Both the systemizing/mechanistic skills characteristic of the male brain
and the empathizing/mentalistic skills characteristic of the female brain are distributed normally in the population. It means that most men and most women have their sex-typical brains in the moderate range, but some people have extremely strong or extremely weak versions (just like most people are of average height, but some people are extremely tall or extremely short). What are the “extreme male brain”? What are the “extreme female brain”?
Simon Baron-Cohen revolutionized the study of autism and autism-spectrum disorders (such as Asperger’s syndrome) by suggesting that autism is a manifestation of an “extreme male brain.” The male brain tends toward systemizing and mechanistic thinking, treating other people as if they were logical systems or machines. If you take this tendency to an extreme, you would treat everyone as if they were machines without minds or feelings. That, according to Baron-Cohen, is the essence of autism, which he calls “mindblindness.” Mindblind people (autistics) are blind to other people’s minds or emotions. In fact, they don’t even know that other people have minds separate from their own; autistics tend to assume that other people know and think exactly what they do. Baron-Cohen’s notion of autism as the extreme male brain explains why an overwhelming majority of autistics (four out of five) are men and there are relatively few female autistics (although, once again, there are exceptions to the general pattern; there is an occasional “girl with a boy’s brain.”)
Even after Baron-Cohen figured out the essence of autism as an extreme male brain, the nature of the other extreme, an extreme female brain, remained a puzzle, until Bernard Crespi and Christopher Badcock figured out what an extreme female brain might entail.
The female brain tends toward empathizing and mentalizing thinking, treating machines and objects as if they were other people. They attribute minds, thoughts, and feelings to inanimate objects. That, according to Crespi and Badcock, is the essence of paranoid schizophrenia. Paranoid schizophrenics hear voices where there are no people, and they attribute minds and thinking where none exist, such as when they believe other people are talking about or conspiring against them when they aren’t. Paranoid schizophrenics are hypermentalistic, and overinfer minds and emotions in other people, just as autistics are hypomentalistic, and underinfer minds and emotions in other people.
In their forthcoming article in the premier journal Behavioral and Brain Sciences, Crespi and Badcock present a very convincing case for paranoid schizophrenia as an extreme female brain. Now the whole picture appears to be complete. When your brain is “too male,” too systemizing, too mechanistic, you become autistic. When your brain is “too female,” too empathizing, too mentalistic, you become paranoid schizophrenic. If the extreme male brain of an autistic is “mindblind,” then you might suggest that the extreme female brain of a paranoid schizophrenia is “logicblind.”
[Postscript: As it turns out, there are subtle differences between Baron-Cohen's theory and Crespi and Badcock's theory which I failed to explain fully in my original post. While Baron-Cohen suggests that autism results from extreme male brains, Crespi and Badcock propose that autism results from paternal brains (under the control of the father's genes) and paranoid schizophrenia results from maternal brains (under the control of the mother's genes). I'd refer interested readers to their forthcoming article in Behavioral and Brain Sciences for further details.]