MOST YOUNG CHILDREN LIKE TO play dress-up, parading around the house in their dad's wing tips or smearing their mom's lipstick all over their face. But for a few youngsters, usually boys, this childhood rite is more than a game. They are obsessed with their mother's clothes and wear them at every opportunity. It is as if a part of their mind were trying to erase the maleness of their body and allow an inherent femaleness to emerge. As they grow older, their discomfort with their gender often increases, until finally they turn to doctors for help. Some take feminizing hormones to grow breasts. Some even have their sex organs surgically altered so they can live completely--including anatomically--as women.
But are such people, who are known as transsexuals, truly women trapped in men's bodies? For years, scientists searched for but never found any measurable differences between most men and the ones who become transsexuals, whether in the level of hormones, the shape of genitalia or the number of chromosomes. Nor did scientists find any fundamental similarities between transsexuals and women.
Last week, however, investigators from the Netherlands Institute for Brain Research in Amsterdam reported preliminary evidence that transsexuals may be inherently different, after all. Their study of six male-to-female transsexuals showed that a tiny structure deep within a part of the brain that controls sexual function appeared to be more like the type found in women than that found in men. If confirmed, the study seems likely to challenge long-held beliefs about what it takes to make someone a man--or, a woman.
The Dutch research is part of a growing body of evidence suggesting that nature is just as important as nurture in determining how we think and behave as sexual beings. Neurobiologists have cataloged apparent differences in the way men's and women's brains process information and interpret facial expressions. Geneticists have begun sifting through tantalizing clues that sexual orientation--as opposed to sexual identity--may at least be partly inherited (see box). Yet the subject matter is so charged from an emotional, political and even religious perspective that evaluating all the various claims dispassionately can be very difficult.
In many respects, studying transsexuals would seem to be the most difficult undertaking of all. Not to be confused with transvestites or cross dressers, true transsexuals are rare. By some estimates, no more than 1 person in 350,000 believes he or she was born the wrong gender. Moreover, the portion of the brain that seems to be different in transsexuals is smaller than a pinhead. Even advanced imaging techniques, like the pet scan or mri, cannot detect such tiny variations. To do their research, the Dutch team, led by Dr. Dick Swaab, had to dissect the brains of transsexuals in autopsies and examine them under a microscope. Little wonder, then, that it took Swaab's team 11 years to find transsexual candidates, persuade them to donate their brains and then wait for them to die to make the comparisons.