What pressures keep homosexuality in populations?
While I’m not going to comment on homosexuality, there is no possible way anyone can claim that anything has been at “10% throughout history”. Tell me what percentage of the US population, today, is homosexual. You should get stuck right about where you try to define the term “homosexual”. Plus the absolute lack of any numerical data on anything more than 100 years ago.
I think the problem with this question is that it assumes that homosexuality has remained at 10% which I doubt to be true, especially when you examine certain cultures that embraced homosexual and bisexual tendencies (Grecian, Roman, Early Japanese cultures leap to mind). You can’t ask a question about society and accept a good answer while accepting a false assumption. Also, I’m not even going to get into genetic causes of homosexuality, but I’m sure some of our more DNA-minded brethren will.
Homosexual representation is actually not 10%. Recent studies give a more reasonable figure of 1-3%. The 10% figure was based on the Kinsey studies, which are full of problems. Also, recent studies have shown that the gay gene in men expresses itself in women as higher fertility traits. So, that advantage alone would ensure the preservation of male homosexuality.
There is a recent theory (Mefi thread) that male homosexuality is contributed to by a gene that’s inherited from the mother’s side, and that it also improves the mother’s fertility. So the reason it doesn’t die out is because it’s a net advantage for the species. Also, it’s in dispute whether it’s 10% (that’s just the Kinsey study number, which used a disproportionate amount of prison inmates for instance); a recent major sex survey has 5% of men self-identifying as gay. Lesbianism, on the other hand, I’m thinking may merely be because females may exist on more of a spectrum sexually (most females respond equally to porn featuring either gender) and those at the far end identify as lesbians, unlike male sexuality which is more binary. One reason this wouldn’t get selected out is that with the male’s aggressive sexual role there’d be no shortage of heterosexual activity regardless of females’ broader tastes.
Assuming homosexuality is genetic, it’s not hard to identify reasons why a seemingly anti-reproductive strategy wouldn’t be selected out of existence: 1) Obviously, homosexuals sometimes marry and mate with someone of the opposite sex (but, almost certainly, this happens more often with Kinsey 4’s and 5’s than 6’s, so we quickly come up against problems in definition, as others have cited.) 2) If a gay person didn’t have kids, but participated in supporting other family members’ kids, that extra support could end up making a sufficient difference in evolutionary fitness for those kids (i.e. surviving long enough to reproduce, and doing so) to be selected for. Remember, in terms of perpetuating one’s genes, on average, the survival of two nephews/nieces = the survival of one child of one’s own. Mind you, while #2 is plausible, I wouldn’t accept any assertion that it has made and does make a difference until I’d seen a very careful (and very difficult to create) study. And that would hav
