Taking one for the team

>> Thursday, June 26, 2008

There's been a lot of discussion about gay marriage lately, a result of the recent California holding striking down a statewide ban on gay marriages and the inevitable effort now being made by some conservatives to get a renewed ban effected by a referendum ballot. Jim Wright's got some nice thoughts on the whole thing here and here if you missed it, and there are some good comments on both threads so make sure you don't miss those.

(I don't think of it as pimpage so much as cross-pollination, and anyway why should I labor a point that someone else has already covered so well?)

Anyway, with all the discussion, it's inevitable that people are taking the "homosexuality isn't natural" tack, and that's where we come to the subject of this post: a team of researchers has just published a study that, if their findings are accurate, provides a damn good evolutionary explanation for male homosexuality.

What the researchers found is evidence that male homosexuality is driven by genetic selection for what Slate's William Saletan aptly describes as androphilia (i.e. "male-loving"), not homosexuality. Here's what the researchers discovered, as described by Saletan (I started to summarize it myself, but Saletan does it very nicely):

First, male homosexuality occurs at low but stable frequency in a wide range of societies. Second, the female relatives of gay men produce children at a higher rate than other women do. Third, among these female relatives, those related to the gay man's mother produce children at a higher rate than do those related to his father. Fourth, among the man's male relatives, homosexuality is more common in those related to his mother than in those related to his father.

The simplest explanation for this pattern is sort of stunning: natural selection for genes that make it more likely that females will procreate at the incidental expense of related males' ability to do so. This kind of pattern is referred to as sexually antagonistic selection, a notion postulated by Richard Dawkins and observed in other species, mainly insects.

Many folks--particularly boneheaded critics in the creationist camp--point to traits and ask how is it possible that an obviously detrimental trait would be the product of natural selection? The implication naturally being that God must have created the creature with such obvious liabilities. (No, I don't quite understand that line of reasoning either--perhaps they think God was hung over at the time.) What those folks fail to see is the larger picture: natural selection can be described as a process of favoring the duplication of certain genes over others, regardless of what actually happens to the creature at a macro level. That is, a creature that sacrifices its life to breed is logical from an evolutionary perspective if that sacrifice optimizes the critter's ability to scatter copies of its genetic material all over the place--what Dawkins infamously referred to as "selfish genes," i.e. the genes don't care what happens to the vehicle that carries them.

From this point of view, a trait that causes 75% of a genotype to successfully and repeatedly copy itself at the expense of 25% is a ringing success. That is, if a woman has three daughters who are, bluntly speaking, sluts, and one son who is, shall we say, an enormous Judy Garland fan, the androphiliac genes win. The genes even win if the male just happens to reproduce--his androphiliac genome is passed on either way. In short, the hypothesis is that homosexual males are essentially taking one for the team, sacrificing individual reproductive opportunities for the sake of their biological families.

I'm not one of those people who believe we are our genes: as an idealist, I find that notion horribly limiting. Nor does it seem all that consistent with observed human behavior. If you point a gun to my head and force me to only choose one, nature or nurture, I'd rather take nurture if I could, please. But the unavoidable truth is that we are both; our genes define the raw material that life sculpts us into. A chunk of granite might be chipped and chiseled into all sorts of things, but it will also always be a piece of rock.

What this study and the research team's explanatory hypothesis offers us is an insight into how a predisposition that's a reproductive dead-end for men is an evolutionary benefit for the species. I can offer nothing more eloquent than, "that... is so... cool," in response. If the hypothesis suffers a flaw, it may be that it's so elegant one has to wonder if one is judging it by the evidence or by how obvious it seems after you've heard about it.

What this study and the hypothesis also offers is a ready rebuttal to arguments about what is "natural." Androphiliac genes, if they exist, don't force anyone--of either gender--to go out and have sex, but they do mean that some people will have a strong predisposition for loving males. What they do about it is another matter--perhaps this is where nurture re-enters the picture--but it seems grossly unfair to tell women they can follow their urges (at least within the socially-approved construct of the nuclear family), but that there is no socially-appropriate or recognized means for men with the same genetic trait to do the same.

