Why We Get Sick Read online

  Acclaim for

  Randolph ML Nesse and George C. Williams’s

  WHY WE GET SICK

  “This is the most important book written about issues in biomedicine in the last fifty years. When the world’s leading evolutionary biologist (Williams) teams up with a thoughtful physician (Nesse), the product is a gripping exploration of why our bodies respond the way they do to injury and disease.”

  —Michael S. Gazzaniga, Ph.D.,

  director, Center for Neuroscience,

  University of California at Davis

  “Darwinian medicine … holds that there are evolutionary explanations for human disease and physical frailties, just as for everything else in biology, and that these insights can inspire better treatments.… In Why We Get Sick … two proponents of Darwinian medicine lay out the ambitious reach of the adventurous new discipline.”

  —The New York Times Magazine

  “Every so often, a book comes along that has the power to change the way we live and die. This splendid book is one, and it could well revolutionize the way physicians are taught, the way they practice, and even the way parents watch over their child with a fever or a cough.”

  —Professor Robert Ornstein,

  author of The Psychology of Consciousness

  “Would you accept that eating certain kinds of red meat could help ward off heart attacks? That taking aspirin when you are sick could make things worse? That mothers should sleep right next to their infants to prevent sudden infant death? You might after hearing how your prehistoric ancestors lived, according to a small but growing tribe of ‘Darwinian medicine’ thinkers. They argue that for too long physicians have ignored the forces that shaped us over evolutionary eons.… Such ideas are … controversial, but that’s the point.”

  —Wall Street Journal

  “Why We Get Sick is certain to be recognized as one of the most important books of the decade, and what’s more, it’s beautifully written.”

  —Roger Lewin,

  author of Human Evolution, 3rd Edition

  “Why We Get Sick offers both a provocative challenge to medicine and a thoughtful discussion of how evolutionary theory applies to people.”

  —Business Week

  Randolph M. Nesse, M.D.

  George C. Williams, Ph.D.

  WHY WE GET SICK

  Randolph M. Nesse, M.D., is a practicing physician and professor and associate chair for education and academic affairs in the Department of Psychiatry at the University of Michigan Medical School.

  George C. Williams, Ph.D., is a professor emeritus of ecology and evolution at the State University at Stony Brook and editor of The Quarterly Review of Biology.

  FIRST VINTAGE BOOKS EDITION, JANUARY 1996

  Copyright © 1994 by Randolph M. Nesse, M.D., and George C. Williams, Ph.D.

  All rights reserved under International and Pan-American Copyright Conventions. Published in the United States by Vintage Books, a division of Random House, Inc., New York, and simultaneously in Canada by Random House of Canada Limited, Toronto. Originally published in hardcover by Times Books, a division of Random House, Inc., New York, in 1995.

  Grateful acknowledgment is made to the following for permission to reprint previously published material:

  Lawrence M. Crapo and James F. Fries, M.D.: Two charts from Vitality and Aging by Lawrence M. Crapo and James F. Fries, M.D.

  (W. H. Freeman & Company, San Francisco, 1981).

  Reprinted by permission.

  Harcourt Brace &. Company: Chart 12-1 from Life: An Introduction to Biology by George C. Simpson, Colin S. Pittendrigh, and Lewis H. Tiffany. Copyright © 1957 by George C. Simpson, Colin S. Pittendrigh, and Lewis H. Tiffany. Copyright renewed 1985 by Anne R. Simpson, Joan Simpson Burns, Ralph Tiffany, Helen Vishniac, and Elizabeth Leonie S. Wurr. Reprinted by permission of Harcourt Brace & Company.

  The Library of Congress has cataloged the Times Books edition as follows: Nesse, Randolph M.

  Why we get sick: the new science of Darwinian medicine Randolph M. Nesse and George C. Williams.—1st ed.

  p. cm.

