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Kinseyian mathematics, of a kind
January 14, 2007 2:36 PM   Subscribe

The "Darwinian paradox" of homosexuality presents the conundrum of how a potential genetic basis for homosexual behavior could provide a survival benefit to offpsring and extend through generations, when sexual reproduction would seem to place strong selection pressure against such a "gene". Recently developed mathematical models (PDF) from researchers Sergey Gavrilets and William Rice not only show how a "gay gene" might proliferate within a population, but also provides testable hypotheses, including predictions of "widespread bisexuality" (subscription req'd).
posted by Blazecock Pileon (68 comments total) 7 users marked this as a favorite

 
Richard Dawkins chimes in on homosexuality in the 3rd question of his FAQ.
posted by furtive at 2:50 PM on January 14, 2007


Intuitively, I would expect homosexuality to flourish in cultures where mass breeding was commanded in the religious doctrine, for the simple reason that the existence of the doctrine implies indifference among enough of the population to justify the doctrine's existence.
posted by Brian B. at 2:56 PM on January 14, 2007


Worker bee's don't procreate but we don't go all boggle thinking about their darwinian doom. It is only overly simplistic thinking about 'selfish genes' that lead to this 'paradox'.
posted by Osmanthus at 2:59 PM on January 14, 2007 [1 favorite]


Bleh. I reject the premise of the inquiry, namely that all genetic mutations must be popular. There is a certain strain of "Darwinism" that views everything in society, everything in nature as the result of selective pressure, rather then a side effect or something. This view is, IMO, as religious as creationism. Not everything needs to be explained in terms of Darwinian evolution.
posted by delmoi at 3:05 PM on January 14, 2007


Brian B - Conservative chritians breed like flies, and if recent everts are anything have huge numbers of closeted gays amongst their ranks, so you may have a point.
posted by Artw at 3:06 PM on January 14, 2007 [1 favorite]


Worker bee's don't procreate but we don't go all boggle thinking about their darwinian doom

Actually they do occasionally, but they also will kill try to kill any offspring not created by the queen. There was an interesting article about this, which I can't find.
posted by delmoi at 3:08 PM on January 14, 2007


Intuitively, I would expect homosexuality to flourish in cultures where mass breeding was commanded in the religious doctrine, for the simple reason that the existence of the doctrine implies indifference among enough of the population to justify the doctrine's existence.

I think there are a couple of different reasons for that, namely that people want to have sexual pleasure without consequence, and therefore invent birth control, or change sexual positions, etc. There is also a desire to out breed neighbors and other religions.
posted by delmoi at 3:10 PM on January 14, 2007


Delmoi and Osmanthus,
Both of you should read the link furtive provided in the first comment to Dawkins' FAQ. His answer addresses exactly the points you've made here (and Osmanthus, I believe you are greatly misunderstanding the "selfish gene" concept based on what you wrote in your comment...)
posted by Sangermaine at 3:18 PM on January 14, 2007


Worker bee's don't procreate but we don't go all boggle thinking about their darwinian doom

Bees (and ants) also have a unique way of breeding. They are haplodiploids, which means they are more related to their sisters than their offspring, so selfish gene theory predicts their interests will be divided accordingly.
Before this tidbit was discovered, scientists did boggle at their seemingly anti-Darwinian logic. We're just now trying to do the same thing with homosexuality. A lot of interesting theories have been proposed, and my hunch is now it's just a matter of pinning down the correct one.

Thanks for the post!
posted by Arthur "Two Sheds" Jackson at 3:23 PM on January 14, 2007


sangarmaine: I don't see how Dawkin's FAQ addresses my point, which is that a "Gay gene" may not carry any advantage and might still be passed along.
posted by delmoi at 3:26 PM on January 14, 2007


It seems to me that cultures which mandate reproduction and persecute homosexuality will have higher numbers of homosexuals if it is genuinely genetic, because in those societies homosexuals will be more likely to marry the opposite sex and reproduce, in order to avoid identification and persecution.

I find this all very interesting, but I hate it when people try to use a basis in "nature" to argue for the permissibility or morality of sexual behaviour. It will just lead to one side or the other denying the science that doesn't support them. And my human rights don't stem from evolutionary necessity.
posted by i_am_joe's_spleen at 3:28 PM on January 14, 2007 [2 favorites]


joe's spleen, you raise another interesting factor. Namely, that societies with more tolerant views toward gays may indeed end up having less of them, as gays will not be under social pressure to reproduce.

