Evolution, Genetics, and Man

Evolution, Genetics,

and Man

THEODOSIUS 'DOBZHANSKY

PROFESSOR OF ZOOLOGY AND MEMBER OF THE

INSTITUTE FOR THE STUDY OF HUMAN VARIATION

COLUMBIA UNIVERSITY

Evolution, Genetics

^i

and Man

JOHN WILEY & SONS, INC. - NEW YORK

CHAPMAN & HALL, LIMITED - LONDON

FOURTH PRINTING, OCTOBER, 1959

Copyright © 1955

by

John Wiley & Sons, Inc.

All Rights Reserved

This book or any part thereof must not

be reproduced in any form without the

written permission of the publisher.

Library of Congress Catalog Card Number: 55-10868

Printed in the United States of America

Preface

For almost a century the influence of the theory of evolution has

been felt far beyond the limits of biology. In fact, this influence has

been growing apace, and in our day the idea of evolution has become

an integral part of the intellectual equipment of Western Civilization.

In biology this idea is pivotal. To a beginning student no less than

to a teacher and to a specialist, the idea of evolution makes sense

of what would otherwise be wearisome descriptions of arid facts to

be memorized, only to be forgotten as soon as the course is over. In

the light of evolution the same facts and descriptions of creatures

which we have seldom or never seen become fascinating. Learning

them turns out to be an intellectual adventure.

Biological evolution is a part of the evolution of the cosmos. The

rise and the development of mankind are a part of the story of bio-

logical evolution. Man cannot reach a valid understanding of his

own nature without a knowledge of his own biological background.

It may, then, be that the study of evolutionary biology is the most

important practical endeavor open to the human mind. Accordingly,

an effort is being made in this book to show to the student that biology

is not only a craft which is interesting to technicians and devotees but

also a part of the fabric of modern humanistic thought. I am quite

conscious that this goal is too ambitious and that it has not been

fully attained.

I hope that this book may be useful not only as a guide in courses

devoted to the study of biological evolution but also as collateral

reading in courses of general biology, general zoology, general botany,

and anthropology. A sizable proportion of the space in this book is

devoted to presentation of material which is usually given in ele-

mentary courses of genetics. Chapters 2, 3, 4, parts of 5 and 11, and

smaller parts of other chapters deal with genetics. This emphasis is

unavoidable, since modern evolutionism is incomprehensible except

on the basis of familiarity with fundamentals of genetics. Therefore,

vii

viii Preface

although it has not been my intention to turn this book into a brief

textbook of genetics, a student who uses it will acquire an elementary

knowledge of the subject. The book will probably fit the require-

ments of courses given in some institutions of higher learning, courses

entitled "Genetics and Evolution" or "Evolution and Genetics."

An effort has been made to use, wherever possible, examples deal-

ing with man and to point out the bearing of the topics discussed

on human problems. The opinion once held fairly widely, that man

is most unfavorable as material for biological and especially for genetic

studies, is becoming less and less prevalent. Even though we cannot

arrange many genetical experiments with man, there is an abundance

of kinds of information bearing on the genetics and evolution of man

which are not available for any other organism. And after all is said

and done, the species Homo sapiens happens to be more interesting

to most students than any other species, no matter how unserviceable

it may be for some experiments. Being men, we understand many

biological phenomena in man more easily and more clearly than we

do the biology of much "simpler" organisms.

Although this book is meant to be comprehensible to a student with

no more than an elementary previous knowledge of biology (at about

high school level), some more "advanced" material and discussion of a

number of unsettled and controversial problems have been included.

As a result, the book contains more material than can be adequately

covered in an average one-term course; but this superabundance of

material is deliberate. The subdivision of the chapters into short

sections with descriptive subheadings should make deletion of the

unwanted material easy. On the other hand, what can be more chal-

lenging and inspiring to a student of average and above-average in-

telligence than to learn that science is not something all completed

and finished, merely to be memorized from books, but a growing body

of knowledge, in the development of which this same student may

have a hand if he so chooses? Is finding this out not equally, or even

more, valuable to a student than learning more "facts"?

In place of a conventional chapter on the history of evolutionary

theories, the history of various ideas and concepts is discussed in this

book in the same chapters which present the modern status of those

ideas and concepts. This arrangement of material does not in any

sense mean an underestimate of the importance of the history of sci-

ence or of its interest to an intelligent student. But modern evolu-

tionary thought is a result of confluence and integration of the work

of many biological disciplines, which even in a recent past were de-

Preface ix

veloping more independently than they are now. The history of the

evolutionary doctrine as a whole, from a modern standpoint, has never

been written, and for the time being it seems more convenient to

present the historical information piecemeal.

The "Suggestions for Further Reading" given at the end of most

chapters are meant to assist the student who may wish to go beyond

the limits of this book in exploring problems of evolutionary biology.

These "Suggestions" are certainly not meant to serve as bibliographies

in which a reference to an authority for every fact and name men-

tioned in the text may be located.

I am deeply indebted to several colleagues and friends who have

read chapters of this book and suggested corrections and improve-

ments. The greatest thanks go to Professors Ernst Mayr, of Harvard

University, Charles Birch, of the University of Sydney, Australia, and

A. B. da Cunha, of the University of Sao Paulo, Brazil, who have read

the manuscript in its entirety. Chapters 1, 2, and 3 were read also by

Drs. Alfred Mirsky and Stanley Gartler; Chapters 4 and 5 by Dr. M.

Demerec; Chapters 6 and 7 by Dr. Phillip M. Sheppard; Chapters 6, 7,

8, and 10 by Professor H. L. Carson; Chapters 8, 10, and 12 by Pro-

fessor John A. Moore; Chapter 9 by Professor P. C. Mangelsdorf; Chap-

ter 11 by Professor Aubrey Gorbman; and Chapters 13 and 14 by Pro-

fessor L. C. Dunn, Mr. Stephen Dunn, and Mr. M. D. Coe. Quite

obviously, I remain solely responsible for all errors of commission and

omission which doubtless will be found in the book. Mr. Stephen R.

Peck has drawn many of the excellent illustrations which adorn the

text. Several colleagues have contributed other illustrations and photo-

graphs, as acknowledged in the legends to these figures. Finally,

thanks are due Miss Adelaide Richardson, who prepared the typescript.

I'll. DOBZHANSKY

Sao Paulo, Brazil

October, 1955

Contents

1 • Nature and Origin of Life 1

2- The Gene as the Basis of Evolution dS3^nzD

a b c d e f ff hi