ABSTRACT
Natural selection is expected to adapt populations to their environments. The selective forces are ecological. Environmental changes may drive genetic changes in populations, as demonstrated by the widespread insecticide resistance following the application of insecticides for pest control. In the early 20th century the phenomenon was widespread enough to attract scientific attention. By then, the frequency of dark or black (‘melanic’) moths had reached 95% in some areas, and the number of species with melanic moths approached 80, not only in England but also in industrial areas in other countries in Europe. H. B. D. Kettlewell chose to work mainly with one species, the peppered moth Biston betularia. This moth has a typical morph, with light, spotted (‘peppered’) wings, and a dark, melanic form, called carbonaria. The genetics of the European land snail, Cepaea nemoralis, and its congener C. arvensis, was intensively studied in the 1950s.
