Martin Raff - Transsexual brain (11/23)

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Born in 1938, Martin Raff is a Canadian-born neurologist and research biologist who has made important contributions to immunology and cell development. He has a special interest in apoptosis, the phenomenon of cell death. He retired from active science in 2002. [Listener: Christopher Sykes]

TRANSCRIPT: So he’s been treated with testosterone for a year and a half now and because this is all being controlled by a clinic at Stanford, he’s psychologically tested every few months. And so interestingly, I mean, even though this is now sex hormones being given to an adult, his brain is clearly changing dramatically so his ability in space… spatial ability is increasing. It’s… males do this better than females, where his verbal abilities, females do this better than males, is decreasing with time.

So it got me interested in this whole question of sex hormones and brain plasticity, and so the history here is quite remarkable. It was believed until the early 1970s that the brain of a male and a female is the same in a mammal, like us, and that the reason our behaviour is so different is that, you know, the external genitals are different and social influences affect your behaviour. So the first clue that that wasn’t right was in 1971 where someone in Britain discovered that the female rat brain is quite different, at least in one area, from the male rat brain and now… this has now been shown in many animals and it’s been shown in humans and there are many differences between the male and female brain.

And then in 1990 I believe Dick Swaab in the Netherlands showed that homosexual men, their brain in this one particular area, in one part of the brain has twice as many nerve cells as males that are not homosexual, that are heterosexual. And then a year later someone else in the States found a different nucleus where in homosexuals it’s different, it’s like a female, so that’s rather remarkable. And then in 1995 the same guy who made the first discovery about homosexual differences in the brain looked at transsexuals, male to female transsexuals, and showed that yet a different region of the brain is different in these males. They, in this region, look like females.

So it’s quite a remarkable thing and the… the second thing that’s I think quite interesting is that there’s a very big difference between your sexual identity and your sexual orientation. So Ben Barres is a transsexual; from as long as he can remember he never felt like a girl, even though he looks entirely female… always felt male. He never felt comfortably in his body and that’s true of all transsexuals, but their sexual orientation can be heterosexual, homosexual, bisexual, asexual. So Ben is now homosexual because always has been attracted to men and still is attracted to men. So your sexual orientation is quite different from your sexual identity, and it turns out it’s different parts of the brain that are doing it.

So how does all this happen, and how much of it is genetic, and how much of it is hormonal, and how much of it is behavioural? So it turns out that a hell of a lot of it is hormonal and it sort of works like this: we are born… earlier… not born. A fertilised egg as it develops can become either a female or a male. It depends on one gene sitting on one chromosome, the Y chromosome. So the male has an X and a Y, the female has two Xs. On the Y chromosome there’s one gene. If you have that, you develop as a male. You put that one gene into a female embryo and, bang, it becomes a male.

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