The main part of the book begins with a study of behavioral development in animals, progresses to the neural and endocrine aspects of behavior, and then to the social behavior of nonhuman primates. The final transition from monkeys to humans, which Hinde made in his own research, leads to an impressive section on the development of social behavior in humans. The last scientific chapter relates to Dr. Hinde's deep concern about aggression and the peculiarly human institution of war. His own commentaries to the book discuss the recurring theme of crossing and recrossing the boundaries among different levels of analysis and the need to study processes. In the final section, his former student Jane Goodall and the late Niko Tinbergen write of their memories of this inspiring man.