have bigger brains than women, even taking into account their larger bodies. This has been documented time and again. To take just one example, Sandra Witelson and her colleagues weighed the brains of 58 women and 42 men post-mortem and found the women's were 1248 grams on average, compared with 1378 grams for the men. Note, there's an overlap between the sexes, so some women will have larger brains than some men. A Danish study of 94 brains published in 1998 estimated that the larger male brain volume translated into an average 16 per cent greater amount of neurons in the neocortex of men versus women. FACT 2 There are sex differences in the size of individual brain structures According to John Gray, author of Why Mars and Venus Collide, men are prone to forgetting to buy the milk because of their more localised brain activity (as quoted by Cordelia Fine). It's tempting to see the brain differences between the sexes, mythical or otherwise, and think that they explain behavioural differences; such as men's milk amnesia, their superiority on mental rotation tasks or women's advantage with emotional processing . In fact, in many cases we simply don't know the implications of the sex-related brain differences. It's even possible that brain differences are responsible for behavioural similarities between the sexes. This is known as the "compensation theory" and it could explain why men and women's performance on various tasks is similar even whilst they show different patterns of brain activity. Bearing