What is an example of stabilizing selection?

Stabilizing selection is a type of natural selection that favors intermediate phenotypes over extreme ones, thereby reducing variation and maintaining the status quo for a particular trait. Baby birth weight is a classic example of stabilizing selection because both low and high birth weights can result in higher mortality rates for newborns. Babies that are of average weight have better survival rates, as they are more likely to be healthy and well-developed than those that are either too small or too large. This selection pressure helps to ensure that birth weights remain within a certain range, demonstrating the effect of stabilizing selection on this trait.

In contrast, Darwin's finches illustrate adaptive radiation, where different species evolve in response to different environmental pressures, and coloration in guppies reflects sexual selection and environmental adaptation rather than stabilizing selection. Resistance to antibiotics involves directional selection, as bacteria that acquire resistance survive and proliferate in the presence of these drugs, shifting the population towards that trait.