This book provides an explanation of how the intense activities of cells and brains are relevant to the work of philosophers and to questions about the nature of man, perception, freedom, determinism, and ethical values. It indicates to biologists the importance of them understanding philosophical concepts. The author argues that facts about the activities of the brain provide understanding of the individual as a responsible agent and so illuminate the problems of body and mind. He examines purpose, choice and value through their counterparts in the brain and their manifestations in other animals as well as man. The author describes what research and experiment have revealed about the brain and its functions. He demonstrates that perception is not a passive process but an active search for information: human knowledge, it is suggested, may be a special development of the process of gathering information for life which is essential for all organisms.