Peppered Moth Evolution - Controversy

Controversy

Michael Majerus in his 1998 book Melanism: Evolution in Action questioned the methodology of Bernard Kettlewell's classic experiments, matching a similar 1998 analysis by Sargent et al.. When the biologist Jerry Coyne reviewed this book in Nature, he mistakenly stated that the most serious problem found by Majerus was that only two peppered moths had been found on tree trunks. He also wrote that the white moths had increased in numbers before the lichen had returned and that Kettlewell's findings of moths choosing matching backgrounds had not been replicated in later experiments. Coyne compared his reaction to "the dismay attending my discovery, at the age of 6, that it was my father and not Santa who brought the presents on Christmas Eve". He concluded that "for the time being we must discard Biston as a well-understood example of natural selection in action, although it is clearly a case of evolution. There are many studies more appropriate for use in the classroom" and that further studies of the animal's habits were needed. In contrast to this review, Majerus had stressed that the wealth of additional data obtained since Kettlewell's initial predation papers had not undermined the basic findings from that work, and that differential bird predation of the dark and light moths in habitats affected by industrial pollution to different degrees (directional selection) "is the primary influence of the evolution of melanism in the peppered moth". Coyne had erred in his statement that only two peppered moths had been found on tree trunks, as the book gives the resting positions of 47 peppered moths Majerus had found in the wild between 1964 and 1996; twelve were on tree trunks (six exposed, six unexposed), twenty were at the trunk/branch joint, and fifteen resting on branches. Majerus found that the review did not reflect the factual content of the book or his own views, and cited an assessment by the entomologist Donald Frack that there was essentially no resemblance between the book and Coyne's review, which appeared to be a summary of the Sargent et al. paper rather than Majerus's book.

The review was subsequently picked up by journalist Robert Matthews, who wrote an article for The Sunday Telegraph, 14 March 1999, claiming that "Evolution experts are quietly admitting that one of their most cherished examples of Darwin's theory, the rise and fall of the peppered moth, is based on a series of scientific blunders. Experiments using the moth in the Fifties and long believed to prove the truth of natural selection are now thought to be worthless, having been designed to come up with the 'right' answer". Majerus regarded this view as surprising, and not one that would be shared by those involved in the field. He noted numerous scientific inaccuracies, misquotations and misrepresentations in the article, but thought this was common in press reports. He stated that he had spoken to Matthews for over half an hour and had to explain many details as Matthews hadn't read the book, but "Even then, he got nearly everything wrong."

The use of the peppered moth as an example of evolution had already come under attack by creationists who disputed it as evidence of evolution. They argued that the "peppered moth story" showed only microevolution, rather than speciation or other changes at the larger macroevolutionary scale. Biologists agree that this example shows natural selection causing evolution within a species, demonstrating rapid and obvious adaptiveness with such change, and accept that it is not proof of the theory of evolution as a whole. Although creationists accept microevolution of varieties within a kind, they claim that macroevolution does not happen. To biologists there is no dividing line between the two, and in the modern evolutionary synthesis the same mechanisms are seen operating at various scales to cause both evolution within species and speciation at a macroevolution level or wider changes, the only difference being of time and scale.

The story of Coyne's review was taken up by intelligent design creationists, and at a seminar presenting the wedge strategy on 13 March 1999, Phillip E. Johnson said that the moths "do not sit on tree trunks", "moths had to be glued to the trunks" for pictures and that the experiments were "fraudulent" and a "scam." This led Frack to exchanges with intelligent design proponent Jonathan Wells, who conceded that Majerus listed six moths on exposed tree trunks (out of 47), but argued that this was "an insignificant proportion". Wells wrote an essay on the subject, a shortened version of which appeared in The Scientist of 24 May 1999, claiming that "In 25 years of fieldwork, C.A. Clarke and his colleagues found only one peppered moth on a tree trunk", and concluding that "The fact that peppered moths do not normally rest on tree trunks invalidates Kettlewell's experiments".

In 2000 Wells wrote Icons of Evolution: Why much of what we Teach About Evolution is Wrong, which claims "What the textbooks don't explain, however, is that biologists have known since the 1980s that the classical story has some serious flaws. The most serious is that peppered moths in the wild don't even rest on tree trunks. The textbook photographs, it turns out, have been staged." The arguments put by Wells have been dismissed by Majerus, Cook and peppered moth researcher Bruce Grant who describes Wells as distorting the picture by selectively omitting or scrambling references in a way that is dishonest. Professional photography to illustrate textbooks uses dead insects because of the considerable difficulty in getting good images of small, relatively fast moving animals. The scientific studies actually consisted of observational data rather than using such photographs. The photographs in Michael Majerus's 1998 book Melanism: Evolution in Action are unstaged pictures of live moths in the wild, and the photographs of moths on tree-trunks, apart from some slight blurring, look no different than the "staged" photographs. While an experiment did involve the gluing of dead moths to trees, this practice was just one of many different ways used to study different individual elements of the overall hypothesis. This particular experiment was not meant to exactly reproduce natural conditions but instead was used to assess how the numbers of moths available (their density) affected the foraging practices of birds.

On 27 November 2000, the school board of Pratt County, Kansas continued efforts to favor intelligent design teaching by requiring the use of specific resources. These included the article by Jerry Coyne, who wrote to object strongly to this creationist misrepresentation of his critical re-evaluation, emphasising that the moth story is a sound example of evolution produced by natural selection and stating that his call for additional research was only to resolve uncertainty regarding bird predation as the cause of the natural selection and evolutionary change. Bruce Grant also wrote to challenge allegations of fraud in the moth experiments based on misrepresentations by Wells.

In 2002, Judith Hooper's Of Moths and Men added to the accusations of scientific fraud. She accused Kettlewell of manipulating his data to prove his hypothesis. The book received strong criticism from the scientific press (e.g., Coyne, B.C. Clarke, Grant). Majerus described it as "littered with errors, misrepresentations, misinterpretations and falsehoods".

Majerus had died before writing up his study, but his work was completed by Cook et al. and published in February 2012, concluding that "These data provide the most direct evidence yet to implicate camouflage and bird predation as the overriding explanation for the rise and fall of melanism in moths." Coyne wrote an article summarising the unfolding of the controversy which had followed his original review, and said "Despite the defensiveness of British evolutionists, I think my criticisms carried some weight, because Cambridge biologist Michael Majerus decided to repeat Kettlewell’s experiments, but doing them correctly this time." He quoted the Cook et al. study's conclusion that "These new data answer criticisms of earlier work and validate the methodology employed in many previous predation experiments that used tree trunks as resting sites. The new data, coupled with the weight of previously existing data convincingly show that ‘industrial melanism in the peppered moth is still one of the clearest and most easily understood examples of Darwinian evolution in action’." Coyne said he was "delighted to agree with this conclusion, which answers my previous criticisms about the Biston story."