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Wednesday, June 21, 2006

Re: Thanks, Science! Now, About That Parade…

Posted by on June 21 at 13:11 PM

OK, I first want to say, I am not an evolutionary biologist. And group selection is not universally repudiated by evolutionary biologists. But I do think that this urge to define homosexuality as a “good” gene is kind of messed up.

We are not our genes. There are a lot of hypothetically adaptive traits (murdering other people’s babies, say) which, if they existed, we would be right to resist, for reasons of morality, social harmony, etc. Imagine if there were a gene that decreed that some men have a violent desire to have sex with women, even if the woman doesn’t show signs of consent. That might very well be be an “adaptive” trait, in the narrow view of natural selection: the raped ladies would give birth to lots of kids with your genotype. (The phenomenal reproductive success of Genghis Khan, recently publicized by this fiasco, is a possible illustration of how this would work—mind, I’m not claiming that Genghis Khan had any specific genotype that expressed itself to that effect.) But those men would be right, in a moral sense, to resist their genetic “destiny.” All “adaptive” means is that a given phenotype is more likely meet with reproductive success in the next generation, thereby passing on its underlying genotype to a greater proportion of the population. It’s completely value-neutral. Conversely, there are a lot of hypothetically maladaptive traits—in the sense that genetic success would be decreased—which we might be inclined to celebrate, because they make our society better, or perhaps the very fact of not resisting them makes those individuals happier and more productive members of our society.

Homosexuality might very well be an example of a technically maladaptive trait. Luckily, there’s not just one or two genes for homosexuality—it’s probably a lot more complex than that. So there’s little chance that it would be bred out in a few generations of gays avoiding getting themselves into unhappy heterosexual marriages.

Now, perhaps I’ll be proved wrong, and group selection will be a convincing explanation for why homosexuality persists in spite of its strictly nonadaptive aspects. But I kind of think it’s a blurry convenient solution to a political annoyance, not a true scientific challenge to natural selection. (Or even sexual selection, which though it might be limited, almost definitely exists in bowerbirds and peacocks and so forth.)

Any real biologists want to weigh in?

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I agree with you completely and I have a bs in evolution, ecology and evolutionary biology.

Homosexuality should never be stigmatized in a society, but the idea that it is an evolutionary stable strategy is ludicrous.

Most examples of group selection are disproven with further study on the population. Well known examples are hymenoptera, stotting, and bird alarm calls.

One more thing...

Huntington's disease is a really bad example for a genetic disease that would be comparable to homosexuality because it doesn't affect the individual until after they are older and already passed on the dominant gene. It doesn't reduce the number of children you have, it reduces how long you are going to live afterwards.

Why is this news? These are really old arguments.
Group selection is a misnomer, what's selected is the trait, the individual carrying the trait.
In the case of something like homosexuality it boils down to the question of whether a population expressing the trait as a conditionally expressed recessive trait (one that is only expressed under a specific set of environmental conditions) might be more reproductively successful. It's easy to imagine numerous ways in which it might be. Non-reproductive members of populations are common in the animal world, and it would be odd if such a common occurrence had nothing to do with natural selection.

The problem with evolutionary biology as applied to humans is that you can always invent completely opposing stories about the adaptiveness of a given trait, yet there's no way to prove which one is correct.

The biggots argue that homosexuality is maladaptive, because homosexuals don't reproduce. Everyone else argues that homosexuality is adaptive because gays can play roles that breeders can't because they're time/resources are dedicated to raising their kids. Others argue that it depends on the time, place, social norms, etc.

Since there's no way to confirm or disconfirm any of this, these discussions are more a reflection of politics than science. As such, you can't ignore them, but it helps to see them for what they are.

Biologist -- please don't call yourself that. Given your argument above, you give the rest of us a bad name.

Roughgarden has it pretty dead-on, IMO. If homosexual tendencies weren't evolutionary beneficial, you wouldn't see them, period.

Now then, I don't agree that being strictly homosexual and monogamous with a strictly homosexual partner is evolutionarily favorable. And I do agree that *group* selection is not supported (but it's been replaced by both kin selection and reciprocal altruism, two of my fave topics because I think it's fascinating how self-sacrifice can actually be selfish.) Nonetheless, I agree with Roughgarden.

If a female can have an easier time raising her offspring by developing a bond with another female, and if that bond is stronger (and thus provides more benefits) because it is strengthened by sex and sexual intimacy between the 2 females, then it's evolutionarily good. If a male can have an easier time obtaining female mates by having a male partner, and homosexual tendencies supports that partnership, then that is good. (So to answer someone else's question in a previous slog, yes, I am one who will totally vindicate bisexuality).

