Scholar J. Philippe Rushton argued that there are at least 3 major races: Negroids, Caucasoids & Mongoloids, and that on a great many traits (i.e. brain size, genital size, size of breasts and buttocks, mental stability, promiscuity, crime) , Negroids were at one extreme, and Mongoloids were at the opposite extreme, with Caucasoids being in the middle. Rushton believed this pattern was caused by the r/K evolutionary spectrum. In other words, he believed Mongoloids evolved a more K genetic profile (lower birth rate but lower death rate) while Negroids evolved a more r genetic profile (higher birth rate but higher death rate) with Caucasoids being in between.
Rushton mapped these differences on to the time period when each of the three races branched off the main trunk of the human evolutionary tree: Negroids first (about 200,000 years ago), Cacuasoids second (about 110,000 years ago) and Mongoloids last (41,000 years ago). Rushton used these splitting off dates to argue that evolution was progressive, and some populations are more advanced than others.
One trait Rushton didn’t focus on since it did not get as much attention until recently, is autism, however it seems likely to me that autism also follows Rushton’s racial pattern. I have no data to support this, but my subjective impression is that Mongoloids are the most autistic race, and Negroids are the least autistic race, with Caucasoids in the middle. I believe this occurred because as humans migrated out of Africa into colder and colder climates, there was an r/K evolutionary trade-off: social IQ (useful for attracting mates and having high birth rates) was reduced, while technological IQ (useful for survival) was increased. So not only did humans become more intelligent as we moved North, but the type of intelligence also changed.
However the corollary of Negroids being the least autistic is that they are probably the most schizophrenic race, and Mongoloids are probably the least schizophrenic race. This is because autism and schizophrenia are in many ways opposites. That is autistics tend to be oblivious to the fact that other people have minds; this results in low social IQ because they treat other humans like objects. But schizophrenics have the opposite problem, they are so good at recognizing the mental states of others that they often perceive mental states where they don’t even exist (i.e. the tree is trying to tell me something).
In psycholgy circles schizophrenia is sometimes called a black condition.
What all of this suggests is that autism is a K trait and schizophrenia is an r trait. Thus even within the same race, we tend to find the upper class are more autistic and the lower class are more schizophrenic. This is probably because the upper class tend to be more K and the lower class tend to be more r.