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An Introduction to Evolution


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Sexual Selection
An Introduction to Evolution
Photo © Rainlady / iStockphoto.

Sexual selection is a type of natural selection that acts on traits related to attracting or gaining access to mates. While natural selection is the result of the struggle to survive, sexual selection is the result of the struggle to reproduce. The outcome of sexual selection is that animals evolve characteristics whose purpose do not increase their chances of survival but instead increases their chances of reproducing successfully.

There are two kinds of sexual selection:

  • Intersexual selection occurs between the sexes and acts on characteristics that make individuals more attractive to the opposite sex. Intersexual selection can produce elaborate behaviours or physical characteristics, such as the feathers of a male peacock, the mating dances of cranes, or the ornamental plumage of male birds of paradise.
  • Intrasexual selection occurs within the same sex and acts on characteristics that make individuals better able to outcompete members of the same sex for access to mates. Intrasexual selection can produce characteristics that enable individuals to physically overpower competing mates, such as the antlers of an elk or the bulk and power of elephant seals.

Sexual selection can produce characteristics that, despite increasing the individual's chances of reproducing, actually diminish the chances of survival. The brightly colored feathers of a male cardinal or the bulky antlers on a bull moose might make both animals more vulnerable to predators. Additionally, the energy an individual devotes to growing antlers or putting on the pounds to outsize competing mates can take a toll on the animal's chances of survival.

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