There are multiple ways in which you can get strict homosexuality via evolution. One is if usually the genes results in bisexuality (getting the best of both worlds, like above) but occassionally the (evolutionarily) fatal combo of homosexuality where the individual will not produce an offspring. Another is via kin selection, where strict homosexuals may pass their genes on by helping their non-strict homosexual siblings be successful at producing offspring (who are related and thus share the homosexual's genes). Another way is via kin selection in an odd way -- one research has said that any time an individual helps another individual out, it is kin selection even if the two individuals are not closely related. The idea is that the two individuals share similar genes, even though they got those genes from different families. Thus, if a strictly homosexual partner had a non-strictly homosexual (and promiscuous) partner, if the strict partner helps the other partner pass on his/her genes, then the strict partner benefits because his/her similar genes are passed on to the offspring.

BTW, Roughgarden f---in' rocks! I had the honor of meeting her and being able to listen to 2 full weeks of lectures by her when I was in grad school. She is not a nutcase to be snubbed; she's a genius!

Sean, I disagree that you can neither confirm nor deny the effect homosexuals have on the success of their genes. Maybe it is difficult (or currently impossible) in humans, but in other animals we can observe and collect data much more easily. If we truly couldn't confirm or deny anything but direct evolutionary success, we wouldn't have concepts such as kin selection and reciprocal altruism, nor the data to support them.

One more comment, and then I promise to STFU until someone else replies ... :)

Actually, the fact that Huntington's allows its victims to reproduce first only supports the idea that homosexuality shouldn't be considered a genetic disease. It means that there are more people with Huntington's than with other genetic diseases (all other things being equal), so theoretically, if there are 3-4X more homosexuals than Huntington's sufferers, there are more than 3-4X more homosexuals than other suffers of individual genetic diseases.

But I doubt that all other things are equal. I agree, it would be nice to have something other than Huntington's (something which would likely have lower numbers) to truly see the difference between homosexuality and genetic diseases.

An interesting evolutionary explanation for the persistence of male homosexuality is that it could be caused by gene(s) that, when expressed in women, increase fertility. Those genes could certainly persist, and descend the matrilineal line.

That doesn't account for female homosexuality though :/

okay, all of this is great. except for sean--the notion that humankind is above and beyond evolution is just silly.

what i'm getting is, an on/off gene for either-sex homosexuality would not be an adaptive trait and probably does not exist. which obviously jives with the evidence. multiple genes (with environmental contributions) that express a phenotype along a spectrum of sexual preference are more likely. and perhaps partial phenotypic expression is adaptive, or kin selection helps pass on unexpressed genotypes.

all of this makes sense. so does the seed article accurately express joan roughgarden's views, or no? sexual selection isn't supposed to explain homosexuality, right? to say that the above are possible examples of natural selection working to perpetuate homosexuality doesn't contradict the existence of sexual selection in some instances.

Uh... is it possible that homosexuality is evolutionarily favorable as a response to unfettered population growth? Couldn't homosexuality, like gender swapping in reptiles, be a regulatory mechanism? It may be maladaptive to the individual, but beneficial to the species. 'Cause we sure could use some population control. Natural disasters just ain't cutting it like they used to.

If dey's fuckin' goin' on heyah, it bettah be BUTT-fuckin'!

Also, the idea that homosexuality is a maladaptive trait because those with it don't reproduce/pass on their genetic info ignores a very important fact. I.e., that for most of recorded human history, most homosexuals have had to be closeted, and hence they've gotten married and had plenty of children.

I think I read somewhere that the mother who is carrying the fetus is determining the sexual orientation of her baby by secreting more or less hormone (testosterone?) in the amnniotic fluid. Thus this would make it less genetically predetermined but more a response to the current environmental/social status of the mother. A nice way to knit together the nature/nurture paradox, in my opinion.

Three things:

1) Annie, while I disagree with Sean, I do have to defend him in the sense that I think you've misinterpreted what he was saying. He wasn't saying that evolution doesn't exist in humans, only that society and politics interfere with studying evolution with respect to homosexuality, and thus you cannot show if homosexuality is adaptive. My only disagreement with him is that you could demonstrate it in non-humans, even if politics, society, and ethics interfere with collecting clean, scientific data on humans.

2) It's not clear to me that Roughgarden is saying sexual selection is wrong, only that it's woefully inadequate to deal with something like homosexuality. I haven't read that book yet, but from what I know about her, I really doubt that she is saying sexual selection is always wrong. The article does a shoddy job of clarifying her opinion on that.

