From the JUN/JUL 2006 issue of Seed:
Credit: Catherine Ledner
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.
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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. Nevertheless, most biologists continue to regard homosexuality as a sexual outlier. According to evolutionary theory, being gay is little more than a maladaptive behavior.
Joan Roughgarden, a professor of biology at Stanford University, wants to change that perception. After cataloging the wealth of homosexual behavior in the animal kingdom two years ago in her controversial book Evolution's Rainbow—and weathering critiques that, she says, stemmed largely from her being transgendered—Roughgarden has set about replacing Darwinian sexual selection with a new explanation of sex. For too long, she says, biology has neglected evidence that mating isn't only about multiplying. Sometimes, as in the case of all those gay sheep, dolphins and primates, animals have sex just for fun or to cement their social bonds. Homosexuality, Roughgarden says, is an essential part of biology, and can no longer be dismissed. By using the queer to untangle the straight, Roughgarden's theories have the potential to usher in a scientific sexual revolution.
Darwin's theory of sex began with an observation about peacocks. For a man who liked to see the world in terms of functional adaptations, the tails of male peacocks seemed like a useless absurdity. Why would nature invest in such a baroque display of feathers? Did male peacocks want to be eaten by predators?
Darwin's hypothesis was typically brilliant: The peacocks did it for the sake of reproduction. The male's fancy tail entranced the staid peahen. Darwin used this idea to explain the biological quirks that natural selection couldn't explain. If a trait wasn't in the service of survival, then it was probably in the service of seduction. Furthermore, the mechanics of sex helped explain why the genders were so different. Because eggs are expensive and sperm are cheap, "Males of almost all animals have stronger passions than females," Darwin wrote. "The female...with the rarest of exceptions is less eager than the male...she is coy." Darwin is telling the familiar Mars and Venus story: Men want sex while women want to cuddle. Females, by choosing who to bed, impose sexual selection onto the species.