Never Mind the Bollocks

Hilary Rose and Steven Rose

  • BuyBrain Storm: The Flaws in the Science of Sex Differences by Rebecca Jordan-Young
    Harvard, 394 pp, £25.95, September 2010, ISBN 978 0 674 05730 2

Aristotle affirmed the essential difference between the sexes: men’s brains were bigger, women were more inconstant, emotional and compassionate, at least in part because they do not produce semen – whence men’s and women’s different behaviour and place in the social order. Symbolically, at least, biology’s long, continuing and often lamentable history of using its authority to define woman’s nature, in order to justify attributing her with inferior status, begins here.

According to naturalists, the origin of gender differences lay in men’s genitals and women’s menstrual cycle. That the testes produced masculinity was apparent from the effeminate nature of eunuchs; ingesting extracts of animal testes has long been assumed to enhance a man’s potency, bellicosity and intellectual pre-eminence. By the end of the 19th century the physiologist Charles Edouard Brown-Séquard was injecting himself with extracts of dog and guinea-pig testicles to restore his youth. (It failed.) In popular culture the scientist’s elixir was transformed into ‘monkey glands’, which had a long, if much satirised, vogue, still extant in the host of testes-related products sold as rejuvenators on the net and in health food stores. Similarly, it was the ovaries and their juices that conveyed a woman’s essential womanhood and accounted for her naturally nurturing role, while making her a stranger to such activities as war or science.

In the 1930s the active principles found in testes and ovaries – hormones – were isolated and their chemical structures determined. The endocrinologists saw them as specifically ‘sex hormones’, and named them testosterone and oestrogen. Alas for the complexities found in subsequent research, the names stuck. No matter that both sexes produce both hormones and that they have many and varied physiological effects; no matter that they are chemically very similar members of a family of steroid molecules readily converted into one another in the body. In popular accounts testosterone is the male principle, oestrogen the female, with the consequence that the Alastair Campbells of this world are invariably described as ‘testosterone driven’.

As for brains, even after the fashion for phrenology had declined by the late 19th century, the science that replaced it – craniometry – assumed that brain size was a powerful surrogate marker for intelligence. Men’s brains, Paul Broca reported, were on average 14 per cent heavier than women’s. Broca’s data were elegantly picked apart by Stephen Jay Gould in The Mismeasure of Man. Most of the difference is accounted for by differences in height and build between men and women, and once corrected for these, the gross difference evaporates. After Broca’s death – it turned out at his post-mortem that his own brain was disappointingly small – the enthusiasm for relating brain size to intelligence receded.

It wasn’t until the 1960s that more refined measurements began to reveal subtle anatomical differences between men’s and women’s brains. Men’s brains seem to be a bit lopsided: the hemispheres are slightly more asymmetric than women’s. There have been claims that the shape and size of the corpus callosum – the broad tract of white matter that connects the two hemispheres – differs between the sexes, but they have been vigorously contested. Even if such differences could be unequivocally substantiated no one has the slightest idea what their implications might be for the allegedly essential differences between the sexes. The myth of the left-brain cognitive male and the right-brain affective female still persists, while women’s supposedly thicker corpus callosum has been invoked to explain why men are more single-minded and women better at multi-tasking.

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