Evolution does not take into account outside sources, technological advancements etc. Evolution, for better or worse, drives us to procreate.
You have to look at evolution at its most basic: survival of the species. Evolution does not know how big our planet is or whether overpopulation would be an issue. It simply drives us to procreate.
Evolution does not know how big our planet is or whether overpopulation would be an issue but these are still very important evolutionary factors. In nature, a "successful" species will continue to procreate until it reaches a natural barrier to population growth - usually availability of habitable land or resources like food, water etc. At that point competition takes over for these limited resources and according to Darwin, the members of the species with "better" characteristics will outlast the weaker ones and survive the competition and go on to procreate, thus ensuring the beneficial characteristics are passed on genetically and thus promoting evolution, achieving a balance with the environment in which they live.
Man is a slightly different matter because increasingly, man's own activities have interfered with this "weak will perish, strong will survive" model. Because of thing like government, organization, social conscience, man is in many cases not reduced to the simple competition for survival in their immediate environment. This allows the continuation of characteristics that might not be considered the "strongest" in pure evolutionary terms.
I doubt any evidence that homosexuality is genetic.
It's just a matter of taste.
In Ancient Greece and Rome, it was the only kind of intercourse intended for pleasure.
Were all Romans and Greeks genetically homosexual?
Well the jury's still out on whether homosexuality is a genetic factor, as a result of environmental factors, or some combination of the two. I find it largely irrelevant, anyway. I do know I did not make any conscious choice to be homosexual, it's just something that I am, and I felt attraction towards other men (not sexually, but simply finding them attractive) when I was still a young child and didn't have the first idea what it meant or whether it was a good idea. Even now, where in large parts of the world it's "easier" to be homosexual that it has been for a good many hundreds of years, I'm not sure many would consciously choose to be so. If it is a matter of taste, in my case and many cases, it's a taste that I got whether I liked it or not, like my love of chocolate and my loathing of celery.
I think what ancient Roman and Greek times etc shows is that homosexuality - at least in the sense of performing homosexual acts - can be an acquired taste. Such is also shown in places like prisons, where the absence of opportunities with the opposite sex lead people to "make do" with what they can get. It might not be their preferred option but they can still do it and get pleasure out of it. Once the initial mental block is overcome about doing it homosexually, they discover that the anatomical arrangements are slightly different and maybe not their first choice, but there's still a lot of fun to be had in spite of that.