Nature Plus Nurture

Article excerpt

Of all the motley forms of humanity, surely the one type that is made-laboriously, painfully-and not born would seem to be transsexuals. These men (and, rarely, women) submit to hormone therapy and complicated surgery to mold the bodies they were born with into the bodies they want. But new research suggests that biology sculpts transsexuals long before surgeons get near them. According to neuroscientists led by Dick Swaab of the Netherlands Institute for Brain Research, one tiny region in the brains of six male-to-female transsexuals is only 52 percent as large as in other men, they report in the journal Nature--and almost exactly the size of the region in female brains. "Our study," they conclude, "is the first to show a female brain structure in genetically male transsexuals."

Other research has also seemed to strengthen the biology-is-destiny camp, at least for sexual orientation. A 1991 study found differences in the brains of gay and straight men. Two years later researchers led by Dean Hamer of the National Cancer Institute reported evidence of what has come to be called a "gay gene." Last week Hamer and colleagues unveiled, in the journal Nature Genetics, stronger evidence that a region of the X chromosome, long enough to contain 200 genes, is linked to homosexuality. The evidence: gay brothers are more likely to both inherit this region are their straight brothers. But instead of clinching the case for predestination, the studies are prodding scientists to search for how experiences influence sexuality.

Consider the male transsexuals. Perhaps they are not born with a brain that tells them they are really female, suggests neurobiologist S. Marc Breedlove of the University of California, Berkeley. …