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?).
If one is making an argument that gay behavior has an adaptive evolutionary basis, as do some evolutionary psychologists, then one must answer at least three questions. These questions, while crucial for any argument about the evolution of human behaviors, are almost never addressed in any work of evolutionary psychology, and the second two aren’t touched by Mooallem.
1. Does gay behavior have a genetic basis? As I said above, we don’t know much about this, but there are indications that there is some genetic basis in some people. That doesn’t mean, however, that all gay behavior stems from “gay genes.” Even if there’s a genetic basis, there is likely a strong interaction with the environment, too, so that one may not be able to impute gay behavior to simply “genes” or “environment.” Complicating this is the additional possibility that some same-sex behaviors may reflect genes or gene-environment interaction, while others could entirely reflect differences in the environment, perhaps based on neurological or hormonal factors not produced by mutations in the DNA.
If the answer to this first question is “no,” then there is no need to go further with explaining an adaptive basis for homosexuality. Without genes there couldn’t be an adaptive basis for the trait. If it’s “yes”—that is, there is at least a partial genetic basis for some gay behavior, you can proceed to question #2.
2. If the behavior is “adaptive,” how is it adaptive? That is, how, exactly, do gay people leave more copies of their “gay genes” than non-gay people? For that is what is implied by saying that the behavior is “adaptive.” Since homosexuality seems patently maladaptive from an evolutionary point of view—presumably gay people don’t leave as many offspring as their non-gay confreres—how come those genes are hanging around in the population? We’d expect natural selection to eliminate them.
Mooallem notes two possibilities. One, originally suggested by E. O. Wilson, is kin selection. As Mooallem notes:
In a paper published earlier this year, Vasey and one of his graduate students at the University of Lethbridge, Doug P. VanderLaan, report that fa’afafine [this is a group of males in Samoa who engage in same-sex behavior] are markedly more willing to help raise their nieces and nephews than typical Samoan uncles: they’re more willing to baby-sit, help pay school and medical expenses and so on. Furthermore, this heightened altruism and affection is focused only on the fa’afafine’s nieces and nephews. They don’t just love kids in general. They are a kind of superuncle. This offers support for a hypothesis that has been toyed around with speculatively since the ’70s, when E. O. Wilson raised it: If a key perspective of evolutionary biology urges us to understand homosexuality in any species as a beneficial adaptation — if the point of life is to pass on one’s genes — then maybe the role of gay individuals is to somehow help their family members generate more offspring. Those family members will, after all, share a lot of the same genes.
This would seem to be the prediction of “adaptive homosexuality” that is most easily tested. It’s not hard to determine whether gay people have more brothers and sisters (or nieces and nephews) than non-gay people, a finding necessary to support the “kin selection” theory. And it has to be more than just a one-for-one replacement with you because, according to kin selection theory, related individuals are devalued by their degree of genetic relationship to the gay person. If a gay person is, as Wilson posited, the human equivalent of a bird “helper at the nest” (birds like Florida scrub jays who forgo reproduction for a while to help their parents raise brothers and sisters), one can make calculations about whether the outcome is “adaptive.” If I become gay and have no offspring, for example, I’d have to help mom and pop raise produce at least two more brothers and sisters than non-gay people, because each brother or sister carries only half my genes. I suspect the “kin selection” idea is wrong, but it would be relatively easy to get the data.
Complicating this explanation, however, is the evolutionary-psychology idea that whatever evolutionary forces promoted the evolution of “gay genes” occurred in the distant past, on the African savanna where most of our evolution took place. Measuring current evolutionary advantages and disadvantages of homosexuality might having nothing to say about why it evolved (if it did evolve) in the first place. This evocation of an unrecoverable past, while it might be true, makes much of the speculation in evolutionary psychology untestable. Can’t find an adaptive advantage in modern society? That’s ok—there was probably an advantage several million years ago.
Mooallem raises a different possibility for how “gay genes” might be selected for:
Vasey and VanderLaan have also shown that mothers of fa’afafine have more kids than other Samoan women. And this fact supports a separate, existing hypothesis: maybe there’s a collection of genes that, when expressed in a male, make him gay but when expressed in a woman, make her more fertile. Like Wilson’s theory, this idea was also meant to explain how homosexuality is maintained in a species and not pushed out by the invisible hand of Darwinian evolution. But unlike Wilson’s hypothesis, it doesn’t try to find a sneaky way to explain homosexuality as an evolutionary adaptation; instead, it imagines homosexuality as a byproduct of an adaptation. It’s not too different from how Vasey explains why his female macaques insistently mount one another.
This may also be true, but it doesn’t necessarily solve the problem. That’s because of question #3, to wit:
3. Are the genes for gay behavior supposed to be fixed in populations or are they polymorphic? That is, do we all have genes that, under the right circumstances, cause us to have same-sex sexual behavior, or are those genes polymorphic—that is, do some individuals have them while others don’t? This latter possibility is what evolutionary psychologists often suggest; and this possibility is required for studies that purport to show that gay behavior has a genetic basis. After all, if we all have gay genes, there’s no genetic variation among people to study and thus no way of demonstrating a genetic basis to gay-ness! And if gay genes are polymorphic, why are they polymorphic? Population-genetic studies show that only under very restricted circumstances can natural selection itself promote the existence of genetic polymorphisms in natural populations. Just showing that gay behavior is sometimes adaptive, or has adaptive side effects, is not enough to explain the persistence of “gay genes” in populations.
Mooallem’s idea that gay genes are maladaptive in males but adaptive in females doesn’t fully answer this question. Genes that are adaptive in one sex but not in the other don’t automatically become polymorphic in a population. In most cases, they’ll either be wiped out of a population (if the disadvantage in males is larger than the advantage in females), or be fixed in a population, so that everyone has them (advantage in females much stronger than disadvantage in males). To explain a polymorphism, the balance between male and female fitness has to be of a very specific character so that, for example, “heterozygotes” (individuals carrying one gay gene and one non-gay gene) have a net advantage in the population. This is by no means the inexorable result if gay genes are maladaptive in males and adaptive in females (or vice versa).
Answering these three questions is a tall order. Question 1, whether homosexuality has a genetic basis, is perhaps the easiest to answer. The other two questions, involving the so-called “adaptive” basis for homosexuality, will be very difficult to answer. In fact, I don’t think—given the difficulties of studying a socially-conditioned behavior in a population on which you can’t do experiments—that they’ll ever be answered to our satisfaction.
In the end, I suppose I’m not much interested in the evolutionary roots of gay behavior. Yes, it would be nice to know, but, given the problems I’ve described above, we’ll likely never know for sure, and perhaps should spend our time studying more tractable questions. The data at hand already show that same-sex behavior in animals is a mixed bag of heterogeneous stuff, and may not illuminate homosexuality in humans. Most of the researchers described in Mooallem’s article seem to recognize this.
And of course, no matter what the evolutionary roots of homosexual behavior are, those are irrelevant (apologies to Sam Harris here) to how we regard gays. Infanticide is “normal” in some species like lions and langurs, but we condemn it and punish it in humans. What is “natural,” “genetic,” or “adaptive” has little relevance, to me at least, to the question of what is right. It’s simply the moral thing to do to ensure that gays have equal rights, regardless of whether same-sex behavior rests on genes, the environment, or both. Perhaps finding a genetic basis for homosexuality would make some Christians and Mulims stop condemning gays as immoral, but what if homosexuality turns out to be largely a product of environments? Making your morality depend on such answers is simply a bad way to proceed.
Anyway, read Mooallem’s article. It’s a remarkably good piece of science reporting.