Meanwhile, less tolerant societies, ones that place strong expectations on homosexuals to reproduce, will end up having more homosexuals over time.

How ironic! :)
posted by darkstar at 3:33 PM on January 14, 2007 [1 favorite]


Well, really, that was the exact point you raised...I merely extrapolated...
posted by darkstar at 3:34 PM on January 14, 2007


delmoi
When Darwinians are challenged by some seemingly un-Darwinian fact of human life, they often invoke the distortions of civilization. Why have we a taste for sugar when it rots our teeth? Because civilization blunts the cutting edge of natural selection, and in our ancestral past sugar was too scarce to do anything but good. Darwinians have framed similar theories about homosexuality: forget the ephemera of modern life, how might homosexual genes have fared during all those millennia on the African savannah?

Yes, perhaps it's a bit different than what you said, but Dawkins is saying here that there are other factors, like human choice and social mores, that affect how genes are passed on. This seemed to be agreeing with your point that, "Not everything needs to be explained in terms of Darwinian evolution."
posted by Sangermaine at 3:35 PM on January 14, 2007


Darwinians have framed similar theories about homosexuality: forget the ephemera of modern life, how might homosexual genes have fared during all those millennia on the African savannah?

This assumes there is a molecular basis to homosexuality, which has not been proven. In this sense, Gavrilets and Rice's study is teleological, in that it "proves" something by assuming it exists.
posted by docgonzo at 3:40 PM on January 14, 2007


PDFs kill my machine and I can't get to Nature until Tuesday. Anyone wanna recap for me?
posted by klangklangston at 3:53 PM on January 14, 2007


Italian geneticists may have explained how genes apparently linked to male homosexuality survive, despite gay men seldom having children. Their findings also undermine the theory of a single “gay gene”.

The researchers discovered that women tend to have more children when they inherit the same - as yet unidentified - genetic factors linked to homosexuality in men. This fertility boost more than compensates for the lack of offspring fathered by gay men, and keeps the “gay” genetic factors in circulation.

The findings represent the best explanation yet for the Darwinian paradox presented by homosexuality: it is a genetic dead-end, yet the trait persists generation after generation.

“We have finally solved this paradox,” says Andrea Camperio-Ciani of the University of Padua. “The same factor that influences sexual orientation in males promotes higher fecundity in females.”
- New Scientist 13 Oct 2004: Survival of genetic homosexual traits explained
posted by furtive at 3:58 PM on January 14, 2007 [1 favorite]


The reports mention data that supports the hypothesis that a homosexual's orientation may be genetic but not caused by his/her genes. It may be the mother's genes that incline her to produce homosexual children.
posted by MonkeySaltedNuts at 3:59 PM on January 14, 2007


Won't anyone think of the lesbians?!
posted by Hildegarde at 4:03 PM on January 14, 2007 [1 favorite]


#Hildegarde: Won't anyone think of the lesbians?!

For some reason lesbians don't seem to be regarded as that same sort of problems as gays. The Bible doesn't say anything about them and most Bible thumpers mainly rail against gays. And up until recently much research into the cause of gayness had behind it the search for a "cure" for the problem.
posted by MonkeySaltedNuts at 4:10 PM on January 14, 2007


Nature link goes to subscription only article.

By not reading it I will be less desirable as a mate for lacking the opportunity of further intelectual stimulation. Fortunately, as a gay man, there should be no long term ramifications for failing to read the link because I am unlikely to produce offspirng. If I did, however, in a fluke, the offspring will have one less iota of intellectual savvy because their father could not read the Nature link. So it would be wise to keep me up to my eyeballs in gay sex and away from any ova.
posted by moonbird at 4:33 PM on January 14, 2007


I recall reading something in the past about the "benevolent uncle" theory to this, where societies with X chance of homosexual genetic recurrence are healthier, because of the role the "benevolent uncle" plays in fostering a healthier community overall. In other words, it's OK that he doesn't breed, because his actions within the community/tribe/society provide a greater good to the community, and the genes of his siblings are more likely to passed on, and those genes contain the chance that others like him will be born, too. So evolution selects not for this individual alone, but for the society in which this individual can appear and flourish.
posted by frogan at 4:46 PM on January 14, 2007


Lesbians seem to produce straight kids. At least that's what I tend to witness.
posted by Holy foxy moxie batman! at 4:49 PM on January 14, 2007


I wonder this so-called paradox would even have occurred to anyone before the advent of the "nuclear family". The childless aunt and uncle were the mainstays of many a family up through the industrial revolution.
posted by tkolar at 4:56 PM on January 14, 2007 [1 favorite]


Frogan: I've heard that theory too, and always liked it as a passable explanation that makes sense evolution-wise. But the female fecundity/male homosexuality link is another plausible explanation and, as always, our pet theories must accomodate new data.
posted by Sparx at 5:00 PM on January 14, 2007


Won't anyone think of the lesbians?!

