Wie Geschlechtsunterschiede im Gehirn durch pränatale Hormone entstehen

In dem Buch „Brain Sex“ wird die Wirkung pränatalen Testosterons auf das Gehirn beschrieben:

The East German scientist, Dr Gunter Dorner, has devoted his life’s work to the theory that exposure to certain hormones before birth determines sexual inclination. He claims that potential future homosexual behaviour can be detected through amniocentesis, the test of the uterine fluid which can reveal Down’s syndrome in the unborn child. Dorner further claims that, with pre-natal injections, homosexuality can be prevented. Dorner has, not surprisingly, attracted anger from homosexuals, who see his theories as equating homosexuality with disease, or as a i930s-style sexual totalitarianism involving ‚the endocrinological euthanasia of homosexuality‘. Scientists, too, were initially sceptical.

But gradually, the weight of scientific opinion has shifted towards Dorner. His theories may need some refining and qualification – but Dorner is increasingly gaining the status of a respected pioneer of sexual science. As we have already learnt, the chromosomes instruct the developing foetus, around the sixth week of pregnancy, to develop female ovaries or male testicles. These in turn produce hormones. Male hormone masculinises the mind. Dorner finds that the brain is not masculinised, as it were, all in one go. The classic experiments with rats described in Chapter Two have shown how behaviour can be modified in the male by castration and injections of female hormones. The male rat will be sexually attracted to other male rats and behave in a female manner when mounted by them -wiggling the ears and arching the back.

But the degree of femininity in the male rat depends critically on the stage at which it was castrated. Castrate it early and, with no male hormones to change its direction, the brain is more likely to retain its original, female pattern. The later castration occurs, however, the less feminine the behaviour. What Dorner concludes is that the maleness of the brain in rats is laid down in a gradual sequence. With normal females, in the absence of testosterone, the brain develops along a naturally female pattern. But should the brain be accidentally dosed with male hormones during development, this natural female pattern can, at any stage, be upset. The more frequently, and the earlier, the brains of females are dosed with male hormone, the more male their sexual behaviour. The later, the less. Dorner suggested that in men and women too it is the presence or absence of male hormones that build the structure of the brain bit by bit into a male or female pattern of sexual identity.

It happens, he says, in three stages – the development of what he calls the sex centres, the mating centres, and the gender-role centres of the brain.

First, with the ’sex centre‘, the hormones set to work on creating typical male or female physical characteristics.

The next, and to some degree overlapping stage, is the transformation of the ‚mating centre‘. This Dorner identifies as the hypothalamus which, it is now known, is arranged differently in men and women, and controls sexual behaviour in adult life.

The last stage is when the hormones get to work on the ‚gender-role centres‘ in the brain of the unborn child, laying down the networks in the brain which determine our general behaviour like the level of aggression or lack of it, our sociability or individualism, our adventurousness or timidity -characteristics which get fully expressed under the hormonal influence of puberty. Dorner believes that each of these centres can be independently upset at each stage of development. Indeed, we’ve seen how at the first stage – the development of primary sexual characteristics – genetically female foetuses exposed to an abnormal level of male hormone may develop male-like organs. The development of the mating centre, the hypothalamus, Dorner argues, can also be upset; in a male, the lower the concentration of androgens, or male hormones, the greater the likelihood that the eventual child will have homosexual tendencies. In girls, a higher level of androgens mouls the hypothalamus in a manner which will produce same-sex attraction. Finally the gender-role centres, the wiring up of the brain, and the way the functions are distributed, may follow a male pattern in the female, or a female pattern in the male, depending on the abnormal presence of male or female hormones.

The beauty of this theory is that it explains how, for instance, obviously physical males, with obviously male identities and mannerisms, may be attracted to same-sex partners; in that case, only the second stage, the development of the hypothalamus, and the mating centre, has been upset. Similarly, it explains how some boys, effeminate in looks and behaviour, may still be robustly heterosexual in their sexual preferences; their sex centres and gender-role centres have been hormonally unbalanced at a key stage of development, but during the development of the mating centre, nothing untoward occurred. In short, it explains why not all sissies are homosexuals, and not all homosexuals are sissies.

A British psychologist, Glen Wilson, the author of Love’s Mysteries, agrees with Dorner that the pre-setting of the brain before birth may sometimes be ‚inappropriate, in that the gender of the child is male and his anatomical appearance 116 is male, but for some reason or another, his brain has not received the necessary hormonal instruction that would cause it to be masculinised.‘ He reminds us that we are dealing with very fine and critical amounts of testosterone, measured in thousand-millionth parts of a gram; a possible explanation of how, in non-identical twins, developing in – virtually identical – conditions in the womb, one may be homosexual and the other not. Another American scientist, Dr Milton Diamond, also comes to the same general conclusion as Dorner, but believes the development of sexual brain tissue involves four, not three, stages.

First, basic sexual patterning, e.g. aggressiveness or passivity; second, sexual identity – what sex people ascribe to themselves; thirdly, sexual object choice, which is the same as Dorner’s mating centre; and finally the control centres for the sexual equipment, including the mechanisms of orgasm. If something goes wrong during the development of each or any of these stages, they will eventually be ‚out of phase‘ with each other. So a man may be assertive and aggressive – typically male – yet have a homosexual choice of sexual object; he may have effeminate mannerisms, yet have a high, heterosexual drive. The brain is not sexed in one ‚big bang‘.

The hormonal theory would explain why sexual deviancy is so much more common in men. Men have to go through a hormonal process to change their brains from the natural female pattern present in all of us, whatever our eventual sex, from the first weeks of our life in the womb; they have to be soaked in extra male hormone and restuctured – so in the process of reconstruction the chance of mistakes is much greater than in the female, who doesn’t need any reconstruction of her brain.

Ich meine, dass diese Theorien in der Tat vieles erklären. Sie sind – im Gegensatz zu den poststrukturalistischen oder queertheoretischen Theorien – mit den diversen Sonderfällen wie CAIS, CAH, Testosteronrezeptoren und ihren Auswirkungen, David Reimers und diversen anderen in Einklang zu bringen.