitherto 
dormant rudiment, or it may be the formation of such ah initio. In 
all organs, stems, roots, leaves, as well as inflorescences, this kind 
of regeneration, which occurs in a great variety of ways according 
to the species, may be observed on detached pieces of the plant. 
Cases are also known, such, for example, as the leaves of many plants 
which readily form roots but not shoots, where a complete regeneration 
does not occur. 

' A considerable number of observations bearing on this question are given by Goebel 
iu his Kxperimentelle Morpholof/ie der Pjianzen, Leipzig, 1908. It is not possible to deal 
here with the alteration in anatomical structure ; cf. Kiister, Pathologische Pjlanztii- 
aiintomie, Jena, 1903. 

^ Knight, Selection from the and Ilortirnlturnl Papers, London, 1841. 

" Vochting, Ueber die Jiildung der Kiiollen, Cassel, 1HS7 ; see also Dot. Zcit. 190'2, 87. 

* Reference may be made to the full summary of results given by Goebel in his Ezperi- 
menttlle ilorphulagie, Leipzig and Berlin, 1908, Section iv. 

234 Influence of Environment on Plants 

The widely spread power of reacting to wounding affords a very 
valuable means of inducing a fresh development of buds and roots 
on places where they do not occur in normal circumstances. Injury 
creates special conditions, but little is known as yet in regard to 
alterations directly produced in this way. Where the injury con- 
sists in the separation of an organ from its normal connections, the 
factors concerned are more comprehensible. A detached leaf, e.g., is 
at once cut off from a supply of water and salts, and is deprived of 
the means of getting rid of organic substances which it produces; 
the result is a considerable alteration in the degree of concentration. 
No experimental investigation on these lines has yet been made. 
Our ignorance has often led to the view that we are dealing with 
a force whose specific quality is the restitution of the parts lost by 
operation; the proof, therefore, that in certain cases a similar pro- 
duction of new roots or buds may be induced without previous 
injury and simply by a change in external conditions assumes an 
importance \ 

A specially striking phenomenon of regeneration, exhibited also 
by uninjured plants, is afforded by polarity, which was discovered by 
Vbchting'^. It is found, for example, that roots are formed from the 
base of a detached piece of stem and shoots from the apex. Within 
the limits of this essay it is impossible to go into this difficult question ; 
it is, however, important from the point of view of our general survey 
to emphasise the fact that the physiological distinctions between base 
and apex of pieces of stem are only of a quantitative kind, that is, 
they consist in the inhibition of certain phenomena or in favouring 
them. As a matter of fact roots may be produced from the apices 
of willows and cuttings of other plants; the distinction is thus 
obliterated under the influence of environment. The fixed polarity 
of cuttings from full gi'o^vn stems cannot be destroyed ; it is the ex- 
pression of previous development. Vochting speaks of polarity as a 
fixed inherited character. This is an unconvincing conclusion, as 
nothing can be deduced from our present knowledge as to the causes 
which led up to polarity. We know that the fertilised egg, like the 
embryo, is fixed at one end by which it hangs freely in the embryo- 
sac and afterwards in the endosperm. From the first, therefore, 
the two ends have different natures, and these are revealed in the 
differentiation into root-apex and stem-apex. A definite direction 
in the flow of food-substances is correlated with this arrangement, 
and this eventually leads to a polarity in the tissues. This view 

' Klebs, Willkilrliche Entwickelung, -p. 100; also, " Probleme der Entwickelung," £io^ 
Centralhl. 1904, p. 610. 

' See the classic work of Vochting, Vcher Organhildung im PJlanzenreich, i. Bonn, 
1R88 ; also Bot. Zeit. 1906, p. 101 ; cf. Goebel, Experimentelle Morphologie, Leipzig and 
Berlin, 1908, Section v, Polaritiit, 

Influence of Environment on Plant-organs 235 

requires experimental proof, which in the case of the egg-cells of 
flowering plants hardly appears possible; but it derives considerable 
support from the fact that in herbaceous plants, e.g. Sempervivum ^, 
rosettes or flower-shoots are formed in response to external con- 
ditions at the base, in the middle, or at the apex of the stem, so that 
polarity as it occurs under normal conditions cannot be the result of 
unalterable hereditary factors. On the other hand, the lower plants 
should furnish decisive evidence on this question, and the experi- 
ments of Stahl, Winkler, Kniep, and others indicate the right method 
of attacking the problem. 

The relation of leaf-form to environment has often been investi- 
gated and is well known. The leaves of bog and water plants^ afibrd 
the most striking examples of modifications : according as they are 
grown in water, moist or dry air, the form of the species characteristic 
of the particular habitat is produced, since the stems are also modi- 
fied. To the same group of phenomena belongs the modification of 
the forms of leaves and stems in plants on transplantation from 
the plains to the mountains^ or vice versa. Such variations are by 
no means isolated examples. All plants exhibit a definite alteration 
in form as the result of prolonged cultivation in moist or dry air, 
in strong or feeble light, or in darkness, or in salt solutions of difi'erent 
composition and strength. 

Every individual which is exposed to definite combinations of 
external factors exhibits eventually the same type of modification. 
This is the type of variation which Darwin termed "definite." It is 
easy to realise that indefinite or fluctuating variations belong essenti- 
ally to the same class of phenomena ; both are reactions to changes 
in environment. In the production of individual variations two 
difi'erent influences undoubtedly cooperate. One set of variations 
is caused by difierent external conditions, during the production, 
cither of sexual cells or of vegetative primordia ; another set is the 
result of varying external conditions during the development of the 
embryo into an adult plant. The two sets of influences cannot as yet 
be sharply differentiated. If, for purposes of vegetative reproduction, 
we select pieces of the same parent-plant of a pure species, the 
second type of variation predominates. Individual fluctuations de- 
pend essentially in such cases on small variations in environment 
during development. 

These relations must be borne in mind if we wisli to understand 
the results of statistical methods. Since the work of Quetelet, 

J KlcbB, "Variationen der Bliiten," Jahrh. Wiss. Lot. 1905, p. 260. 
» Cf. Goebcl, loc. cit. cliop. ii. ; also Gluck, UtUersuchuiigen iiber Waster- und Sumpf- 
gewiichge, Jena, Vols. i. — ii. 1905 — 00. 

* Bonnier, Recherchet $ur iAtiatomie exp6rimentale des Vegttaux, Corbeil, 1895. 

236 Infiuence of Environment on Plants 

Gallon, and others the statistical examination of individual differ- 
ences in animals and plants has become a special science, which is 
primarily based on the consideration that the application of the 
theory of probability renders possible mathematical statement and 
control of the results. The facts show that any character, size of 
leaf, length of stem, the number of members in a flower, etc. do not 
vary haphazard but in a very regular manner. In most cases it is 
found that there is a value which occurs most commonly, the average 
or medium value, from which the larger and smaller deviations, the 
so-called plus and minus variations fall away in a continuous series 
and end in a limiting value. In the simpler cases a falling off occurs 
equally on both sides of the curve ; the curve constructed from such 
data agrees very closely with the Gaussian curve of error. In more 
complicated cases irregular curves of difierent kinds are obtained 
which may be calculated on certain suppositions. 

The regular fluctuations about a mean according to the rule of 
probability is often attributed to some law underlying variability \ 
But there is no such law which compels a plant to vary in a par- 
ticular manner. Every experimental investigation shows, as we have 
already remarked, that the fluctuation of characters depends on 
fluctuation in the external factors. The applicability of the method 
of probability follows from the fact that the numerous individuals of a 
species are influenced by a limited number of variable conditions^. 
As each of these conditions includes within certain limits all possible 
values and exhibits all possible combinations, it follows that, accord- 
ing to the rules of probability, there must be a mean value, about 
which the larger and smaller deviations are distributed. Any cha- 
racter will be found to have the mean value which corresponds with 
that combination of determining factors which occurs most frequently. 
Deviations towards plus and minus values will be correspondingly 
produced by rarer conditions. 

A conclusion of fundamental importance may be drawn from 
this conception, which is, to a certain extent, supported by experi- 
mental investigation ^ There is no normal curve for a particular 
character, there is only a curve for the varying combinations of 
conditions occurring in nature or under cultivation. Under other 
conditions entirely difierent curves may be obtained with other 
variants as a mean value. If, for example, under ordinary conditions 
the number 10 is the most frequent variant for the stamens of Sedum 
spectablle, in special circumstances (red light) this is replaced by the 
number 5. The more accurately we know the conditions for a par- 

1 de Vries, Blutationstheorie, Vol. i. p. 35, Leipzig, 1901. 

2 Klebs, WiUkilrl. Ent. Jena, 1903, p. 141. 

« Klebs, " Studien iiber Variation," Arch, fiir Entw. 1907. 

Monstrosities 237 

ticular form or number, and are able to reproduce it by experiment, 
the nearer we are to achieving our aim of rendering a particular 
variation impossible or of making it dominant. 

In addition to the individual variations of a species, more pro- 
nounced fluctuations occur relatively rarely and sporadically which 
are spoken of as "single variations," or if specially striking as ab- 
normalities or monstrosities. These forms have long attracted the 
attention of morphologists ; a large number of observations of this 
kind are given in the handbooks of Masters^ and Penzig^. These 
variations, which used to be regarded as curiosities, have now 
assumed considerable importance in connection with the causes of 
form-development. They also possess special interest in relation to 
the question of heredity, a subject which does not at present concern 
us, as such deviations from normal development undoubtedly 
arise as individual variations induced by the influence of environ 

Abnormal developments of all kinds in stems, leaves, and flowers, 
may be produced by parasites, insects, or fungi. They may also be 
induced by injury, as Blaringhem^ has more particularly demonstrated, 
which, by cutting away the leading shoots of branches in an early 
stage of development, caused fasciation, torsion, anomalous flowers, 
etc. The experiments of Blaringhem point to the probability that 
disturbances in the conditions of food-supply consequent on injury 
are the cause of the production of monstrosities. This is certainly 
the case in my experiments with species of Sempervivum* ; indi- 
viduals, which at first formed normal flowers, produced a great 
variety of abnormalities as the result of changes in nutrition. We 
mav call to mind the fact that the formation of inflorescences occurs 
normally when a vigorous production of organic compounds, such as 
starch, sugar, etc. follows a diminution in the supply of mineral salts. 
On the other hand, the development of inflorescences is entirely 
suppressed if, at a suitable moment before the actual foundations 
have been laid, water and mineral salts are supplied to the roots. 
If, during the week when the inflorescence has just been laid dowi 
and is growing very slowly, the supply of w ater and salts is increased, 
the internal conditions of the cells are essentially changed. At a later 
stage, after the elongation of the inflorescence, rosettes of leaves are 
produced instead of flowers, and structures intermediate between the 
two kinds of organs; a number of peculiar plant-forms are thus 
obtained^ Abnormalities in the greatest variety are produced in 

1 Masters, Vegetable Teratolo[iij, London, 18G9. 

' Penzig, Pjlanzen-Teratologie, Vols. i. and ii. Genua, 1890—94. 

* Blaringliem, Mutation et traurtiatisincs, Paris, 1907. 

♦ Klebs, KiinslUche Melavtorphosen, Stuttgart, 1906. 

'' Cf. Lotsy, VorlesuiKjcn iiber Dcszendenztheorien, Vol. ii. pi. 3, Jena, 1903. 

238 Influence of Environment on Plants 

flowers by varying the time at which the stimulus is applied, and by 
the cooperation of other factors such as temperature, darkness, etc. 
In number and arrangement the several floral members vary within 
wide limits ; sepals, petals, stamens, and carpels are altered in form and 
colour, a transformation of stamens to carpels and from carpels to 
stamens occurs in varying degrees. The majority of the deviations 
observed had not previously been seen either under natural con- 
ditions or in cultivation ; they were first brought to light through the 
influence of external factors. 

Such transformations of flowers become apparent at a time, which 
is separated by about two months from the period at which the 
particular cause began to act. There is, therefore, no close con- 
nection between the appearance of the modifications and the external 
conditions which prevail at the moment. When we are ignorant of 
the causes which are operative so long before the results are seen, 
we gain the impression that such variations as occur are spontaneous 
or autonomous expressions of the inner nature of the plant. It is 
much more likely that, as in Sempervivum, they were originally 
produced by an external stimulus which had previously reached the 
sexual cells or the young embryo. In any case abnormalities of this 
kind appear to be of a special type as compared with ordinary 
fluctuating variations. Darwin pointed out this diflerence; Bateson^ 
has attempted to make the distinction sharper, at the same time 
emphasising its importance in heredity. 

Bateson applies the term co7itimious to small variations connected 
with one another by transitional stages, while those which are more 
striking and characterised from the first by a certain completeness, 
he names discontinuous. He drew attention to a great difficulty 
which stands in the way of Lamarck's hypothesis, as also of Darwin's 
view. "According to both theories, specific diversity of form is 
consequent upon diversity of environment, and diversity of environ- 
ment is thus the ultimate measure of diversity of specific form. 
Here then we meet the difficulty that diverse environments often 
shade into each other insensibly and form a continuous series, 
whereas the Specific Forms of life which are subject to them on the 
wliole form a Discontinuous Series." This difficulty is, however, not 
of fundamental importance as well authenticated facts have been 
adduced showing that by alteration of the environment discontinuous 
variations, such as alterations in the number and form of members 
of a flower, may be produced. We can as yet no more explain 
how this happens than we can explain the existence of continuous 
variations. We can only assert that both kinds of variation arise in 
response to (quantitative alterations in external conditions. The 

1 Bateson, Materials for the study of Variatio7i, London, 1894, p. 5. 

The Control of Plant-form 239 

question as to which kind of variation is produced depends on the 
greater or less degree of alteration; it is correlated with the state 
of the particular cells at the moment. 

In this short sketch it is only possible to deal superficially with a 
small part of the subject. It has been clearly shown that in view ot* 
the general dependence of development on the factors of the environ- 
ment a number of problems are ready for experimental treatment. 
One must, however, not forget that the science of the physiology of 
form has not progressed beyond its initial stages. Just now our first 
duty is to demonstrate the dependence on external factors in as 
many forms of plants as possible, in order to obtain a more thorough 
control of all the different plant-forms. The problem is not only to 
produce at will (and independently of their normal mode of life) 
forms which occur in nature, but also to stimulate into operation 
potentialities which necessarily lie dormant under the conditions 
which prevail in nature. The constitution of a species is much 
richer in possibilities of development than would appear to be the 
case under normal conditions. It remains for man to stimulate into 
activity all the potentialities. 

But the control of plant-form is only a preliminary step — the 
foundation stones on which to erect a coherent scientific structure. 
We must discover what are the internal processes in the cell pro- 
duced by external factors, which as a necessary consequence result in 
the appearance of a definite form. We are here brought into contact 
with the most obscure problem of life. Progress can only be made 
jyari jyassu with progress in physics and chemistry, and with the 
growth of our knowledge of nutrition, growth, etc. 

Let us take one of the simplest cases — an alteration in form. 
A cylindrical cell of the alga Stigeoclonium assumes, as Livingstone^ 
has shown, a spherical form when the osmotic pressure of the culture 
fluid is increased; or a spore of Mucor, which, in a sugar solution 
grows into a branched filament, in the presence of a small quantity 
of acid (hydrogen ions) becomes a comparatively large sphere^. In 
both cases there has undoubtedly been an alteration in the osmotic 
pressure of the cell-sap, but this does not suffice to explain the 
alteration in form, since the unknown alterations, which are induced 
in the protoplasm, nuist in their turn influence the cell-membrane. 
In the case of the very much more complex alterations in form, such 
as we encounter in the course of development of plants, there do 
not appear to be any clues which lead us to a deeper insight into the 
phenomena. Nevertheless we continue the attempt, seeking with the 

' Livingstone, " On the nature of the stimulus which causes the change of form, etc." 
Botanical Gazette, xix. 1900 ; also xxxii. I'JOl. 

"^ Kittor, " Ueber Kugelhefe, etc.," Der. hot. Gesell. Berlin, xxv. p. 255, 1007. 

240 Influence of Environment on Plants 

lielp of any available hypothesis for points of attack, which may enable 
us to acquire a more complete mastery of physiological methods. 
To quote a single example ; I may put the question, what internal 
changes produce a transition from vegetative growth to sexual repro- 
duction ? 

The facts, which are as clearly established for the lower as for the 
higher plants, teach us that quantitative alteration in the environ- 
ment produces such a transition. This suggests the conclusion that 
quantitative internal changes in the cells, and with them disturbances 
in the degree of concentration, are induced, through which the 
chemical reactions are led in the direction of sexual reproduction. 
An increase in the production of organic substances in the presence 
of light, chiefly of the carbohydrates, with a simultaneous decrease 
in the amount of inorganic salts and water, are the cause of the 
disturbance and at the same time of the alteration in the direction 
of development. Possibly indeed mineral salts as such are not in 
question, but only in the form of other organic combinations, par- 
ticularly proteid material, so that we are concerned with an alteration 
in the relation of the carbohydrates and proteids. The difiiculties 
of such researches are very great because the methods are not yet 
sufficiently exact to demonstrate the frequently small quantitative 
differences in chemical composition. Questions relating to the 
enzymes, wliich are of the greatest importance in all these life- 
processes, are especially complicated. In any case it is the necessary 
result of such an hypothesis that we must employ chemical methods 
of investigation in dealing with problems connected with the phy- 
siology of form. 

II. IjNfluence of environment on the transformation 


The study of the physiology of form-development in a pure species 
has already yielded results and makes slow but sure progress. The 
physiology of the possibility of the transformation of one species into 
another is based, as yet, rather on pious hope than on accomplished 
fact. From the first it appeared to be hopeless to investigate physio- 
logically the origin of Linnean species and at the same time that of 
the natural system, an aim which Darwin had before him in his 
enduring work. The historical sequence of events, of which an 
organism is the expression, can only be treated hypothetically with 
the help of facts supplied by comparative morphology, the history 
of development, geographical distribution, and palaeontology \ A 
glance at the controversy which is going on to-day in regard to 
difleient hypotheses shows that the same material may lead dili'erenfc 

* See Lotsy, Vorlesuncjen (Jena, i. 190G, ii. I'JOS), fur summary of the facts. 

Transformation of Species 241 

investigators to form entirely different opinions. Our ultimate aim 
is to find a solution of the problem as to the cause of the origin of 
species. Indeed such attempts are now being made : they are justi- 
fied by the fact that under cultivation new and permanent strains 
are produced ; the fundamental importance of this was first gi'asped 
by Darwin. New points of view in regard to these lines of inquiry 
have been adopted by H. de Vries who has succeeded in obtaining 
from Oenothera Lamarckiana a number of constant "elementary" 
species. Even if it is demonstrated that he was simply dealing with 
the complex splitting up of a hybrid \ the facts adduced in no sense 
lose their very great value. 

We must look at the problem in its simplest form ; we find it in 
every case where a new race differs essentially from the original type 
in a single character only ; for example, in the colour of the flowers 
or in the petalody of the stamens (doubling of flowers). In this con- 
nection we must keep in view the fact that every visible character in 
a plant is the resultant of the cooperation of specific structure, with 
its various potentialities, and the influence of the environment. We 
know, that in a pure species all characters vary, that a blue-flowering 
Oampaimla or a red Sempervivum can be converted by experiment 
into white-flowering forms, that a transformation of stamens into 
petals may be caused by fungi or by the influence of changed con- 
ditions of nutrition, or that plants in dry and poor soil become 
dwarfed. But so far as the experiments justify a conclusion, it would 
appear that such alterations are not inherited by the offspring. 
Like all other variations they appear only so long as special con- 
ditions prevail in the surroundings. 

It has been shown that the case is quite different as regards the 
white-flowering, double or dwarf races, because these retain their 
characters when cultivated under practically identical conditions, 
and side by side with the blue, single-flowering or tall races. The 
problem may therefore be stated thus : how can a character, which 
appears in the one case only under the strictly limited conditions of 
the experiment, in other cases become apparent under the very much 
wider conditions of ordinary cultivation ? If a character appears, in 
these circumstances, in the case of all individuals, we then speak of 
constant races. In such simple cases the essential point is not the 
creation of a new character but rather an alteratlou of this character 
in accordance with the environment. In the examples mentioned 
the modified character in the simple varieties (or a number of 
characters in elementaiy species) appears more or less suddenly and 
is constant in the above sense. The result is what de Vries has 

' Bateson, Reports to the Evolution Committee of the Eoj/al Society, London, 1002 ; cf. 
also Lotsy, Vorlemngen, Vol. i. p. '234. 

D. 16 

242 Influence of Enviro7iment on Plants 

termed a Mutation. In this connection we must bear in mind the 
fact that no difference, recognisable externally, need exist between 
individual variation and mutation. Even the most minute quanti- 
tative difference between two plants may be of specific value if it 
is preserved under similar external conditions during many successive 
generations. We do not know how this happens. We may state the 
problem in other terms; by saying that the specific structure must 
be altered. It is possible, to some extent, to explain this sudden 
alteration, if we regard it as a chemical alteration of structure either 
in the specific qualities of the proteids or of the unknown carriers of 
life. In the case of many organic compounds their morphological 
characters (the physical condition, crystalline form, etc.) are at once 
changed by alteration of atomic relations or by incorporation of new 
radicals \ Much more important, however, would be an answer to the 
question, whether an individual variation can be converted experi- 
mentally into an inherited character— a mutation in de Vries's sense. 

In all circumstances we may recognise as a guiding principle the 
assumption adopted by Lamarck, Darwin, and many others, that the 
inheritance of any one character, or in more general terms, the trans- 
formation of one species into another, is, in the last instance, to be 
i-eferred to a change in the environment. From a causal-mechanical 
point of view it is not a priori conceivable that one species can 
ever become changed into another so long as external conditions 
remain constant. The inner structure of a species must be essen- 
tially altered by external influences. Two methods of experimental 
research may be adopted, the effect of crossing distinct species and, 
secondly, the effect of definite factors of the environment. 

The subject of hybridisation is dealt with in another part of this 
essay. It is enough to refer here to the most important fact, that as 
the result of combinations of characters of different species new 
and constant forms are produced. Further, Tschermack, Bateson 
and others have demonstrated the possibility that hitherto unknown 
inheritable characters may be produced by hybridisation. 

The other method of producing constant races by the influence of 
special external conditions has often been employed. The sporeless 
races of Bacteria and Yeasts^ are well known, in which an internal 
alteration of the cells is induced by the influence of poison or higher 
temperature, so that the power of producing spores even under 
normal conditions appears to be lost. A similar state of things is 

^ For instance ethylchloride (CjjHgCl) is a gas at 21° C, ethjlencchloride (CgHjCL,) a 
fluid boiling at 84" C, j3 trichloretbane (CgHjCla) a fluid boiling at 113" C, perchlorethane 
(CjClj) a crystalline Bubstance. Klebs, Willkilrliche Entwickelungscinderungen, p. 158. 

* Cf. Detto, Die Theorie der dirckten Anpassitng..., pp. 98 et seq., Jena, 1904; see also 
Lotsy, Vorlenxingcn, ii. pp. 636 et seq., where other similar cases are described. 

Production of Constant Races 243 

found in some races which under certain definite conditions lose 
their colour or their virulence. Among the phanerogams the in- 
vestigations of Schiibler on cereals afford parallel cases, in which the 
influence of a northern climate produces individuals which ripen their 
seeds early ; these seeds produce plants which seed early in southern 
countries. Analogous results were obtained by Cieslar in his experi- 
ments ; seeds of conifers from the Alps when planted in the plains 
produced plants of slow growth and small diameter. 

All these observations are of considerable interest theoretically; 
they show that the action of environment certainly induces such 
internal changes, and that these are transmitted to the next gene- 
ration. But as regards the main question, whether constant races 
may be obtained by this means, the experiments cannot as yet supply 
a definite answer. In phanerogams, the influence very soon dies out 
in succeeding generations; in the case of bacteria, in which it is 
only a question of the loss of a character it is relatively easy for 
this to reappear. It is not impossible, that in all such cases there is 
a material hanging-on of certain internal conditions, in consequence 
of which the modification of the character persists for a time in 
the descendants, although the original external conditions are no 
longer present. 

Thus a slow dying-out of the effect of a stimulus was seen in my 
experiments on Veronica chama€dri/s\ During the cultivation of 
an artificially modified inflorescence I obtained a race showing modi- 
fications in different directions, among which twisting was especially 
conspicuous. This plant, however, does not behave as the twisted 
race of Dipsacus isolated by de Vries^, which produced each year a 
definite percentage of twisted individuals. In the vegetative repro- 
duction of this Veronica the torsion appeared in the first, also in 
the second and third year, but with diminishing intensity. In spite 
of good cultivation this character has apparently now disappeared; 
it disappeared still more quickly in seedlings. In another 
character of the same Veronica chamaedri/s the influence of 
the environment was stronger. The transformation of the in- 
florescences to foliage-shoots formed the starting-point ; it occurred 
only under narrowly defined conditions, namely on cultivation as a 
cutting in moist air and on removal of all other leaf-buds. In the 
majority (^) of the plants obtained from the transformed shoots, 
the modification appeared in the following year without any inter- 
ference. Of the three plants which were under observation several 
years the first lost the character in a short time, while the two others 

1 Klebs, Kitmtliche Mctamorphonfn, Stuttgart, 1906, p. 132. 
^ de Vries, Mututiojisthcorie, Vol. ii. Leipzig, l'J03, p. 573. 


244 Influence of Enviromnent on Plants 

still retain it, after vegetative propagation, in varying degrees. The 
same character occurs also in some of the seedlings; but anything 
approaching a constant race has not been produced. 

Another means of producing new races has been attempted by 
Blaringhem^ On removing at an early stage the main shoots of 
different plants he observed various abnormalities in the newly 
formed basal shoots. From the seeds of such plants he obtained 
races, a large percentage of which exhibited these abnormalities. 
Starting from a male Maize plant with a fasciated inflorescence, on 
which a proportion of the flowers had become male, a new race was 
bred in which hermaphrodite flowers were frequently produced. In 
the same way Blaringhem obtained, among other similar results, a 
race of barley with branched ears. These races, however, behaved 
in essentials like those which have been demonstrated by de Vries to 
be inconstant, e.g. Trifol'mm pratense quinquefoUum and others. 
The abnormality appears in a proportion of the individuals and only 
under very special conditions. It must be remembered too that 
Blaringhem worked with old cultivated plants, which from the first 
had been disposed to split into a great variety of races. It is possible, 
but difficult to prove, that injury contributed to this result. 

A third method has been adopted by MacDougaF who injected 
strong (10%) sugar solution or weak solutions of calcium nitrate and 
zinc sulphate into young carpels of difibrent plants. From the seeds 
of a plant of Rcdmannia odorata the carpels of which had been thus 
treated he obtained several plants distinguished fi-om the parent- 
forms by the absence of hairs and by distinct forms of leaves. 
Further examination showed that he had here to do with a new ele- 
mentary species. MacDougal also obtained a more or less distinct 
mutant of Oenothera biemiis. We cannot as yet form an opinion as 
to how far the effect is due to the wound or to the injection of fluid 
as such, or to its chemical properties. This, however, is not so 
essential as to decide whether the mutant stands in any relation 
to the influence of external factors. It is at any rate very 
important that this kind of investigation should be carried further. 

If it could be shown that new and inherited races were ob- 
tained by MacDougal's method, it would be safe to conclude that the 
same end might be gained by altering the conditions of the food-stuff" 
conducted to the sexual cells. New races or elementary species, how- 
ever, arise without wounding or injection. Tliis at once raises the much 
discussed question, how far garden-cultivation has led to the creation 
of new races ? Contrary to the opinion expressed by Darwin and 

^ Blaringhem, Mutation et Traumatisme, Paris, 1907. 

" MacDou^j'al, " Heredity and Origin of species," Monist, 1906; " Report of department of 
botanical research," Fifth Year-book of the Carnegie Institution of Washington, p. 119, 1907. 

Effect of Cultivation 245 

others, de Vries^ tried to show that g^ardeii-races have been produced 
only from spontaneous types which occur in a Avild state or from 
sub-races, which the breeder has accidentally discovered but not 
originated. In a small number of cases only has de Vries adduced 
definite proof. On the other side we have the work of Korschinsky^ 
which shoAvs that whole series of garden-races have made their 
appearance only after years of cultivation. In the majority of races 
Ave are entirely ignorant of their origin. 

It is, hoAvever, a fact that if a plant is removed from natural 
conditions into cultivation, a Avell-marked variation occurs. The 
well-knoAvn plant-breeder, L. de Vilmorin^, speaking from his OAvn 
experience, states that a plant is induced to "aiFoler," that is to 
exhibit all possible variations from Avhich the breeder may make a 
further selection only after cultivation for several generations. The 
effect of cultivation was particularly striking in Veronica chamaedrys^ 
Avhich, in spite of its wide distribution in nature, varies very little. 
After a fcAv years of cultivation this "good" and constant species 
becomes highly variable. The specimens on which the experiments 
were made were three modified inflorescence cuttings, the parent- 
plants of Avhich certainly exhibited no striking abnormalities. In a 
short time many hitherto latent potentialities became apparent, so 
that characters, never previously observed, or at least very rarely, 
were exhibited, such as scattered leaf-arrangement, torsion, terminal 
or branched inflorescences, the conversion of the inflorescence into 
foliage-shoots, every conceivable alteration in the colour of flowers, 
the assumption of a green colour by parts of the floAvers, the 
proliferation of floAvers. 

All this points to some disturbance in the species resulting from 
methods of cultivation. It has, hoAvever, not yet been possible to pro- 
duce constant races with any one of these modified characters. But 
variations appeared among the seedlings, some of which, e.g. yelloAV 
variegation, Avere not inheritable, Avhile others have proved constant. 
This holds good, so far as we know at present, for a small rose-coloured 
form Avhich is to be reckoned as a mutation. Thus the prospect of 
producing neAv races by cultivation appears to be full of promise. 

So long as the vieAv is held that good nourishment, i.e. a plentiful 
supply of Avater and salts, constitutes the essential characteristic of 
garden-cultivation, Ave can hardly conceive that new mutations can 
be thus produced. But perhaps the view here put forAvard in regard 
to the production of form throAvs ncAv light on this puzzling problem. 

^ Mutationstheorie, Vol. i. pp. 412 et scq. 

2 Koischiusky, " Heterogenesis und Evolution," Flora, 1901. 

^ L. de Vilmorin, Notices sur Vamelioration des ]>I<intcs, Paris, 1686, p. 30. 

* Elebe, KUnctUche Metamorphosen, Stuttgart, 190C, p. 152. 

246 Influence of Environment on Plants 

Good manuring is in the highest degree favourable to vegetative 
growth, but is in no way equally favourable to the formation of 
flowers. The constantly repeated expression, good or favourable 
nourishment, is not only vague but misleading, because circum- 
stances favourable to gi-owth differ from those which promote repro- 
duction ; for the production of every form there are certain favourable 
conditions of nourishment, which may be defined for each species. 
Experience shows that, within definite and often very wide limits, it 
does not depend upon the absolute amount of the various food sub- 
stances, but upon their respective degrees of concentration. As we 
have already stated, the production of flowers follows a relative 
increase in the amount of carbohydrates formed in the presence of 
light, as compared with the inorganic salts on which the formation of 
albuminous substances depends^ The various modifications of flowers 
are due to the fact that a relatively too strong solution of salts is 
supplied to the rudiments of these organs. As a general rule every 
plant form depends upon a certain relation between the different 
chemical substances in the cells and is modified by an alteration of 
that relation. 

During long cultivation under conditions which vary in very 
different degrees, such as moisture, the amount of salts, light in- 
tensity, temperature, oxygen, it is possible that sudden and special 
disturbances in the relations of the cell substances have a directive 
influence on the inner organisation of the sexual cells, so that not 
only inconstant but also constant varieties will be formed. 

Definite proof in support of this view has not yet been furnished, 
and we must admit that the question as to the cause of heredity 
remains, fundamentally, as far from solution as it was in Darwin's 
time. As the result of the work of many investigators, particularly 
de Vries, the problem is constantly becoming clearer and more 
definite. Tlie penetration into this most difficult and therefore 
most interesting problem of life and the creation by experiment 
of new races or elementary species are no longer beyond the region 
of possibility. 

^ Klebs, Kiiimliche Metamorphose n, p. H7t 



By Jacques Loeb, M.D. 

Professor of Physiology in the University of California, 

I. Introductory Remarks. 

"What the biologist calls the natural environment of an animal is 
from a physical point of view a rather rigid combination of definite 
forces. It is obvious that by a purposeful and systematic variation 
of these and by the application of other forces in the laboratory, re- 
sults must be obtainable which do not appear in the natural environ- 
ment. This is the reasoning underlying the modern development 
of the study of the efiects of environment upon animal life. It was 
perhaps not the least important of Darwin's services to science that 
the boldness of his conceptions gave to the experimental biologist 
courage to enter upon the attempt of controlling at will the life- 
phenomena of animals, and of bringing about effects which cannot 
be expected in Nature. 

