Why has the number of dark moths decreased in the last 50 years?
The Correct Answer and Explanation is:
The number of dark moths, particularly the Biston betularia (peppered moth), has decreased in the last 50 years due to changes in environmental conditions, specifically the reduction in air pollution and the restoration of cleaner air.
Explanation:
Historically, during the Industrial Revolution in the 19th century, the environment in parts of the UK, especially near industrial areas, became heavily polluted with soot and smoke. The trees and buildings in these areas became darkened with soot, providing a camouflage for dark-colored (melanic) moths. These moths, which were darker than the typical lighter-colored moths, were better able to survive and reproduce because they blended in with the soot-covered surfaces, avoiding predation by birds. This led to a rise in the population of dark-colored moths, as they were more likely to survive and pass on their genes.
However, in the latter half of the 20th century, air quality improved significantly due to stricter environmental regulations and efforts to reduce industrial pollution. As a result, the soot that had darkened the environment began to decrease, and surfaces like tree trunks and buildings became lighter again. This change in the environment made the darker moths more visible to predators, as the lighter-colored moths, which blended better with the now-cleaner environment, had a survival advantage.
The decrease in pollution led to the gradual increase in the population of lighter-colored moths and a decrease in the number of dark moths. This process of natural selection, where the lighter moths became better camouflaged and the darker moths became more visible to predators, has been a significant factor in the decline of dark moth populations over the past 50 years.
This example illustrates how environmental changes can influence evolutionary pressures, shifting the survival advantages of certain traits in response to changing conditions.