Final answer:
Disruptive selection is defined as the natural selection against intermediate phenotypes in favor of both extremes, leading to increased genetic variance and two distinct subgroups within a population.
Step-by-step explanation:
The primary characteristic of disruptive selection in the context of continuous traits in a population is the selection against intermediate phenotypes and the consequent favoring of individuals at both extremes of the phenotypic distribution. This leads to an increase in genetic variance and the development of two distinct populations within the same species, each adapted to different environmental conditions or strategies for survival. Examples include sexually dimorphic species where extremes in size or behavior are beneficial, and populations where environmental heterogeneity favors distinctly different phenotypes, such as light-colored and dark-colored mice in a patchy environment of sand and grass.