Geary writes in the Preface: “Since the publication of the first edition, the literature on human sex differences and on related topics, such as the evolution of sexual reproduction, has increased substantially. This required a thorough rewriting of all of the chapters, including breaking topics that were covered in a single chapter in the first edition into two chapters in this one, as well as adding new chapters. With the expanded coverage and more thorough organization and integration across chapters there was no room (in terms of page limitations) to include a chapter on implications for modern societies. However, I do cover the gist of these topics—sex differences in academic competence (e.g., reading, mathematics), behavioral (e.g., accidents) and psychological disorders (e.g., depression), and occupational outcomes (e.g., achievement level)—in the afterword.” – Make sure you pick up the second edition of this book.

The book starts out with an overview of basic mechanisms of natural selection and the evolution of sex before moving on to the evolution of sex differences in different species of birds, mammals, insects, fish, etc. in the light of Darwin’s theory of sexual selection, and finally applies it to the evolution of sex differences in hominids. The main part of the book is focused on sex differences in humans. - Geary argues that gorillas may provide a better model for the family and kinship structure of our hominid ancestors than does e.g. chimpanzees:
“Unlike men, male chimpanzees and bonobos show little to no paternal investment. And unlike women, female chimpanzees and bonobos show conspicuous estrous swellings and mate promiscuously. On the basis of these and other differences, Geary and Flinn (2001) proposed that modern humans' ancestors might have been more similar to our distant cousin, the gorilla (see also Lovejoy, 1981). This is because moving from a gorilla-like pattern to the current human pattern would require fewer evolutionary changes than needed to move from a chimpanzee-like or bonobo-like pattern to the human pattern.” (p. 138) “Unlike the unrestricted mating of female chimpanzees (during estrous) or bonobos, and a corresponding low level of paternity certainty (de Waal & Lanting, 1997; Goodall, 1986), adult male and female gorillas often form long-term social relationships. DNA fingerprinting indicates that male lowland gorillas show high levels of paternity certainty (greater than 95%; Bradley et al., 2004).. (...) The genetic findings indicate that the male-kinship structure for lowland gorillas is close to that currently found with humans (Bradley et al., 2004). The primary difference is the degree of cooperation among adult males as related to coalitional competition. Such coalitions could easily evolve from the social structure described by Bradley et al. The formation of more closely knit male kinships would result in greater proximity of males and through this the creation of the multimale, multifemale communities found in all human societies..” (p. 139)

I find it interesting that three people gave the book a very low rating (one star) at Amazon - for widely different reasons. One person criticized it for justifying “current politically correct presumptions,” which wouldn’t have surprised me since this book is published by the APA. I didn’t find much of that however. I did note that Geary does tend to make caveats quite often, but this is mainly when the findings aren’t clear enough, or because research specifically focusing on sexual selection is sometimes lacking. This lack however, is possibly due to said political correctness, but it’s hardly something you can put blame on Geary for. There is however, some degree of difference between to two editions of this book, which is worth noting in this connection, because at the time of the new edition (2009) much more data was available, and the last chapter of the first edition, dealing with “Sex Differences in Modern Society” was dropped, possibly not only due to lack of space but simply because it had become more or less redundant. It seems much will in fact hinge on which edition is reviewed. - One of the other Amazon reviewers again criticized the book for being “biological determinist” and the third simply dismissed the book suggesting you read some feminist literature instead. – So, in addition to the evolution vs. creationism debate, you can join the evolution vs. feminism debate - if you have some time to waste, that is. Or, lacking time to waste, you can simply read e.g. Geary’s empirical work on evolution and sex differences.

Geary deals methodically and comprehensively with such different areas as intrasexual competition, mating strategy and choice, parenting (one chapter is devoted to the evolution of fatherhood), prenatal and child development, and finally sex differences in brain structure and cognition. There are copious references, all of them provided in parentheses throughout the text, and often over several lines. This breaks up the text too often for my liking, but on the whole there’s far more to like about this book than not. In brief, this is a massive work of impressive scope and erudition.

I’ll end with a quote from the author’s Afterword: “Evolution is not just another psychological, sociological, or anthropological theory; it has proven to be the unifying meta-theory for all of the biological sciences. Eventually, all psychological, sociological, and anthropological models will need to be reconciled with the principles of natural and sexual selection. One can choose to be part of the discovery process or one can let these forthcoming scientific advances pass one by.”




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