Developmental psychology is not only a psychology of development from childhood to old age but a psychology of human development in world history. Eighty years of cross-cultural empirical research findings indicate that the adolescent stage of formal operations evolved late in history and is not a universal development of adult humans across cultures and history. Correspondingly, preoperational or concrete operational stages describe adult psychological stages in past or premodern cultures, as Jean Piaget and some of his followers have mentioned. Developmental psychology is likewise a historical or anthropological psychology capable of describing humans in premodern cultures. The article develops a general anthropological or psychological theory answering the many questions that arise from the correspondences between (modern) children and ancient adults. On this psychological basis, the new structural genetic theory program is capable of explaining, better than previous approaches, the history of humankind from prehistory through ancient to modern societies, the history of economy, society, culture, religion, philosophy, sciences, morals, and everyday life. The accomplishment of this task was once demanded of some classical founders of psychology, sociology, history, and ethnology but was largely avoided by the postwar generations of authors for political and ideological reasons.