An American study has found new evidence that male homosexuality is influenced by genes – but environmental and social factors also play a role.

In the study, which was presented at a Science of Sex and Attraction event in Chicago, scientists tested the DNA of more 400 sets of gay brothers and their heterosexual relatives, to find out if some men are predisposed to being gay.

Genetic factors account for between 30 per cent and 40 per cent of what decides whether a man is gay or straight, according to the research.

Scientists found that a region of the X chromosome Xq28 had an impact on male sexuality, as did a stretch of DNA on chromosome 8.

Dr Michael Bailey, of Northwestern University, Illinois, who col-led the study said: “Sexual orientation has nothing to do with choice. Our findings suggest there may be genes at play – we found evidence for two sets that affect whether a man is gay or straight.

“But it is not completely determinative; there are certainly other environmental factors involved.”

The work has not yet been published, but it builds on a previous study carried out in 1993 by Dr Dean Hamer from the US National Cancer Institute, who also found that gay men shared genetic signatures on the X chromosome.

However, the findings of the study raise the prospect of a genetic test that could be used to determine a bay’s sexual orientation in the womb.

http://www.independent.co.uk/news/world ... 27683.html

So other 60-70% is environment or what?

the_5th_ape wrote:

However, the findings of the study raise the prospect of a genetic test that could be used to determine a bay’s sexual orientation in the womb.

Can't wait for that one. I'm sure it'll be used responsibly.

I would be very surprised if sexuality in general does not have some epigenetic input as well.

I have long thought, and this suports it, that since SEXUALITY is a complicated, multi-faceted namje tag for a very wide spectrum of sometimes only partially related things, that no SINGLE set of genes will be found to explain sexual orientation.

I noticed, again long ago, that although we apply only a handful of labels to human sexual orientation, that in reality, there are potentially hundreds of categories.

Classically, someone who doesn't have sex with ANYONE, EVER, gets listed as being Heterosexual. As does someone who finds their own gender repulsive, and rapes and murders the opposite gender.

I know in my own direct experience, that I can find someone visually stunning, but have zero attraction to them, owning to how they move, or how they talk, or how they smell, and so on.

I have personally known people who behaved outwardly as though they were classic homosexuals (males who spoke in "gay" tones, and carried themselves physically as though they were wearing high heals all the time), but who were nevertheless 100% heterosexual in their hungers for intimacy, and found other men to be disgusting. That sort of thing.

Therefore, the idea that a gene here and there can be found to be common to 60% of gay people sounds about right. I would bet that it takes dozens of genes, all set to the "right" direction, for a person to be 100% anything.

As for the influence of environment, I have some doubts. I have again directly witnessed, that some behaviors occur no matter what the environment of the human is. The odd speech pattern of the classic "queenish" sort of gay male, for example (I don't know any way to describe it that doesn't sound as though I am a gay-basher, and welcome suggestions) , turns up entirely by itself, at an early age, no matter where a kid grows up. Clearly, if environment had any real power to it, no homosexual behaviors or characteristics would appear anywhere that such were disapproved of, but they happen everywhere, including in cases where twins are one gay and one straight.

I am convinced therefore that duh, yes of COURSE sexuality is genetically determined. Because it's so complicated, no, you wont find a single chromosome pair to blame it on.

Environment will ultimately be found to have two basic influences: one, how an organism is fed and grows biologically, will result in various existing qualities being enhanced or damaged; and two, oppression or encouragement will cause an organism to reveal, or to try to hide their natural desires, more or less.

Genes clearly affect morphology, I see no good reason why they can't canalize behaviors as well. By "canalise" I mean to create probably tendencies in behavours, and of course many of these effects are indirect. Morphologies certainly seem to canalize behavior in the sense I have described it. Male dung beetles can either hornless gracile or horned, and this seems to prompt different sexual strategies based on such morphologies. The gracile is not overtly aggressive for example, and prefers to avoid combat with other males and sneak past the horned male defenses.
Simple birth order is an empirical indicator of behaviour on the heterosexual/homosexual spectrum in humans, at least for males. So "environmental" influences include hormone interactions between the male offspring and their mother. Like intelligence or mental well-being, sexual orientation is a complex trait. Therefore it is not surprising that genetic influences are "fuzzy", IMHO.
What we do know is that there are windows in development that open and close quickly, and so any genetic potential to express X is locked out if the environmental stimulus is missing during that time window. perhaps this is another reason why there is no straightforward relationship between genes and complex traits.
Once sex has been determined, the fuzziness generally fades. However, even fruit flies are capable of novel behaviors with a mere 10,000 neurons. I see no good reason why we should expect behavioral phenotypes to match genotypes. In short, there are probably multiple causes for behaviors in the heterosexual, bisexual, homosexual spectrum. Indeed, i imagine that the last is not a linear spectrum but probably multidimensional.
But nature, nurture or both, I do agree that such behaviors, once established, are solidly held and thus not changeable by religiously motivated attempts to modify behaviours to please gods.

