This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book manipulates an extended cold shower of epistomological caveats to the technical procedures in research on the broad subject of sex-linked behavior. It offers a cautious and probing outline of the biological mechanisms operating towards physical and behavioral differentiation of males and females in a variety of species. The book argues undue devotion to hierarchical notions of a conventional, formal male kind may interfere with efficient operation of social groups confronting rapid social, economic, or other changes. It observes dominance in primate communities relates not predominantly to the control of resources or violence but, more importantly, to the amount of deference, by visual attention, paid to the leading animals by subordinate ones. The book also argues firmly for a consideration of the chimpanzees as providing the primate model most relevant to the human.