Industrial melanism in peppered moths

Industrial melanism in the peppered moth Biston betularia is a well-known example of the process of natural selection.^[14][15] The typical wing color phenotype of B. betularia is black and white flecks, but variant 'melanic' phenotypes with increased amounts of black also occur.^[14] In the nineteenth century, the frequency of these melanic variants increased rapidly. Many biologists proposed explanations for this phenomenon. It was demonstrated in the early 1910s, and again in many later studies, that the melanic variants were a result of dominant alleles at a single locus in the B. betularia genome.^[14] The proposed explanations, then, centered around various environmental factors that could contribute to natural selection. In particular, it was proposed that bird predation was selecting for the melanic moth forms, which were more cryptic in industrialized areas.^[15] H. B. D. Kettlewell investigated this hypothesis extensively in the early 1950s.

Uncertainty surrounding whether birds preyed on moths at all posed an initial challenge, leading Kettlewell to perform a series of experiments with captive birds.^[14][15] These experiments, while inititally unsuccessful, found that when a variety of insects are provided, the birds did preferentially prey on the most conspicuous moths: those with coloration unmatched to their surroundings. Kettlewell then performed field experiments using mark-recapture techniques to investigate the selective predation of moths in their natural habitat. These experiments found that, in woods near industrialized areas, melanic moth forms were recaptured at much higher rates than the traditional lighter-colored forms, while in non-industrialized woods, the reverse held true.^[15]

More recent research has further emphasized the role of genetics in the case of industrialized melanism in B. betularia. While research had already emphasized the role of alleles in determining wing-color phenotype, it was still unknown whether the melanic alleles had a single origin or had arisen multiple times independently. The use of molecular marking and chromosomal mapping in conjunction with population surveys demonstrated in the early 2010s that the melanic B. betularia variants have one single ancestral origin.^[16] Additionally, the melanic variants appear to have arisen by mutation from a typical wing-color phenotype.