Well, we need to keep in perspective the timelines in which species evolve, and compare that to the timeline of human society. Homo sapiens has been a thing for roughly 500,000 years, civilization has been a thing for 10,000 years, and homosexuality as a conceptual construction has been a thing for maybe a century. Men have been banging men for a very long time, as we all know, but a Spartan who fucked a Spartan while marching toward some foreign war still eventually went home to his wife and made babies. Hence, even if there is a such thing as a gene "for" being gay, it wouldn't have started to work its way out of the genome until one could be gay, or you know, since the 70's. There are a lot of examples of homosexual sex in nature (elephants and bonobos, for example), but there doesn't (as far as I know) appear to be gay behavior (that is, exclusively favoring one's own sex, but I'm no behaviorist; I'd love to hear if anyone knows an example of this). I think homosexuality, as we currently know it, is a by product of society more so than a genetic aberration (although, as with most traits, I'm sure some are more genetically predisposed to such behavior when exposed to certain environments). So the short answer, is that if there is a gene for being gay, then it has only recently started to be whittled out of the genome, and for it to really be worked out it would require everyone who feels a little bit gay to stop breeding altogether. Not very likely.