What's interesting is that homophobia is almost certainly significantly more genetic than male homosexuality:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2292426/

Which actually makes excellent evolutionary sense.

I thought homophobia was usually the product of religious belief or repressed homosexuality. Not genetics.

trogs wrote:What's interesting is that homophobia is almost certainly significantly more genetic than male homosexuality:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2292426/

Which actually makes excellent evolutionary sense.

Why does homophobia make evolutionary sense? I imagine I might just have too limited imagination to come up with scenarios where homophobes on average get more offspring than non-homophobes. I would love to hear what mechanism would account for this!

One possible mechanism would be that a homophobe might reasonably be said to be less likely to experiment in the hot tub with Randy Marsh. If you don't try it there's no chance of you preferring it and so more chance you'll stick with the more...erm...generative erotic passtimes.

Darwinsbulldog wrote:I would be very surprised if sexuality in general does not have some epigenetic input as well.

I fully agree, and I'm pretty sure that it's absolutely essential.

If nothing else, that poor little Y chromosome is overworked as it is. It's amazing that it can even manage the gross physical difference between the sexes.

Zwaarddijk wrote:

trogs wrote:What's interesting is that homophobia is almost certainly significantly more genetic than male homosexuality:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2292426/

Which actually makes excellent evolutionary sense.

Why does homophobia make evolutionary sense? I imagine I might just have too limited imagination to come up with scenarios where homophobes on average get more offspring than non-homophobes. I would love to hear what mechanism would account for this!

Well, when we see heredity and selection, the only thing that we can know for certain is that it's genetic, but not why. It's all guesswork. All we know for sure is that twins separated at birth tend to have similar minds, we're not a blank slate. But, why is always guesswork.

But, it's not hard to imagine how homophobia might be advantageous in Sapiens. In a social ecosystem like that of the bonobo, homophobia probably would reduce reproductive success. But in a human ecosystem, with a higher/more dangerous STD load, and higher odds of homosexual behavior leading to aggression from men and/or shunning by women, homophobia might mean more kids.

This is probably a bit off topic, but following on from the quote at the bottom of the article, I'm reminded of an interesting Cafe-Sci lecture I went to a while back by a professor from the local uni. It was primarily about arguments for/against gay rights and how the arguments have been massively distracted by attempts to make the arguments be based on science.

While it may be valuable in terms of pure research, whether homosexuality is genetic/social or any ratio thereof is irrelevant to gay rights. - And the professor gave several historical examples where both scientific evidence suggesting causes were primarily social, and on other occasions scientific evidence suggesting causes were primarily genetic, was used to support judgements that homosexuality is unnatural, and wrong, and horrific practices of attempted correction, and on other occasions used to support arguments that it's natural and perfectly acceptable.

Ultimately, the current argument for gay rights that is quite widely used, - i.e. that homosexuals are genetically 'born this way' and are therefore deserving of equality rights, fails to address that even if the cause wasn't genetic they should still be deserving of equality rights. The actual balance of causes ought to be a matter that's purely academic, but all too often it's not.

minininja wrote:This is probably a bit off topic, but following on from the quote at the bottom of the article, I'm reminded of an interesting Cafe-Sci lecture I went to a while back by a professor from the local uni. It was primarily about arguments for/against gay rights and how the arguments have been massively distracted by attempts to make the arguments be based on science.

While it may be valuable in terms of pure research, whether homosexuality is genetic/social or any ratio thereof is irrelevant to gay rights. - And the professor gave several historical examples where both scientific evidence suggesting causes were primarily social, and on other occasions scientific evidence suggesting causes were primarily genetic, was used to support judgements that homosexuality is unnatural, and wrong, and horrific practices of attempted correction, and on other occasions used to support arguments that it's natural and perfectly acceptable.