  1. Medicine—Philosophy. 2. Human evolution.

  3. Human biology. 4. Adaptation (Physiology)

  I. Williams, George C. (George Christopher), 1926– II. Title.

  R723.N387 1995

  610’.1-dc20 94-27651

  eISBN: 978-0-307-81600-9

  Illustrations by Jared M. Brown

  v3.1

  ACKNOWLEDGMENTS

  Our work has benefited enormously from comments made by many colleagues and friends who know more than we do about certain aspects of medicine and evolution. We have not always had the sense to take their advice, so don’t blame them for our mistakes. Among those who have offered comments or other suggestions on the manuscript are: James Abelson, M.D., Ph.D., Laura Betzig, Ph.D., Helena Cronin, Ph.D., Lyubica Dabich, M.D., Wayne Davis, Ph.D., William Ensminger, M.D., Paul Ewald, Ph.D., Joseph Fantone, M.D., Rosalind Fantone, R.N., Robert Fekety, M.D., Linda Garfield, M.D., Robert Green, M.D., Daniel Hrdy, M.D., Sarah Hrdy, Ph.D., Matt Kluger, Ph.D., Isaac Marks, M.D., Steven Myers, M.D., James Neel, M.D., Ph.D., Margie Profet, M.A., Robert Smuts, M.A., William Soloman, M.D., Paul Turke, Ph.D., Alan Weder, M.D., Brant Wenegrat, M.D., and Elizabeth Young, M.D. For help in finding references we especially thank Doris Williams, Jeanette Underhill, M.D., and Joann Tobin. A sabbatical provided by The University of Michigan with support from John Greden, M.D., and George Curtis, M.D., made it possible for Randolph Nesse to work on the manuscript at Stanford University, where Brant Wenegrat, M.D., and Anne O’Reilly offered hospitality beyond measure. Barbara Polcyn’s loyal and effective secretarial support was wonderful. We are grateful to our agent, John Brockman, for convincing us that we could present serious new science in a book for a general audience and for handling negotiations and publishing details with great effectiveness, and to Barbara Williams for persuading us to take John Brockman seriously. The style and structure of the book are much improved thanks to detailed editing by Margaret Nesse and by our editor at Times Books, Elizabeth Rapoport.

  Our greatest debt is to those who made us realize that we had a reason to write this book. They are the pioneers and visionaries whose ideas and investigations form the heart of the now flourishing field of Darwinian medicine. Some, like Paul Ewald and Margie Profet, figure prominently in several places in our text. Others are mentioned more briefly or merely have their publications listed in our endnotes. We are confident that, over the next few years, they will all be getting growing shares of the recognition they richly deserve.

  CONTENTS

  Cover

  Title Page

  Copyright

  Acknowledgments

  Preface

  1. The Mystery of Disease

  2. Evolution by Natural Selection

  3. Signs and Symptoms of Infectious Disease

  4. An Arms Race Without End

  5. Injury

  6. Toxins: New, Old, and Everywhere

  7. Genes and Disease: Defects, Quirks, and Compromises

  8. Aging as the Fountain of Youth

  9. Legacies of Evolutionary History

  10. Diseases of Civilization

  11. Allergy

  12. Cancer

  13. Sex and Reproduction

  14. Are Mental Disorders Diseases?

  15. The Evolution of Medicine

  Notes

  PREFACE

  We first met and discovered our shared interests in 1985 at a meeting of a group that later developed into the Human Behavior and Evolution Society. One of us (Nesse) was a physician in the Department of Psychiatry at the University of Michigan Medical School. Frustration with psychiatry’s lack of theoretical foundation and fascination
with the extraordinary progress that evolutionary ideas had brought to the field of animal behavior had led to his association with the University of Michigan Evolution and Human Behavior Program. Colleagues in that interdisciplinary group, on hearing about his long-term interest in the evolutionary origins of aging, suggested a 1957 paper by a biologist named George Williams. The paper was a revelation. Aging had an evolutionary explanation. Why not anxiety disorders or schizophrenia? Thanks to subsequent years of conversations with evolutionists, especially Williams, and with medical school residents and faculty, he has found that an evolutionary perspective on patients’ disorders has become steadily more natural and useful.

