What is a characteristic of directional selection?

Directional selection is a form of natural selection that favors individuals with traits at one extreme end of the phenotypic spectrum, leading to a shift in the population's trait distribution over time. This process occurs when the environment changes in such a way that individuals possessing certain advantageous traits have a higher fitness compared to those with traits at the opposite end of the spectrum.

For example, if a certain bird species adapts to a change in food source that requires longer beaks, birds with longer beaks will have a survival advantage and will reproduce more successfully than those with shorter beaks. Over time, this results in an increase in the frequency of the long-beaked phenotype in the population.

In contrast, options that suggest no change in trait frequency, decrease in genetic variation, or promotion of balanced traits do not accurately reflect the nature of directional selection. Specifically, directional selection typically leads to a decrease in genetic variation as the population becomes more homogeneous for the favored trait, but it does not promote balanced traits, as the focus is on one extreme.