Pheromones and sexual orientation

A brain imaging study just published yesterday suggests that gay men's brains respond to putative pheromones similarly to straight women's brains, but differently from straight men's brains. Here's the NY Times' write-up:

The two chemicals in the study were a testosterone derivative produced in men's sweat and an estrogen-like compound in women's urine, both of which have long been suspected of being pheromones.

Most odors cause specific smell-related regions of the human brain to light up when visualized by a form of brain imaging that tracks blood flow in the brain and therefore, by inference, sites where neurons are active. Several years ago, Dr. Savic and colleagues showed that the two chemicals activated the brain in a quite different way from ordinary scents.

The estrogen-like compound, though it activated the usual smell-related regions in women, lighted up the hypothalamus in men. This is a region in the central base of the brain that governs sexual behavior and, through its control of the pituitary gland lying just beneath it, the hormonal state of the body.

The male sweat chemical, on the other hand, did just the opposite; it activated mostly the hypothalamus in women and the smell-related regions in men. The two chemicals seemed to be leading a double life, playing the role of odor with one sex and of pheromone with another.

The Swedish researchers have now repeated the experiment but with the addition of gay men as a third group. The gay men responded to the two chemicals in the same way as did women, Dr. Savic reports, as if the hypothalamus's response is determined not by biological sex but by the owner's sexual orientation.

I'd first like to point out that this study tells us exactly zero about whether male sexuality is innate, learned, a choice, or anything like that. This study is not about nature v. nurture. As I've noted before, a biological basis for behavior is very different from a genetic or innate cause for behavior. All behaviors are somehow mediated by the brain, so there must be something happening in the brain that is correlated with behavior - it's just a question of developing methods sensitive enough to detect it, which is why cognitive neuroscience has only exploded in the last decade. Happily, the NY Times article recognizes this and goes into as much depth with it as one might hope for in a newspaper article.

One objection that Charles Todd has over at Majikthise is that the NY Times article presents the result as "gay men's brains are like women's brains" rather than "gay men's brains are like straight women's brains." Luckily, the scientific article is careful to specify that gay men's brains behaved like straight women's brains. (Sexual orientation appears to have been assessed by interview / self-report via the Kinsey scale.) Now, the most intuitively appealing result would be if lesbians' brains behaved like straight men's brains in response to these pheromones, but of course science is never so simple:

Dr. Savic said that she had also studied gay women, but that the data were "somewhat complicated" and not yet ready for publication.

So it's not the researchers who are falling prey to the "gay man = woman" fallacy, but the NY Times (seriously - how hard is it to add the adjective "straight" into the lede?). [By the way, I love the euphemism "somewhat complicated."]

On one level, the study isn't very surprising at all in terms of sexual orientation. Imagine if someone did a study showing beautiful male faces and beautiful female faces to subject and showed that gay men and straight women had their "sexual attraction" brain areas activated when viewing beautiful male faces, whereas straight men had the same brain areas activated when viewing beautiful female faces. Not so interesting.

What's interesting is, rather, that these chemicals seem to be acting as pheromones, when people thought that humans didn't respond to pheromones (because the relevant sensory organ in other mammals, the vomeronasal organ, is largely inactive in humans). And even this was shown almost 4 years ago comparing just straight men and straight women - it's just that the finding that responses are different for gay and straight men provides additional support for the theory that they are pheromones.

See Rob Helpy-Chalk for some more intelligent dissection of this study.

Update: The BBC brings more news about pheromones - apparently there has been another study showing that

The preferences of gay men were strikingly different from those of heterosexual men and women, and lesbian women. Gay men preferred the odours of other gay men, and heterosexual women. The smell of gay men were the least liked by heterosexual men and women, and lesbians.

So maybe this is how gaydar works??

Seriously though, again I'd like to point out that the conclusion that "gender preference has a biological component" (as the lead author of this second study says) is very different from the conclusion that gender preference has an innate component. [NB - I have been unable to find the scientific article - I think it hasn't been published yet.]

Interestingly, the BBC article does make the distinction between "women" and "heterosexual women" that the NY Times missed out on.