Its a bit of leap but its an interesting finding, says Dr. Alan DeCherney, chairman of the Department of Obstetrics and Gynecology at the University of California, Los Angeles School of Medicine. And it does validate a biologic phenomenon to explain homosexuality.
Even Before Birth
Womens index fingers tend to be the same length as their ring fingers, while in men, the second finger is generally shorter than the fourth. Scientists know that differences between genders occur because male fetuses are exposed to high levels of testosterone and other male sex hormones, collectively known as androgens, in the womb.
This means that gender differences in digit length probably indicate a fetuss exposure to androgens, according to Marc Breedlove, a professor of psychology at the University of California, Berkeley, and the author of the finger-length study, published in the journal Nature. The higher the exposure, the more likely that the index finger will be shorter than the ring finger.
With this in mind, Breedlove set out to compare the finger lengths of gay and straight people to see if he could find any indication that their sexual orientation stemmed from differences in exposure to androgens.
He and a group of undergraduates went to street fairs in the San Francisco area during the fall of 1999. Armed with a portable copy machine, they asked 720 people to lay their hands flat on the copiers glass surface. The subjects also filled out questionnaires about their sexual orientation and birth order.
Taking a ruler to the handprints, Breedlove found that homosexual womens fingers tended to be more masculine. In other words, their index fingers tended to be shorter than their ring fingers, just like on a typical mans hand. Breedlove interprets this to mean that exposure to androgens before birth may affect a womans eventual sexual orientation.
It is reasonable that mothers might contribute to the masculinization of their female fetuses, says J. Richard Udry, a professor of maternal and child health and sociology at the University of North Carolina, Chapel Hill, because a female fetus produces practically no testosterone herself.
Men More Problematic
Breedlove found no difference between the finger lengths of gay and straight men. When he scratched deeper, he found men with two or more older brothers tended to have more masculine finger lengths. Other studies have shown that the more elder brothers a boy has, the more likely he is to develop a homosexual orientation.
Via a somewhat convoluted argument, Breedlove takes this finding as an indication that gay men, instead of being exposed to fewer male sex hormones in the womb, as society might expect, are exposed to more.
This calls into question all of our cultural assumptions that gay men are feminine, Breedlove says. He goes on to suggest that a mothers body appears to remember previously carried sons, and this makes it produce a lot of androgens, which influences the sexual orientation of her later sons.
This is where the whole thing begins to fall apart, says Udry. The male fetus produces so much testosterone during the time when gender differences like finger length are taking place, Udry says, that the amount the mother contributes is trivial. So the idea that androgens from the mother could have a measurable effect on finger length is unlikely.
Nonetheless, as DeCherney points out, everybody is going to be measuring their fingers.