Male, Female: The Evolution of Human Sex Differences. - Review - book review

Journal of Sex Research, Feb, 2001 by Paul Okami

Male, Female: The Evolution of Human Sex Differences. By David C. Geary. Washington, DC: American Psychological Association, 1998, 410 pages. Cloth, $49.95. Why Sex Matters. By Bobbi Low. Princeton, NJ: Princeton University Press, 1999, 328 pages. Cloth, $29.95. Sex Differences: Developmental and Evolutionary Strategies. By Linda Mealey. San Diego, CA: Academic Press, 2000, 492 pages. Cloth, $79.95.

The books under review here exemplify a simple principle: If you're going to do something, do it right! All three of these authors--Geary, Low, and Mealey--have chosen to enter the contentious territory of sex differences and have done so with the best possible armor: exhaustive knowledge of their subject matter and a determination to communicate this knowledge. These books represent a fine harvest of the maturing movement toward "evolution mindedness" in psychology and the sexual sciences.

Indeed, one of the books, Male, Female: The Evolution of Human Sex Differences by Geary is undoubtedly the finest scholarly work to date reviewing theory and research findings on sex differences. However, to a large degree, comparisons are not fair because each of the books under review fills a fairly specific niche. For example, unlike Male, Female, which is written primarily for a professional audience, Sex Differences is written as an upper-level undergraduate or graduate-level textbook, and Mealey has not aspired to do what Geary has done. (It is clear from her text, however, that she could have had that been her goal). In Why Sex Matters, Low presents her case for taking an ecological evolutionary perspective on sex and sex differences to an educated lay audience. Thus, each of the books under review addresses a very different group of readers.

Male, Female

Perhaps the most important accomplishment of Male, Female is not its massively comprehensive look at evidence of sex differences in human and nonhuman animals but its serious attempt to integrate analyses of phylogeny (ultimate evolutionary history) with ontogeny (developmental mechanisms and proximate mediating variables). Thus, Geary pays more than lip service to the notion that evolutionary mechanisms interact with social-ecological, developmental, and neurohormonal contingencies. He attempts to explore these contingencies at some depth. Male, Female, therefore, reads quite a bit differently from some of the more well-known works of evolutionary psychology which stress ultimate mechanisms, sometimes to the virtual exclusion of serious considerations of proximate mechanisms--including emotion and motivation, hormonal fluctuation, cultural differences, sex roles and ideology, and historical/demographic factors such as the operational sex ratio.

In Chapter 1, Geary starts "at the beginning" and describes theories of the origin of sexual reproduction. Because sexual reproduction results in variability among the individuals of a sexually-reproducing species, there is also variability in the "mate value" of individuals. This in turn results in (a) competition for the most desirable mates, and (b) the exercise of choice among each sex for mates with the most desirable characteristics. The name Darwin gave to this process is sexual selection and it is the theoretical basis for Geary's exploration of sex differences to follow. Geary defines and elaborates on this theory in Chapter 2.

Chapter 3 is devoted to exploring the work of sexual selection among nonhuman primates and early hominids. For those (such as creationists and many social scientists) who appear to view humans as somehow "special" and only marginally related in behavior to nonhuman primates and other animals, this material should be sobering. Contrary to the exclusive emphasis on female choice and male competition found in some evolutionary accounts, Geary presents ample evidence among primates for choice and competition among both sexes.

Chapter 4 begins coverage of sex differences among modern humans with a discussion of maternal and paternal investment in reproduction. Of particular interest is the discussion of paternal investment. Because Trivers' influential theory of parental investment and sexual selection focuses on minimal parental investment as the determining factor in the evolution of sex differences, it is sometimes assumed that, in fact, men typically invest relatively little in offspring. Geary disabuses us of this idea.

Chapter 5 discusses the dynamics of choice and competition among the sexes. Geary brings in copious cross-cultural and historical data as exemplars.

Chapter 6 presents Geary's original theoretical contribution to Male, Female, and, for me, the meat and potatoes of the book. Here Geary attempts to weave analyses of ultimate and proximate mechanisms into a theory of motivation, moored in sexual selection. The basic idea is that childhood is the formative period for the adaptation of human emotional, motivational, and cognitive-brain mechanisms to local ecological conditions. Selection has shaped these mechanisms so that they will assist the individual in his or her attempts to control the available resources--social and environmental--that support survival and reproduction. Thus, the central motivation of the behavior of human beings, according to Geary, is control over resources.