Final answer:
Stabilizing selection occurs when extremes are selected against, directional selection favors one extreme, and disruptive selection selects against the middle range of phenotypes.
Step-by-step explanation:
Stabilizing selection occurs when phenotypes at both extremes of the phenotypic distribution are selected against, narrowing the range of variation. An example is human birth weight. Directional selection occurs when one extreme phenotype is favored, shifting the distribution toward that extreme. An example is the beak size of Galápagos finches. Disruptive selection occurs when phenotypes in the middle of the range are selected against, resulting in two overlapping phenotypes at each end of the distribution. Examples include sexual dimorphism in humans.