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  1. The replacement of light colored moths by dark colored melanic species due to industrial smoke is called industrial melanism.
  2. In England, there were two varieties of moths, namely white colored (Bison betularia) and black colored (Bison carbonaria) ones sitting on the lichen covered trees.
  3. Before industrial revolution, the white colored moths were not visible insect eating birds (predators), but black colored moths were easily located and eaten by their predators.
  4. Hence, the white colored moths were prevalent in large numbers, while the population of black colored moths went on decreasing.
  5. Large number of industries came up in England during the industrial revolution.
  6. The smoke and soot from chimneys of factories darkened the tree trunks.
  7. This gave an advantage to the black colored moths as they were less conspicuous on the dark background of trees and were not noticed by their predators.
  8. So, their population increased.
  9. On the contrary, the white colored moths which became conspicuous on the dark background of trees were gradually eliminated as they had fallen prey to their predators.
  10. This caused drastic reduction in the population of the white variety of moths.
  11. Thus, population of individuals showing favorable variations increase due to selective force in present, while the one’s showing unfavorable variations perish.