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Three modes of Natural Selection

Stabilizing selection favors the modal phenotypic trait values, by selecting against the upper and lower tails of the distribution. The mean remains the same, while the variance decreases. Divergent selection favors the upper and lower tails, by selecting against the modal values; the mean remains the same, while the variance increases. In the extreme case of Disruptive selection, the distribution may become bimodal, with two means. Directional selection favors one tail over both the modal values and the other tail: the mean shifts unidirectionally, and the variance remains unchanged.


Figure modified after © 2019 Sætre & Ravinet; Text material © 2019 by Steven M. Carr