Lots of (largely unjustified) journalistic fuss over that “gay gene” paper published last week. But here’s the reality, which the Associated Press’s Lindsay Tanner summed up best: “A large study of gay brothers adds to evidence that genes influence men’s chances of being homosexual, but the results aren’t strong enough to prove it.”
Let me unpack that for you. One reason to be intrigued by this study, published November 17 in the journal Psychological Medicine, is that it is the largest so far that has looked for genetic factors in male homosexuality, involving 409 pairs of gay brothers.
Another reason to pay attention is that the paper confirmed a much smaller study from 1993 that associated male homosexuality with a particular section of the X chromosome. Although the researchers set out to see if there was anything to that original study, they really didn’t expect to confirm it, according to one of them quoted by Kelly Servick at Science. The new study also confirmed hints in a 2005 paper of a region related to male homosexuality on chromosome 8.
One reason both the early X chromosome study and this one are particularly noteworthy is that they provide an explanation for an evolutionary puzzle about same-sex sex: if it’s partly genetic, why does it persist, since homosexuals have few children to pass on these genetic tendencies? (Remember that the various forms of assisted reproduction that make children more possible for gays than they used to be is quite a recent development. Even with ART, the gay male reproductive rate is still lower than the rate for heterosexual men.)
But if the genetic factor(s) for being sexually attracted to men lies on the X chromosome, that evolutionary question fades, for both cultural and genetic reasons. For one thing, homosexual men, having no family obligations of their own, are still in a position to help pass on their family genes by contributing to the upbringing of their nephews and nieces, their heterosexual siblings’ children. For another, women who inherit that X chromosome may be exceptionally attracted to men too, and may have more children as a result. At least one study has supported that idea. It found that women with homosexual brothers did have more children than others.
Caveats about this new study
And here are the howevers. Because they were trying to replicate the original 1993 study, the researchers used the same study methodology. That approach, known as linkage analysis, has long since been supplanted. In linkage analysis, researchers are trying to home in on an area of the genome that might influence a trait. But the area is big, containing many genes, perhaps hundreds of them. So it’s not helpful in figuring out just which genes might be involved.
Linkage studies have been replaced by a technique called genome-wide association studies (GWAS), which can identify particular candidate genes worthy of further examination. Which makes this the place to point out that, despite the headlines, scientists don’t ever expect to unearth a single “gay gene.” As Servick notes, twin and family studies have long suggested genetic factors in homosexuality, but researchers who accept those findings believe genetic predispositions interact with environmental factors in developing a person’s sexual orientation.
Another reason for caution: although the data in the new study showed a trend to being statistically significant, most of the numbers never really got there. One of the things that might mean is that the idea of genetic factors in male homosexuality is hogwash, a position with a good number of devotees, including some researchers.
But another thing it could mean is that this area of the X chromosome might figure in homosexual behavior in some men, but it is definitely not a universal explanation for same-sex sex. That would allow for other explanations that have been proposed, such as events in the womb. In short, sexual orientation could be the result of many factors, some genetic and some not, interacting in intricate ways that we have not yet fathomed. Accepting that lots of elements go into sexuality seems pretty reasonable to me, given that sexual behavior is nothing if not complicated.
Furthermore, this research involves male homosexuals only. It says absolutely nothing about female homosexuality or bisexual behavior, where genetic factors have hardly been studied at all. This is a point made in Samantha Allen’s skeptical piece at The Daily Beast; she claims that bisexuals account for half of the LGBT community.
( I suppose you could speculate that perhaps that interesting stretch of the X chromosome influences attraction to females. Males with that DNA might have more children than average and pass on more of the family genes, compensating for the low reproductive rate of their lesbian sisters. Let me emphasize: sheer speculation, with no supporting data that I know of.)
We may know more soon about what (if anything) about sexual orientation is going on on the X chromosome, and on chromosome 8 too. The same researchers, fully aware that there are now better tools for gene identification than linkage studies, have already launched a GWAS. It will include data from the men in the recent study and DNA from an additional 1,000 gay men.
Geneticist Razib Khan, the well-known blogger at Gene Expression, is confident that clarification will be forthcoming. “[A]at some point in the next ten years I’m pretty sure we’ll localize the genes which carry variants which do result in a higher than typical likelihood of an individual exhibiting homosexual orientation,” he predicts.
A minefield of ethical and policy issues
If Khan’s forecast comes to pass, what might be the policy outcomes for more precise explanations of how genes play a role in homosexuality?
Dean Hamer, who led the 1993 study of the X chromosome’s role in male homosexuality, thinks a biological answer to that question has been crucial for the speedy cultural acceptance of gays in the the past few years. In an opinion piece that appeared last July in The Scientist, he argued many surveys have shown that, “while most of those who believe that people are born gay agree that same-sex relations should remain legal, nearly 70 percent of people who believe it’s a choice think that antisodomy laws should be reinstated.” To make the point exceedingly personal, he noted that such people believe he himself should be in jail.
One of the authors of the new paper, Northwestern University psychologist Michael Bailey, agrees. “Pro-gay liberals tend to emphasize innate causes, and anti-gay conservatives “choice” and malleability,” he said in another July opinion piece at The Scientist. Samantha Allen, however, argues that acceptance is based mostly on whether a person knows someone who is gay. What matters, she says, is friendship, not belief that gays are “born that way.” She also insists that attitudes are changing among gay men and women, that they are becoming more comfortable in challenging the biological origin story.
Despite many years of research on sexual orientation, Bailey believes the influence of genes on sexual behavior is “modest.” He also says it’s possible this research could lead eventually to knowledge about how to change sexual orientation. Parents, he believes, would have the right to use that knowledge because shaping children is what parenthood is about. He declares, “Changing a baby’s future sexual orientation isn’t harming the baby.” I daresay some would challenge that notion. Loudly.
