What are the causes of homosexual behavior in animals? Contrary to what most people probably think, homosexual behavior is not just common in animals, it is catholic.
A new paper in TREE has gotten a lot of press (most papers on sex do, I suspect): Same-sex sexual behavior and evolution, by Bailey and Zuk at UC Riverside.
In their table 2 (email me for copy of PDF) they list a wealth of hypotheses about the nature of homosexual behavior, but I find it very incomplete:
Adaptive explanations: Social glue, Intrasexual conflict, Practice, Kin selection, Indirect insemination, Overdominance, Sexually antagonistic selection
Non-adaptive explanations: Mistaken identity, Prison effect, Evolutionary byproduct, Maladaptation, Infection
I do very much appreciate this list, because so many people insist - consciously or not - that there must be an adaptive reason for homosexuality. There need not be. My own personal, unfounded, suspicion is that homosexuality in humans can best be described as a by-product; hormonal balances in utero that sometimes (say, about 10 percent of the time) shift slightly, changing the preference for sexual partners. But notice that whether an adaptive or non-adaptive hypothesis is supported, they all imply that the animal does not choose to be sexually attracted to one sex or the other. It would be rather hard to argue that fruit flies and penguins choose it (I dare you to try), and if so, it makes me wonder what basis there is left to suppose that humans do.
I said I find the list incomplete, so what missing? This:
The Christian explanation: Choice
It's more than a common idea among American Christian homophobes that homosexual people choose their own sexual desires. For example, one person commented on my post about Safeway posters that "Homosexuals choose a lifestyle, they are not born that way." Which is completely unfounded. There are many Christian prayer groups that try to help homosexuals change their ways (e.g. Exodus International). Their stupid prayer groups does nothing but suppress the nature of homosexuals. Why do I believe that? Because that's what the evidence tells us. The evidence from animals, and the fact that no heterosexual would ever admit that they chose to be heterosexuals, which leaves no argument left that anyone ever chose to be homosexual either.
Nathan W. Bailey, Marlene Zuk (2009). Same-sex sexual behavior and evolution Trends in Ecology & Evolution
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