Disruptive selection is a type of natural selection that favors extreme phenotypes over intermediate phenotypes within a population. This process can lead to increased variance in a trait and can promote speciation by encouraging the development of two or more distinct subpopulations.
In disruptive selection, individuals at both ends of the phenotypic spectrum have a higher fitness than those with average traits. For example, in a population of birds with varying beak sizes, if both very large and very small beaks are advantageous for accessing different food sources, while medium-sized beaks are less effective, the population may evolve to have more individuals with either large or small beaks. This can ultimately lead to the divergence of the population into two distinct groups with different adaptations.