The genetic variation within the population of peppered moths during and after the Industrial Revolution in London is significant because it illustrates a clear example of natural selection driven by environmental change. Before industrialization, the light-colored, speckled form of the moth was predominant because it was camouflaged against lichen-covered trees, protecting it from predators. However, as industrial pollution darkened tree trunks with soot and killed lichens, a genetic mutation causing a dark-colored (melanic) form of the moth became advantageous. This dark form, caused by a "jumping gene" mutation in the cortex gene, provided better camouflage on soot-darkened surfaces, allowing these moths to survive predation more effectively and increase in frequency in polluted areas
. This shift in the moth population's coloration is a classic and well- documented example of industrial melanism and natural selection in action. It demonstrates how genetic variation within a population provides the raw material for evolution, enabling species to adapt to changing environments. When pollution levels later decreased due to clean air laws, the frequency of the light-colored moths rose again, showing the reversibility of this evolutionary change in response to environmental conditions
. Thus, the significance of genetic variation in the peppered moth population lies in its role as a textbook case of evolution by natural selection, confirming Darwin's theory and illustrating how environmental pressures can shape the genetic makeup and phenotype of a species over relatively short timescales
