Hen’s Teeth and Horse’s Toes

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Hen’s Teeth and Horse’s Toes
BY STEPHEN JAY GOULD

IN NORTON

EVER SINCE DARWIN

Reflections in Natural History

THE PANDA’S THUMB

More Reflections in Natural History

THE MISMEASURE OF MAN

HEN’S TEETH AND HORSE’S TOES

Further Reflections in Natural History

THE FLAMINGO’S SMILE

Reflections in Natural History

AN URCHIN IN THE STORM

Essays about Books and Ideas

WONDERFUL LIFE

The Burgess Shale and the Nature of History

BULLY FOR BRONTOSAURUS

Reflections in Natural History

FINDERS, KEEPERS

Treasures and Oddities of Natural History Collectors from Peter the Great to Louis Agassiz
(with R. W. Purcell)

THE BOOK OF LIFE

An Illustrated History of Life on Earth
(general editor)

EIGHT LITTLE PIGGIES

Reflections in Natural History

Hen’s Teeth and Horse’s Toes
Stephen Jay Gould

W. W. NORTON & COMPANY

NEW YORK LONDON

“Phyletic Size Decrease in Hershey Bars:” from
Junk Food
by Charles J. Rubin, David Rollert, John Farago, Rick Stark, Jonathan Etra.
Copyright © 1980 by Charles J. Rubin, David Rollert, John Farago, Rick Stark, Jonathan Etra. Used by permission of Dell Publishing Company.
Robert Frost: “Design” from
The Poetry of Robert Frost
edited by Edward Connery Lathem. Copyright 1936 by Robert Frost. Copyright © 1964 by Lesley Frost Ballantine. Copyright © 1969 by Holt, Rinehart and Winston. Reprinted by permission of Holt, Rinehart and Winston, Publishers. Also reprinted by permission of the Estate of Robert Frost and Jonathan Cape Limited, 30 Bedford Square, London.

Copyright © 1983 by Stephen Jay Gould
All rights reserved

First published as a Norton 1984; reissued 1994

Library of Congress Cataloging in Publication Data
Gould, Stephen Jay.

Hen’s teeth and horse’s toes.
1. Evolution I. Title.
QH366.2.G66 1983 575 82-22259

ISBN: 978-0-393-31103-7

W. W. Norton & Company, Inc.
500 Fifth Avenue, New York, N. Y. 10110
www.wwnorton.com

W. W. Norton & Company Ltd.
Castle House, 75/76 Wells Street, London WIT 3QT

F
OR
M
Y
M
OTHER

Brave woman

Wise owl

Contents
Three Geologists
Three Biologists
Adaptation
Development
Creationism
Race and Creed
Hen’s Teeth and Horse’s Toes
Prologue

ALL THE WORLD LOVES
a centennial; we can’t resist the temptation to celebrate something clean and even in a ragged and uncertain world. I am gathering this third volume of collected essays
*
in the midst of worldwide festivities for the third Darwinian centennial of our century. The first, in 1909, celebrated the 100th anniversary of Darwin’s birth; the second, in 1959, the 100th year since publication of the
Origin of Species;
the third, in 1982, the 100th anniversary of his death. Darwin and evolutionary theory have been the focal point of all my writing in this series (my personal tribute to Darwin on his third centennial appears as essay 9 in this volume). The sequence of centennials provides us with a fine epitome of evolutionary theory in our century, and with some insight into its present successes and tribulations.

The organizers of the major 1909 shindig at Cambridge University had to cover up an embarrassing fact in preparing their hagiographical centennial volume. Although no thinking person doubted the fact of evolution by 1909, Darwin’s own theory about its mechanism—natural selection—was not then at the height of its popularity. Indeed, 1909 marked the acme of confusion about how evolution happened in the midst of complete confidence that it had occurred. An embattled group of strict Darwinians, led by the aging A. R. Wallace in England and by A. Weismann in Germany, continued to hold that virtually all evolutionary change occurred by the cumulative power of natural selection building adaptation step-by-step from the random raw material of small-scale genetic variation. Lamarckism remained strong and provided an alternative to natural selection for the gradual building of adaptations—creative organic response to perceived needs and the transmission of these favorable responses to offspring through the inheritance of acquired characters. Mendelian inheritance, when properly elucidated, tipped the scales in Darwin’s favor; but, in 1909, it had (in the gropings of its youth) merely sown more confusion by adding yet a third mechanism to the swirling competition—production of new species all at once by large and fortuitous mutations.

