The author describes many observations and experiments that have not previously appeared outside specialized journals and brings an abundance of simple yet accurate examples of animal behavior to bear on explanations of ethological concepts and evolutionary theory. No attempt is made to skim over the gaps of knowledge apparent in the study of behavior evolution; rather, the author discusses the limitations and difficulties of different approaches, critically reviews the deductions that can be and have been made from them, and tries to present enough evidence on controversial points for the reader himself to judge the validity of specific arguments. Indicating how ethological method, firmly based on biological principles, can intensively investigate and illuminate a single area of animal behavior, the book will be valuable to students and professionals in zoology, animal behavior, and experimental psychology.