Melanic polymorphism in the peppered moth,Biston betularia, and other Lepidoptera

Abstract

The phenomenon of industrial melanism, whereby dark forms of many species of moth have evolved in response to the darkening of some habitats since the industrial revolution, is one of the classical teaching examples of evolution in action. However, the precis versions of the evolution of melanism given in most school texts are rarely accurate and never complete. This paper reviews the story of industrial melanism with specific reference to the most famous example, the peppered moth, concentrating on the influence of ecological and behavioural factors on the evolution of melanic polymorphism. The prominence given to the case of the peppered moth in school texts suggests that all melanic Lepidoptera are industrial and evolved in a similar way to the carbonaria form of this species. Yet over half the British Lepidoptera which now have melanic forms, had such forms prior to the industrial revolution. Furthermore, variation in the morphologies, ecologies, and behaviours of different species means that the course of melanic evolution will have had peculiarities specific to each case. The other factors which may affect the evolution of melanic polymorphism are discussed. Finally, the lack of work on species other than the peppered moth is highlighted and it is suggested that other species which exhibit melanism provide outstanding opportunities for original and valuable research, that may be undertaken as class or project work.