Naturally, a limit to that rebuttal is that many of the people who think homosexuality is unnatural and a sin don't have much use for the science of evolution. Ah, well.

And it should also be noted that this study doesn't address female homosexuality at all.

The study also doesn't provide a course of social guidance. Saletan, for instance, seems concerned that male homosexuality might come to be seen in the same light as sickle-cell anemia, as a medical condition to be cured. I think he's reaching: sickle-cell anemia has the kinds of medical consequences that are hard to associate with gayness. E.g. death. It's also not clear what, if anything, could or should be done to keep parents from using some futuristic gene therapy to guarantee their posterity's genome, should the technology ever become available to do so. The whole point of medical science is to largely prevent Nature from taking its course, and that horse left that particular barn around the time some dim ancestor of ours decided to shove mud into his wounds instead of bleeding to death the way Nature intended for a man gored by a mammoth to. If--and we're talking science fiction here, but what the hey?--if you're going to allow prospective parents access to gene therapy to avoid autism it seems like you'll just have to accept that they may want grandkids, too.

At any rate, it's an interesting study and a fascinating hypothesis, and it offers yet another reason not to discriminate against people because of who they love. What's not to like about that?


Jim Wright Thursday, June 26, 2008 at 12:55:00 PM EDT  

I was going to finish this week out at Stonekettle with a discussion of this very topic.

I've changed my mind.

You said it extremely well, and I really don't have anything to add.

Excellent post, Eric, thanks.

Tania Thursday, June 26, 2008 at 2:00:00 PM EDT  

You've just confirmed your status as my platonic internet crush. Like Janiece's on Vince.

Nathan Thursday, June 26, 2008 at 10:26:00 PM EDT  

Excellent post Eric.

However, I think it's pretty much inevitable that gene therapy will be used for some pretty specious ends. I don't like it, but it's just going to happen.

Not to be indelicate, but in a world that thinks nothing of spending thousands of dollars to go through surgery to have huge tits that don't look, feel or move like any tit born into the world, I have no doubt that parents will choose blue eyes, 130 I.Q.'s and breeders.

John the Scientist Friday, June 27, 2008 at 12:17:00 AM EDT  

Uh, speaking as a blue-eyed Celtic / German who will be prone to Macular Degeneration in my old age, I'm glad my kids have brown eyes.

On the other hand, I probably would do the GM for breeding if it were simple. Thing is, there are probably hundreds of genes involved, and messing around with that much basic code is bound to have unforeseen consequences.

Michelle K Friday, June 27, 2008 at 11:47:00 AM EDT  

Dark sunglasses John. Really dark sunglasses.

I have huge ethical problems with gene therapy.

How do we determine what conditions should be "fixed" and what conditions are acceptable?

Disease like CF and MS are no brainers. However as Eric mentioned, some parents see homosexuality as a disease. Should they be allowed to fix that? Nathan mentions traits like blond hair and blue eyes. Should parents be allowed to fix that?

Some deaf parents argue that surgery to repair the hearing of their children is unethical and immoral, that those children would then be excluded from the deaf community.

And what about IQ? Is that a trait that should be changed? What about strength, agility, and reflexes? Hell, I'd love to be less clumsy, but is that an illness? A trait that should be changed?

And most importantly, how do we keep from creating a permanent underclass of individuals who cannot afford genetic modification and so will remain less intelligent, less strong, less agile than the general population?

It seems to me that for all the amazing things gene therapy can accomplish, we have a grave danger when such therapies are available only to the wealthy.

Jeri Sunday, June 29, 2008 at 1:12:00 AM EDT  

You mean genetic selection for wealth isn't part of the prosperity doctrine? :P

Well put together, Eric! You've written more substantive posts this week than I have in the past six months. Way to skew the bell curve.

Eric Sunday, June 29, 2008 at 9:32:00 AM EDT  

This coming week is likely to end up being a whole lot of "derpy-derpy-derp" posts: work tends to be "feast or famine," and next week's a plateful. I'm just glad it's only a four-day work week (tho' it's looking like they're trying pretty hard to get five days crammed into it).

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