Jon Mooallem had a really interesting article in the Times Magazine yesterday. It reviewed some recent research on animal “homosexuality,” with an emphasis on scientists who argue that same-sex behavior is not a single adaptation or mutation, but rather reflects a panoply of different instincts, spandrels, and evolutionary accidents:
Something similar may be happening with what we perceive to be homosexual sex in an array of animal species: we may be grouping together a big grab bag of behaviors based on only a superficial similarity. Within the logic of each species, or group of species, many of these behaviors appear to have their own causes and consequences — their own evolutionary meanings, so to speak.
It’s also possible that some homosexual behaviors don’t provide a conventional evolutionary advantage; but neither do they upend everything we know about biology. For the last 15 years, for example, Paul Vasey has been studying Japanese macaques, a species of two-and-a-half-foot-tall, pink-faced monkey. He has looked almost exclusively at why female macaques mount one another during the mating season. Vasey now says he is on to the answer: “It isn’t functional,” he told me; the behavior has no discernible purpose, adaptationally speaking. Instead, it’s a byproduct of a behavior that does, and the supposedly streamlining force of evolution just never flushed that byproduct from the gene pool. Female macaques regularly mount males too, Vasey explained, probably to focus their attention and reinforce their bond as mates. The females are physically capable of mounting any gender of macaque. They’ve just never developed an instinct to limit themselves to one. “Evolution doesn’t create perfect adaptations,” Vasey said. As Zuk put it, “There’s a lot of slop in the system — which,” she was sure to add, “is not the same as saying homosexuality is a mistake.”
My favorite line in the piece: “One primatologist speculated that the real reason two male orangutans were fellating each other was nutritional.” We’re so good at explaining away what we don’t want to believe.
A few years ago, I wrote about the controversial theories of Stanford evolutionary biologist Joan Roughgarden, who has a somewhat different take on homosexuality in the animal kingdom. She argues that homosexuality evolved in tandem with vertebrate societies, in which a motley group of individuals has to either live together or die alone. In fact, Roughgarden even argues that homosexuality is a defining feature of advanced animal communities, which require communal bonds in order to function. “The more complex and sophisticated a social system is,” she writes, “the more likely it is to have homosexuality intermixed with 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. 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.