During the period when the number of coal-burning factories in England was increasing (during the Industrial Revolution), it was noticed that the number of melanic individuals of the species of peppered Moth (Biston betularie) became more common. Originally rare in the population of normally light-coloured moths, the frequency of the melanic form increased in polluted areas until it was over 90%. This change in colour has come to be known as 'Industrial melanism'.
Before industrialisation set in, thick growth of almost white-coloured lichen covered the trees; in that background, the white-winged moth survived but the dark-coloured moth was picked out by predators. Post-industrialization, the tree trunks became covered in soot and turned black. This allowed the dark coloured moth to camouflage themselves, whereas their light coloured forms were easily hunted.