Some of the biggest challenges to evolutionary theory come from traits which apparently make no adaptive sense. If a feature isn’t helping an animal to survive, how does that feature survive? For example, why do people still exist who wear toe shoes outside of the gym? Certain mysteries will never be solved.
Homosexuality is a particularly interesting attribute when you’re thinking about selection. Assuming there is a genetic basis– and for the purposes of this discussion, I am– its existence is completely baffling. How can a trait persist that by definition should mean that those exhibiting it won’t reproduce? It’s the same reason I expect the dress-up-like-My-Little-Pony-characters gene to be worked out of the human race within the next 50 years. Yet homosexuality persists, not just in humans but in animals, too. It’s been shown in worms, for God’s sakes, and I’m not even sure how we know about that.
But just because there’s no obvious explanation does not mean natural selection can’t explain it. Actually, I’d say this is where the theory gets interesting. When you can’t just point to an obvious advantage of a characteristic or behavior, that’s when you have to start thinking outside the box. Here are a few ideas scientists have devised as to why “the gay” is here to stay:
Kin selection – This theory, along with many of the coming theories, is predicated on the idea that family members can carry the homosexual genes and pass them to their progeny without displaying the phenotype themselves. Now suppose that those family members actually have a better chance of raising healthy, happy kids because their gay relatives, who have no kids, are spending their time helping them. In other words, it could be beneficial, selection-wise, to have a gay brother giving you a hand at home. Not to mention he’s bound to do something about your tacky purple drapes.
Social prestige – There is some evidence that gay people have a better-than-random chance of ending up in positions of high social status. Their relatives (who, again, are carrying the homosexual genes) now have an increased chance of reproduction, because it is scientifically proven that nothing turns a woman on faster than to hear your uncle is the Eldest Shaman of Panguma.
Balanced polymorphism – Sometimes less advantageous genes are naturally paired with others which do promote survival. For example, sickle-cell disease is common in Africa because the gene causing it also prevents malaria. Likewise, gay people are immune to rabies. I made that up. But there could be, I don’t know, something else.
Sexually antagonistic selection – It is possible that a gene which works against reproduction in one sex, works for it in the other. For example, the genes which make a man homosexual might make a female carrier more sexually successful. In fact, a study has has found that “female relatives of gay men have more children than those of straight men.”
Nonadaptive byproduct – Of course, there’s always a chance that there really is nothing adaptive about homosexuality, and it’s persisted simply due to the selection of other, related traits. But this is like answering “none of the above” on a test– you better damn well rule out every other possibility first. You’d be surprised how much evolution can explain.