A form of natural selection that favors intermediate variants by acting against extreme phenotypes is a fundamental evolutionary process. It reduces phenotypic variation within a population, concentrating traits around the mean. For instance, birth weight in human populations is often subject to this phenomenon; babies with weights significantly below or above the average tend to have lower survival rates, leading to a concentration of birth weights around the optimal range.
This type of selection maintains the status quo by preserving well-adapted traits in a stable environment. Its importance lies in its ability to prevent drastic evolutionary change when the current average phenotype is already highly suited to the existing environmental conditions. Historically, this concept has been crucial in understanding how populations maintain their characteristics over time, particularly in the absence of significant environmental pressures that would favor directional or disruptive selection.
