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Fact and Fiction about the Peppered Moth


According to the online critique of Explore Evolution by the National Center for Science Education (NCSE):

(A) "Textbooks do not use peppered moths as an example of something new being created, they use it to demonstrate what natural selection can do in mere decades."[1]
(B) EE "claims that many research scientists think Kettlewell's experiments were invalid because he released his moths during the daytime, when moths are sleepy and sluggish," but "no research scientists think this. This claim is found nowhere in the research literature." [2]
(C) EE "claims that because peppered moths don't rest on tree trunks, which is where Kettlewell put them, his experiments are invalid," but "peppered moths do rest on trunks." [3]

(A) Use of Peppered Moths in Explore Evolution

EE does not claim that textbooks "use peppered moths as an example of something new being created," only that they use it as a "classic example of natural selection producing microevolution." (EE, p. 88) According to Charles Darwin, however--and according to most modern evolutionary biologists--natural selection is the main creative force in evolution.

Darwin wrote in The Origin of Species: "Slow though the process of selection may be, if feeble man can do much by artificial selection, I can see no limit to the amount of change, to the beauty and complexity of the coadaptations between all organic beings, one with another and with their physical conditions of life, which may have been effected in the long course of time through nature's power of selection." In 2002, Stephen Jay Gould wrote that Darwin's theory "cannot be equated with the simple claim that natural selection operates. Nearly all his colleagues and predecessors accepted this postulate. Darwin, in his characteristic and radical way, grasped that this standard mechanism for preserving the type could be inverted, and then converted into the primary cause of evolutionary change. Natural selection obviously lies at the center of Darwin's theory, but we must recognize, as Darwin's second key postulate, the claim that natural selection acts as the creative force of evolutionary change. The essence of Darwinism cannot reside in the mere observation that natural selection operates--for everyone had long accepted a negative role for natural selection in eliminating the unfit and preserving the type." [4]

A major criticism of Darwin's theory--a criticism made even by some modern biologists--is that natural selection lacks the creative power Darwin ascribed to it. The NCSE would prefer that students not hear about this criticism, and EE provides a needed counterbalance to the Darwinists' one-sided approach.

(B) Kettlewell's Experiments

Peppered moths are night-fliers, and several articles in the scientific research literature point out the artificiality of releasing them in the daytime, as Bernard Kettlewell did in his experiments. For example, in 1984 Finnish zoologist Kauri Mikkola noted that "night-active moths, released in an illumination bright enough for the human eye, may well choose their resting sites as soon as possible and most probably atypically." Thus "the results of Kettlewell fail to demonstrate the qualitative predation of the morphs of the peppered moth by birds or other predators in natural conditions." [5]

In a 1998 book on industrial melanism, British biologist Michael Majerus (cited as an authority by the NCSE Critique) defended Kettlewell's results but criticized the "artificiality" of predation experiments in which peppered moths were "positioned on vertical tree trunks, despite the fact that they rarely chose such surfaces to rest upon in the wild." According to University of Chicago evolutionary biologist Jerry Coyne (in a review of Majerus's book published in Nature), the fact that peppered moths do not normally rest on tree trunks "alone invalidates Kettlewell's release-and-recapture experiments, as moths were released by placing them directly onto tree trunks." In a 1998 article published in Evolutionary Biology, University of Massachusetts biologist Theodore Sargent, with New Zealand colleagues Craig Millar and David Lambert, re-analyzed Kettlewell's experiments and concluded that although "the 'classical' explanation may be true, in whole or in part," there "is little persuasive evidence, in the form of rigorous and replicated observations and experiments, to support this explanation at the present time." [6]

EE's statement that peppered moths released in the daytime are "sleepy and sluggish" is consistent with the fact that they normally fly at night, and with Mikkola's observations that in daylight they tend to stay where they are put. In addition, British peppered moth expert Laurence M. Cook noted in 1998 that it was easy to photograph live moths because they are "very torpid during the day" and will remain still when placed on a tree trunk. [7]

(C) Where Do Peppered Moths Rest?

