Final answer:
The correct answer to the question is C. disruptive selection, wherein two or more extreme phenotypes are more advantageous than the intermediate phenotype, leading to increased genetic variance within the population.
Step-by-step explanation:
The mode of natural selection in which two or more extreme phenotypes are fitter than the intermediate phenotype is C. disruptive selection. Disruptive selection, also sometimes referred to as diversifying selection, relates to situations where environmental pressures result in the favoring of multiple phenotypes at the extremes of the spectrum, as opposed to intermediate phenotypes. Sexual dimorphism in humans is a good example of disruptive selection, where males and females present different phenotypes, such as height and body shape, with both extremes having their advantages.
Another example of disruptive selection is the mouse population living at the beach, where light-colored mice that blend in with the sand and dark-colored mice that can hide in the tall grass are favored, while mice with medium coloring that do not blend into either environment are at a disadvantage. This type of selection results in increased genetic variance within the population as it adapts to diverse environmental pressures.