Claim CB601:

According to the traditional peppered moth story, cryptic coloration confers protection to the moths from predators, and as the habitat changed due to industrial pollution, natural selection caused the frequencies of different color varieties of the moth to change. As the trees became darker, the lighter moths stood out more, so the darker ones became more plentiful, and vice versa as the pollution cleared. That story is no longer supportable because of flaws found in the experiments, such as where the moths rested, and the occurrence of contrary data, such as unaccountable frequencies of uncamouflaged moths in areas.

Source:

Wells, Jonathan, 1999. Second thoughts on peppered moths. http://www.arn.org/docs/wells/jw_pepmoth.htm or http://www.trueorigin.org/pepmoth1.asp
Wells, Jonathan, 2000. Icons of Evolution, Washington DC: Regnery Publishing Inc., pp. 137-157.

Response:

  1. Although the experiments were not perfect, they were not fatally flawed. Even though Kettlewell released his moths in daylight when a night release would have been more true to nature, he used the same procedure in areas that differed only in the amount of industrial pollution, showing conclusively that industrial pollution was a factor responsible for the difference in predation between color varieties. Similar arguments can be made for all other experiments. Although no experiment is perfect (nor can be), even imperfect experiments can give supporting or disconfirming evidence. In the case of peppered moths, many experiments have been done, and they all support the traditional story (Grant 1999).

  2. Even without the experiments, the peppered moth story would be well established. Peppered moth melanism has both risen and fallen with pollution levels, and they have done so in many sites on two continents (Cook 2003; Grant 1999).

  3. The peppered moth story is consistent with many other experiments and observations of crypsis and coloration in other species. For example, bird predation maintains the colorations of Heliconius cydno, which has different coloration in different regions, in both regions mimicking a noxious Heliconius species (Kapan 2001). Natural selection acting on the peppered moth would be the parsimonious hypothesis even if there were no evidence to support it.

  4. The peppered moth story is not simple. The full story as it is known today fills thousands of pages of journal articles. Familiarity with the literature and with the moths in the field is needed to evaluate all the articles. But the research and the debates over its implications have all been done in the open. Charges of fraud and misconduct stem from neglect and misrepresentation of the research by the people making the charges (Grant 2000). Of those familiar with the literature, none doubt that bird predation is of primary importance in the changing frequencies of melanism in peppered moths (Majerus 1999).

    In teaching any subject to beginners, simplifying complex topics is proper. The peppered moth story is a valuable tool for helping students understand how nature really works. Teachers would be right to omit the complexities from the story if they judged that their students were not yet ready for that higher level of learning (Rudge 2000).

Links:

Gishlick, Alan D., n.d. Icons of evolution? Peppered moths. http://www.ncseweb.org/icons/icon6moths.html

Tamzek, Nic, 2002. Icon of obfuscation. http://www.talkorigins.org/faqs/wells/iconob.html#moths

References:

  1. Cook, L. M., 2003. The rise and fall of the carbonaria form of the peppered moth. Quarterly Review of Biology 78(4): 399-417.
  2. Grant, Bruce S., 1999. Fine tuning the peppered moth paradigm. Evolution 53(3): 980-984.
  3. Grant, Bruce, 2000. Letter: Charges of fraud misleading. Pratt Tribune, 13 Dec. 2000. Reprinted at http://www.indiana.edu/~ensiweb/lessons/icon.cr.html
  4. Kapan, Durrell D., 2001. Three-butterfly system provides a field test of mullerian mimicry. Nature 409: 338-340.
  5. Majerus, Michael E. N., 1999. (Letter). Quoted by Frack, Don. 1999. Peppered moths, round 2, part 2. http://www.calvin.edu/archive/evolution/199904/0103.html
  6. Rudge, David Wyss, 2000. (see below)

Further Reading:

Majerus, Michael E. N. 1998. Melanism: Evolution in Action, Oxford University Press, Oxford. (technical)

Rudge, David Wyss. 1999. Taking the peppered moth with a grain of salt. Biology and Philosophy 14: 9-37.

Rudge, D. W. 2000. Does being wrong make Kettlewell wrong for science teaching? Journal of Biological Education 35(1): 5-11.

Rudge, D. W. 2005. The beauty of Kettlewell's classic experimental demonstration of natural selection. BioScience 55: 369-375.
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created 2001-4-29, modified 2005-5-2