Some days, I find it difficult to think of anything else.

Example!
posted by sparkletone at 5:20 PM on January 14, 2007


In other words, it's OK that he doesn't breed,

I'm betting that nature could care less about most males breeding, because only the females count and one average male could impregnate them all with time to spare. I'm wondering why there aren't less males, which eliminates the question.
posted by Brian B. at 5:25 PM on January 14, 2007



I always felt that it made sense for social mammals to have homosexuality because it would take one or more males out of the always fierce competition for stud rights and pack dominance and the "gay uncle" phenomenon (seriously) within packs would mean more males spending their time protecting young and working to find water and food. And the more tenderness you have the more endorphins get released, lowers stress, they live longer. Male baboons engaged in struggles for dominance often die of the same heart diseases associated with stress that we do. Then there is the Spartan idea that if two warriors are lovers they will fight more bravely together in battle. Caretaking tenderness between males has vastly improved my quality of life in innumerable little ways that could never be quantified by a scientist's survey.
posted by bukharin at 5:42 PM on January 14, 2007


Elsewhere in the animal kingdom --

The Fabulous Kingdom of Gay Animals.

The Gay Animal Kingdom.

Gay Animals: Alternate Lifestyles in the Wild.
posted by ericb at 5:43 PM on January 14, 2007 [2 favorites]


Gay Animals Out of the Closet?
‘‘From male killer whales that ride the dorsal fin of another male to female bonobos that rub their genitals together, the animal kingdom tolerates all kinds of lifestyles.

A first-ever museum display, ‘Against Nature?,’ which opened last month at the University of Oslo's Natural History Museum in Norway, presents 51 species of animals exhibiting homosexuality.

‘Homosexuality has been observed in more than 1,500 species, and the phenomenon has been well described for 500 of them,’ said Petter Bockman, project coordinator of the exhibition.

The idea, however, is rarely discussed in the scientific community and is often dismissed as unnatural because it doesn't appear to benefit the larger cause of species continuation.
‘I think to some extent people don't think it's important because we went through all this time period in sociobiology where everything had to be tied to reproduction and reproductive success,’ said Linda Wolfe, who heads the Department of Anthropology at East Carolina University. ‘If it doesn't have [something to do] with reproduction it's not important.’

However, species continuation may not always be the ultimate goal, as many animals, including humans, engage in sexual activities more than is necessary for reproduction.

‘You can make up all kinds of stories: Oh it's for dominance, it's for this, it's for that, but when it comes down to the bottom I think it's just for sexual pleasure,’ Wolfe told LiveScience.

Conversely, some argue that homosexual sex could have a bigger natural cause than just pure pleasure: namely evolutionary benefits.

Copulation could be used for alliance and protection among animals of the same sex. In situations when a species is mostly bisexual, homosexual relationships allow an animal to join a pack.

‘In bonobos for instance, strict heterosexual individuals would not be able to make friends in the flock and thus never be able to breed,’ Bockman told LiveScience. ‘In some bird species that bond for life, homosexual pairs raise young. If they are females, a male may fertilize their eggs. If they are males, a solitary female may mate with them and deposit her eggs in their nest.’

Almost a quarter of black swan families are parented by homosexual couples. Male couples sometimes mate with a female just to have a baby. Once she lays the egg, they chase her away, hatch the egg, and raise a family on their own.

‘Homosexuality’ and ‘heterosexuality’ are terms defined by societal boundaries, invisible in the animal kingdom.

‘Many species are hermaphrodites,’ Bockman said. Hermaphrodites have both male and female sex organs. A lot of marine species have no sex life at all, but just squirt their eggs or semen into sea.

Some creatures even reproduce asexually, by dividing themselves into two organisms. In one species of gecko, females clone themselves.

Like most complex issues, animal homosexuality is challenging and poorly understood. Therefore, educators tend to shy away from covering it in their teaching. Many scientists don't even want to be associated with this type of research.

