indeed.. the midigating factor seems to be our ability to reason above animals. perhaps this is why such behaviour always seems to pop up in every culture while the same cant be said for the animal kindom. I mean, who hasn't seen a male dog hump a leg? Certainly, this behaviour wouldn't perpetuate canines but.. in an animal that is aware of the proverbial "I"? We have the benefit to behave according to desire rather than reflex or instinct. I could be totally wrong but, in regards to the evolutionary construct of homosexuality, no other animal kills because two males of its specie are humping each other.