Originally, peppered moths lived where light-colored lichens covered the trees. For camouflage from predators against that clean background, they had generally light coloration. During the Industrial Revolution in England, sulphur dioxide pollution in the atmosphere reduced the lichen cover, while soot blackened the bark of urban trees, making the light-colored moths more vulnerable to predation. This provided a selective advantage to the gene responsible for melanism, and the darker-colored moths increased in frequency. The melanic phenotype of "Biston betularia" has been calculated to give a fitness advantage as great as 30 per cent. By the end of the 19th century it almost completely replaced the original light-coloured type (var. "typica"), forming a peak of 98% of the population in 1895.