TIME: Very regularly: roughly half of male dolphin sex occurs with other males. Among insects, same-sex sexual behavior is usually a case of mistaken identity. Male fruit flies, for instance, may romance other males because they lack a gene that enables them to distinguish between sexes.
Most animals that engage in same-gender sex acts do so only when an opposite-sex partner is unavailable.
Younger animals (particularly males, and including humans) sometimes engage in same-sex sexual behavior as practice, which may improve their reproductive success when they are ready for a heterosexual relationship later.
SHOOT: And here's a question:
Will "the liberation of homosexuals, which allows them to come out of the closet and not pretend to be straight" actually turn out to "contribute to the end of homosexuality?" We may not know for a thousand years, but it's a great question.
One particularly charged finding is that in most species besides humans, same-gender pairings rarely lead to lifelong relationships. In other words, when one attractive bonobo male eyes another in a lovely patch of Congo swamp forest, they occasionally kiss and then move on to other oral pleasures, but they don't bother anyone afterward about trying to legalize their right to an open-banana-bar ceremony. In fact, they are likely to move on to girl bonobos