Industrial melanism

Industrial melanism is an evolutionary effect prominent in several arthropods, where dark pigmentation (melanism) has evolved in an environment affected by dark soot deposits from industrial pollution. Darker pigmented individuals have a higher fitness and are thus favored by natural selection. This change as a result of modification in selection pressure is a popular teaching example in Darwinian evolution, providing evidence for natural selection.

Industrial melanism is widespread in the Lepidoptera (butterflies and moths), involving species such as Hamadryas feronia (variable cracker butterfly), Odontopera bidentata (scalloped hazel moth),Oligia latruncula (tawny marbled minor moth), Oligia strigilis (marbled minor moth), Lymantria monacha (dark arches), and many other species of moth; the most studied example is in the peppered moth, Biston betularia. It is also seen in a beetle, Adalia bipunctata (two-spot ladybird), where camouflage is not involved as the insect has conspicuous warning coloration. The rapid decline of melanism that has accompanied the reduction of pollution makes natural selection "the only credible explanation".Camouflage against a darker background is the usual historical explanation.

Other explanations for the observed correlation with industrial pollution have been proposed, including strengthening the immune system in a polluted environment, and absorbing heat more rapidly when sunlight is reduced by air pollution.

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