What does the theory of natural selection state?

Explanation

Darwin.s theory of natural selection does not explain what exactly evolution is, but explains how evolution might have occurred in nature. A classical example for natural selection is industrial melanism, exhibited, by peppered moth-Biston betularia. These moths were available in two colours grey and black. Grey moths were abundant before industrial revolution in all over England. The reason for the existence of large number of grey moths during that period was camouflage on the trunks of trees. But after the establishment of industries in England, black coloured moths were more and grey forms were less. This is due to pollution from industries in the form of soot turned barks of trees into black. So grey moths were easily identified and were more predated by birds. Thus grey moths decreased in number, black moths increased in the population.
Thus natural selection favoured the melanic moths (black) to reproduce more successfully. Natural selection of darker forms in response to industrial pollution is known as industrial melanism.