  The other author (Williams) has divided his career between marine ecological research and theoretical studies on evolution. His interest in medical applications of evolutionary ideas was aroused by reading a 1980 article by Paul Ewald in The Journal of Theoretical Biology, “Evolutionary Biology and the Treatment of the Signs and Symptoms of Infectious Disease.” Ewald’s work suggested that evolutionary ideas might well have significance for many medical problems, not just those that arise from infection. Williams’ general knowledge of evolutionary genetics included many principles with obvious implications for genetic diseases, and his early work on the evolution of the aging process suggested a basic relevance of evolution to gerontology.

  We convinced each other, shortly after we met, that the potential contribution of evolutionary biology to medical progress was important enough to justify a real effort to bring this idea to others. We decided to put our reasoning and some obvious examples into print as a way of stimulating other workers to explore many other possibilities. After our jointly written article, “The Dawn of Darwinian Medicine,” published in The Quarterly Review of Biology in March 1991, drew a favorable reception from the press as well as colleagues in both medicine and evolutionary biology, we decided that it could easily be expanded into a book that would interest a wide range of readers.

  Charles Darwin’s theory of natural selection as the explanation for the functional design of organisms is the foundation of almost everything in this book. The discussion centers on the concept of adaptation by natural selection: adaptations by which we combat pathogens, adaptations of pathogens that counter our adaptations, maladaptive but necessary costs of our adaptations, maladaptative mismatches between our body’s design and our current environments, and so on.

  As we wrote, we kept discovering new ways in which Darwinism can aid the progress of medicine. We gradually realized that Darwinian medicine is not just a few ideas, but a whole new field, with exciting new developments arising at an ever-increasing rate. However, we must emphasize that Darwinian medicine is still in its infancy. The examples of Darwinian thinking applied to medical problems should not be taken as authoritative conclusions or medical advice. They are designed only to illustrate the use of evolutionary thinking in medicine, not to instruct people on how to protect their health or treat their diseases. This is not to say that we believe Darwinian medicine is merely a theoretical endeavor. Far from it! We have every expectation that the pursuit of evolutionary questions will demonstrably improve human health. That will require effort, money, and time. In the meanwhile, we hope this book will stimulate people to think about their illnesses in a different way, to ask questions of their doctors, perhaps even argue with them, but certainly not to ignore their instructions.

  Having made that disclaimer, we will also make a few others. This book does not arise from a disapproval of current medical research or practice in Western industrialized nations. It is based on the conviction that medical research and practice would be even better if questions of adaptation and historical causation were routinely considered along with those of immediate physical and chemical causation. We are urging not an alternative to modern medical practice but rather an additional perspective from a well-established body of scientific knowledge that has been largely neglected by the medical profession. We would be very much against Darwinian medicine being viewed as a kind of alternative cult opposed to some supposed orthodoxy. It is likewise not our purpose to make political recommendations, although we believe that some of our reasoning might prove important to those who formulate health care or environmental policies.

  In addition to trying to make this book interesting and informative to a wide audience, we have tried to make it a preliminary but scientifically valid guide for physicians and researchers who are asking evolutionary questions in their own areas of expertise. We well realize that many medical professionals have already been asking such questions. Often, however, they have done so apologetically, treating their own ideas not as serious hypotheses but as mere speculations undeserving of serious inquiry. We challenge this attitude as strongly as possible and hope that the examples in this book will make many scientists realize that their evolutionary hypotheses are legitimate and deserve scientific testing, in ways that may be easier and more decisive than they suspect. This book does not offer formal instruction on how to test evolutionary hypotheses, but it does give many examples of such testing.

  We hope readers will realize that this meager book can provide only a brief glimpse of a few current evolutionary ideas in relation to a select list of medical examples. Medicine is now such a huge field that no one can master more than a small part of it. Even specialties such as internal medicine are quickly splitting into subspecialties, such as cardiology, and into subsubspecialties. Neither of us claims to have mastered more than a small fraction of the knowledge encompassed by modern medicine. We are well aware that any discussion of such a wide range of topics as is found in this book must of necessity be superficial and oversimplified. We hope that this will not seriously mislead anyone and that specialists will forgive us for any minor inaccuracies they may find. These risks seem worth it because of the potential utility of a broad overview of Darwinian medicine and because we believe that readers will derive real pleasure from an evolutionary understanding of their bodies’ functioning, and occasional malfunctioning.

