Nowadays, cosmopolitan populations increasingly applaud the broad physical, ethnic, racial, and cultural diversity of human beings. So long as we behave within sanctioned norms. This presentation will focus upon the above paradox: In contrast to delighting in physical, ethnic and cultural expressions of human diversity, present-day cosmopolitan societies increasingly call for conformity in behavioral and experiential realms. For example, at meetings such as this, we can freely express and celebrate racial, ethnic, and culturally differences, but we must communicate–within remarkably narrow ranges–cordiality, spontaneity, agreeableness, respectful disagreement and tact. And if we cannot?? We propose that the phenomenon of mental illness arises as a consequence of the phenomenon of human diversity coming up against constraints and limitations in mental and behavioral realms. This presentation will focus upon evolutionary, genetic, biological, anthropological, historical and cultural aspects of the primary role that human diversity plays in mental illness. We will discuss the adaptive origins and strengths associated with the extraordinary diversity of humans (and our pets/domestic animals) as well accompanying vulnerabilities. For example, diversity of skin pigmentation has enabled humans to extend across the globe. A consequence however, is enhanced vulnerability to skin cancer for some with fair skin and vitamin D deficiency for others with dark skin. Psychological diversities can be viewed analogously. The thesis that mental illness is an inevitable consequence of the singular diversity of humanity will be exemplified by disorders such as ADHD, melancholia, schizophrenia and sociopathy.