Industrial Melanism

Michael E. N. Majerus

University of Cambridge

Industrial melanism may be defined as a proportional increase of dark, or melanin, pigments in individuals of a population, caused by changes in the environment resulting from industrial pollution. Both increases in the frequencies of distinct melanic forms and the general darkening of some or all forms within a population may be involved.

The increase in dark forms of some species of moth in industrial regions of western Europe, and latterly elsewhere, has provided some of the best known, most easily understood, and most often quoted examples of evolution in action. Increases in pollution following the industrial revolution led to changes in the environment. In particular, sulfur dioxide denuded trees and other substrates of lichens, while particulate air pollution blackened the resulting surfaces. In response to these changes, many species of moth and some other invertebrates that rely on camouflage for defense against some predators have changed their coloration, becoming darker, in line with the darkening of the substrates that they rest upon by day. These changes have occurred largely in the past 150 years and are cited as examples that illustrate the central mechanism of Charles Darwin's theory of evolution: natural selection.

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