Illustration showing sexual selection. A fancy decoration may attract the females, but eventually it could become a liability.

Sexual selection

In natural selection the fittest individuals survive and pass on their genes to the next generation

Animals’ features are highly functional, otherwise they wouldn’t survive. But what possible function could a peacock’s tail have? The answer lies in another of Charles Darwin’s great ideas – sexual selection.

Sexual selection is based on the theory that competition for a mate drives the evolution of certain characteristics. In nature males typically have to compete to be chosen by females. If females favour some attractive feature of a male, the genes for that feature will thrive, as will genetic changes that enhance it – until the benefits in the mating game are balanced by the cost of such extravagant and useless features.

But why do females choose decorated males? Possibly, showy features help females to choose a mate with the ‘best’ genes. An extravagant display, in beautiful condition, suggests that the male has managed to acquire plenty of food, and has defended himself well against predators and disease. While he might just have been lucky, more likely he has a fine set of genes.

Lead image:

Illustration showing sexual selection. A fancy decoration may attract the females, but eventually it could become a liability.

Illustration © Glen McBeth

About this resource

This resource was first published in ‘Evolution’ in January 2006 and reviewed and updated in October 2014.

Topics:
Genetics and genomics, Health, infection and disease
Issues:
Evolution, Sex and Gender
Education levels:
16–19, Continuing professional development