Peppered moths in the wild only rarely rest on tree trunks. Even Kettlewell knew this. Regarding his method of releasing moths onto nearby tree trunks, Kettlewell wrote in 1955: "I admit that, under their own choice, many would have taken up position higher in the trees." Mikkola noted in 1984 that "the normal resting place of the peppered moth is beneath small, more or less horizontal branches (but not on narrow twigs), probably high up in the canopies, and the species probably only exceptionally rests on tree trunks." In 1985, British biologist Cyril Clarke and his colleagues reported that in twenty-five years of field work they had found only one peppered moth naturally perched on a tree trunk; they concluded that they knew primarily "where the moths do not spend the day." When Rory Howlett and Michael Majerus studied the natural resting sites of peppered moths in various parts of England, they concluded that "exposed areas of tree trunks are not an important resting site for any form of B. betularia." In 1987, British biologists Tony Liebert and Paul Brakefield confirmed Mikkola's observations that "the species rests predominantly on branches.... Many moths will rest underneath, or on the side of, narrow branches in the canopy." [8]

The NCSE critique claims: "In a comprehensive study of peppered moth resting places in the wild, fully 25% of moths were found resting on trunks." This figure is based on a table in Michael Majerus's 1998 book (cited above) that lists the resting positions of 47 peppered moths "found in the wild between 1964 and 1996," of which 12 were on tree trunks. [9] In that same 32-year period, however, many thousands of peppered moths lived and died in those same woodlands. One study published in 1977 tabulated over 8,000 moths caught in southern England alone. [10] An honest statistic would have divided the 12 moths listed by Majerus by at least 8,000; the result would have shown that the percentage of moths normally resting on tree trunks is much less than 1%. The NCSE's "25%" figure is bogus. [11]

The NCSE critique also cites "a later, extensive 6 year study" by Majerus in which "37% of peppered moths were found on trunks." In 2007, The Independent (London) reported that Majerus "spent the past seven years collecting data from a series of experiments he has carried out in his own rambling back garden. It has involved him getting up each day before dawn and then spending several hours looking out of his study window armed with a telescope and notepad." Majerus himself reported in an August 2007 lecture in Sweden that he "had occasion to spend time carefully scrutinizing the trunks, branches and twigs of a limited set of trees at the experimental site. During this time I have found 135 peppered moths, resting in what I have no reason to presume are not their freely chosen natural resting sites." Of those, 37% were on tree trunks. Majerus concluded: "While the results may be somewhat biased towards lower parts of the tree, due to sampling technique, I believe that they give the best field evidence that we have to date of where peppered moths spend the day." He called this "proof of Darwinian evolution."[12]

Yet Majerus's 37% figure was no more accurate than the NCSE's 25%. During the seven years in which Majerus was peering out his window, far more than 135 peppered moths visited his back yard, but (as previous research showed) he couldn't see most of them because they were resting high in the upper branches of his trees. The moths he could see from the ground represented only a tiny fraction of the total. The first chapter of Darrell Huff's 1954 classic, How To Lie With Statistics, was devoted to sampling bias. Huff wrote: "The test of the random sample is this: Does every name or thing in the whole group have an equal chance to be in the sample?" [13] Obviously, the vast majority of peppered moths were not in Majerus's sample, because they were resting where he couldn't see them. No unbiased scientist would take his statistic seriously, yet the NCSE critique cites it as the final word in this matter.

References Cited
[1] NCSE, Critique of Explore Evolution. October 2, 2008. "Peppered Moths." Available online (2008) at http://ncseweb.org/creationism/analysis/peppered-moths.

[2] NCSE, Critique of Explore Evolution. October 2, 2008. "Kettlewell's Experiments." Available online (2008) at http://ncseweb.org/creationism/analysis/kettlewells-experiments.

[3] NCSE, Critique of Explore Evolution. October 2, 2008. "Where Peppered Moths Rest." Available online (2008) at http://ncseweb.org/creationism/analysis/where-peppered-moths-rest.

