Question

Explain the increase in the numbers of melanic (dark-winged) moths in the urban areas of post-industrialisation period in England. OR
How does industrial melanism support Darwin's theory of Natural Selection? Explain.

Answer 1

In a collection of moths in 1850 before the advent of industrialization, it was observed that there were more white winged moths on trees than dark winged one or melanised moths. However, in 1920, the population of dark winged ones increased and white winged ones reduced. The explanation put forth for this observation was that predators could spot a moth against a contrasting background. During post industrialization period, the tree trunks became dark due to industrial smoke and soot. Under this condition, white moths did not survive due to predators but dark winged or melanised moths survived.

Before industrialization, white coloured lichens grew thickly and covered the trees. In that background, the white winged moths survived but dark ones were picked up by the predators. Hence, moths that were able to camouflage in both the backgrounds were able to survive. No variant was wiped out completely.