Final answer:
The selection of the high and low extreme versions of a trait over the average version is known as disruptive selection, favoring both extremes while intermediate forms are less fit.
Step-by-step explanation:
The pattern of natural selection where the high and low extreme versions of a trait are favored over the average version of the trait is known as disruptive selection. This process selects for phenotypes at both ends of the spectrum while the intermediate phenotypes are, on average, less favorable. An example of disruptive selection can be seen in populations of mice living in areas with a mix of light-colored sand and patches of tall grass where light-colored mice blend into the sand and dark-colored mice hide in the grass, but medium-colored mice are more easily spotted by predators.