DARWIN, AND AFTER DARWIN

III

POST-DARWINIAN QUESTIONS
ISOLATION AND PHYSIOLOGICAL SELECTION

BY THE SAME AUTHOR.

DARWIN, AND AFTER DARWIN. An Exposition of the Darwinian Theory and a Discussion of Post-Darwinian Questions.

AN EXAMINATION OF WEISMANNISM. With portrait of Weismann. 236 pages. Cloth, $1.00.

THOUGHTS ON RELIGION. Edited by Charles Gore, M.A., Canon of Westminster. Third Edition. 184 pages. Cloth, gilt top, $1.25.

THE OPEN COURT PUBLISHING COMPANY,
324 Dearborn Street, Chicago.

DARWIN, AND AFTER DARWIN

AN EXPOSITION OF THE DARWINIAN THEORY
AND A DISCUSSION OF
POST-DARWINIAN QUESTIONS

BY THE LATE
GEORGE JOHN ROMANES, M.A., LL.D., F.R.S.
Honorary Fellow of Gonville and Caius College, Cambridge

III
POST-DARWINIAN QUESTIONS
ISOLATION
AND PHYSIOLOGICAL SELECTION

Chicago
THE OPEN COURT PUBLISHING COMPANY
1906

CHAPTER 1. COPYRIGHTED BY
THE OPEN COURT PUBLISHING CO.
1897.

The Lakeside Press
R. R. DONNELLEY & SONS CO., CHICAGO

PREFACE

Of the six chapters which constitute this concluding volume of G. J. Romanes' Darwin, and after Darwin, three, the first two and the last, were in type at the time of his death. I have not considered myself at liberty to make any alterations of moment in these chapters. For the selection and arrangement of all that is contained in the other three chapters I am wholly responsible.

Two long controversial Appendices have been omitted. Those marked A and B remain in accordance with the author's expressed injunctions. In a third, marked C, a few passages from the author's note-books or MSS. have been printed.

The portrait of the Rev. J. Gulick, which forms the frontispiece, was prepared for this volume before the author's death. Mr. Gulick's chief contributions to the theory of physiological selection are to be found in the Linnean Society's Journal (Zoology, vols. xx and xxiii), and in four letters to Nature (vol. xli. p. 536; vol. xlii. pp. 28 and 369; and vol. xliv. p. 29).

I have to thank Mr. Francis Galton, D.C.L., F.R.S. and Mr. F. Howard Collins for valuable assistance generously rendered for the sake of one whom all who knew him held dear. For he was, if I may echo the words of Huxley, "a friend endeared to me, as to so many others, by his kindly nature, and justly valued by all his colleagues for his powers of investigation and his zeal for the advancement of science."

C. Lloyd Morgan.

Bristol, May 1897.

CONTENTS

CHAPTER I.

Isolation 1

CHAPTER II.

Isolation (continued) 28

CHAPTER III.

Physiological Selection 41

CHAPTER IV.

Evidences of Physiological Selection 62

CHAPTER V.

Further Evidences of Physiological Selection 81

CHAPTER VI.

A Brief History of Isolation as a Factor in Organic Evolution 101

General Conclusions 144

Appendix A. Mr. Gulick's Criticism of Mr. Wallace's Views on Physiological Selection 151

Appendix B. An Examination by Mr. Fletcher Moulton of Mr. Wallace's Calculation touching the Possibility of Physiological Selection ever acting alone 157

Appendix C. Some Extracts from the Author's Note-books 169

ISOLATION

CHAPTER I.
Isolation.

This treatise will now draw to a close by considering what, in my opinion, is one of the most important principles that are concerned in the process of organic evolution—namely, Isolation. I say in my opinion such is the case, because, although the importance of isolation is more or less recognized by every naturalist, I know of only one other who has perceived all that the principle involves. This naturalist is the Rev. J. Gulick, and to his essays on the subject I attribute a higher value than to any other work in the field of Darwinian thought since the date of Darwin's death