In some populations, individuals choose their mates, showing a preference for certain characteristics and thus favoring the genes associated with them in a nonrandom way. Individuals choose amongst themselves for sexual reasons. With time, certain genes disappear from the population while others become more common.

The mating dances of the birds of paradise in Papua, New Guinea, and eastern Australia are an example of sexual selection. The males are showier than the females, with more colorful feathers.

They perform nuptial dances to attract females. In some cases, various males get together on the branches of the same tree and put on a show. The females approach the tree and decide which males they want to mate with.

Sometimes, the males clear out a small jungle area to show off their magnificent plumage. The females choose the showiest males, and their descendants inherit the genes responsible for showy plumage.