Do the first two years of life really determine a child's future development? Are human beings, like other primates, only motivated by pleasure? And do people actually have stable traits, like intelligence, fear, anxiety, and temperament? This book, the product of a lifetime of research by one of the founders of developmental psychology, takes on the powerful assumptions behind these questions - and proves them mistaken. Ranging with impressive ease from cultural history to philosophy to psychological research literature, Jerome Kagan weaves an argument that will rock the social sciences and the foundations of public policy.