‘I've had primatologists offer to give me their data on homosexual behavior because they didn't want to publish it,’ Wolfe said.

Against Nature?’ was set up partly to demystify the concept.

The argument that a homosexual way of living cannot be accepted because it is against the ‘laws of nature’ can now be rejected scientifically, said Geir Soli, project leader for the exhibition. ‘A main target for this project was to get museums involved in current debate; to show that museums are more than just a gallery for the past.’’’
posted by ericb at 5:53 PM on January 14, 2007 [1 favorite]


I don't understand why anybody needs a "scientific" or "evolutionary" explanation for a simple matter of taste. So some people prefer their own sex; so what?!?

In this matter the gay movement is as fucked as the homophobes.
posted by davy at 5:55 PM on January 14, 2007


In this matter the gay movement is as fucked as the homophobes.

I think it was in response to dogmatically religious people saying that nature, like God, would never produce gay individuals, therefore being gay is a matter of choice, and therefore a legitimate target of civil persecution. Of course, their reasoning historically derives, in part, from the social conflicts of not having people pair off in orderly monogamy, males and females provided in equal numbers as they are. However, it doesn't follow that everyone is suited to the ordered pair arrangement if we admit that monogamy was a human remedy to primitive forms of rutting in the first place.
posted by Brian B. at 6:05 PM on January 14, 2007


Finally, we emphasize that over 79% of the variance in male sexual orientation in our sample remains unaccounted for by the factors of an excess of maternal homosexual kin and number of older brothers. This is consistent with theoretical and empirical studies, which show that individual experiences are a powerful determinant of
human sexual behaviour and self-identity
Wow 79% of variance is possibily determined by choice and educational factors ? (and I don't mean education as parent given, school proposed...I mean education as the whole set of experiences, logical processes, memories etc).

On a tangent: even if research on the field of gender genetics is quite interesting, let's remember that there shouldn't be any reason to look for a "out of control cause" justifying non violent, consensual hetero or homosexual behavior. There isn't much consensus on the topic , or at least it seems some continue to oppose a behavior when they not even remotely affected by it, or as if they were directly concerned.
posted by elpapacito at 6:09 PM on January 14, 2007


Won't anyone think of the lesbians?!

I promise I do. Damn nearly everyday.
posted by Ynoxas at 6:16 PM on January 14, 2007 [1 favorite]


If you folks would bet reject the silliness of Darwinian evolution junk and recognize the truthfulness of Intelligent Design you wouldhave no problem in know why there is always homosexuality amindst us to bedevil us and to make us even more steadfast in supporting Goodness.
posted by Postroad at 6:32 PM on January 14, 2007


I agree with davy, as I noted above. And as for this:

dogmatically religious people saying that nature, like God, would never produce gay individuals

All sorts of behaviours condemned by traditional morality occur in nature: murder, rape, adultery, theft, etc. Conversely, most of the behaviours that define civilisation are clearly unnatural. If the dogmatically religious were to be consistent in their views on nature they would have to accept many, many things they currently condemn. Not to mention that the identification of "nature" with "God" could be theologically problematic... if you are devout, in many religions, piety requires you to suppress natural instinct.

I would always counter the cry "it's unnatural" with "yes, like wearing clothes and eating cooked food. Now about my civil rights..."

Pretty much heterosexual but I reserve the right to put my penis where I see fit.
posted by i_am_joe's_spleen at 6:39 PM on January 14, 2007 [1 favorite]


I wonder this so-called paradox would even have occurred to anyone before the advent of the "nuclear family". The childless aunt and uncle were the mainstays of many a family up through the industrial revolution.

I dunno, that argument sounds rather teleological to me.
posted by Blazecock Pileon at 6:46 PM on January 14, 2007


I am unlikely to produce offspirng. If I did, however, in a fluke, the offspring will have one less iota of intellectual savvy because their father could not read the Nature link.

This statement smacks of Lamarkianism. Heretic!
posted by homunculus at 7:09 PM on January 14, 2007


Ethnographers who have studied hunter-gatherer cultures around the world find extremely low rates of homosexuality, usually non-existent. For example, the San Bushmen, considered the oldest human ethnic human group, have no homosexuality.
posted by stbalbach at 7:32 PM on January 14, 2007


Really, stbalbach? I'm vindicated! That is exactly what my idea would predict, since it's agriculturalists who fetishize fertility in order to get lots of workers.

