Simon LeVay, Oxford University Press USA, £17.99
Brain scientist Simon LeVay argues in his new book that the sexuality of lesbians and gay men is rooted in biology. In many subtle ways, he claims, gay men are like women and lesbians like men, the result of hormone levels in the womb.
However, humanity doesn't divide up neatly between homosexuals and heterosexuals. What about bisexual people? What about people whose sexual desires change during their lives? What about other cultures and periods of history where the concepts "gay" and "straight" are unknown? LeVay begins the book by raising and then sidestepping these issues.
He then makes comparisons with animals' mating habits. A female rat who wants to mate swings her tail to one side and wiggles her ears, we learn, and a male rat mounts her. However, human sexuality is a more complex business, because sexual practices are part of diverse human cultures. So LeVay's "lesbian" monkeys and "resolutely heterosexual" fruit flies aren't relevant.
He then summarises hundreds of scientific studies covering everything from hearing to finger length. Some studies are poorly done - one draws conclusions about how a certain medical condition affects sexuality based on a sample of only 61 women. Some are just bizarre - one asserts that lesbians and gays have higher IQs than heterosexuals, while another claims that gay men smell different to other people.
The real problem is that the studies don't consistently back up LeVay's theory. He's too honest to cover this up, but also too obsessed with his hypothesis to accept that it doesn't work. He spends a chapter summarising research which claims that men with older brothers are more likely to be gay. But then, he comments, people two centuries ago had more children, so more boys would have had older brothers - but there is no evidence that more men in 1800 were gay.
LeVay is open about his motivation for pursuing his theory in spite of the contradictory evidence. As a gay man himself, based in the US, he wants to prove that people are born gay and so undermine right wing Christians who claim that people sinfully "choose" same-sex desires. And, if people are gay because of their biology, that strengthens their claim to protection from the courts.
This is a terribly mistaken strategy. It involves LeVay repeatedly accepting sexist stereotypes about men and women. And people are undoubtedly female or black because of biology - but that hasn't stopped sexism and racism. Early in the 20th century German gay campaigner Magnus Hirschfeld argued that lesbians and gays were biologically different - a "third sex". The idea that they were neither men nor women made Nazi persecution easier, not harder. This confused book does nothing to help us understand or liberate sexuality.