The case of the emergence of a new shade within the species is an example of Evolution by Natural Selection. Moths use the colour of their wings as camouflage against predators. The environment they live in is mostly brown, and thus when resting on tree trunks or on the ground, their brown wings increase their chances of survival by making it harder for predators (birds) to spot them. After the outbreak of the industrial revolution, the environment around big cities went through relatively great changes; the products of coal-burning factories covered the surrounding forests darkening their trees. The so far advantageous pale brown wings became a disadvantage as they contrasted the black bark. Light-coloured individuals were not able to pass on their genes because they were easily spotted by birds; however, black-winged moths were blending in perfectly in the new environment, and thus this adaptation increased their chances of survival and reproduction. In the course of time, the allele responsible for black colour became more and more abundant in the population.