The systematic physico-chemical analysis of the effect of outside 
forces upon the form and reactions of animals is also our only means 
of unravelling the mechanism of heredity beyond the scope of the 
Mendelian law. The manner in which a germ-cell can force upon 
the adult certain characters will not be understood until we succeed 
in varying and controlling hereditary characteristics ; and this can 
only be accomplished on the basis of a systematic study of the effects 
of chemical and physical forces upon living matter. 

Owing to limitation of space this sketch is necessarily very in- 
complete, and it must not be inferred that studies which are not 
mentioned here were considered to be of minor importance. All the 
writer could hope to do was to bring together a few instances of the 
experimental analysis of the effect of environment, which indicate the 
nature and extent of our control over life-phenomena and which also 
have some relation to the work of Darwin. In the selection of these 
instances preference is given to those problems which are not too 
technical for the general reader. 

248 Influence of environment on animals 

The forces, the influence of which Ave shall discuss, are in succession 
chemical agencies, temperature, light, and gravitation. We shall also 
treat separately the eflfect of these forces upon form and instinctive 

II. The Effects of Chemical Agencies. 

{a) Heterogeneous hybridisation. 

It was held until recently that hybridisation is not possible except 
between closely related species and that even among these a successful 
hybridisation cannot always be counted upon. This view was well 
supported by experience. It is, for instance, well known that the 
majority of marine animals lay their unfertilised eggs in the ocean 
and that the males shed their sperm also into the sea-water. The 
numerical excess of the spermatozoa over the ova in the sea-water 
is the only guarantee that the eggs are fertilised, for the sper- 
matozoa are carried to the eggs by chance and are not attracted 
by the latter. Tliis statement is the result of numerous experi- 
ments by various authors, and is contrary to common belief. 
As a rule all or the majority of individuals of a species in a given 
region spawn on the same day, and when this occurs the sea- water 
constitutes a veritable suspension of sperm. It has been shown by 
experiment that in fresh sea- water the sperm may live and retain its 
fertilising power for several days. It is thus unavoidable that at 
certain periods more than one kind of spermatozoon is suspended in 
the sea- water and it is a matter of surprise that the most heterogeneous 
hybridisations do not constantly occur. The reason of this becomes 
obvious if we bring together mature eggs and equally matm-e and 
active sperm of a dilFerent family. When this is done no egg is, as 
a rule, fertilised. The eggs of a sea-urchin can be fertilised by sperm 
of their own species, or, though in smaller numbers, by the sperm of 
other species of sea-urchins, but not by the sperm of other groups of 
echinoderms, e.g. starfish, brittle-stars, holothurians or crinoids, and 
still less by the sperm of more distant groups of animals. The 
consensus of opinion seemed to be that the spermatozoon must enter 
the egg through a narrow opening or canal, the so-called micropyle, 
and that the micropyle allowed only the spermatozoa of the same or 
of a closely related species to enter the egg. 

It seemed to the writer that the cause of this limitation of 
hybridisation might be of another kind and that by a change in the 
constitution of the sea-water it might be possible to bring about 
heterogeneous hybridisations, Avhich in normal sea-Avater are im- 
possible, lliis assumption proved correct. Sea-Avater has a faintly 
alkaline reaction (in terms of the physical chemist its concentration 

Heterogeneous hyhridisation 249 

of hydroxy! ions is about \0~^N at Pacific Grove, California, and 
about 10"^-^ at Woods Hole, Massachusetts). If we slightly raise 
the alkalinity of the sea-water by adding to it a small but definite 
quantity of sodium hydroxide or some other alkali, the eggs of the 
sea-urchin can be fertilised with the sperm of widely different gi'oups 
of animals, possibly with the sperm of any marine animal which sheds 
it into the ocean. In 1903 it was shown that if we add from about 
0'5 to 0*8 cubic centimetre NjlO sodium hydroxide to 50 cubic 
centimetres of sea- water, the eggs of Strongylocentrotus 2^ur2mratus 
(a sea-urchin which is found on the coast of California) can be 
fertilised in large quantities by the sperm of various kinds of starfish, 
brittle-stars and holothurians ; while in normal sea-water or >vith 
less sodium hydroxide not a single egg of the same female could be 
fertilised with the starfish sperm which proved effective in the 
hyper-alkaline sea- water. The sperm of the various forms of starfish 
was not equally effective for these hybridisations ; the sperm of 
Aster ias ochracea and A. ccqntata gave the best results, since it was 
possible to fertilise 50 7o or more of the sea-urchin eggs, while the 
sperm of Pycnopodia and Asterina fertilised only 2 °/„ of the same 

Godlewski used the same method for the hybridisation of the sea- 
urchin eggs with the sperm of a crinoid {Antedon rosacea). Kupel- 
wieser afterwards obtained results which seemed to indicate the 
possibility of fertilising the eggs of Strongylocentrotus with the 
sperm of a mollusc (Mytilus). Recently, the writer succeeded in 
fertilising the eggs of Strongylocentrotus franciscamis with the 
sperm of a mollusc — Chlorostoma. This result could only be obtained 
in sea-water the alkalinity of which had been increased (through the 
addition of 0*8 cubic centimetre NjlO sodium hydroxide to 50 cubic 
centimetres of sea-water). We thus see that by increasing the 
alkalinity of the sea-water it is possible to effect heterogeneous 
hybridisations which are at present impossible in the natural en- 
vironment of these animals. 

It is, however, conceivable that in foraier periods of the earth's 
history such heterogeneous hybridisations were possible. It is known 
that in solutions like sea-water the degree of alkalinity must in- 
crease when the amount of carbon-dioxide in the atmosphere is 
<liminished. If it be true, as Arrhenius assumes, that the Ice age 
was caused or preceded by a diminution in the amount of carbon- 
dioxide in the air, such a diminution must also have resulted in an 
increase of the alkalinity of the sea-water, and one result of such an 
increase must have been to render possible heterogeneous hybridi- 
sations in the ocean which in the present state of alkalinity are 
practically excluded. 

250 Influence of environment on animals 

But granted that such hybricHsations were possible, would they 
have influenced the character of the fauna ? In other words, are the 
hybrids between sea-urchin and starfish, or better still, between 
sea-urchin and mollusc, capable of development, and if so, what is 
their character? The first experiment made it appear doubtful 
whether these heterogeneous hybrids could live. The sea-urchin 
eggs which were fertilised in the laboratory by the spermatozoa of 
the starfish, as a rule, died earlier than those of the pure breeds. 
But more recent results indicate that this was due merely to 
deficiencies in the technique of the earlier experiments. The writer 
has recently obtained hybrid larvae between the sea-urchin eg^ and 
the sperm of a mollusc (Chlorostoma) which, in the laboratory, 
developed as well and lived as long as the pure breeds of the sea- 
urchin, and there was nothing to indicate any difierence in the 
vitality of the two breeds. 

So far as the question of heredity is concerned, all the experi- 
ments on heterogeneous hybridisation of the e^g of the sea-urchin 
with the sperm of starfish, brittle-stars, crinoids and molluscs, have 
led to the same result, namely, thart the larvae have purely maternal 
characteristics and difier in no way from the pure breed of the form 
from which the egg is taken. By way of illustration it may be said 
that the larvae of the sea-urchin reach on the third day or earlier 
(according to species and temperature) the so-called pluteus stage, in 
which they possess a typical skeleton ; while neither the larvae of 
the starfish nor those of the mollusc form a skeleton at the corre- 
sponding stage. It was, therefore, a matter of some interest to find 
out whether or not the larvae produced by the fertilisation of the 
sea-urchin egg with the sperm of starfish or mollusc would form the 
normal and typical pluteus skeleton. This was invariably the case 
in the experiments of Godlewski, Kupelwieser, Hagedoorn, and the 
writer. These hybrid larvae were exclusively maternal in character. 

It might be argued that in the case of heterogeneous hybridisa- 
tion the sperm-nucleus does not fuse with the egg-nucleus, and that, 
therefore, the spermatozoon cannot transmit its hereditary substances 
to the larvae. But these objections are refuted by Godlewski's 
experiments, in which he showed definitely that if the egg of the 
sea-urchin is fertilised with the sperm of a crinoid the fusion of the 
egg-nucleus and sperm-nucleus takes place in the normal way. It 
remains for further experiments to decide what the character of the 
adult hybrids would be. 

(6) Artijicial Parthenogenesis. 

Possibly in no other field of Biology has our ability to control 
life-phenomena by outside conditions been proved to such an extent 

Artificial Parthenogenesis 251 

as in the domain of fertilisation. The reader knows that the eggs of 
the overM'helming majority of animals cannot develop unless a 
spermatozoon enters them. In this case a living agency is the cause 
of development and the problem arises whether it is possible to 
accomplish the same result through the application of well-kno^vn 
physico-chemical agencies. This is, indeed, true, and during the last 
ten years living larvae have been produced by chemical agencies 
from the unfertilised eggs of sea-urchins, starfish, holothurians and 
a number of annelids and molluscs ; in fact this holds true in regard 
to the eggs of practically all forms of animals with which such 
experiments have been tried long enough. In each form the method 
of procedure is somewhat dilTerent and a long series of experiments 
is often required before the successful method is found. 

The facts of Artificial Parthenogenesis, as the chemical fertilisa- 
tion of the egg is called, have, perhaps, some bearing on the problem 
of evolution. If we wish to form a mental image of the process of 
evolution we have to reckon with the possibility that parthenogenetic 
propagation may have preceded sexual reproduction. This suggests 
also the possibility that at that period outside forces may have 
supplied the conditions for the development of the egg which at 
present the spermatozoon has to supply. For this, if for no other 
reason, a brief consideration of the means of artificial partheno- 
genesis may be of interest to the student of evolution. 

It seemed necessary in these experiments to imitate as completely 
as possible by chemical agencies the eflfects of the spermatozoon upon 
the egg. When a spermatozoon enters the egg of a sea-urchin or 
certain starfish or annelids, the immediate efibct is a characteristic 
change of the surface of the egg, namely the formation of the so-called 
membrane of fertilisation. The writer found that we can produce 
this membrane in the unfertilised egg by certain acids, especially the 
monobasic acids of the fatty series, e.g. formic, acetic, propionic, 
butyric, etc. Carbon-dioxide is also very efficient in this direction. 
It was also found that the higher acids are more efficient than 
the lower ones, and it is possible that the spermatozoon induces 
membrane-formation by carrying into the egg a higher fatty acid, 
namely oleic acid or one of its salts or esters. 

The physico-chemical process which underlies the formation of 
the membrane seems to be the cause of the development of the egg. 
In all cases in which the unfertilised egg has been treated in such a 
way as to cause it to form a membrane it begins to develop. For 
the eggs of certain animals membrane-formation is all that is 
re<iuired to induce a complete development of the unfertilised egg, 
e.g. in the sttirfish and certain annelids. For the eggs of other 
animals a second treatment is necessary, presumably to overcome 

252 Tiifluence of environment on animals 

some of the injurious effects of acid treatment. Thus the unfertilised 
eggs of the sea-urchin Strongylocentrofus purpuratus of the Californian 
coast begin to develop when m.embrane-formation has been induced 
by treatment with a fatty acid, e.g. butyric acid ; but the develop- 
ment soon ceases and the eggs perish in the early stages of segmen- 
tation, or after the first nuclear division. But if we treat the same 
eggs, after membrane-formation, for from 35 to 55 minutes (at 15° C.) 
with sea-water the concentration (osmotic pressure) of which has 
been raised through the addition of a definite amount of some salt or 
sugar, the eggs will segment and develop normally, when transferred 
back to normal sea- water. If care is taken, practically all the eggs 
can be caused to develop into plutei, the majority of which may be 
perfectly normal and may live as long as larvae produced from eggs 
fertilised with sperm. 

It is obvious that the sea-urchin egg is injured in the process of 
membrane-formation and that the subsequent treatment with a 
hypertonic solution only acts as a remedy. The nature of this 
injury became clear Avhen it was discovered that all the agencies 
which cause haemolysis, i.e. the destruction of the red blood 
corpuscles, also cause membrane-formation in unfertilised eggs, e.g. 
fatty acids or ether, alcohols or chloroform, etc., or saponin, solanin, 
digitalin, bile salts and alkali. It thus happens that the phenomena 
of artificial parthenogenesis are linked together with the phenomena 
of haemolysis which at present play so important a role in the study 
of immunity. The difference between cytolysis (or haemolysis) and 
fertilisation seems to be this, that the latter is caused by a superficial 
or slight cytolysis of the egg, while if the cytolytic agencies have 
time to act on the whole egg the latter is completely destroyed. If 
we put unfertilised eggs of a sea-urchin into sea- water Avhich contains 
a trace of saponin we notice that, after a few minutes, all the eggs 
form the typical membrane of fertilisation. If the eggs are then 
taken out of the saponin solution, freed from all traces of saponin 
by repeated washing in normal sea-water, and transferred to the 
hypertonic sea-water for from 35 to 55 minutes, they develop into 
larvae. If, hovrever, they are left in the sea-water containing the 
saponin they undergo, a few minutes after membrane-formation, the 
disintegration known in pathology as cytolysis. JNIembrane-formation 
is, therefore, caused by a superficial or incomplete cytolysis. The 
writer believes that the subsequent treatment of the egg "wdth 
hypertonic sea-water is needed only to overcome the destructive 
effects of this partial cytolysis. Tlie full reasons for this belief 
cannot be given in a short essay. 

]\Iany pathologists assume that haemolysis or cytolysis is due to 
a liquefaction of certain fatty or fat-like con)pounds, the so-called 

Action of blood on eggs 253 

lipoids, in the cell. If this view is correct, it would be necessary to 
ascribe the fertilisation of the egg to the same process. 

The analogy between haemolysis and fertilisation throws, 
possibly, some light on a curious observation. It is well known 
that the blood corpuscles, as a rule, undergo cytolysis if injected 
into the blood of an animal which belongs to a different family. 
The writer found last year that the blood of mammals, e.g. the 
rabbit, pig, and cattle, causes the egg of Strongylocentrotus to 
form a typical fertilisation-membrane. If such eggs are afterwards 
treated for a short period with hypertonic sea-water they develop 
into normal larvae (plutei). Some substance contained in the 
blood causes, presumably, a superficial cytolysis of the egg and 
thus starts its development. 

We can also cause the development of the sea-urchin egg without 
membrane-formation. The early experiments of the writer were 
done in this way and many experimenters still use such methods. It 
is probable that in this case the mechanism of fertilisation is essen- 
tially the same as in the case where the membrane-formation is 
brought about, with this difference only, that the cytolytic effect is 
less when no fertilisation-membrane is formed. This inference is 
corroborated by observations on the fertilisation of the sea-urchin 
egg with ox blood. It very frequently happens that not all of the 
eggs form membranes in this process. Those eggs which form 
membranes begin to develop, but perish if they are not treated with 
hypertonic sea-water. Some of the other eggs, however, which do 
not form membranes, develop directly into normal larvae without any 
treatment with hypertonic sea-water, provided they are exposed to 
the blood for only a few minutes. Presumably some blood enters the 
eggs and causes the cytolytic effects in a less degree than is necessary 
for membrane-formation, but in a sufficient degree to cause their 
development. The slightness of the cytolytic efiect allows the egg to 
develop without treatment with hypertonic sea-water. 

Since the entrance of the spermatozoon causes that degree of 
cytolysis which leads to membrane-formation, it is probable that, 
in addition to the cytolytic or membrane-forming substance (pre- 
sumably a higher fatty acid), it carries another substance into the 
egg which counteracts the deleterious cytolytic effects underlying 

The question may be raised whether the larvae produced by 
artificial parthenogenesis can reach the mature stage. This question 
may be answered in the affirmative, since Delage has succeeded in 
raising several parthcnogenetic sea-urchin larvae beyond the meta- 
morphosis into the adult stage and since in all the experiments made 
by the writer the ])artlienogcneLic plutei lived as long as the plutei 
produced from fertilised eggs. 

254 Influence of environment on animals 

(c) On the jn'oduction of twins from one egg through a change 
in the chemical constitution of the sea-water. 

The reader is probably familiar with the fact that there exist two 
diflferent types of human twins. In the one type the twins differ as 
much as two children of the same parents born at different periods ; 
they may or may not have the same sex. In the second type the 
tmns have invariably the same sex and resemble each other most 
closely. Twins of the latter type are produced from the same egg, 
while twins of the former type are produced fi-om two different eggs. 

The experiments of Driesch and others have taught us that twins 
originate from one egg in this manner, namely, that the first two cells 
into which the egg divides after fertilisation become separated from 
each other. This separation can be brought about by a change in the 
chemical constitution of the sea- water. Herbst observed that if the 
fertilised eggs of the sea-urchin are put into sea- water which is freed 
from calcium, the cells into which the eg'g divides have a tendency 
to fall apart. Driesch afterwards noticed that eggs of the sea-urchin 
treated with sea-water which is free from lime have a tendency to give 
rise to twins. The writer has recently found that twins can be pro- 
duced not only by the absence of lime, but also through the absence of 
sodium or of potassium ; in other words, through the absence of one 
or two of the three important metals in the sea-water. There is, how- 
ever, a second condition, namely, that the solution used for the produc- 
tion of twins must have a neutral or at least not an alkaline reaction. 

The procedure for the production of twins in the sea-urchin egg 
consists simply in this: — the eggs are fertilised as usual in normal 
sea-w^ater and then, after repeated washing in a neutral solution of 
sodium chloride (of the concentration of the sea- water), are placed in 
a neutral mixture of potassium chloride and calcium chloride, or of 
sodium chloride and potassium chloride, or of sodium chloride and 
calcium chloride, or of sodium chloride and magnesium chloride. The 
eggs must remain in this solution until half an hour or an hour after 
they have reached the two-cell stage. They are then transferred into 
normal sea- water and allowed to develop. From 50 to 90 7o of the 
eggs of Strongylocentrotus 2)ur2mratiis treated in this manner may 
develop into t\vins. These twins may remain separate or grow 
partially together and form double monsters, or heal together so 
completely that only slight or even no imperfections indicate that the 
individual started its career as a pair of twins. It is also possible to 
control the tendency of such twins to grow together by a change in 
the constitution of the sea-water. If we use as a twin-producing solu- 
tion a mixture of sodium, magnesium and potassium chlorides (in the 
proportion in which these salts exist in the sea-Avater) the tendency of 
the twins to grow together is much more pronounced than if we use 
simply a mixture of sodium chloride and magnesium chloride. 

Origin of twins 255 

Tlie mechanism of the origin of twins, as the result of altering 
the composition of the sea-water, is revealed by observation of the 
first segmentation of the e^g in these solutions. This cell-division is 
modified in a way which leads to a separation of the first two cells. 
If the egg is afterwards transferred back into normal sea-water, each 
of these two cells develops into an independent embryo. Since 
normal sea-water contains all three metals, sodium, calcium, and 
potassium, and since it has besides an alkaline reaction, we perceive 
the reason w^hy twins are not normally produced from one egg. 
These experiments suggest the possibility of a chemical cause for the 
origin of twins fi'om one egg or of double monstrosities in mammals. 
\i, for some reason, the liquids which surround the human egg a 
short time before and after the first cell-division are slightly acid, 
and at the same time lacking in one of the three important metals, 
the conditions for the separation of the first two cells and the forma- 
tion of identical twins are provided. 

In conclusion it may be pointed out that the reverse result, 
namely, the fusion of normally double organs, can also be brought 
about experimentally through a change in the chemical constitution 
of the sea-water. Stockard succeeded in causing the eyes of fish 
embryos {Fundulus heteroclitiis) to fuse into a single cyclopean eye 
through the addition of magnesium chloride to the sea- water. "Wlien 
he added about 6 gi-ams of magnesium chloride to 100 cubic centi- 
metres of sea-water and placed the fertilised eggs in the mixture, 
about 50 7o of the eggs gave rise to one-eyed embryos. "AVlien 
the embryos were studied the one-eyed condition was found to result 
from the union or fusion of the * anlagen ' of the two eyes. Cases 
were observed which showed various degrees in this fusion ; it 
appeared as though the optic vessels were formed too far forward 
and ventral, so that their antero-ventro-median surfaces fused. This 
produces one large optic cup, which in all cases gives more or less 
evidence of its double nature \" 

We have confined ourselves to a discussion of rather simple 
efiects of the change in the constitution of the sea-water upon de- 
velopment. It is a priori obvious, however, that an unlimited 
number of pathological variations might be produced by a variation 
in the concentration and constitution of the sea-water, and experience 
confirms this statement. As an example we may mention the abnor- 
malities observed by Herbst in the development of sea-urchins through 
the addition of lithium to sea-water. It is, however, as yet impossible 
to connect in a rational way the effects produced in this and similar 
cases witli the cause which produced them ; and it is also impossible 
to define in a simple way the character of the change produced. 

1 stockard, Archiv /. Entwickelungsmeclianik, Vol. 23, p. 249, 1907. 

256 Influence of environment on animals 

III. The Influence of Temperature. 

{a) The influence of temperature upon the density of pelagic 
organisms and the dui'ation of life. 

It has often been noticed by explorers who have had a chance to 
compare the faunas in different climates that in polar seas such 
species as thrive at all in those regions occur, as a rule, in much 
greater density than they do in the moderate or warmer regions 
of the ocean. This refers to those members of the fauna which live 
at or near the surface, since they alone lend themselves to a 
statistical comparison. In his account of the Valdivia expedition, 
Chun^ calls especial attention to this quantitative difference in the 
surface fauna and flora of different regions. "In the icy water of 
the Antarctic, the temperature of which is below 0° C, we find an 
astonishingly rich animal and plant life. The same condition with 
Avhich we are familiar in the Arctic seas is repeated here, namely, that 
the quantity of plankton material exceeds that of the temperate and 
warm seas." And again, in regard to the pelagic fauna in the region 
of the Kerguelen Islands, he states: "The ocean is alive with 
transparent jelly fish, Ctenophores (Bolina and Callianira) and of 
Siphonophore colonies of the genus Agalma.' 

The paradoxical character of this general observation lies in the 
fact that a low temperature retards development, and hence should 
be expected to have the opposite effect from that mentioned by 
Chun. Recent investigations have led to the result that life-pheno- 
mena are affected by temperature in the same sense as the velocity 
of chemical reactions. In the case of the latter van't Hoff had 
shown that a decrease in temperature by 10 degrees reduces their 
velocity to one half or less, and the same has been found for the 
influence of temperature on the velocity of physiological processes. 
Thus Snyder and T. B. Robertson found that the rate of heartbeat in 
the tortoise and in Daphnia is reduced to about one-half if the 
temperature is lowered 10° C, and Maxwell, Keith Lucas, and 
Snyder found the same influence of temperature for the rate ^vith 
which an impulse travels in the nerve. Peter observed that the 
rate of development in a sea-urchin's egg is reduced to less than one- 
half if the temperature (within certain limits) is reduced by 10 
degrees. The same efiect of temperature upon the rate of develop- 
ment holds for the egg of the frog, as Cohen and Peter calculated 
from the experiments of 0. Hertwig. Tlie writer found the same 
tenipcrature-coeflicient for the rate of maturation of the e^g of a 
mollusc (Lottia). 

'I Chun, Aui den Tie/en des Weltmeeres, p. 225, Jena, 1903. 

Duration of life 257 

All these facts prove that the velocity of development of animal 
life in Arctic regions, where the temperature is near the freezing 
point of water, must be from two to three times smaller than in 
regions where the temperature of the ocean is about 10° C. and fi'om 
four to nine times smaller than in seas the temperature of which 
is about 20° C. It is, therefore, exactly the reverse of what we 
should expect when authors state that the density of organisms at or 
near the surface of the ocean in polar regions is greater than in more 
temperate regions. 

The writer believes that this paradox finds its explanation in 
experiments which he has recently made on the influence of tempera- 
ture on the duration of life of cold-blooded marine animals. The 
experiments were made on the fertilised and unfertilised eggs of the 
sea-urchin, and yielded the result that for the lowering of tempera- 
ture by 1° C the duration of life was about doubled. Lowering the 
temperature by 10 degrees therefore prolongs the life of the organism 
2^°, i.e. over a thousand times, and a lowering by 20 degrees pro- 
longs it about one million times. Since this prolongation of life 
is far in excess of the retardation of development through a lowering 
of temperature, it is obvious that, in spite of the retardation of 
development in Arctic seas, animal life must be denser there than in 
temperate or tropical seas. The excessive increase of the duration of 
life at the poles will necessitate the simultaneous existence of more 
successive generations of the same species in these regions than in 
the temperate or tropical regions. 

The writer is inclined to believe that these results have some 
bearing upon a problem which plays an important role in theories of 
evolution, namely, the cause of natural death. It has been stated 
that the processes of differentiation and development lead also to the 
natural death of the individual. If we express this in chemical 
terms it means that the chemical processes which underlie develop- 
ment also determine natural death. Physical chemistry has taught 
us to identify two chemical processes even if only certain of their 
features are known. One of these means of identification is the 
tenipcrature coefficient. When two chemical processes are identical, 
their velocity nmst be reduced by the same amount if the tempera- 
ture is lowered to the same extent. The temperature coefficient for 
the duration of life of cold-blooded organisms seems, however, to 
differ enormously from the temperature coefficient for their rate of 
development. For a difference in temperature of 10° C. the duration 
of life is altered five hundred times as much as the rate of develop- 
ment ; and, for a change of 20° C, it is altered more than a hundred 
thousand times as much. From this we may conclude that, at least 
for the sea-urchin eggs and embryo, the chemical processes which 

p. 17 


Influence of environment on animals 

determine natural death are certainly not identical with the pro- 
cesses which underlie their development. T. B. Robertson has also 
arrived at the conclusion, for quite different reasons, that the process 
of senile decay is essentially different from that of growth and 

(b) Changes in the colour of butterflies produced through the 
influence of temperature. 

The experiments of Dorfmeister, Weismann, Merrifield, Standfuss, 
and Fischer, on seasonal dimorphism and the aberration of colour in 
butterflies have so often been discussed in biological literature that 
a short reference to them will suffice. By seasonal dimorphism is 
meant the fact that species may appear at different seasons of the 
year in a somewhat different form or colour. Vanessa prorsa is the 
summer form, Vanessa levana the winter form of the same species. 
By keeping the pupae of Va^iessa prorsa several weeks at a tempera- 
ture of from 0° to 1° Weismann succeeded in obtaining from the 
summer chrysalids specimens which resembled the winter variety, 
Vanessa levana. 

If we wish to get a clear understanding of the causes of variation 
in the colour and pattern of butterflies, we must direct our attention 
to the experiments of Fischer, who worked Avith more extreme 
temperatures than his predecessors, and found that almost identical 
aberrations of colour could be produced by both extremely high and 
extremely low temperatures. This can be clearly seen from the 
following tabulated results of his observations. At the head of each 
column the reader finds the temperature to which Fischer submitted 
the pupae, and in the vertical column below are found the varieties 
that were produced. In the vertical column A are given the normal 
forms : 

0° to - 20° C. 

0° to + 10° C. 



+ 35° to 
+ 37° C. 

+ 3G° to 
+ 41°C. 

+ 42° to 
+ 46° C. 













































Effect of temperature on development 259 

The reader will notice that the aberrations produced at a very 
low temperature (from 0° to — 20° C.) are absolutely identical with 
the aberrations produced by exposing the pupae to extremely high 
temperatures (42° to 46° C). Moreover the aberrations produced l3y 
a moderately low temperature (from 0° to 10° C.) are identical with 
the aberrations produced by a moderately high temperature (36 ^' to 
41° C). 

From these observations Fischer concludes that it is erroneous to 
speak of a specific effect of high and of low temperatures, but that 
there must be a common cause for the aberration found at the high 
as well as at the low temperature limits. This cause he seems to find 
in the inhibiting effects of extreme temperatures upon development. 

If we try to analyse such results as Fischer's from a physico- 
chemical point of view, we must realise that what we call life consists 
of a series of chemical reactions, which are connected in a catenary 
way ; inasmuch as one reaction or group of reactions (a) (e.g. hydro- 
lyses) causes or furnishes the material for a second reaction or group 
of reactions (6) (e.g. oxydations). We know that the temperature 
coeflficient for physiological processes varies slightly at various parts 
of the scale ; as a rule it is higher near 0° and louver near 30°. 
But we know also that the temperature coefficients do not vary 
equally for the various physiological processes. It is, therefore, to be 
expected that the temperature coefficients for the group of reactions 
of the type {a) will not be identical through the whole scale with 
the temperature coefficients for the reactions of the type (6). If 
therefore a certain substance is formed at the normal temperature 
of the animal in such quantities as are needed for the catenary 
reaction (b\ it is not to be expected that this same perfect balance 
will be maintained for extremely high or extremely low tempera- 
tures ; it is more probable that one group of reactions will exceed 
the other and thus produce aberrant chemical effects, which may 
underlie the colour aberrations observed by Fischer and other 

It is important to notice that Fischer was also able to produce 
aberrations tln-ough the application of narcotics. Wolfgang Ostwald 
has produced experimentally, through variation of temperature, 
diinoipliism of form in Daphnia. Lack of space precludes an account 
of these important experiments, as of so many others. 

IV. The Effects of Light. 

At the present day nobody seriously questions the statement that 
the action of light upon organisms is primarily one of a chemical 
character. While this chemical action is of the utmost importance 


260 Influence of environment on animals 

for oi'ganisms, the nutrition of which depends upon the action of 
chlorophyll, it becomes of less importance for organisms devoid of 
chloroi^hyll. Nevertheless, we find animals in which the formation of 
organs by regeneration is not possible unless they are exposed to 
light. An observation made by the writer on the regeneration of 
polyps in a hydroid, Eudendrium racemosum, at Woods Hole, may 
be mentioned as an instance of this. If the stem of this hydroid, 
which is usually covered with polyps, is put into an aquarium the 
polyps soon fall ofl*. If the stems are kept in an aquarium where 
light strikes them during the day, a regeneration of numerous polyps 
takes place in a few days. If, however, the stems of Eudendrium are 
kept permanently in the dark, no polyps are formed even after an 
interval of some weeks ; but they are formed in a few days after the 
same stems have been transferred from the dark to the light. Diffused 
daylight suffices for this effect. Goldfarb, who repeated these experi- 
ments, states that an exposure of comparatively short duration is 
sufficient for this effect. It is possible that the light favours the 
formation of substances which are a prerequisite for the origin of 
polyps and their growth. 

Of much greater significance than this observation are the facts 
which show that a large number of animals assume, to some extent, 
the colour of the ground on which they are placed. Pouchet found 
through experiments upon crustaceans and fish that this influence of 
the ground on the colour of animals is produced through the medium 
of the eyes. If the eyes are removed or the animals made blind 
in another way these phenomena cease. The second general fact 
found by Pouchet was that the variation in the colour of the animal 
is brought about through an action of the nerves on the pigment-cells 
of the skin ; the nerve-action being induced through the agency of the 

The mechanism and the conditions for the change in colouration 
were made clear through the beautiful investigations of Keeble and 
Gamble, on the colour-change in crustaceans. According to these 
authors the pigment-cells can, as a rule, be considered as consisting of 
a central body from which a system of more or less complicated rami- 
fications or processes spreatls out in all directions. As a rule, the 
centre of the cell contains one or more different pigments which under 
the influence of nerves can spread out separately or together into the 
ramifications. These phenomena of spreading and retraction of the 
pigments into or from the ramifications of the pigment-cells form 
on the whole the basis for the colour changes under the influence 
of environment. Thus Keeble and Gamble observed that Macromysis 
Jlexuosa appears transparent and colourless or grey on sandy ground. 
On a dark ground their colour becomes darker. These animals have 

Effect of colour 261 

two pigments in their chromatophores, a brown pigment and a whitish 
or yellow pigment ; the former is much more plentiful than the latter. 
\Vhen the animal appears transparent all the pigment is contained in 
the centre of the cells, while the ramifications are free from pigment. 
When the animal appears brown both pigments are spread out into 
the ramifications. In the condition of maximal spreading the animals 
appear black. 

This is a comparatively simple case. Much more complicated 
conditions were found by Keeble and Gamble in other crustaceans, 
e.g. in Hippolyte cranchii, but the influence of the surroundings upon 
the colouration of this form was also satisfactorily analysed by these 

While many animals show transitory changes in colour under the 
influence of their surroundings, in a few cases permanent changes can 
be produced. The best examples of this are those which were 
observed by Poulton in the chrysalids of various butterflies, especially 
the small tortoise-shell. These experiments are so well known that a 
short reference to them will suffice. Poulton^ found that in gilt 
or white surroundings the pupae became light coloured and there 
Mas often an immense development of the golden spots, "so that in 
many cases the whole surface of the pupae glittered with an apparent 
metallic lustre. So remarkable was the appearance that a physicist 
to whom I showed the chrysalids, suggested that I had played a trick 
and had covered them with goldleaf." When black surroundings 
were used "the pupae were as a rule extremely dark, with only the 
smallest trace, and often no trace at all, of the golden spots which are 
so conspicuous in the lighter form." The susceptibility of the animal 
to this influence of its surroundings was found to be greatest during 
a definite period when the caterpillar undergoes the metamorphosis 
into the chrysalis stage. As far as the writer is aware, no physico- 
chemical explanation, except possibly Wiener's suggestion of colour- 
photography by mechanical colour adaptation, has ever been offered 
for the results of the type of those observed by Poulton. 

