Which type of selection reduces variation by eliminating extreme phenotypes?

Stabilizing selection reduces variation by selecting against extreme phenotypes and favoring intermediate traits.

In a population experiencing stabilizing selection, individuals near the average often survive and reproduce more successfully than individuals at either extreme. Over generations, the population’s mean trait value may remain relatively stable while the range of phenotypes becomes narrower.

A classic example is human birth weight. Very low-birth-weight infants and unusually large infants have historically faced greater risks than babies closer to an intermediate size, although medical care and environmental conditions can change the pattern. Similar selection can affect body size, clutch size, or other traits when extremes are less advantageous.

Stabilizing selection is different from directional selection, which favors one extreme and shifts the population average. It is also the opposite of disruptive selection, which favors both extremes and can increase variation. Stabilizing selection may reduce observable phenotypic variation, but it does not automatically eliminate every genetic difference; hidden genetic variation can remain in a population and become useful if the environment changes.