 Cochran and his colleagues hypothesize that the occupational profile of the Jewish community in medieval Europe had resulted in selection pressure for mutations that increase intelligence, but can also result in hereditary neurological disorders.Cochran has claimed that homosexuality can be considered a disease because it generally reduces or eliminates reproductive output, and he has speculated that homosexuality might be caused by infection by an unknown virus.However, he does not suggest that the infectious agent that causes homosexuality is spread by homosexuals.