V. Effects of Gravitation 

(a) Experiments on the egg of the frog. 

Gravitation can only indirectly affect life-phenomena ; namely, 
when we have in a cell two different non-miscible liquids (or a liipiid 
and a solid) of different specific gravity, so that a change in the 
position of the cell or the organ may give results which can be traced 
to a change in the position of the two substances. This is very nicely 

» Poulton, E. B., Colours oj Animals (The International Scientific Series), London, 
1890, p. 121. 

262 Influence of environment on animals 

illustrated by tlic frog's egg, which has two layers of very viscous 
protoplasm one of which is black and one white. The dark one 
occupies normally the upper position in the egg and may therefore be 
assumed to possess a smaller specific gravity than the white substance. 
When the egg is turned with the white pole upwards a tendency 
of the white protoplasm to flow down again manifests itself. It is, 
however, possible to prevent or retard this rotation of the highly 
viscous protoplasm, by compressing the eggs between horizontal 
glass plates. Such compression experiments may lead to rather 
interesting results, as 0. Schultze first pointed out. Pflueger had 
already shown that the first plane of division in a fertilised frog's 
egg is vertical and Roux established the fact that the first plane 
of division is identical with the plane of symmetry of the later embryo. 
Schultze found that if the frog's egg is turned upside down at the 
time of its first division and kept in this abnormal position, through 
compression between two glass plates for about 20 hours, a small 
number of eggs may give rise to twins. It is possible, in this case, 
that the tendency of the black part of the egg to rotate upwards 
along the surface of the egg leads to a separation of its first cells, 
Bucli a separation leading to the formation of twins. 

T. H. Morgan made an interesting additional observation. He 
destroyed one half of the egg after the first segmentation and found 
that the half which remained alive gave rise to only one half of an 
embryo, thus confirming an older observation of Roux. Wlien, how- 
ever, Morgan put the egg upside down after the destruction of one of 
the first two cells, and compressed the eggs between two glass plates, 
the surviving half of the egg gave rise to a perfect embryo of half 
size (and not to a half embryo of normal size as before). Obviously 
in this case the tendency of the protoplasm to flow back to its normal 
position was partially successful and led to a partial or complete 
separation of the living from the dead half ; whereby the former was 
enabled to form a whole embryo, which, of course, possessed only 
half the size of an embryo originating from a whole egg. 

(b) Experiments on hydroids. 

A striking influence of gravitation can be observed in a hydroid, 
Antenmdaria antennina, from the bay of Naples. This hydroid 
consists of a long straight main stem which grows vertically upwards 
and which has at regular intervals very fine and short bristle-like 
lateral branches, on the upper side of which the polyps grow. The 
main stem is negatively geotropic, i.e. its apex continues to grow 
vertically upwards when we put it obliquely into the aquarium, 
while the roots grow vertically downwards. The writer observed 
that when the stem is put horizontally into the water the short 

Instinct-reactions of animals 263 

lateral branches on the lower side give rise to an altogether different 
kind of organ, namely, to roots, and these roots grow indefinitely in 
length and attach themselves to solid bodies ; while if the stem had 
remained in its normal position no further growth would have 
occurred in the lateral branches. From the upper side of the hori- 
zontal stem new stems gi-ow out, mostly directly fi-om the original 
stem, occasionally also fi-om the short lateral branches. It is thus 
possible to force upon this hydroid an arrangement of organs which 
is altogether different from the hereditary arrangement. The writer 
had called the change in the hereditary arrangement of organs or the 
transformation of organs by external forces heteroi7iorpJwsis. We 
cannot now go any further into this subject, which should, however, 
prove of interest in relation to the problem of heredity. 

If it is correct to apply inferences drawn from the observation on 
the frog's egg to the behaviour of Antennularia, one might conclude 
that the cells of Antennularia also contain non-miscible substances of 
different specific gravity, and that wherever the specifically lighter 
substance comes in contact with the sea-water (or gets near the 
surface of the cell) the gi-owth of a stem is favoured ; while contact 
with the sea-water of the specifically heavier of the substances, will 
favour the formation of roots. 

VI. The Experimental Control of Animal Instincts. 

(a) Experiments on the mechanism of heliotrojxic reactions in 

Since the instinctive reactions of animals are as hereditary as 
their morphological character, a discussion of experiments on the 
physico-chemical character of the instinctive reactions of animals 
should not be entirely omitted from this sketch. It is obvious that 
such experiments must begin with the simplest type of instincts, if 
they are expected to lead to any results ; and it is also obvious that 
only such animals must be selected for this purpose, the reactions of 
which are not complicated by associative memory or, as it may 
preferably be termed, associative hysteresis. 

The simplest type of instincts is represented by the purposeful 
motions of animals to or from a source of energy, e.g. light ; and it is 
with some of these that we intend to deal here. When we expose 
winged apliides (after they have flown away from the plant), or 
young caterpillars of Porthesia chri/sorrhoea (when they are aroused 
from their winter sleep) or marine or freshwater copepods and many 
other animals, to diffused dayliglit falling in from a window, we notice 
a tendency among these animals to move towards the source of light. 

264 Influence of environment on animals 

If the animals are naturally sensitive, or if they are rendered sensitive 
through the agencies which we shall mention later, and if the light is 
strong enough, they move towards the source of light in as straight a 
line as the imperfections and peculiarities of their locomotor apparatus 
will permit. It is also obvious that we are here dealing with a forced 
reaction in which the animals have no more choice in tlie direction of 
their motion than have the iron filings in their arrangement in a 
magnetic field. This can be proved very nicely in the case of starving 
caterpillars of Porthesia. The writer put such caterpillars into a 
glass tube the axis of which was at right angles to the plane of the 
window: the caterpillars went to the window side of the tube and 
remained there, even if leaves of their food-plant were put into the 
tube directly behind them. Under such conditions the animals 
actually died from starvation, the light preventing them from turning 
to the food, which they eagerly ate when the light allowed them to 
do so. One cannot say that these animals, which we call positively 
heliotropic, are attracted by the light, since it can be shown that 
they go towards the source of light even if in so doing they move 
fi'om places of a higher to places of a lower degree of illumination. 

The writer has advanced tlie following theory of these instinctive 
reactions. Animals of the type of those mentioned are automatically 
orientated by the light in such a way that symmetrical elements of 
their retina (or skin) are struck by the rays of light at the same 
angle. In this case the intensity of light is the same for both retinae 
or symmetrical parts of the skin. 

This automatic orientation is determined by two factors, first a 
peculiar photo-sensitiveness of the retina (or skin), and second a 
peculiar nervous connection between the retina and the muscular 
apparatus. In symmetrically built heliotropic animals in which the 
symmetrical muscles participate equally in locomotion, the symmetrical 
muscles work with equal energy as long as the photo-chemical pro- 
cesses in both eyes are identical. If, however, one eye is struck by 
stronger light than the other, the symmetrical muscles will work 
unequally ahd in positively heliotropic animals those muscles will 
work with greater energy which bring the plane of symmetry back 
into the direction of the rays of light and the head towards the 
source of light. As soon as both eyes are struck by the rays of light 
at the same angle, there is no more reason for the animal to deviate 
from this direction and it will move in a straight line. All this holds 
good on the supposition that the animals are exposed to only one 
source of light and are very sensitive to light. 

Additional proof for the correctness of this theory was furnished 
through the exj)crimcnts of G. H. Parker and S. J. Holmes. The 
former worked on a butterfly, Vanessa antiojje, the latter on other 

Helioti'opism of animals 265 

arthropods. All the animals were in a marked degree positively 
heliotropic. These authors found that if one cornea is blackened in 
such an animal, it moves continually in a circle when it is exposed to 
a source of light, and in these motions the eye which is not covered 
with paint is directed towards the centre of the circle. The animal 
behaves, therefore, as if the darkened eye were in the shade. 

(6) The j)roduction of positive hdiotrojnsm hy acids and other 
means and the jjer iodic depth-migrations of pelagic anitnals. 

When Ave observe a dense mass of copepods collected from a 
freshwater pond, we notice that some have a tendency to go to the 
light Avhile others go in the opposite direction and many, if not the 
majority, are indifferent to light. It is an easy matter to make 
the negatively heliotropic or the indifferent copepods almost instantly 
positively heliotropic by adding a small but definite amount of carbon- 
dioxide in the form of carbonated water to the Avater in Avhicli the 
animals are contained. If the animals are contained in 50 cubic 
centimetres of Avater it suffices to add from three to six cubic centi- 
metres of carbonated Avater to make all the copepods energetically 
positively heliotropic. This heliotropism lasts about half an hour 
(probably until all the carbon-dioxide has again diffused into the 
air). Similar results may be obtained Avith any other acid. 

The same experiments may be made Avith another fresliAvater 
crustacean, namely Daphnia, Avith this difference, hoAvever, that it is 
as a rule necessary to loAver the temperature of the Avater also. If 
the Avater containing the Daphniae is cooled and at the same time 
carbon-dioxide added, the animals Avhich Avere before indifferent to 
light noAv become most strikingly positively heliotropic. Marine 
copepods can be made positively heliotropic by the loAvering of the 
temperature alone, or by a sudden increase in the concentration of 
the sea-Avater. 

These data have a bearing upon the depth-migrations of pelagic 
animals, as Avas pointed out years ago by Theo. T. Groom and the 
Avriter. It is Avell knoAvn that many animals living near -the surface 
of the ocean or fi-eshAvater lakes, have a tendency to migrate 
upAvards toAvards evening and doAvuAvards in the morning and during 
the day. lliese ])eriodic motions are determined to a large extent, if 
not exclusively, by the heliotropism of these animals. Since the 
consumption of carbon-dioxide by the green plants ceases toAvards 
evening, the tension of this gas in the Avater must rise and tliis nmst 
have the effect of inducing positive heliotropism or increasing its 
intensity. At the same time the temperature of the Avater near the 
surface is lowered and this also increases the positive heliotropism in 
tlie organisms. 

266 Influence of environment on animals 

The faint light from the sky is sufficient to cause animals which 
are in a high degree positively heliotropic to move vertically upwards 
towards the light, as experiments with such pelagic animals, e.g. 
copepods, have shown. When, in the morning, the absorption of 
carbon-dioxide by the gi-een algae begins again and the temperature 
of the water rises, the animals lose their positive heliotropism, and 
slowly sink doAvn or become negatively heliotropic and migrate 
actively downwards. 

These experiments have also a bearing upon the problem of the 
inheritance of instincts. The character which is transmitted in this 
case is not the tendency to migrate periodically upwards and down- 
wards, but the positive heliotropism. The tendency to migrate is 
the outcome of the fact that periodically varying external conditions 
induce a periodic change in the sense and intensity of the heliotropism 
of these animals. It is of course immaterial for the result, whether 
the carbon-dioxide or any other acid diffuse into the animal from the 
outside or whether they are produced inside in the tissue cells of the 
animals. Davenport and Cannon found that Daphniae, which at the 
beginning of the experiment, react sluggishly to light react much 
more quickly after they have been made to go to the light a few 
times. The writer is inclined to attribute this result to the effect of 
acids, e.g. carbon-dioxide, produced in the animals themselves in 
consequence of their motion. A similar effect of the acids was shown 
by A. D. Waller in the case of the response of nerve to stimuli. 

The writer observed many years ago that winged male and female 
ants are positively heliotropic and that their heliotropic sensitiveness 
increases and reaches its maximum towards the period of nuptial 
flight. Since the workers show no heliotropism it looks as if an 
internal secretion fi-om the sexual glands were the cause of their 
heliotropic sensitiveness. V. Kellogg has observed that bees also 
become intensely positively heliotropic at the period of their wedding 
flight, in fact so much so that by letting light fall into the observation 
hive from above, the bees are prevented from leaving the hive through 
the exit at the lower end. 

We notice also the reverse phenomenon, namely, that chemical 
changes produced in the animal destroy its heliotropism. The cater- 
pillars of Porthesia chrysorrhoea are very strongly positively helio- 
tropic when they are first aroused from their winter sleep. This 
heliotropic sensitiveness lasts only as long as they are not fed. If 
they are kept permanently without food they remain permanently 
positively heliotropic until they die from starvation. It is to be 
inferred that as soon as these animals take up food, a substance or 
substances are formed in their bodies which diminish or annihilate 
their heliotropic sensitiveness. 

Tropic reactions of tissue-cells 267 

The heliotropism of animals is identical with the heliotropism of 
plants. The writer has shown that the experiments on the effect of 
acids on the heliotropism of copepods can be repeated with the same 
result in Volvox. It is therefore erroneous to try to explain these 
heliotropic reactions of animals on the basis of peculiarities (e.g. 
vision) which are not found in plants. 

We may briefly discuss the question of the transmission through 
the sex cells of such instincts as are based upon heliotropism. This 
problem reduces itself simply to that of the method whereby the 
gametes transmit heliotropism to the larvae or to the adult. The writer 
has expressed the idea that all that is necessary for this transmission 
is the presence in the eyes (or in the skin) of the animal of a plioto- 
sensitive substance. For the transmission of this the gametes need 
not contain anything more than a catalyser or ferment for the syn- 
thesis of the photo-sensitive substance in the body of the animal. 
What has been said in regard to animal heliotropism might, if space 
permitted, be extended, mutatis mutandis, to geotropism and stereo- 

(c) The troinc reactions of certain tissue-cells and the morpho- 
genetic effects of these reactions. 

Since plant-cells show heliotropic reactions identical with those of 
animals, it is not surprising that certain tissue-cells also show 
reactions which belong to the class of tropisms. These reactions of 
tissue-cells are of special interest by reason of their bearing upon the 
inheritance of morphological characters. An example of this is found 
in the tiger-like marking of the yolk-sac of the embryo of Fundulus 
and in the marking of the young fish itself. The wTiter found that 
the former is entirely, and the latter at least in part, due to the 
creeping of the chromatophores upon the blood-vessels. The 
chromatophorcs are at first scattered irregularly over the yolk-sac 
and show their characteristic ramifications. There is at that time no 
definite relation between blood-vessels and chromatophores. As 
soon as a ramification of a chromatophore comes in contact with a 
blood-vessel the whole mass of the chromatophore creeps gradually 
on the blood-vessel and forms a complete sheath around the vessel, 
until finally all the chromatophores form a sheath around the vessels 
and no more pigment cells are found in the meshes between the 
vessels. Nobody who has not actually watched the process of the 
creeping of the chromatophores upon the blood-vessels would antici- 
pate that the tiger-like colouration of the yolk-sac in the later stages 
of development was brought about in this way. Similar facts can 
be observed in regard to the first marking of the embryo itself. 
The writer is inclined to believe that we are here dealing with a case 

268 Influence of environment on animals 

of chemotropism, and that the oxygen of the blood may be the cause 
of the spreading of the chromatophores around the blood-vessels. 
Certain observations seem to indicate the possibility that in the adult 
the chromatophores have, in some forms at least, a more rigid 
structure and are prevented from acting in the >vay indicated. It 
seems to the writer that such observations as those made on Fundulus 
might simplify the problem of the hereditary transmission of certain 

Driesch has found that a tropism underlies the arrangement of 
the skeleton in the plut^s larvae of the sea-urcliin. The position of 
this skeleton is predetermined by the arrangement of the mesen- 
chyme cells, and Driesch has shown that these cells migrate actively 
to the place of their destination, possibly led there under the 
influence of certain chemical substances. When Driesch scattered 
these cells mechanically before their migration, they nevertheless 
reached their destination. 

In the developing eggs of insects the nuclei, together with some 
cytoplasm, migrate to the periphery of the Qgg. Herbst pointed out 
that this might be a case of chemotropism, caused by the oxygen 
surrounding the egg. The writer has expressed the opinion that the 
formation of the blastula may be caused generally by a tropic 
reaction of the blastomeres, the latter being forced by an outside 
influence to creep to the surface of the egg. 

These examples may suffice to indicate that the arrangement 
of definite groups of cells and the morphological eflfects resulting 
therefrom may be determined by forces lying outside the cells. Since 
these forces are ubiquitous and constant it appears as if we were 
dealing exclusively with the influence of a gamete ; while in reality 
all that it is necessary for the gamete to transmit is a certain form 
of irritability. 

{d) Factors ivkich determine place and time for the deposition 
of eggs. 

For the preservation of species the instinct of animals to lay 
their eggs in places in which the young larvae find their food and 
can develop is of paramount importance. A simple example of this 
instinct is the fact that the common fly lays its eggs on putrid 
material Avhich serves as food for the young larvae. When a piece 
of meat and of fat of the same animal arc placed side by side, the 
fly will deposit its eggs upon the meat on which the larvae can grow, 
and not upon the fat, on which they would starve. Here we are 
dealing with the effect of a volatile nitrogenous substance which 
reflexly causes the peristaltic motions for the laying of the egg in 
the female fly. 

Conditions governing deposition of eggs 269 

Kammerer has investigated the conditions for the laying of eggs in 
two forms of salamanders, e.g. Salamandra atra and S. maculosa. 
In both forms the eggs are fertilised in the body and begin to 
develop in the uterus. Since there is room only for a few larvae in 
the uterus, a large number of eggs perish and this number is the 
greater the longer the period of gestation. It thus happens that 
when the animals retain their eggs a long time, very few young ones 
arc born ; and these are in a rather advanced stage of development, 
owing to the long time which elapsed since they were fertilised. 
When the animal lays its eggs comparatively soon after copulation, 
many eggs (from 12 to 72) are produced and the larvae are of course 
in an early stage of development. In the early stage the larvae 
possess gills and can therefore live in water, while in later stages 
they have no gills and breathe through their lungs. Kammerer 
showed that both forms of Salamandra can be induced to lay their 
eggs early or late, according to the physical conditions surrounding 
them. If they are kept in Avater or in proximity to water and in 
a moist atmosphere they have a tendency to lay their eggs earlier 
and a comparatively high temperature enhances the tendency to 
shorten the period of gestation. If the salamanders are kept in 
comparative dryness they show a tendency to lay their eggs rather 
late and a low temperature enhances this tendency. 

Since Salamandra atra is found in rather dry alpine regions 
with a relatively low temperature and Salamandra maculosa in 
lower regions with plenty of water and a higher temperature, the 
fact that >S^. atra bears young which are already developed and 
beyond the stage of aquatic life, while >S^. maculosa bears young ones 
in an earlier stage, has been termed adaptation. Kammerer's experi- 
ments, however, show^ that we are dealing with the direct eHects 
of definite outside forces. ^Miile we may speak of adaptation when 
all or some of the variables which determine a reaction are un- 
known, it is obviously in the interest of further scientific progress 
to connect cause and efiect directly whenever our knowledge allows 
us to do so. 

VII. Concluding Remarks. 

The discovery of De Vries, that new species may arise by muta- 
tion and tlic wide if not universal applicability of Mendel's Law 
to phenomena of heredity, as shown especially by Bateson and his 
pupils, must, for the time being, if not permanently, serve as a basis 
for theories of evolution. These discoveries place before the experi- 
mental l)iologist the definite task of producing nmtations by physico- 
chemical means. It is true that certain authors claim to have 

270 Influence of environment on animals 

succeeded in this, but the writer wishes to apologise to these authors 
for his inability to convince himself of the validity of their claims 
at the present moment. He thinks that only continued breeding 
of these apparent mutants through several generations can afford 
convincing evidence that we are here dealing with mutants rather 
than with merely pathological variations. 

^Vhat was said in regard to the production of new species by 
physico-chemical means may be repeated with still more justification 
in regard to the second problem of transformation, namely the 
making of living from inanimate matter. The purely morphological 
imitations of bacteria or cells which physicists have now and then 
proclaimed as artificially produced living beings ; or the plays on 
words by which, e.g. the regeneration of broken crystals and the 
regeneration of lost limbs by a crustacean M^ere declared identical, 
will not appeal to the biologist. We know that growth and develop- 
ment in animals and plants are determined by definite although 
complicated series of catenary chemical reactions, which result in 
the synthesis of a definite compound or group of compounds, namely, 

The nucleins have the peculiarity of acting as ferments or 
enzymes for their own synthesis. Thus a given type of nucleus will 
continue to synthesise other nuclein of its own kind. This determines 
the continuity of a species ; since each species has, probably, its own 
specific nuclein or nuclear material. But it also shows us that 
Avhoever claims to have succeeded in making living matter from 
inanimate will have to prove that he has succeeded in producing 
nuclein material which acts as a ferment for its own synthesis and 
thus reproduces itself. Nobody has thus far succeeded in this, 
although nothing warrants us in taking it for granted that this task 
is beyond the poAver of science. 




By E. B. Poulton. 

Hope Professor of Zoology in the University of Oxford. 


The following pages have been written almost entirely from 
the historical stand point Their principal object has been to give 
some account of the impressions produced on the mind of Darwin 
and his great compeer Wallace by various difficult problems sug- 
gested by the colours of living nature. In order to render the brief 
summary of Darwin's thoughts and opinions on the subject in any 
way complete, it was found necessary to say again much that has 
often been said before. No attempt has been made to display as a 
whole the vast contribution of Wallace ; but certain of its features 
are incidentally revealed in passages quoted from Darwin's letters. 
It is assumed that the reader is familiar with the well-known theories 
of Protective Resemblance, Warning Colours, and Mimicry both 
Batesian and Miillerian. It would have been superfluous to explain 
these on the present occasion ; for a far more detailed account than 
could have been attempted in these pages has recently appeared \ 
Among the older records I have made a point of bringing together 
the principal observations scattered through the note-books and 
collections of W. J. Burchell. These have never hitherto found 
a place in any memoir dealing with the significance of the colours of 

Incidental Colours. 

Darwin fully recognised that the colours of living beings are not 
necessarily of value as colours, but that they may be an incidental 
result of chemical or physical structure. Thus he >vrote to T. Median, 
Oct. 9, 1874 : " I am glad that you are attending to the colours of 

1 Poulton, EssayB on Evolution, Oxford, 1908, pp. 293—382. 

272 Colour and the Struggle for Life 

dioecious flowers ; but it is well to remember that their colours may 
be as unimportant to them as those of a gall, or, indeed, as the colour 
of an amethyst or ruby is to these gems^" 

Incidental colours remain as available assets of the organism ready 
to be turned to account by natural selection. It is a probable specu- 
lation that all pigmentary colours were originally incidental ; but now 
and for immense periods of time the visible tints of animals have been 
modified and arranged so as to assist in the struggle with other 
organisms or in courtship. The dominant colouring of plants, on the 
other hand, is an essential element in the paramount physiological 
activity of chlorophyll. In exceptional instances, however, the shapes 
and visible colours of plants may be modified in order to promote 

Teleology and Adaptation. 

In the department of Biology which forms the subject of this essay, 
the adaptation of means to an end is probably more evident than in 
any other ; and it is therefore of interest to compare, in a brief 
introductory section, the older with the newer teleological views. 

The distinctive feature of Natural Selection as contrasted with 
other attempts to explain the process of Evolution is the part played 
by the struggle for existence. All naturalists in all ages must have 
known something of the operations of ''Nature red in tooth and 
claw"; but it was left for this great theory to suggest that vast 
extermination is a necessary condition of progress, and even of main- 
taining the ground already gained. 

Realising that fitness is the outcome of this fierce struggle, thus 
turned to account for the first time, we are sometimes led to associate 
the recognition of adaptation itself too exclusively with Natural 
Selection. Adaptation had been studied with the warmest enthusiasm 
nearly forty years before this great theory was given to the scientific 
world, and it is difficult now to realise the impetus which the works 
of Paley gave to the study of Natural History. Tliat they did inspire 
the naturalists of the early part of the last century is clearly shown in 
the following passages. 

In the year 1824 the Ashmolean Museum at Oxford was intrusted 
to the care of J. S. Duncan of New College. He was succeeded in 
this office by his brother, P. B. Duncan, of the same College, author 
of a History of the INIuseum, which shows very clearly the influence of 
Paley upon the study of nature, and the dominant position given to 
his teachings : "Happily at this time [1824] a taste for the study of 

^ More Letters of Charles Darwin, Vol. i. pp. 354, 355. See also the admirable 
account of incidental colours in Descent of Man {2nd edit.), 1874, pp. 261, 262. 
2 See pp. 273, 276. 

Teleology and Adaptation 273 

natural history had been excited in the University by Dr Paley's very 
interesting work on Natural Theology, and the very popular lectures 
of Dr Kidd on Comparative Anatomy, and Dr Buckland on Geology." 
In the arrangement of the contents of the Museum the illustration of 
Paley's work was given the foremost place by J. S. Duncan : " The 
first division proposes to familiarize the eye to those relations of all 
natural objects which form the basis of argument in Dr Paley's 
Natural Theology ; to induce a mental habit of associating the view 
of natural phenomena >nth the conviction that they are the media of 
Divine manifestation ; and by such association to give proper dignity 
to every branch of natural science^" 

The great naturalist, W. J. Burchell, in his classical work shows 
the same recognition of adaptation in nature at a still earlier date. 
Upon the subject of collections he wrote^ : " It must not be supposed 
that these charms [the pleasures of Nature] are produced by the mere 
discovery of new objects : it is the harmony with which they have 
been adapted by the Creator to each other, and to the situations in 
which they are found, which delights the observer in countries where 
Art has not yet introduced her discords." The remainder of the 
passage is so admirable that I venture to quote it : " To him who is 
satisfied with amassing collections of curious objects, simply for the 
pleasure of possessing them, such objects can afford, at best, but a 
childish gratification, faint and fleeting ; while he who extends his 
view beyond the narrow field of nomenclature, beholds a boundless 
expanse, the exploring of which is worthy of the philosopher, and of 
the best talents of a reasonable being." 

On September 14, 1811, Burchell was at Zand Valley (Vlei), or 
Sand Pool, a few miles south-west of the site of Prieska, on the Orange 
River. Here he found a Mesembrytmthemum {31. turbinifoiinc, now 
M. truncatnm) and also a "Grylliis" (Acridian), closely resembling the 
pebbles with which their locality was strewn. He says of both of 
these, "The intention of Nature, in these instances, seems to have 
been the same as when she gave to the Chameleon the power of 
accommodating its color, in a certain degree, to that of the object 
nearest to it, in order to compensate for the deficiency of its 
locomotive powere. By their form and color, this insect may pass 
unobserved by those birds, which otherwise would soon extirpate a 
species so little able to elude its pursues, and this juicy little 
Mesembryanthemum may generally escape the notice of cattle and 

1 From History and Arrangement of the Ashmolean Stuseum, by P. B. Duncan: see 
pp. vi, vii of A Catalogue of the Ashmolean Museum, Oxford, 1836. 

- Travels in the Interior of Southern Africa, London, Vol. i. 1822, p. 505. The 
references to Burchell's observations in the present essay are adapted from the author's 
article in Report of the British and South African Associations, 1905, Vol. ni. pp. 57 — 110. 

D. l^ 

274 Colour aiid the Struggle for Life 

wild animals \" Burchell here seems to miss, at least in part, the 
meaning of the relationship between the quiescence of the Acridian 
and its cryptic colouring. Quiescence is an essential element in the 
protective resemblance to a stone — probably even more indispensable 
than the details of the form and colouring. Although Burchell 
appears to overlook this point he fully recognised the community 
between protection by concealment and more aggressive modes of 
defence ; for, in the passage of which a part is quoted above, he 
specially refers to some earlier remarks on p. 226 of his Vol. i. We 
here find that when the oxen were resting by the Juk rivier (Yoke 
river), on July 19, 1811, Burchell observed "Geranium spinosum, with 
a fleshy stem and large white flowers... ; and a succulent species of 
Pelargonium... BO defended by the old panicles, grown to hard woody 
thorns, that no cattle could browze upon it." He goes on to say, *' In 
this arid country, where every juicy vegetable would soon be eaten 
up by the wild animals, the Great Creating Power, with all-provident 
wisdom, has given to such plants either an acrid or poisonous juice, 
or sharp thorns, to preserve the species from annihilation...." All 
these modes of defence, especially adapted to a desert environment, 
have since been generally recognised, and it is very interesting to 
place beside Burchell's statement the following passage from a letter 
written by Darmn, Aug. 7, 1868, to G. H. Lewes: "That Natural 
Selection would tend to produce the most formidable thorns will be 
admitted by every one who has observed the distribution in South 
America and Africa {vide Livingstone) of thorn-bearing plants, for 
they always appear where the bushes grow isolated and are exposed 
to the attacks of mammals. Even in England it has been noticed 
that all spine-bearing and sting-bearing plants are palatable to 
quadrupeds, when the thorns are crushed-." 

Adaptation and Natural Selection. 

I have preferred to show the influence of the older teleology upon 
Natural History by quotations from a single great and insufficiently 
appreciated naturalist. It might have been seen equally well in the 
pages of Kirby and Spence and those of many other writers. If the 

1 Loc. cit. pp. 310, 311. See Sir William Thiselton-Dyer "Morphological Notes," xi.; 
"Protective Adaptations," i. ; Aniials of Botany, Vol. xx. p. 124. In plates vii. viii. and 
IX. accompanying this article the author represents the species observed by Burchell, 
together with others in which analogous adaptations exist. He writes: "Burchell was 
clearly on the track on which Darwin reached the goal. But the time had not come for 
emancipation from the old teleology. This, however, in no respect detracts from the merit 
or value of his work. For, as Huxley has pointed out (Life and Letters of Thomas Henry 
Huxley, London, 1900, i. p. 457), the facts of the old teleology are immediately transferable 
to Darwinism, which simply supplies them with a natural in place of a supernatural 

* More Letters, i. p. 308. 

Natural Selection and Ada^ytation 275 

older naturalists who thought and spoke with Burchell of "the intention 
of Nature " and the adaptation of beings " to each other, and to the 
situations in which they are found," could have conceived the 
possibility of evolution, they must have been led, as Darwin was, by 
the same considerations to Natural Selection. This was impossible 
for them, because the philosophy which they followed contemplated 
the phenomena of adaptation as part of a static immutable system. 
Darwin, convinced that the system is dynamic and mutable, was 
prevented by these very phenomena from accepting anything short of 
the crowning intei-pretation offered by Natural Selection^. And the 
birth of Darwin's unalterable conviction that adaptation is of 
dominant importance in the organic world, — a conviction confirmed 
and ever again confirmed by his experience as a naturalist — may 
probably be traced to the influence of the great theologian. Thus 
Darwin, speaking of his Undergraduate days, tells us in his Auto- 
biography that the logic of Paley's Evidences of Christianity and 
Moral Philosophy gave him as much delight as did Euclid. 

"The careful study of these works, without attempting to learn 
any part by rote, was the only part of the academical course which, 
as I then felt and as I still believe, was of the least use to me in the 
education of my mind. I did not at that time trouble myself about 
Paley's premises ; and taking these on trust, I was charmed and 
convinced by the long line of argumentation-." 

When Darwin came to write the Origin he quoted in relation to 
Natural Selection one of Paley's conclusions. "No organ will be 
formed, as Paley has remarked, for the purpose of causing pain or for 
doing an injury to its possessor^." 

The study of adaptation always had for Darwin, as it has for 
many, a peculiar charm. His words, written Nov. 28, 1880, to 
Sir W. Thiselton-Dyer, are by no means inapplicable to-day : "Many 
of the Germans are very contemptuous about making out use of 
organs ; but they may sneer the souls out of their bodies, and I for 
one shall think it the most interesting part of natural history ^" 

Protective and Aggressive Resemblance: Procryptic and 

Anticryptic colouring. 

Colouring for the purpose of concealment is sometimes included 
under the head Mimicry, a classification adopted by H. W. Bates in 

^ "I had always been much struck by such adaptations [e.g. woodpecker and tree-frog 
for climbing, seeds for dispersal], and until these could be explained it seemed to me 
almost useless to endeavour to prove by indirect evidence that species have been modified." 
Autobiography in Life and Letters of Charles Darwin, Vol. i. p. 82. The same thought is 
repeated again and again in Darwin's letters to his friends. It is forcibly urged in the 
Introduction to the Origin (1859), p. 3. 

- Life and Letters, i. p. 47. » Origin of Species {1st edit.) 1859, p. 201. 

* More Letters, u. p. 428. 


276 Colour and the Struggle for Life 

his classical paper. Such an arrangement is inconvenient, and I have 
followed Wallace in keeping the two categories distinct. 

The visible colours of animals are far more commonly adapted for 
Protective Resemblance than for any other purpose. The concealment 
of animals by their colours, shapes and attitudes, must have been well 
known from the period at which human beings first began to take an 
intelligent interest in Nature. An interesting early record is that of 
Samuel Felton, who (Dec. 2, 1763) figured and gave some account 
of an Acridian (Phi/Uotettlx) from Jamaica. Of this insect he says 
"the thorax is like a leaf that is raised perpendicularly from the 

Both Protective and Aggressive Resemblances were appreciated 
and clearly explained by Erasmus Darwin in 1794 : "The colours of 
many animals seem adapted to their purposes of concealing them- 
selves either to avoid danger, or to spring upon their prey^." 

