 Although biological determinism of the kind endorsed by Geddes and Thompson is nowadays uncommon, the idea that behavioural and psychological differences between women and men have biological causes has not disappeared. In the 1970s, sex differences were used to argue that women should not become airline pilots since they will be hormonally unstable once a month and, therefore, unable to perform their duties as well as men (Rogers 1999, 11). More recently, differences in male and female brains have been said to explain behavioural differences; in particular, the anatomy of corpus callosum, a bundle of nerves that connects the right and left cerebral hemispheres, is thought to be responsible for various psychological and behavioural differences. For instance, in 1992, a Time magazine article surveyed then prominent biological explanations of differences between women and men claiming that women’s thicker corpus callosums could explain what ‘women’s intuition’ is based on and impair women’s ability to perform some specialised visual-spatial skills, like reading maps (Gorman 1992). Anne Fausto-Sterling has questioned the idea that differences in corpus callosums cause behavioural and psychological differences. First, the corpus callosum is a highly variable piece of anatomy; as a result, generalisations about its size, shape and thickness that hold for women and men in general should be viewed with caution. Second, differences in adult human corpus callosums are not found in infants; this may suggest that physical brain differences actually develop as responses to differential treatment. Third, given that visual-spatial skills (like map reading) can be improved by practice, even if women and men’s corpus callosums differ, this does not make the resulting behavioural differences immutable. (Fausto-Sterling 2000b, chapter 5).