Why Men Don’t Iron: The New Reality of Gender Differences. Anne Moir
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longings, if he had any, would be focused on males; the testosterone drench reverses his polarity and from now on he will be attracted to girls. But if the testosterone dose falls below a critical high level the brain remains female. All foetuses receive some testosterone, even those destined to be born girls, but samples taken from the amniotic fluid suggest that the ‘brain-sexing’ drench of testosterone is eight to nine times higher for boys than it is for girls.36
Now it does not take much imagination to hypothesize that a shortfall in testosterone at the crucial moment of pregnancy might leave an otherwise conventional male with a female sexual orientation. The result would be an adult man who is, quite naturally, attracted to other males. It is possible that a ‘gay gene’ influences the crucial testosterone levels, but whether that is the case or not, the evidence for this hormonal cause of homosexuality is overwhelming.
Overwhelming but not absolutely proven, for we cannot experiment on developing human foetuses to test the hypothesis. So the evidence, however compelling, is indirect. A study by Lee Ellis has shown that mothers who suffer from severe stress (stress reduces the levels of testosterone) during the third month of pregnancy produce a higher than average incidence of homosexual offspring.37 We cannot prove this absolutely because, rightly, ethics forbids us to experiment on human foetuses, but animal studies support the biological explanation. Humans and rats share specific sex hormones and have similar areas at the base of their brains that control sexual behaviour (the hypothalamus). Roger Gorski and his team have demonstrated that a rat’s sexual orientation can be changed at will by manipulation of foetal hormones.38 A male rat deprived of testosterone in its early foetal stage becomes female in its sexual behaviour. No amount of male hormones given in later pregnancy can reverse this behaviour – the animal’s brain has been permanently organized into the female pattern.
A female rat dosed in the same critical period with male hormones becomes masculine in its sexual behaviour and, again, no amount of later female hormonal influence will reverse the orientation. Gorski’s work suggests that there is a critical stage during the development of the mammalian brain when male or female sexuality is established.39 Once that critical moment is passed no amount of ‘corrective’ hormone will make any difference. The sexual orientation of rats, and most probably that of humans too, is determined in the womb.
The researchers went on to investigate whether there were any structural differences between the brains of male and female rats and discovered an area of the hypothalamus that was seven times larger in the male brain than the female brain. ‘The difference is so large,’ one researcher wrote, ‘that you can see it with the naked eye.’40 Other researchers agreed with the finding, and confirmed, moreover, that it was just this area of the brain that controlled sexual behaviour. ‘Experimental damage to this area produces a marked and significant reduction in masculine sexual behaviour.’41
Roger Gorski and his team then experimented by manipulating the hormones delivered to a developing rat foetus to see if they made any difference to the hypothalamus, and discovered they could determine the hypothalamus’s structure by restricting the hormone dosage.42 This was a breakthrough discovery for, though it had been inferred that hormones changed brain structure and behaviour, it was the first time anyone had demonstrated that process in a laboratory. Gorski and his team had shown that sexual orientation was determined by hormones, and that the brain’s physical structure could be manipulated by the same hormones, and all this in an area of the brain that was well established as central to controlling sexual behaviour.
These experiments have been replicated by many different laboratories and in other animal species,43 and inevitably lead to the question of whether homosexuality occurs outside the laboratory in species other than man. For a long time this has been denied (thus providing ammunition to those who ascribe homosexuality to social or cultural causes), but more recent research has demonstrated frequent male–male sex in primates and in mountain sheep. Such sex is often ‘rape’, in which the dominant male uses sexual assault to demonstrate his higher status, but genuine, consensual homosexuality has been observed in domestic sheep. It was first observed in Iowa where farmers were disturbed by the number of ‘dud studs’: rams that were not interested in ewes, but in other rams.44 Research is still going on into the dud studs, but it suggests that there are definite biological reasons ‘that brain structures involved in sensing or perceiving potential mates may be different in homosexual and non-sexual rams’. The dud rams it seems have a different brain from the heterosexual rams.
But what about humans? Empirical evidence suggests that human sexual orientation is determined by exposure to testosterone during the third month of pregnancy, but is there any physical evidence? Again it is the hypothalamus that most interests scientists because the human hypothalamus, like the rat’s, controls sexual behaviour, and, just as in rats, distinct differences have been found in the male and female human hypothalamus. There is an area in the hypothalamus called the sexually dimorphic nucleus of the preoptic area, and researchers have demonstrated that this area is always larger in male brains than in female brains; in rats it is between five and seven times larger, while in humans it appears to be two or three times larger.45
This same area was investigated in homosexual men. Simon LeVay, in a controversial discovery, announced that the sexually dimorphic nucleus of the preoptic area was twice as large in heterosexual men as in homosexual men, which meant, simply, that gay men presented a female brain structure.46 LeVay’s announcement made headlines all over the world and, not surprisingly, excited controversy. If he was correct, the gay lobby could no longer be confident that homosexuality was a ‘social construct’. It looked more and more like a biological phenomenon, so it was with some relief that the gay lobby announced that LeVay’s findings had to be wrong because the brains he had dissected had all come from gay men who had died of AIDS, and AIDS can cause changes in brain structure. That criticism lost its force after LeVay investigated the brains of homosexuals who had not died of AIDS, and once again discovered that they presented a typical female pattern.47
LeVay’s findings are no longer controversial. Indeed, other researchers are discovering still more differences between the structures of the homosexual and heterosexual brains – the suprachiasmatic nucleus, also in the hypothalamus, seems to be larger in women and gays than in straight men,48 while the anterior commissure, a kind of telephone exchange that joins the right and left temporal lobes of the brain and is significantly larger in women than in men, has now, it should come as no surprise, proved larger in gays too.49
The probability that sexual orientation is determined in the womb looks more and more likely, except to those blinded by sexual politics. Yet more proof of the power of foetal hormones to affect adult behaviour comes from studying children who, because of a genetic abnormality, were exposed to abnormal levels of sex hormones while in the womb. Certain girls have an abnormality in their adrenal gland that leads to an overproduction of androgens or male hormones. The condition is called congenital adrenal hyperplasia, or CAH, and CAH girls are born with internal female sex organs but partly masculinized external genitals. Surgery can usually correct the genital abnormality and drugs can control the build-up of male hormone, but many studies have shown that these girls still behave quite differently from girls who were not subjected to high foetal levels of androgens.50 The androgen-affected girls are masculine in their general behaviour: they are more aggressive than other girls, more ‘tomboyish’, preferring male toys (guns and model trucks) to dolls, and are more interested in competitive sports. Even at a very young age children look to their own sex for playmates, but the androgen-affected girls instinctively seek to play with boys. In adulthood they are far less interested in men, marriage and sex than other women, 48% of them confess to having homosexual fantasies,51 and 44% are actively lesbian.52
These studies provide further evidence of the power of foetal hormones to determine sexual behaviour and orientation, though some critics dismiss the CAH studies on the grounds that the affected girls, because they were born with male genitalia, were raised by their parents as though they were boys. This reinforces the postmodern belief that sexual orientation is constructed by societal pressure, though in fact there is no evidence that the parents of androgen-affected girls do compromise their children’s sexual