This is something I've been pondering myself recently, the leading scientific opinion is that jomosexuality is based on biology rather than being a choice, but I still wonder. I think Nature vs Nuture comes into play. Just wondering what others thoughts are.
No has yet identified a 'gay gene'. So talking as if its existence is undisputed is jumping the gun.
First, there is no such thing as a "gay gene". At least, there isn't any specific thing we know of that could conclusively be called that and fit in with what we know about genes and how they work.
Second, gay individuals have always had the ability to procreate, in nature or otherwise. But evolution works in populations, not just individuals. Heritable traits can be passed down by other relatives. For example, gay men never need to procreate to have their genetics passed on when they have sisters who do so for them (gay uncle theory?). A great example of this is bees. Only the queen passes on her genes with the support of the hive.
completely natural and found throughout the animal kingdom.
Natural selection selects for traits that help creatures survive. It doesn't necessarily eliminate ones which play no role.