Which type of selection would likely increase the prevalence of two contrasting phenotypes?

Disruptive selection is a type of natural selection that favors extreme phenotypes over intermediate phenotypes within a population. This occurs when environmental conditions favor individuals at both ends of the spectrum of variation for a particular trait, leading to an increase in the prevalence of these contrasting phenotypes. For example, if a species of bird has a range of beak sizes, and the available food sources are only accessible to individuals with either very small or very large beaks, then birds with intermediate beak sizes may struggle to survive and reproduce. Over time, this selective pressure can result in the population's phenotypic distribution shifting toward the extremes, thereby amplifying the presence of the two contrasting forms.

In contrast, stabilizing selection tends to reduce variation and promote the average phenotype, while directional selection favors one extreme phenotype over the other. Sexual selection focuses on traits that improve mating success and can lead to differences in phenotypes based on reproductive advantages, but it does not inherently promote the prevalence of two contrasting phenotypes. Therefore, disruptive selection is the mechanism that would be most likely to increase the prevalence of contrasting phenotypes in a population.