Determinants and evolutionary mechanisms of homosexuality

Debates over the rights of homosexuals in the United States, particularly the right to marry, often get hung up on a thoroughly inane point: whether homosexuality is "chosen" or "innate". While this may seem to be a question of moral import, it is not, and moreover it presents a false dichotomy. Like nearly all human behaviors, sexuality is too complex to be reduced to a choice or a destiny; it is neither, or both, depending on your view. However, the degree to which different factors contribute to sexuality, and the mechanisms by which they do this, are fit subjects for scientific inquiry. Two articles this week present interesting findings, sure to be distorted by all sides of the argument, that may prove enlightening in this regard. I will endeavor, along with others, to be a resource providing an unbiased view.

First, however, a plea for sanity. If science finds, by some transcension of nature, that sexual orientation is entirely chosen, or entirely innate, it does not matter to any debate over the rights of homosexuals. Men may have an innate tendency to try to spread their genes as widely as possible, but we would not forgive adultery on this basis. Toddlers have an innate tendency to become frustrated and throw tantrums, but we still make them sit in the corner. That a behavior is innate is not a basis for withholding moral judgment. And if sexual orientation is a choice? Well, we frequently forbid discrimination on the basis of chosen behaviors—religion, for instance, or political affiliation. What is truly at issue is not choice, but whether it is just to deny rights and protections to one group of citizens for no reason beyond the moral opprobrium of another group.

Thus, the question of rights for homosexuals does not depend, one way or the other, on whether people choose to be gay. I firmly believe one side of this question to be in the right, but this opinion is not informed by my scientific knowledge, because it cannot be. I would urge my readers (all three of you) to view these results strictly as what they are: interesting scientific findings related to a political question that do not support one side of the argument or the other. I would ask advocates for both sides to refrain (for once) from distorting the conclusions of these reports, not only because of the raw immorality of lying, but because by misrepresenting these findings they will have sacrificed their integrity for no gain in the debate.

There, I feel better now. On to the science!

In the first study, a team analyzed the results of a survey of Swedish twins in hopes of parsing out the relative contributions of heredity, shared environment, and unshared environment in shaping sexuality (1). Although the survey was answered by a fairly large number of twins, the authors draw their conclusions using two questions that do not directly ask for sexual orientation. The survey only requested information about actual sexual partners, and did not address homosexual feelings that might not have been acted upon. After excluding twin pairs that were opposite-sex or unclear with respect to zygosity, they had 3826 pairs to work with, of which 5% of men and 8% of women reported at least one same-sex sexual encounter. Because it is suspected that the factors influencing homosexuality may differ between the sexes, males and females were treated separately. By comparing the concordance and discordance of sexual behaviors between monozygotic and dizygotic twins it should be possible to parse out the degree to which genetics and the environment contribute to sexuality.

Despite the limited materials, the authors were able to reach some conclusions, with the caveat that the 95% confidence intervals were quite wide. For instance, for males they found that genetic factors explained 39% of the observations with respect to whether a twin had any same-sex partner in his life. However, the 95% CI on this prediction was 0% to 59%. For men, shared environmental factors appeared to contribute nothing, while unique environmental factors explained 61%. For women, it was determined that genetic factors contributed 19%, shared environment 17%, and unique environment 64%. Similar distributions were seen for comparisons of total numbers of same-sex partners. While the confidence intervals for all factors are quite large, the numbers largely agree with a previous study on Australian twins (less so with a study on American twins).

Obviously, the small sample size and broad confidence intervals on these results suggest that they should be interpreted cautiously. It should also be noted that "unique environmental factors" may run the gamut from hormone exposure in utero to childhood illness to personal experiences. Many unique environmental factors, even for twins, are just as involuntary as genetics, but some result from conscious choices of the individual (which is different from choosing to be gay). Despite their limitations, these results generally support the idea that sexual orientation results from a confluence of genetic and environmental factors.

