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Claim CB601.2:

Various aspects of the change in frequencies of the varieties of peppered moth and their geographical distribution are inconsistent with its proposed explanation in terms of natural selection resulting from differential predation.


Wells, Jonathan, 1999. Second thoughts about peppered moths. ,
Wells, Jonathan, 2000. Icons of Evolution, Washington DC: Regnery Publishing Inc., pp. 144-149.


  1. The claim is based on the naive assumption that local observations of differential predation rates are sufficient to make accurate predictions of the relative frequencies of the different varieties of peppered moth. It also falsely insinuates that early attempts to explain these phenomena relied exclusively on visually selective predation to the exclusion of all other factors.

    Differential predation was originally proposed as a highly plausible, and probably the most important, factor influencing the observed changes in relative frequencies of the varieties of peppered moth (Tutt 1896, as reported by Berry 1990, 317). However, even before Kettlewell's famous experiments, Ford (1937, 484-498) had already noted that visually selective predation alone could not account for all the facts associated with the spread of industrial melanism, and suggested that non-visual selection (i.e. selection resulting from something other than visually selective predation) could also have been an important factor. In fact, I am not aware of any evolutionary biologist who has ever suggested that natural selection resulting from differential predation would by itself account completely for all details of the geographical distributions of the peppered moth's varieties, or of their change in relative frequencies.

    Predictions based on the naive assumption mentioned above cannot be expected to match the observed data with anything more than a very rough degree of approximation, so it would not have been much of a surprise to anyone when some discrepancies besides those already pointed out by Ford were noted between such predictions and observational data (Haldane 1956). Almost all these discrepancies have quite natural and obvious possible explanations that were immediately pointed out whenever the matter was discussed in the scientific literature.

    Besides non-visual selection, already proposed by Ford, factors which were suggested as possible explanations for the discrepancies include gene flow, heterozygous advantage (Haldane 1956), and frequency dependent selection (Bishop et al. 1978, 505). Mani (1990) described the results of incorporating the effects of gene flow and non-visual selection into a more comprehensive mathematical model than the one Haldane had used. Though still crude, the model was nevertheless found to account for most of the discrepancies left unexplained by Haldane's, and to provide a "consistent and reasonable picture of the gross pattern of changes in the melanic frequencies." Thus, the conclusion from earlier investigations that differential predation is likely to be the most important single factor influencing the relative frequencies of the varieties of the peppered moth in Britain has by no means been called into question by later ones. On the contrary, it has been complemented and strengthened by them.


  1. Berry, R. J., 1990. Industrial melanism and peppered moths (Biston betularia (L.)), Biological Journal of the Linnean Society, 39: 301-322.
  2. Bishop, J. A., L. M. Cook and J. Muggleton, 1978. The response of two species of moths to industrialization in northwest England, I Polymorphisms for melanism, Phil. Trans. R. Soc. Lond. (B), 281: 489-515
  3. Ford, E. B., 1937. Problems of heredity in the lepidoptera, Biol. Rev., 12: 461-503.
  4. Haldane, J. B. S., 1956. The theory of selection for melanism in Lepidoptera, Proceedings of the Royal Society of London, Series B 145: 303-306.
  5. Mani, G. S., 1990. Theoretical models of melanism in Biston betularia -- a review, Biological Journal of the Linnean Society, 39: 355-371.

Further Reading:

Grant, Bruce S., 1999. Fine tuning the peppered moth paradigm. Evolution 53(3): 980-984.
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created 2001-2-17