Figure 7.16 Reversing the effects of pollution. As industries around Kirby, England, reduced the amount of sulfur dioxide pollution they emitted into the air, the color of the trees became lighter. After a decade of declining pollution, the frequency of the dark form of the peppered moth began to decline rapidly.

Data from C. A. Clarke et al., Evolution in reverse: Clean air and the peppered moth, Biological Journal of the Linnean Society 26 (1985): 189–199; G. S. Mani and M. E. N. Majerus, Peppered moth revisited: Analysis of recent decreases in melanic frequency and predictions for the future, Biological Journal of the Linnean Society 48 (1993): 157–165.