In fact, once post-industrial societies have finished relaxing their restrictions on homosexual behaviour, perhaps we'll see a drop in the numbers of homosexuals too.

If any wants to turn this evolutionary Just So story into a paper, I demand credit.
posted by i_am_joe's_spleen at 7:37 PM on January 14, 2007


Conversely in Papua New Guinea, the closest thing on earth to a stone age society, they bugger each other all the time.
posted by Artw at 7:39 PM on January 14, 2007


I don't understand why anybody needs a "scientific" or "evolutionary" explanation for a simple matter of taste. So some people prefer their own sex; so what?!?

In this matter the gay movement is as fucked as the homophobes.


Or maybe many human beings, regardless of orientation, like to investigate why the world works the way it does and how we got to be here and why we are the way we are.

Is it fucked for a straight person to study why they're attracted to people of the opposite sex? The answer to that happens to be trivially explained by Darwinism; non-reproductive sexual behavior (whether between creatures of the same or differing sexes) isn't as easily explained and thus is arguably even more interesting.

No, explaining it is not needed, but very little in the world really "needs" to be explained. I'm glad people try, though.
posted by BaxterG4 at 8:57 PM on January 14, 2007


The search for an evolutionary reason for homosexuality is as fucked as the idea that "homosexuality" as we understand it has existed for more than the last few centuries. Which is to say, fucked.
posted by maxreax at 9:55 PM on January 14, 2007


Why does no one argue that Darwinism would argue that masturbation would be bred out of the species, since it doesn't bring reproduction? How is this any less 'legitimate' than the argument about homosexuality?

The understanding of the cause of homosexuality is interesting in and of itself, regardless of religious intolerence of the behavior.
posted by Goofyy at 10:12 PM on January 14, 2007


maxreax: I'm not sure I'm reading you properly. Are you suggesting that men just starting having sex with men in the last 200 years or so?
posted by Ynoxas at 10:14 PM on January 14, 2007


maxreax: Do you have a mouse in your pocket, or multiple heads? What do you mean by "as we understand it"? Which 'we' are you speaking of?

Homosexuality is a behavior and/or a preference. Why should anyone suggest this is something new "in the last few centuries", especially in light of the behavior exhibited amongst other species? Perhaps you confuse the social phenomenom of gayness with homosexuality.
posted by Goofyy at 10:21 PM on January 14, 2007


Why does no one argue that Darwinism would argue that masturbation would be bred out of the species, since it doesn't bring reproduction? How is this any less 'legitimate' than the argument about homosexuality?

Because, according to the argument, the homosexual phenotype should produce fewer offspring, thus decreasing the frequency of the allele (assuming selection pressure is the dominant force on the allele.) Fecundity and masturbation does not have the same association.
posted by docgonzo at 10:38 PM on January 14, 2007


(drunkonabsinthefiltrer) I figure for the majority of human existence we were pretty rare puppies just getting by so having a certain portion of the population gay makes sense to deal with tribes that had a gender imbalance. (Goes back to sleep.)
posted by Iron Rat at 11:04 PM on January 14, 2007


So how come I'm attracted to women in Nazi uniforms?
posted by Astro Zombie at 11:19 PM on January 14, 2007 [1 favorite]


In this matter the gay movement is as fucked as the homophobes.
posted by davy at 5:55 PM PST on January 14 [+][!]

As a fag, I agree. Arguments about the evil of homosexuality need no response as they are inherently absurd, and another argument will always spring up to replace them. Nobody rationally concludes that homosexuals are evil, they just hate them.

Scientifically, this has merit. The predictions of "widespread bisexuality" I find fascinating and correlate nicely from my life experiences.

The occurrence of bisexuality is obviously higher than what it appears to be, as bisexuality can go unrecognized or repressed in an individual, since they are afforded a natural heterosexual disguise. Even in the most liberal of societies I am positive that many "potential bisexuals" restrict themselves to heterosexual activity for the sake of normalcy. There is also a statistically significant "covert bisexual" population, who engage in homosexual activities but do not have homosexual relationships. (This is all, of course, not so scientifically concluded)
posted by mek at 11:51 PM on January 14, 2007


"non-reproductive sexual behavior (whether between creatures of the same or differing sexes) isn't as easily explained and thus is arguably even more interesting."

