| Summary: | The outcome of sexual selection is the evolution of secondary sexual characteristics that are designed to attract and compete over mates. Traits that evolve via sexual selection do so as a result of competition for mates (intrasexual competition) or mate attraction (epigamic selection). Intrasexual competition is competition between members of the low investment sex (usually males) for copulations with the high investment sex (usually females). Since males are usually the low investment sex, they are the most intrasexually selected. This results in traits beneficial for competing with other males such as organs of threat (antlers, large size, aggressiveness, etc.). In some cases, these traits will be used in direct physical combat with other male; in other cases, they may be used to establish dominance hierarchies where the males at the top monopolize mating opportunities. An example of intrasexual selection for size is found in elephant seals where males are substantially larger than females, spend much of their time competing for females, and the most dominant males father the majority of pups in any given season. Epigamic selection is competition between members of the low investment sex for features that are attractive to the high investment sex. As with intrasexual selection, the sex that invests less per offspring is usually the male. Thus, this type of selection is often referred to as female choice; the females choose on the basis of male displays or attributes. The result of female choice is the elaboration of displays, coloration, and courtship rituals as the males try to “impress” the females by competing with other males via display mechanisms. Under female choice, highly elaborated traits can evolve, such as the peacock’s tail (Petrie 1994). Such traits exist because of the female preference for them. Males with those traits, or the most impressive examples of such, were the most successful at reproducing and passed those traits on to their offspring. However, this raises the question of what benefit those traits are to the reproductive success of females? Why do they choose them?
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