Final answer:
In a stable environment where an average phenotype has a survival advantage, A) stabilizing selection occurs, favoring those individuals and leading to reduced genetic variance in the population.
Step-by-step explanation:
When a species lives in a constant environment for a long time and the "average type" of individual has the best chance of surviving and producing the most offspring, this scenario describes A) stabilizing selection.
Stabilizing selection occurs when natural selection favors an average phenotype and selects against extreme variations, thereby reducing the genetic variance in a population.
An example of this could be how mice with fur color that closely matches the forest floor are less likely to be preyed upon compared to those with lighter or darker fur.
This type of selection promotes the survival of individuals that have traits closely aligned with the mean trait value and is typically found in stable, unchanging environments.
As a result, the population becomes more genetically homogeneous over time, which can make it less capable of adapting to sudden changes in the environment.