No, non-reproductive sexual behavior can be seen as an offshoot of reproductive sexual behavior. That dudes have sex with dudes isn't particularly interesting. It's dudes forming relationships with dudes that is kinda counter-intuitive from a scientific point of view.

"Homosexuality is a behavior and/or a preference. Why should anyone suggest this is something new "in the last few centuries", especially in light of the behavior exhibited amongst other species? Perhaps you confuse the social phenomenom of gayness with homosexuality."

Your third sentence tags it: It's hard to equate the homosexuality of today with the homosexuality of many other past cultures. Greek and Roman homosexuality functioned very differently in society and culture. On the other hand, though I'm no buggerologist, I'd wager that the actual sex was likely pretty similar.
posted by klangklangston at 12:08 AM on January 15, 2007


I recall reading something in the past about the "benevolent uncle" theory to this, where societies with X chance of homosexual genetic recurrence are healthier, because of the role the "benevolent uncle" plays in fostering a healthier community overall.

Personally, I've thought that homosexuality would be a benefit in warfare (for example the ancient Greek military and the Japanese samurai) so you would have soldiers that could go off and fight and have strong emotional attachments with fellow soldiers and not worry about getting back to their wife and family. I've also read about the connection between homosexuality and left handedness, and also of the evolutionary benefit of left handedness in combat (southpaws) (southpaws would have a evoutionary advantage in combat but as they became more common the benefit would diminish and the number of southpaws would fall back down till you have this equilibrium of 1 in 7 or so, I vaguely recall reading this somewhere 15 years ago) but haven't seen these theories tied together at all. In any case it wouldn't be homosexuality that would be passed on but the ability to produce some homosexual offspring. All this is off the top of my head though.
posted by bobo123 at 12:16 AM on January 15, 2007


including predictions of "widespread bisexuality"...

Drat, I knew I was ahead of my time.
posted by Asparagirl at 12:34 AM on January 15, 2007


Let us not also forget that there's potentially widespread problems with self-reporting on issues of sexuality. We assume that gay-behaving or bi-behaving folks self-report as gay or bi respectively, but there's a lot of social pressure to report as heterosexual.

It seems from some sexuality studies that, for instance, there are men who self-report as heterosexual who don't think that getting a blowjob from a man makes them less heterosexual.

I'll see if I can't get citations, but I know that among my sexuality-researcher friends, this is a baseline assumption they have to contend with.
posted by kalessin at 5:06 AM on January 15, 2007


Yey! Selfish gene theory wins again! Pbttt! :)
posted by jeffburdges at 7:04 AM on January 15, 2007


i_am_joes_spleen: It seems to me that cultures which mandate reproduction and persecute homosexuality will have higher numbers of homosexuals if it is genuinely genetic, because in those societies homosexuals will be more likely to marry the opposite sex and reproduce, in order to avoid identification and persecution.

Good call. So, then, the "paradox" just needs a little tweak, and it's no longer such a paradox:

Italian geneticists may have explained how genes apparently linked to male homosexuality survive, despite [openly] gay men seldom having children. [The closeted men are socially (and often legally) coerced into heterosexual relationships and hence continue breeding, passing along teh ghey. Nothing to see here; move along, please.]
posted by LordSludge at 8:14 AM on January 15, 2007


Goofyy: Homosexuality is a behavior and/or a preference. Why should anyone suggest this is something new "in the last few centuries", especially in light of the behavior exhibited amongst other species? Perhaps you confuse the social phenomenom of gayness with homosexuality.

Well, a big problem with any kind of study of behavior is linking what we can observe with hypothetical theoretical constructs like, "sexual orientation" or "preference." Not all preferences result in observable behavior. And not all observable behavior is necessarily signs of an overall preference. And especially when you mix in social taboos which means that some behavior is going to be hidden away.

And one of the nice things about knowing some gay men from other cultures is finding out that other cultures don't define heterosexuality and homosexuality along the same lines. So there is a lot of doubts out there among people who study this stuff that you can have a definition of sexual orientation that is not socially constructed to some degree.

Perhaps one of the central problems is that everyone takes "heterosexuality" for granted as a theoretical construct, when I don't think anyone knows what makes us heterosexual.
posted by KirkJobSluder at 6:08 AM on January 16, 2007


In regards to the main article, I have to admit that I am bisexual, have been given a weak introduction to quantitative genetics, and have been given a much stronger introduction to multi-factorial models of human development, so that biases my view somewhat.

