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Class 12th Biology 2012 Set1 Outside Delhi Board Paper Solution

Question 20

How does industrial melanism support DarwinÂ’s theory of Natural Selection? Explain.

Industrial melanism shows the effect of industrial pollution on the population of moth on a nearby tree.
Before industrialization, number of white coloured moth is more than the dark coloured moth on a tree whose condition is reversed after industrialization. Before industrialization, light coloured lichen used to grow on trees and therefore moth predators could not spot white moths easily and thus dark moths are lesser in population. But due to industrial pollution, lichens could not grow on trees and now it became difficult to spot dark moths on the dark background of stem bark and thus population of white moths became less than that of dark moths. Thus this process is termed as industrial melanism. Thus industrial melanism supported Darwin’s theory of natural selections that as natural condition changes, the organism which is more fit for the environment survives better than the other. Here before industrialization, white moths are better adapted towards nature but after industrialization, dark coloured moths were more fit towards the changed environmental conditions.