(HealthSCOUT) -- It turns out that maybe you really can tell a lot about a man by the size of his gloves. Or, for, that matter, a woman.
California psychologists say a specific comparison of finger length is a good predictor of homosexuality in women and men. The test, which measures the ratio of the index to ring fingers, gives a hand to the hypothesis that high prenatal exposure to male sex hormones is an important factor in future sexual orientation.
A report on the finding appears in the latest issue of the journal Nature.
The latest work isn't the only study to find physical differences between homosexuals and heterosexuals. Two years ago, for example, researchers at the University of Texas in Austin showed that the inner ears of lesbians were less sensitive to soft sounds than those of straight women.
"It's an interesting additional piece of evidence that there are physiological concomitants to homosexuality in both females and males," says Dennis McFadden, an experimental psychologist at the University of Texas who discovered the auditory link to lesbianism.
But, McFadden cautions, don't think you can predict your neighbor's sexual preference by looking at his fingers. "Anything as complex as sexual orientation is bound to have a number of different factors contributing to it," he says.
Scientists have postulated for some time that sexual orientation is programmed, at least in part, by exposure to sex hormones in the womb. Since all fetuses are female unless bathed in the androgens, such as testosterone, these chemicals are implicated in sexual orientation and other gender traits.
Hormonal link to digits
Testing this theory in adults is difficult, as prenatal exposure to androgens is long past. But researchers have come up with a digital proxy.
As it happens, finger lengths -- in fact, all nongenital sex characteristics -- are sensitive to androgens. Women typically have identical or nearly identical index and ring fingers, while in men, the second digit is generally shorter than the fourth
Yet among lesbians, research suggests, the ratio of the index to ring finger is closer to that of men -- consistent with the idea that they were exposed in the womb to masculinizing hormones that also guided their sexual orientation down the road.
Psychologists at the University of California at Berkeley, led, appropriately, by S. Marc Breedlove, queried 720 men and women during three San Francisco street fairs in 1999.
Breedlove's group gathered information on sexual orientation, family size, birth order, handedness and age. They also took photocopies of the subject's hands, and used those to measure the ratio of the lengths of their index and ring fingers.
Among women, sexual preference was linked to the finger size ratio, which was particularly prominent on the right hand.
Finger length was less telling among homosexual men, though some had index fingers particularly short relative to their ring fingers. That, the researchers argue, implies gay men get heavier doses of androgens in utero than their heterosexual counterparts.
The possibility that gay men are more "masculinized" than straight men might unsettle some people with preconceived notions about human sexuality. But, as Breedlove's team points out, gay men have a number of hyper-masculine traits, including a tendency toward having more sex partners, higher levels of androgens in the blood, and larger genitalia.
Intriguingly, men with two or more older brothers were significantly more likely to be homosexual than men with one or no male siblings, Breedlove's group found, supporting an earlier report by Canadian scientists.
"It is just mind-boggling to think that some men are gay because of the number of boys their mothers had before their own birth. These events must register in the woman's body before an individual is even conceived," says Breedlove in a statement released Wednesday. The same pattern didn't hold for lesbians.
What To Do: This HealthSCOUT story describes how scientists have come up empty so far in their search for a gay gene.
