Currently there is an increase in the number of articles published in scientific journals and in the popular scientific media that claim a biological basis for sex differences in cognition and in certain structures in the brain. It can be argued that there is over-emphasis on the differences rather than similarities between the sexes, but it is even more important to question the assumed causation of the differences. This paper discusses recent evidence for an interactive role of early experience and hormonal condition in determining sex differences in brain structure and function. Although early studies using rats were thought to show that the male sex hormone, testosterone, acts on the brain in early life to direct its differentiation into either the male or female form, it is know known that this result comes about indirectly by changing the mother’s behaviour towards the pups. The hormone does not act on the brain directly but rather it alters the environment in which the young animals are rasied and this, in turn, influences the development of the brain. Indeed, the brain is in dynamic register with its environment both during development and in adulthood. Other examples also show that old ideas of rigid biological determination of brain structure and function need to be laid aside.
The hypotheses for hormonal causation of sex differences humans rely heavily, if not exclusively, on the earlier interpretation of the experiments with rats, and there seems to be resistance to changing these notions based on the new discoveries. Apparently, there is strong pressure to cling on to biological determinist theories for sex differences in behaviour, and this has profound effects on social and educational policy. For example, biological determinism has been used to justify under representation of women in certain professions. Realisation of the dramatic effects that environmental stimulation and learning can have on the development of brain and behaviour leads us to an optimistic position for social change towards equality for women.