Sir Geoffrey Lloyd presents a cross-disciplinary study of the problems posed by the unity and diversity of the human mind. On the one hand, as humans we all share broadly the same anatomy, physiology, biochemistry, and certain psychological capabilities--the capacity to learn a language, for instance. On the other, different individuals and groups have very different talents, tastes, and beliefs, for instance about how they see themselves, other humans and the world around them. These issues are highly charged, for any denial of psychic unity savors of racism, while many assertions of psychic diversity raise the specters of arbitrary relativism, the incommensurability of beliefs systems and their mutual unintelligibility.