By 1959, confusion had ceded to the opposite undesired state of complacency. Strict Darwinism had triumphed. The flowering of Mendelian genetics had finally laid Lamarckism to rest since the workings of DNA provided no mechanism for an inheritance of acquired characters. Early fascination with large mutations had ceded to a recognition that copious and continuous small-scale variation also had a Mendelian base, and provided a far better source for the raw material of evolutionary change than occasional and detrimental large mutations. But random, small-scale variation produces no change by itself and requires a shaping force to preserve and enhance its favorable component. By 1959, nearly all evolutionary biologists had concluded that natural selection, after all, provided this creative mechanism of evolutionary change. At age 150, Darwin had triumphed. Yet, in the flush of victory, his latter-day disciples devised a version of his theory far narrower than anything Darwin himself would have allowed.

The strict version went well beyond a simple assertion that natural selection is a predominant mechanism of evolutionary change (a proposition that I do not challenge). It emphasized a program for research that almost dissolved the organism into an amalgam of parts, each made as perfect as possible by the slow but relentless force of natural selection. This “adaptationist program” downplayed the ancient truth that organisms are integrated entities with pathways of development constrained by inheritance—not pieces of putty that selective forces of environment can push in any adaptive direction. The strict version, with its emphasis on copious, minute, random variation molded with excruciating but persistent slowness by natural selection, also implied that all events of large-scale evolution (macroevolution) were the gradual, accumulated product of innumerable steps, each a minute adaptation to changing conditions within a local population. This “extrapolationist” theory denied any independence to macroevolution and interpreted all large-scale evolutionary events (origin of basic designs, long-term trends, patterns of extinction and faunal turnover) as slowly accumulated microevolution (the study of small-scale changes within species). Finally, proponents of the strict version sought the source of all change in adaptive struggles among individual organisms, thus denying direct causal status to other levels in the rich hierarchy of nature with its “individuals” both below the rung of organisms (genes, for example) and above (species, for example). The strict version, in short, emphasized gradual, adaptive change produced by natural selection acting exclusively upon organisms.

At the second centennial, some experts even declared that the immense complexity of evolution had yielded to final resolution. One leader remarked in a famous essay: “Differences of opinion on relatively minor points naturally persist and many details remain to be filled in, but the essentials of the explanation of the history of life have probably now been achieved.”

Now, at the third centennial, Darwinian theory is in a vibrantly healthy state. Confidence in the basic mechanism of natural selection provides a theoretical underpinning and point of basic agreement that carries us beyond the pessimistic anarchy of 1909. But the constraints of an over-zealous strict version, so popular in 1959, are loosening. Exciting discoveries in molecular biology and in the study of embryological development have reemphasized the integrity of organic form and hinted at modes of change different from the cumulative, gradual alteration emphasized by strict Darwinians. Direct study of fossil sequences has also challenged gradualistic biases (the “punctuated equilibrium” pattern of long-term stasis within species and geologically rapid origin of new species) and asserted the idea of explanatory hierarchy in identifying species as discrete and active evolutionary agents (just as molecular biology has extended hierarchy in the other direction by discovering evolutionary processes at genic levels that are “invisible” to organisms—see essay 13).

However, and ironically, the early 1980s have also witnessed an utterly different and perverse debate about evolution, often conflated in the public mind with these legitimate and exciting arguments about evolutionary mechanisms. I refer, of course, to the political resurgence of the pseudoscience known to its supporters as “scientific creationism”—strict Genesis literalism masquerading as science in a cynical attempt to bypass the First Amendment and win legislatively mandated inclusion of particular (and minority) religious views into public school curricula. As in 1909, no scientist or thinking person doubts the basic fact that life evolves. Intense debates about
how
evolution occurs display science at its most exciting, but provide no solace (only phony ammunition by willful distortion) to strict fundamentalists.