That genetics play a role in homosexuality may seem curious, because in terms of the classic expression, "survival of the fittest", homosexuality would appear to be a non-starter. After all, a reluctance or outright inability to mate with the opposite sex would seem to result in a substantial reduction in reproductive fitness. However, contrary to what a certain ignoramus would have you believe, the Theory of Evolution has advanced substantially since the days of Darwin, and we are aware of numerous additional evolutionary mechanisms that operate alongside the law of natural selection. In the case of male homosexuality, a new paper by Camperio Ciani et al. argues that sexually antagonistic selection may be at work (2). PLoS ONE is open access, so feel free to open up the article in another window and skim it yourself.

Camperio Ciani et al. begin with the observations that male homosexuality has a matrilineal association, and that the mothers (and maternal aunts) of homosexuals are somewhat more fecund than the population at large. From these pieces of data, and from the fact that homosexuality appears to have been present at low levels in every society that has left written records, the researchers created a set of requirements for some evolutionary simulations, based on different supposed properties of the genetic factors influencing male homosexuality (GFMH). Most of the simulations failed to satisfy the parameters. In many cases (especially with single-locus traits) the GFMH either became extinct or gained too high of a frequency; in others the matrilineal association was not preserved.

Ultimately, the researchers found that the model that best fit the parameters featured two alleles (one of them X-linked), and was sexually antagonistic. What this means is that the trait increases the reproductive fitness of one sex while decreasing that of the other. For instance, a heightened sexual response to men could make women more likely to pass on their genes, while making men possessing the trait less likely to do so. Provided that the effects of this trait are balanced with respect to the population proportion of each gender, it should be possible for it to survive in a population at a relatively constant level.

This result is interesting, and provides some hypotheses that can be tested with genetics. However, it does not prove that homosexuality is genetic, or even that it has a genetic component. Like all simulations, these results merely inform us that a particular possibility is consistent with what we already know. In this case, we now know that the observed aspects of homosexuality are consistent with a 2-locus trait that is sexually antagonistic. However, this model was arrived at simply through process of elimination, and there may be some superior model or more-accurate mechanism that simply hasn't yet been tested. There is always a model we haven't thought of; sometimes that model is the right one. Moreover, as Långström et al. note, some of the data used to determine criteria for successful simulations remain controversial. Camperio Ciani et al. convincingly show how the preservation of homosexuality through evolution could happen, but that is not the same as demonstrating how it did happen. That will require a positive identification of the actual GFMH.

The results of Långström et al. indicate that any GFMH eventually identified, whether or not they materially resemble the predictions of Camperio Ciani et al., will only give rise to a heightened propensity for homosexuality. Environmental factors play a significant, perhaps even dominant, role in determining sexual orientation. Whether genetic or environmental, most factors contributing to homosexuality are involuntary, but some are chosen. If that answer doesn't satisfy you, perhaps you were asking the wrong question.

1. Långström, N., Rahman, Q., Carlström, E., Lichtenstein, P. (2008). Genetic and Environmental Effects on Same-sex Sexual Behavior: A Population Study of Twins in Sweden. Archives of Sexual Behavior DOI: 10.1007/s10508-008-9386-1

2. Camperio Ciani, A., Cermelli, P., Zanzotto, G., Brooks, R. (2008). Sexually Antagonistic Selection in Human Male Homosexuality. PLoS ONE, 3(6), e2282. DOI: 10.1371/journal.pone.0002282 OPEN ACCESS

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"You may have left me before / but you can't leave me behind."

The two or three of you that have perused my link section have probably come across the oddly-named Ray Bradbury's Love-Camel, Eric's teamblog about pop culture. In a moment of insanity, he invited me to cross-post my own economy-priced cultural musings, and I've decided to do so until the comments get too mean or he returns to his senses.

