Homosexual behavior seems pointedly un-Darwinian. An animal that doesn't pass along genes by mating with the opposite sex at every, well, conceivable opportunity, seems to be at an evolutionary disadvantage. So what’s in it for the 450-plus species that go for same-sex sex? Two evolutionary biologists from University of California, Riverside, set out to answer that question in a paper published today in Trends in Ecology and Evolution. "It's been observed a lot," says Nathan Bailey, a post-doctoral researcher at U.C. Riverside and lead study author, of same-sex sexual behavior in animals. "But it took people a long time to...