Why do we have schizophrenia in every culture on this planet? From an evolutionary perspective, schizophrenia is not a cool thing to have.... Schizophrenia is not an adaptive trait. You can show this formally: schizophrenics have a lower rate of leaving copies of their genes in the next generation than unaffected siblings. By the rules, by the economics of evolution, this is a maladaptive trait. Yet, it chugs along at a one to two percent rate in every culture on this planet.
So what's the adaptive advantage of schizophrenia? It has to do with a classic truism — this business that sometimes you have a genetic trait which in the full-blown version is a disaster, but the partial version is good news.

Emperor Has No Clothes Award acceptance speech (2003)