What is Sexual Selection?
If you asked people to name the world’s showiest animal, a fair number of people would probably name the peacock. Male peacocks have a massive, colorful tail that makes it very difficult for them to fly or camouflage. Now that you’re learning about natural selection, you might wonder why peacocks have such an ostentatious tail when that clearly makes it harder for them to hide or escape from predators.
The answer is sexual selection. Female peacocks (called peahens) find males with larger and more colorful tails to be the most attractive, so males with big, bold tails are able to father more offspring. Over time this endless competition to have the most attractive and attention-getting tail led to the extreme tails seen in peacocks today.
But why do peahens prefer males with showy tails, if the long-tail genes they pass on might harm the survival prospects of that peahen’s offspring? Though it looks mostly useless, the showy tail can actually be an indirect advertisement of the male’s health and strength. If a male can survive and evade predators even with a massively handicapping tail that proves he must be extremely good at staying alive.
Sexual selection is a type of natural selection, and it has led to some of the most extreme, show-off traits in the animal kingdom. Sexual selection is the reason that many male birds are more brightly colored than the females. Some male birds of paradise even do complicated, hugely impressive dances to gain mates. This proves to the female that the male is healthy enough to spend precious energy on something as frivolous as dancing.
However, sexual selection can also have a dark side. Some scientists believe that sexual selection can get out of control and possibly even drive a species extinct. This is called “runaway sexual selection.”
If females keep selecting for more and more extreme traits, eventually these showy traits may eventually get so out of hand that they seriously harm the survival of every male of the species. This may have been what happened to the Irish elk, an extinct type of deer that had intricate, twelve-foot antlers. These extreme antlers may have been the result of runaway sexual selection, and it’s suspected that this was one of the factors that drove the Irish elk over the brink of extinction.
PublicDomainPictures (photographer). (2010). Peacock Bird Plumage [photography]. Retrieved from