Like everyone with an Internet connection, earlier this month I heard a fair bit about U.S. 7th Circuit Court Judge Richard Posner’s ruling striking down bans on same-sex marriage in Indiana and Wisconsin. As Mark Joseph Stern put it at Slate, “Posner … sounds like a man who has listened to all the arguments against gay marriage, analyzed them cautiously and thoroughly, and found himself absolutely disgusted by their sophistry and rank bigotry.” Here’s a choice sample from the full opinion:
The challenged laws discriminate against a minority defined by an immutable characteristic, and the only rationale that the states put forth with any conviction—that same-sex couples and their children don’t need marriage because same-sex couples can’t produce children, intended or unintended—is so full of holes that it cannot be taken seriously.
What I hadn’t heard before is that Posner’s opinion also includes a short run-down on research about the biological basis of sexual orientation, and it has more than one familiar citation:
Although it seems paradoxical to suggest that homosexuality could have a genetic origin, given that homosexual sex is non-procreative, homosexuality may, like menopause, by reducing procreation by some members of society free them to provide child-caring assistance to their procreative relatives… There are other genetic theories of such attraction as well. See, e.g., Nathan W. Bailey and Marlene Zuk, “Same-Sex Sexual Behavior and Evolution,” forthcoming in Trends in Ecology and Evolution…
That’s actually a reference to a 2009 review, which is online in PDF format—it covers the diversity of same-sex sexual behaviors across the animal kingdom. It hardly mentions Homo sapiens, but it is one of the sources I give to people who want a solid introduction to current scientific thinking about how same-sex attraction could have evolved. If you ask me, one could do a lot worse than having a paper cited in a groundbreaking legal ruling. And it’s a reminder to those of us studying the history of life in general that our work can have unexpected consequences beyond the lab.
So, I’ve already announced this in other venues, but, what the heck: I’m collaborating on a new survey of lesbian, gay, bisexual, and trans* folks working in science, technology, engineering, and mathematics (STEM) fields. If that describes you, my collaborator and I would really like you to answer some questions. It’s all anonymous (unless you volunteer for a followup interview), and it’ll help fill a real gap in our understanding.
John Corvino, the chair of the Philosophy Department at Wayne State University, has recently published a book, What’s Wrong With Homosexuality, which systematically knocks down objections to the equality of LGBTQ folks. He’s been discussing major points from the book in a series of clever and widely-circulated videos, and I just recently discovered that, in an episode about the biological basis of sexual orientation, he talks about that review article proposing a possible epigenetic basis for sexual orientation that I discussed here a few months ago.
Full disclosure: I found Corvino’s post, actually, because he linked to my piece about the epigenetics paper, and he did so while paying it what I consider the highest compliment it’s possible to pay a science blogger: “A nice explanation of the paper can be found here.” Which: look at me blushing.
But Corvino comes at the question from a somewhat different angle than a biologist: he says it really doesn’t matter whether there’s an inborn basis to sexual orientation.
In the light of much of what we know about evolution, human homosexuality doesn’t make a lot of sense. Available data suggests that sexual orientation has some inborn, probably genetic, basis. But it’s hard to reconcile that with the fact that gay men and lesbians aren’t, by definition, particularly interested in doing what it takes to pass on any genes that might have contributed to creating their orientation. Natural selection is, all things being equal, pretty good at eliminating genes that make people less likely to make babies.
I’m gay. I’m also an evolutionary biologist. You could say this particular puzzle is tailor-made to attract my interest.
It turns out that there are a number of ways that human populations might accommodate gene variants for same-sex attraction without suspending the rules of natural selection. But it’s also possible that human sexual orientation has a biological basis without being genetic. Natural selection can’t do anything about a trait if variation in that trait isn’t linked to variation at the genetic level. So I was immediately interested by the recent announcement that a team of biologists at NIMBioS, the National Institute for Mathematical and Biological Synthesis, had found that human homosexuality is due not to genetics, but to epigenetics.
However, as soon as I secured a copy of the study itself (available in PDF format here), I was disappointed to find out that the reports of a solution to this particular evolutionary enigma are somewhat exaggerated. The paper doesn’t present any new data that directly links a specific developmental process to human sexual orientation — it’s a review article, gathering existing results in support of a hypothesis that isn’t, at its most basic level, entirely new. But it’s not the job of a review article to present new data; reviews are supposed to gather up what is already known on a topic and identify what new research could do to better answer the questions that remain. And that’s exactly what the new study does.