"Not every sexual act has a reproductive function.... That's true of humans and non-humans.... Some scientists have proposed that being gay may serve its own evolutionary purpose. It could be a way that you strengthen bonds - that's one hypothesis.... Another is that it could be practice for heterosexual sex. Bottlenose dolphin calves mount each other a lot. That might benefit them later on.... The funny thing is that people say homosexuality is unnatural, that non-humans don't engage in homosexual behavior, but that's not true. Then they'll say it's base and animalistic."

Janet Mann, a biologist at Georgetown University who studies dolphins which commonly exhibit homosexual behavior. (Live Science)