THE MOLECULAR BASIS
OF
EVOLUTION
 

The
MOLECULAR BASIS

NEW YORK = JOHN WILEY & SONS, INC.

London * Chapman & Hall, Limited

OF EVOLUTION

CHRISTIAN B. ANFINSEN

National Heart [Institute
National Institutes of Health

Bethesda, Maryland
Copyright © 1959 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: 59-11794

Printed in the United States of America

TO MY MOTHER
AND

TO THE MEMORY OF
MY FATHER
PREFACE

The writing of this book has been stimulated
by the excitement and promise of contemporary protein chem-
istry and genetics and by the possibilities of integration of these
fields toward a greater understanding of the fundamental forces
underlying the evolutionary process. It has become, inevitably,
a highly personal volume expressing the experimental and_phil-
osophical outlook which has resulted from a process of self-education
in an unfamiliar area of science. As with many biochemists, pure
biology, including genetics, has not been a major exposure in my
education, and the process of learning something about these subjects
has been both a revelation and a struggle. Various kind, and
frequently amused, friends, versed in the complexities of modern
genetics, have sifted through these pages, and I hope that most of
the misinterpretations and frank mistakes have been eliminated.

It has been highly interesting of late to observe how many scientists,
working either in protein chemistry or in genetics, or for that matter
in relatively unrelated fields, have arrived at long-range research plans
that are similar to. my own, down to almost the last detail of experi-
mental planning. This book, therefore, will undoubtedly represent the
point of view of numerous other biologically oriented individuals. On
the other hand, some of the ideas to be discussed are so new and
controversial that for every well-informed reader of this book who,

vii
in general, approves them there may be another who considers them
nonsense,

The recent advances in the development of techniques for the study
of protein structure have made it possible to elucidate the complete
amino acid sequences of a number of rather large polypeptides pos-
sessing hormonal activity, and nearly complete sequences should soon
be available for several with enzymatic activity as well. Concomitantly,
there have been developed methods for the analysis of the finer,
more subtle, structural aspects of proteins, concerned with folding,
intramolecular bonds of various types, and intermolecular interactions.
These advances now begin to enable us to discern the vague outlines
of macromolecules, in the three-dimensional sense, and to ascribe
their physical behavior and biological activity to specific covalent and
noncovalent structural features.

We like to believe that Nature has been extremely wise and effi-
cient in the design of the chemical compounds, however large and
complicated, which make up the structure and machinery of living
things. Thus, although chemical differences are found among the
representatives of a given protein as isolated from a variety of species,
we tend to suppose that such variations, rather than being fortuitous
and unimportant irrelevancies, are part of a complicated and highly
integrated set of variations in all the functionally and structurally
important elements of the cell, the summation of which accounts for
the unique morphology and phenotypic character of the individual
organism.

In the last few years, a number of studies have shown that various
biologically active molecules may be subjected to considerable degra-
dation without loss of functional competency. It becomes necessary,
therefore, to consider that the “macromoleculariness” of proteins and
other large molecules may, in many cases, be concerned not only with
a specific biological property but with other, more subtle, phenomena
of cellular activity and engineering not yet apparent, such as adsorp-
tion to surfaces or substrates. We must, perhaps, expect a multiplicity
of variables in the “natural selection” of variants in molecules, all of
which may, together, determine the biological suitability of a particu-
lar molecular species.

An understanding of the underlying principles governing the
species specific variations in molecular structure and of the effect of
such variations on species characteristics must involve a clarification
of the process of translating information present in the genetic ma-
terial of the cell into the chemical language of enzymes, regulators,
and the like. Such considerations are only now becoming possible as

viii PREFACE

the result of the dramatic strides taken in the Jast few years in genetic
theory and methodology, and a portion of the discussion in the fol-
lowing pages will have to do with the experimental background of
the analysis of genetic fine structure and with the possible significance
of such analysis to the question of protein biosynthesis.

It is abundantly clear that the metabolic organization of all living
cells, whether plant or animal, shows a remarkable uniformity. Even
a cursory examination of the literature of comparative biochemistry
and physiology indicates that such biochemical functions as glycolysis,
proteolysis, and fatty acid degradation, as well as more integrated
processes such as electromotor activity and active transport through
membranes, are ubiquitous in nature. Discounting the likelihood of
completely parallel evolution in the plant and animal kingdoms, and
in their major branches, we are led to conclude that, long before
significant specialization, there existed in the waters of the earth vari-
ous primeval forms of life which were endowed with representatives
of most of, if not all, the important biological processes characterizing
living things as we know them today. Although it is unlikely that we
shall ever have more than opinions regarding the origin of life, it
does seem possible to approach, experimentally, the nature of the
speciation which began when such primeval cells had become estab-
lished. This approach must involve a backward extrapolation of the
information we can obtain on the chemical and genetic factors in
organisms chosen from our modern environment.

