“In the 1930s an anthropologist named Paul Radin first described it as "shamans being half mad," shamans being "healed madmen."”

This fits exactly. It's the shamans who are moving separate from everyone else, living alone, who talk with the dead, who speak in tongues, who go out with the full moon and turn into a hyena overnight, and that sort of stuff. It's the shamans who have all this metamagical thinking. When you look at traditional human society, they all have shamans. What's very clear, though, is they all have a limit on the number of shamans. That is this classic sort of balanced selection of evolution. There is a need for this subtype — but not too many.
The critical thing with schizotypal shamanism is, it is not uncontrolled the way it is in the schizophrenic. This is not somebody babbling in tongues all the time in the middle of the hunt. This is someone babbling during the right ceremony. This is not somebody hearing voices all the time, this is somebody hearing voices only at the right point. It's a milder, more controlled version.
Shamans are not evolutionarily unfit. Shamans are not leaving fewer copies of their genes. These are some of the most powerful, honored members of society. This is where the selection is coming from. … In order to have a couple of shamans on hand in your group, you're willing to put up with the occasional third cousin who's schizophrenic.
Emperor Has No Clothes Award acceptance speech (2003)