What change occurred in the moth population after industrialization by 1920?

Step-by-step solution

After industrialization by 1920, the population of dark-winged moths increased, reversing the earlier proportion observed before industrialization.During post- industrialisation period, the tree trunks became dark due to industrial smoke and soots. Under this condition the white-winged moth did not survive due to predators, dark-winged or melanised moth survived. Before industrialisation set in, thick growth of almost white-coloured lichen covered the trees - in that background the white winged moth survived but th