Before examining for the reader the aspects of the mechanism of
evolution that have been particularly illuminated by recent advances
in biology and chemistry, it has been necessary to outline, in a broad
sort of way, some of the basic fundamentals of evolution and the
specific sciences, particularly genetics, that have contributed so essen-
tially to its understanding. In the opening chapter, therefore, I have
collected and rephrased some gleanings from the massive literature
of morphological evolution to serve as a background for what follows.
In several subsequent chapters is presented further preparatory ma-
terial dealing with classical and contemporary genetics and with the
basic facts of protein structure. Finally, after some discussion of the
rapidly expanding body of knowledge relating structure to function
in biological systems, I have considered a few aspects of natural selec-
tion in evolution which suggest themselves as a result of contemporary
research, as well as some experimental approaches at the molecular
level.

This book was written for pleasure, with the desire for self-en-
lightenment as the major stimulus. Since I cannot help but feel that

t
PREFACE Ix
everyone in science must be interested in the evolutionary process as
the central theme of biology, I have listed a number of the original
articles and books which contributed to the subject matter of this
book.

I am greatly indebted to many of my friends and colleagues, includ-
ing Dr. W. F. Harrington, Dr. Daniel Steinberg, Dr. W. R. Carroll,
Dr. E. D. Korn, and Dr. W. D. Dreyer, who have read and helped
improve various chapters of this book. I should also like to express
my gratefulness to Dr. Bruce Ames for his patient help in connection
with some of the discussions of genetic subjects. My special thanks are
due Professor John T. Edsall of Harvard University and Dr. Michael
Sela of the Weizmann Institute of Science, Rehovoth, Israel, who have
read the entire manuscript and whose suggestions have been invalu-
able in the avoidance of error and in the improvement of style and
organization. Finally, I should like to thank my wife, Florence Anfin-
sen, for the cheerful and understanding support she gave to a fre-
quently rather morose husband.

CHRISTIAN B. ANFINSEN

Bethesda, Maryland
May 1959

x PREFACE

GROUND RULES
FOR
THE READER

A prospectus of this book was circulated to a num-
ber of experts by the publisher before the actual job of writing was
begun. The opinions received have been very helpful in establishing
what I hope is the proper slant. One opinion, in particular, expressed
a point of view so similar to my own that I have asked its author, Dr.
William Stein, of the Rockefeller Institute for Medical Research, for
permission to reproduce it here.

It has always seemed to me, and I may be wrong in this, that when an
expert communicates with the relatively non-expert, he has a responsibility
to stay pretty close to the facts. An expert can speculate to other experts
without scruple. They have the equipment to meet him on his own grounds,
evaluate the evidence and accept or reject the speculation as they choose.
The non-expert has no such basis for evaluation. He has to accept rela-
tively uncritically what the expert tells him, and hypothesis and fact soon
become confused in his mind. “A plausible speculation—and the speculations
of the true expert are always plausible—can soon masquerade successfully
as gospel. In the present state of our ignorance, I would regard this as
unfortunate. It would seem to me that a book such as this one should aim
to stimulate thought and experiment among practicing scientists, and
should not lull the uninitiated into thinking that we understand more than
we do.

xi
We shall deal, in this book, with many contemporary hypotheses,
some of which are far from general acceptance. Consequently, I
would like to emphasize two points of caution to the reader. First,
simple examples have purposely been chosen to illustrate the presen-
tation of subjects which in fact are sometimes complicated by excep-
tions and inconsistencies. Second, it will be apparent that the author,
like anyone else, has occasionally taken sides.

m0...

We...

xii GROUND RULES FOR THE READER

CONTENTS

. The Time Scale and Some Evolutionary Principles 1
. Genes as Determinants of Heredity 15

. The Chemical Nature of Genetic Material 39

. The Substructure of Genes 67

. Protein Structure 98

. The Biological Activity of Proteins in Relation

to Structure 126

. Species Variation in Protein Structure 142

. Genes as Determinants of Protein Structure 164
. On the Accuracy of Protein Synthesis 185

. The Biosynthesis of Proteins 195

. Genes, Proteins, and Evolution 21)

xiii