[4] Charles Darwin, The Origin of Species, Sixth Edition, p. 85. Available online (2008) at http://darwin-online.org.uk/content/frameset?viewtype=side&itemID=F391&pageseq=415; Stephen Jay Gould, The Structure of Evolutionary Theory. Cambridge, MA: Harvard University Press, 2002, p. 139. Available online (2008) at http://www.stephenjaygould.org/library/gould_selection.html.

[5] Kauri Mikkola, "On the selective forces acting in the industrial melanism of Biston and Oligia moths (Lepidoptera: Geometridae and Noctuidae)," Biological Journal of the Linnean Society 21 (1984): 409-421; See also Kauri Mikkola, "Resting Site Selection by Oligia and Biston moths (Lepidoptera: Noctuidae and Geometridae)," Annales Entomologici Fennici 45 (1979): 81-87.

[6] Michael E. N. Majerus, Melanism: Evolution in Action. Oxford: Oxford University Press, 1998, p. 116; Jerry Coyne, "Not black and white," a review of Michael Majerus's Melanism: Evolution in Action. Nature 396 (1998): 35-36; Theodore D. Sargent, Craig D. Millar & David M. Lambert, "The 'Classical' Explanation of Industrial Melanism: Assessing the Evidence," Evolutionary Biology 30 (1998): 299-322; Jonathan Wells, "Second Thoughts about Peppered Moths," The Scientist (May 24, 1999): 13. Expanded version available online (2008) at http://www.discovery.org/a/590; Jonathan Wells, "The Peppered Myth," a review of Judith Hooper's Of Moths and Men: An Evolutionary Tale. In Books & Culture (September 30, 2002). Available online (2008) at http://www.discovery.org/a/1263.

[7] Laurence M. Cook, personal communication to Jonathan Wells (October 5, 1998).

[8] H. B. D. Kettlewell, "Selection experiments on industrial melanism in the Lepidoptera," Heredity 9 (1955): 323-342; Cyril A. Clarke, G. S. Mani and G. Wynne, "Evolution in reverse: clean air and the peppered moth," Biological Journal of the Linnean Society 26 (1985): 189-199; Kauri Mikkola, "On the selective forces acting in the industrial melanism of Biston and Oligia moths (Lepidoptera: Geometridae and Noctuidae)," Biological Journal of the Linnean Society 21 (1984): 409-421; Rory J. Howlett and Michael E. N. Majerus, "The understanding of industrial melanism in the peppered moth (Biston betularia) (Lepidoptera: Geometridae)," Biological Journal of the Linnean Society 30 (1987): 31-44; Tony G. Liebert & Paul M. Brakefield, "Behavioural studies on the peppered moth Biston betularia and a discussion of the role of pollution and lichens in industrial melanism," Biological Journal of the Linnean Society 31 (1987): 129-150; Arthur S. Lodge (moderator), "Do peppered moths, in the wild, often settle on tree trunks?" An online exchange (January 1, 2000). Available online (2008) at
http://www.discovery.org/a/1242.

[9] Majerus, Melanism: Evolution in Action, p. 123.

[10] R. C. Steward, "Industrial and non-industrial melanism in the peppered moth, Biston betularia," Ecological Entomology 2 (1977): 231-243.

[11] Jonathan Wells, "Moth-eaten Statistics: A Reply to Kenneth R. Miller." Discovery Institute (April 16, 2002). Available online (2008) at
http://www.discovery.org/a/1147.

[12] Steve Connor, "Moth study backs classic 'test case' for Darwin's theory," The Independent [London] (August 25, 2007). Available online (2008) at http://news.independent.co.uk/sci_tech/article2893896.ece; Michael E. N. Majerus, "The Peppered Moth: The Proof of Darwinian Evolution," a lecture delivered in Uppsala, Sweden (August 23, 2007). Available online (2008) at http://www.gen.cam.ac.uk/Research/majerus.htm.

[13] Darrell Huff, How to Lie With Statistics. New York: W. W. Norton, 1954, p. 21; Jonathan Wells, "Exhuming the Peppered Mummy." Discovery Institute
(August 30, 2007). Available online (2008) at http://www.discovery.org/a/4198.

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