May 12, 2005

Gay men and pheromones:

A lot of attention has been paid to Nicholas Wade's NYT article "For Gay Men, an Attraction to a Different Kind of Scent" about a study that found:

Using a brain imaging technique, Swedish researchers have shown that homosexual and heterosexual men respond differently to two odors that may be involved in sexual arousal, and that the gay men respond in the same way as women.

It's not terribly amazing that gay men are more like women than straight men on a particular trait. (Back in 1994 in "Why Lesbians Aren't Gay," I listed three dozen common traits for gay men and found they were more like straight women than straight men on roughly half the measures, just as lesbians are more like straight men than straight women about half the time. Gays are most like lesbians on only a few traits.)

However, the story is drawing attention for the two reasons Wade summarizes:

The new research may open the way to studying human pheromones, as well as the biological basis of sexual preference.

As Wade makes clear later on, pheromones have long been an underachiever. A decade ago they held the promise of revealing a sixth sense among humans, a sort of subsonic or infrared sense of smell. Perfume companies tried to bring out pheromone-based products that would drive the opposite sex wild, but nothing much panned out. So, any positive finding about pheromones is news, although the odds remain high that pheromones aren't terribly important among humans.

And, of course, anything about the biology of sexual orientation tends to be a nine-days-wonder. I do need to point out that the normally highly reliable Wade muffs up an important point about the putative gay gene when he writes:

Some researchers believe there is likely to be a genetic component of homosexuality because of its concordance among twins. The occurrence of male homosexuality in both members of a twin pair is 22 percent in nonidentical twins but rises to 52 percent in identical twins.

That's from an outdated study, unfortunately, which had some methodological problems with how it recruited its sample (advertising in a gay newspaper) that biased it in favor of a higher concordance rate, because concordant gay twins had twice the chance of seeing the ad in the gay newspaper than nonconcordant twins. I asked Prof. J. Michael Bailey of Northwestern U. about what is the state of the art in this field. He replied:

That figure is mine, and it was the best I could do at the time. A better figure was from 2000 and was about 20%, still well above 2-4%, the base rate in the population.

So, if one member of a pair of male identical twins is gay, four out of five times the other twin will be straight. (I don't believe Bailey is fully satisfied with this second study of his either, but by starting with the Australian government's official twin registry, it's an improvement over the first study ).

That 20% is a rather low concordance rate compared to other traits. So, about all that we can safely say about the cause(s) of male homosexuality is that the topic remains one of leading scientific mysteries of the 21st Century.

My published articles are archived at -- Steve Sailer


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