Much of my early work on sexual orientation focused on behavioral genetics. I did several twin and family studies, which suggested that both male and female homosexuality run in families, and that male and female sexual orientation are moderately (but far from completely) heritable. You can download the most recent twin study.
Like you see he suggests that sexual orientation is partly heritable.
Because identical (monozygotic, or MZ) twins are often discordant for homosexuality, environment must matter. It is important to realize, though, that "environmental" is not equivalent to "social." There can be biological causes of MZ twin differences. We hope to begin a study of discordant MZ twins (i.e., twin pairs with one homosexual and one heterosexual twin).
With collaborators Alan Sanders, Khytam Dawood, Elliot Gershon, and others, we have begun a genetic linkage study to try to replicate Dean Hamer's famous finding of linkage on chromosomal site Xq28, and to search for other linkage sites. This study will take several years, but we expect a definitive answer to the question whether there is linkage at Xq28.
Maybe it's something you can overcome... I'm curious to know if there are found some linkages in scientific literature.
Experiments that claim to ‘cure’ homosexual rams spark anger
quote:SCIENTISTS are conducting experiments to change the sexuality of “gay” sheep in a programme that critics fear could pave the way for breeding out homosexuality in humans.
The technique being developed by American researchers adjusts the hormonal balance in the brains of homosexual rams so that they are more inclined to mate with ewes.
It raises the prospect that pregnant women could one day be offered a treatment to reduce or eliminate the chance that their offspring will be homosexual. Experts say that, in theory, the “straightening” procedure on humans could be as simple as a hormone supplement for mothers-to-be, worn on the skin like an anti-smoking nicotine patch.
By the way, if you are an evolutionist, how do think homosexuality, if it is a normal condition, evolved as an adaptation that is beneficial to the propagation or survival of an individual's genetic traits?
The most convincing argument I have heard is social congruency. Homosexuality in a group of organisms increases the amount of care an empathy expressed in a group. A group that is more cohesive and cares for each other is more likely to survive. Therefore a group with homosexuality is more likely to survive than one without it. It's a pretty reasonable idea, as long as you are ok with group selection.
Note: this is only a hypothesis with no supporting evidence, though I'd imagine the evidence would be quite easy to collect. Look at two groups of organisms with different amounts of homosexualiy, and determine how their fitness differs.
The male-male behavior that is documented is "penis-fencing" - a rubbing behavior similar to female-female clitoris rubbing. Nor has this been documented as occurring after male-female sex the way the female-female rubbing is.
Nor is there documentation of fisting and other more esoterotic human behaviors.
The females seems to dominate and are more sexual than the males, which may be a crucial difference.
I think one thing to consider with the Bonobos, is that there is virtually no sexual selection because sex is shared so frequently and willingly, and this may have resulted in Bonobos being overall less fit than Chimps, thus explaining why there are one kind of Bonobos and three kinds of Chimps.
This would be kind of like our removal of a lot of natural selection through medicine, but without the benefit of the medicine.
RAZD, thanks for the info on evidence of gay bonobos behavior. Maybe I should ask if there are ANY observations of males of ANY species, other than humans, that have oral or anal sex with each other. The fact that human males do it may reflect some kind of perverse bottlenecking brought on by civilization. I'll hazard a guess that pre-civilized humans, in their tribal organizations, did not have gay sex, but I have nothing to support my speculation.
Given that dogs will lick themselves to masturbate (why? because they can ...) as well as sniff and lick each other, I don't think it is a difference in kind of behavior so much as a difference in degree.
... some kind of perverse bottlenecking brought on by civilization ...
Or like dog masturbation it is because we can do it and it feels good to those that like it.
I'm not sure that civilization has much to do with it, other than increasing the likelihood that people of like minds will find each other.
Or the effect of civilization has some hormonal effect we have yet to discern. We know that households of women living together have tended to caused the women to align their menstrual cycles to the same rhythm, so there could also be an effect on women in houses dominated by males (especially male children) to have a hormonal effect that influences the development of new male children.
