Final answer:
Negative frequency-dependent selection promotes rare phenotypes within a population, thereby increasing genetic variance and encouraging diversity.
Step-by-step explanation:
Negative frequency-dependent selection favors rare phenotypes within a population. This type of selection increases the population's genetic variance by giving an advantage to phenotypic traits that are less common. An example of this can be found in the male common side-blotched lizards of the Pacific Northwest, where the less common yellow males, who are sneakier in their mating behavior, are favored when orange and blue males are more prevalent.
While positive frequency-dependent selection would favor more common phenotypes and decrease genetic variance, negative frequency-dependent selection does the opposite, which promotes diversity and can often lead to a balanced polymorphism within a population where multiple strategies or traits coexist.