Stabilizing selection (also called optimizing selection or normalizing selection) is one of three main forms of natural selection. In stabilizing selection, selection acts to maintain a well-adapted balance with regard to fitness among the forms of a gene (alleles) that exist in a given population. According, stabilizing selection conserves existing genetic balances and continues to do so until there is a sufficient change in environment to cause directional or disruptive selection. As with directional and disruptive selection, stabilizing selection is based upon differences in greater reproductive success of individuals within the population. Stabilizing selection specifically acts on visible characters or traits that result in difference in reproductive success (differential reproduction).

The existing fossil record provides abundant evidence for the dominance of stabilizing selection over the majority of the history of life on Earth. The other main mechanisms of natural selection include directional selection (when an extreme...