Interesting to bring up animals. Ever seen a dog hump a leg? Sex is instinctual for an animal, but for a human its a design of emotional investment and a way to check compatibility.
It might have a role in evolution. Epigenetics make it so, that the more boys a woman is pregnant with, the bigger the likelihood of the you younger to be gay. I don't see that as de-evolution since man is not a solitary animal. For man, it is also a survival of the species. With too many men, it serves a purpose if a few are gay.
Desiring men is neither a male or female trait. If it was a female trait and you're a man masturbating what the heck are you then? A malefemale?