What are the main types of natural selection?

The correct answer identifies three primary modes of natural selection: directional, stabilizing, and disruptive selection. These types describe how environmental pressures can shape the traits of populations over time.

Directional selection occurs when one extreme phenotype is favored over others, leading to a shift in the population's trait distribution. For example, if larger body size provides a survival advantage due to climate changes, the population will gradually show an increase in size over generations.

Stabilizing selection acts against extreme phenotypes and favors average individuals. This type of selection is common in stable environments where extremes may be less advantageous. An example would be human birth weights, where both very low and very high weights may increase the risk of survival complications, leading to a predominance of average weights in the population.

Disruptive selection favors individuals at both extremes of the trait spectrum while selecting against average individuals. This can lead to the formation of two distinct phenotypes within a population, as seen in certain species of birds where individuals with either very large or very small beaks may be better suited for specific food sources while those with average-sized beaks may struggle to survive.

These three types of natural selection illustrate the dynamic processes that influence evolutionary change and are foundational to understanding evolutionary biology.