If you need some practice making up just-so stories then get on over to
Pharyngula and join the party. The commenters are having a gay old time making up adaptationist explanations for homosexuality [
Gay roundup]. If you don't want to make up your own stories then you can vote for your favorite on
seyd [
Evolution and Homosexuality]. All the tired old standards are there including ...
Likewise, removing a portion of the population from breeding relieves the breeders of some of these costs either directly by assisting with child rearing, or indirectly by taking over other costly activities (like food collection) so that t he parents can spend more resources on their progeny.
Naturally, PZ is not joining in. He doesn't believe that an adaptationist explanation is required. I agree. In fact, I'm not even sure that an evolutionary explanation is needed since the evidence for a heterosexual gene is practically nonexistent. (Note that if there's a gay and/or lesbian allele then there has to be a heterosexual one as well.)
If you need some practice making up just-so stories then get on over to Pharyngula and join the party. The commenters are having a gay old time making up adaptationist explanations for homosexuality [Gay roundup]. If you don't want to make up your own stories then you can vote for your favorite on seyd [Evolution and Homosexuality]. All the tired old standards are there including ...
9 comments :
Personally, I think it's something to do with intense selective pressure for better interior design... But before anyone protests that I'm perpetuating a stereotype, let me immediately say: some of my best friends are gays with ratty furniture.
Yes, I'm kidding. More seriously: I buy PZ's developmental constraints explanation as being at least as plausible as anything I've heard. And I'd second his comment on plasticity too. And I'd say finally that I think the weight of evidence is, right now, that sexual preference isn't particularly heritable, anyway.
(Note that this is in no way to be construed by raving evangelical 'teh ghey can and should be cured' types as support for their position. Just because it might actually be fixed later in development, and more environmentally than genetically, doesn't mean preference couldn't become pretty effectively irreversibly fixed nonetheless.)
Are you saying there is no physiological basis for sexual orientation? Is it just a "lifestyle" choice then?
John Poeret says,
Are you saying there is no physiological basis for sexual orientation? Is it just a "lifestyle" choice then?
I'm saying that it's wrong to assume that there's a gene for homosexuality and heterosexuality and then to create just-so stories based on that, possibly incorrect, assumption.
I don't know whether there's a major genetic component that makes most people exclusively heterosexual, and one that makes some people bisexual, and other people homosexual. I very much doubt it, but the jury is still out.
I don't known whether there's a non-genetic physiological factor that makes most people become heterosexual. It's possible. If there's a difference in physiology, it doesn't necessarily have to have a heritable genetic component.
I certainly don't think that the exclusive heterosexuality of most people is simply a "lifestyle choice." I certainly don't feel like I had much of a choice in the matter. Most gays feel the same way.
I suspect that it's a combination of physiology and the society that one grows up in. I suspect that if we lived in ancient Greece we would all be much more likely to be bisexual.
Well, I'm at a loss. If it is physiological, even if only in part, how can it be without some heritable genetic component? For example, if sexual orientation was developmental, due to hormonal influences in the womb, say, wouldn't that still be due, at least in part, to the mother's genetic inheritance?
Are you saying that there is some lower limit of selection? If so, what mechanism could possibly cause that? Even if the genetic cause was secondary or weak, wouldn't selection scenerios still be relevant (though I agree that just-so stories aren't worth much without some way to empirically test them)?
John Pieret says,
Well, I'm at a loss. If it is physiological, even if only in part, how can it be without some heritable genetic component?
Because not all physiological effects have genetic components. To take a simple example, human development is affected by how many children a woman has had previously and whether they were boys of girls. It's also affected by the presence of a twin brother or sister in the womb. The age of the mother has an effect.
Furthermore, there's a certain amount of sloppiness in all biological effects. It's simply not true that the exact amount of a hormone that's produced in an individual is precisely controlled by your genes.
For example, if sexual orientation was developmental, due to hormonal influences in the womb, say, wouldn't that still be due, at least in part, to the mother's genetic inheritance?
No, not necessarily. It could, for example, be due to what she's had to eat or her overall health.
Are you saying that there is some lower limit of selection?
Of course there is. Below some lower limit, natural selection becomes ineffective.
If so, what mechanism could possibly cause that?
Cause what? An insignificant selection coefficient?
Even if the genetic cause was secondary or weak, wouldn't selection scenerios still be relevant (though I agree that just-so stories aren't worth much without some way to empirically test them)?
If there's a genetic cause and if the allele has a measurable selection coefficient so that it exerts an influence of the survival of the individual, then heterosexuality and/or homosexuality genes might be adaptive.
Because not all physiological effects have genetic components.
You mean that those influences map one-on-one to observable effects? If not, how do you know there is no genetic factor involved?
Below some lower limit, natural selection becomes ineffective.
And you know that is not the result of multiple selection factors how? Just because the overall effect is small or neutral, does that mean selection isn't occurring? Isn't dismissing the possibility of selection because of supposed "ineffectiveness" just as much a just-so story in the absence of empiric testing?
Cause what? An insignificant selection coefficient?
