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individual makes is determined jointly by e, s, l, n, and the w distribution.

When Darwin’s critics said that natural selection (Darwin, 1859) could not explain the evolution of traits such as the outrageous tails of peacocks that reduce their bearers’ survival probabilities, he countered with sexual selection (Darwin, 1871). He argued that costly traits would evolve if they also increased males’ abilities to attract females or to win behavioral contests over access to females. In “Principles of Sexual Selection,” the first chapter of Part II of The Descent of Man, and Selection in Relation to Sex (Darwin, 1871), Darwin defined sexual selection as that type of selection that “depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction” (1871, p. 256). Darwin distinguished sexual selection from natural selection as selection that arises from some individuals having a reproductive advantage over other same-sex, conspecific individuals, not from different “habits of life,” but from reproductive competition with rivals. Darwin’s discussion focused overwhelmingly on traits in males that could be explained by 2 mechanisms of sexual selection—male-male competitive interactions and female choice—each of which could result in variation among males in fitness and thereby favor traits that helped males win fights and attract females (see Jones and Ratterman, Chapter 9, this volume). Most modern discussions of typical sex roles begin with Darwin’s 1871 volume, and statements about choosy females and profligate, competitive males. However, Darwin probably suspected that male choice was common; he argued in Part I of the 1871 book that men’s choice of mates was seemingly more common than women’s at least in “civilized societies.” He even argued that the beauty of women was due to male choice. In Part II he also described cases of male domestic and companion animals refusing to copulate with some females. He was aware too of gaudy, pugnacious, and competitive females in some bird species. Controversy over whether females had the esthetic capability for discrimination dogged Darwin and his followers into the 20th century.

After most people finally agreed that females had the sensibilities to choose, focus narrowed so that modern students of sexual selection simply assumed that males were competitive and indiscriminate and females “coy,” passive, and discriminating. For example, when Bateman (1948) studied sex differences in fitness variances in Drosophila melanogaster, he attributed the larger variances of males to their “undiscriminating eagerness” and the “discriminating passivity” of the females (p. 367), even though he did not watch behavior (Dewsbury, 2005). Bateman’s study



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