In the early 19th century, almost all peppered moths collected by biologists in the U.K. were pale and mottled. Only rarely was a collector able to find a dark-peppered moth. After the Industrial Revolution, when furnaces filled the air with dark soot, the light-peppered moth became rare and the dark-peppered moth was most common in industrial cities. A reasonable explanation for this change is that the dark moth was less likely to be seen and eaten by birds against the dark background. This explanation illustrates the principle of
Explanation
Natural selection is the process whereby the members of the species who are best able to survive and reproduce in an environment thrive, passing their genes on to next generations. The pollution in the environment selected for darkness in peppered moths.