There's no nicer way to say this but...

[Mister Agenda]

And how, might I ask, does homosexuality help for a population to survive?
For that to happen, homosexuality should only come forward in rather weak individuals, with little chance to reproduce other than by force, if they want to, as to drive them out of the genepool. I personally think it has little to do with the survival of the population.

Well, there's the 'gay uncle' hypothesis. A 'gay gene' isn't directly advantageous for a male homosexual to reproduce, but a gene that results in a higher chance of you having a gay brother could be advantageous to you and your lineage. If your brother is gay and contributes to the survival of your children, the genes you have in common with him will survive. Having some men in the tribe willing to go without female mates could have been handy in several ways. One that immediately occurs is that they could be trusted to stay and help protect the women without trying to steal them while the other men went out to hunt. Another is that (sorry gay guys) they could have been given more dangerous tasks since they were less likely to have children depending on them as fathers. Another is that you and your gay brother or brother-in-law can team up in raising your children, for example, hunting together and both sharing the food brought back with your children. As for lesbian women, it likely wasn't much of a barrier to them being bred, given the likely treatment of women in prehistoric and ancient times, but it may have helped them delay breeding until their bodies were better equipped to survive childbirth.

And then there is the norm that gays weren't that unlikely to have children through most of history (and prehistory), and more of their children may have survived because they would tend to have fewer of them and have proportionately more resources for each of them.