Readers of his Op-Ed column in The New York Times know that David Brooks is an aficionado of research in the social sciences, especially psychology, and that he believes it has great practical importance. Now he has written a book, “The Social Animal,” in order to assemble the evidence for a certain conception of the human mind, the wellsprings of action and the causes of success and failure in life, and to draw implications for social policy. The book is really a moral and social tract, but Brooks has hung it on the life stories of two imaginary people, Harold and Erica, who are used to illustrate his theory in detail and to provide the occasion for countless references to the psychological literature and frequent disquisitions on human nature and society