Mental disorders are usually conceptualized in terms of pathology and disease. I describe a new  perspective, based in evolutionary biology and genetics, that  the forms and risks of human psychiatric conditions have evolved. Under this rubric, such  conditions represent  hypo-development, or  hyper-development, of human­ evolved adaptations and tradeoffs. I present evidence from genetics, endocrinology, neuroscience, psychology and psychiatry that autism spectrum and psychotic-affective conditions (mainly schizophrenia, bipolar disorder  and  depression)  represent  diametric (opposite) conditions with  regard to  human social and  non-social cognition. This evolutionary perspective has  direct implications for  the  study, understanding and treatment of psychiatric conditions.