Why yes. What goes into selection coefficients except selection? If exclusive homosexuality logically should have some negative effect on subsequent reproductive success, wouldn't one possible explanation of an insignificant selection coefficient for that trait be that there is selection in its favor in some other, non-obvious way?
When I said that natural selection is ineffective below some minimum selective coefficient, John Pieret asked,
And you know that is not the result of multiple selection factors how? Just because the overall effect is small or neutral, does that mean selection isn't occurring? Isn't dismissing the possibility of selection because of supposed "ineffectiveness" just as much a just-so story in the absence of empiric testing?
John, John, John, as usual you are mixing up generalities and particulars. Do you do it on purpose?
The idea that natural selection is indistinguishable from random genetic drift at low values of s (selection coefficient) is an integral part of population genetics and nearly neutral theory. That's all I was saying in response to your earlier question. It wasn't directly related to any gene (allele) for heterosexuality or homosexuality.
I am not dismissing the possibility of selection. I'm just saying that there doesn't seem to be any strong evidence to support it. That's why making up "just-so" stories about adaptation is so silly.
Expressing skepticism about adaptationist just-so stories is not the same as making up one yourself. That's the part you don't seem to understand.
Is it just a "lifestyle" choice then?
... just to clarify, no, I absolutely don't think that, either. And it excludes other possibilities, it seems to me, suggesting saying sexual preference not particularly heritable means as much, methinks.
... actually, tho', in fairness, 'not especially heritable' isn't that good a description of what the evidence is saying, either, looking again at the papers more closely. Mea culpe. I'd now go with: probably heritable as a predisposition, but the significance of the predisposition in determining final preference is probably small.
To expand, I know about two things about this:
i) I know there have been several twin studies on heritability of sexual orientation. They've differed in their results, general opinion is: we need better, bigger, more random studies to draw more solid conclusions. Some showed some pretty strong heritability, but they were smallish, and not very random. The largest (see paper to follow) showed much less correlation between genetic similarity and similar sexual preference, and an intriguing difference between men and women: correlation was stronger in the males. For a review, see Bearman and Bruckner 2002 ... at this link (PDF). General conclusion: there's a heritable component, but that's only a very small part of the picture; 'social influences' play a substantial role.
ii) I know there's a 2002 peer-reviewed study that says so-called 'reparative therapy' (attempts to reduce homosexual desire through conditioning) fails at an incredible rate (Shidlo et al, Sexual conversion therapy: ethical, clinical, and research perspectives, Hawthorne Press, 2002).
... which, generally confirms the testimony of gays themselves, which generally is: even if they wanted to change, even if they thought they should (and no, just for the record, I absolutely don't think they should, either), they couldn't anyway.
(And though this is anecodtal/personal, I buy that. Entirely. Again, just speaking as a layman, it seems rather what you'd expect. Because I'm pretty sure I can't just 'choose' to stop being attracted to women, either.)
Anyway: putting these two things together:
i) Sexual preference probably is probably partially about heritability, though there is work to do. Looks like probably you can inherit some predisposition toward one preference or the other, but it's far from determining anything entirely. Non-genetic factors appear to play a substantial role. Putting it even more generally: yes, as PZ puts it, genetics does not entirely determine who you fall in love with.
ii) However, regardless, preference fixes extremely firmly, once it's set up.
(This, I might add, I'd say as a layman, also doesn't seem surprising. A lot of stuff about sexuality seems to fix pretty hard. Note that I'm absolutely *NOT* saying sexual preference is 'fetish' by this, but we also know: a lot of fetishes are also pretty hard to deprogram. Some of them seem to set up pretty hard, too.)
Anyway, so no. It's absolutely *NOT* a lifestyle choice. That much, at least, is bullshit, no question, probably mostly from beknighted superstitious types who'd like to call homosexuality (and, usually, for that matter, most other types of sexuality) a sin.
Getting back to the evolutionary question: actually, I'm not sure how much this has to do with needing or not needing an 'explanation' for why that predisposition might have evolved. Again, I still buy PZ's explanation as plausible at least: that there could be side-effects of sharing a genome between the sexes. So you probably wouldn't expect to find a selective pressure 'for' homosexual behaviour, exactly.
Actually, I'd go one incredibly hazy conjecture past that, though: it really seems to me that the sorts of mutational genetic change that would change this: make men only want women, and women only want men, and which you'd think natural selection would grab and fix through the population awfully quickly, due to the obvious advantage in terms of improving reproductive rates, it just doesn't seem to me such a development is even likely to be possible, from where we are now, really. Human brains just aren't much like that. I'd be frankly amazed if there was some especially simple way you could easily make them that way through small changes, and major changes that *did* make them so would seem to me likely to change so much else of what it is about the brain that's to our advantage: its essential plasticity, again, in particular.
John, John, John, as usual you are mixing up generalities and particulars. Do you do it on purpose?
Hell no ... I come by my ignorance honestly and I'm proud of it.
I am not dismissing the possibility of selection. I'm just saying that there doesn't seem to be any strong evidence to support it. That's why making up "just-so" stories about adaptation is so silly.
Of course it is ... unless they are treated as hypotheses to actually test. Still, saying that you don't believe that an adaptationist or even an evolutionary explanation is needed is a bit more than saying that just-so stories are superfluous.
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