This book seeks to explain how gender affects human development from infancy through adolescence and into adulthood. The book's introduction states the two theses of the book: first, gender differences appear primarily in group, or social, contexts; and second, gender differentiation can be understood only in a developmental context--the sexes diverge at certain stages of development, and converge at others. The book identifies a complex combination of biological, cognitive, and social factors that contribute to gender segregation and group differentiation. Childhood experiences in same-sex groups are shown to profoundly influence how members of the two sexes relate to one another in adulthood--as lovers, coworkers, and parents. The book is divided into three sections. The chapters in the first part, "Divergence in Childhood," are: (1) "Gender Segregation in Childhood"; (2) "The Two Cultures of Childhood"; and (3) "Cross-Sex Encounters." The chapters in the second part, "The Explanatory Web," are: (4) "What Needs to Be Explained"; (5) "The Biological Component"; (6) "The Socialization Component"; and (7) "The Cognitive Component." The chapters in the third part, "Convergence in Adulthood," are: (8) "Heterosexual Attraction and Relationships"; (9) "The Two Sexes in the Workplace"; and (10) "Men and Women as Parents." The book concludes with an overview. Contains 499 references. (AMC)