On the origin of homosexuality

On its website at the moment Scientific American has a very interesting guest blog, called “The Intelligent Homosexual’s Guide to Natural Selection and Evolution, with a Key to Many Complicating Factors“. It’s a fascinating read if you’ve ever wondered why homosexuality, with its apparently obvious evolutionary disadvantages, has been a relatively common (according to a recent survey, about seven per cent of US women and eight per cent of US men identify themselves as either gay, lesbian, transgendered or bisexual) constant throughout recorded history.
The author, Jeremy Yoder, discusses the evidence for a genetic basis for homosexuality, the nature of genetic drift and selection pressures, and points out that sheer randomness could easily account for a lot of the reason it has never bred out. He speculates on the implications of indirect fitness: so-called “kin selection”, wherein the survival to reproduction of a younger brother, or two nieces or nephews, is worth the same to one’s reproductive fitness as a child of one’s own is – although he rather rules it out as a possible mechanism – and wonders whether it is a secondary effect of genes that have other purposes.
He also reminds us, pointedly and accurately, “it’s so easy for the discussion to slip from what is ’selectively beneficial’ to what is ‘right.’ A superficial understanding of what natural selection favors or doesn’t favor is a horrible standard for making moral judgements. A man could leave behind a lot of children by being a thief, a rapist, and a murderer – but only a sociopath would consider that such behavior was justified by high reproductive fitness.”
Anyway, it’s a great post, and well worth a look. What I find particularly amusing, though, is a small aside – he wonders whether one thing that may have lowered the selection pressure against homosexuality is the intolerance and bigotry of earlier generations:

Before the gay rights movement, social expectations probably led many people who today would identify as gay or lesbian to enter into straight marriages and raise families. This kind of social pressure may explain why gay and lesbian couples are more likely to be raising children if they live in the conservative southern United States–not because adoption is more common in that region, but because in the South, gay men and lesbians are more likely to have heterosexual relationships, and children, before they come out.

Hilarious irony, if it’s true: the attempts to stamp out or marginalise homosexuality may have helped its proliferation. This might be my favourite piece of science writing on the subject since this trial was published in 1996: “Is homophobia associated with homosexual arousal?” The answer will not surprise you at all.