Ultimately, the current argument for gay rights that is quite widely used, - i.e. that homosexuals are genetically 'born this way' and are therefore deserving of equality rights, fails to address that even if the cause wasn't genetic they should still be deserving of equality rights. The actual balance of causes ought to be a matter that's purely academic, but all too often it's not.

Right, the genetic determinist argument is deeply stupid, and deeply repulsive, even to me as a geneticist and bioinformatician. Rapists, pedophiles, and violent homophobes are at least equally "born that way", yet are perfectly capable of self-restraint, and perfectly punishable if they are unwilling to do so. The genetic-determinist "my genes did it" argument is viscerally disgusting to rational free thought.

On the other hand, your choice of which god to worship, which art to love, and which particular heterosexual partner to marry, is not genetic, yet we recognise that the sacredness of choice on these matters is among our highest principles. I'm the first to say that genetic determinism adds nothing to these principles, in fact can only detract from the responsibility and dignity of choice.

Homosexuals are perfectly capable of living a (miserable...) life without homosexual acts, many of them are even likely capable of learning to enjoy a heterosexual life. It's just that there's no good reason to.

trogs wrote:What's interesting is that homophobia is almost certainly significantly more genetic than male homosexuality:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2292426/

Which actually makes excellent evolutionary sense.

Good point and probably accurate.

On a similar note, behavioral sex characteristics are probably less genetic than is sexism. Which, unfortunately, makes it impossible to talk intelligently about sexism without getting called a bunch of names. Especially the people who claim most strenuously to oppose sexism have that wiring, particularly strong.

trogs wrote:

Zwaarddijk wrote:

trogs wrote:What's interesting is that homophobia is almost certainly significantly more genetic than male homosexuality:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2292426/

Which actually makes excellent evolutionary sense.

Why does homophobia make evolutionary sense? I imagine I might just have too limited imagination to come up with scenarios where homophobes on average get more offspring than non-homophobes. I would love to hear what mechanism would account for this!

Well, when we see heredity and selection, the only thing that we can know for certain is that it's genetic, but not why. It's all guesswork. All we know for sure is that twins separated at birth tend to have similar minds, we're not a blank slate. But, why is always guesswork.

But, it's not hard to imagine how homophobia might be advantageous in Sapiens. In a social ecosystem like that of the bonobo, homophobia probably would reduce reproductive success. But in a human ecosystem, with a higher/more dangerous STD load, and higher odds of homosexual behavior leading to aggression from men and/or shunning by women, homophobia might mean more kids.

Homosexuality =/= anal sex or STDs.

Thomas Eshuis wrote:

trogs wrote:

Zwaarddijk wrote:Homosexuality =/= anal sex or STDs.

http://www.ncbi.nlm.nih.gov/pubmed/6893897
It is what it is. Homosexuality = higher STD rate, currently.

trogs wrote:

Thomas Eshuis wrote:

trogs wrote:

Zwaarddijk wrote:
Why does homophobia make evolutionary sense? I imagine I might just have too limited imagination to come up with scenarios where homophobes on average get more offspring than non-homophobes. I would love to hear what mechanism would account for this!

Well, when we see heredity and selection, the only thing that we can know for certain is that it's genetic, but not why. It's all guesswork. All we know for sure is that twins separated at birth tend to have similar minds, we're not a blank slate. But, why is always guesswork.

But, it's not hard to imagine how homophobia might be advantageous in Sapiens. In a social ecosystem like that of the bonobo, homophobia probably would reduce reproductive success. But in a human ecosystem, with a higher/more dangerous STD load, and higher odds of homosexual behavior leading to aggression from men and/or shunning by women, homophobia might mean more kids.

Homosexuality =/= anal sex or STDs.

http://www.cdc.gov/std/life-stages-popu ... ct-msm.htm
http://www.ncbi.nlm.nih.gov/pubmed/6893897

Homosexuality is the attraction to the same sex, nothing more.
Not all homosexuals have anal sex.
Nor is anal sex between two men inherently more riskful than between a man and a woman.
You're making the same correlation-causation fallacy homophobes do.
It's non-monogamous, unprotected sex that increases the risk, not homosexuality itself.

You know which group has the highest rate of STDs?
African women. Does that prove that racism and sexism are evolutionary traits?

Also, going by your logic, lesbians have the least risk of STDs compared to boht gay men and straight people.
Kinda refutes the homophobia > evolutionary STD fear.