frequency-dependent selection

Frequency-dependent selection is a type of natural selection where the fitness of a genotype is related to its frequency within a population. This means that if a particular genotype becomes common, its fitness may decrease, and if it becomes rare, its fitness may increase.1

This phenomenon can lead to the maintenance of genetic diversity within a population, known as polymorphism. For example, in fruit flies, certain genotypes have higher fitness when they are rare, contributing to a stable mix of genotypes in the population. Frequency-dependent selection can also be influenced by factors like sexual preferences, where rare traits might be more attractive, or by environmental conditions that favor different genotypes at different frequencies. This contrasts with other forms of natural selection where fitness is constant regardless of frequency.12