An August, 2007 study in Biological Psychology has come in under the radar. The study of twins provides some interesting findings of interest to discussions here. For now, I am going to post the abstract, discussion section and reference.
Abstract
We investigated the potential to engage in homosexual behavior in 6001 female and 3152 male twins and their siblings finding that 32.8% of the men and 65.4% of the women reported such potential ( p < 0.001). 91.5% of these men and 98.3% of these women reported no overt homosexual behavior during the preceding 12 months. The potential to engage in homosexual behavior was influenced by genetic effects for both men (37.4%) and women (46.4%) and these overlapped only partly with those for overt homosexual behavior.
Discussion
The results show, for the first time, prevalent potential for homosexual response in both men and women, even among individuals who do not report any overt homosexual behavior. Women reported more potential which is in accordance with previous findings showing that their sexual orientation may be more changeable (Kinnish et al., 2005). These results suggest that sexual identity, behavior and potential may often be quite disentangled as suggested by both Escoffier (2003) and Pathela et al. (2006). The phrasing of the question does not suggest that the homosexual sex would take place in the absence of possibilities for heterosexual sex, indicating that the responses refer to homosexual behavior by choice. Therefore, the concept of PHR should not be mixed with situational homosexuality occurring in all-male or all-female environments such as prisons.
PHR was also influenced by genes. These genetic effects overlapped only partly with overt homosexual behavior. Any alleles underlying the genetic effect on PHR should be relatively common and, therefore, also likely to have served some evolutionary purpose, such as limiting the aggressiveness of males and thereby making them more attractive to females (Miller, 2000). PHR was more prevalent among women, a result that is not in line with suggestions that the alleles influencing homosexuality would be predominantly linked to the X-chromosome (Hamer, 2002). It is also of interest to note that there was no evidence of any shared environmental effects on either phenotype. Such results suggest no role for neither intrauterine effects, arguing against hormonal theories of sexual orientation, nor for familial effects shared by all siblings to the same degree, arguing against simple parental personality or parenting style effects.
Conclusion
The results imply that we should rethink how the phenotype of homosexuality is defined. Finally, previous
psychological and genetic correlates of homosexual orientation may actually have more to do with why some people engage in homosexual behavior as opposed to being correlates of a potential to do so.
jag
I suppose I’m wondering why it matters why people are gay. If it is a choice or natural inclination – why does this matter at all?
I know that wthrockmorton.com is a values based site my core interest is the cause of SSA. For me at least the answer to that question answers nearly every other question I have.
And of course, we just don’t know yet.
Jag,
I’m of the belief that the only reason orientation is such a big deal, is because religion has made it a big deal.
Behaviors tend to be polygenic, meaning that there are more than one gene involved…and how these are expressed can vary from person to person. So, either way, you are not going to get 100% gay individuals even if a gay person was cloned and there is a genetic link. Even with things that are extremely genetic, like height, nutrition can contribute to its varied expression.
I suppose I’m wondering why it matters why people are gay. If it is a choice or natural inclination – why does this matter at all? It only matters if you see this behavior as bad or you wish to change it. Perhaps this is it?
In a world where our country does not have a theocracy, shouldn’t people have a choice? Isn’t that, in part, what this blog is about? Letting people have the choice who wish to challenge their same-sex attractions…but, if neutral, this sort of approach should swing both ways…can’t people have the right to just be gay?
I guess I’m not sure why it matters. Why not live life according to your own standards, let people live theirs according to theirs (you know, not a theocracy), and have rules that govern us all so that we do not harm each other or ourselves.
Seems okay to me.
Ken,
I’m not even sure about that – Again, it depends on what we mean by “openly” – I know some gay people, who say they are open, who might very well not label themselves as gay on a survey!
I’m pretty sure the 2-4% figure represents those that are openly gay.
jayhuck
I’ve read that in New York city about 10% of the adult, male population is gay. However that’s gotta be at the high end of the spectrum. 2% to 4% seems to be the number that floats around as a decent average which is why I picked 3%.
But realitistically, I dunno. Until scientists get some better tools we can’t know for sure.
Drowssap –
I would be curious to know how genes/socialization/child abuse/etc…. create Opposite Sex Attractions (OSAs) as well.
I’m also curious where you came up with the 3% of men figure? Especially since we still don’t, and may never have, a definitive percentage of people who are gay. The best I’ve seen is in a Wikipedia article that pulls several studies together to suggest that anywhere from 2% – 7% of the population is gay. Remember, any figure we DO have is probably an UNDER-REPRESENTATION of the true number, since people are likely not to report their true orientation if they are gay. Using the percentages above that means that anywhere from 6 – 21 million people in this country are homosexual.
Mary
Ther may be more than one kind of expression for SSA. I do believe it is part genetic and part environment. Some a little more to one side or the other.
I’m sure you are right. For most people SSA is probably the result of a few common gene/enviro combinations.
However I wouldn’t want to exclude either genes or socialization. I’m sure that a few people have SSA due exclusively to one or the other. When I was growing up in the 70s/80s people thought SSA was the result of child abuse. In fact thats probably true in some cases, but certainly not 3% of men.
