Der Abstract zu einem Beitrag von Herr Swaab mit dem Namen „Sexual Differentiation of the Human Brain and Male/Female Behaviour“ fasst eigentlich den Stand ganz gut zusammen:
Once the differentiation of our sexual organs into male or female is settled, the next thing to be differentiated is the brain. The difference in brain structures resulting from the interaction of sex hormones and developing brain cells, is thought to be the basis of sex differences in behaviour, in gender identity, in gender roles, in our sexual orientation (hetero-, bi- or homosexuality) and in the obvious sex differences in cognition and aggressive behaviour. Our sexual orientation is determined during early foetal development, under the influence of our genetic background and of factors that affect the complex interactions between sex hormones and the developing brain. Although it has often been postulated that postnatal development is also important for the direction of our sexual differentiation, any solid proof for this is lacking. The broadly accepted view on the importance of the social environment on sexual differentiation has been extensively put into words by Simone de Beauvoir and others. It turns out, however, that sex differences revealed through play, drawings and aggression are determined by exposure to hormones in the womb rather than by what society demands later on. The apparent impossibility to get someone to change their sexual orientation is a major argument against the importance of the social environment in the emergence of homosexuality, as well as against the idea that homosexuality is a lifestyle choice. Our sexual orientation is fixed during prenatal development and is beyond influencing in adulthood. Apparently, and despite the feminist ideals, we tend to choose what best fits our programmed (by natural sexual selection developed) brains. Our sexually differential brains will not lend themselves for a completely equal division of tasks between men and women in the family or on the labour market. There is great public interest in research of the brain and in research of our sexual behaviour, but the combination of these two subjects has turned out to be dynamite.