There is a very interesting article of this title in the current issue of New York magazine. Author David France was on "The Colbert Report" last night, making a mild case for the tantalizing physical correlates of homosexual orientation. What Colbert focused on were the headline-grabbing findings like the comparative lengths of index and ring fingers (gay men more like women, lesbians more like men), or the fact that later-born brothers are a third more likely to be gay than their next-oldest brother. A new finding is that gay men are significant more likely to have a counter-clockwise swirl to their hair (23% vs. 8%) -- a literal "headline" story.
In the article, France reports more of the detailed work on less visible body features that correlated with homosexuality. He talked to Simon LeVay, who did a pathbreaking study on the size of the hypothalmus, the brain structure most seaped in sex-controlling hormones, in which gay men's brains are more like women's. He reviewed the research on the most probable chromosomal region for a hypothetical gay gene. France talked to researchers working on how hormone sequences in the womb influence all kinds of expressions of masculinity and femininity -- a line of research that I am guessing will prove the most instructive in the end.
France also discusses the inevitable politics of even doing such research. Most of the researchers in this field are homosexual, and they, like France, are looking for an account of their own lives. Some gay activists, though, oppose even asking the question, for fear that suggesting a biological cause will then lead to a search for a biological cure. I am sure, as France is, that how individuals turn out is a complex mix of nature and nurture. I fear no research, because I know good science will yield appropriately complex answers.
In facing the question of where to draw the nature/nurture line in understanding sex differences, I was driven some years ago from the "overwhelmingly nurture" position that most sociologists take, to a more balanced position. I find it best to think that sex and gender are a 50/50 balance of nature and nurture -- recognizing that these are imprecise metaphors for a complex set of causes on both sides of the divide. I believe the science of sexual orientation, like the science of sex itself, will turn out the same way: 50/50.