Determining genetic influence on sexuality

Let me cut this off right now. As interesting as I might find the topic of homosexuals in the military, it has nothing to do with whether genes influence sexuality.I would be happy for you to start a thread on the other subject as you are wrong and your quote from congress means nothing... but I suspect you already know this.I might end up being almost on your side here, let's keep it that way.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

Hey, no problem. I was just responding!

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That review I mentioned says 2-5% of males and 1-2% of females are "exclusively homosexual". It's a review though, and they don't show their data.

Yes, that is unfortunately the case. Unfortunately the papers they cite for their statement that sexuality in men is largely bimodal are unavailable for me so I can't check their validity.Overall it is a (quite long) review of the understanding of genetics in sexual orientation and some of the hypotheses as to how it evolved.They first cover the evidence for genetics in sexual orientation - familial clustering and twin studies in particular. They then go on to say that these suffer from ascertainment bias - most of the twins were recruited primarily through gay organisations and word-of-mouth, and that a more rigorous study found concordance rates of about 30%. Either way this is still significant (similar figures are found for type 1 diabetes, for instance).The authors point out several other traits that are correlated with homosexuality in men - increased chance of left-handedness, different ring-finger to index-finger length ratios as well as a lot of other traits: The authors then cover several theories as to the evolution of homosexuality - kin selection, parental selection, balanced polymorphism and same-sex affiliation. The authors are most in favour of the last one - essentially that homosexuality is an extreme form of genes evolved for same-sex affiliation to reduce violence between males or increase female aggression to aid offspring care.

I brought up the military question as part of a discussion on whether there was genetic selection for homosexuality because it could enhance same sex bonding of say - a military unit. It did digress after that but the original reference was very much on topic.

I'm not sure if you caught Mammuthus's post in the other thread to Wikipedia's entry on Genetics and sexual orientation. It had an interesting discussion regarding the issues involved with the research (including what you mentioned above).This seems rather problematic, not the least of which this does not rule out tertiary connection between genes and orientation. For example that the genes are involved with ability to process societal norms, and thus those with a "rebel" gene might ignore or actively choose opposite sexual norms, and those with "conformist" genes would end up strictly following sexual norms. Thus the genes interact with the social environment.I mention again the anthropological evidence of the tribe where homosexual sex is the norm, except for procreation purposes, because of myths regarding loss of male potency when having sex with women. Without my hands on the actual studies I can't say anything about them. However I will note that this seems dangerously close to "phrenological" or "atavism" in its approach. Frankly I am looking at the work Bailey is listed as doing here, and in connection with the problematic study above, makes me seriously question how much to trust these results without further investigation.This is not to dismiss your cites. I thank you for them and hopefully they'll give me a foothold on some of the research.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

While this is certainly a possibility, I'd have to argue for parsimony here. If there is a genetic influence on sexual orientation it is simpler to assume a direct relationship rather than a tertiary one. Not necessarily correct, but in absence of any evidence to the contrary I'd go with that. That is interesting, I hadn't heard of that. Just goes to show how social factors can play a role. I wonder though - if that myth was dispelled, and they knew there would be no loss of potency, whether they would remain like that. I think this may be a distinction between the action and the attraction - I dare say in countries such as Iran, where homosexuality is punishable by death, there are people who would be considered "gay" otherwise but are essentially heterosexual in practice to avoid punishment. The assumption here is that both handedness and finger lengths are correlated with foetal hormone exposure. The Wikipedia article notes foetal hormone exposure has been postulated as a possible environmental influence - and this would also fit in nicely with the increased concordance rates between MZ twins versus non-twin siblings (ie. they share the same womb and so are exposed to the same hormones).As far as I can see there is not very much solid data on this issue. What we do have says that:
a) Sexual orientation is not 100% genetic (or at least not completely penetrant)
b) Homosexuality does show familial clustering (whether due to shared genetics or shared environment is arguable)

Well the problem, the way I see it, comes from very real societal/anthropological evidence. Given that societies seemingly depart from what would be seen in a genetic driven model, it is hard to accept a direct correlation outright.To add to the tribe example, I just got done watching a documentary on sex in Greece, which showed that bisexuality tilted toward homosexuality in males was dominant within Greece for a century or more until changes in social customs allowed female equality and therefore sexuality to be better noticed by men.Now its hard to believe that the society of Greece was having massive genetic changes on a population level, especially given the restrictive nature placed on having children. Excellent question. Maybe it was in the other thread, but I have said that personally that is what I feel is a greater, plausible, factor. Genes seem so remote to me, compared to gestational chemical, and developmental social, environments. Agreed though I would rephrase b to be "preliminary evidence suggests" family clustering.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

