Positive Liberty

A reader has sent in a number of questions on evolution and the origins of same-sex attractions. His questions appear in italics; my replies to each of them follow.

(1) There exist evolutionary roots such that homosexuality is adaptive for some reason that remains obscure, and is environmentally evoked in utero in response to a “perceived” environmental pressure that may have been significant in the primordial Serengeti, but has since lost its significance.

I have trouble with this argument, in part because “an obscure reason” is always pretty much untestable. It seems to take way too much on faith and to explain way too little. There isn’t even a way to test this proposition without clarifying it further.

(2) “Homosexuality” is a constellation of separate traits that individually are adaptive, but in conjunction render an individual unlikely to perpetuate his genes.

This, however, is a reasonable and even a testable proposition. The simplest example of this type of trait is the gene for sickle cell anemia. Most people have two “normal” hemoglobin-forming genes. If you possess a copy of the sickle-cell gene paired with a “normal” gene, it is believed that you are more resistant to malaria. But if you possess two copies of the sickle-cell gene, you instead got a very serious disease that could not be treated until recently.

Here is another example, this one without the connotation of disease. Skin color is much more complex genetically, yet it too comes from a combination of different genes, and this means it is almost certainly closer to what we are looking for. Scientists presume that skin color is genetic, yet many of the specific genes remain elusive. It seems probable that there are several dozen of them. Here is one overview of the issue.

Now let us consider what the world might look like if homosexuality were a constellation of many different genetic traits, sort of like skin color. Let us also keep in mind that homosexuality is a behavioral trait over which the individual clearly has at least some short-term control. Does this theory explain what we observe in real life?

First, it would seem to explain bisexuality quite elegantly. Given a group of several dozen genes that incline people toward preferring mates of one sex or the other, we might expect to find a gradient between exclusive heterosexuality and exclusive homosexuality. Given that exclusive homosexuality is an adaptive disadvantage, we would expect the population cline to be skewed heavily toward heterosexuals. And so it is: Studies from Kinsey to the present all confirm it.

Assuming that highly accurate information could be found about the sexual orientation gradient, the degree of inclination toward the homosexual end would give us at least some information about how adaptive the genes of the homosexuality constellation are when they are expressed in isolation or in small groups. This would be difficult research to conduct given the stigma against homosexuals and the popular tendency to label everyone as “gay,” “straight,” or “bi.” These labels are far too crude for the work we would be doing.

Second, the constellation theory would explain quite well why homosexuality seems to run in families yet not follow classical Mendelian expression. In my own family, I have at least two relatives with orientations other than heterosexual; this is far more than the populational average, and many gays and lesbians report similar findings.

Third, the constellation theory would help explain how different people claim to have varying introspective experiences of their sexuality. “I knew I was gay when I was five years old,” some people say. Others take longer to figure it out. Personally, I didn’t know until puberty, but my parents claimed to see it a lot earlier.

Fourth, a smooth, mostly genetic variation between hetero- and homosexuality could explain how at least some people seem to have changed their orientations, while others find themselves completely incapable of doing it: The closer one is to being a purebred genetic heterosexual, the easier heterosexual behavior will seem. Those genetically in the middle may be able to suppress homosexual behaviors and even desires; people on the far extremes, though, won’t be able to do it so well.

There is only one strike against the constellation theory that I know of, but it is very serious. Twin and sibling studies suggest that a genetic component may not cause homosexuality, but merely predisposition people toward it. Here are some numbers from a study done on the siblings of gays and lesbians:

* 52% of identical (monozygotic) twins of homosexual men were likewise homosexual
* 22% of fraternal (dizygotic) twins were likewise homosexual
* 11% of adoptive brothers of homosexual men were likewise homosexual

* 48% of identical (monozygotic) twins of homosexual women were likewise homosexual (lesbian)
* 16% of fraternal (dizygotic) twins were likewise homosexual
* 6% of adoptive sisters of homosexual women were likewise homosexual

The figures for identical twins are quite high–and the numbers for men and women are intriguingly close to one another. Still, they are not anywhere near 100%. The constellation of gay genes, if there is one, is probably far more complex than anything we have seen with skin color, and it may yield only predispositions, not firm certainties.

(3) Homosexuality is one of Stephen J. Gould’s famous “spandrels,” overly reified in modern society. In other words, homosexuality could represent an inevitable, emergent consequence of traits that are adaptive for other reasons (e.g., females attracted by heightened emotional sensitivity, the additional brachiation skills afforded by limper wrists (!), etc.).

Overly reified? Oh hell yes!

