The evolution of the peppered moth is an evolutionary instance of directional colour change in the moth population as a consequence of air pollution during the Industrial Revolution. The frequency of dark-coloured moths increased at that time, an example of industrial melanism. Later, when pollution was reduced, the light-coloured form again predominated. Industrial melanism in the peppered moth was an early test of Charles Darwin's natural selection in action, and it remains a classic example in the teaching of evolution. In 1978, Sewall Wright described it as "the clearest case in which a conspicuous evolutionary process has actually been observed."
Biston betularia f. typica, the white-bodied peppered moth.
Biston betularia f. carbonaria, the black-bodied peppered moth.
Typica and carbonaria morphs on the same tree. The light-coloured typica (below the bark's scar) is nearly invisible on this pollution-free tree, camouflaging it from predators.
Creationists have disputed the occurrence or significance of the melanic carbonaria morph's increase in frequency.
Industrial melanism is an evolutionary effect prominent in several arthropods, where dark pigmentation (melanism) has evolved in an environment affected by industrial pollution, including sulphur dioxide gas and dark soot deposits. Sulphur dioxide kills lichens, leaving tree bark bare where in clean areas it is boldly patterned, while soot darkens bark and other surfaces. Darker pigmented individuals have a higher fitness in those areas as their camouflage matches the polluted background better; they are thus favoured by natural selection. This change, extensively studied by Bernard Kettlewell (1907–1979), is a popular teaching example in Darwinian evolution, providing evidence for natural selection. Kettlewell's results have been challenged by zoologists, creationists and the journalist Judith Hooper, but later researchers have upheld Kettlewell's findings.
Intermediate insularia form (between pale typica and dark carbonaria in tone) of peppered moth on a lichen-covered birch tree: Bernard Kettlewell counted the frequencies of all three forms.
Tree bark covered in shrubby and leafy lichens forms a patterned background against which non-melanic disruptively patterned moth camouflage is effective.
Image: Odontopera bidentata, Scalloped Hazel, Trawscoed, North Wales, June 2016 Flickr janetgraham 84
Image: Odontopera bidentata (7275071212)
