This book about the role of steroid hormones in the social life of animals is motivated by the belief that further progress in understanding social behavior requires considering these hormones and their actions. Why? One simple reason is that no behavior is completely understood without knowledge of its underlying physiological mechanisms. This point was made long ago by the
ethologist Niko Tinbergen (1963), who provided a simple and clear agenda for a science of animal behavior in the form of four basic aims or problems that must be solved: causation, survival value, ontogeny, and evolution. Today these are often phrased as proximate mechanisms, function or adaptive value, development, and phylogeny. As a major category of physiological mechanisms for the development and expression of social behavior, hormones are an essential ingredient for two of the four aims.