If natural selection favors an average phenotype, selecting against extreme variation, the population will undergo stabilizing selection (see the figure below). In a population of mice that live in the woods, for example, natural selection is likely to favor individuals that best blend in with the forest floor and are less likely to be spotted by predators.
Assuming the ground is a fairly consistent shade of brown, those mice whose fur is most closely matched to that color will be most likely to survive and reproduce, passing on their genes for their brown coat. Mice that carry alleles that make them a bit lighter or a bit darker will stand out against the ground and be more likely to fall victim to predation. As a result of this selection, the population’s genetic variance will decrease.
In stabilizing selection, the population mean stabilizes on a particular non-extreme trait value. This is thought to be the most common mechanism of action for natural selection because most traits do not appear to change drastically over time. Stabilizing selection commonly uses negative selection (a.k.a. purifying selection) to select against extreme values of the character. Stabilizing selection is the opposite of disruptive selection. Instead of favoring individuals with extreme phenotypes, it favors the intermediate variants.
Stabilizing selection tends to remove the more severe phenotypes, resulting in the reproductive success of the norm or average phenotypes. This means that most common phenotype in the population is selected for and continues to dominate in future generations. Because most traits change little over time, stabilizing selection is thought to be the most common type of selection in most populations.