Protective Resemblance of a very marked an(i beautiful kind is 
found in certain plants, inhabitants of desert areas. Examples ob- 
served by Burchell almost exactly a hundred years ago have already 
been mentioned on p. 273. In addition to the resemblance to stones 
Burchell observed, although he did not publish the fact, a South 
Afi'ican plant concealed by its likeness to the dung of birds ^ The 
observation is recorded in one of the manuscript journals kept by the 
great explorer during his journey. I owe the opportunity of studying 
it to the kindness of Mr Francis A. Burchell of the Rhodes University 
College, Grahamstown. The following account is given under the 
date July 5, 1812, Avlien Burchell was at the Makkwdrin River, about 
half-way between the Kuruman River and Litakun the old capital of 
the Bachapins (Bechuanas) : " I found a curious little Crassula (not 
in flower) so snow white, that I should never has [have] distinguished 

it from the white limestones It was an inch high and a little 

branchy, and was at first mistaken for the dung of birds of the 

passerine order. I have often had occasion to remark that in stony 
place[s] there grow many small succulent plants and abound insects 
(chiefly Grylli) which have exactly the same color as the ground and 
must for ever escape observation unless a person sit on the ground 
and observe very attentively." 

1 Phil. Trans. Roy. Soc. Vol. liv. Tab. vi. p. 55. 

- Zoonomia, Vol. i. p. 509, London, 1794. 

» Sir William Thiselton-Dyer has suggested the same method of concealment (Annals of 
Botany, Vol. xx. p. 123). Eeferring to Anacampseros papyracea, figured ou plate ix., the 
author says of its adaptive resemblance: "At the risk of suggesting one perhaps somewhat 
far-fetched, I must confess that the aspect of the plant always calls to my mind the 
dejecta of some bird, and the more so owing to the whitening of the branches towards the 
tips" (loc. cit. p. 126). The student of insects, who is so familiar with this very form of 
protective resemblance in larvae, and even perfect insects, will not be inclined to 
consider the suggestion far-fetched. 

Protective Reseniblance 277 

The cryptic resemblances of animals impressed Darwin and 
Wallace in very ditFerent degrees, probably in part due to the fact 
that Wallace's tropical experiences were so largely derived from the 
insect world, in part to the importance assigned by Darwin to Sexual 
Selection " a subject which had always greatly interested me," as he 
says in his Autobiography'^. There is no reference to Cryptic 
Resemblance in Darwin's section of the Joint Essay, although he 
gives an excellent short account of Sexual Selection (see p. 295). 
Wallace's section on the other hand contains the following statement : 
"Even the peculiar colours of many animals, especially insects, so 
closely resembling the soil or the leaves or the trunks on which they 
habitually reside, are explained on the same principle ; for though in 
the course of ages varieties of many tints may have occurred, yet 
those races having colours best adapted to concealment from their 
enemies would inevitably survive the longestV 

It would occupy too much space to attempt any discussion of 
the difference between the views of these two naturalists, but it 
is clear that Darwin, although fully believing in the efficiency of 
protective resemblance and replying to St George Mivart's con- 
tention that Natural Selection was incompetent to produce it^ never 
entirely agreed with Wallace's estimate of its importance. Thus the 
following extract fi-om a letter to Sir Joseph Hooker, May 21, 1868, 
refers to Wallace : " I find I must (and I always distrust myself when 
I difier from him) separate rather Avidely from him all about birds' 
nests and protection ; he is riding that hobby to death*." It is clear 
from the account given in The Descent o/Man^, that the divergence 
was due to the fact that Darwin ascribed more importance to Sexual 
Selection than did Wallace, and Wallace more importance to Pro- 
tective Resemblance than Darwin. Thus Darwin wrote to Wallace, 
Oct. 12 and 13, 1867: "By the way, I cannot but think that you push 
protection too far in some cases, as with the stripes on the tiger*'." 
Here too DarAvin was preferring the explanation oifered by Sexual 
Selection^, a preference which, considering the relation of the colouring 
of the lion and tiger to their respective environments, few naturalists 
will be found to share. It is also shown on p. 289 that Darwin con- 
templated the possibility of cryptic colours such as those of Patagonian 
animals being due to sexual selection influenced by the aspect of 
surrounding nature. 

' Life and Letters, Vol. i. p. 94. 

- Journ. Proc. Linn. Sac. Vol. m. 1859, p. 61. The italics are Wallace's. 
» Origin (6th edit.) London, 1872, pp. 181, 182; Bee alBO p. 66. 
* More Letters, i. p. 304. 

5 London, 1874, pp. 452—458. See also Life and Letters, in. pp. 123—125, and More 
Letters, ii. pp. 59—63, 72—74, 76—78, 84—90, 92, 93. 

' More Letters, i. p. 283. ^ Descent of Man (2nd edit.) 1874, pp. 545, 546. 

278 Colour and the Struggle for Life 

Nearly a year later Darwin in his letter of May 5, 1868?, expressed 
his agreement with Wallace's views : " Except that I should put 
sexual selection as an equal, or perhaps as even a more important 
agent in giving colour than Natural Selection for protection'." The 
conclusion expressed in the above quoted passage is opposed by 
the extraordinary development of Protective Resemblance in the 
immature stages of animals, especially insects. 

It must not be supposed, however, that Darwin ascribed an 
unimportant role to Cryptic Resemblances, and as observations 
accumulated he came to recognise their efficiency in fresh groups of 
the animal kingdom. Thus he wrote to Wallace, May 5, 1867 : 
*' Hackel has recently well shown that the transparency and absence 
of colour in the lower oceanic animals, belonging to the most different 
classes, may be well accounted for on the principle of protection ^" 
Darwin also admitted the justice of Professor E. S. Morse's con- 
tention that the shells of molluscs are often adaptively coloured ^ 
But he looked upon cryptic colouring and also mimicry as more 
especially Wallace's departments, and sent to him and to Professor 
Pdeldola observations and notes bearing upon these subjects. Thus 
the following letter given to me by Dr A. R. Wallace and now, by kind 
permission, published for the first time, accompanied a photograph 
of the chrysalis of Papilio sarpedon choredon, Feld,, suspended from 
a leaf of its food-plant : 

July 9th, 

Beckenham, Kent. 

My Dear Wallace, 

Dr G. Krefft has sent me the enclosed from Sydney. A 
nurseryman saw a caterpillar feeding on a plant and covered the 
whole up, but when he searched for the cocoon [pupa], was long 
before he could find it, so good was its imitation in colour and form 
to the leaf to which it was attached. I hope that the world goes well 
with you. Do not trouble yourself by acknowledging this. 

Ever yours, 

Ch. Darwin. 

Another deeply interesting letter of Darwin's, bearing upon pro- 
tective resemblance, has only recently been s]lo^v^l to me by my friend 
Professor E. B. Wilson, the great American Cytologist. With his kind 

^ More Letters, ii. pp. 77, 78. 

- More Letters, u. p. 62. See also Descent o/ Man, p. 261. 

3 ilore Letters, u. p. y5. 

Protective Resemblance 279 

consent and that of Mr Francis Darwin, this letter, written four months 
before Darwin's death on April 19, 1882, is reproduced here^ : 

December 21, 1881. 

Dear Sir, 

I thank you much for having taken so much trouble in 
describing fully your interesting and curious case of mimickry. 

I am in the habit of looking through many scientific Journals, and 
though my memory is now not nearly so good as it was, I feel pretty 
sure that no such case as yours has been described (amongst the 
nudibranch) molluscs. You perhaps know the case of a fish allied 
to Hippocampus, (described some years ago by Dr Giinther in Proc. 
Zoolog. Socy) which clings by its tail to sea-weeds, and is covered 
with waving filaments so as itself to look like a piece of the same sea- 
weed. The parallelism between your and Dr Gunther's case makes 
both of them the more interesting ; considering how far a fish and 
a mollusc stand apart. It w.*^ be difficult for anyone to explain 
such cases by the direct action of the environment. — I am glad that 
you intend to make further observations on this mollusc, and I hope 
that you will give a figure and if possible a coloured figure. 

With all good wishes from an old brother naturalist, 

I remain, Dear Sir, 

Yours faithfully, 

Charles Darwin. 

Professor E. B. Wilson has kindly given the following account of 
the circumstances under which he had written to Darwin : "The case 
to wliich Darwin's letter refers is that of the nudibranch mollusc 
Scyllaea, which lives on the floating Sargassum and shows a really 
astonishing resemblance to the plant, having leaf-shaped processes 
very closely similar to the fronds of the sea-weed both in shape and 
in color. The concealment of the animal may be judged from the 
fact that we found the animal quite by accident on a piece of 
Sargassum that had been in a glass jar in the laboratory for some 
time and had been closely examined in the search for hydroids and 
the like without disclosing the presence upon it of two large specimens 
of the Scyllaea (the animal, as I recall it, is about two inches long). 
It was first detected by its movements alone, by someone (I think a 
casual visitor to the laboratory) who was looking closely at the 
SargassHiu and exclaimed ' ^V"hy, the sea-weed ia moving its leaves ' ! 

1 The letter is addressed : 
"Edmund B. WUsod, Eijq., Assistant in Liology, John Hopkins University, Baltimore 

Md., U. States." 

280 Colour and the Struggle for Life 

We found the example in the summer of 1880 or 1881 at Beaufort, 
N.C., where the Johns Hopkins laboratory was located for the time 
being. It must have been seen by many others, before or since. 

"I wrote and sent to Darwin a short description of the case at the 
suggestion of Brooks, with whom I was at the time a student. I was, 
of course, entirely unknown to Darwin (or to anyone else) and to me 
the principal interest of Darwin's letter is the evidence that it gives 
of his extraordinary kindness and friendliness towards an obscure 
youngster who had of course absolutely no claim upon his time or 
attention. The little incident made an indelible impression upon my 
memory and taught me a lesson that was worth learning." 

Variable Protective Resemblance. 

The wonderful power of rapid colour adjustment possessed by the 
cuttle-jfish was observed by Darwin in 1832 at St Jago, Cape de Verd 
Islands, the first place visited during the voyage of the Beagle. 
From Rio he wrote to Henslow, giving the following account of his 
observations, May 18, 1832: "I took several specimens of an Octopus 
v>'hich possessed a most marvellous power of changing its colours, 
equalling any chameleon, and evidently accommodating the changes 
to the colour of the ground which it passed over. Yellowish green, 
dark brown, and red, were the prevailing colours ; this fact appears 
to be new, as far as I can find out\" 

Darwin was well aware of the power of individual colour ad- 
justment, now knoAvn to be possessed by large numbers of Lepi- 
dopterous pupae and larvae. An excellent example was brought 
to his notice by C. V. Riley ^ while the most striking of the early 
results obtained with the pupae of butterflies — those of Mrs M. E. 
Barber upon Pa^nllo nireus — was communicated by him to the 
Entomological Society of London ^ 

It is also necessary to direct attention to C. W. Beebe's* recent 
discovery that the pigmentation of tlie plumage of certain birds is 
increased by confinement in a superhumid atmosphere. In Scarda- 
fella iiica, on which the most complete series of experiments was 
made, the changes took place only at the moults, Avhether normal and 
annual or artificially induced at shorter periods. There was a corre- 
sponding increase in the choroidal pigment of tlie eye. At a certain 

^ Life and Letters, i. pp. 235, 236. See also Darwin's Journal of Researches, 1876, 
pp. 6 — 8, where a far more detailed account is given together with a reference to Encycl. of 
Anat. and Physiol. 

- More Letters, n. pp. 385, 386. 

^ Trans. Ent. Sac. Land. 1874, p. 519. See also More Letters, ii. p. 403. 

* Zoologica: N.Y. Zool. Soc. Vol. i. No. 1, Sept. 25, 1907: Geographic variation in 
birds with especial reference to the effects of liumiditij. 

Warning Colours 281 

advanced stage of feather pigmentation a brilliant iridescent bronze 
or green tint made its appearance on those areas where iridescence 
most often occurs in allied genera. Thus in birds no less than in 
insects, characters previously regarded as of taxonomic value, can be 
evoked or withheld by the forces of the environment. 

Warning or Aposematic Colours. 

From Darwin's description of the colours and habits it is evident 
that he observed, in 1833, an excellent example of warning colouring 
in a little South American toad {Phryniscus nigricans). He described 
it in a letter to Henslow, written from Monte Video, Nov. 24, 1832 : 
"As for one little toad, I hope it may be new, that it may be 
christened ' diabolicus.' Milton must allude to this very individual 
when he talks of ' squat like a toad ' ; its colours are by Werner 
[Nomenclature of Colouts, 1821] ink black, vermilion red and buff 
orange \" In the Journal of Researches^ its colours are described as 
follows : "If we imagine, first, that it had been steeped in the blackest 
ink, and then, when dry, allowed to crawl over a board, freshly 
painted with the brightest vermilion, so as to colour the soles of 
its feet and parts of its stomach, a good idea of its appearance will 
be gained." "Instead of being nocturnal in its habits, as other toads 
are, and living in damp obscure recesses, it crawls during the heat of 
the day about the dry sand-hillocks and arid plains,. . .." The appearance 
and habits recall T. Belt's well-known description of the conspicuous 
little Nicaraguan frog which he found to be distasteful to a 

The recognition of the Warning Colours of caterpillars is due 
in the first instance to Darwin, who, reflecting on Sexual Selection, 
was puzzled by the splendid colours of sexually immature organisms. 
He applied to Wallace " who has an innate genius for solving 
difficulties*." Darwin's original letter exists^ and in it we are told 
that he had taken the advice given by Bates : "You had better ask 
Wallace." After some consideration Wallace replied that he believed 
tlie colours of conspicuous caterpillars and perfect insects were a 
warning of distastefulness and that such forms would be refused 
by birds. Darwin's reply ^ is extremely interesting both for its 

' More Letters, i. p. 12. 2 1876, p. 97. 

* The Naturalist in Nicaragua (2nd edit.) London, 1888, p. 321. 

* Descent of Man, p. 325. On this and the following page an excellent account 
of the discovery will be found, as well as in Wallace's Natural Selection, London, 1875, 
pp. 117—122. 

* Life and Letters, in. pp. 93, 94. 
Life and Letters, in. pp. <J4, 95. 


282 Colour and the Struggle for Life 

enthusiasm at the brilliancy of the hypothesis and its caution in 
acceptance without full confirmation : 

" Bates was quite right ; you are the man to apply to in a 
difficulty. I never heard anything more ingenious than your 
suggestion, and I hope you may be able to prove it true. That is 
a splendid fact about the white moths ^ ; it warms one's very blood to 
see a theory thus almost proved to be true." 

Two years later the hypothesis was proved to hold for caterpillars 
of many kinds by J. Jenner Weir and A. G. Butler, whose observa- 
tions have since been abundantly confirmed by many naturalists. 
Darwin wrote to Weir, May 13, 1869 : " Your verification of Wallace's 
suggestion seems to me to amount to quite a discovery V 

Recognition or Episematic Characters. 

This principle does not appear to have been in any way foreseen 
by Darwin, although he draws special attention to several elements 
of pattern which would now be interpreted by many naturalists as 
episemes. He believed that the markings in question interfered with 
the cryptic effect, and came to the conclusion that, even when 
common to both sexes, they "are the result of sexual selection 
primarily applied to the male^" The most familiar of all recognition 
characters was carefully explained by him, although here too ex- 
plained as an ornamental feature now equally transmitted to both 
sexes : " The hare on her form is a familiar instance of concealment 
through colour ; yet this principle partly fails in a closely -allied 
species, the rabbit, for when running to its burrow, it is made 
conspicuous to the sportsman, and no doubt to all beasts of prey, by 
its upturned white tail*." 

The analogous episematic use of the bright colours of flowers 
to attract insects for effecting cross-fertilisation and of fruits to 
attract vertebrates for effecting dispersal is very clearly explained 
in the Origin^. 

It is not, at this point, necessary to treat sematic characters at 
any greater length. They will form the subject of a large part of the 
following section, where the models of Batesian (Pseudaposematic) 
mimicry are considered as well as the Miillerian (Synaposematic) 
combinations of Warning Colours. 

^ A single white moth which was rejected by young turkeys, while other moths were 
greedily devoured: Natural Selection, 1875, p. 78. 

^ More Letters, ii. p. 71 (footnote). 3 Descent of Man, p. 544. 

* Descent of Man, p. 542. 

' Ed. 1872, p. ICl. For a good example of Darwin's caution in dealing with exceptions 
Bee the allusion to brightly coloured fruit in More Letters, n. p. 348. 

Mimicry 283 

Mimicry, — Batesian or Pseudaposematic, Miillerian or 


Tlie existence of superficial resemblances between animals of 
various degrees of affinity must have been observed for hundreds 
of years. Among the early examples, the best known to me have 
been found in the manuscript note-books and collections of W. J. 
Burchell, the great traveller in Africa (1<S10 — 15) and Brazil (1825 — 
30). The most interesting of his records on this subject are brought 
together in the following paragraphs. 

Conspicuous among well-defended insects are the dark steely or 
iridescent greenish blue fossorial wasps or sand-wasps, Sjyhex and 
the allied genera. Many Longicorn beetles mimic these in colour, 
slender shape of body and limbs, rapid movements, and the readiness 
with which they take to flight. On Dec. 21, 1812, Burchell captured 
one such beetle (Provieces vlridis) at Kosi Fountain on the journey 
fi-om the source of the Kuruman River to Klaarwater. It is correctly 
placed among the Longicorns in his catalogue, but opposite to its 
number is the comment " Sphex ! totus purpureus." 

In our own country the black-and-yellow colouring of many 
stinging insects, especially the ordinary wasps, affords perhaps the 
commonest model for mimicry. It is reproduced with more or less 
accuracy on moths, flies and beetles. Among the latter it is again a 
Longicorn which offers one of the best-known, although by no means 
one of the most perfect, examples. The appearance of the well- 
known "wasp-beetle" (Clytus arietis) in the living state is sufiiciently 
suggestive to prevent the great majority of people from touching it. 
In Burchell's Brazilian collection there is a nearly allied species 
(Neoclf/tus cAirvatus) which appears to be somewhat less wasp-like 
than the British beetle. The specimen bears the number "1188," 
and the date March 27, 1827, when Burchell was collecting in the 
neighbourhood of San Paulo. Turning to the corresponding number 
in the Brazilian note-book we find this record : " It runs rapidly 
like an ichneumon or wasp, of which it has the appearance." 

Tlie formidable, well-defended ants are as freely mimicked by 
other insects as the sand- wasps, ordinary wasps and bees. Thus 
on February 17, 1901, Guy A. K. Marshall captured, near Salisbury, 
Mashonaland, three similar species of ants (Hymenoptera) with a bug 
(Hemiptera) and a Locustid (Orthoptera), the two latter mimicking 
the former. All the insects, seven in number, were caught on a single 
plant, a small bushy vetch \ 

This is an interesting recent example from South Africa, and 
large numbers of others might be added — the observations of many 

1 Trans. Ent. Soc. Lond. 1902, p. 5'6o, plate xix. figs. 53—59. 

284 Colour and the Struggle for Life 

naturalists in many lands ; but nearly all of them known since that 
general awakening of interest in the subject which Avas inspired 
by the great hypotheses of H. W. Bates and Fritz Miiller. We find, 
however, that Burchell had more than once recorded the mimetic 
resemblance to ants. An extremely ant-like bug (the larva of a 
species of Ali/dus) in his Brazilian collection is labelled " 1141," with 
the date December 8, 1826, when Burchell was at the Rio das Pedras, 
Cubatao, near Santos. In the note-book the record is as follows : 
"1141 Omiex. I collected this for a Formica." 

Some of the chief mimics of ants are the active little huntinsr 
spiders belonging to the family Attidae. Examples have been 
brought forward during many recent years, especially by my friends 
Dr and Mrs Peckham, of Milwaukee, the great authorities on this 
group of Araneae. Here too we find an observation of the mimetic 
resemblance recorded by Burchell, and one which adds in the most 
interesting manner to our knowledge of the subject. A fragment, 
all that is now left, of an Attid spider, captured on June 30, 1828, 
at Goyaz, Brazil, bears the following note, in this case on the specimen 
and not in the note-book : "Black... runs and seems like an ant with 
large extended jaws." My friend Mr R. I. Pocock, to whom I have 
submitted the specimen, tells me that it is not one of the group 
of species hitherto regarded as ant-like, and he adds, "It is most 
interesting that Burchell should have noticed the resemblance to an 
ant in its movements. This suggests that the perfect imitation in 
shape, as well as in movement, seen in many species was started in 
forms of an appropriate size and colour by the mimicry of movement 
alone." Up to the present time Burchell is the only naturalist who 
has observed an example which still exhibits this ancestral stage in 
the evolution of mimetic likeness. 

Following the teachings of his day, Burchell was driven to believe 
that it was part of the fixed and inexorable scheme of things that 
these strange superficial resemblances existed. Thus, when he found 
other examples of Hemipterous mimics, including one (Luteva 
niacrophthcdma) with " exactly the manners of a Mantis," he added 
the sentence, "In the genus Cimex (Linn.) are to be found the 
outward resemblances of insects of many other genera and orders " 
(February 15, 1829). Of another Brazilian bug, which is not to be 
found in his collection, and cannot therefore be precisely identified, 
he wrote: "Cmea?... Nature seems to have intended it to imitate 
a Sphex, both in colour and the rapid palpitating and movement of 
the antennae" (November 15, 1826). At the same time it is im- 
possible not to feel the conviction that Burchell felt the advantage 
of a likeness to stinging insects and to aggressive ants, just as he 
recognised the benefits conferred on desert plants by spines and by 

Mimicry 285 

concealment (see pp. 275, 2/6, 278). Such an interpretation of 
mimicry was perfectly consistent with the theological doctrines of 
his day\ 

Tlie last note I have selected from Burchell's manuscript refers to 
one of the chief mimics of the highly protected Lycid beetles. The 
whole assemblage of African insects with a Lycoid colouring forms 
a most important combination and one which has an interesting 
bearing upon the theories of Bates and Fritz Miiller. This most 
wonderful set of mimetic forms, described in 1902 by Guy A. K. 
Marshall, is composed of flower-haunting beetles belonging to the 
family Lycidae, and the heterogeneous group of varied insects which 
mimic their conspicuous and simple scheme of colouring. The Lycid 
beetles, forming the centre or " models " of the whole company, are 
orange-brown in front for about two-thirds of the exposed surface, 
black behind for the remaining third. They are undoubtedly pro- 
tected by qualities which make them excessively unpalatable to the 
bulk of insect-eating animals. Some experimental proof of this has 
been obtained by Mr Guy Marshall. What are the forms which 
surround them? According to the hypothesis of Bates they would 
be, at any rate mainly, palatable hard-pressed insects which only 
hold their own in the struggle for life by a fraudulent imitation of 
the trade-mark of the successful and powerful Lycidae. According 
to Fritz Muller's hypothesis we should expect that the mimickers 
would be highly protected, successful and abundant species, which 
(metaphorically speaking) have found it to their advantage to possess 
an advertisement, a danger-signal, in common with each other, and 
in common with the beetles in the centre of the group. 

How far does the constitution of this wonderful combination — the 
largest and most complicated as yet known in all the world — convey 
to us the idea of mimicry working along the lines supposed by Bates 
or those suggested by Miiller ? Figures 1 to 52 of Mr Marshall's 
coloured plate^ represent a set of forty-two or forty-three species or 
forms of insects captured in Mashonaland, and all except two in the 
neighbourhood of Salisbury. The combination includes six species of 
Lycidae ; nine beetles of five groups all specially protected by 
nauseous qualities, Telephoridae, Melyridae, Phytophaga, Lagriidae, 
Cantharidae ; six Longicorn beetles ; one Coprid beetle ; eight 
stinging Hymenoptera ; three or four parasitic Hymenoptera {Dracon- 
idae, a group much mimicked and sho^Mi by some experiments to 
be distasteful) ; five bugs (Hemiptera, a largely unpalatable group) ; 
three moths (Arctiidae and Zygaenidae, distasteful families) ; one fly. 

' See Kirby and Spence, An Introduction to Entomology (1st edit.), London, Vol. ii. 1817, 
p. 223. 

' Trans. Ent. Soc. Lond. 1902, plate xviii. See also p. 517, where the group is analysed. 

286 Colour and the Struggle for Life 

In fact the whole combination, except perhaps one Phytophagous, one 
Coprid and the Longicorn beetles, and the fly, fall mider the hypothesis 
of Miiller and not under that of Bates. And it is very doubtful 
whether these exceptions will be sustained : indeed the suspicion of 
unpalatability already besets the Longicorns and is always on the 
heels, — I should say the hind tarsi — of a Phytophagous beetle. 

This most remarkable group which illustrates so well the 
problem of mimicry and the alternative hypotheses proposed for its 
solution, was, as I have said, first described in 1902. Among the 
most perfect of the mimetic resemblances in it is that between the 
Longicorn beetle, AmpMdemius analis, and the Lycidae. It was with 
the utmost astonishment and pleasure that I found this very re- 
semblance had almost certainly been observed by Burchell. A 
specimen of the Amphidesmus exists in his collection and it bears 
"651." Turning to the same number in the African Catalogue we 
find that the beetle is correctly placed among the Longicorns, that it 
was captured at Uitenhage on Nov. 18, 1813, and that it was found 
associated with Lycid beetles in flowers ("consocians cum Lycis 
78 — 87 in floribus"). Looking up Nos. 78 — 87 in the collection and 
catalogue, three species of Lycidae are found, all captured on Nov. 18, 
1813, at Uitenhage. Burchell recognised the wide difference in affinity, 
shown by the distance between the respective numbers ; for his 
catalogue is arranged to represent relationships. He observed, what 
students of mimicry are only just beginning to note and record, the 
coincidence between model and mimic in time and space and in 
habits. We are justified in concluding that he observed the close 
superficial likeness although he does not in this case expressly allude 
to it. 

One of the most interesting among the early observations of super- 
ficial resemblance between forms remote in the scale of classification 
was made by Darwin himself, as described in the following passage 
from his letter to Henslow, written from Monte Video, Aug. 15, 1832 : 
"Amongst the lower animals nothing has so much interested me as 
finding two species of elegantly coloured true Planaria inhabiting 
the dewy forest ! The false relation they bear to snails is the most 
extraordinary thing of the kind I have ever seen\" 

Many years later, in 1807, he wrote to Fritz Miiller suggesting 
that the resemblance of a soberly coloured British Planarian to a 
slug might be due to mimicry^. 

The most interesting copy of Bates's classical memoir on Mimicry', 
read before the Linnean Society in 1861, is that given by him to the 

1 More Letters, i. p. 9. ^ Life and Letters, iii. p. 71. 

* "Contributions to an Insect Fauna of the Amazon Valley." Trans. Linn. Soe. Vol. 
XXIII. 18C2, p. 495. 

Mimicry 287 

man who has done most to support and extend the theory. My kind 
friend has given that copy to me ; it bears the inscription : 

Only a year and a half after the publication of the Origin, Ave find 
that Darwin wrote to Bates on the subject which was to provide such 
striking evidence of the truth of Natural Selection: "I am glad 
to hear that you have specially attended to 'mimetic' analogies — a 
most curious subject ; I hope you publish on it. I have for a long 
time wished to know M'hether what Dr Collingwood asserts is true — 
that the most striking cases generally occur between insects in- 
habiting the same country \" 

The next letter, written about six months later, reveals the re- 
markable fact that the illustrious naturalist who had anticipated 
Edward Forbes in the explanation of arctic forms on alpine heights^, 
had also anticipated H. W. Bates in the theory of Mimicry : " ^^^lat a 
capital paper yours will be on mimetic resemblances ! You will make 
quite a new subject of it. I had thought of such cases as a difficulty ; 
and once, when corresponding with Dr Collingwood, I thought of your 
explanation ; but I di-ove it from my mind, for I felt that I had not 
knowledge to judge one way or the other^" 

Bates read his paper before the Linnean Society, Nov. 21, 1861, 
and Darwin's impressions on hearing it were conveyed in a letter 
to the author dated Dec. 3: "Under a general point of view, I am 
quite convinced (Hooker and Huxley took the same view some months 
ago) that a philosophic view of nature can solely be driven into 
naturalists by treating special subjects as you have done. Under 
a special point of view, I think you have solved one of the most 
perplexing problems which could be given to solve*." The memoir 

1 The letter is dated April 4, 1861. More Letters, i. p. 183. 

- " I was forestalled in only one important point, which my vanity has always made 
me regret, namely, the explanation by means of the Glacial period of the presence of 
the same species of plants and of some few animals on distant mountain summits and in 
the arctic regions. This view pleased me so much that I wrote it out in extenso, and 
I believe that it was read by Hooker some years before E. Forbes published his celebrated 
memoir on the subject. In the very few points in which we differed, I still think that I 
was in the right. I have never, of course, alluded in print to my having independently 
worked out this view." Antubioyrapliy, Life and Letters, i. p. 88. 

« The letter is dated Sept. 25, 18G1 : More Letters, i. p. 107. 

* Life and Letters, ii. p. 378. 

288 Colour and the Struggle for Life 

appeared in the following year, and after reading it Darwin 
wrote as follows, Nov. 20, 1862: "...In my opinion it is one 
of the most remarkable and admirable papers I ever read in my 

life I am rejoiced that I passed over the whole subject in the 

Or-igin, for I should have made a precious mess of it. You have 

most clearly stated and solved a wonderful problem Your paper is 

too good to be largely appreciated by the mob of naturalists without 
souls ; but, rely on it, that it will have lasting value, and I cordially 
congratulate you on your first great work. You will find, I should 
think, that Wallace will fully appreciate it\" Four days later, 
Nov. 24, Darwin wrote to Hooker on the same subject: "I have 
now finished his paper...; it seems to me admirable. To my mind 
the act of segregation of varieties into species was never so plainly 
brought forward, and there are heaps of capital miscellaneous 

Darwin was here referring to the tendency of similar varieties 
of the same species to pair together, and on Nov. 25 he wrote to 
Bates asking for fuller information on this subject ^ If Bates's 
opinion were well founded, sexual selection would bear a most im- 
portant part in the establishment of such species*. It must be 
admitted, however, that the evidence is as yet quite insufficient to 
establish this conclusion. It is interesting to observe how Darwin at 
once fixed on the part of Bates's memoir which seemed to bear upon 
sexual selection. A review of Bates's theory of Mimicry was con- 
tributed by Darwin to the Natural History Review^ and an account 
of it is to be found in the Origin^ and in The Desce^it of Man''. 

Darwin continually writes of the value of hypothesis as the 
inspiration of inquiry. We find an example in his letter to Bates, 
Nov. 22, 1860: "I have an old belief that a good observer really 
means a good theorist, and I fully expect to find your observations 
most valuable^." Darwin's letter refers to many problems upon 
which Bates had theorised and observed, but as regards Mimicry itself 
the hypothesis was thought out after the return of the letter from the 
Amazons, when he no longer had the opportunity of testing it by the 
observation of living Nature. It is by no means improbable that, 
had he been able to apply this test, Bates would have recognised 
that his division of butterfly resemblances into two classes, — one due 

1 LAje and Letters, ii. pp. 391 — 393. 

2 More Letters, i. p. 214. 

2 More Letters, i. p. 215. See also parts of Darwin's letter to Bates in Life and 
Letters, ii. p. 392. 

•• See Poulton, Essays on Evolution, 1908, pp. 65, 85 — 88. 

» New Ser. Vol. m. 1863, p. 219. « Ed. 1872, pp. 375—378. 

' Ed. 1874, pp. 323—325. « More Letters, i. p. 176. 

Mimicry 289 

to the theory of mimicry, the other to the influence of local con- 
ditions, — could not be sustained. 

Fritz JNIiiller's contributions to the problem of Mimicry were all 
made in S.E. Brazil, and numbers of them were communicated, with 
other observations on natural history, to Darwin, and by him sent 
to Professor R. Meldola who published many of the facts. Darwin's 
letters to Meldola^ contain abundant proofs of his interest in MUller's 
work upon Mimicry. One deeply interesting letter ^ dated Jan. 23, 
18/2, proves that Fritz Midler before he originated the theory of 
Common Warning Colours (Synaposematic Resemblance or Mullerian 
Mimicry), which will ever be associated with his name, had conceived 
the idea of the production of mimetic likeness by sexual selection. 

