Evolution in Health and Disease edited by S.C. Stearns

Abstract

Oxford University Press, 1999. £23.50 (xv + 328 pages)ISBN 0 19 850 4454Early Hippocratic medicine emphasized the environment. Post-Renaissance scientific medicine arose within a world dominated by ideas of creation and design – an engineering paradigm where anatomy and physiology explain the workings of the human machine. To such mechanistic explanations, Darwin added evolutionary explanations. Why do women, elephant shrews, chimps and a few bats menstruate visibly, whereas most mammals do not? What are the functions of sadness? What are the best ways of preventing breast cancer, heart diseases or the spread of drug-resistant bacteria? Questions like these, considered in this volume, have evolutionary dimensions, and cannot be adequately answered by a medical science that concentrates solely on mechanistic or proximate explanations.The popular press talks simplistically of genes for all kinds of diseases, HIV, ‘superbugs’ and genetic modification of organisms, but often sees evolution as something in the distant past, of philosophical but no practical significance. A realisation that evolution is a pervasive ongoing process, shaping nature and ourselves in health and disease, is often conspicuously absent. This is hardly surprising as basic evolutionary concepts are more recent than many concepts in mechanistic biology, and are more difficult to grasp because of their multidimensional contingent character.Mechanistic biology, including biochemistry and genetics, dramatically influenced 20th century medicine. The time is ripe for evolutionary biology to shape 21st century health sciences equally profoundly: so think the organisers of the conference that resulted in this multiauthor volume. It is a sampler of insights into medical problems using evolutionary thinking. I remember when it was difficult to get the medical establishment to include a modicum of basic mendelian genetics in the medical curriculum; now departments of medical genetics abound. This book and others like it should help evolutionary thinking permeate medicine more rapidly. Stearns' chapter provides one of the most lucid, brief introductions to evolutionary biology available, while Nesse and Williams, whose writings on darwinian medicine stimulated the conference, raise interesting philosophical and methodological questions.The book covers four major themes: how evolutionary history influenced human genetic variation and life cycle; the evolution of pathogens, their virulence and resistance to drugs; and the evolutionary dimension to non-infectious diseases. Following chapters by individual experts, each theme has a summary by a larger discussion group. Though useful, these involve some repetition, giving the book a disjointed air. It should appeal to medical practitioners or researchers wishing to learn something of new evolutionary approaches to their field, but would not be ideal as a textbook.The complexity of the interactions between genes and environment, and of the trade-offs between different phases of the human life cycle, mean that quick and simple answers may prove elusive for many of the problems discussed, such as senescence or manic depressive illness. The story of how human races spread across the world, and how their genetic diversity mirrors linguistic evolution is well told. It indicates that the dichotomy between genetic and cultural evolution is less sharp than is sometimes thought. Because language is predominantly vertically inherited, differential net reproductive rates, whether caused by cultural innovations (eg. agriculture or warfare) or environmental factors such as diseases, or a complex interplay of both, can cause a simultaneous spread of different genotypes, languages and associated cultural features such as religions. Conversely, other cultural features (eg. fashions for blue jeans or pop music), that spread predominantly horizontally, may evolve quite independently of genes. Multiple discordant clines in genotypes describe human genetic diversity better than simplistic racial classifications into white, black or Asian, as in bureaucratic statistics. I, however, do not favour the common view that more sophisticated racial groupings have no value. Despite much miscegination (my second daughter is Sino-Caucasian), especially in the Americas, it is useful to recognise that Africans comprise two or more major racial and linguistic groups whereas pale Caucasians and dark Indians are basically the same race, as are Amerindians and Mongolians, while Oceanians are closest to South East Asians.Two areas covered in detail will interest evolutionary biologists not specifically concerned with medical matters: evolution of pathogens and human genetic diversity. Owing to huge medical efforts, these fields provide some of the best examples of general evolutionary processes. Human genetic variation affects our responses to drugs and pathogens, and gives convincing examples of balancing, frequency-dependent, and directional selection, and of drift or founder effects (as in the 12 diseases unexpectedly common in Ashkenazi Jews). Processes and patterns of evolution of pathogens and virulence are well treated. The many first-rate contributors successfully demonstrate the importance of evolutionary thinking to medicine.