Or it could be a build up of anti-bodies to male hormones from previous children developing in the womb and suffusing the mother with a surfeit of male hormones that her body objects to.
Setting aside Lesbians for a moment. I think homosexuality in human males arises from either nurturing influences or a natural predisposition, which would seem to be genetic. I don't think nurturing alone will do the trick—if nurturing encourages the gay gene to express itself, the trait is still genetically predisposed. If there is a gay gene on the Y chromosome or any where else I suppose scientists will locate it. Aferwards I expect them to learn how to turn it on and off. And after that being gay will be entirely a matter of choice.
Aferwards I expect them to learn how to turn it on and off. And after that being gay will be entirely a matter of choice.
Then we can attack the important issues, like being blond.
If there is a gay gene on the Y chromosome or any where else I suppose scientists will locate it.
I think it is affected by several locii not just one, and that these are susceptible to womb environmental factors during development, so "eliminating" the gene(s) won't necessarily eliminate the behavior.
Re: Experiments that claim to ‘cure’ homosexual rams spark anger
I can't help but relate this to the movie X-Men 3 The Last Stand.
Obviously. And for the same reason - xenophobia of what you don't understand. One of the great reasons for culture wars down through history eh? "They are different, therefore bad" has been one of the mainstays, and is particularly virulent in the religiuos culture wars where it becomes "They are different, therefore wrong, therefore evil, and evil must be wiped out" ...
It seems to me that if we are going to eliminate some genetic predisposition in people we could do well to start with one that has caused a lot of bloodshed and grief -- the "religious gene" -- and get rid of the religious wars.
I had heard that male-male ram behaviour included anal penetration, but I can't find the reference for that. But here is an article I did find (although because I'm not a student any more I can't look up the actual paper, but the title makes it fairly explicit).
Erwin, J. & Maple, T., 1976 Ambisexual behavior with male-male anal penetration in male rhesus monkeys. ARCH. SEXUAL BEHAV. 5(1): 9-14
One pair of male rhesus monkeys reared in the laboratory with exclusive social access to each other during their second year of life were observed to display reciprocal mounting with anal penetration on several occasions. Their mounts were of comparable duration to those which have been observed in matching heterosexual pairs, by contrast with the brief mounts which are often observed in dominance interactions. The postures exhibited by the mounted male resembled those typical of females during heterosexual coitus, while the mounting male displayed the species-typical male copulatory position. Each male at times assumed either role. Ejaculation was not documented during these male-male interactions, although it may have occurred. Both males performed adequately with familiar and unfamiliar females (including ejaculation), but a preference test demonstrated that these males preferred contact with one another to contact with a sexually receptive unfamiliar female. These males displayed an unusual amount of affectionate behavior (by contrast with other rhesus males) including extended periods of contact with embracing and grooming. It is suggested that the relationship between these males was primarily based on mutual affection, although a sexual component was unmistakably present.
I had heard that male-male ram behaviour included anal penetration, but I can't find the reference for that. But here is an article I did find (although because I'm not a student any more I can't look up the actual paper, but the title makes it fairly explicit). Erwin, J. & Maple, T., 1976 Ambisexual behavior with male-male anal penetration in male rhesus monkeys. ARCH. SEXUAL BEHAV. 5(1): 9-14.
Thanks. I've been curious about this, mainly bercause I was chasing an idea that civilization and its consequences of excess may account for such sexually deviant behavior. Given these occurances in other mammals I'd have to say the origin of gay behavior is genetic. I suspect that no amount of gay nurturing in a human male will cause him to become gay UNLESS he has gay genes.
That does seem to be pretty much the consensus among scientists, at least from what I have read.
You have to be careful though - there is strong evidence that environmental factors during gestation (hormone levels, for example) could play a role as well. The most likely answer is that there are multiple genetic loci that can affect the chance of a child being homosexual, as well as environmental influences - but it does appear that these environmental influences act at a very early stage, probably before birth.