... it doesn't increase reproduction? You, of course, won't hear this argument much from those who don't believe in evolution. But for those who do, it raises an interesting question: how can homosexuality be a recurring natural occurrence, when on the surface it appears to decrease the number of offspring who will survive to reproduce themselves?
Not that this article answers the question, but it brings up many scientists who are now delving into the details of that very question. Enjoy:
Can animals be gay?