Sexual Selection: Traits That Win Mates

0:00A peacock's huge, bright tail makes him easier for predators to spot. So how could a trait like this evolve?

0:08The answer is sexual selection: a kind of natural selection in which inherited traits spread because they help animals win mates.

0:18It works in two main ways: mate choice and competition.

0:23In mate choice, members of one sex choose which partners to mate with.

0:28Peahens, the females, tend to choose males with bigger, showier tails.

0:34In competition, members of the same sex, like these male elk, battle each other for the chance to mate.

0:42Male elk fight with their antlers, and the winners get more mates.

0:47But the bright tail that attracts peahens also makes the peacock easier for predators, like leopards, to spot.

0:55This is a trade-off: one trait brings both a benefit, more mates, and a cost, more danger.

1:03More mates means more offspring that inherit the trait, so the trait spreads, even with the danger.

1:11So sexual selection can spread traits that win mates, even when they cost survival.