Homosexuality For instance, these two male black swans hooking up, building a nest, and then stealing fertile eggs from straight black swans which they then hatch and raise the chicks. Fascinating -- but is it an evolutionary advantage or just something that happens? In their case, two male swans carry a lot of social weight in the flock, and their borrowed chicks tend to do quite well. But then, everything else being equal, most swans do a pretty good job of hatching their eggs. — Bitter Crank
Homosexuality could be considered an evolutional advantage in that families that have homosexuals in them have members that are not directly implicated in the reproduction race, but who still have a stake in it, and have ressources to contribute to the other members of the family who are directly implicated.
Lets say you, as an homosexual man, have an heterosexual sister. Her genetic material is not yours, but it is about as similar as it can possibly get. If all you can do is make sure that her child is well taken care off, and she does successfully, even if you didn't, you didn't
quite lose the reproduction race.
The second possibility (which is actually not exclusive to the previous one) is that homosexuality is the result of the interaction of multiple individually-advantageous genes with specific foetal conditions. There's a gene for better health, for better diction, for shinier hair, which are all great by themselves or in group, but as a group, they come with the additionnal possibility of changing your sexual orientation. Because they are still great genes to have, and because you could potentially have all of them without the orientation trigger, and because, this is important to note,
homosexuals aren't sterile , whatever genes end up in their jeans, aren't really condemned to stay there.