The peppered moth story is simple, easy to illustrate, and makes intuitive sense. When newly industrialized parts of Britain became polluted in the nineteenth century, smoke killed lichens growing on trees and blackened their bark. Pale colored moths which had been well camouflaged before when they rested on tree trunks became very conspicuous and were eaten by birds. Rare dark moths, which had been conspicuous before, were now well camouflaged in the black background. As birds switched from eating mainly dark moths to mainly pale moths, the most common moth color changed from pale to dark. Natural selection had caused a change in the British moth population. The moths had evolved.
The Peppered Moth is widespread in Britain and Ireland and frequently found in ordinary back gardens, yet its amazing story has made it famous all over the world. It is one of the best known examples of evolution by natural selection, Darwin's great discovery, and is often referred to as 'Darwin's moth'.
Natural Selection - Peppered Moth
Characteristic & Moth Story
Peppered Moths are normally white with black speckles across the wings, giving it its name. This patterning makes it well camouflaged against lichen-covered tree trunks when it rests on them during the day.
The evidence that predation by birds has caused the change in frequency of moth color rests on a series of experiments which are now known to have been flawed. Bernard Kettlewell, who carried out most of the studies, assumed that the moths rested on tree trunks during the day. However, it is very difficult to find wild moths in their natural resting places (most textbook photos are of dead moths glued to tree trunks). Painstaking subsequent observations of wild moths have shown that they prefer to settle in locations higher in the tree than those used by Kettlewell. Another problem is that Kettlewell released his moths at the wrong time of day. This meant that they were not able to settle naturally in their preferred resting site. Furthermore, he released large numbers of moths, which may have created an artificial magnet for predatory birds. The experiments were simply too artificial – the moths were released at the wrong time of day, in the wrong places, and in the wrong numbers.
Evolution of the Peppered Moth