As it turns out, my first post for rblc is actually inspired by Eric's post yesterday about Blankets, which reminded me of one of my favorite graphic novels, and so even though it was a little early for me to hit it on the decadal rotation I went home last night and re-read Stuck Rubber Baby by Howard Cruse. Although it's a work of fiction, Cruse admits that it is heavily influenced by his time in Birmingham in the sixties, and this shows through in much of the plot and also in some of the characters. The inspiration for Sutton Chopper, for instance, will be immediately obvious to anyone who remembers any part of their Black History Month lessons. But Stuck Rubber Baby is not about the Civil Rights Movement, except to the degree that the characters' reactions to it help define their relationships with each other. This story is about a young man coming to terms with his homosexuality in an extraordinary and difficult time, and the mistakes he and others make in the course of that effort.

This isn't a subject that everyone wants to read about, and I'll forgive you if it turns you off, while warning you that you are missing out on a wonderful story. On the other hand, both civil rights and gay coming-of-age are hardly topics lightly served by literature; it's tempting to dismiss this book (if you haven't read it) as a retread of overdone themes. Yet Cruse manages to avoid the all-too-easy trap of populating this kind of story with saints and sinners. Despite the enormous cast, almost every character who appears on more than one page comes across as realistically mixed. You will find something to criticize in every protagonist (especially the main character), and also something to like, or at least a basis for forgiveness, in the villains. The saintly black preacher unleashes a sarcastic, acid tongue, and the obese bigot who commits one of the book's worst acts comes across as genuinely remorseful and ashamed at the end.

The black-and-white art reflects this sensibility. The characters are highly detailed, and the lines used to draw them are very curvy. This style allows Cruse to create very expressive faces, and yet at the same time it seems to highlight physical imperfections. These characters are not supermen, nor are they ostentatiously ugly. They simply seem real—not in the trivial way one associates with photorealistic artwork, but rather the deeper reality of memory and emotion. Even the sexual content works, a rare example of art avoiding pitfalls I have mentioned before.

Who knows how much of this tale is drawn from Cruse's experience and how much is entirely made up? The strength of Stuck Rubber Baby is that you simply can't tell. This story, though it is fiction, feels real, almost frighteningly so. It has no perfect heroes, no perfect villains, and the last page holds no happy ending... only the impression that someone else's memories, with all their joy and sorrow, have been made your own.

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Playing it safe

Is it really such a big deal that Dumbledore was crushing on young Gellert back in the heady, free-loving days before the war? Does it really change anything about the books? Heck, does it even change anything about the fans' perceptions of the books? Rowling commented, "God, the fanfiction," but that just shows she's never heard of rule 34. The body of fanfiction based on the Potter novels is so vast as to be beyond the comprehension of any sane man, and at least a quarter of it is probably porn. Rowling, imaginative as she may be, could not possibly conceive of anything that fanfic writers have not already turned into treacly, overwrought prose riddled with misspellings, atrocious grammar, and cell-phone language.

I don't doubt that this will add more fuel to the fire of fundamentalists already out to burn the books for daring to mention witchcraft and to promote tolerance. And I have already been subjected to a diatribe accusing Rowling of using this to "drum up publicity" for the books, which is patently ridiculous. For one thing, Harry Potter has so thoroughly permeated popular culture that it is almost certainly impossible to publicize it further. For another, J.K. Rowling is already wealthier than the Queen of England. If your personal wealth overmasters that of a family that spent centuries sucking dry the marrow-bones of indigenous peoples then you hardly need the extra publicity a gay controversy will give you.

Even in the context of the books, this is a minor fact. It fills out the story of Dumbledore's fascination with Gellert, but this is hardly necessary as the books themselves give a strong account of his feelings. It casts an interesting light on his relationships with Snape and Harry, but it doesn't really make any more sense of them. While it might be interesting for the fans to know that Rowling thought of Dumbledore as gay, knowing this doesn't really add much to the depth of the story.