3) Ivan -- what you are talking about is the debunked group selection others have mentioned. Genes act to insure their survival, even at the detriment of the species, the individual, and even other genes within the individual. A gene which does not work to pass itself on to the next generation is a dead gene. Evolution will always work to eliminate individuals who sacrifice to benefit the species without benefit to the individual's genes.

Jean - If I recall correctly, Roughgarden did state in her Science paper from earlier this year (the one mentioned in the SEED article) that "the theory of sexual selection is always wrong".

Anyway, I think everyone should brush off their classics, and go back to Gould and Lewontin's "Spandrels of San Marco". Not everything in nature need be adaptive. Not every trait has an adaptive purpose. Evolution is powerful, but its not perfect.

Boyd, I just quickly checked out the Feb Science paper, and you're right -- the authors say, "We suggest that sexual selection is always mistaken ..." Note that they aren't saying it's proven that sexual selection is wrong, but it's a pretty damn bold statement nonetheless. I look forward to reading the full article when I have more time to see if I agree with their rationale for that statement.

Also, I agree that not everything need be adaptive, but in the case of homosexuality, I think it is highly likely. Homosexuality doesn't just appear to be non-adaptive -- it looks maladaptive. It is clear that homosexuals are less likely to directly reproduce than heterosexuals, and thus heterosexual genes/alleles have an advantage over homosexual genes/alleles. Something must be counteracting that, IMO, in order to see the frequency of homosexual acts that we see in the natural world. Could the strength of those counteracting favors equal the strength of detriment caused by decreased direct reproduction? Possibly, but I doubt it.

To oversimplify the situation (terrible oversimplify!), I see the genes balancing kind of like they do in sickle-cell anemia in countries with malaria. No sickle-cell alleles are okay because you don't get sickle-cell, but you're more susceptible to malaria. One allele is best because you usually don't exhibit sickle-cell, but the cells will sickle if you contract malaria, thus helping you defeat the malaria. Two alleles are not so good, since you will always exhibit sickle-cell, regardless of whether or not you are infected with malaria, and you are less likely to survive to reproduce. Similiarly, having only heterosexual alleles is okay because you get direct reproduction, but you might have a harder time raising your offspring to adulthood because you get less cooperation. Having a mix of hetero and homosexual alleles is best, because you're still directly reproducing but also more successful because you have more cooperation in raising your offspring due to homosexual relationships. Having only homosexual alleles is not so good because you rarely get direct reproduction, but you could still get reproduction indirectly (which may or may not be greater than individuals who have only heterosexual alleles; even if it's not greater, the ultimate success of those with mixed alleles will insure that some offspring will always be strictly homosexual and some will always be strictly heterosexual).

People are entirely too hung up on the "genetics" of sexuality in my opinion. The most compelling evidence suggests that the chemistry of the intra-uterine environment is far more likely to play a causal role in the devolopment of human sexual behaviors. Think epigenetic, people!

Some of this has been hinted at already, but your rape example can be pretty easily refuted, Annie (one could think of a dozen ways in which the kind of a violent, rape-filled society the scenario you describe would result in would be less conducive to overall survival of the genotype).

Edmund Wilson's work on altruism is germane here (which Jean seems to have hinted at) -- he did some really ground-breaking work demonstrating the evolutionary advantage of seemingly disadvantageous behavior. Gist of it is that more of your genetic material could be passed on through an altruistic act that allows your siblings/relatives (who carry a lot of your genetic material) to survive at the expense of your own reproducing. I'm no trained biologist, so I won't try to go into more detail, but very relevant when analyzing seemingly evolutionarily maladaptive characteristics that have persisted through the centuries.

A couple of people have mentioned the environment, in the form of the mother's body/chemistry, as influencing sexuality. But those people are talking as if that negates genetics as a factor behind homosexuality. First, that environment is only 1 factor -- while we don't know exactly what affects a person's sexual orientation, it's likely to be affected by a lot of other things, some genetic and some environment. Second, are you really going to argue that the mother's body/chemistry is completely unrelated to her genetics???? Alleles which have a 50% chance of being found in that offspring?

Don't get me wrong, I understand that almost nothing is strictly genetic, but pointing out factors which are partially environmental doesn't mean there's not a genetic component for sexual orientation.


It seems like it'll be at least a millenium before we free sex from biology.

Genes can say I have black hair and I don't have a vagina. Beyond that it doesn't say much.

Concerning adaptivity, sure the smaller the group, the smaller the generic variation--probably. Sorry for being so ignorant. I've only read some Gould and Lewtontin. I don't know much about mutation or another causes of change.

Ascribing value to anything is really troubling.

What I would say about homosexuality--biology gives us the ability to have sex--anything beyond that lies outside of our genes.

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