JagHammer
Senior Troll
Some animals might have taught themselves be bisexual, but in most cases, in the wild, there's always the male animals fighting each other over the female animals of their kind. And whichever male wins, they are given the pleasure to procreate with the females. The other males go somewhere to lick their wounds and their balls to fight another day.
Some rape others of their own gender to show dominance, like hippos and prisoners.