Industrial melanism in peppered moth occurred due to natural selection. The significant reason for this is

mutation in light coloured moths  due to increases in industrial pollution

advantageous selection of white months from trees on polluted areas, resulting in increased population of white moths

the light coloured white moths could not be noticed by predatory birds after deposition of soot on bark of trees

advantageous selection of black moths on trees in polluted areas, resulting in increase population of black moths