The sexuality of even a few centuries ago is an unknown continent to most of us. While some aspects of sexuality are obviously coded by our genes, what we do with them has become so entangled with culture that I despair of ever separating the two.

To give one historical example: In 18th-century Europe, oral sex was considered to be an utterly filthy and degrading act for the person who performed it. An echo of that attitude remains in American culture today, where some of our most cherished insults refer to the various forms of that act. Today, though, most people find anal sex a lot more repulsive.

In the eighteenth century, these attitudes were reversed. Homosexuals shared the distaste, if you will, for oral sex, and among them, being penetrated anally was commonly thought less degrading than to perform oral sex. By contrast, though, today’s gay culture usually finds oral sex a far more “casual” activity, one that implies much less intimacy than anal sex.

Another historical example is masturbation, which has gone through some fascinating cultural metamorphoses during the last few hundred years. Everyone knows, for instance, that at one time children were sometimes told that masturbation would make them go blind. Non-Jewish Americans also first started circumcizing infant males because they believed it would prevent masturbation and the harms it caused.

Many people do not know, however, that many early moderns found masturbation a more serious sin than fornicating with a prostitute. Why? Because visiting a prostitute was at least a “natural” sex act, and because one more client could hardly be said to corrupt a prostitute much further. Masturbation, on the other hand (ahem), was an “unnatural” act, one that corrupted the person who performed it.

I could go on, but I want to look at something more fundamental.

When people look for the “cause” of homosexuality, it is almost inevitably because they are opposed to homosexuality and wish to stamp it out. The reader who submitted these questions is certainly not among them, but it’s an important point to note anyway. Certain writers have thus expressed hostility toward the entire project of finding the “origins” of gay sexuality. Among others, Eve Kosofsky Sedgwick’s The Epistemology of the Closet makes this point if I remember correctly (I would look it up, but I’m snowed in at home today and can’t get to the library).

How does this hostility play out in the search for origins?

First, it is sometimes claimed that it does not matter whether genes incline someone toward homosexuality–Genetic or not, it’s still an evil. This argument strikes me as deeply flawed.

Now, we do not find people with different skin pigmentation to be evil, or at least most of us do not. While it is possible to change one’s skin pigment, the most natural course is to let it alone. It does not harm anyone, and the natural variation of skin color gives beauty and variety to the human race.

Conversely, we find sickle cell anemia is indeed harmful. By its very nature, it inflicts pain and suffering on its victims. We try very hard to treat sickle cell anemia, and every decent person hopes that one day it will be cured for good. But under no circumstances do we demonize the people who suffer from sickle cell anemia.

We do not, for instance, ridicule them for being genetic mistakes. With gays, and for reasons unknown, there is a disturbing tendency to slip from “you are a biological mistake” to “our laws must discriminate against you” to “let’s beat you up in the street.” But we do not treat other biological mistakes in this fashion.

And why should it be that a biological mistake that encourages different behavior should be viewed so differently from a biological mistake that causes different skin color? If the behavior harms no one else, then it is simply a part of natural human diversity. It ought to add complexity and beauty to the human condition just like all our other variations.

So… Are gay people biological mistakes? As we’ve just seen, it’s a loaded question, yet let us try to answer it anyway. In one sense, of course we are mistakes: Predominantly gay people are far less likely to reproduce than heterosexuals.

But in a more important sense, biology does not make mistakes. When someone says that evolution has made a mistake, it almost always indicates only that the speaker does not understand evolution. Even the most ill-adapted genetic forms, such as the many embryos that fail in the regular course of human fertility, are a part of a larger process, an algorithm that seeks out more highly adapted forms by creating and then discarding millions of so-called “mistakes.” These mistakes are the very heart of the evolutionary process; without them, evolution cannot occur.

For proof, consider the common banana. I read once that the banana has been accepted as food in every culture where it has been tried; clearly it is well-adapted to the task we have set for it. Yet every living banana is a precise clone of all other bananas, and all of them are highly vulnerable to the black Sigatoka fungus, a fatal disease that could end the banana as we know it.

This example shows how the best chance for a species to survive lies not in the creation of a purified master race, but with a rich, diverse, and multifunctional gene pool. The latter can far more easily adapt to new environments and new threats. Eliminating “bad” genes often comes back to haunt selective breeders, who have inadvertently pruned from their fruit trees or livestock a vital though seemingly harmful genetic “mistake.”

Were all the copies of the human genome somehow made identical, and all the subsequent copies somehow made perfect, human evolution would grind to a halt. New environmental conditions could no longer be answered by new genetic innovations. It is best, both ethically and genetically, not to go down that road, and not inquire too deeply about genetic mistakes. Evolution has taken care of itself for billions of years without us; it is sheer arrogance to suggest that it needs our help.

