In February, the world of genetics news was inundated with “gay gene” headlines. At the annual American Association for the Advancement of Science meeting in Chicago, John Michael Bailey of Northwestern University presented findings that confirmed the heritability of male homosexuality—not a biologically shocking conclusion but one that sent unsettling ripples across the political spectrum. There was a disturbing trend by some writers, however, to catastrophize the results as fuel for the intolerant fire. If there’s a “gay gene” (which Bailey did not find nor claim to find) then what’s to stop a sterilization campaign against gay people?
I wrote about the blowback for the GLP during the flurry of headlines, but a recent post from Geneticist Kevin Mitchell of Trinity College, Dublin, at his blog Wiring the Brain has prompted me to revisit the topic. He articulates several points that I had neglected. Mitchell starts by emphasizing the fact that sexual preference is one of the most strongly genetically determined aspects of behavior we know of:
A single genetic element is responsible for most of the variation in this trait across the population. Nearly all (>95%) of the people who inherit this element are sexually attracted to females, while about the same proportion of people who do not inherit it are attracted to males.
But he’s not talking about any specific “gay gene”. He’s talking about the Y chromosome. The specific proportions really don’t matter: the point is that the piece of our genomes that determines our sex is strongly linked to our sexual preference. To accept his point you only need to accept that there are markedly more straight people in the overall population than gay people, a point which no one is arguing.
It would seem there is one case in which we already accept a strong genetic component to sexuality, but what Mitchell clarifies is the difference between sexual preference and sexual orientation: We are able to talk about preference without a socio-political explosion but orientation is extremely touchy.
In brief: Preference is whether you are attracted to males or females. Orientation is preference in relation to the Y chromosome (or, for simplicity’s sake “biological sex”). For the purposes of discussion, Mitchell breaks orientation down into four categories: men attracted to women; men attracted to men; women attracted to men; and women attracted to women. (Note: he immediately acknowledges that “this ignores the many individuals whose sexual preferences are not so exclusive or rigid.”)
Bailey was studying the heritability of orientation. He made two major claims: orientation is moderately heritable; and there are regions of the Y chromosome that seem to influence the development of sexual orientation in men. The first conclusion only serves, writes Mitchell, to “confirm and extend findings from multiple previous twin studies across several different countries, which have all found fairly similar results.”
The second is fascinating from a genetics perspective but isn’t quite the “gay gene” finding several reports touted (as I noted in my earlier piece). It’s also a relatively small piece of the orientation puzzle because there are differences in the heritability of orientation between males and females. In other words, there’s no universal path to homosexuality across all people.
Here is Mitchell’s hammer dropping: “Sexual orientation in males and females is influenced by distinct sets of genetic variants” and this “leads to a fundamental insight: heterosexuality is not a single default state.” (Emphasis mine.)
The complex pathways that align the human brain and body to produce heterosexuality or homosexuality are different for men and women and thus may involve a variety of different genes in which variation will influence sexual orientation. The development of heterosexuality is as much a process as the development of homosexuality, and just because one is more common in the population doesn’t necessary make it good or natural. (We’ll get back to that in a moment.)
Mitchell makes one further point about the difference between “heritable” and “innate.” The fact that orientation is “only partly heritable does not at all undermine the conclusion that it is a completely biological trait.” He uses handedness as an analogy: left-handedness is only moderately heritable but it is completely innate and intrinsic to an individual. They have no “choice” in their handedness.
Though some may try to twist the science so that a gap in heritability is “evidence” that homosexuality is a choice, they’d be in the wrong. And as far as going in the other direction and taking homosexuality’s innateness and using it to create a “disorder” out of it, I’ll let Mitchell’s conclusion stand on its own:
Concerns that these findings could be used as justification for labelling homosexuality a disorder … are probably somewhat justified – no doubt some people will use it like that. And that places a responsibility on geneticists to explain that just because something is caused by genetic variants – i.e., mutations – does not mean it necessarily should be considered a disorder. We don’t consider red hair a disorder, or blue eyes, or pale skin, or – any longer – left-handedness…
Homosexuality is only a disorder if society makes it one.
Read Kevin Mitchell’s original post at his Wiring the Brain blog: “Gay genes? Yeah, but no, well kind of… but, so what?”
Kenrick Vezina is Gene-ius Editor for the Genetic Literacy Project and a freelance science writer, educator, and amateur naturalist based in the Greater Boston area.
Additional Resources:
- “Is “reductionism” in behavioral genetics a boon or curse?,” Kenrick Vezina | Genetic Literacy Project
- “Gay people are not genetic aberrations,” Nick Cohen | The Guardian
- “There’s nothing wrong with looking for ‘gay genes’,” Tom Chivers | The Telegraph
