Due to the resources been limited in nature, organisms having traits that favor survival and reproduction will tend to leave more offspring than their peers. This results for those traits to increase in frequency/expression over generations. Such a phenomenon is called natural selection as nature is selecting the variation suitable for the particular environment.

The response of a peppered moth Biston betularia to the industrial change is a classic example of natural selection. This moth is found in all parts of England. Industrial melanism is an adaptation where the moths living in the industrial areas developed melanin pigment to hide themselves from their predators and this adaptation is called industrial melanism. Due to industrial pollution and soot deposition, the bark of trees became darker in colour which was advantageous for black moths as they were camouflaged and difficult for predators to identify. As a consequence, the white coloured moths were easily visible and got hunted more than black coloured. The population of black coloured moths increased due to natural selection as they were better adapted to the current environment.