The distribution of schizophrenia within populations bears upon the genetic nature of the disorder. From the World Health Organization Ten-Country Study of incidence Jablensky et al concluded that: Schizophrenic illnesses are ubiquitous, appear with similar incidence in different cultures and have clinical features that are more remarkable by their similarity across cultures than by their difference.
The WHO study included populations in Japan, India and Europe that have been separated for tens of thousands of years. Moreover illnesses with essentially the same characteristics are commonplace in the Australian aboriginal population that separated from other human populations 50,000 years ago.
