INTRODUCTION

Sexual selection theory has provided a successful framework for studying sex differences in behaviour, morphology, development and reproductive strategies, as well as the resulting mating systems (Campbell, 1972; Emlen & Oring, 1977; Bradbury & Andersson, 1987; Andersson, 1994). Humans and other primates have played an important stimulating role in the original development of the second pillar of modern evolutionary theory (Darwin, 1871; Clutton-Brock, this volume), and primates were the subjects of the first scientific paper devoted to sexual selection (Darwin, 1876). After languishing for nearly a century, sexual selection theory was re-discovered by evolutionary biologists and students of animal behaviour, who made it one of the most active fields of organismal biology by refining the theoretical framework and testing it with many new empirical data, mainly from insects and birds (Andersson, 1994). Studies of sexual selection in primates, in contrast, were not resumed with the same general enthusiasm and vigour, but there were notable exceptions (e.g. Crook, 1972; Clutton-Brock et al., 1977; Harvey et al., 1978; Hrdy, 1979; Smuts & Smuts, 1993; van Schaik et al., 1999; van Schaik, 2000a). The first aim of this chapter is to provide an introductory summary of the main concepts and mechanisms of sexual selection theory in a way that highlights these contributions and questions of general interest from primatology, and to introduce the subsequent chapters of this volume.