This peculiar juxtaposition of utterly different debates ostensibly about the same subject reminds me either of Wagner’s two operas about song contests,
Tannhäuser
and
Die Meistersinger—
one sublime, the other comic; or of Spielberg’s two films about oddities in suburbia for a 1982 summer,
E. T.
and
Poltergeist—
one joyful, the other sinister. But life is a continual conflation of sacred and profane, and who would have it any other way?

The present collection of essays about evolution was born amidst these tensions. It treats both the purely political and non-intellectual controversy stirred up by modern creationists (Section 5) and the fascinating debates now occurring within evolutionary theory. I discuss, for example, the role of alterations in embryonic development as a possible mechanism for rapid evolutionary transformations (Section 3); chance as a source of evolutionary change, not merely raw material (essay 26); evolution at hierarchical levels both above and below the traditional Darwinian focus on organisms (essay 13); and constraints of development and inheritance as arguments for the integrity of organisms and against an overly atomistic and deterministic view of adaptation (Section 3, but also as a major theme in essays 3, 10, and 29).

An ultimately more important tension—one that makes evolution such an exciting subject both for scientists and for all of us—contrasts these lively controversies that divide us with the enormous uniting power and extension of evolutionary theory itself. As I have explored the arguments, so too have I written about a view of life that has, since Darwin’s day, transformed our concept of ourselves and our world. “Big” questions about the history of our earth and its life provide a way to explore the thought of exemplary past scientists, and to understand the process of science itself, when done best (Section 2). (If readers emerge from this section with the message that science traffics in answerable questions, not in every fascinating reverie of the human mind, they will also understand why modern creationism is not science.) The seepage of evolutionary questions into ostensibly distant political debates (Section 5) displays both the pervasive scope of this view of life and also the inextricable union of scientific and social issues. The broader and distinctive view that emerges from evolutionary theory could enlarge our concept of science and of explanation in general by emphasizing historical contingency and quirky change (but sensible in retrospect) against the predictable and regular world preached by the stereotype of so-called “hard” science. I explore this issue throughout, but primarily in essay 4 (the one piece that should probably be read twice if you deem any essay worthy of such attention).

These issues are all abstract; but my vehicle for raising them remains the peculiar and mysterious particulars of nature. I have never been able to raise much personal enthusiasm for disembodied theory. Thus, when I wish to explore the explanatory power of evolutionary theory (Section 1), I write about apparent oddities resolved by Darwin’s view—dwarf male anglerfishes parasitically united with females, wasps that paralyze insects to provide a living feast for their larvae, young birds that kill their siblings by simply pushing them outside a ring of guano serving as a “nest,” and male mites that cycle through their lives in a fraction of the time alotted to females. Other essays treat generalities through the agency of particular mysteries; why are the genitalia of female spotted hyenas dead ringers for the male penis and scrotum; why do no large animals move on wheels; how can hens be induced to form teeth when no birds have produced them for more than fifty million years; how can some flies form legs in their mouths (I even discuss an “ouchless” mosquito, so afflicted); why did the demise of dinosaurs coincide with an extinction of at least twenty-five percent of marine invertebrate families; are zebras white on black or black on white, and what general rule unites their varied patterns of striping? I even think that a generality lies behind my piece on shrinking Hershey Bars, but I won’t push it. Pure humor (or attempts thereat) has its place as well.

Darwin, at his third centennial, would be satisfied indeed with the vigor of his child, now grown so large and strong. He would also welcome the legitimate and far-reaching debates that surround his theory, for absence of dogmatism is the truest mark of a great scientist. At the first centennial of 1909, William Bateson (see essay 11), perhaps the least Darwinian of all participants, paid the finest of all tributes by writing of Darwin: “We shall honor most in him not the rounded merit of finite accomplishment, but the creative power by which he inaugurated a line of discovery endless in variety and extension.”

BOOK: Hen’s Teeth and Horse’s Toes
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