Darwin's letter to Meldola shows that he was by no means inclined 
to dismiss the suggestion as worthless, although he considered it 
daring. "You will also see in this letter a strange speculation, which I 
should not dare to publish, about the appreciation of certain colours 
being developed in those species which frequently behold other forms 
similarly ornamented. I do not feel at all sure that this view is 
as incredible as it may at first appear. Similar ideas have passed 
through my mind when considering the dull colours of all the 
organisms which inhabit dull-coloured regions, such as Patagonia and 
the Galapagos Is." A little later, on April 5, he wi-ote to Professor 
August Weismann on the same subject: "It may be suspected that 
even the habit of vieAving differently coloured surrounding objects 
would influence their taste, and Fritz Midler even goes so far as to 
believe that the sight of gaudy butterflies might influence the taste 
of distinct species^" 

This remarkable suggestion aflbrds interesting evidence that 
F. Miiller was not satisfied with the sufficiency of Bates's theory. 
Nor is thlF sui-prising when we think of the numbers of abundant 
conspicuous butterflies which he saAV exhibiting mimetic likenesses. 
The conunon instances in his locality, and indeed everywhere in 
tropical America, were anything but the hard-pressed struggling 
forms assumed by the theory of Bates. They belonged to the groups 
which were themselves mimicked by other butterflies. Fritz IMiiller's 
suggestion also shows that he did not accept Bates's alternative 
explanation of a superficial likeness between models themselves, based 
on some unknown influence of local physico-chemical forces. At the 
same time Midler's own suggestion was subject to this apparently 
fatal objection, that the sexual selection he invoked would tend 
to produce resemblances in the males rather than the females, while it 

' Poulton, Charles Darwin and the theory of Natural Selection, London, 1896, pp 


Loc. cit. pp. 201, 202. » Life and Letters, in. p. 157. 

D- 19 

290 Colour and the Struggle for Life 

is well known that when the sexes differ the females are almost 
invariably more perfectly mimetic than the males and in a high 
proportion of cases are mimetic while the males are non-mimetic. 

The difficulty was met several years later by Fritz MUller's well- 
known theory, published in 1879\ and immediately translated by 
Meldola and brought before the Entomological Society ^ Darwin's 
letter to Meldola dated June 6, 1879, shows "that the first intro- 
duction of this new and most suggestive hypothesis into this country 
was due to the direct influence of Darwin himself, who brought it 
before the notice of the one man who was likely to appreciate it 
at its true value and to find the means for its presentation to English 
naturalists^" Of the hypothesis itself Darwin wrote "F. Miiller's 
view of the mutual protection was quite new to me^" The hypo- 
thesis of Miillerian mimicry was at first strongly opposed. Bates 
himself could never make up his mind to accept it. As the Fellows 
were walking out of the meeting at which Professor Meldola explained 
the hypothesis, an eminent entomologist, now deceased, was heard to 
say to Bates: "It's a case of save me from my friends!" The new 
ideas encountered and still encounter to a great extent the difficulty 
that the theory of Bates had so completely penetrated the literature 
of natural history. The present writer has observed that naturalists 
who have not thoroughly absorbed the older hypothesis are usually 
far more impressed by the newer one than are those whose allegiance 
has already been rendered. The acceptance of Natural Selection itself 
was at first hindered by similar causes, as Darwin clearly recognised : 
"If you argue about the non-acceptance of Natural Selection, it seems 
to me a very striking fact that the Newtonian theory of gravitation, 
which seems to every one now so certain and plain, was rejected by a 
man so extraordinarily able as Leibnitz. The truth will not penetrate 
a preoccupied mind^" 

There are many naturalists, especially students of insects, who 
appear to entertain an inveterate hostility to any theory of mimicry. 
Some of them are eager investigators in the fascinating field of 
geographical distribution, so essential for the study of Mimicry itself. 
The changes of pattern undergone by a species oiErebia as we follow 
it over dilfercnt parts of the mountain ranges of Europe is indeed 
a most interesting inquiry, but not more so than the differences 
between e.g. the Acraea johnstoni of S.E. Rhodesia and of Kiliman- 
jaro. A naturalist who is interested by the Erehia should be equally 
interested by the Acraea ; and so he would be if the student ot 

1 Kosvws, May 1879, p. 100. "^ Proc. Ent. Soc. Lond. 1879, p. xx. 

3 Charles Danoin and the. Theory of Natural Selection, p. 214. * Ibid. p. 213. 

* To Sir J. Hooker, July 28, 18G8, More Letters, i. p. 305. See also the letter to 
A. R. Wallace, April 30, 1868, in More Letters, ii. p. 77, lines G— 8 from top. 

Mimicry 291 

mimicry did not also record that the characteristics which distinguish 
the northern from the southern individuals of the African species 
correspond with the presence, in the north but not in the south, 
of certain entirely different butterflies. That this additional informa- 
tion should so greatly weaken, in certain minds, the appeal of a 
favourite study, is a psychological problem of no little interest. 
This curious antagonism is I believe confined to a few students of 
insects. Those naturalists who, standing rather farther ofl', are able 
to see the bearings of the subject more clearly, will usually admit the 
general support yielded by an ever-growing mass of observations 
to the theories of Mimicry propounded by H. W. Bates and Fritz 
Miiller. In like manner natural selection itself was in the early days 
often best understood and most readily accepted by those who were 
not naturalists. Thus Darwin wrote to D. T. Ansted, Oct. 27, 1860: 
"I am often in despair in making the generality of naturalists even 
comprehend me. Intelligent men who are not naturalists and have 
not a bigoted idea of the term species, show more clearness of 

Even before the Origin appeared Darwin anticipated the first 
results upon the mind of naturalists. He wrote to Asa Gray, Dec. 21, 
1859: "I have made up my mind to be well abused; but I think it of 
importance that my notions should be read by intelligent men, 
accustomed to scientific argument, though not naturalists. It may 
seem absurd, but I think such men will drag after them those 
naturalists who have too firmly fixed in their heads that a species 
is an entity-." 

Mimicry was not only one of the first great departments of zoo- 
logical knowledge to be studied under the inspiration of Natural 
Selection, it is still and will always remain one of the most interesting 
and important of subjects in relation to this theory as well as to 
evolution. In mimicry we investigate the effect of environment in its 
simplest form : we trace the effects of the pattern of a single species 
upon that of another far removed from it in the scale of classification. 
^\^leu there is reason to believe that the model is an invader from 
another region and has only recently become an element in the 
environment of the species native to its second home, the problem 
gains a special interest and fascination. Although we are chiefly 
dealing with the fleeting and changeable element of colour we expect 
to find and we do find evidence of a comparatively rapid evolution. 
T)ie invasion of a fresh model is for certain species an unusually 
sudden change in the forces of the environment and in some instances 
we have grounds for the belief that the mimetic response has not 
been long delayed. 

^ More Letters, i. p. 175. ' Life and Letters, n. p. 246. 


292 Colour and the Struggle for Life 

Mimicry and Sex. 

Ever since Wallace's classical memoir on mimicry in the Malayan 
Swallowtail butterflies, those naturalists who have written on the 
subject have followed his interpretation of the marked prevalence of 
mimetic resemblance in the female sex as compared with the male. 
Tliey have believed with Wallace that the greater dangers of the 
female, with slower flight and often alighting for oviposition, have 
been in part met by the high development of this special mode of pro- 
tection. The fact cannot be doubted. It is extremely common for a 
non-mimetic male to be accompanied by a beautifully mimetic female 
and often by two or three diflferent forms of female, each mimicking a 
diffierent model. The male of a polymorphic mimetic female is, in fact, 
usually non-mimetic (e.g. Papilio dardanus = merope), or if a mimic 
(e.g. the Nymphaline genus Euripus), resembles a very difiereut model. 
On the other hand a non-mimetic female accompanied by a mimetic 
male is excessively rare. An example is afforded by the Oriental 
Nymphaline, Cethosia, in which the males of some species are rough 
mimics of the brown Danaines. In some of the orb-weaving spiders 
the males mimic ants, while the much larger females are non-mimetic. 
Wlien both sexes mimic, it is very common in butterflies and is also 
known in moths, for the females to be better and often far better 
mimics than the males. 

Although still believing that Wallace's hypothesis in large part 
accounts for the facts briefly summarised above, the present writer 
has recently been led to doubt whether it offers a complete explana- 
tion. Mimicry in the male, even though less beneficial to the species 
than mimicry in the female, would still surely be advantageous. 
Why then is it so often entirely restricted to the female ? While the 
attempt to find an answer to this question was haunting me, I re-read 
a letter written by Darwin to Wallace, April 15, 1868, containing the 
following sentences: "When female butterflies are more brilliant than 
their males you believe that they have in most cases, or in all cases, 
been rendered brilliant so as to mimic some other species, and thus 
escape danger. But can you account for the males not having 
been rendered equally brilliant and equally protected ? Although 
it may be most for the welfare of the species that the female should 
be protected, yet it would be some advantage, certainly no dis- 
advantage, for the unfortunate male to enjoy an equal immunity from 
danger. For my part, I should say that the female alone had happened 
j to vary in the right manner, and that the beneficial variations had 
been transmitted to the same sex alone. Believing in this, I can 
see no improbability (but from analogy of domestic animals a strong 
/ probability) that variations leading to beauty must often have occurred 

Mimicry and Sex 293 

in the males alone, and been transmitted to that sex alone. Thus 
I should account in many cases for the greater beauty of the male 
over the female, without the need of the protective principled" 

The consideration of the facts of mimicry thus led Darwin to the 
conclusion that the female happens to vary in the right manner more 
commonly than the male, while the secondary sexual characters of 
males supported the conviction "that from some unknown cause such 
characters [viz. new characters arising in one sex and transmitted to 
it alone] apparently appear oftener in the male than in the female I" 

Comparing these conflicting arguments we are led to believe that 
the fii'st is the stronger. Mimicry in the male would be no dis- 
advantage but an advantage, and when it appears would be and is 
taken advantage of by selection. The secondary sexual characters 
of males would be no advantage but a disadvantage to females, and, 
as Wallace thinks, are withheld from this sex by selection. It is 
indeed possible that mimicry has been hindered and often prevented 
from passing to the males by sexual selection. We know that Darwin 
was much impressed^ by Thomas Belt's daring and brilliant suggestion 
that the white patches which exist, although ordinarily concealed, on 
the wings of mimetic males of certain Pierinae {Dismorplua), have 
been preserved by preferential mating. He supposed this result 
to have been brought about by the females exhibiting a deep-seated 
preference for males that displayed the chief ancestral colour, inherited 
from periods before any mimetic pattern had been evolved in the 
species. But it has always appeared to me that Belt's deeply interest- 
ing suggestion requires much solid evidence and repeated confirmation 
before it can be accepted as a valid interpretation of the facts. In the 
present state of our knowledge, at any rate of insects and especially 
of Lepidoptcra, it is probable that the female is more apt to vary than 
the male and that an important element in the interpretation of 
prevalent female mimicry is provided by this fact. 

In order adequately to discuss the question of mimicry and sex it 
would be necessary to analyse the whole of the facts, so far as they are 
known in butterflies. On the present occasion it is only possible to 
state the inferences which have been drawn from general impressions, 
— inferences wliich it is believed will be sustained by future inquiry. 

^ More Letters, ii. pp. 73, 74. Ou the same subject — "the gay-coloured females of 
Pieria" [Pcrrhybrit (Mylothris) pyrrha of Binzil], Darwin wrote to Wallace, May 5, 1868, as 
follows: "I believe I quite follow you in believing that the colours are wholly due to 
mimicry; and I farther believe that the male is not brilliant from not having received 
through inheritance colour from the female, and from not himself having varied ; in short, 
that he has not been influenced by pelectiou." It should be noted that the male of this 
species docs exhibit a mimetic pattern on the under surface. Jiiore Letters, ii. p. 78. 

« Letter from Darwin to Wallace, May 5, 1867, More Letters, ii. p. 61. 

' Descent of Man, p. 325. 

294 Colour and the Struggle for Life 

(1) Mimicry may occasionally arise in one sex because the 
differences which distinguish it from the other sex happen to be such 
as to afford a starting-point for the resemblance. Here the male 
is at no disadvantage as compared with the female, and the rarity 
of mimicry in the male alone (e.g. Cethosia) is evidence that the great 
predominance of female mimicry is not to be thus explained. 

(2) The tendency of the female to dimorphism and polymorphism 
has been of great importance in determining this predominance. 
Thus if the female appear in two different forms and the male in only 
one it will be twice as probable that she will happen to possess a 
sufficient foundation for the evolution of mimicry. 

(3) The appearance of melanic or partially melanic forms in the 
female has been of very gi*eat service, providing as it does a change of 
ground-colour. Thus the mimicry of the black generally red-marked 
American "Aristolochia swallowtails" (Pharmacophagus) by the 
females of Papilio swallowtails was probably begun in this way. 

(4) It is probably incorrect to assume with Haase that mimicry 
always arose in the female and was later acquired by the male. Both 
sexes of the third section of swallowtails (Cosmodesmns) mimic 
Pharmacophagus in America, far more perfectly than do the females 
of Papilio. But this is not due to Cosmodesmus presenting us with 
a later stage of the history begun in Papilio ; for in Africa Cosmo- 
desmus is still mimetic (of Danainac) in both sexes although the 
resemblances attained are imperfect, while many African species of 
Papilio have non-mimetic males with beautifully mimetic females. 
The explanation is probably to be sought in the fact that the females 
of Papilio are more variable and more often tend to become di- 
morphic than those of Cosmodesmus, while the latter group has more 
often happened to possess a sufficient foundation for the origin of 
the resemblance in patterns which, from the start, were common to 
male and female. 

(5) In very variable species with sexes alike, mimicry can be 
rapidly evolved in both sexes out of very small beginnings. Thus 
the reddish marks which are common in many individuals of Limenitis 
arthemis were almost certainly the starting-point for the evolution of 
the beautifully mimetic L. archip>pus. Nevertheless in such cases, 
although there is no reason to suspect any greater variability, the 
female is commonly a somewhat better mimic than the male and 
often a very much better mimic. Wallace's priucii^le seems here 
to supply the obvious interpretation. 

(6) AVhen the difference between the patterns of the model and 
presumed ancestor of the mimic is very great, the female is often alone 
mimetic ; when the difference is comparatively small, both sexes are 
comnkonly mimetic. The Nymphaline genus Hypolimnas is a good 

Sexual Selection 295 

example. In Hypolimnas itself the females mimic Danainae with 
patterns very different from those preserved by the non-mimetic 
males: in the sub-genus Euralia, both sexes resemble the black 
and white Ethiopian Danaines with patterns not very dissimilar from 
that which we infer to have existed in the non-mimetic ancestor. 

(7) Although a mclanic form or other large variation may be 
of the utmost imiwrtance in facilitating the start of a mimetic 
likeness, it is impossible to explain the evolution of any detailed 
resemblance in this manner. And even the large colour variation 
itself may well be the expression of a minute and "continuous" 
change in the chemical and physical constitution of pigments. 

Sexual Selection {E^ngamic Characters). 

We do not know the date at which the idea of Sexual Selection 
arose in DarAvin's mind, but it was probably not many years after the 
sudden flash of insight which, in October 1838, gave to him the 
theory of Natural Selection. An excellent account of Sexual 
Selection occupies the concluding paragraph of Part i. of Darwin's 
Section of the Joint Essay on Natural Selection, read July 1st, 1858, 
before the Linnean Society \ The principles are so clearly and 
sufficiently stated in these brief sentences that it is appropriate to 
quote the whole : "Besides this natural means of selection, by which 
those individuals are preserved, whether in their egg, or larval, or 
mature state, which are best adapted to the place they fill in nature, 
there is a second agency at work in most unisexual animals, tending 
to produce the same efi'ect, namely, the struggle of the males for the 
females. These struggles are generally decided by the law of battle, 
but in the case of birds, apparently, by the charms of their song, 
by their beauty or their power of courtship, as in the dancing rock- 
thrush of Guiana. The most vigorous and healthy males, implying 
perfect adaptation, must generally gain the victory in their contests. 
This kind of selection, however, is less rigorous than the other; it 
docs not require the death of the less successful, but gives to them 
fewer descendants. The struggle ftills, moreover, at a time of year 
when food is generally abundant, and perhaps the effect chiefly pro- 
duced would be the modification of the secondary sexual characters, 
which are not related to the power of obtaining food, or to defence 
from enemies, but to fighting with or rivalling other males. The 
result of this struggle amongst the males may be compared in some 
respects to that produced by those agriculturists who pay less 
attention to the careful selection of all their young animals, and more 
to the occasional use of a choice mate." 

^ Journ. I'loc. Linn. Soc. Vol. iii. 1859, p. 50. 

296 Colour and the Struggle for Life 

A full exposition of Sexual Selection appeared in The Descent of 
Man in 1871, and in the greatly augmented second edition, in 1874. 
It has been remarked that the two subjects, The Descent of Man and 
Selection in Relation to Sex, seem to fuse somewhat imperfectly 
into the single work of which they form the title. The reason for 
their association is clearly shown in a letter to Wallace, dated May 
28, 1864: "...I suspect that a sort of sexual selection has been the 
most powerful means of changing the races of man\" 

Darwin, as we know fi-om his Autobiography"^, was always greatly 
interested in this hypothesis, and it has been shown in the preceding 
pages that he was inclined to look favourably upon it as an interpre- 
tation of many appearances usually explained by Natural Selection. 
Hence Sexual Selection, incidentally discussed in other sections of 
the present essay, need not be considered at any length, in the section 
specially allotted to it. 

Although so interested in the subject and notwithstanding his 
conviction that the hypothesis was sound, Darwin was quite aware 
that it was probably the most vulnerable part of the Origin. Thus 
he wrote to H. W. Bates, April 4, 1861 : "If I had to cut up myself in 
a review I would have [worried?] and quizzed sexual selection; there- 
fore, though I am fully convinced that it is largely true, you may 
imagine how pleased I am at what you say on your belief^." 

The existence of sound-producing organs in the males of insects 
was, Darwin considered, the strongest evidence in favour of the 
operation of sexual selection in this group*. Such a conclusion has 
received strong support in recent years by the numerous careful 
observations of Dr F. A. Dixey^ and Dr G. B. LongstafF^ on the 
scents of male butterflies. The experience of these naturalists 
abundantly coniirms and extends the account given by Fritz Miiller'^ 
of the scents of certain Brazilian butterflies. It is a remarkable fact 
that the apparently epigamic scents of male butterflies should be 
pleasing to man while the apparently aposematic scents in both sexes 
of species with warning colours should be displeasing to him. But 
the former is far more surprising than the latter. It is not perhaps 
astonishing that a scent which is ex hi/pothesi unpleasant to an 
insect-eating Vertebrate should be displeasing to the human sense ; 
but it is certainly wonderful that an odour M'hicli is ex hypothesi 
agreeable to a female butterfly should also be agreeable to man. 

^ More Letters, ii. p. 33. ^ Life and Letters, i. p. 9i. 

3 More Letters, i. p. 183. •* Life and Letters, iii. pp. 94, 138. 

» Proc. Ent. Soc. Land. 1904, p. Ivi; 1905, pp. xxxvii, liv; 1900, p. ii. 
« Proc. Ent. Soc. Lond. 1905, p. xxxv; Trans. Ent. Soc. Land. 1905, p. 136; 1908, 
p. G07. 

■ Jen. Zeit. Vol. xi. 1877, p. 99; Trans. Ent. Soc. Lond. 1878, p. 211. 

Sexual Selection 297 

Entirely new light upon the seasonal appearance of epigamic 
characters is shed by the recent researches of C. W. Beebe\ who 
caused the scarlet tanager {Piranga erythromelas) and the bobolink 
{Dolichonyx oryzivoms) to retain their breeding plumage through 
the whole year by means of fattening food, dim illumination, and 
reduced activity. Gradual restoration to the light and the addition 
of meal-worms to the diet invariably brought back the spring song, 
even in the middle of Avinter. A sudden alteration of temperature, 
either higher or lower, caused the birds nearly to stop feeding, and 
one tanager lost weight rapidly and in two weeks moulted into the 
olive-green winter plumage. After a year, and at the beginning of 
the normal breeding season, "individual tanagers and bobolinks were 
gradually brought under normal conditions and activities," and in 
every case moulted from nuptial plumage to nuptial plumage. " The 
dull colors of the winter season had been skipped." The author justly 
claims to have established "that the sequence of plumage in these 

birds is not in any way predestined through inheritance , but 

that it may be interrupted by certain factors in the environmental 

1 The American Naturalist, Vol. xlii. No. 433, Jau. 1908, p. 34. 


By Sir William Thiselton-Dyer, K.C.M.G., CLE., Sc.D., F.R.S. 

The publication of The Origin of Species placed the study of 
Botanical Geography on an entirely new basis. It is only necessary 
to study the monumental G4ographie Botanique raisonn^e of 
Alphonse De Candolle, published four years earlier (1855), to realise 
how profound and far-reaching was the change. After a masterly 
and exhaustive discussion of all available data De Candolle in his 
final conclusions could only arrive at a deadlock. It is sufficient to 
quote a few sentences : — 

"L'opinion de Lamarck est aujourd'hui abandonn^e par tons les 
naturalistes qui ont etudi^ sagement les modifications possibles des 
etres organises. . . . 

" Et si Ton s'^carte des exag^rations de Lamarck, si Ton suppose 
un premier type de chaque genre, de chaque famille tout au moins, 
on se trouve encore h regard de I'origine de ces types en pr(5sence de 
la grande question de la creation. 

" Le seul parti k prendre est done d'envisager les etres organises 
comme existant depuis certaines c^poques, avec leurs qualit(5s par- 

Reviewing the position fourteen years afterwards, Bentham re- 
marked: — "These views, generally received by the great majority 
of naturalists at the time De Candolle wrote, and still maintained 
by a few, must, if adhered to, check all further enquiry into any 
connection of facts with causes," and he added, " there is little doubt 
but that if De Candolle were to revise his work, he would follow the 
example of so many other eminent naturalists, and... insist that the 
present geographical distribution of plants was in most instances a 
derivative one, altered from a very different former distribution^." 

Writing to Asa Gray in 1856, Darwin gave a brief preliminary 
account of his ideas as to the origin of species, and said that 

1 Vol. II. p. 1107. 2 Pres. Addr. (18G9) Proc. Linn. Soc. 1868—60, p. Ixviii. 

Permanence of Continents 299 

geographical distribution must be one of the tests of their validity^ 
What is of supreme interest is that it was also their starting-point. 
He tells us:— "When I visited, during the voyage of H.M.S. Beagle, 
the Galapagos Archipelago,...! fancied myself brought near to the 
very act of creation. I often asked myself how these many peculiar 
animals and plants had been produced : the simplest answer seemed 
to be that the inhabitants of the several islands had descended from 
each other, undergoing modification in the course of their descent-." 
We need not be surprised then, that in Avriting in 1845 to Sir Joseph 
Hooker, he speaks of ''that grand subject, that almost keystone of the 
laws of creation. Geographical Distribution^" 

Yet De Candolle was, as Bentham saw, unconsciously feeling his 
way, like Lyell, towards evolution, without being able to gi-asp it. 
They both strove to explain phenomena by means of agencies which 
they saw actually at work. If De Candolle gave up the ultimate 
problem as insoluble : — " La creation ou premiere formation des etres 
organises ^chappe, par sa nature et par son anciennet^, k nos moyens 
d'observation*," he steadily endeavoured to minimise its scope. At 
least half of his great work is devoted to the researches by which he 
extricated himself from a belief in species having had a multiple 
origin, the view which had been held by successive naturalists from 
Gmelin to Agassiz. To account for the obvious fact that species 
constantly occupy dissevered areas, De Candolle made a minute study 
of their means of transport. This was found to dispose of the vast 
majority of cases, and the remainder he accounted for by geographical 

But Darwin strenuously objected to invoking geographical change 
as a solution of every difficulty. He had apparently long satisfied 
himself as to the "permanence of continents and great oceans." 
Dana, he tells us, "was, I believe, the first man who maintained" 
this*', but he had himself probably arrived at it independently. 
Modern physical research tends to confirm it. The earth's centre 
of gravity, as pointed out by Pratt from the existence of the Pacific 
Ocean, does not coincide with its centre of figure, and it has been 
conjectured that the Pacific Ocean dates its origin from the separa- 
tion of the moon from the earth. 

The conjectui-c aj)pear8 to be unnecessary. Love shows that "the 
force that keeps the I'acific Ocean on one side of the earth is gi-avity, 
directed more towards tlie centre of giavity than the centre of the 

* Life and Letten, ii. p. 78. 

' The Variation of Animals and Plants (2nd edit.), 1890, i. pp. 9, 10. 

* Life and Letters, i. p. 336. * Loc. cit. p. 1100. » Loc. cit. p. 1116. 
' Life and Letters, iii. p. 247. Dana says: — "The continents and oceans had their 

general outline or form defined in earliest time," Manual of Geology, revised edition. 
Philadelphia, 1869, p. 732. I have uo access to au earlier edition. 

300 Geographical Distribution of Plants 

figured" I can only summarise the conclusions of a technical but 
masterly discussion. " The broad general features of the distribution 
of continent and ocean can be regarded as the consequences of simple 
causes of a dynamical character," and finally, "As regards the contour 
of the great ocean basins, we seem to be justified in saying that the 
earth is approximately an oblate spheroid, but more nearly an 
ellipsoid with three unequal axes, having its surface furrowed 
according to the formula for a certain spherical harmonic of the 
third degi'eeV' and he shows that this furrowed surface must be 
produced " if the density is greater in one hemispheroid than in the 
other, so that the position of the centre of gravity is eccentric^." 
Such a modelling of the earth's surface can only be referred to a 
primitive period of plasticity. If the furrows account for the great 
ocean basins, the disposition of the continents seems equally to 
follow. Sir George Darwin has pointed out that they necessarily 
" arise from a supposed primitive viscosity or plasticity of the earth's 
mass. For during this course of evolution the earth's mass must 
have suffered a screwing motion, so that the polar regions have 
travelled a little from west to east relatively to the equator. This 
affords a possible explanation of the north and south trend of our 
great continents^" 

It would be trespassing on the province of the geologist to pursue 
the subject at any length. But as Wallace^, who has admirably 
vindicated Darwin's position, points out, the "question of the per- 
manence of our continents... lies at the root of all our inquiries into 
the gi-eat changes of the earth and its inhabitants." But he proceeds : 
"The very same evidence which has been adduced to prove the 
general stability and permanence of our continental areas also goes 
to prove that they have been subjected to wonderful and repeated 
changes in detail^." Darwin of com-se would have admitted this, for 
with a happy expression he insisted to Lyell (1856) that "the 
skeletons, at least, of our continents are ancient^." It is impossible 
not to admire the courage and tenacity with which he carried on the 
conflict single-handed. But he failed to convince Lyell. For we 
still find him maintaining in the last edition of the Principles: 
"Continents therefore, although permanent for whole geological 
epochs, shift their positions entirely in the course of ages*^." 

Evidence, however, steadily accumulates in Darwin's support. 

' Report of the 11th Meeting of the British Association (Leicester, 1907), London, 1908, 
p. 431. 

- Ibid. p. 436. ^ Ibid. p. 431. 

•» Encijcl. Brit. (9th edit.), Vol. xxiii. "Tides," p. 379. 

» Island Life (•2nd edit.), 1895, p. 103. » Loc. cit. p. 101. 

' More Letters, ii. p. 135. 

8 Lyell'fi Principles of Geology (Uth edit.), London, 1872, i. p. 258. 

Permanence of Continents 301 

His position still remains inexpugnable that it is not permissible to 
invoke geographical change to explain difficulties in distribution 
without valid geological and physical support. Writing to Mellard 
Reade, who in 1878 had said, "'While believing that the ocean-depths 
are of enormous age, it is impossible to reject other evidences that 
they have once been land," he pointed out " the statement from the 
Challenger that all sediment is deposited within one or two hundred 
miles from the shores \" The following year Sir Archibald Geikie^ 
informed the Royal Geographical Society that "No part of the 
results obtained by the Challenger expedition has a profounder 
interest for geologists and geographers than the proof which they 
furnish that the floor of the ocean basins has no real analogy among 
the sedimentary formations which form most of the framework of the 

Nor has Darwin's earlier argument ever been upset. "The fact 
which I pointed out many years ago, that all oceanic islands are 
volcanic (except St Paul's, and now that is viewed by some as the 
nucleus of an ancient volcano), seem to me a strong argument that 
no continent ever occupied the great oceans^." 

Dr Guppy, who devoted several years to geological and botanical 
investigations in the Pacific, found himself forced to similar con- 
clusions. " It may be at once observed," he says, " that my belief in 
the general principle that islands have always been islands has not 
been shaken," and he entirely rejects "the hypothesis of a Pacific 
continent." He comes back, in full view of the problems on the 
spot, to the position from which, as has been seen, Darmn started : 
" If the distribution of a particular group of plants or animals does 
not seem to accord with the present arrangement of the land, it is 
by far the safest plan, even after exhausting all likely modes of 
explanation, not to invoke the intervention of geographical changes ; 
and I scarcely think that our knowledge of any one group of organ- 
isms is ever sufficiently precise to justify a recourse to hypothetical 
alterations in the present relations of land and sea*." Wallace 
clinches the matter when he finds "almost the whole of the vast 
areas of the Atlantic, Pacific, Indian, and Southern Oceans, without 
a solitary relic of the great islands or continents supposed to have 
sunk beneath their waves^" 

Writing to Wallace (1876), Darwin warmly approves the former's 
"protest against sinking imaginary continents in a quite reckless 

1 More Letters, ii. p. lid. 

2 "Geographical Evolution," Proc. R. Geogr. Soc. 1879, p. 427. 
* More Lcttvrs, ii. p. 146. 

< Obnervations of a Naturalist in the Pacific beticeen 1890 and 1899, London, 1903, 
I. p. 380, 

^ Island Life, p. 105. 

302 Geographical Distribution of Plants 

manner, as was stated by Forbes, followed, alas, by Hooker, and 
caricatured by Wollaston and [Andrew] Murray \" The transport 
question thus became of enormously enhanced importance. We need 
not be surprised then at his writing to Lyell in 185G: — "I cannot 
avoid thinking that Forbes' 'Atlantis' was an ill-service to science, 
as checking a close study of means of dissemination V and Darwin 
spared no pains to extend our knowledge of them. He implores 
Hooker, ten years later, to "admit how little is known on the 
subject," and summarises with some satisfaction what he had himself 
achieved: — "Remember how recently you and others thought that 
salt water would soon kill seeds.... Remember that no one knew that 
seeds would remain for many hours in the crops of birds and retain 
their vitality; that fish eat seeds, and that when the fish are de- 
voured by birds the seeds can germinate, etc. Remember that 
every year many birds are blown to Madeira and to the Bermudas. 
Remember that dust is blown 1000 miles across the Atlantic^" 

It has always been the fashion to minimise Darwin's conclusions, 
and these have not escaped objection. The advocatus diaholi has a 
useful function in science. But in attacking Darwin his brief is 
generally found to be founded on a slender basis of facts. Thus Winge 
and Knud Andersen have examined many thousands of migratory birds 
and found " that their crops and stomachs were always empty. They 
never observed any seeds adhering to the feathers, beaks or feet of 
the birds ^" Tlie most considerable investigation of the problem of 
Plant Dispersal since Darwin is that of Guppy. He gives a striking 
illustration of how easily an observer may be led into error by relying 
on negative evidence. 

""When Ekstam published, in 1895, the results of his observations 
on the plants of Nova Zembla, he observed that he possessed no data 
to show whether swimming and wading birds fed on berries ; and he 
attached all importance to dispersal by winds. On subsequently 
visiting Spitzbergen he must have been at first inclined, therefore, 
to the opinion of Nathorst, who, having found only a solitary species 
of bird (a snow-sparrow) in that region, naturally concluded that 
birds had been of no importance as agents in the plant-stocking. 
However, Ekstam's opportunities were greater, and he tells us that 
in the craws of six specimens of Lagopus hyperhoreus shot in Spitz- 
bergen in August he found represented almost 25 per cent, of the 
usual phanerogamic flora of that region in the form of fruits, seeds, 
bulbils, flower-buds, leaf-buds, &c " 

" The result of Ekstam's observations in Spitzbergen was to lead 
him to attach a very considerable importance in plant dispersal to 

1 lAfc and Letters, iii. p. 230. 2 jii,i „_ p_ yg^ a j^jore Letters, i. p. 483. 

* E. F. Scbarff, European Animals, p. 64, London, 1907. 

