The type of natural selection that occurs when one extreme phenotype is favored is known as directional selection. This process leads to a shift in a population's phenotype distribution over time, favoring individuals at one end of the phenotypic spectrum. It often occurs in response to changes in the environment, enhancing the survival and reproduction of advantageous traits. An example is the evolution of antibiotic resistance in bacteria, where the resistant phenotype thrives while non-resistant individuals decline.