Via Jerry Coyne:
Today’s New York Times Magazine has a long article by Jon Mooallem, “Can Animals Be Gay?,” that discusses recent observations of same-sex sexual behavior in animals. It’s a pretty good piece, showing the minefield that is animal research on homosexuality. On one hand you have researchers with a more ideological agenda, studying or describing phenomena in the hopes that they’ll somehow vindicate gay behavior in humans (see my review of Joan Roughgarden’s Evolution’s Rainbow); on the other hand are researchers who explicitly disavow any connection between their studies of same-sex sexual behavior in animals and gay behavior in humans.
The polarization around this work is equally strong among laypeople. Mooallem describes one study of a mutation that produces same-sex courtship in Drosophila males:
In 2007, for instance, the University of Illinois neurobiologist David Featherstone and several colleagues, while searching for new drug treatments for Lou Gehrig’s disease, happened upon a discovery: a specific protein mutation in the brain of male fruit flies made the flies try to have sex with other males. What the mutation did, more specifically, was tweak the fruit flies’ sense of smell, making them attracted to male pheromones — mounting other males was the end result. To Featherstone, how fruit flies smell doesn’t seem to have anything to do with human sexuality. “We didn’t think about the societal implications — we’re just a bunch of dorky biologists,” he told me recently. Still, after publishing a paper describing this mutation, he received a flood of phone calls and e-mail messages presuming that he could, and would, translate this new knowledge into a way of changing people’s sexual orientations. One e-mail message compared him with Dr. Josef Mengele, noting “the direct line that leads from studies like this to compulsory eradication of gay sexuality . . . whether [by] burnings at the stake or injections with chemical suppressants. You,” the writer added, “just placed a log on the pyre.” (Earlier that year, PETA and the former tennis star Martina Navratilova, among others, were waging similar attacks on a scientific study of gay sheep, presuming it was a precursor to developing a “treatment” for shutting off homosexuality in human fetuses.)
And, in talking to gay people, I find some who would prefer that human homosexuality be shown to be genetic, so that they won’t be derided for making a supposedly immoral “choice” and can impute their behavior to a genetic imperative. Other gays would prefer a more “nurture-ist” finding, since they envision a kind of pogrom or eugenics program if gay behavior were found to be genetic. And there are those, myself included, who think that the question is irrelevant, since the morality seeing gays as having equal rights does not depend on any genetic or evolutionary basis. (Or, if you take a Sam-Harris-an approach to the question, you can say that our well being is best served if we don’t discriminate against gay people or legally regulate the sexual behavior of consenting adults).
Can animal studies really inform work on human homosexuality? I’m not an expert in this area, but Mooallem doesn’t paint an optimistic picture. He shows, and I had guessed this, that “gay” behavior in animals (by this I mean “same-sex” sexual behavior) is a grab-bag of diverse phenomena that don’t support a single evolutionary explanation. Some same-sex behavior, such as the occasional tendency of males to mount other males, could simply be a byproduct of a general tendency for males to copulate with anything moving, which is itself adaptive since sperm is cheap. (Some flies, for example, will try to copulate with balls of wax, and some orchids, to gain pollination, have flowers mimicking female bees, with which overstimulated males try to mate). In other cases same-sex behavior may have evolutionary roots, reflecting specific adaptations. Mooallem describes “lesbian” behavior in albatrosses in Hawaii, for instance, in which pairs of females will nest together (sans males) to incubate a single egg. While this behavior isn’t yet understood, it may reflect the advantage of brooding an egg even when you’re not sure it’s yours, just because there’s a dearth of males in the population and it’s better to have half a chance of producing an offspring than no chance at all. In other cases, like the polymorphous sexuality in bonobo chimps, sexual behavior may have been co-opted into forms of social bonding. I wouldn’t expect, for instance, that same-sex mounting in Drosophila would have an evolutionary explanation similar to that of male mammals fellating each other.
So we shouldn’t hold out a lot of hope that these kinds of studies will shed much illumination on human homosexuality. It may, but I’m not hopeful. For one things, humans have a rich and mercurial culture that is unlike anything seen in animals. Social stigma or conventions can change quite quickly, and this can affect the propensity of same-sex behavior. Was prolific gay behavior in ancient Athens the same thing, biologically, as the behavior of gays in 1930s Chicago? Who knows?
The controversy about the roots of gay behavior in our culture is often couched as a dichotomy: is it genetic or is it a “choice”? Because I’m a physical determinist who believes that there’s no such thing as true free will or a genuine “choice”, I prefer to couch the dichotomy as one of nature versus nurture: are there genes whose presence results in gay behavior, or is that behavior entirely due to environmental influences, including social pressures and the behavior of one’s peers? The most likely answer is “both.” There is some evidence that homosexual behavior in our species has a genetic basis, but we don’t know much about this, and of course how genes produce traits depends, with few exceptions, on the relevant environments. “Gay” genes may show environmental effects on expressivity (the degree to which gay behavior actually appears when one has “gay genes”) and penetrance (is such behavior even seen at all when one has the genes?).