Now that I have attempted to make the very idea of human nature respectable, it is time to say something about what it is and what difference it makes for our public and private lives. The chapters in Part IV present some current ideas about the design specs of the basic human faculties. These are not just topics in a psychology curriculum but have implications for many arenas of public discourse. Ideas about the contents of cognition—concepts, words, and images—shed light on the roots of prejudice, on the media, and on the arts. Ideas about the capacity for reason can enter into our policies of education and applications of technology. Ideas about social relations are relevant to the family, to sexuality, to social organization, and to crime. Ideas about the moral sense inform the way we evaluate political movements and how we trade off one value against another.

In each of these arenas, people always appeal to some conception of human nature, whether they acknowledge it or not. The problem is that the conceptions are often based on gut feelings, folk theories, and archaic versions of biology. My goal is to make these conceptions explicit, to suggest what is right and wrong about them, and to spell out some of the implications. Ideas about human nature cannot, on their own, resolve perplexing controversies or determine public policy. But without such ideas we are not playing with a full deck and are vulnerable to unnecessary befuddlement. As the biologist Richard Alexander has noted, “Evolution is surely most deterministic for those still unaware of it.” 1