WK, there is only ONE way for evolution to take place. There is only ONE reason why a specie proliferates. There is only ONE way a mutation could be fixed in a population-
Right, and that would be the ability for the individual to reach reproductive age.
Oh wait, did you think it was something else?
You are taking basically a 5th grade interpretation of evolution and assuming that's all there is. This is incorrect.
It is true that sexual attractiveness is a big thing that natural selection selects for. It is also true that it is prehaps the most obvious thing.
However, you could be the sexiest damn beetle on the block, if you aren't immune to the local fungus, you aren't going to live long enough to strut your stuff.
Sexual attractiveness (or your ability to be attracted to people with whom you can have reproductive sex) is not the ONLY thing natural selection pays attention to.
Further, humans are deliberate breeders. We can choose when and with whom we have sex. Homosexuality is not a barrier to reproduction.
If you still believe that it is, I suggest you pick any right wing anti-gay legislator and see if he has kids. If he does, that's proof positive that gays can reproduce.