Arizona State University (ASU) BIO182 General Biology II Exam 2 Practice

Stabilizing selection is a form of natural selection that favors intermediate traits, leading to a reduction in the expression of extreme traits in a population. This type of selection occurs when individuals with traits closer to the average in a given population have a higher fitness compared to those with more extreme characteristics.

An example of stabilizing selection can be seen in human birth weights; babies born with weights that are too high or too low have higher mortality rates compared to those that are of average weight. Consequently, over generations, the population's average weight tends to be favored, illustrating how stabilizing selection works to maintain those intermediate traits that are most beneficial for survival and reproduction.

In contrast, directional selection favors one extreme of a trait distribution over the others, resulting in a shift of the population trait mean in one direction. Disruptive selection, on the other hand, favors individuals at both extremes of the trait spectrum, which can lead to increased variance and potentially speciation. Sexual selection involves traits that enhance an individual's chances of mating rather than survival directly.

Thus, stabilizing selection is characterized by its promotion of average phenotypes, ensuring that these intermediate traits are more common over time while extreme traits are diminished.