Alternative Hypotheses
Several alternative hypotheses to explain industrial melanism, particularly noted in the peppered moth, were proposed during the 1920s and 1930s. Some dissenters within the scientific community have criticized the peppered moth story, notably Sargent et al. (1998), but peppered moth researchers remain unconvinced.
Several alternative selection mechanisms have been proposed. Note that a change in allele frequency, be it caused by natural selection, mutation, migration or genetic drift by definition, is differential. However, the magnitude of the changes observed can only be accounted for by natural selection. It can be seen from population genetics that a non-differential change will not cause evolution. If the allele frequencies are denoted by the algebraic terms p and q, and (say) p = 0.6 and q = 0.4, then a non-differential reduction in population size from say 2000 to 100 individuals, will still produce the same values of (approximately) p = 0.6 and q = 0.4.
Read more about this topic: Peppered Moth Evolution
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