Kettlewell's hypothesis is confirmed. In the polluted environment, more pepper morphs are eaten, while in the unpolluted environment, more melanic morphs are eaten. Intustrial melanism is genetically controlled by a single locus in B. betularia . Populations have undergone evolutionary change in color pattern. That change is consistent with the interpretation that it was due to natural selection, in that there is differential survival of the genotypes caused by differential predation on a particular background.
Results confirm qualitative prediction of equation for gene frequency change.
Industrial melanism is seen in more than 70 species of British moths, and all show patterns similar to that seen in B. betularia . As a result, many of the formerly polluted woodlands have returned to their original condition, in which the color of the tree trunks is light and mottled. As would be expected from Kettlewell's work, the melanic forms that were once so prevalent in these areas have almost disappeared. Properties of evolution by natural selection illustrated by this example. Natural selection is directional.