Intersexual selection.
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   Natural  selection for mating success may result in sexual dimorphism,
   marked   differences   between   the   sexes   in   secondary   sexual
   characteristics.
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   Many   species  exhibit  intersexual  selection  (mate  choice),  when
   individuals of one sex (usually females) are choosy in selecting their
   mates.
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   Experiments  show  that  peahens  prefer  to  mate  with peacocks with
   greater numbers of eyespots.