The worldwide press has recently rekindled the debate on sexual orientation: is it down to nature or nurture? A familiar argument from the nurture camp is this: “If male homosexuality has a genetic component and homosexuals reproduce less than heterosexuals, then why is this trait maintained in the population?” (The Independent, UK, 13 October, 2004). A study1 now answers precisely this question: “The genes that make men gay also help their female relatives to have bigger families” (The Times, UK, 13 October, 2004). The scientist interviewed the families of 98 homosexual and 100 heterosexual men – a total of 4,600 individuals – and found that mothers and maternal aunts (but not paternal relatives) of the homosexuals were more fertile than those of the straight men, and also produced more gay offspring. This indicates that the gene(s) that favours homosexuality also boosts female fertility and that homosexuality is passed through the maternal line, and so might be located on the X chromosome.

But 'gay genes' might not necessarily increase fertility itself. Neuroscientist Simon LeVay suggests that the genes might in fact be involved in sexual attraction to men. “They could predispose men towards homosexuality and women towards 'hyper-heterosexuality', causing women to have more sex with men and thus have more offspring” (New Scientist, UK, 13 October, 2004).

The research team that carried out the study point out that increased fertility linked with homosexuality in males “would not explain the majority (80%) of cases” (BBC News Online, UK, 13 October, 2004), and “stressed that there was ample room left for the influence of non-biological factors linked to culture and upbringing” (Herald Sun, Australia, 14 October, 2004).