Sex on the Brain: The Biological Differences Between Men and Women

  • Deborah Blum
Viking: 1997. Pp. 329 $24.95

It is hard to write a good book about psychological sex differences. The topic is relevant to attitudes and social policy in many areas, including who should take primary responsibility for childcare, whether education should differ for girls and boys, whether laws should prohibit certain sexual practices, and to what extent choice of occupation is dictated by sex.

The scope of this book is broad. For a general idea of its factual accuracy, I looked at its coverage of my own research areas: sex differences in the human brain and the role of androgen and oestrogen in shaping gender development. Here the disappointment began.

A simple example is whether prenatal exposure to high concentrations of androgen (‘male’ hormone) improves mathematical ability. In this book Deborah Blum says that it does, suggesting that prenatal brain programming by hormones causes males to excel at mathematics. But the only two existing studies of the relationship between prenatal androgen and mathematical ability found impaired ability.

The trouble with sex is that people, scientists and non-scientists alike, have their own theories about how men and women differ. Developmental psychologists call these theories ‘gender schemas’ and find that they influence memory. For example, children shown pictures of male nurses and female doctors later confidently recall seeing female nurses and male doctors. Those writing popular books on psychological sex differences often seem to have similar problems with remembering research findings.

The book relies heavily on theories from evolutionary psychology. These theories are difficult to test empirically and are particularly prone to contamination by gender schemas. They seem sensible only because they correspond to popular preconceptions. For instance, Blum describes a theory that men prefer blondes because men are evolutionarily predisposed to prefer youthful mates, and blondness is a sign of youth. But the blondness of youth usually disappears by puberty.

If preference for blondes reflects an evolutionary predisposition to youthful mates, men would be predisposed to paedophilia. If this suggestion seems more absurd than the original, it is because prevailing gender schemas suggest that men have innate preferences for young women but not children.

The book also suffers from a failure to screen information for reliability. Everything, from replication of results in refereed journals, through presentations and comments at scientific conferences, to reports in the popular press, is given equal credibility. This casual approach to facts, combined with phrases like “those nitpicky cell-counting studies”, left me feeling as if I had eaten too much junk food.

Some might argue that accuracy is unimportant, because a popular book can stimulate interest in a research area. But facts do matter. Take again the supposed androgen-induced predisposition to mathematical ability. Research into attitudes and performance shows that an assumption of inability can become a self-fulfilling prophecy. This misinformation itself could therefore impair mathematical performance in girls and women.

Research into psychological sexual differentiation has produced surprising findings that sometimes contradict prevailing gender schemas. For instance, although we think of sex as being determined by the sex chromosomes (XX or XY), their role is minor compared with that of gonadal hormones. Also, although hormones from the male gonads are essential for masculine development, hormones from the female gonads have relatively little influence on feminine psychological development. Even more remarkably, what we think of as the major ‘female’ hormone, oestrogen, can have powerful masculinizing influences during development. For further information consult scientific publications, but mind your gender schemas.