The peppered moth, Biston betularia, occurs as light- or dark-colored variants. Prior to the Industrial Revolution, the light-colored moths were more prevalent because they could camouflage well on lichen-covered trees. With the advent of the Industrial Revolution and increasing air pollution, dark-colored moths became more prevalent. What is the type of evolutionary force at work? Why do the darker moths become more prevalent?
directional selection; because lighter moths were killed by the air pollution
directional selection; because darker moths escaped being spotted by predators
genetic drift; because lighter moths were killed by the air pollution
genetic drift; because darker moths escaped being spotted by predators
The correct answer is: directional selection; because darker moths escaped being spotted by predators.
Directional selection refers to the process where a certain phenotype is favored over others, leading to a shift in the frequency of that phenotype in a population. In this case, the dark-colored moths became more prevalent because they had an advantage over the light-colored moths in surviving and avoiding predation.
Due to increasing air pollution from the Industrial Revolution, the lichen-covered trees that the light-colored moths relied on for camouflage became less common, making the light-colored moths more visible to predators. On the other hand, the dark-colored moths had better camouflage against the newly darkened trees and were less likely to be spotted by predators. This selective advantage for the dark-colored moths caused their frequency to increase in the population over time.