I've even seen some comments saying that it was brave of Rowling to admit that Dumbledore was gay. Well, it fits her books' themes of tolerance. But "brave"? For admitting that a secondary character was gay months after the final volume of her series wrung its billions from the best-seller list? Not a chance. "Brave" would apply if Harry had secretly crushed on Oliver Wood, gotten beaten up for glancing one too many times at the other blokes in the Quidditch showers, and shyly asked Ron to be his date at the Yule Ball. But Rowling never took such chances.

For all that can be praised about the Potter books, it's important to realize that Rowling always played them perfectly safe. The teenage romance was chaste and hardly emotional. The abuses Harry suffered in his adoptive home were never of a kind that truly threatened his well-being. Neither Harry nor any of his friends was ever truly tempted by evil. She rarely played with ambiguity — with very few exceptions, Harry's foes were completely unhinged monsters or obstinately ignorant to the point of irrationality (or, like Umbridge, both). Neither Harry nor the reader was ever remotely tempted to take their side. I'm not criticizing her for this — were I lucky enough to be in her position I might take the same approach. But let's not make the Potter novels into something they're not. And let's not give Rowling's pronouncements about them more than the momentary notice they're due.

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"Jealousy among men is a terrible thing..."

Last night I rented and watched Taboo, or Gohatto if you use the original Japanese title. I don't think I would have found it on my own, but the Netflix recommendation algorithm spat it out and I gave it a try. Taboo is a fascinating, well-acted gay samurai mystery art film, and you cannot be any more surprised by reading that than I was by writing it.

The conceit of the film is that an exceptionally pretty boy named Kano Sozaburo joins a samurai military unit towards the end of the Shogunate (the politics of this era play a minor, but substantive role in the story). Many of the men become infatuated with him, and their jealousy starts to tear the unit apart until a bloody episode that ends the film. Beat Takeshi stars as the unit's second-in-command Hijikata Toshizo, who is the one that has to deal with the problems Kano creates. These are many, as Kano seems to catch absolutely everyone's eye, including the commander, at least one lieutenant, and even perhaps Hijikata himself.

This is not the best movie I've ever seen by any standard. The plot seems to come and go at times, and the tension builds only unevenly towards the final confrontation. While the movie centers on Kano little is done to give the viewer a real handle on his character. He blows hot and cold, and Matsuda Ryuhei at times just doesn't seem equal to his task. Takeshi does more with less; Hijikata is much easier to grasp, even though he has his own set of unresolved questions. In the end the viewer is left to resolve most of the movie's central mysteries.

The directing is very interesting. Oshima Nagisa's camera tries to let action speak for itself, which works splendidly in some scenes (Kano's embarrassing kendo bout against his lover) and not so well in others (an extended entrance by a geisha). As is often the case, color features prominently in the film (Kano's frequent wearing of white against the black of the militia's livery), but it bears thinking about what the colors mean in the cultural context.

Some cultural context may also be needed for westerners watching the film. An American might find it strange that all these men are attracted to Kano, who seems by our standards pale and rather pinched. The seeming lack of romance in the love scenes (there is one sex scene, but barely anything is shown) may also seem a little odd. These aren't flaws but rather important components of the historical and cultural setting, ultimately helping to build a fairly accurate picture of this world.

Taboo isn't easy to understand and just isn't for some people. I don't mean this pejoratively; you aren't a better person if it is for you. It's the strangest case ever made against gays in the military -- beware, all the straight men might become infatuated! And yet, though some of the plot seems totally alien, it works, even the slightly strained ending. Beat Takeshi is to be credited for this, as he grounds a film that could have easily flown off into space. Sakagami Jiro, Takeda Shinji, and a few others in the supporting cast also do great work, propping up (in my opinion) Matsuda, who just doesn't seem to have quite enough poison in his eyes for this role. If you think a gay samurai mystery art film might be for you, then try to get your hands on it, at least for a rental.

I also watched Hot Fuzz; all you need to know about this film is that it is very funny and you should rent it.

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