When it comes to sex, we're just like the other animals

Sex differences are always a hot topic and the perennial nature-nurture debate runs on in the popular press. In Why Sex Matters , Bobbi Low sets out to demonstrate that humans are subject to the same fundamental pressures as any other species - all organisms have been selected by evolutionary processes to reproduce successfully and seek the resources to do so.

Men and women face different obstacles in achieving this aim, leading to sex differences in behaviour analogous to those found in many other species. The sheer variation in human experience makes such an approach seem simplistic, but Low's skill is to show how simple rules can generate complexity in behaviour. In doing so, she demonstrates the futility of attempts to dichotomise nature and nurture. Sex differences are exaggerated, reduced or reversed in different environments as a result of ecological factors and historical accident, but throughout history and across the world behaviours that serve reproductive interests profit at the expense of those that do not.

The basis of Low's Darwinian argument will be familiar to those interested in an evolutionary analysis of behaviour and can be summarised succinctly: individuals who are reproductively successful leave more descendants than individuals who are less fecund. If the behaviours that lead to successful reproduction have a genetic component, these effective genes will prosper, apparently selfishly, at the expense of others. Selfish genes are the foundation of biological theories of nepotism, parental investment and sexual conflict and they lead to a coherent explanation of sex differences and social evolution in most species. The insights of biologists such as William Hamilton, G. C. Williams and Robert Trivers are familiar territory thanks to many popular science writers and Why Sex Matters introduces the basics of the sociobiological argument clearly and competently. For most species in most environments, it has been genetically advantageous for males to invest more resources in mating and females to invest more resources in parenting. But the strength of the book lies in the serious consideration of the ecological, cultural and biological factors that interact to produce the enormous diversity seen in human behaviour around the world. Low stresses the role of unique human life, history factors and the complexity and variation in cultural practices,such as formal inheritance rules, that let resources be transferred between individuals.

The evidence Low collects is wide ranging. We are taken through an impressive amount of ethnographic and historical data detailing human reproductive activity and social organisation, ranging from accounts of traditional societies such as Paraguay's Ache and Kenya's Kipsigis to historical records of demographic transition in Sweden and Imperial China. We are shown how factors such as pathogen prevalence and seasonality of rainfall are linked to social rules concerning polygamy and how inheritance laws and female access to resources influence mating systems. Other chapters touch on infanticide, sex differences in education, coalition building, social stratification, politics and war are discussed with respect to their effects on an individual's ability to gain resources and hence genetic posterity through reproduction. Low sees arbitrary cultural practices as biologically rational responses to environment and history.

Low's aims are ambitious, but she avoids sensationalism when discussing politically sensitive topics and points out where data are weak or lacking. Those with a basic grasp of the subject will have little trouble following her arguments. To specialists and students the book will be a useful resource, for although little of the material is new it is well organised. An excellent example of how evolutionary theory can be applied to human behaviour without hyperbole.

Ian Penton-Voak is lecturer in psychology, University of St Andrews.