Outed at last] The gay hypothalamus

SIMON LeVAY, a 49-year-old gay neuro-anatomist in a Seventies jacket and party tie, stood in a small seminar room at the ICA in London on Thursday night and delivered his theory with some authority: size is important after all. Mr LeVay has dined out on this one for a while, ever since his research into post- mortem brains showed that homosexuals had a smaller hypothalamus - the area of the brain regarded as having influence on sexual behaviour - than heterosexuals, suggesting to him that gays and lesbians may be born not made.

A hot topic for such a cool-headed man. Mr LeVay was born in Oxford, educated at Cambridge and gravitated to California. He knew he was gay from his teens and followed the nature/nurture debate with interest. His belief that Freud was mostly wrong - that homosexuals are not the product of over-bearing mothers and weak or hostile fathers - may please his own dad, one of very few breeders in a sardined audience.

Mr LeVay's theory is as controversial as sex gets. If you're gay in the womb, and if these gay genes can be isolated, then the political resonances would be profound. On the plus side, advances in civil rights for gays and lesbians would be immense; bible-bashers would have a tough time with their 'sin' argument; Bill Clinton would solve his battle with the military; anxious parents would no longer fear the 'corrupting' influence of homosexual teachers. On the downside, we'd have what Mr LeVay calls the 'nightmarish science fiction' scenario of abortion, eugenics, 'cleansing' and 'curing'.

Mr LeVay was in Britain partly on holiday, partly on a sales drive. The Sexual Brain, his crisp account of his determination theories is just out, its back cover boasting endorsements from two Nobel laureates stressing that Mr LeVay is a responsible scientist, anything but a crank with a hidden agenda.

At the ICA he put forth his stall with eloquence, but it was riddled with woodworm. He stressed that his kind of work had a long way to go, and was not conducted in isolation: there were hundreds of people in laboratories throughout the US working feverishly to find the key stretch of DNA that may confirm his theories. His own analysis is based on the examination of less than 50 brains (19 gay men who had died of Aids, 16 presumed heterosexual men, and six presumed heterosexual women), as well as some monkeys and rats.

Consistently he found that a certain region of the hypothalamus was smaller in gay men. In the case of the male monkeys, those that had had their hypothalamus removed showed little interest in female apes, while the control group got it on like the good old days. But this was a tiny survey and posed many problems: the brains were those of adults, so who was to say that size had not changed over time? And what of the effects of Aids on the brain?

We then had a little slide show, as Mr LeVay displayed pictures of identical twins (who shared identical genes), comparing them to pictures of non-identical twins (who did not): the snaps revealed that even identical twins who had been separated after birth and reunited years later showed similar facial expressions and posture. He quoted other research suggesting that a man who has a gay brother is seven times more likely than average to be gay himself. But the fact that some gay identical twins had brothers who were not gay rather dampened Mr LeVay's hypothesis.

Mr LeVay acknowleged the grey areas in his work. Mandy Merck, a writer, producer and author of the book Perversions, took the scepticism a bit further. She catalogued the erroneous brain science of the past. 'It used to be thought that because the size of women's brains were smaller than men's, women were therefore less intelligent.' Later, noses were regarded as a sign of intelligence, the bigger your nose, the cleverer you were. 'Then people started asking why weren't the anteaters in charge.' Ms Merck feared the possible negative applications of Mr LeVay's work, citing the continued intolerance of society towards lesbians and gays, although she believed that he recognised the dangers. Mr LeVay's attitude? 'I think it would be nice to keep gays and lesbians, but why should I expect people to agree with me? I shouldn't, unless we can persuade them we're worth keeping.'

Another panellist, Patrick Wall, Professor of Anatomy at University College, London, called Mr LeVay one of 'the new phrenologists working in three dimensions, with very large microscopes'. Professor Wall showed us animal slides he had recently bought at the nearby National Gallery: grazing sheep, lions eating horses, a stuffed horse that once belonged to Gustavus Adolphus, the 17th-century king of Sweden. His argument was droll but vague: humans act in strange ways, ways stranger than animals, ways not always explicable by Mr LeVay's determinist reductionist approach.

Questioners were primarily concerned with the politics of it all and the responsibility of science. Mr LeVay replied that you can't hold science back and the more we understand each other, the less prejudiced we become. He thought it would be useful for teenagers worried about their sexual orientation to be able to go to a doctor and have a test. Pushing the PC boundaries to extremes, he said he would support a woman's right to abort a gay or lesbian foetus if she wished.

The audience hummed. This was the ultimate homophobic dilemma: you were anti-gay, you had all the knowledge of gene science at your disposal, but you were pro-life . . .

The tone was lightened by a therapist in the front row, who said that his experience of sexual behaviour was so diverse that he wondered if it could ever be adequately explained by pure science. He had met men who could only be sexually aroused by watermelons. No one hung around after that.

'The Sexual Brain' is published by MIT Press, pounds 14.95.

Sandra Barwick returns next week.