Just to clarify - I certainly don't believe there is any one factor we can put our finger on and say "that is what causes homosexuality". Humans are just too complex, particularly with behavioural traits. Sexual orientation is, I believe, a complex human trait with influence from both genetic and environmental factors. That certainly does show that culture can have a huge impact on the actual sexual actions taken by individuals. A similar example could be made of the apparent increase in homosexuality in the last few hundred years - but I believe that this is merely due to increased societal acceptance rather than any change in the frequency of homosexual attraction. But that is just a personal opinion, I don't have any data to back that up. It's more of a gut feeling, really. Unfortunately we probably don't have any data about how people felt back then, just how they acted.On hormone exposure in the womb - you do have the increased correlation in DZ vs non-twins, but you also have an increase in MZ vs DZ twins. The only difference I can see here is that the MZ twins share more genes. Now these two factors could be related - there may be genetic "susceptibility" factors which, when combined with the right uterine environment, give a shunt towards homosexuality.Either way, I think you're right in that it is difficult to explain the anthropological evidence using genetics.

Sorry to break into the discussion in-progress - Holmes directed me to this thread to discuss further my source in claiming that there is a genetic component to sexual orientation.In the previous thread, I referenced a study in which fruit flies exhibited the exact same mating behavior as flies of the opposite gender when a single gene was changed. My original source was a news article, but here is the study itself: LinkAnd here is the Abstract of the paper:

quote:

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Sexual orientation and courtship behavior in Drosophila are regulated by fruitless (fru), the first gene in a branch of the sex-determination hierarchy functioning specifically in the central nervous system (CNS). The phenotypes of new fru mutants encompass nearly all aspects of male sexual behavior. Alternative splicing of fru transcripts produces sex-specific proteins belonging to the BTB-ZF family of transcriptional regulators. The sex-specific fru products are produced in only about 500 of the 105 neurons that comprise the CNS. The properties of neurons expressing these fru products suggest that fru specifies the fates or activities of neurons that carry out higher order control functions to elicit and coordinate the activities comprising male courtship behavior.

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A copy of the news article I first read can be found here.I am not claiming, as Tal has represented me, that a single gene will alter human sexuality, or that genetics are the sole determining factor in human sexual orientation. What I AM claiming is that this study shows that genetics are a factor.The female flies whose genes had been altered showed exactly the same behavior as male fruit flies, right down to the complex mating steps and partner selection (ie, they tried to mate with other females as if they were male).I don't see how this could mean anything other than proving that genetics play a role (though they are by no means the only factor) in determining sexual orientation.The FULL text of the paper can be found here.

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Every time a fundy breaks the laws of thermodynamics, Schroedinger probably kills his cat.

Let me apologize at this point. I had not been following the other thread carefully enough. I saw somebody refer to Tal's position and where it was generated (yet another thread which this thread came from), and when you commented about your article, I had made the assumption that it was the one from which Tal had based his opinion.Assumption in this case certainly made an ass out of me, but not you.Your article is much more directed than the one I had been addressing. It seems interesting and I will peruse it and the rather extensive supporting documentation over the next couple of days. Like I said, I am still reading through this, but you must be careful how strong of an inference you can make from this research. That certain behavior is scripted in FFs does not suggest at all that this is true of other species' brains/CNSs. This is especially true when one looks at genes which effect both organs and specific male mating behavior beyond sex recognition.At best, this would indicate that the sexual behavior of FFs are linked to genes. The other links which have been posted (in the original "gay" thread where Tal got his gene zapping thing) mentioned that similar genes had not been found outside of FFs.In any case, I made a mistake in thinking I had read your link. I am now. Will return later.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

Okay, let me start by admitting that some of this was well beyond my knowledge base. I cannot argue competently on whether their methodology of cloning and testing was appropriate. I will give them the benefit of the doubt on those areas and deal with their discussion of what results they achieved, and how this is able to be compared.Actually, let me just let them say this themselves... This seems to suggest that environment can play significant and perhaps dominant roles, especially during development, but perhaps even afterward, of influencing sexual behavior. Hormonal environments during gestation appear increasingly significant.I realize that you were not suggesting genes were everying, and can include hormones, I just raise the point that there is a point where we should stop refering to genes as an influence, if they are rather insignificant to other factors. Ouch! But they do go on... Unfortunately this is not very helpful. None exclude and some in fact directly bring in hormonal environment, only suggesting that hormonal environments are genetically controlled. That misses the fact that it does not necessarily require the genes of the child, but rather the parent, as well as that other factors can control the hormonal environment. They also make reference, their fourth point, to studies which have been shown to be problematic elsewhere.The study is most interesting in showing that some complex instinctual behaviors are controlled by genes to some very large degree. The problem is moving it out beyond that result, to conclusions regarding sexual behavior of mammals in general. The fact that our brains have increased experiential components, which flies do only to a minor degree (which can still effect their sexual behavior) draws lines for experimental conclusions.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)