It was only last week that I wrote about why it was necessary to remain sceptical about any research announcements supposedly identifying a genetic basis for homosexuality, so the timing of this report in Science could hardly be more exquisite.
Why are some people gay? Most researchers who study sexual orientation think that both genetic and environmental factors play a role, but the relative contributions of each remain unclear. A new study of Swedish twins reinforces earlier findings that environmental influences--including the environment in the womb--may play a greater role than genes.
Earlier twin studies of sexual orientation have suggested varying degrees of genetic and environmental influences. But they have suffered from the limitations typical of all twin studies. These include small sample sizes and assumptions that identical and fraternal twins both have the same family environments; if identical twins are treated more similarly by their parents than fraternal twins, for example, this could be mistaken for a genetic influence. Recruitment biases are also an issue: Some studies have enlisted participants who openly identify themselves as gay, who may not be typical of the entire homosexual population. To try to get around these problems, a team led by Niklas Langström, a psychiatrist at the Karolinska Institute in Stockholm, recruited subjects from the Swedish Twin Registry, the world's largest. All 43,808 twins born in Sweden between 1959 and 1985 were invited to participate in a Web-based survey that comprised a wide range of questions about personal behaviors and experiences. The team ended up with a sample of 3826 twin pairs, of which 2320 were identical and 1506 fraternal [...] The results, published online this month in the Archives of Sexual Behavior, confirm earlier findings that identical twins are more concordant for same-sex behaviors than fraternal twins are but only modestly so: In men, genetic effects appeared to explain 34% to 39% of the differences between the two twin groups, whereas in women, genetics accounted for only about 18% to 19% of the difference--a finding consistent with other research showing that sexual orientation in women is not as rigidly determined as it is in men.
But wait, there's more!
J. Michael Bailey, a psychologist at Northwestern University in Evanston, Illinois, who led earlier twin studies of sexual orientation, calls the new study "good, important, and one unlikely to be bettered in the near future." But Jonathan Beckwith, a geneticist at Harvard Medical School in Boston, says that the new work fails to overcome a number of problems faced by previous twin studies. He notes that the final sample included only 12% of the males in the Swedish registry, leaving open the possibility of recruitment bias. And Beckwith says that the failure to control for family environment could inflate estimates of genetic influence. (emph. added)
I've highlighted the final statement because the problem Beckwith notes is one which plagues all twin studies, including (most notoriously) those done in the name of IQ "research"; if anything, the 34-39% attributed to genetics* by this study is likely to be an overstatement rather than the opposite. In Sweden, at least, the evidence for homosexuality as something driven by genes is looking very shaky indeed.
For me, the real question isn't whether or not "gay genes" exist - given how easy it is to induce "straight" men to engage in homosexual activities, I strongly suspect that they do not, or that if they do exist, they explain only a minute proportion of homosexual acts - but why any of this should actually matter. Arguments for political rights which hinge on the genetic origin of sexual orientation seem entirely beside the point to me, seeing as many other rights which are taken for granted need resort to no such basis. One can join the Green Party or become a Mormon without having to explain one's actions as forced upon one by genetics, so why should sexual orientation not be the same?
The fundamental problem with all of the "born this way" rhetoric, and the reason why I have repeatedly revisited the issue, is that - apart from attempting to hijack science to serve a moral and political agenda - by phrasing the argument for gay rights as a concession to be made on behalf of an innately aberrant minority which cannot help its faulty wiring, it cedes far too much ground to the religious lunatics and busybodies who would like to tell everyone else what to do with their private lives. Why is that gay rights activitists are unable to see that there is something pathetic about asking for equal treatment on essentially the same basis as the disabled ask for special accommodations in public facilities? The whole business reeks to me of internalized homophobia: at heart, I'm convinced that a great many of those who favor "born this way" argumentation really do believe that gays are in some way inferior, which is why they are so blind to the implications of what they are saying.
*To be precise, this figure has to be a reference to the "heritability" of the trait, but as we all know by now, "heritability" is not the same as "genetic."