How does industrial melanism support Darwin's theory of Natural Selection? Explain

Before industrial revolution the environment was unpolluted. The lichens on the barks of trees were pale. The white-winged moths could easily camouflage, while the dark winged were spotted out by the birds for food. Hence, they could not survive. After industrial revolution the lichens became dark. This favored the dark-winged moths while the white-winged were picked by birds. The population of the former which was naturally selected increased.