I wish I could say this will be the final nail in the coffin of the “homosexuality is a choice” camp, but I doubt it.  Still, it’s a very important piece of work.  I strongly suggest you go read The Gay Animal Kingdom:

Joan Roughgarden thinks Charles Darwin made a terrible mistake. Not about natural selection—she’s no bible-toting creationist—but about his other great theory of evolution: sexual selection. According to Roughgarden, sexual selection can’t explain the homosexuality that’s been documented in over 450 different vertebrate species. This means that same-sex sexuality—long disparaged as a quirk of human culture—is a normal, and probably necessary, fact of life. By neglecting all those gay animals, she says, Darwin misunderstood the basic nature of heterosexuality.

Male big horn sheep live in what are often called “homosexual societies.” They bond through genital licking and anal intercourse, which often ends in ejaculation. If a male sheep chooses to not have gay sex, it becomes a social outcast. Ironically, scientists call such straight-laced males “effeminate.”

Giraffes have all-male orgies. So do bottlenose dolphins, killer whales, gray whales, and West Indian manatees. Japanese macaques, on the other hand, are ardent lesbians; the females enthusiastically mount each other. Bonobos, one of our closest primate relatives, are similar, except that their lesbian sexual encounters occur every two hours. Male bonobos engage in “penis fencing,” which leads, surprisingly enough, to ejaculation. They also give each other genital massages.

As this list of activities suggests, having homosexual sex is the biological equivalent of apple pie: Everybody likes it. At last count, over 450 different vertebrate species could be beheaded in Saudi Arabia. You name it, there’s a vertebrate out there that does it.

I guess those more than 450 species are all choosing to be gay, huh?