Much of the debate regarding this has centered on the fallacy that there must be some mechanism that selects for homosexual behavior as a phenotype. And out of this, we have the old "altruistic uncle/aunt" theory. My point of view has been that genetic contributions to homosexual behavior may be a side effect of other social processes. Especially when you consider that some of the hormonal agents that contribute to sexual attraction are also active to some degree in social interaction.
posted by KirkJobSluder at 6:33 AM on January 16, 2007


Much of the debate regarding this has centered on the fallacy that there must be some mechanism that selects for homosexual behavior as a phenotype.

That fallacy has not been established, though there is certainly mass discomfort in admitting that behavior may have a genetic component. In any case, in the studies listed, the definition of homosexuality is not based on social constructs that may differ from culture to culture, but rather on a very clear definition of sex with a member of the same gender (which has little or no fitness).
posted by Blazecock Pileon at 9:57 AM on January 16, 2007


Blazecock Pileon:

Let me add emphasis: Much of the debate regarding this has centered on the fallacy that there must be some mechanism that selects for homosexual behavior as a phenotype.

The broader fallacy is that all phenotypes can be explained through some narrative about natural selection. For example, why do male mammals have nipples? It's only in a few exceptional cases that male nipples contribute to reproductive success. Female nipples do seem to offer reproductive advantages for most mammals. So male nipples as a phenotype is probably just a by-product, or in Gould's term a spandrel.

It is quite possible that the genes that contribute to homosexual behavior also contribute to other behavioral phenotypes that do offer a clear evolutionary advantage.
posted by KirkJobSluder at 10:52 AM on January 16, 2007


For example, why do male mammals have nipples?

I can come up with a quick model why males have nipples. For example, "going backwards" on male nipples during fetal development presents too much of a fitness cost. That's a hand-waving argument, but not one I have much reticence making since the point is that these kinds of models are about cost.

Sexual behavior is certainly genetically innate; primitive humans didn't have porn or its primitive cultural equivalent to teach them how to get busy. The question is how best to characterize that behavior in language that population biologists can use, as that allows for testable theories. Cultural or identity issues simply don't enter into the model, when the line between non-reproductive and reproductive sex — as a function for spreading genes — seems mechanically clear.

It seems to me that the confusion is about what the model actually says. The model itself doesn't seem to establish the "gay gene", but rather says, if it existed, here's how it might behave under various selection pressures, and whether it would propagate along the mother's X chromosome or would be autosomal. Those are testable theories, and of course require corroboration with other ongoing research.

I think the benefits of the Gavrilets and Rice model are two-fold: their framework may be extensible to ask the kinds of questions you're hinting at — namely, linkage — and two, it generates empirically testable theories, such as the extent to which a population displays, say, heterosexual, bisexual and homosexual behaviors. Those behavior types can be (and have been) classified in quantitative, culturally-independent ways to allow theories to be tested.
posted by Blazecock Pileon at 2:29 PM on January 16, 2007


Why do men have nipples?
posted by ericb at 2:59 PM on January 16, 2007


Blazcock Pileon: I can come up with a quick model why males have nipples. For example, "going backwards" on male nipples during fetal development presents too much of a fitness cost. That's a hand-waving argument, but not one I have much reticence making since the point is that these kinds of models are about cost.

In which case, it's a fallacy to talk about male nipples as if they themselves offered an adaptive advantage. The existence of male nipples is a byproduct of gender dimorphism and development.

Sexual behavior is certainly genetically innate; primitive humans didn't have porn or its primitive cultural equivalent to teach them how to get busy. The question is how best to characterize that behavior in language that population biologists can use, as that allows for testable theories. Cultural or identity issues simply don't enter into the model, when the line between non-reproductive and reproductive sex — as a function for spreading genes — seems mechanically clear.

Except of course that we know that almost all phenotypes are dependent to some degree on environmental factors. This is a central feature of the models proposed by Galverits & Rice when they propose that the relative fitness of a gay allele is a function of its effect size. At least as far as we can know about primates, we know that many of them are social animals, which means that we know social dynamics does play a role in sexual behavior.

It seems to me that the confusion is about what the model actually says. The model itself doesn't seem to establish the "gay gene", but rather says, if it existed, here's how it might behave under various selection pressures, and whether it would propagate along the mother's X chromosome or would be autosomal. Those are testable theories, and of course require corroboration with other ongoing research.

