Color in peppered moths is controlled by genes. A light-colored variety and a dark-colored variety of a peppered moth species exist in nature. The moths often rest on tree trunks, and several different species of birds are predators of this moth.

Before industrialization in England, the light-colored variety was much more abundant than the dark-colored variety and evidence indicates that many tree trunks at that time were covered with light-colored lichens.

Later, industrialization developed and brought pollution which killed the lichens leaving the tree trunks covered with dark colored soot. The results of a study made in England are shown in the graph below.

State one possible reason that the light-colored variety was not completely eliminated from the polluted environment. Be sure your reason can be supported by the evidence shown.

Natural selection is the phenomenon in the biology in which the group of organisms which is most suitable to the changing environment will survive and increase its population by reproduction while non suitable group will decrease in number due to low ability to cope with changing environment.

In this question before industrial revolution, light color moths have very light places like lichens to hide themselves from the predators by attaching to light color lichens.

But after industrial revolution due to pollution white lichen die and the habitat for white moths become less and they are more visible to the predators.

That's why their number decreases and dark color moths increase in number.