Sexual selection in females

Abstract

Darwin developed the theory of sexual selection to account for the evolution of weaponry, ornamentation and other secondary sexual characters that are commonly more developed in males and which appeared unlikely to contribute to survival. He argued that these traits had evolved either through intrasexual competition between males to monopolize access to females or through consistent female preferences for mating with superior partners. Since 1871, a substantial body of research has confirmed his explanation of the evolution of secondary sexual characters in males, although sex differences in reproductive behaviour are more diverse and the evolutionary mechanisms responsible for them are more complex than was initially recognized. However, secondary sexual characters are also widespread in females but, as yet, their evolution and distribution have received relatively little attention from evolutionary biologists. Here, I suggest that the mechanisms responsible for the evolution of secondary sexual characters in females are similar to those operating in males and include intrasexual competition between females for breeding opportunities, male mating preferences and female competition to attract mates. Unlike males, females often compete more intensely for resources necessary for successful reproduction than for access to mating partners and the development of secondary sexual characters in females may be limited by costs to fecundity rather than to survival.