Actually, the multiple models of Galverits & Rice don't propose a gay gene, but a gene that likely has other functions beyond just creating homosexual individuals. Such a gene might serve to protect one gender from masculinizing/feminizing environmental effects, be beneficial in a heterozygous condition, or improve fitness for one gender and not the other.
posted by KirkJobSluder at 3:38 PM on January 16, 2007


In which case, it's a fallacy to talk about male nipples as if they themselves offered an adaptive advantage.

I think this analogy doesn't really fit what we're discussing, but if you like, "keeping" male nipples provides a fitness advantage over a fetus somehow evolving a complicated, energy-expensive mechanism to get rid of them. There is a selective pressure against male fetuses evolving a pathway to lose nipples, even if they serve no obvious post-term function. Following one genderless, "abstract" genetic blueprint during development might provide a larger overall cost benefit.

Except of course that we know that almost all phenotypes are dependent to some degree on environmental factors.

This does not agree with the general vibe in this thread that is threatened by the idea of a genetic component for sexual behavior. All I'm saying is that there are a priori reasons to believe that sexual behavior has a genetic component, since we have no cultural "instruction manual" for reproduction. A cultural guidebook for the ephemera of mating rituals exists, perhaps, but the end mechanism of the ritual itself has been consistent over thousands of years. In the end, reproductive behavior and offspring are what a model can characterize and measure.
posted by Blazecock Pileon at 6:39 AM on January 17, 2007


"I think this analogy doesn't really fit what we're discussing, but if you like, "keeping" male nipples provides a fitness advantage over a fetus somehow evolving a complicated, energy-expensive mechanism to get rid of them."

Except that both male and female fetuses develop nipple ridges, and then delete all but two of the nipples anyway. Some people are born wih extra nipples along that ridge.
(Just pointing out that your argument seems mighty tautological).
posted by klangklangston at 8:12 AM on January 17, 2007


Just pointing out that your argument seems mighty tautological

Worse than that, it's just mighty hand-waving. :) However, it is established in developmental biology that there are points from which the embryo can't turn back, and from that I'm just trying to make a general point (from a developmental "point-of-no-return", fitness could provide a legitimate explanation for why any particular phenotype is present, even if, or especially if the phenotype is non-functional or vestigial).
posted by Blazecock Pileon at 9:46 AM on January 17, 2007


Blazecock Pileon: I think this analogy doesn't really fit what we're discussing, but if you like, "keeping" male nipples provides a fitness advantage over a fetus somehow evolving a complicated, energy-expensive mechanism to get rid of them.

Perhaps RTFA? The authors make the point that the selective pressure for/against a given trait depends on the effect size of the allele for that trait. With gender dimorphism, effect sizes are often different for males and females. The effect size of an allele for nipple morphology is trivial for human males, but critical for human females. So the selective pressure driving the prevalence of a gene within a population is based on the expression of that gene in females. Whether that gene has expression in males is irrelevant, (because there is no fitness advantage or disadvantage.) Male nipples are a side effect

Likewise, it is possible that homosexuality is a side effect of genes that do other things in regards to gender dimorphism or social behavior. The authors propose that rather than focus on homosexuality as an effect on those alleles, we should focus on potential other effects the genes might have.

This does not agree with the general vibe in this thread that is threatened by the idea of a genetic component for sexual behavior. All I'm saying is that there are a priori reasons to believe that sexual behavior has a genetic component, since we have no cultural "instruction manual" for reproduction.

Well, I'm not overly concerned with the general vibe in this thread. I'm talking about the ways in which biologists model the actions of genes in populations. Every quantitative genetic model has at least one term for environmental factors. An exclusive nature or nurture model should be treated with a high degree of skepticism.
posted by KirkJobSluder at 12:16 PM on January 17, 2007


Likewise, it is possible that homosexuality is a side effect of genes that do other things in regards to gender dimorphism or social behavior. The authors propose that rather than focus on homosexuality as an effect on those alleles, we should focus on potential other effects the genes might have.

To pretty much equal degree they focus on both heredity and environment, although they do not include kin-altruism as an effect. The goal is testable models.

Every quantitative genetic model has at least one term for environmental factors. An exclusive nature or nurture model should be treated with a high degree of skepticism.

We're talking past each other. All I questioned was the idea in this thread that there is no genetic component to sexual behavior, and that homosexuality is only a response to environment, which has not been established.
posted by Blazecock Pileon at 2:45 PM on January 17, 2007


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