What is directional selection?

Directional selection is a type of natural selection that favors one extreme phenotype over others in a population. This results in a shift in the frequency of traits in a specific direction. For example, if individuals with a greater beak size in a bird species are better suited to their environment because they can access food more efficiently, over time, the average beak size in the population will increase as these individuals reproduce more successfully. This can lead to significant evolutionary changes within the population as the trait spreads.

In contrast, the other options describe different patterns of selection. Favoring average individuals is characteristic of stabilizing selection, which reduces variation and maintains the status quo. Selecting for both extremes describes disruptive selection, where both ends of the phenotype spectrum are favored, leading to increased variation in the population. The process that stabilizes population traits does not apply to directional selection, as directional selection actively shifts traits rather than maintaining them.