-In Berkeley, I met a number of really interesting people who seemed quite similar to me along a lot of dimensions, but also very different along some other dimensions having to do with how they were currently living their life! (I see where the pattern-matching facilities in Yudkowsky's brain got that 20% figure from.) This prompted me to do a little bit more reading in some corners of the literature that I had certainly _heard of_, but hadn't already mastered and taken seriously in the previous twelve years of reading everything I could about sex and gender and transgender and feminism and evopsych. (Kay Brown's blog, [_On the Science of Changing Sex_](https://sillyolme.wordpress.com/), was especially helpful.)
+In Berkeley, I met some really interesting people who seemed quite similar to me along a lot of dimensions, but also very different along some other dimensions having to do with how they were currently living their life! (I see where the pattern-matching faculties in Yudkowsky's brain got that 20% figure from.) This prompted me to do a little bit more reading in some corners of the literature that I had certainly _heard of_, but hadn't already mastered and taken seriously in the previous twelve years of reading everything I could about sex and gender and transgender and feminism and evopsych. (Kay Brown's blog, [_On the Science of Changing Sex_](https://sillyolme.wordpress.com/), was especially helpful.)
+
+Between the reading, and a series of increasingly frustrating private conversations, I gradually became increasingly persuaded that Blanchard _wasn't_ dumb and wrong, that his taxonomy of male-to-female transsexualism is _basically_ correct, at least as a first approximation. So far this story has just been about _my_ experience, and not anyone's theory of transsexualism (which I had assumed for years couldn't possibly apply to me), so let me take a moment to explain the theory now.
+
+(With the caveated understanding that psychology is complicated and there's more to be said about what "as a first approximation" is even supposed to mean, but I need a few paragraphs to talk about the _simple_ version of the theory that makes _pretty good_ predictions on _average_, before I can elaborate on more complicated theories that might make even better predictions including on cases that diverge from average.)
+
+The idea is that male-to-female transsexualism isn't actually one phenomenon; it's two completely different phenomena that don't actually have anything to do with each other, except for the (perhaps) indicated treatment of HRT, surgery, and social transition. (Compare to how different medical conditions might happen to respond to the same drug.)
+
+In one taxon, the "early-onset" type, you have same-sex-attracted males who have just been extremely feminine (in social behavior, interests, _&c._) their entire lives, in a way that causes huge social problems for them—the far tail of effeminate gay men who end up fitting into Society better as straight women. _That's_ where the "woman trapped inside a man's body" trope comes from. [This one probably _is_ a brain-intersex condition.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3180619/)
+
+That story is pretty intuitive. Were an alien AI to be informed of the fact that, among humans, some fraction of males elect to undergo medical interventions to resememble females and aspire to be perceived as females socially, "brain-intersex condition such that they already behave like females" would probably be its top hypothesis for the cause of such behavior, just on priors.