This phenomena was studied by Bernard Kettelwell. The study of this experiment made it clear that the stems of plants before industrial development in England were brown in color because they had a layer of brown lichen on them. At that time the number of brown colored moths was very high there and the black colored moths Carbonaria were less and rare in number. The probable reason for this was that the brown color of the stems was providing protection to the brown moth from carnivorous birds as the moths could not be identified due to the similar background on the stems. Due to industrial development, excessive use of coal started, due to which the amount of soot in the environment increased, as a result, due to accumulation of soot on the stems, their color became black. At this time, brown moths became easily identified by birds, they preyed them and destroyed them. After some time it was observed that the number of brown colored moths had reduced but the number of black colored moths had increased drastically because at this time the black color of the stem was providing them safety. At present, electricity is being used in place of coal in the industries. It started being used due to which black and smoke in the atmosphere almost got eliminated and as a result, the stems of plants returned to their previous color i.e. became bad. This color change also affected the number of black colored slugs. Now due to identification of black moths by the birds, they started being eaten easily but due to the birds not being able to identify the brown moths, they were saved from being hunted. In this way, nature plays an important role in the selection of life.