Multiple Origins 303 

the agency of birds; and when in explanation of the Scandinavian 
elements in the Spitzbergen flora he had to choose between a former 
land connection and the agency of birds, he preferred the bird\" 

Darwin objected to "continental extensions" on geological grounds, 
but he also objected to Lyell that they do not " account for all the 
phenomena of distribution on islands"," such for example as the 
absence of Acacias and Banksias in Xew Zealand. He agreed 
with De Candolle that " it is poor work putting together the merely 
possible means of distribution." But he also agreed with him that 
they were the only practicable door of escape from multiple origins. 
If they would not work then "every one who believes in single 
centres will have to admit continental extensions V and that he 
regarded as a mere counsel of despair: — "to make continents, as 
easily as a cook does pancakes ^" 

The question of multiple origins however presented itself in another 
shape where the solution was much more difficult. The problem, as 
stated by Darwin, is this : — "The identity of many plants and animals, 
on mountain-summits, separated from each other by hundreds of 
miles of lowlands... without the apparent possibility of their having 
migrated from one point to the other." He continues, " even as long 
ago as 1747, such facts led Gmelin to conclude that the same species 
must have been independently created at several distinct points; 
and we might have remained in this same belief, had not Agassiz 
and others called vivid attention to the Glacial period, which affords 
...a simple explanation of the facts^" 

The "simple explanation" w^as substantially given by E. Forbes 
in 184G. It is scarcely too much to say that it belongs to the same 
class of fertile and far-reaching ideas as "natural selection" itself. 
It is an extraordinary instance, if one were Avanted at all, of 
Darwin's magnanimity and intense modesty that though he had 
arrived at the theory himself, he acquiesced in Forbes receiving the 
well-merited credit. "I have never," he says, "of course alluded 
in print to my having independently worked out this view." But 
he would have been more than human if he had not added: — "I was 
forestalled in... one important point, which my vanity has always 
made me regret*'." 

Darwin, however, by applying the theory to trans-tropical 
migration, went far beyond Forbes. The first enunciation to this is 
apparently contained in a letter to Asa Gray in 1858. The whole is 
too long to quote, but the pith is contained in one paragraph. "There 
is a considerable body of geological evidence that during the Glacial 

' Guppy, op. cit. u. pp. 511, 512. ' Life arid Letter.^, ii. p. 77. 

8 Ibid. II. p. 82. * Ibid. II. p. 74. 

* Origin of Species (6th ed.) p. 330. " Life and Letters, i. p. 88. 

304 Geographical Distribution of Plants 

epoch the whole world was colder; I inferred that,... from erratic 
boulder phenomena carefully observed by me on both the east and 
west coast of South America. Now I am so bold as to believe that 
at the height of the Glacial epoch, and when all Tropical productions 
must Imve been considerably distressed, several temperate forms 
slowly travelled into the heart of the Tropics, and even reached the 
southern hemisphere ; and some few southern forms penetrated in 
a reverse direction northward ^" Here again it is clear that though 
he credits Agassiz with having called vivid attention to the Glacial 
period, he had himself much earlier grasped the idea of periods of 

Putting aside the fact, which has only been made known to us 
since Darwin's death, that he had anticipated Forbes, it is clear 
that he gave the theory a generality of which the latter had no 
conception. This is pointed out by Hooker in his classical paper 
On the Distribution of Arctic Plants (1860). "The theory of a 
southern migration of northern types being due to the cold epochs 
preceding and during the glacial, originated, I believe, with the late 
Edward Forbes ; the extended one, of the trans-tropical migration, 
is Mr Darwin's^." Assuming that local races have derived from a 
common ancestor. Hooker's great paper placed the fact of the migra- 
tion on an impregnable basis. And, as he pointed out, Darwin has 
shown that " such an explanation meets the difficulty of accounting 
for the restriction of so many American and Asiatic arctic types to 
their own peculiar longitudinal zones, and for what is a far greater 
difficulty, the representation of the same arctic genera by most closely 
allied species in different longitudes." 

The facts of botanical geography were vital to Darwin's argument 
He had to show that they admitted of explanation without assuming 
multiple origins for species, which would be fatal to the theory of 
Descent. He had therefore to strengthen and extend De Candolle's 
work as to means of transport. He refused to supplement them by 
hypothetical geographical changes for which there was no inde- 
pendent evidence : this was simply to attempt to explain ignotum 
per ignotius. He found a real and, as it has turned out, a far- 
reaching solution in climatic change due to cosmical causes which 
compelled the migration of species as a condition of their existence. 
The logical force of the argument consists in dispensing with any 

^ Life and Letters, ii. p. 136. 

2 Linn. Trans, xxiii. p. 253. The attempt appears to have been made to claim for Heer 
priority in what I may term for short the arctic-alpine theory (Scharff, European Animals^ 
p. 128). I find no suggestion of his having hit upon it in his correspondence with Darwin 
or Hooker. Nor am I aware of any reference to his having done so in his later 
publications. I am indebted to his biographer, Professor Schroter, of Zurich, for an 
examination of his earlier papers with an equally negative result. 

Plant Migration 305 

violent assumption, and in showing that the principle of descent is 
adequate to explain the ascertained facts. 

It does not, I think, detract from the merit of Darwin's con- 
clusions that the tendency of modern research has been to show 
that the effects of the Glacial period were less simple, more localised 
and less general than he perhaps supposed. He admitted that 
"equatorial refrigeration... must have been smalP." It may prove 
possible to dispense with it altogether. One cannot but regi'et that 
as he wrote to Bates: — '"the sketch in the Origin gives a very 
meagre account of my fuller MS. essay on this subject'-." Wallace 
fully accepted "the effect of the Glacial epoch in bringing about 
the present distribution of Alpine and Arctic plants in the northern 
Jiemisphere," but rejected "the lowering of the temperature of the 
tropical regions during the Glacial period " in order to account for 
their presence in the southern hemisphere^ The divergence how- 
ever does not lie very deep. Wallace attaches more importance to 
ordinary means of transport. "If plants can pass in considerable 
numbers and variety over wide seas and oceans, it must be yet more 
easy for them to traverse continuous areas of land, wherever mountain- 
chains offer suitable stations*." And he argues that such periodical 
changes of climate, of which the Glacial period may be taken as a 
type, would facilitate if not stimulate the process ^ 

It is interesting to remark that Darwin drew from the facts of 
plant distribution one of his most ingenious arguments in support 
of this theory*^. He tells us, "I was led to anticipate that the species 
of the larger genera in each country would oftener present varieties, 
than the species of the smaller general" He argues " where, if we 
may use the expression, the manufactory of species has been active, 
we ought generally to find the manufactory still in action*^." This 
proved to be the case. But the labour imposed upon him in the 
studv was immense. He tabulated local floras "belting the whole 
northern hemisphere^" besides voluminous works such as De Can- 
doUe's Prodromus. The results scarcely fill a couple of pages. This 
is a good illustration of the enormous pains which he took to base 
any statement on a secure foundation of evidence, and for this the 
world, till the publication of his letters, could not do him justice. 
He was a gi-eat admirer of Herbert Spencer, whose "prodigality 
of original tliought " astonished him. " But," he says, " the reflection 
constantly recurred to me that each suggestion, to be of real value to 
service, would rec^uire years of work^''." 

1 More Letters, r. p. 177. ^ Loc. cit. 

' More Letters, u. p. 25 (footnote 1). ■• Island Life (2nd eilit.), London, 18D5, p. 512. 

' Loc. cit. p. 518. ' See More Letters, i. p. 4'2i. 

^ Or if/in, p. 44. ' Ibid. p. 45. 

» More Letters, i. p. 107. " Ibid. n. p. 233. 

D. 20 

306 Geographical Distribution of Plants 

At last the ground was cleared and we are led to the final 
conclusion. " If the difficulties be not insuperable in admitting that 
in the long course of time all the individuals of the same species 
belonging to the same genus, have proceeded from some one source ; 
then all the grand leading facts of geographical distribution are 
explicable on the theory of migration, together with subsequent 
modification and the multiplication of new forms \" In this single 
sentence Darwin has stated a theory which, as his son F. Darwin 
has said wth justice, has "revolutionized botanical geography I" It 
explains how physical barriers separate and form botanical regions ; 
how allied species become concentrated in the same areas ; how, 
under similar physical conditions, plants may be essentially dissimilar, 
showing that descent and not the surroundings is the controlling 
factor ; how insular floras have acquired their peculiarities ; in short 
liow the most various and apparently uncorrelated problems fall 
easily and inevitably into line. 

The argument from plant distribution was in fact irresistible. 
A proof, if one were wanted, was the immediate conversion of what 
Hooker called "the stern keen intellect^" of Bentham, by general 
consent the leading botanical systematist at the time. It is a striking 
historical fact that a paper of his own had been set do^vn for reading 
at the Linnean Society on the same day as Darwin's, but had to 
give way. In this he advocated the fixity of species. He withdrew 
it after hearing Darwin's. We can hardly realise now the momentous 
eflect on the scientific thought of the day of the announcement of the 
new theory. Years afterwards (1882) Bentham, notwithstanding his 
habitual restraint, could not write of it without emotion. "I was 
forced, however reluctantly, to give up my long-cherished convictions, 
the results of much labour and study." The revelation came without 
preparation. Darwin, he wrote, "never made any communications 
to me in relation to his views and labours." But, he adds, "I... fully 
adopted his theories and conclusions, notwithstanding the severe 
pain and disappointment they at first occasioned me*." Scientific 
history can have few incidents more worthy. I do not know what 
is most striking in the story, the pathos or the moral dignity of 
Bentham's attitude. 

Darwin necessarily restricted himself in the Griffin to establishing 
the general principles which would account for the facts of distribu- 
tion, as a part of his larger argument, without attempting to illustrate 
them in particular cases. This he appears to have contemplated 
doing in a separate work. But writing to Hooker in 1868 he 

' Origin, p. SCO. 

» "The Botauical Work of Darwin," Ann. Bot. 1809, p. xi. 

* More Lettcm, i. p. 134. * Life and Letters, ii. p. '29i. 

Ilooker''s Contributions to Geographical Botany 307 

said : — " I shall to the day of my death keep up my full interest in 
Geographical Distribution, but I doubt whether I shall ever have 
strength to come in any fuller detail than in the Origin to this grand 
subject^" This must be always a matter for regi-et. But we may 
gather some indication of his later speculations from the letters, the 
careful publication of Avhich by F. Darwin has rendered a service to 
science, the value of which it is difficult to exaggerate. They admit 
us to the workshop, where we see a great theory, as it were, in the 
making. The later ideas that they contain were not it is true public 
property at the time. But they were communicated to the leading 
biologists of the day and indirectly have had a large influence. 

If Darwin laid the foundation, the present fabric of Botanical 
Geography must be credited to Hooker. It was a happy partnership. 
The far-seeing, generalising power of the one was supplied with data 
and checked in conclusions by the vast detailed knoAvledge of the 
other. It may be permitted to quote Darwin's generous acknowledge- 
ment when writing the Origin : — " I never did pick any one's pocket, 
but whilst writing my present chapter I keep on feeling (even when 
differing most from you) just as if I were stealing from you, so much 
do I owe to your writings and conversation, so much more than mere 
acknowledgements show-." Fourteen years before he had written 
to Hooker : " I know I shall live to see you the first authority in 
Europe on..,Geogi'aphical Distribution V We owe it to Hooker that 
no one now undertakes the flora of a country without indicating 
the range of the species it contains. Bentham tells us : " after 
De Candolle, independently of the great Avorks of Darwin... the first 
important addition to the science of geographical botany was that 
made by Hooker in his Introductori/ Essay to tJie Flora of Tasmania, 
which, though contemporaneous only with the Origin of Species, was 
drawn up with a general knowledge of his friend's observations and 
views*." It cannot be doubted that this and the great memoir on 
the Distribution of Arctic Plants were only less epoch-making than 
the Origin itself, and must have supplied a ijowerful support to the 
general theory of organic evolution. 

Darwin always asserted his "entire ignorance of Botany ^" But 
this was only part of his constant half-humourous self-deprecia- 
tion. He had been a pupil of Henslow, and it is evident that he 
had a good Avorking knowledge of systematic botany. He could find 
his way about in the literature and always cites the names of plants 
with scrupulous accuracy. It was because he felt the Mant of such 
a work for his own researches that he urged the preparation of the 
Index Kewcnsis, and undertook to defray the expense. It has been 

* More Letters, ii. p. 7. '^ Life and Letters, ii. p. 148 (footnote). ' Ihid. i. p. 33G. 

* i'rca. Addr. (IbG'J), Froc. Linn. Soc. 18C8-0y, p. kxiv. » More Letters, i, p. 400. 


308 Geographical Distribution of Plants 

thought singular that he should have been elected a "correspondant " 
of the Academic des Sciences in the section of Botany, but it is not 
surprising that his work in Geographical Botany made the botanists 
anxious to claim him. His heart went with them. " It has always 
pleased me," he tells us, "to exalt plants in the scale of organised 
beings ^" And he declares that he finds "any proposition more easily 
tested in botanical works^ than in zoological." 

In the Introductory Essay Hooker dwelt on the "continuous 
current of vegetation from Scandinavia to Tasmania V' but finds 
little evidence of one in the reverse direction. " In the New World, 
Arctic, Scandinavian, and North American genera and species are 
continuously extended from the north to the south temperate and 
even Antarctic zones ; but scarcely one Antarctic species, or even 
genus advances north beyond the Gulf of Mexico*," Hooker con- 
sidered that this negatived "the idea that the Southern and Northern 
Floras have had common origin within comparatively modern geo- 
logical epochs \" This is no doubt a correct conclusion. But it is 
difficult to explain on Darwin's view alone, of alternating cold in 
the two hemispheres, the preponderant migration from the north to 
the south. He suggests, therefore, that it "is due to the greater 
extent of land in the north and to the northern forms... having... 
been advanced through natural selection and competition to a higher 
stage of perfection or dominating power*^." The present state of the 
Flora of New Zealand afibrds a striking illustration of the correctness 
of this view. It is poor in species, numbering only some 1400, of 
which three-fourths are endemic. They seem however quite unable 
to resist the invasion of new comers and already 600 species of foreign 
origin have succeeded in establishing themselves. 

If we accept the general configuration of the earth's surface as 
permanent a continuous and progressive dispersal of species from 
the centre to the circumference, i.e. southwards, seems inevitable. 
If an observer were placed above a point in St George's Channel 
from which one half of the globe was visible he would see the greatest 
possible quantity of land spread out in a sort of stellate figure. The 
maritime supremacy of the English race has perhaps flowed from the 
central position of its home. That such a disposition would facilitate 
a centrifugal migration of land organisms is at any rate obvious, and 
fluctuating conditions of climate operating from the pole would 
supply an eflbctive means of propulsion. As these became more 

1 Life and Letters, i. p. 98. = jjy^i u. p. 99. 

^ Introductory Essay to the Flora of Tasmania, London, 1859. Reprinted from the 
Botany of the Antarctic Expedition, Part in., Flora of Tasmania, Vol. i. p. ciii. 
* p. civ. 5 Loc. cit. 

^ Origin of Species (Otli edit.), p. 310; cf. also Life and Letters, 11. p. 142. 

Plant Mi(jration 309 

rigorous animals at an}- rate would move southwards to escape them. 
It would be equally the case with plants if no insuperable obstacle 
interposed. This implies a mobility in plants, notwithstanding what 
we know of means of transport which is at first sight paradoxical. 
Bentham has stated this in a striking way : " Fixed and immovable 
as is the individual plant, there is no class in which the race is 
endowed with greater facilities for the widest dispersion.... Plants cast 
away their offspring in a dormant state, ready to be carried to any 
distance by those external agencies Avhich we may deem fortuitous, 
but ^vithout which many a race might perish from the exhaustion of 
the limited spot of soil in which it is rooted\" 

I have quoted this passage from Bentham because it emphasises 
a point which Darwin for his purpose did not find it necessary to 
dwell upon, though he no doubt assumed it. Dispersal to a distance 
is, so to speak, an accidental incident in the life of a species. 
Lcpidium Draha, a native of South-eastern Europe, owes its pre- 
valence in the Isle of Thanet to the disastrous Walcheren expedition ; 
the straw-stuffing of the mattresses of the fever-stricken soldiers who 
Mere landed there was used by a farmer for manure. Sir Joseph 
Hooker- tells us that landing on Lord Auckland's Island, which was 
uninhabited, "the first evidence I met >vith of its having been 
previously visited by man was the English chickweed ; and this I 
traced to a mound that marked the grave of a British sailor, and 
that was covered with the plant, doubtless the offspring of seed that 
bad adhered to the spade or mattock with which the grave had 
been dug." 

Some migration from the spot where the individuals of a species 
have germinated is an essential provision against extinction. Their 
descendants otherwise would be liable to suppression by more vigorous 
competitors. But they would eventually be extinguished inevitably, 
as pointed out by Bentham, by the exhaustion of at any rate some 
one necessary constituent of the soil. Gilbert showed by actual 
analysis that the production of a " fairy ring " is simply due to the 
using up by the fimgi of the available nitrogen in the enclosed area 
which continually enlarges as they seek a fresh supply on the out- 
side margin. Anyone who cultivates a garden can easily verify the 
fact that every plant has some adaptation for varying degrees of seed- 
dispersal. It caimot be doubted that slow but persistent terrestrial 
migration has played an enormous i)art in bringing about existing 
plant-distribution, or that climatic changes would intensify the effect 
because they Mould force the abandonment of a former area and the 
occupation of a new one. We are compelled to admit that as an 

1 Tree. Addr. (18C9), Proc. Linn. Soc. 1868— «9, pp. Ixvi, Ixvii. 
« Itoyal Institution Lecture, April 12, 1878. 

310 Geographical Distribution of Plants 

incident of the Glacial period a whole flora may have moved down and 
up a mountain side, while only some of its constituent species would 
be able to take advantage of means of long-distance transport. 

I have dwelt on the importance of what I may call short-distance 
dispersal as a necessary condition of plant life, because I think it 
suggests the solution of a difficulty which leads Guppy to a conclusion 
with which I am unable to agree. But the work which he has done 
taken as a whole appears to me so admirable that I do so with the 
utmost respect. He points out, as Bentham had already done, that 
long-distance dispersal is fortuitous. And being so it cannot have 
been provided for by previous adaptation. He says^: "It is not 
conceivable that an organism can be adapted to conditions outside 
its environment." To this we must agree ; but, it may be asked, do 
the general means of plant dispersal violate so obvious a principle ? 
He proceeds : " The great variety of the modes of dispersal of seeds 
is in itself an indication that the dispersing agencies avail themselves 
in a hap-hazard fashion of characters and capacities that have been 
developed in other connections^." "Their utility in these respects is 
an accident in the plant's life^" He attributes this utility to a 
"determining agency," an influence which constantly reappears in 
various shapes in the literature of Evolution and is ultra-scientific 
in the sense that it bars the way to the search for material causes. 
He goes so far as to doubt whether fleshy fruits are an adaptation for 
the dispersal of their contained seeds*. Writing as I am from a 
hillside which is covered by hawthorn bushes sown by birds, I confess 
I can feel little doubt on the subject myself. The essential fact 
which Guppy brings out is that long-distance unlike short-distance 
dispersal is not universal and purposeful, but selective and in that 
sense accidental. But it is not difficult to see how under favouring 
conditions one must merge into the other. 

Guppy has raised one novel point wliich can only be briefly 
referred to but which is of extreme interest. There are grounds for 
thinking that flowers and insects have mutually reacted upon one 
another in their evolution. Guppy suggests that something of the 
same kind may be true of birds. I must content myself with the 
quotation of a single sentence. "With the secular drying of the 
globe and the consequent difierentiation of climate is to be connected 
the suspension to a great extent of the agency of birds as plant 
dispcrsers in later ages, not only in the Pacific Islands but all over 
the tropics. The changes of climate, birds and plants have gone on 
together, the range of the bird being controlled by the climate, and 
the distribution of the plant being largely dependent on the bird^" 

^ Guppy, op. cit. II. p. 99. ' Loc. cit. p. 102. * Loc. cit. p. 100. 

* Loc. cit. p. 102. » Loc. cit. n. p. 221. 

Plant Migration 311 

Darwin was clearly prepared to go further than Hooker m ac- 
counting for the southern flora by dispersion from the north. Thus 
he says: "We must, I suppose, admit that every yard of land has 
been successively covered with a beech-forest between the Caucasus 
and Japan \" Hooker accounted for the dissevered condition of the 
southern flora by geographical change, but this Darwin could not 
admit. He suggested to Hooker that the Australian and Cape floras 
miglit have had a point of connection through Abyssinia'-, an idea 
which Avas promptly snufted out. Similarly he remarked to Bentham 
(1869): "I suppose you think that the Restiaceae, Proteaceae, etc., 
etc. once extended over the whole world, leaving fragments in the 
soutli^" Eventually he conjectured "that there must have been a 
Tertiary Antarctic continent, from which various forms radiated to 
the southern extremities of our present continents*." But character- 
istically he could not admit any land connections and trusted to 
" floating ice for transporting seed^" I am far from saying that this 
theory is not deserving of serious attention, though there seems to 
be no positive evidence to support it, and it immediately raises the 
difficulty how did such a continent come to be stocked ? 

We must, however, agree with Hooker that the common origin 
of tlie northern and southern floras must be referred to a remote 
past. That Darwin had this in his mind at the time of the publication 
of the Origin is clear from a letter to Hooker. " The view which 
I should have looked at as perhaps most probable (though it hardly 
differs from yours) is that the whole world during the Secondary 
ages was inhabited by marsupials, araucarias (Mem. — Fossil wood 
of tliis nature in South America), Banksia, etc. ; and that these were 
supplanted and exterminated in the greater area of the north, but 
were left alive in the south^" Remembering that Araucaria, unlike 
Banksia, belongs to the earlier Jurassic not to the angiospermous 
flora, this view is a germinal idea of the widest generality. 

The extraordinary congestion in species of the peninsulas of the 
Old World points to the long-continued action of a migration south- 
wards. Each is in fact a ad-de-sac into which they have poured 
and from which there is no escape. On the other hand the high 
degree of specialisation in the southern floras and the little power 
tlie species possess of holding their own in competition or in adapta- 
tion to new conditions point to long-continued isolation. " An island 
...will prevent free immigration and competition, hence a greater 
number of ancient forms will survived" But variability is itself 
subject to variation. The nemesis of a high degree of protected 

1 More Letters, ii. p. 9. * Ibid. i. p. 447. ' Ibid. i. p. 330. 

* Life and Letters, ni. p. 231. " Hore Letters, i. p. lUi. 

« Ibid. I. p. 453. ' Ibid. I. p. 481. 


12 Geographical Distrihution of Plants 

specialisation is the loss of adaptability \ It is probable that many 
elements of the southern flora are doomed: there is, for example, 
reason to think that the singular Stapelieae of S. Africa are a dis- 
appearing group. The tree Lobelias which linger in the mountains 
of Central Africa, in Tropical America and in the Sandwich Islands 
have the aspect of extreme antiquity. I may add a further striking 
illustration from Professor Seward : " The tall, graceful fronds of 
Matonia pect'mata, forming miniature forests on the slopes of 
Mount Ophir and other districts in the Malay Peninsula in associa- 
tion Avith Dipteris conjngata and Dipteris lohhiana, represent a 
phase of Mesozoic life which survives 

' Like a dim picture of the drowned past^.' " 

The Matonineae are ferns with an unusually complex vascular system 
and were abundant " in the northern hemisphere during the earlier 
part of the Mesozoic era." 

It was fortunate for science that Wallace took up the task which 
his colleague had abandoned. Writing to him on the publication 
of his Geographical Distribution of Animals Darwin said: "I feel 
sure that you have laid a broad and safe foundation for all future 
work on Distribution. How interesting it will be to see hereafter 
plants treated in strict relation to your views^" This hope was 
fulfilled in Island Life. I may ({uote a passage from it which 
admirably summarises the contrast between the northern and the 
southern floras. 

"Instead of the enormous northern area, in which highly organised 
and dominant groups of plants have been developed gifted with 
great colonising and aggressive powers, we have in the south three 
comparatively small and detached areas, in which rich floras have 
been developed with special adaptations to soil, climate, and organic 
environment, but comparatively impotent and inferior beyond their 
own domain ^" 

It will be noticed that in the summary I have attempted to give 
of the history of the subject, eflbrts have been concentrated on bring- 
ing into relation the temperate floras of the northern and southern 
hemispheres, but no account has been taken of the rich tropical 
vegetation which belts the world and little to account for the original 
starting-point of existing vegetation generally. It must be re- 
membered on the one hand that our detailed knowledge of the 
floras of the tropics is still very incomplete and far inferior to that 

* See Lyell, The Geological Evidences of the Antiquity of Man, London, 1863, p. 446. 
' Report of the 73rd Meeting of the British Assoc. (Southport, 1903), London, 1904, 
p. 644. 

^ More Letters, n. p. 12. * Wallace, Island Life, pp. 527, 528. 

Ancestry of Angiosj^erms 313 

of temperate regions ; on the other hand palaeontological discoveries 
have put the problem in an entirely new light. Well might Darwin, 
writing to Heer in 1875, say: "Many as have been the wonderful 
discoveries in Geology during the last half-centur}', I think none have 
exceeded in interest your results with respect to the plants which 
formerly existed in the arctic regions^" 

As early as 1848 Debey had described from the Upper Cre- 
taceous rocks of Aix-la-Chapelle Flowering plants of as high a 
degree of development as those now existing. The fact was com- 
mented upon by Hooker-, but its full significance seems to have been 
scarcely appreciated. For it implied not merely that their evolution 
must have taken place but the foundations of existing distribution 
must have been laid in a preceding age. We now know from the 
discoveries of the last fifty years that the remains of the Neocomian 
flora occur over an area extending through 30° of latitude. Th« con- 
clusion is irresistible that within this was its centre of distribution 
and probably of origin. 

Darwin was immensely impressed with the outburst on the world 
of a fully-fledged angiospermous vegetation. He warmly approved 
the brilliant theory of Saporta that this happened "as soon [as] 
flower-frequenting insects were developed and favoured intercross- 
ing^" Writing to him in 1877 he says: "Your idea that dicoty- 
ledonous plants were not developed in force until sucking insects 
had been evolved seems to me a splendid one. I am surprised that 
the idea never occurred to me, but this is always the case when 
one first hears a new and simple explanation of some mysterious 

Even with this help the abruptness still remains an almost insoluble 
problem, though a forecast of floral structure is now recognised in some 
Jurassic and Lower Cretaceous plants. But the gap between this and 
the structural complexity and diversity of angiosperms is enormous. 
Darwin thought that the evolution might have been accomplished 
during a period of prolonged isolation. Writing to Hooker (1881) he 
says: "Nothing is more extraordinary in the history of the Vegetable 
Kingdom, as it seems to me, than the apparently/ very sudden or 

' Mare Letters, ii. p. 240. ' Iiitrod. Essay to the Flora of Tasmania, p. sx. 

* More Letters, ii. p. 21. 

* Life and Letters, iii. p. 285. Substantially the same idea had occurred earlier to 
P. W. A. Miquel. Remarking that "sucking insects (Haustellata)... perform in nature 
the important duty of maintaining the existence of the vegetable kingdom, at least as far 
as the higher orders are concerned," he points out that " the appearance in great numbers 
of hauBtellate insects occurs at and after the Cretaceous epoch, when the plants with 
pollen and closed carpels (Angiowperms) are found, and acquire httle by little the pre- 
ponderance in the vegetable kingdom." Archives Nierlandaises, iii. (1868). English 
translation in Journ. of Hot. 186'J, p. 101. 

314 Geoyraphical Distribution of Plants 

abrupt development of the higher plants. I have sometimes specu- 
lated wliether there did not exist somewhere during long ages an 
extremely isolated continent, perhaps near the South Pole^" 

The present trend of evidence is, however, all in favour of a 
northern origin for flowering plants, and we can only appeal to the 
imperfection of the geological record as a last resource to extricate 
us from the difficulty of tracing the process. But Darwin's instinct 
that at some time or other the southern hemisphere had played an 
important part in the evolution of the vegetable kingdom did not 
mislead him. Nothing probably would have given him greater 
satisfaction than the masterly summary in which Seward has brought 
together the evidence for the origin of the Glossopteris flora in 
Gondwana land. 

"A vast continental area, of which remnants are preserved in 
Australia, South Africa and South America.... A tract of enormous 
extent occupying an area, part of Avhich has since given place to 
a southern ocean, while detached masses persist as portions of more 
modern continents, which have enabled us to read in their fossil 
plants and ice-scratched boulders the records of a lost continent, 
in which the Mesozoic vegetation of the northern continent had its 
birth'^." Darwin would probably have demurred on physical grounds 
to the extent of the continent, and preferred to account for the 
transoceanic distribution of its flora by the same means which Jiiust 
have accomplished it on land. 

It must in fairness be added that Guppy's later views give some 
support to the conjectural existence of the "lost continent." "The 
distribution of the genus Dammara" (Agathis) led him to modify 
his earlier conclusions. He tells us : — " In my volume on the geology 
of Vanua Levu it was shown that the Tertiary period was an age of 
submergence in the Western Pacific, and a disbelief in any previous 
continental condition was expressed. My later view is more in 
accordance with that of Wichmann, who, on geological grounds, 
contended that the islands of the Western Pacific were in a con- 
tinental condition during the Palaeozoic and Mesozoic periods, and 
that their submergence and subsequent emergence took place in 
Tertiary times ^." 

The weight of the geological evidence I am unable to scrutinise. 
But though I must admit the possibility of some unconscious bias in 
my own mind on the subject, I am impressed with the fact that the 
known distribution of the Glossopteris flora in the southern hemi- 
sphere is precisely paralleled by that of Proteaceae and Rcstiaceac in 

^ Life and Letters, in. p. 248. 

2 Emycl. Brit. (lOtb edit. 1902), Vol. xxxi. ('• Palaeobotany; Mesozoio"), p. 422. 

2 Guppy, op. cit. II. p. 301. 

Ancestry of Angiosperms 315 

it at the present time. It is not unreasonable to suppose that both 
phenomena, so similar, may admit of the same explanation. I confess 
it would not surprise me if fresh discoveries in the distribution of 
the Glossopteris flora were to point to the possibility of its also 
having migrated 80uthward;s from a centre of origin in the northern 

Darwin, however, remained sceptical "about the travelling of 
plants from the north except during the Tertiary period." But 
he added, "such speculations seem to me hardly scientific, seeing 
how little we know of the old floras ^" That in later geological 
times the south has been the grave of the weakened offspring of 
the aggressive north can hardly be doubted. But if we look to 
the Glossopteris flora for the ancestry of Angiosperms during the 
Secondary period, Darwin's prevision might be justified, though he 
has given us no clue as to how he arrived at it. 

It may be true that technically Darwin was not a botanist. But 
in two pages of the Origin, he has given us a masterly explanation 
of "the relationship, with very little identity, between the productions 
of North America and Europe'-." He showed that this could be 
accounted for by their migration southwards from a common area, 
and he told Wallace that he " doubted much whether the now called 
Palaearctic and Nearctic regions ought to be separated^" Catkin- 
bearing deciduous trees had long been seen to justify Darwin's doubt : 
oaks, chestnuts, beeches, hazels, hornbeams, birches, alders, willows 
and poplars are common both to the Old and New World. Newton 
found that the separate regions could not be sustained for birds, and 
he is now usually followed in uniting them as the Holarctic. One feels 
inclined to say in reading the two pages, as Lord Kelvin did to a 
correspondent who asked for some further development of one of 
his papers, It is all there. We have only to apply the principle 
to previous geological ages to understand why the flora of the 
Southern United States preserves a Cretaceous facies. Applying it 
still further we can understand why, when the northern hemisphere 
gradually cooled through the Tertiary period, the plants of the 
Eocene "suggest a comparison of the climate and forests with those 
of the Malay Archipelago and Tropical America*." Writing to 
Asa Gray in 185G with respect to the United States flora, Darwin 
said that " Nothing has surprised me more than the greater generic 
and specific affinity with East Asia than with West America ^" The 
recent discoveries of a Tulip tree and a Sassafras in China afford 

» Life and Letten, in. p. 247. » pp. 333, 334. 

' Life and Letters, iii. p. 230. 

* Clement Reid, Encycl. Drit. (10th edit.), Vol, xsxi. ("Palaeobotany ; Tertiary"), 
p. 435. 

* More Letters, i. p. 434. 

316 Geographical Distribution of Plants 

fresh illustrations. A few years later Asa Gray found the explanation 
in both areas being centres of preservation of the Cretaceous flora 
from a common origin. It is interesting to note that the paper in 
which this was enunciated at once established his reputation. 

In Europe the latitudinal range of the great mountain chains 
gave the Miocene flora no chance of escape during the Glacial period, 
and the Mediterranean appears to have equally intercepted the flow 
of alpine plants to the Atlas \ In Southern Europe the myrtle, the 
laurel, the fig and the dwarf-palm are the sole representatives of as 
many great tropical families. Another great tropical family, the Gesne- 
raceae has left single representatives from the Pyrenees to the Balkans ; 
and in the former a diminutive yam still lingers. These are only 
illustrations of the evidence which constantly accumulates and which 
finds no rational explanation except that which Darwin has given 
to it. 

The theory of southward migration is the key to the interpretation 
of the geogi-aphical distribution of plants. It derived enormous 
support from the researches of Heer and has now become an accepted 
commonplace. Saporta in 1888 described the vegetable kingdom as 
" ^^migrant pour suivre une direction d^termin^e et marcher du nord 
au sud, k la recherche de regions et de stations plus favorables, mieux 
approprices aux adaptations acquises, k meme que la temperature 
terrestre perd ses conditions premieres^." If, as is so often the case, 
the theory now seems to be a priori inevitable, the historian of 
science will not omit to record that the first germ sprang from the 
brain of Darwin. 

