Review (2): Why We Get Sick

Why We Get Sick:

The new science of Darwinian medicine

By Randolph M. Nesse and George C. Williams. 291 pp. New York, Times Books, 1995. ISBN 0-8129-2224-7. (Published in England as Evolution and Healing: The new science of Darwinian medicine.)

Reinventing Darwin: The great debate at the high table of evolutionary theory

By Niles Eldredge. 244 pp. New York, John Wiley, 1995. ISBN 0-471-30301-1

Why We Get Sick is the result of a collaboration between a practicing physician and an evolutionary biologist. A model of scientific popularization, it acquaints readers with some fundamental ideas of evolutionary theory and suggests ways to apply this perspective to medical problems. The introductory chapters set out, in an extremely clear and nontechnical way, the basic principles of evolutionary biology, modern population biology, and behavioral genetics. Nesse and Williams then probe the evolutionary significance of various aspects of disease. Their discussion runs through assorted issues -- for instance, our idiosyncratic food preferences and ability to deal with environmental toxins, our numerous genetic quirks, and the evolutionary significance of senescence.

Some of their examples are familiar and straightforward, such as the rise of antibiotic-resistant microorganisms. Other examples, particularly those involving behavioral traits, are less obvious. Is colicky crying in babies adaptive? How can the functions of various emotional states and mental disorders be assessed? What is the evolutionary origin of sleep and of sleep disorders? Some of the behavioral problems discussed in the book would not be considered medical disorders, but the authors include these examples for the sake of completeness.

Their discussion draws on the recent literature in sociobiology, which has grown steadily in the past 20 years but remains controversial. The explanations offered by sociobiologists have been criticized for the way they interpret complex behavior hypothetically from the gene's point of view. The social and political implications of these interpretations raised a great storm in the 1970s. Nesse and Williams steer clear of these political overtones and stress that evolutionary explanations can and should be testable, although not all the hypotheses presented in this book have been tested. The authors mainly want to throw out as many ideas as they can to stimulate readers to consider how an evolutionary perspective can shed light on a multitude of problems.

Nesse and Williams are puzzled that evolutionary thinking has taken so long to gain a foothold in medicine and note that many of their own ideas have been derived from very recent work. Evolutionary medicine has not been as neglected as they imply, for it has had some prominent champions in the past century. But certainly the synthesis of evolutionary genetics and medicine that Nesse and Williams are advocating is a recent and overdue development. Although they have no explanation for why Darwinian medicine is so neglected, they encourage any form of reform in medical teaching that will make room for an evolutionary approach. One might more fruitfully consider reform at the premedical level, where students still have some flexibility in designing their programs. Indeed, although the book jacket exhorts readers to give a copy of this book to their doctors, it would be better to give it to premedical students as a way of encouraging them to study more genetics and evolutionary biology.

The scientific arguments that Nesse and Williams review involve the problem of identifying what an adaptation is, or exactly how a trait serves an adaptive purpose, and how genes and the environment interact to produce a given outcome. Niles Eldredge, in Reinventing Darwin, draws attention to the same problems in reviewing the 20-year history of a debate between paleontologists and geneticists in which he has had a prominent role. In the early 1970s, Eldredge led an attack on certain cherished notions of gradual evolutionary change that had become entrenched in modern paleontology. His hypothesis, known as the theory of "punctuated equilibrium" or the punctuational model, proposed that the origin of new species occurred in fairly rapid bursts ("rapid" in geologic terms, meaning tens of thousands of years) and that apart from these bursts of change most species were remarkably stable for long periods.

This model, subsequently developed by other paleontologists, generated great controversy. Eldredge's book is a polemical response to such critics as sociobiologist Richard Dawkins, who tried to deflate many of the punctuationist arguments. In particular, Eldredge criticizes the premise of sociobiology that competition for reproductive success drives all biologic systems. He lashes out at the simplistic view taken by sociobiologists, who he feels are somewhat in thrall to the reductionist tendencies exemplified in molecular biology.

Eldredge labels these biologists "ultra-Darwinians," and while admitting that their approaches have led to much impressive research, he blames sociobiology for the blatant distortion of natural systems. The opposing camp, with which he identifies, consists of self-styled "naturalists." This dichotomy is somewhat misleading and forces Eldredge to spend time trying to categorize people who either do not fit into one or the other camp or who seem to switch allegiances as the debate unfolds. And although the polemical tone ensures a lively, entertaining style, clarity sometimes suffers. It is difficult, for instance, in the historical sections of the book, to grasp exactly how and why the conceptual problems that Eldredge identifies arose and became so entrenched. One would appreciate more discussion of the conceptual difficulty of translating between the vastly different time scales of paleontology and genetics, since this problem appears central to the dispute. When, in the end, Eldredge claims that naturalists offer a less assumption-ridden and less theory-laden description of nature than the ultra-Darwinians, even a sympathetic reader may not fully grasp why the naturalists' picture is a better one. A few more citations of the literature mentioned in the discussion would also have been helpful.

Despite these quibbles, Eldredge's book is valuable for the way it brings out the human dimension of science. He makes the reader aware of how many obstacles there are to interdisciplinary thinking, how alliances develop and are maintained, how disputes are conducted, and how biologists bend the history of science to support their arguments as part of the rhetorical tactics that serve their larger strategic purposes. Eldredge openly admits the difference between what scientists say ought to be done in science and how they actually behave. His candid tone in sketching the social processes of science helps us to understand what lies behind the division between medicine and evolutionary biology that Nesse and Williams seek to break down. Reading Eldredge's book, one might also approach the sociobiologic arguments advanced by Nesse and Williams with a little more critical caution. Putting these books together, one is left with intriguing speculations about how a synthesis of these two perspectives would look. The reader can only guess how the punctuational model, which has been applied to human evolution, might influence the medical hypotheses advanced by Nesse and Williams. Both books offer much food for thought on the subject of human evolution and its implications and on the importance of thinking historically in medicine as well as science.

Internet Source: http://www.nejm.org/publicM/1996/0334/0016/1067/1.htm

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