A "U-shaped" distribution for a trait, with high frequencies of individuals who exhibit extreme values for a trait (and few individuals with medium values), is most likely to be caused by selection. frequency-dependent stabilizing neutral directional disruptive

Disruptive selection

Explanation:

Disruptive selection, which is also referred to as Diversifying selection, is a type of natural selection in which evolutionary forces favor the selection of extreme values of a trait as against average values of the trait or individuals of with intermediate traits. In a population where this type of natural selection occurs, genetic variance increases as extreme phenotypes are favored, and therefore reproduce more than intermediate phenotype. When the values of the trait in which disruptive selection occurs is plotted on a graph, a "U-shaped" distribution showing more individuals of both extreme values compared to individuals with intermediate values of that population.

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equal distribution i think.