In attempting this sketch of Darwin's influence on Geographical 
Distribution, I have found it impossible to treat it from an external 
point of view. His interest in it Avas unflagging; aU I could say 
became necessarily a record of that interest and could not be detached 
fi'om it. He was in more or less intimate touch with everyone who 
was working at it. In reading the letters we move amongst great 
names. With an extraordinary charm of persuasive correspondence 
he was constantly suggesting, criticising and stimulating. It is 
hardly an exaggeration to say that from the quiet of his study at 
Down he was founding and directing a wide-world school. 

1 John Ball in Appendix G, p. 438, in Journal of a Tour in Morocco and the Great Atlas, 
J. D. Hooker and J. Ball, London, 1878. 

2 Orlfjine FaUontologigue des arbra, Paris, lbS8, p. 28. 

The New Flora of Krakatau 317 


Since this essay was put in type Dr Ernst's striking account of 
the Neio Flora of the Volcanic Island of Krakatau^ has reached 
me. All botanists must feel a debt of gratitude to Prof. Seward for 
his admirable translation of a memoir which in its original form is 
practically unprocurable and to the liberality of the Cambridge 
University Press for its publication. In the preceding pages i 
have traced the laborious research by which the methods of Plant 
Dispersal were established by Darwin. In the island of Krakatau 
nature has supplied a crucial experiment which, if it had occurred 
earlier, would have at once secured conviction of their efficiency. 
A quarter of a century ago every trace of organic life in the island 
was " destroyed and buried under a thick covering of glowing stones." 
Now, it is " again covered with a mantle of green, the gi"owth being 
in places so luxuriant that it is necessary to cut one's way laboriously 
through the vegetation ^" Ernst traces minutely how this has been 
brought about by the combined action of wind, birds and sea currents, 
as means of transport. The process will continue, and he concludes : — 
" At last after a long interval the vegetation on the desolated island 
will again acquire that wealth of variety and luxuriance which we 
see in the fullest development which Nature has reached in the 
primaeval forest in the tropics ^" The possibility of such a result 
revealed itself to the insight of Darwin with little encouragement 
or support from contemporary opinion. 

One of the most remarkable facts established by Ernst is that 
this has not been accomplished by the transport of seeds alone, 
"Tree stems and branches played an important part in the coloni- 
sation of Krakatau by plants and animals. Large piles of floating 
trees, stems, branches and bamboos are met with everywhere on the 
beach above high- water mark and often carried a considerable 
distance inland. Some of the animals on the island, such as the 
fat Iguana {Varanus salvator) which suns itself in the beds of 
streams, may have travelled on floating wood, possibly also the 
ancestors of the numerous ants, but certainly plants ^" Darwin 
actually had a prevision of this. Writing to Hooker he says : — 
"Would it not be a prodigy if an unstocked island did not in the 
course of ages receive colonists from coasts whence the currents 
flow, trees arc drifted and birds are driven by gales^?" And ten 
years earlier : — "I must believe in the... whole plant or branch beir)g 
washed into the sea ; with floods and slips and eartliquakes ; this 

» Cambridge, 1909. * Op. cit. p. 4. o Op. cit. p. 72. 

* Op. cit. p. 5C. • Alore Letters, r. p. 483. 

318 Geographical Distribution of Plants 

must continually be happening^'' If we give to "continually" a 
cosmic measure, can the fact be doubted? All this, in the light of our 
present knowledge, is too obvious to us to admit of discussion. But 
it seems to me nothing less than pathetic to see how in the teeth 
of the obsession as to continental extension, Darwin fought single- 
handed for what we now know to be the truth. 

Guppy's heart failed him when he had to deal with the isolated 
case of Agathis which alone seemed inexplicable by known means of 
transport. But when we remember that it is a relic of the pre- 
Angiospermous flora, and is of Araucarian ancestry, it cannot be 
said that the impossibilit}', in so prolonged a history, of the bodily 
transference of cone-bearing branches or even of trees, compels us 
as a last resort to fall back on continental extension to account for 
its existing distribution. 

When Darwin was in the Galapagos Archipelago, he tells us that 
he fancied himself " brought near to the very act of creation." He 
saw how new species might arise from a common stock. Krakatau 
shows us an earlier stage and how by simple agencies, continually at 
vfork, that stock might be supplied. It also shows us how the mixed 
and casual elements of a new colony enter into competition for the 
ground and become mutually adjusted. The study of Plant Distri- 
bution from a Darwinian standpoint has opened up a new field of 
research in Ecology. The means of transport supply the materials 
for a flora, but their ultimate fate depends on their equipment for 
the " struggle for existence." The whole subject can no longer be 
regarded as a mere statistical inquiry which has seemed doubtless 
to many of somewhat arid interest. The fate of every element of 
the earth's vegetation has sooner or later depended on its ability to 
travel and to hold its own under new conditions. And the means by 
which it has secured success is in each case a biological problem 
which demands and will reward the most attentive study. This is 
the lesson which Darwin has bequeathed to us. It is summed up in 
the concluding paragraph of the Origin'^ : — " It is interesting to 
contemplate a tangled bank, clothed Avith many plants of many 
kinds, Avith birds singing on the bushes, with various insects flitting 
about, and Avith Avorms craAvling through the damp earth, and to 
reflect that these elaborately constructed forms, so diflerent from 
each other, and dependent upon each other in so complex a manner, 
have all been produced by laAvs acting around us." 

1 Life and LcUm, u. j-p. 6b, 57. ' Orijjiu oj iijjccies (6tli edit.), p 4.20. 


By Hans Gadow, M.A., Ph.D., F.R.S. 

Strickland Curator and Lecturer on Zoology in the Universitij of Cambridge. 

The first general ideas about geogi-aphical distribution maybe found 
in some of the brilliant speculations contained in Buffon's Histoire 
Naturelle. The first special treatise on the subject was however 
written in 1777 by E. A. W. Zimmermann, Professor of Natural Science 
at Brunswick, whose large volume. Specimen Zoologiae Geographicae 
Quadmjyedum..., deals in a statistical way with the mammals ; im- 
portant features of the large accompanying map of the world are the 
ranges of mountains and the names of hundreds of genera indicating 
their geographical range. In a second work he laid special stress 
on domesticated animals with reference to the spreading of the 
various races of Mankind. 

In the follomng year appeared the Philosophia Entomologica 
by J. C. Fabricius, who was the first to divide the world into eight 
regions. In 1803 G. R. Treviranus^ devoted a long chapter of his 
great work on Biologie to a philosophical and coherent treatment of 
the distribution of the whole animal kingdom. Remarkable progi-ess 
was made in 1810 by F. Tiedemann^ of Heidelberg. Few, if any, of 
the many subsequent Ornithologists seem to have appreciated, or 
known of, the ingenious May in which Tiedemann marshalled his 
statistics in order to arrive at general conclusions. There are, for 
instance, long lists of birds arranged in accordance with their 
occurrence in one or more continents: by correlating the distribu- 
tion of the birds with their food he concludes " that the countries of 
the East Indian flora have no vegetable feeders in common with 
America," and "that it is probably due to the great peculiarity of 
the African flora that Africa has few phytoi)hagou8 kinds in common 
with other countries, >vhilst zoophagous birds have a far more 
independent, often cosmopolitan, distribution." There are also 
remarkable cliapters on the influence of environment, distribu- 
tion, and nn'gration, ui)on the structure of the Birds ! In sliort, 

^ Biologif Oder Pliilosophie der lehenden Nutiir, Vol. ii. Gottingeu, 1803. 
* Anatomie und Nulurgtcchichte der Vo(jfl. Heidelberg, 1810. 

320 Geographical Distribution of Animals 

this anatomist dealt witli some of the fundamental causes of distri- 

Whilst Tiedemann restricted himself to Birds, A. Desmoulins in 
1822 wrote a short but most suggestive paper on the Vertebrata, 
omitting the birds ; he combated the view recently proposed by the 
entomologist Latreille that temperature was the main factor in distri- 
bution. Some of his ten main conclusions show a peculiar mixture 
of evolutionary ideas coupled with the conception of the stability of 
species : whilst each species must have started from but one creative 
centre, there may be several " analogous centres of creation " so far 
as genera and families are concerned. Countries with different 
faunas, but lying within the same climatic zones, are proof of the 
effective and permanent existence of barriers preventing an exchange 
between the original creative centres. ' 

The first book dealing with the " geography and classification " of 
the whole animal kingdom was wi'itteu by W. Swainson^ in 1835. He 
saw in the five races of Man the clue to the mapping of the world 
into as many "true zoological divisions," and he reconciled the five 
continents with his mystical quinary circles. 

Lyell's Principles of Geology should have marked a new epoch, 
since in his Elements he treats of the past history of the globe and 
the distribution of animals in time, and in his Princijyles of their 
distribution in space in connection with the actual changes undergone 
by the surface of the world. But as the sub-title of his great work 
''Modern changes of the Earth and its inhabitants" indicates, he 
restricted himself to comparatively minor changes, and, emphatically 
believing in the permanency of the great oceans, his numerous and 
careful interpretations of the effect of the geological changes upon 
the dispersal of animals did after all advance the problem but 

Hitherto the marine faunas had been neglected. This was 
remedied by E. Forbes, who established nine homozoic zones, based 
mainly on the study of the mollusca, the determining factors being 
to a great extent the isotherms of the sea, whilst the 25 provinces 
were given by the configuration of the land. He was followed by 
J. D. Dana, who, taking principally the Crustacea as a basis, and 
as leading factors the mean temperatures of the coldest and of the 
warmest months, established five latitudinal zones. By using these 
as divisors into an American, Afro-European, Oriental, Arctic and 
Antarctic realm, most of which were limited by an eastern and 
western land-boundary, he arrived at about threescore provinces. 

^ "A Treatise on the Geography and Classificatiou of Animals," Lardaer's Cabinet 
Cyclopaedia, London, 1835. 

Geographical Regions 321 

In 1853 appeared L. K. Schmarda's^ two volumes, embracing the 
whole subject. Various centres of creation being, according to him, 
still traceable, he formed the hypothesis that these centres were 
originally islands, which later became enlarged and joined together 
to form the great continents, so that the original faunas could overlap 
and mix whilst still remaining pure at their respective centres. After 
devoting many chapters to the possible physical causes and modes of 
dispersal, he divided the land into 21 realms which he shortly charac- 
terises, e.g. Australia as the only country inhabited by marsupials, 
monotremes and meliphagous birds. Ten main marine divisions 
were diagnosed in a similar way. Although some of these realms 
were not badly selected from the point of view of being applicable to 
more than one class of animals, they were obviously too numerous for 
general purposes, and this drawback was overcome, in 1857, by 
P. L. Sclater^. Starting with the idea, that "each species must have 
been created within and over the geographical area, which it 
now occupies," he concluded "that the most natural primary onto- 
logical divisions of the Earth's surface " were those six regions, which 
since their adoption by Wallace in his epoch-making work, have become 
classical. Broadly speaking, these six regions are equivalent to the 
great masses of land; they are convenient terms for geogi-apliical 
facts, especially since the Palaearctic region expresses the unity of 
Europe with the bulk of Asia. Sclater further brigaded the regions of 
the Old World as Palaeogaea and the two Americas as Neogaea, a 
fundamental mistake, justifiable to a certain extent only since he 
based his regions mainly upon the present distribution of the Passerine 

Unfortunately these six regions are not of equal value. The 
Indian countries and the Ethiopian region (Afi'ica south of the 
Sahara) are obviously nothing but the tropical, southern continua- 
tions or appendages of one greater complex. Further, the gi'eat 
eastern mass of land is so intimately connected with North America 
that this continent has much more in common with Europe and Asia 
than with South America. Therefore, instead of dividing the world 
longitudinally as Sclater had done, Huxley, in 1868^ gave weighty 
reasons for dividing it transversely. Accordingly he established 
two primary divisions, Arctogaea or the North world in a wider 
sense, comprising Sclater's Indian, African, Palaearctic and Nearctic 
regions ; and Notogaea, the Southern world, which he divided into 

^ Die gcographische Verbreitung der Thiere. Wien, 1853. 

* " On tlie general Geographical Distribution of the members of the class Aves," Proc. 
Linn. Sue. {Zoology), ii. 1858, pp. 130—145. 

* "On the classification and distribution of the Alectoromorphae and Hcteromorphae," 
Proc. Zovl. Soc. 1808, p. 2^di. 

D. 21 

322 Geographical Distribution of Animals 

(1) Aiistro-Coliimbia (an unfortunate substitute for the neotropical 
region), (2) Australasia, and (3) New Zealand, the number of big 
regions thus being reduced to three but for the separation of New 
Zealand upon rather negative characters. Sclater was the first 
to accept these four great regions and showed, in 1874^, that they 
were well borne out by the present distribution of the Mammals. 

Although applicable to various other groups of animals, for 
instance to the tailless Amphibia and to Birds (Huxley himself had 
been led to found his two fundamental divisions on the distribution 
of the Gallinaceous birds), the combination of South America with 
Australia was gradually found to be too sweeping a measure. The 
obvious and satisfactory solution was provided by W. T. Blanford^, 
who in 1890 recognised three main divisions, namely Australian, South 
American, and the rest, for which the already existing terms (although 
used partly in a new sense, as proposed by an anonymous writer in 
Natural Science, in. p. 289) Notogaea, Neogaea and Arctogaea have 
been gladly accepted by a number of English writers. 

After this historical survey of the search for larger and largest or 
fundamental centres of animal creation, which resulted in the mapping 
of the world into zoological regions and realms of after all doubtful 
value, we have to return to the year 1858. The eleventh and twelfth 
chapters of The Origin of Species (1859), dealing with "Geographical 
Distribution," are based upon a great amount of observation, experi- 
ment and reading. As Darwin's main problem was the origin of 
species, nature's way of making species by gradual changes from 
others previously existing, he had to dispose of the view, held uni- 
versally, of the independent creation of each species and at the 
same time to insist upon a single centre of creation for each species ; 
and in order to emphasise his main point, the theory of descent, he 
had to disallow convergent, or as they were then called, analogous 
forms. To appreciate the difficulty of his position we have to take 
the standpoint of fifty years ago, when the immutability of the species 
was an axiom and each was supposed to have been created within 
or over the geographical area which it now occupies. If he once 
admitted that a species could arise from many individuals instead of 
from one pair, there was no way of shutting the door against the 
possibility that these individuals may have been so numerous that 
they occupied a very large district, even so large that it had become 
as discontinuous as the distribution of many a species actually is. 
Such a concession would at once be taken as an admission of multiple, 
independent, origin instead of descent in Darwin's sense. 

^ " The geographical distribution of Mammals," Manchester Science Lectures, 1874. 
2 Anniversary address (Geological Society, 188'J), Proc. Geol. Soc. 1889—90, p. 67; 
Quart. Journ. xlvi. 1890. 

''The Origin of Species'' 323 

For the so-called multiple, independently repeated creation of 
species as an explanation of their very wide and often quite dis- 
continuous distribution, he substituted colonisation from the nearest 
and readiest source together with subsequent modification and better 
adaptation to their new home. 

He was the first seriously to call attention to the many accidental 
means, "which more properly should be called occasional means of 
distribution," especially to oceanic islands. His specific, even in- 
dividual, centres of creation made migi*ations all the more necessary, 
but their extent Mas sadly baulked by the prevailing dogma of the 
permanency of the oceans. Any number of small changes ("many 
islands having existed as halting places, of which not a wi-eck now re- 
mains^") were conceded freely, but few, if any, great enough to permit 
migration of truly terrestrial creatures. The only means of getting 
across the gaps was by the principle of the " flotsam and jetsam," a 
theory which Darwin took over from Lyell and further elaborated so as 
to make it applicable to many kinds of plants and animals, but sadly 
deficient, often gi-otesque, in the case of most terrestrial creatures. 

Another very fertile source was Darwin's strong insistence upon 
the great influence which the last glacial epoch must have had upon 
the distribution of animals and plants, ^\^ly was the migration of 
northern creatures southwards of far-reaching and most significant 
importance ? More northerners have established themselves in south- 
ern lands than vice versd, because there is such a great mass of land 
in the north and greater continents imply greater intensity of selection. 
" The productions of real islands have everywhere largely yielded to 
continental forms ^."..." The Alpine forms have almost everywhere 
largely yielded to the more dominant forms generated in the larger 
areas and more efficient workshops of the North." 

Let us now pass in rapid survey the influence of the publication 
of The Origin of Species upon the study of Geogi-aphical Distribution 
in its wider sense. 

Hitherto the following thought ran through the minds of most 
writers: AVherever we examine two or more widely separated 
countries their respective faunas are very different, but where two 
faunas can come into contact with each other, they intermingle. 
Consequently these faunas represent centres of creation, whence 
the component creatures have spread peripherally so far as existing 
boundaries allowed them to do so. This is of course the funda- 
mental idea of " regions." There is not one of the numerous wi-iters 
who considered the possibility that these intermediate belts might 
represent not a mixture of species but transitional forms, the result of 
changes undergone l)y the most i)cripheral migrants in adaptation to 

» The Origin of Species (Ist edit.), p. 396. ' Hid. p. 380. 

21 '2 

324 Geographical Distribution of Animals 

tlieir new surroundings. The usual standpoint was also that of 
Pucheran^ in 1855. But what a change within the next ten years ! 
Pucheran explains the agreement in coloration between the desert 
and its fauna as "une harmonie post-^tablie " ; the Sahara, formerly a 
marine basin, was peopled by immigrants from the neighbouring 
countries, and these new animals adapted themselves to the new 
environment. He also discusses, among other similar questions, 
the Isthmus of Panama with regard to its having once been a strait. 
From the same author may be quoted the following passage as a 
strong proof of the new influence : " By the radiation of the con- 
temporaneous faunas, each from one centre, whence as the various 
parts of the world successively were formed and became habitable, 
they spread and became modified according to the local physical 

The "multiple" origin of each species as advocated by Sclater 
and Murray, although giving the species a broader basis, sufl'ered 
from the same difficulties. There was only one alternative to the 
old orthodox view of independent creation, namely the bold accept- 
ance of land-connections to an extent for wliich geological and 
palaeontological science was not yet ripe. Those who shrank from 
either view, gave up the problem as mysterious and beyond the 
human intellect. This was the expressed opinion of men like 
Swainson, Lyell and Humboldt. Only Darwin had the courage to 
say that the problem was not insoluble. If we admit "that in the 
long course of time the individuals of the same species, and likewise 
of allied species, have proceeded from some one source ; then I think 
all the grand leading facts of geographical distribution are explicable 
on the theory of migration. . .together with subsequent modifica- 
tion and the multiplication of new forms." We can thus under- 
stand how it is that in some countries the inhabitants "are linked 
to the extinct beings which formerly inhabited the same continent." 
We can see why two areas, having nearly the same physical 
conditions, should often be inhabited by very diiferent forms of 
life,... and "we can see why in two areas, however distant from 
each other, there should be a correlation, in the presence of iden- 
tical species... and of distinct but representative species'-." 

Darwin's reluctance to assume great geological changes, such as 
a land-connection of Europe with North America, is easily explained 
by the fact that he restricted himself to the distribution of the 
present and comparatively recent species. " I do not believe that it 
will ever be proved that within the recent period continents which 

1 " Note Bur I'^quateur zoologique," Eev. et Mag. de Zoologie, liiu5 ; also several 
other papers, ibid. 18C5, 1866, and 1867. 

2 The Origin of Species (1st edit.), pp. 408, 409. 

Murray's Work on Distribution 325 

are now quite separate, have been continiionsly, or almost con- 
tinuously, united with each other, and with the many existing oceanic 
islands^" Again, "believing. . .that our continents have long remained 
in nearly the same relative position, though subjected to large, but par- 
tial oscillations of level," that means to say within the period of existing 
species, or "within the recent period^" The difficulty was to a great 
extent one of his own making. Whilst almost everybody else believed 
in the immutability of the species, which implies an enormous age, 
logically since the da^vn of creation, to him the actually existing 
species as the latest results of evolution, were necessarily something 
very new, so young that only the very latest of the geological epochs 
could have affected them. It has since come to our knowledge that 
a great number of terrestrial "recent" species, even those of the 
higher classes of Vertebrates, date much farther back than had been 
thought possible. Many of them reach well into the Miocene, a 
time since which the world seems to have assumed the main outlines 
of the present continents. 

In the year 1866 appeared A. Murray's work on the Geogra2oMcal 
Distribution of Maimnals, a book which has perhaps received less 
recognition than it deserves. His treatment of the general intro- 
ductory questions marks a considerable advance of our problem, 
although, and partly because, he did not entirely agree with Darwin's 
views as laid do^vn in the first edition of The Origin of Species, 
which after all was the great impulse given to Murray's work. Like 
Forbes he did not shrink from assuming enormous changes in the 
configuration of the continents and oceans because the theory of 
descent, with its necessary postulate of great migrations, required 
them. He stated, for instance, " that a Miocene Atlantis sufficiently 
explains the common distribution of animals and plants in Europe 
and America up to the glacial epoch." And next he considers how, 
and by what changes, the rehabilitation and distribution of these 
lands themselves were effected subsequent to that period. Further, 
he deserves credit for having cleared up a misunderstanding of the 
idea of specific centres of creation. Whilst for instance Schmarda 
assumed without hesitation that the same species, if occurring at 
places separated by great distances, or by apparently insurmountable 
barriers, had been there created independently (multiple centres), 
Lyell and Darwin held that each species had only one single centre, 
and with this view most of us agree, but their starting point was 
to them represented by one individual, or rather one single pair. 
According to Murray, on the other hand, this centre of a species is 
formed by all the individuals of a species, all of which ecpuilly undergo 
those changes which new conditions may impose upon them. In this 
respect a new species has a multiple origin, but tiiis in a sense very 

1 Ibid. p. 3.57. » Ibid. p. 370. 

326 Geographical Distribution of Animals 

different from that which was upheld by L. Agassiz. As Murray 
himself puts it: "To my multiple origin, communication and direct 
derivation is essential. The species is compounded of many influences 
brought together through many individuals, and distilled by Nature 
into one species ; and, being once established it may roam and spread 
wherever it finds the conditions of life not materially different from 
those of its original centre^." This declaration fairly agi*ees with 
more modern views, and it must be borne in mind that the application 
of the single-centre principle to the genera, families and larger groups 
in the search for descent inevitably leads to one creative centre for the 
whole animal kingdom, a condition as unwarrantable as the myth of 
Adam and Eve being the first representatives of Mankind. 

It looks as if it had required almost ten years for The, Origin of 
Species to show its full effect, since the year 1868 marks the publica- 
tion of Haeckel's Natiirliche SchoepfimgsgeschicJite, in addition to 
other great works. The terms Oecology (the relation of organisms 
to their environment) and Chorology (their distribution in space) 
had been given us in his Generelle MorpJiologie in 1866. The 
fourteenth chapter of the History of Creation is devoted to the 
distribution of organisms, their chorology, with the emphatic asser- 
tion that " not until Darwin can chorology be spoken of as a separate 
science, since he supplied the acting causes for the elucidation of the 
hitherto accumulated mass of facts." A map (a "hypothetical sketch ") 
shows the monophyletic origin and the routes of distribution of Man. 

Natural Selection may be all-mighty, all-sufficient, but it requires 
time, so much that the countless aeons required for the evolution of 
the present fauna were soon felt to be one of the most serious draw- 
backs of the theory. Therefore every help to ease and shorten this 
process should have been welcomed. In 1868 M. Wagner^ came to 

^ Murray. The Geographical Distribution of Mammals, p. 14. London, 1866. 

2 The first to formulate clearly the fundamental idea of a theory of migration and its 
importance in the origin of new species was L. von Buch, who in his Physikalische 
Beschreihung der Canarischen Inseln, written in 1825, wrote as follows: "Upon the con- 
tinents the individuals of the genera by spreading far, form, through differences of the 
locality, food and soil, varieties which finally become constant as new species, since owing 
to the distances they could never be crossed with other varieties and thus be brought back 
to the main type. Next they may again, perhaps upon different roads, return to the old 
home where they find the old type likewise changed, both having become so different that 
they can interbreed no longer. Not so upon islands, where the individuals shut up in 
narrow valleys or within narrow districts, can always meet one another and thereby 
destroy every new attempt towards the fixing of a new variety." Clearly von Buch explains 
here why island types remain fixed, and why these types themselves have become so 
different from their continental congeners. — Actually von Buch is aware of a most 
important point, the difference in the process of development which exists between a new 
species b, which is the result of an ancestral species a having itself changed into b and 
thereby vanished itself, and a new species c which arose through separation out of the 
same ancestral a, which itself persists as such unaltered. Von Buch's prophetic view seems 
to have escaped Lyell's and even Wagner's notice. 

Wagner, Huxley, and Wallace 327 

the rescue with his Darvnn'scfie Theorie niul das Migrations-Gesetz 
der Orgamsme)t\ He shows that migration, i.e. change of locality, 
implies new environmental conditions (never mind whether these be 
new stimuli to variation, or only acting as their selectors or 
censors), and moreover secures separation from the original stock 
and thus eliminates or lessens the reactionary dangers of panmixia. 
Dar^dn accepted Wagner's theory as "advantageous." Through the 
heated polemics of the more ardent selectionists Wagner's theory 
came to grow into an alternative instead of a help to the theory of 
selectional evolution. Separation is now rightly considered a most 
important factor by modern students of geogi-aphical distribution. 

For the same year, 1868, we have to mention Huxle}^, whose 
Arctogaea and Notogaea are nothing less than the reconstructed 
main masses of land of the Mesozoic period. Beyond doubt the 
configuration of land at that remote period has left recognisable 
traces in the present continents, but whether they can account for 
the distribution of such a much later gi'oup as the Gallinaceous birds 
is more than questionable. In any case he took for his text a large 
natural gi-oup of birds, cosmopolitan as a whole, but with a striking 
distribution. The Peristeropodes, or pigeon-footed division, are re- 
stricted to the Australian and Neotropical regions, in distinction to 
the Alectoropodes (with the hallux inserted at a level above the front 
toes) which inhabit the whole of the Arctogaea, only a few members 
having spread into the South World. Further, as Asia alone has its 
Pheasants and allies, so is Africa characterised by its Guinea-fowls and 
relations, America has the Turkey as an endemic genus, and the 
Grouse tribe in a wider sense has its centre in the holarctic region : 
a splendid object lesson of descent, world-wide spreading and subse- 
quent differentiation. Huxley, by the way, was the first — at least in 
private talk — to state that it mil be for the morphologist, the well- 
trained anatomist, to give the casting vote in questions of geographical 
distribution, since he alone can determine whether we have to deal 
with homologous, or analogous, convergent, representative forms. 

It seems late to introduce Wallace's name in 1876, the year 
of the publication of his standard work'-. We cannot do better than 
quote the author's own words, expressing the hope that his "book 
should bear a similar relation to the eleventh and twelfth chapters 
of the Origin of Species as Darwin's Animals and Plants under 
Domestication does to the first chapter of that work," and to add 
that he has amply succeeded. Pleading for a few primary centres he 
accepts Sclater's six regions and does not follow Huxley's courageous 
changes wliicli Sclater himself had accepted in 1874. Holding the 

1 Lt.-ipzig, 1868. 

* The Geographical Distribution of Animals, 2 vols. London, 1870. 

328 Geographical Distribution of Aiiimals 

view of the permanence of the oceans he accounts for the colonisation 
of outlying islands by further elaborating the views of Lyell and 
Darwin, especially in his fascinating Island Life, with remarkable 
chapters on the Ice Age, Climate and Time and other fundamental 
factors. His method of arriving at the degree of relationship of the 
faunas of the various regions is eminently statistical. Long lists of 
genera determine by their numbers the affinity and hence the source 
of colonisation. In order to make sure of his material he performed 
the laborious task of evolving a new classification of the host of 
Passerine birds. This statistical method has been followed by many 
authors, who, relying more upon quantity than quality, have obscured 
the fact that the key to the present distribution lies in the past 
changes of the earth's surface. However, with Wallace begins the 
modern study of the geogi-aphical distribution of animals and the 
sudden interest taken in this subject by an ever widening circle of 
enthusiasts far beyond the professional brotherhood. 

A considerable literature has since grown up, almost bewildering 
in its range, diversity of aims and style of procedure. It is a chaos, 
with many paths leading into the maze, but as yet very few take us 
to a position commanding a view of the whole intricate terrain with 
its impenetrable tangle and pitfalls. 

One line of research, not initiated but greatly influenced by 
Wallace's works, became so prominent as to almost constitute a 
period which may be characterised as that of the search by specialists 
for either the justification or the amending of his regions. As class 
after class of animals was brought up to reveal the secret of the true 
regions, some authors saw in their difi*erent results nothing but the 
faultiness of previously established regions ; others looked upon 
eventual agreements as their final corroboration, especially when for 
instance such diverse groups as mammals and scorpions could, with 
some ingenuity, be made to harmonise. But the obvious result of 
all these eflbrts was the gi'owing knowledge that almost every class 
seemed to follow principles of its ovm. Tlie regions tallied neither in 
extent nor in numbers, although most of them gravitated more and 
more towards three centres, namely Australia, South America and 
the rest of the world. Still zoologists persisted in the search, and the 
various modes and capabilities of dispersal of the respective groups 
were thought sufficient explanation of the divergent results in trying 
to bring the mapping of the world under one scheme. 

Contemporary literature is full of devices for the mechanical 
dispersal of animals. Marine currents, warm and cold, were favoured 
all the more since they showed the probable original homes of the 
creatures in question. If these could not stand sea-water, they 
floated upon logs or icebergs, or they were blown across by storms ; 

The Past the Key to the Present 329 

fishes were lifted over barriers by waterspouts, and there is on record 
even an hypothetical land tortoise, full of eggs, which colonised an 
oceanic island after a perilous sea voyage upon a tree trunk. 
Accidents will happen, and beyond doubt many freaks of discon- 
tinuous distribution have to be accounted for by some such means. 
But whilst sufficient for the scanty settlers of true oceanic islands, 
they cannot be held seriously to account for the rich fauna of a large 
continent, over which palaeontology shows us that the immigi-ants 
have passed like waves. It should also be borne in mind that there 
is a great difference between flotsam and jetsam, A current is an 
extension of the same medium and the animals in it may suffer no 
change during even a long voyage, since they may be brought from 
one literal to another where they will still be in the same or but 
slightly altered environment. But the jetsam is in the position of a 
passenger who has been carried off by the wTong train. Almost 
every year some American land birds arrive at our western coasts 
and none of them have gained a permanent footing although such 
visits must have taken place since prehistoric times. It was there- 
fore argued that only those groups of animals should be used for 
locating and defining regions which were absolutely bound to the 
soil. This method hkewise gave results not reconcilable with each 
other, even when the distribution of fossils was taken into account, 
but it pointed to the absolute necessity of searching for former 
land-connections regardless of their extent and the present depths 
to which they may have sunk. 

That the key to the present distribution lies in the past had 
been felt long ago, but at last it was appreciated that the various 
classes of animals and plants have appeared in successive geological 
epochs and also at many places remote from each other. The key to 
the distribution of any group lies in the configuration of land and 
water of that epoch in which it made its first appearance. x\lthough 
this sounds like a platitude, it has frequently been ignored. If, for 
argument's sake. Amphibia were evolved somewhere upon the great 
southern land-mass of Carboniferous times (supposed by some to have 
stretched from South America across Africa to Australia), the dis- 
tribution of this developing class must have proceeded upon lines 
altogether different from that of the mammals which dated perhaps 
from lower Triassic times, when the old south continental belt was 
already broken up. The broad lines of this distribution could never 
coincide with that of the other, older class, no matter whether the 
original mammalian centre was in the Afro-Indian, Australian, or 
Brazilian portion. If all the various groups of animals had come into 
existence at the same time and at the same place, then it would be 
possible, with sufficient geological data, to construct a map showing 

330 Gcogra/pliical Distribution of Animals 

the generalised results applicable to the whole animal kingdom. 
But the premises are wrong. Whatever regions we may seek to 
establish applicable to all classes, we are necessarily mixing up several 
principles, namely geological, historical, i.e. evolutionary, with present 
day statistical facts. We might as well attempt one compound 
picture representing a chick's growth into an adult bird and a child's 
growth into manhood. 

In short there are no general regions, not even for each class 
separately, unless this class be one which is confined to a com- 
paratively short geological period. Most of the gi-eat classes have 
far too long a history and have evolved many successive main groups. 
Let us take the mammals. Marsupials live now in Australia and in 
both Americas, because they already existed in Mesozoic times ; 
Ungulata existed at one time or other all over the world except in 
Australia, because they are post-Cretaceous ; Insectivores, although 
as old as any Placentalia, are cosmopolitan excepting South America 
and Australia ; Stags and Bears, as examples of comparatively recent 
Arctogaeans, are found everywhere with the exception of Ethiopia 
and Australia. Each of these groups teaches a valuable historical 
lesson, but when these are combined into the establislunent of a few 
mammalian "realms," they mean nothing but statistical majorities. 
If there is one at all, Australia is such a realm backed against the 
rest of the world, but as certainly it is not a mammalian creative 
centre ! 