  1

  THE MYSTERY OF DISEASE

  Why, in a body of such exquisite design, are there a thousand flaws and frailties that make us vulnerable to disease? If evolution by natural selection can shape sophisticated mechanisms such as the eye, heart, and brain, why hasn’t it shaped ways to prevent nearsightedness, heart attacks, and Alzheimer’s disease? If our immune system can recognize and attack a million foreign proteins, why do we still get pneumonia? If a coil of DNA can reliably encode plans for an adult organism with ten trillion specialized cells, each in its proper place, why can’t we grow a replacement for a damaged finger? If we can live a hundred years, why not two hundred?

  We know more and more about why individuals get specific diseases but still understand little about why diseases exist at all. We know that a high-fat diet causes heart disease and sun exposure causes skin cancer, but why do we crave fat and sunshine despite their dangers? Why can’t our bodies repair clogged arteries and sun-damaged skin? Why does sunburn hurt? Why does anything hurt? And why are we, after millions of years, still prone to streptococcal infection?

  The great mystery of medicine is the presence, in a machine of exquisite design, of what seem to be flaws, frailties, and makeshift mechanisms that give rise to most disease. An evolutionary approach transforms this mystery into a series of answerable questions: Why hasn’t the Darwinian process of natural selection steadily eliminated the genes that make us susceptible to disease? Why hasn’t it selected for genes that would perfect our ability to resist damage and enhance repairs so as to eliminate aging? The common answer—that natural selection just isn’t powerful enough—is usually wrong. Instead, as we will see, the body is a bundle of careful compromises.

  The body’s simplest structures reveal exquisite designs unmatched by any human creations. Take bones. Their tubular form maximizes strength and flexibility while minimizing weight. Pound for pound, they are stronger than solid steel bars. Specific bones are masterf
ully shaped to serve their functions—thick at the vulnerable ends, studded with surface protrusions where they increase muscle leverage, and grooved to provide safe pathways for delicate nerves and arteries. The thickness of individual bones increases wherever strength is needed. Wherever they bend, more bone is deposited. Even the hollow space inside the bones is useful: it provides a safe nursery for new blood cells.

  Physiology is still more impressive. Consider the artificial kidney machine, bulky as a refrigerator yet still a poor substitute that performs only a few of the functions of its natural counterpart. Or take the best man-made heart valves. They last only a few years and crush some red blood cells with each closure, while natural valves gently open and close two and a half billion times over a lifetime. Or consider our brains, with their capacity to encode the smallest details of life that, decades later, can be recalled in a fraction of a second. No computer can come close.

  The body’s regulatory systems are equally admirable. Take, for instance, the scores of hormones that coordinate every aspect of life, from appetite to childbirth. Controlled by level upon level of feedback loops, they are far more complex than any man-made chemical factory. Or consider the intricate wiring of the sensorimotor system. An image falls onto the retina; each cell transmits its signal via the optic nerve to a brain center that decodes shape, color, and movement, then to other brain centers that link with memory banks to determine that the image is that of a snake, then to fear centers and decision centers that motivate and initiate action, then to motor nerves that contract exactly the right muscles to jerk the hand away—all this in a fraction of a second.

  Bones, physiology, the nervous system—the body has thousands of consummate designs that elicit our wonder and admiration. By contrast, however, many aspects of the body seem amazingly crude. For instance, the tube that carries food to the stomach crosses the tube that carries air to the lungs, so that every time we swallow, the airway must be closed off lest we choke. Or consider nearsightedness. If you are one of the unlucky 25 percent who have the genes for it, you are almost certain to become nearsighted and thus unlikely to recognize a tiger until you are nearly its dinner. Why haven’t these genes been eliminated? Or take atherosclerosis. An intricate network of arteries carries just the right amount of blood to every part of the body. Yet many of us develop cholesterol deposits on the walls of our arteries, and the resulting blockage in blood flow causes heart attacks and strokes. It is as if a Mercedes-Benz designer specified a plastic soda straw for the fuel line!