What is the effect of stabilizing selection on variation within a species?

Stabilizing selection is a type of natural selection that favors individuals with traits that are average or intermediate in their phenotypic characteristics. This selection pressure acts to reduce the extremes in a population, thereby maintaining the status quo for specific traits rather than allowing for significant variation. As a result, individuals that exhibit extreme phenotypes—whether they are more extreme on the lower or upper end—are less likely to survive and reproduce.

The process leads to a decrease in overall variation in those traits being selected against, because the average or intermediate phenotypes are preserved and proliferated within the population. Thus, stabilizing selection contributes to the stability of existing phenotypic traits in a species, ensuring that the advantageous traits remain prevalent while limiting the diversity of extreme phenotypes. This is important for the species’ adaptation to its environment, as it keeps the population well-suited for its niche without permitting the introduction of potentially maladaptive traits that could disrupt the organism's fitness.