(4) Homosexuality isn’t adaptive at all, but rather is a “mutation” (in a very loose sense) that would ordinarily eventually be weeded out by natural selection (unless we find a way to combine DNA from two male gametes to produce and gestate viable offspring, which I’m sure is just around the corner). Not all human traits are adaptive or necessarily the product of evolution, in other words.

I disagree that this is a likely scenario. Homosexuality has been observed in so many animal species that it is hard to believe such a detrimental “mutation” could have developed independently in all of them (see Bruce Bagemihl’s Biological Exuberance for some fascinating reading in this area). I think the “spandrel” theory has a lot more going for it, wherein homosexuality is a by-product of something undiscovered yet highly beneficial. This goes a long way toward explaining its prevalence among many different animals–an area where few other theories succeed.

(5) Homosexuality is adaptive, because it is one extreme expression of genetic variability in the trait that motivates men to “screw it if it looks vaguely humanoid.” We can liken this idea, in a crude way, to the tendency for goslings to form attachments to any large moving object, because such objects are likely to be caregiving parents and UNlikely to be Konrad Lorenz.

I have seen it suggested that sexuality in general plays an adaptive role in humans that it does not play in many other creatures. Humans are interested in sex almost all the time, which is rare in the animal world. Religious explanations would attribute this to the Fall, but I would not.

Surely the human sex drive would be an evolutionary disadvantage, as screwing all the time doesn’t leave much energy for hunting and gathering. Might there be an evolutionary purpose to it? I tend to think that we use sex–and I know this sounds terribly mercenary–as a way of bonding among members of a group. Bonobos, a near relative of ours, represent a somewhat different permutation than the one observed in humans, but the principle is the same:

[Bonobos are] best characterized as female-centered and egalitarian and as one that substitutes sex for aggression. Whereas in most other species sexual behavior is a fairly distinct category, in the bonobo it is part and parcel of social relations–and not just between males and females. Bonobos engage in sex in virtually every partner combination (although such contact among close family members may be suppressed). And sexual interactions occur more often among bonobos than among other primates. Despite the frequency of sex, the bonobo’s rate of reproduction in the wild is about the same as that of the chimpanzee. A female gives birth to a single infant at intervals of between five and six years. So bonobos share at least one very important characteristic with our own species, namely, a partial separation between sex and reproduction.

This separation between sex and reproduction serves–even the Catholic Church affirms it–to create bonds between the partners (Sex among Catholics should always be open to reproduction, but a married couple may have sex simply out of love, even if they know they are infertile or if the woman is already pregnant). If sex serves this bonding purpose in humans, then sex between two males or two females suddenly has a reason after all.

(6) Homosexuality is adaptive because it facilitated kin selection in the primordial Serengeti (e.g., “I’m gay, but I’ll help my brother with the cooking and increase his chances of reproducing”). This explanation is rather doubtful and ad hoc, but I thought I would state it for completeness’ sake because it works in other contexts.

Before you speculate about the clear utility of having nonreproductive males in the village, remember that natural selection does not operate at the group level, but rather at the level of the individual. Genes are selfish, and can’t perpetuate a trait unless their carriers reproduce.

I disagree with the statement that “natural selection does not operate at the group level.” If this were true, one would be hard pressed to understand the origin of social insects, among whom only a tiny fraction ever reproduces. There is a clear utility, though, to the division of labor that social insects achieve, and part of it comes from making sure that most individuals are infertile.

A further example comes from very early in evolutionary history: How did multicellular organisms come to be, when only some of the cells in these clumps went on to reproduce? There is a great evolutionary advantage, for instance, in convincing my liver and intestines never to go it alone. I might, after all, reproduce–and then their genes would be passed on, too. Why is this not the case with communities?

While I disagree with the claim about the reproductive fitness of communities, I find the “clear utility of nonreproductive males” somewhat doubtful among humans: The male contribution to reproduction can easily be kept to a minimum if that is how society sets things up. Unlike the female half of things, reproduction on the part of males is not debilitating in the least, and there seems to be little incentive for males not to breed among humans.

So, while I can’t see the benefits of the nonbreeding male as a factor in male homosexuality, I could definitely see the benefits of the nonbreeding female as a contributor toward female homosexuality. And this is exactly what social insects have done.

To sum up, I don’t know what causes homosexuality–but I don’t think that arguments for or against ethical or public policy positions ought to depend on the answer. The many possible explanations that remain open do not frighten me–but some of their advocates certainly do.

Trackback URI | Comments RSS