Timothy Kincaid
My prediction: the sheep will be “gay” far more frequently than the regular 8% occurance rate but not 100%.
100% agreement on that one. If the average is 8% I’d guess that clones might be 2 or 3 times that likely to be gay. I wish I could go forward 5 or 10 years to find out.
Drowssap,
Ther may be more than one kind of expression for SSA. I do believe it is part genetic and part environment. Some a little more to one side or the other.
Drowssap
My prediction: the sheep will be “gay” far more frequently than the regular 8% occurance rate but not 100%.
As for my eyes, it’s a bit of a battle. I take drops to keep the pressures down and they more or less work. I have red irritated eyes for much of the time but that’s a small price to pay for keeping my vision. Thanks for asking 🙂
Mary
Timothy Kincaid
Regarding gene expression.
This one is going to get figured out, probably sooner than later. We can’t clone gay people, but we can certainly clone gay sheep. Somebody somewhere, maybe Dr. Roselli, will eventually clone a gay sheep.
If the clones are all gay, it’s settled. SSA is genetic.
If they clones are straight, it’s also settled. Genes may play a part but SSA is triggered by something in the environment.
… at least in sheep. But that will be close enough for me.
Timothy Kincaid
Though I don’t disagree with your initial point that a single gene is unlikely to cause orientation, I think this illustration may challenge rather than support that contention.
Lately when I re-read my posts I see that I’m not doing a solid job of expressing my opinions. (must be my eye)
What I actually meant to say was that 3%+/- of men are gay. Genes are certainly involved on some level. However these genes are probably present in 10 times that many people. So maybe 30% of of the male population has “gay” genes but only 3% of the population is “wired up” gay. That’s my official GUESS based on how genes typically work and the fact that if one identical twin is gay, the other twin is straight between 50% and 80% of the time.
I don’t think it’s going to be a situation where having a certain gene or gene cluster (expressed or not) automatically wires someone for SSA. My guess is that they’ll find considerable outside input. Hormones get a lot of attention but I think they are more of a marker that shows something has happened rather than a cause of SSA.
This is the best graph I’ve ever seen that makes that point.
Timothy Kincaid
Hi Tim,
I’m sorry to hear that you have Glaucoma. Is it both eyes? Is it treatable? I hope there is something that they can do for your type. There is MASSIVE research in the emerging field of tissue engineering. Hopefully in two or three decades they will be able to repair any damage that your eyes might suffer.
My right eye has been irritated for about 6 weeks. Nothing seems to help. Thats it, I’m getting it checked out.
The gene LOXL1 is present in approximately 25% of the population. People with this gene have a lifetime risk of Glaucoma that is over 100 times higher than the general popuation. 22% of the people with this gene develop Glaucoma while only 1.5% of people without this gene develop Glaucoma.
I think that perhaps you are using an example that is not applicable.
“Glaucoma” is a more general term used for a number of different conditions – their commonality being that they all cause a similar result, the increase of eye pressure.
If I understand correctly, LOXL1 is tied to Exfoliation Glaucoma, a buildup of fibers on the front surface of the eye. Interestingly, this is one of the few cases where virtually all instances of occurance are tied to a single gene, as opposed to multi-gene factors.
But to suggest that Glaucoma may occur without the presence of this gene may be missing the point. It misunderstands the inclusive nature of the term glaucoma.
My own case of glaucoma is probably not tied to LOXL1. I fall into the 1.5%. But I don’t have exfoliation glaucoma, I have pigmentary glaucoma. And though they share a name, they are very different things. My glaucoma results not from the breakoff of fibrous tissues but rather the flaking off of the eye’s pigments (literally, my eyes are changing color due to loss of pigment).
Though I don’t disagree with your initial point that a single gene is unlikely to cause orientation, I think this illustration may challenge rather than support that contention.
Need to look at epigenomes
PHR was more prevalent among women, a result that is not in line with suggestions that the alleles influencing homosexuality would be predominantly linked to the X-chromosome
I don’t quite understand this one. If the prevalance of PHR was more common in women wouldn’t we expect any genes involved to be X related?
You know, I’ll bet that once epigenetic studies start to flourish more we will begin to know a whole lot more about the variation in sexual/social make ups.
“Any alleles underlying the genetic effect on PHR should be relatively common and, therefore, also likely to have served some evolutionary purpose”
Exclusive SSA is present in about 3% of men. However any genes that increases the odds of SSA will likely be present in 10 times that many people. The next time a scientist makes an announcement that he has found the gene for something common (1% of the popuation or more) read the fine print. It rarely does anything more than increase susceptability to something that probably hasn’t been identified yet.
Example
The gene LOXL1 is present in approximately 25% of the population. People with this gene have a lifetime risk of Glaucoma that is over 100 times higher than the general popuation. 22% of the people with this gene develop Glaucoma while only 1.5% of people without this gene develop Glaucoma.
Admittedly SSA isn’t Glaucoma but since scientists aren’t narrowing in on a gene that creates a preference for apples over oranges I’ll have to stick to common disorders.