without reading the rest of the thread
The thing is, diggleblop, that you can’t say, “Okay if evolution is this big survival of the fittest thing, then why…” and proceed to ignore the whole thing that evolution is talking about. Survival of the fittest is talking about the survival of a random set of traits. And those are random.
So if you ask why homosexuality would exist when they obviously can’t survive as their own species (given that they can’t procreate), then you’re quite obviously attaching some blinders. By equal measure, why would people ever be born sterile? Hermaphroditic? With genetic diseases that will cause them to die before they ever reach puberty? You can’t separate out homosexuality and say that’s obviously unnatural because you can’t procreate, and then ignore the other thousands of things people are born with that will also result in an inability to have children. And of course many homosexual people do have children.
Now, as I recall, species generally have a 5% randomness factor to what they are born with (in terms of DNA–there are further random factors as the body is actually constructed.) So that means that they’ll have 47.5% of their father’s, and 47.5% of their mother’s, and 5% of entirely random settings in their DNA. This doesn’t mean that for every 100 children, there’s some chance that one of them will be born as a turtle instead of a human. Simply, there’s more than 5% difference between us. If the randomness factor was 50% though, there might be some chance of having a child who looked like a turtle. The odds that a turtle will be able to procreate with children who were born as humans or cats is pretty low though. Thus, a species with 50% randomness isn’t going to survive.
But, then the question is, “But why would there be any sort of DNA setting for homosexuality?” Well why wouldn’t there be? DNA is a strand of chemicals, not an all-knowing god. The only reason we have any DNA strands that create valid creatures is because we’ve had millenia of time to get rid of non-valid species who 1) can’t generally last to procreation, nor 2) create progeny that can last to procreate. And that’s all that is needed. So long as enough last to procreate of the species, it doesn’t matter how many were invalid–and so, DNA doesn’t need to be intelligent.
And further, who is to say that male-male or female-female pairings will always be sterile? There are unisexual species in the world. It’s entirely possible that eventually human men will start gaining some trait which allows them to become impregnated by other men. DNA doesn’t care if you think it squicky or not. If a couple of male humans can impregnate each other, then so it goes. It could just mean the beginning of a split in the human species; one unisexual, and the other dual.