Final answer:
Stabilizing selection narrows the range of variation by selecting against extreme phenotypes. Directional selection favors one extreme phenotype, shifting the distribution. Disruptive selection selects against intermediate phenotypes, resulting in two overlapping phenotypes at the extremes.
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, where babies that are very large or very small have lower survival rates, maintaining birth weight within a narrow range. Directional selection occurs when one extreme phenotype is favored, shifting the distribution towards that extreme. This type of selection was observed in 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. An example is sexual dimorphism, where males and females of the same species display different heights and body shapes in humans.