Final answer:
The color change in moth populations from light to dark was caused by environmental changes due to the Industrial Revolution, leading to increased predation of lighter moths and favoring the survival of darker moths.
Step-by-step explanation:
The change from a light variety to a dark variety of moths, particularly the peppered moth, is a classic example of natural selection driven by environmental changes. The Industrial Revolution led to the increase of soot and pollution, which darkened the tree trunks where the moths rested. As a result, predation by birds shifted to target the light-colored moths that were now more visible against the soot-darkened trees, causing the darker varieties to be favored and survive at higher rates.
Thus, the population of moths changed in coloration from predominantly light to dark—a process known as directional selection. When the environment cleaned up, and trees returned to their lighter state, the light-colored moths were once again favored, leading to their resurgence in the moth population.