At the National Review, Wesley Smith wonders if genetic testing can be far behind discovery of genetic factors in sexual orientation. He is thinking especially of prenatal diagnosis and even applications in assisted reproduction, diagnosis of embryos before implanting them. He’s concerned about abortion for possible genetic tendencies toward homosexuality. But as long as we’re speculating, why not speculate about the opposite attitude: abortion for lack of these genetic tendencies, in an attempt make a homosexual child?
Discovery of genes involved in sexual orientation, if any, won’t put an end to these debates.
Tabitha M. Powledge is a long-time science journalist and a contributing columnist for the Genetic Literacy Project. She also writes On Science Blogs for the PLOS Blogs Network. Follow her @tamfecit.
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To be fair, this is a relatively exceptionally well written example of its type, but I still basically agree with “the idea of genetic factors in male homosexuality is hogwash”.
Human homosexuality is not unusual in nature, at all. In fact there are no known social animals which don’t show homosexual behaviours. http://www.amazon.co.uk/Biological-Exuberance-Homosexuality-Diversity-Stonewall/dp/031225377X Non-human animals who have a stable individual sexual ‘orientation’ and homosexual pair-bonding seem to be extremely rare, maybe some penguins, but homosexual *behaviours* are extremely common.
There are a bunch of evolutionary theories for why homosexual behaviours are maintained by selection (or at least not eliminated by selection), some of which are touched upon above.
Some of those evolutionary theories for why homosexual behaviours are so widespread in social animals, including humans, suggest that ‘homosexuality’ is extremely unlikely to be a single trait, but that homosexual behaviours can develop based on a partially overlapping but diverse range of general social and sexual flexible behavioural capacities in different individuals.
So the idea that you might find even a *region* of one chromosome with several gene complexes involved in development and intensity of homosexual behaviours would be a very unlikely hypothesis IF almost any of those evolutionary theories about why it’s maintained by selection were true. I’d expect development and intensity of homosexual behaviours to be based on a very wide range of social and sexual traits, maybe even *all* social and sexual behaviour traits can be involved.
Psychologists tend to be quite bad at recognising the risk that their independent variables might be just notional categories in our culture and not really clearly defined independent variables. I.e. Are we even really sure that “homosexuality” is a biological category and not primarily a cultural category that loosely fits a bunch of different behaviours in humans and other animals? Especially when you get to distinguishing bisexuality from homosexuality – how can you be so sure these are really different behavioural categories? Structure of the behaviour is the same and function of the behaviour may easily be the same, so what objective basis could there possibly be to define separate behavioural categories for ‘bisexuality’ and ‘homosexuality’?
Flexibility is the norm for social behaviours. Without meaning to invalidate anyone’s personal freedom to choose to ‘have’ an ‘orientation’, in non-human social animals without advanced cultural transmission of behaviours (such as the cultural category of ‘orientation’), discrete and fixed sexual orientations don’t seem to exist (except maybe penguins). It’s also interesting to wonder about why penguins are maybe a bit of an exception – what is it about their specific ecological niche which makes them more likely than other animals to develop an individually stable homosexual pair-bonding behavioural preference? Is there some general property of environments which makes evolving the capacity to develop more a more stable individual sexual ‘orientation’ or something like it more likely?
I recognise the political associations with preference for a nature or a nurture explanation, but I think they’re both confused about the question they’re trying to answer. I doubt the thing they’re trying to measure (sexual orientation) even really exists in the discrete stable way they’re looking for!
Are you equally sceptical of a heterosexual orientation rooted in genetics?
Would you consider heterosexuality a cultural construct?
Yes, and to the same extent as homosexuality yes. Exactly.
Homosexuality is present in other animals which shows a natural explanation. I agree there won’t be a single gene or chromosome explanation. Most likely it will be a combination of genes, evolutionary reasons, hormones and neuro-biochemistry. Basically nature just like heterosexuality. Everything can be reduced to the natural sciences is my bias though.
http://news.sciencemag.org/evolution/2012/12/homosexuality-may-start-womb
That’s what I was going say :-)
The overwhelming evidence from science shows that gender preference is primarily determined by our genetics and prenatal biochemistry, especially embryological hormone balance. Almost everyone is born attracted to members of the opposite sex. A small percentage — perhaps as few as one to two percent (but probably not as high as ten percent, as some estimates have put it) — are attracted to members of the same sex.
Asking a homosexual when he or she chose to become gay is like asking a heterosexual when he or she chose to become straight. The answer you will get (I know because I’ve asked) is “Uh? I didn’t choose. I’ve always felt that way.” And that’s the answer I get from straights as well as gays.
Getting from genetics and prenatal biochemistry to sexual orientations is a journey. There are cultural influences.
Before the emergence of a gay identity, there is lots of evidence of same-sex sexual activity.
The expression of it can sometimes be more paederastic, as in ancient Greek society, or with the bacha bazi phenomenon in Afghanistan today. In these cultures, misogyny makes women out to be of lesser value. These cultures sing the praises of beautiful boys, desire sex with them, but don’t identify as being gay.
Even in Greek times, if two men continued a relationship past when the younger began growing his beard, and they were considered equals, they brought down disapproval on themselves.
Also, your one or two percent estimate might be closer to the number of people who identify as being gay, but it seems to leave out the many people who admit to being bisexual. Since gay liberation, the number of people identifying as wholly gay probably hasn’t changed, but it does seem that there are many more people who can admit to some same-sex desire, even if they don’t go out of their way to act upon it.
So culture matters in how we understand ourselves.