Scientific Proof of Transsexualism
By CURT SUPLEE
Washington Post
Scientists in Holland have found preliminary evidence that male
transsexuals - men who identify sexually with women - have a strikingly
different brain structure from "ordinary" men, at least in one key area about
one-eighth of an inch wide.
In today's Nature, a team of researchers from Amsterdam reports that they
conducted post-mortem exams on the brains of six male-to female transsexuals.
Specifically, they studied one particular part of hypothalamus, called the
central division of the bed nucleus of the stria terminalis (BSTc).
This area, which is thought to influence sexual behavior, is on average 44
percent larger in men than women. Yet all six subjects had BSTc regions that
were female sized, Dick Swaab of the Netherlands Institute for Brain Research
and colleagues found.
BSTc volume is not related to homosexuality, the researchers concluded from
post-mortem analyses of 36 other brains, including those of homosexual men
and het erosexuals of both sexes: "The BSTc was 62 percent larger in
homosexual men than in heterosexual women." Nor does it appear to be a factor
in sexual orientation in general. Of the six transsexuals, three had been
attracted to women, two to men and one was bisexual.
Psychiatrist Sandra Witelson of McMaster University in Hamilton Ontario,
said the work adds "to the body of knowledge that has been accumulating in
the past five or six years, all of which shows that there are biological
correlates to variation in human sexual behavior." Per haps the most
celebrated such find ing came in 1991 when Simon LeVay, then at the Salk
Institute in California, reported that gay and straight men differed
dramatically in yet another area of the hypothalamus.
The authors of today's paper argue that the transsexuals' "feminine" BSTc
volume arose from biochemical conditions early in life perhaps during fetal
development. The findings, they conclude, "support the hypothesis that gender
identity develops as a result of an interaction between the developing brain
and sex hormones."
In an accompanying commentary, however, neuroscientist Marc Breedlove of
the University of California at Berkeley warns that "this will be far from
the final word on the subject."
Breedlove notes that of the six subjects, five had had their testicles
surgically removed and all had tak en the female hormone estrogen, as well as
a drug that blocks the action of male hormones called androgens. Those
conditions, he writes, might have affected the size of the BSTc region.
Moreover, he writes, it is impossible to know whether the small BSTc size
influenced the subjects' transsexuality or vice versa.
Richard Restak, a Washington, D.C., neurologist who has written extensively
on brain research, observed that recent studies have shown that "estrogen has
an enhancing and modulating effect on neurotransmitters in the brain. Thus,
it's conceivable that it might encourage or discourage some change in brain
structure."
The researchers acknowledge that possibility but cite the fact that two
transsexual subjects who quit taking estrogen shortly before their deaths
nonetheless had "a small, female-like BSTc." They also stud ied two other men
whose testicles had been removed in the course of treatment for prostate
cancer, elim inating their bodies' main source of androgens. Both had BSTc
volume "at the high end of the norrnal male range."
The new research "doesn't mean that learning or culture or environ ment
are irrelevant" to transsexuality, Witelson said, "not at all. But it is one
more report of a relationship between anatomy and behavior."