Well then, if the idea of generally applicable regions is a mare's 
nest, as was the search for the Holy Grail, what is the object of the 
study of geographical distribution? It is nothing less than the 
history of the evolution of life in space and time in the widest sense. 
The attempt to account for the present distribution of any group of 
organisms involves the aid of every branch of science. It bids fair to 
become a history of the world. It started in a mild, statistical way, 
restricting itself to the present fauna and flora and to the present 
configuration of land and water. Next came Oceanography concerned 
with the depths of the seas, their currents and temperatures; then 
inquiries into climatic changes, culminating in irreconcilable astro- 
nomical hypotheses as to glacial epochs ; theories about changes of 
the level of the seas, mainly from the point of view of the physicist 
and astronomer. Then came more and more to the front the import- 
ance of the geological record, hand in hand with the palaeontological 
data and the search for the natural affinities, the genetic system of 
tlic organisms. Now and then it almost seems as if the biologists 
had done their share by supplying the problems and that the 
physicists and geologists would settle them, but in reality it is not 
so. The biologists not only set the problems, they alone can check 

The Value of Fossils 331 

the offered solutions. The mere fact of palms having flourished in 
Miocene Spitzbergen led to an hj'pothetical shifting of the axis of 
the world rather than to the assumption, by way of explanation, that 
the palms themselves might have changed their nature. One of the 
most valuable aids in geological research, often the only means for 
reconstructhig the face of the earth in by-gone periods, is afforded by 
fossils, but only the morphologist can pronounce as to their trust- 
worthiness as vWtnesses, because of the danger of mistaking analogous 
for homologous forms. This difficulty applies equally to living groups, 
and it is so important that a few instances may not be amiss. 

There is undeniable similarity between the faunas of INIadagascar 
and South America. This was supported by the Centetidae and Den- 
drobatidae, two entire " families," as also by other facts. The value 
of the Insectivores, Solenodon in Cuba, Centetes in Madagascar, has 
been much lessened by their recognition as an extremely ancient 
group and as a case of convergence, but if they are no longer put 
into the same family, this amendment is really to a gi-eat extent due 
to their widely discontinuous distribution. The only systematic 
difference of the Dendrobatidae from the Ranidae is the absence of 
teeth, morphologically a very unimportant character, and it is now 
agreed, on the strength of their distribution, that these little arboreal, 
conspicuously coloured frogs, Dendrobates in South America, Mantella 
in i\Iadagascar, do not form a natural group, although a third genus, 
Cardioglossa in West Africa, seems also to belong to them. If these 
creatures lived all on the same continent, we should unhesitatingly 
look upon them as forming a well-defined, natural little group. On 
the other hand the Aglossa, with their three very divergent genera, 
namely Pipa in South America, Xenopus and Hymenochirus in Africa, 
are so well characterised as one ancient group that we use their 
distribution unhesitatingly as a hint of a former connection between 
the two continents. We are indeed arguing in vicious circles. The 
Ratitae as such are absolutely worthless since they are a most 
heterogeneous assembly, and there are untold gi-oups, of the arti- 
ficiality of which many a zoo-geographer had not the slightest 
suspicion when he took his statistical material, the genera and 
families, from some systematic catalogues or similar lists. A lament- 
able instance is that of certain flightless Rails, recently extinct or 
sub-fossil, on the islands of Mauritius, Rodriguez and Chatham. Being 
flightless they have been used in supi)ort of a former huge Antarctic 
continent, instead of ruling them out of court as Rails which, 
each in its island, have lost the power of flight, a process which 
must have taken place so recently that it is dillicult, upon morpho- 
logical gi-ounds, to justify their separation into Aphanapteryx in 
Mauritius, Erythromachus in Rodriguez and Diaphorapteryx on 

332 Geographical Bistribiition of Animals 

Chatham Island. Morphologically they may well form but one genus, 
since they have sprung from the same stock and have developed upon 
the same lines ; they are therefore monogenetic : but since we know 
that they have become what they are independently of each other 
(now unlike any other Rails), they are polygenetic and therefore 
could not form one genus in the old Darwinian sense. Further, they 
are not a case of convergence, since their ancestry is not divergent 
but leads into the same stratum. 

The reconstruction of the geography of successive epochs. 

A promising method is the study by the specialist of a large, widely 
distributed group of animals from an evolutionary point of view. Good 
examples of this method are afforded by A. E. Ortmann's^ exhaus- 
tive paper and by A. W. Grabau's "Phylogeny of Fusus and its 
Allies" {Smithsonian Misc. Coll. 44, 1904). After many important 
groups of animals have been treated in this way — as yet sparingly 
attempted — the results as to hypothetical land-connections etc. are 
sure to be corrective and supplementary, and their problems will be 
solved, since they are not imaginary. 

The same problems are attacked, in the reverse way, by starting 
with the whole fauna of a country and thence, so to speak, letting 
the research radiate. Some groups will be considered as autoch- 
thonous, others as immigi-ants, and the directions followed by them 
will be inquired into ; the search may lead far and in various direc- 
tions, and by comparison of results, by making compound maps, certain 
routes will assume definite shape, and if they lead across straits and 
seas they are warrants to search for land-connections in the past^. 
There are now not a few maps purporting to show the outlines of 
land and water at various epoclis. Many of these attempts do not 
tally with each other, owing to the lamentable deficiencies of geological 
and fossil data, but the bolder the hypothetical outlines are drawii, 
the better, and this is preferable to the insertion of bays and similar 
detail wliich give such maps a fallacious look of certainty where none 
exists. Moreover it must be borne in mind that, when we draw a 
broad continental belt across an ocean, this belt need never have 
existed in its entirety at any one time. The features of dispersal, 
intended to be explained by it, would be accomplished just as well 
by an unkno^\Ti number of islands which have joined into larger com- 
plexes while elsewhere they subsided again : like pontoon-bridges 

^ " The geographical distribution of Freshwater Decapods and its bearing upon ancient 
geography," Proc. Amer. Phil. Soc. Vol. 41, 1902. 

' A fair sample of this method is C. H. Eigenmann's " The Freshwater Fishes of 
South and Middle America," Popular Science Monthly, Vol. 68, 1906. 

Mesozoic Geography 333 

which may be opened anywhere, or like a series of superimposed 
dissolving views of land and sea-scapes. Hence the reconstructed 
maps of Europe, the only continent tolerably known, show a con- 
siderable number of islands in puzzling changes, while elsewhere, 
e.g. in Asia, we have to be satisfied with sweeping generalisations. 

At present about half-a-dozen big connections^ are engaging our 
attention, leaving as comparatively settled the extent and the duration 
of such minor ''bridges" as that between Afi-ica and Madagascar, 
Tasmania and Australia, the Antilles and Central America, Europe 
and North Afi-ica. 

Connectio?i of South Eastern Asia with Australia. Neumayr's 
Sino- Australian continent during mid-Mesozoic times was probably a 
much changing Archipelago, with final separations subsequent to the 
Cretaceous period. Henceforth Australasia was left to its own fate, 
but for a possible connection with the antarctic continent. 

Africa, Madagascar, India. The "Lemuria" of Sclater and 
Haeckel cannot have been more than a broad bridge in Jurassic 
times ; whether it was ever available for the Lemurs themselves must 
depend upon the time of its duration, the more recent the better, 
but it is difficult to show that it lasted into the Miocene. 

Africa and South America. Since the opposite coasts show an 
entire absence of marine fossils and deposits during the Mesozoic 
period, whilst further north and south such are kno\\^l to exist and are 
mostly identical on either side, Neumayi* suggested the existence of 
a great Afi*o-South American mass of land during the Jurassic epoch. 
Such land is almost a necessity and is supported by many facts ; it 
would easily explain the distribution of numerous gi'oups of terrestrial 
creatures. Moreover to the north of this hypothetical land, some- 

' Not a few of those who are fascinated by, and satisfied with, the statistical aspect of 
distribution still have a strong dislike to the use of "bridges" if these lead over deep 
seas, and they get over present discontinuous occurrences by a former "universal or 
sub-universal distribution " of their groups. This is indeed an easy method of cutting 
the knot, but in reality they shunt the question only a stage or two back, never troubling 
to explain how their groups managed to attain to that sub-universal range ; or do they 
Btill suppose that the whole world was originally one paradise where everything lived side 
by side, until sin and strife and glacial epochs left nothing but scattered survivors'? 

The permanence of the great ocean-basins had become a dogma since it was found 
that a universal elevation of the land to the extent of 100 fathoms would produce but 
little changes, and when it was shown that even the 1000 fathom-line followed the great 
masses of land rather closely, and still leaving the great basins (although transgression of 
the sea to the same extent would change the map of the world beyond recognition), by 
general consent one mile was allowed as the utmost speculative limit of subsidence. 
Naturally two or three miles, the average depth of the oceans, seems enormous, and yet 
such a difference in level is as nothing in comparison with the size of the Earth. On 
a clay model globe ten feet in diameter an ocean bed three miles deep would scarcely be 
detected, and thu higliest mountains would be smuller than the unavoidable grains in the 
glazed surface of our model. There are but few countries which have not been submerged 
at some time or other. 

o34 Geographical Distribution of Animals 

where across from the Antilles and Guiana to North Africa and South 
Western Europe, existed an almost identical fauna of Corals and 
Molluscs, indicating either a coast-line or a series of islands interrupted 
by shallow seas, just as one would expect if, and when, a Brazil- 
Ethiopian mass of land were breaking up. Lastly from Central 
America to the Mediterranean stretches one of the Tertiary tectonic 
lines of the geologists. Here also the great question is how long this 
continent lasted. Apparently the South Atlantic began to encroach 
fi-om the south so that by the later Cretaceous epoch the land was 
reduced to a comparatively narrow Brazil -West Africa, remnants of 
which persisted certainly into the early Tertiary, until the South 
Atlantic joined across the equator with the Atlantic portion of the 
"Thetvs," leaving what remained of South America isolated from the 
rest of the world. 

Antarctic connections. Patagonia and Argentina seem to have 
joined Antarctica during the Cretaceous epoch, and this South Georgian 
bridge had broken down again by mid-Tertiary times when South 
America became consolidated. The Antarctic continent, presuming 
that it existed, seems also to have been joined, by way of Tasmania, 
with Australia, also during the Cretaceous epoch, and it is assumed 
that the gi'eat Australia- Antarctic-Patagonian land was severed first 
to the south of Tasmania and then at the South Georgian bridge. 
No connection, and this is important, is indicated between Antarctica 
and either Africa or Madagascar. 

So far we have followed what may be called the vicissitudes of 
the great Permo-Carboniferous Gondwana land in its fullest imaginary 
extent, an enormous equatorial and south temperate belt from South 
America to Africa, South India and Australia, which seems to have 
provided the foundation of the present Southern continents, two of 
which temporarily joined Antarctica, of which however we know 
nothing except that it exists now. 

Let us next consider the Arctic and periarctic lands. Unfortunately 
very little is knoAvn about the region Avithin the arctic circle. If it 
was all land, or more likely great changing archipelagoes, faunistic 
exchange between North America, Europe and Siberia would present 
no difficulties, but there is one connection which engages much atten- 
tion, namely a land where now lies the North temperate and Northern 
part of the Atlantic ocean. How far south did it ever extend and 
Avhat is the latest date of a direct practicable communication, say 
fi-om North Western Europe to Greenland? Connections, perhaps 
often interrupted, e.g. between Greenland and Labrador, at another 
time between Greenland and Scandinavia, seem to have existed at 
least since the Permo-Carboniferous epoch. If they existed also in 
late Cretaceous and in Tertiary times, they would of course easily 

Distribution of Perqmtus 835 

explain exchanges which we know to have repeatedly taken place 
between America and Europe, but they are not proved thereby, since 
most of these exchanges can almost as easily have occurred across 
the polar regions, and others still more easily by repeated junction of 
Siberia with Alaska. 

Let us now describe a hypothetical case based on the supposition 
of connecting bridges. Not to work in a circle, we select an important 
gi'oup which has not served as a basis for the reconstruction of 
bridges ; and it must be a group which we feel justified in assuming 
to be old enough to have availed itself of ancient land-connections. 

The occurrence of one species of Peripatus in the whole of Aus- 
tralia, Tasmania and New Zealand (the latter being joined to Australia 
by way of New Britain in Cretaceous times but not later) puts the 
genus back into this epoch, no unsatisfactory assumption to the 
morphologist. The apparent absence of Peripatus in Madagascar 
indicates that it did not come ft-om the east into Africa, that it was 
neither Afro-Indian, nor Afro-Australian ; nor can it have started in 
South America. We therefore assume as its creative centre Australia 
or Malaya in the Cretaceous epoch, whence its occurrence in Sumatra, 
Malay Peninsula, New Britain, New Zealand and Australia is easily 
explained. Then extension across Antarctica to Patagonia and Chile, 
whence it could spread into the rest of South America as this 
became consolidated in early Tertiary times. For getting to the 
Antilles and into Mexico it would have to wait mitil the Miocene, 
but long before that time it could arrive in Africa, there surviving as 
a Congolese and a Cape species. This story is unsupported by a 
single fossil. Peripatus may have been "sub-universal" all over 
greater Gondwana land in Carboniferous times, and then its absence 
from Madagascar would be difficult to explain, but the migrations 
suggested above amount to little considering that the distance 
from Tasmania to South America could be covered in far less time 
than that represented by the whole of the Eocene epoch alone. 

There is yet another field, essentially the domain of geogi-aphical 
distribution, the cultivation of which promises fair to throw much 
light upon Nature's way of making species. This is the study of the 
organisms with regard to their environment. Instead of revealing 
pedigi'ees or of showing how and when the creatures got to a 
certain locality, it investigates how they behaved to meet the ever 
changing conditions of their habitats. There is a facies, characteristic 
of, and often peculiar to, the fauna of tropical moist forests, another 
of deserts, of high mountains, of underground life and so forth ; 
these same facies are stamped upon whole associations of animals and 
plants, although these may be — and in widely sepaiatod countries 
generally are — drawn from totally dillerent families of their respec- 

336 Geographical Distribution of Animals 

tive orders. It does not go to the root of the matter to say that 
these facies have been brought about by the extermination of all the 
others which did not happen to fit into their particular environment. 
One might almost say that tropical moist forests must have arboreal 
frogs and that these are made out of whatever suitable material 
happened to be available ; in Australia and South America Hylidae, 
in Afi'ica Ranidae, since there Hylas are absent. The deserts must 
have lizards capable of standing the glare, the great changes of tem- 
perature, of running over or burrowing into the loose sand. When 
as in America Iguanids are available, some of these are thus modified, 
while in Africa and Asia the Agamids are drawn upon. Both in the 
Damara and in the Transcaspian deserts, a Gecko has been turned 
into a runner upon sand ! 

We cannot assume that at various epochs deserts, and at others 
moist forests were continuous all over the world. The different facies 
and associations were developed at various times and places. Are 
we to suppose that, wherever tropical forests came into existence, 
amongst the stock of humivagous lizards were always some which 
presented those nascent variations which made them keep step with 
the similarly nascent forests, the overwhelming rest being eliminated? 
This principle would imply that the same stratum of lizards always 
had variations ready to fit any changed environment, forests and 
deserts, rocks and swamps. The study of Ecology indicates a different 
procedure, a gi'eat, almost boundless plasticity of the organism, not 
in the sense of an exuberant moulding force, but of a readiness to 
be moulded, and of this the "variations" are the visible outcome. 
In most cases identical facies are produced by heterogeneous con- 
vergences and these may seem to be but superficial, affecting only 
what some authors are pleased to call the physiological characters ; 
but environment presumably affects first those parts by which the 
organism comes into contact with it most directly, and if the internal 
structures remain unchanged, it is not because these are less easily 
modified but because they are not directly affected. Wlien they are 
affected, they too change deeply enough. 

That the plasticity should react so quickly — indeed this very 
quickness seems to have initiated our mistaking the variations called 
foi-th for something performed — and to the point, is itself the out- 
come of the long training which protoplasm has undergone since its 

In Nature's workshop he does not succeed who has ready an arsenal 
of tools for every conceivable emergency, but he who can make a 
tool at the spur of the moment. The ordeal of the practical test is 
Charles Darwin's glorious conception of Natural Selection. 



By J. W. JuDD, C.B., LL.D., F.RS. 

In one of the very interesting conversations which I had with 
Charles Darwin during the last seven years of his hfe\ he asked 
me in a very pointed manner if I were able to recall the circum- 
stances, accidental or otherwise, which had led me to devote myself 
to geological studies. He informed me that he was making similar 
inquiries of other friends, and I gathered from what he said that 
he contemplated at that time a study of the causes producing 
scientific bias in individual minds. I have no means of knowing how 
far this project ever assumed anything like concrete form, but certain 
it is that Darwin himself often indulged in the processes of mental 
introspection and analysis ; and he has thus fortunately left us — in 
his fragments of autobiography and in his correspondence — the 
materials from which may be reconstructed a fairly complete history 
of his own mental development. 

There are two perfectly distinct inquiries which we have to 
undertake in connection with the development of Darwin's ideas on 
the subject of evolution : 

First. How, when, and under what conditions was Darwin led 
to a conviction that species were not immutable, but were derived 
from pre-existing forms? 

Secondly. By what lines of reasoning and research was he 
brought to regard " natural selection " as a vera causa in the process 
of evolution ? 

* Mr Francis Darwin baa related how hia father occasionally came up from Down 
to spend a few days with his brother Erasmus in Loudon, and, after his brother's death, 
with his daughter, Mrs Litchfield. Ou these occasions, it was his habit to arrange 
meetings with Huxley, to talk over zoological questions, with Hooker, to discuss botanical 
problems, and with Lyell to hold conversations on geology. After the death of Lj-ell, 
Darwin, knowing my close intimacy with his friend during his later years, used to ask me 
to meet him when he came to town, and "talk geology." The "talks" took place 
sometimes at Jermyn Street Museum, at other times in the Royal College of Science, 
South Kensington ; but more frequently, after having lunch with him, at his brother's 
or his daughter's house. Ou several occasions, however, I had the pleasure of visiting 
him at Down. In the postscript of a letter (of April 15, 1880) arranging one of these 
visits, he writes : " Since poor, dear Lyell's death, I rarely have the pleasure of geological 
talk with anyone." 

D. 99 

338 Darwin and Geology 

It is the first of these inquiries which specially interests the 
geologist ; though geology undoubtedly played a part — and by no 
means an insignificant part — in respect to the second inquiry. 

When, indeed, the history comes to be written of that great 
revolution of thought in the nineteenth century, by which the 
doctrine of evolution, from being the dream of poets and visionaries, 
gradually grew to be the accepted creed of naturalists, the para- 
mount influence exerted by the infant science of geology — and 
especially that resulting from the publication of Lyeli's epoch- 
making work, the Principles of Geology — cannot fail to be regarded 
as one of the leading factors. Herbert Spencer in his Autobiography 
bears testimony to the efifect produced on his mind by the recently 
published Principles, when, at the age of twenty, he had already 
begun to speculate on the subject of evolution^ ; and Alfred Russel 
Wallace is scarcely less emphatic concerning the part played by 
Lyeli's teaching in his scientific education I Huxley wrote in 1887 
" I owe more than I can tell to the careful study of the Princi^des of 
Geology in my young days^" As for Charles Darwin, he never 
tired — either in his published writings, his private correspondence 
or his most intimate conversations — of ascribing the awakening of 
his enthusiasm and the direction of his energies towards the 
elucidation of the problem of development to the Principles of 
Geology and the personal influence of its author. Huxley has well 
expressed what the author of the Origin of Species so constantly 
insisted upon, in the statements "Darwin's greatest work is the 
outcome of the unflinching application to Biology of the leading 
idea and the method applied in the Principles to Geology*," and 
''Lyell, for others, as for myself, was the chief agent in smoothing 
the road for Darwin ^" 

We propose therefore to consider, first, what Darwin owed to 
geology and its cultivators, and in the second place how he was able 
in the end so fully to pay a great debt which he never failed to 
acknowledge. Thanks to the invaluable materials contained in the 
Life and Letters of Charles Darivin (3 vols.) published by Mr Francis 
Darwin in 1887 ; and to More Letters of Charles Darwin (2 vols.) 
issued by the same author, in conjunction with Professor A. C. 
Seward, in 1903, we are permitted to follow the various movements 

1 Herbert Spencer's Autobiography, London, 1904, Vol. i. pp. 175 — 177. 

^ See My Life ; a record of Events and Opinions, London, 1905, Vol. i. p. 355, etc. 
Also his review of Lyeli's Principles in Quarterly Ilevieio (Vol. 126), 1869, pp. 359 — 394. 
See also The Darwin-Wallace Celebration by the Linnean Society (1909), p. 118. 

" " Science and Pseudo Science;" Collected Essays, London, 1902, Vol. v. p. 101. 

■• Proc. Roy. Soc. Vol. xliv. (1888), p. viii. ; Collected Essays, ii. p. 268, 1902. 

' Life and Letters of Charles Darwin, ii. p. 190. 

In Childhood aiiul School Life 339 

in Danvin's mind, and are able to record the story almost entirely in 
his own words \ 

From the point of view of the geologist, Darwin's life naturally 
divides itself into four periods. In the first, covering twenty-two 
years, various influences were at work militating, now for and now 
against, his adoption of a geological career ; in the second period — 
the five memorable years of the voyage of the Beagle — the ardent 
sportsman with some natural-history tastes, gradually became the 
most enthusiastic and enlightened of geologists ; in the third period, 
lasting ten years, the valuable geological recruit devoted nearly all 
his energies and time to geological study and discussion and to 
preparing for publication the numerous observations made by him 
during the voyage ; the fourth period, which covers the latter half of 
his life, found Dar^vin gradually drawn more and more from geological 
to biological studies, though always retaining the deepest interest in 
the progress and fortunes of his " old love." But geologists gladly 
recognise the fact that Darwin immeasurably better served their 
science by this biological work, than he could possibly have done by 
confining himself to purely geological questions. 

From his earliest childhood, Darwin was a collector, though up 
to the time when, at eight years of age, he went to a preparatory 
school, seals, franks and similar trifles appear to have been the only 
objects of his quest. But a stone, which one of his schoolfellows 
at that time gave to him, seems to have attracted his attention and 
set him seeking for pebbles and minerals ; as the result of this newly 
acquired taste, he says (writing in 1838) " I distinctly recollect the 
flesire I had of being able to know something about every pebble 
in front of the hall door — it Avas my earliest and only geological 
aspiration at that time ^" He further states that while at Mr Case's 
school "I do not remember any mental pursuits except those of 
collecting stones," etc...." I was born a naturalist^" 

The court-yard in front of the hall door at the Mount House, 
Darwin's birthi)lace and the home of his childliood, is surrounded 
by beds or rockeries on which lie a number of pebbles. Some of 
these pebbles (in quite recent times as I am informed) have been 
collected to form a " cobbled " space in front of the gate in the outer 
wall, which fronts the hall door ; and a similar " cobbled area," there 
is reason to believe, may have existed in Darwin's childhood before 
the door itself The pebbles, which were obtained from a neighbour- 
ing gravel-pit, being derived from the glacial drift., exhibit very 

' The first of these works is indicated in the following pages by the letters L. L. \ the 
second )>y M. L. 

* AI. L. I. p. 3. * iV. L. I. p. 4. 


340 Darwi7i and Geology 

striking differences in colour and form. It was probably this circum- 
stance which awakened in the child his love of observation and 
speculation. It is certainly remarkable that ''aspirations" of the 
kind should have arisen in the mind of a child of 9 or 10 ! 

When he went to Shrewsbury School, he relates "I continued 
collecting minerals with much zeal, but quite unscientifically — all 
that I cared about was a new-named mineral, and I hardly attempted 
to classify theniK" 

There has stood fi-om very early times in Darwin's native 
town of Shrewsbury, a very notable boulder which has probably 
marked a boundary and is known as the "Bell-stone" — giving its 
name to a house and street. Darwin tells us in his Antohiographij 
that while he was at Shrewsbury School at the age of 13 or 14 
"an old Mr Cotton in Shropshire, who knew a good deal about 
rocks " pointed out to me " . . .the ' bell-stone ' ; he told me that there 
was no rock of the same kind nearer than Cumberland or Scotland, 
and he solemnly assured me that the world would come to an end 
before anyone would be able to explain how this stone came where it 
now lay " ! Darwin adds " This produced a deep impression on me, 
and I meditated over this wonderful stone ^." 

The "bell-stone" has now, owing to the necessities of building, 
been removed a short distance from its original site, and is carefully 
preserved within the walls of a bank. It is a block of irregular 
shape 3 feet long and 2 feet wide, and about 1 foot thick, weighing 
probably not less than one-third of a ton. By the courtesy of \ 
the directors of the National Provincial Bank of England, I have 
been able to make a minute examination of it, and Professors 
Bonney and Watts, with Mr Harker and Mr Fearnsides have given 
me their valuable assistance. The rock is a much altered andesite 
and was probably derived from the Arenig district in North Wales, 
or possibly from a point nearer the Welsh Border^. It was of course 
brought to where Shrewsbury now stands by the agency of a glacier — 
as Darwin afterwards learnt. J 

We can well believe from the perusal of these reminiscences that, 
at this time, Darwin's mind was, as he himself says, "prepared 
for a philosophical treatment of the subject" of Geology*. Wlien at 

1 L. L. I. p. 34. 2 i^ L I. p. 41. 

^ I am greatly indebted to the Managers of the Bank at Shrewsbury for kind assistance 
in the examination of this interesting memorial : and Mr H. T. Beddoes, the Curator 
of the Shrewsbury Museum, has given me some archaeological information concerning 
the stone. Mr Richard Cotton was a good local naturalist, a Fellow both of the 
Geological and Linnean Societies ; and to the officers of these societies I am indebted 
for information concerning him. He died in 1839, and although he does not appear to 
have published any scientific papers, he did far more for science by influencing the career 
of tlie school boy ! 

* L. L. I. p. 41. 

At Edinhurgh University 341 

the age of 16, however, he was entered as a medical student at 
Edinburgh University, he not only did not get any encouragement 
of his scientific tastes, but Avas positively repelled by the ordinary 
instruction given there, Dr Hope's lectures on Chemistry, it is true, 
interested the boy, who with his brother Erasmus had made a 
laboratory in the toolhouse, and was nicknamed "Gas" by his school- 
fellows, while undergoing solemn and public reprimand from Dr Butler 
at Shrewsbury School for thus wasting his time ^ But most of the 
other Edinburgh lectures were ''intolerably dull," "as dull as the 
professors" themselves, "something fearful to remember." In after 
life the memory of these lectures was like a nightmare to him. He 
speaks in 1840 of Jameson's lectures as something "I... for my sins 
experienced- ! " Darwin especially signalises these lectures on Geology 
and Zoology, which he attended in his second year, as being worst of 
aU "incredibly dull. The sole effect they produced on me was the 
determination never so long as I lived to read a book on Geology, or 
in any way to study the science^!" 

The misfortune was that Edinburgh at that time had become the 
cockpit in which the barren conflict between "Neptunism" and "Plu- 
tonism " was being waged with blind fury and theological bitterness. 
Jameson and his pupils, on the one hand, and the friends and disciples 
of Hutton, on the other, went to the wildest extremes in opposing 
each other's peculiar tenets. Darwin tells us that he actually heard 
Jameson "in a field lecture at Salisbury Craigs, discoursing on a 
trap-dyke, with amygdaloidal margins and the strata indurated on 
each side, with volcanic rocks all around us, say that it was a fissure 
filled with sediment from above, adding with a sneer that there were 
men who maintained that it had been injected from beneath in a 
molten condition*." "When I think of this lecture," added DarNvin, 
" I do not wonder that I determined never to attend to Geology ^" 
It is probable that most of Jameson's teaching was of the same 
controversial and unilluminating character as this field-lecture at 
Salisbury Craigs. 

There can be no doubt that, while at Edinburgh, Darwin must 
have become acquainted with the doctrines of the Huttonian School. 
Though so young, he mixed freely with the scientific society of the 
city, Macgillivray, Grant, Leonard Horner, Coldstream, Ainsworth 
and others being among his acquaintances, while he attended and 
even read papers at the local scientific societies. It is to be feared, 
however, that what Darwin would hear most of, as characteristic 

' L. L. I. p. 35. ■ L. L. I. p. 340. 

3 L. L. I. p. 41. " L. L. I. pp. 41—42. 

' This was written in 1876 and Darwin had in the summer of 1839 revisited and 
carefully studied the locality (L. L. i. p. 290). 

342 Darwin and Geology 

of the Hiittonian teaching, would be assertions that chalk-flints were 
intrusions of molten silica, that fossil wood and other petrifactions 
had been impregnated with fused materials, that heat — but never 
water — was always the agent by which the induration and crystallisa- 
tion of rock-materials (even siliceous conglomerate, limestone and 
rock-salt) had been effected ! These extravagant " anti-Wernerian " 
views the young student might well regard as not one whit less 
absurd and repellant than the doctrine of the "aqueous precipitation" 
of basalt. There is no evidence that Darwin, even if he ever heard 
of them, was in any way impressed, in his early career, by the 
suggestive passages in Hutton and Playfair, to which Lyell afterwards 
called attention, and which foreshadowed the main principles of 

As a matter of fact, T believe that the influence of Hutton and 
Playfair in the development of a philosophical theory of geology has 
been very greatly exaggerated by later writers on the subject. Just 
as Wells and Matthew anticipated the views of Dar>vin on Natural 
Selection, but without producing any real influence on the course of 
biological thought, so Hutton and Playfair adumbrated doctrines 
which only became the basis of vivifying theory in the hands of 
Lyell. Alfi-ed Russel Wallace has very justly remarked that when 
Lyell wrote the Principles of Geology, " the doctrines of Hutton and 
Playfair, so much in advance of their age, seemed to be utterly 
forgotten \" In proof of this it is only necessary to point to the 
works of the great masters of English geology, who preceded Lyell, 
in which the works of Hutton and his followers are scarcely ever 
mentioned. This is true even of the Researches in Theoretical 
Geology and the other works of the sagacious De la Beche^. Darwin 
himself possessed a copy of Playfair's Illustrations of the Huttonian 
Theory, and occasionally quotes it ; but I have met with only one 
reference to Hutton, and that a somewhat enigmatical one, in all 
Darwin's writings. In a letter to Lyell in 1841, when his mind was 
much exercised concerning glacial questions, he says " What a grand 
new feature all this ice work is in Geology ! How old Hutton would 
have staredl" 

As a consequence of the influences brought to bear on his mind 

^ Quarterly Review, Vol. cxxvi. (1869), p. 363. 

■^ Of the strength and persistence of the prejudice felt against Lyell'a views by his 
contemporaries, I had a striking illustration some little time after Lyell's death One 
of the old geologists who in the early years of the century had done really good work 
in connection with the Geological Society expressed a hope that I was not "one of those 
who had been carried away by poor Lyell's fads." My surprise was indeed great when 
further conversation showed me that the whole of the Principles were included in the 

3 M. L. II. p. 149. 

At Cambridge University 343 

during his two years' residence in Edinburgh, Darwin, who had 
entered that University with strong geological aspirations, left it and 
proceeded to Cambridge with a pronounced distaste for the whole 
subject. The result of this was that, during his career as an under- 
graduate, he neglected all the opportunities for geological study. 
During that important period of life, when he was between eighteen 
and twenty years of age, Darwin spent his time in riding, shooting and 
beetle-hunting, pursuits which were undoubtedly an admirable 
preparation for his future work as an explorer ; but in none of his 
letters of this period does he even mention geology. He says, how- 
ever, " I was so sickened with lectures at Edinburgh that I did not 
even attend Sedg^vick's eloquent and interesting lectures^" 

It was only after passing his examination, and when he went up 
to spend two extra terms at Cambridge, that geology again began to 
attract his attention. The reading of Sir John Herschel's Intro- 
duct ion to the Study of Natural Philosophy, and of Humboldt's Per- 
sonal Narrative, a copy of which last had been given to him by his 
good friend and mentor Henslow, roused his dormant enthusiasm for 
science, and awakened in his mind a passionate desire for travel. 
And it was fi'om Henslow, whom he had accompanied in his excursions, 
but without imbibing any marked taste, at that time, for botany, that 
the advice came to think of and to "begin the study of geology I" 
This was in 1831, and in the summer vacation of that year we find 
him back again at Shrewsbury " working like a tiger " at geology and 
endeavouring to make a map and section of Shropshire — work which 
he says was not "as easy as I expected^." No better field for 
geological studies could possibly be found than Darwin's native 

Writing to Henslow at this time, and referring to a form of the 
instrument devised by his friend, Darmn says : " I am very