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Monday, February 03, 2003
The “Piltdown Moth”?
The "peppered moth", Biston betularia, is probably the best known, and most often cited proof of "evolution in action". It has been highly touted as an example of gradualistic evolution for more than forty years. Almost all textbooks on evolution include the peppered moth as THE classic example of evolution by natural selection. According to Majerus, "everyone knows the basic peppered moth story, because it is in all the textbooks" (Majerus, Michael 1998. Melanism: Evolution in Action. Oxford: Oxford University Press. P 97). Teachers at all levels love this story: it has become standard fare in biology and genetics texts precisely because it is "extremely visual" and thus easily understood and remembered. In searching the Web for information on this topic I came across a number of lesson plans, museum workshops and other educational activities based upon the "peppered moth" story.
There are two types of peppered moths, a light colored speckled variety and a dark variety. Prior to the industrial revolution, almost all peppered moths were the light variety. Tree trunks at that time were covered with light colored lichens, which, it was supposed, provided camouflage for the light colored peppered moths as they rested on the tree trunks. The black variety stood out against the light bark and was easily seen and eaten by birds, thus favoring the light moths.
But the industrial revolution created pollution that eliminated the lichens and covered the tree trunks with soot. Now the dark variety of moth was camouflaged better as it rested on the dark, sooty trunks, so birds now ate more of the light moths that they could see better. Natural selection now favored the dark variety, and it became the most common form by 1950 in industrial areas of England.
When anti-pollution laws were passed in England in the 1950’s, the percentage of light moths began to increase, supposedly because lichens started growing on tree trunks again, providing the light moths with the better camouflage once more. In addition, experiments with peppered moths in the 1950’s appeared to confirm the key points of the hypothesis. The peppered moth story has thus been promoted since the 1950s as proof positive that evolution by natural selection is true. (Summarized from an article by Dr Margaret Helder)
The peppered moth has generated enormous amounts of evolutionary enthusiasm. Consider the following.
Professor Steve Jones of University College, London: "Evolution's best evidence is from a revolution; the Industrial Revolution that polluted much of England. The nation's moths turned black as birds ate those whose genes made them conspicuous against sooty trees. With smoke control, the story worked in reverse, and now the black moths are down to a fraction of what they once were." (Daily Telegraph, Feb 10, 1999, page 16.)
Entomologist Bernard Kettlewell: "the most striking evolutionary change ever actually witnessed in any organism" (Kettlewell HBD. 1955. Selection experiments on industrial melanism in the Lepidoptera. Heredity 9: 323-342).
Geneticist P. M. Sheppard : "the most spectacular evolutionary change ever witnessed and recorded by man, with the possible exception of some examples of pesticide resistance" (Sheppard PM. 1975. Natural Selection and Heredity. 4th ed. London: Hutchinson University Library.)
Professor John Maynard Smith: "We should expect to find the most rapid evolutionary changes in populations suddenly exposed to new conditions. It is therefore natural that one of the most striking changes which has been observed in a wild population ... is the phenomenon of 'industrial melanism', the appearance and spread of dark forms of a number of species of moths.” (The Theory of Evolution, J. Maynard Smith. Penguin Books, Harmondsworth:1966 (2nd ed.). p.137.)
Sir Gavin De Beer, (1974): "One of the most striking examples of observable evolution is the phenomenon known as industrial melanism." (Evolution, Sir Gavin De Beer. In Encyclopaedia Britannica, Chicago:1974. Vol. 7. p.14.)
J S Jones: [Industrial melanism in peppered moths is] "the textbook example of natural selection in action" ( Jones JS. 1982. More to melanism than meets the eye. Nature 300: 109-110.)
Richard Leakey : "The peppered moth is a striking example of evolution in action. ... but, sadly for Darwin, no one knew it at the time. This is just the evidence he needed to show the effectiveness of natural selection." (The illustrated Origin of Species, Richard Leakey. Faber and Faber, London:1979. p.30.)
Stephen Jay Gould: "... we have abundant, direct, observational evidence of evolution in action [including] the famous populations of British moths that became black when industrial soot darkened the trees upon which the moths rest.” (Hen's Teeth and Horses' Toes, Stephen Jay Gould. Penguin Books (Pelican edition), Harmondsworth: 1984. p.257.)
Geneticist Seawall Wright (1978): [the peppered moth is] "the clearest case in which a conspicuous evolutionary process has actually been observed.” ( Wright S. 1978. Evolution and the Genetics of Populations. Volume 4: Variability Within and Among Natural Populations. Chicago: Chicago Press)
M & R Burton: "[the case of the peppered moths] is the most striking evolutionary change ever to be witnessed by man." (The International Wildlife Encyclopaedia, M. and R. Burton (eds.). Marshall Cavendish, New York:1970. p.2706.)
M Ridley: "a classic example of natural selection" which is "perhaps the best-known story in evolutionary biology," ( Ridley M. 1996. Evolution. 2nd ed. Cambridge (MA): Blackwell Science.)
In his famous 1959 article, Dr. Bernard Kettlewell described his research on the peppered moth as the "consummation and confirmation" of Darwin's theories. (B. Kettlewell. 1959. Darwin's Missing Evidence. Scientific American. March pp.53)
According to Majerus, however, evidence gathered in the 40 years since Kettlewell's work shows that "the basic peppered moth story is wrong, inaccurate, or incomplete, with respect to most of the story's component parts" (Majerus 1998, p. 116).
Ridley concedes that the situation is "now known to be more complex" than originally thought (Ridley 1996, pp. 109).
Professor Jerry A. Coyne, Department of Ecology and Evolution, University of Chicago, wrote revealingly in an article entitled ‘Not Black and White” in the journal “Nature:
“From time to time, evolutionists re-examine a classic experimental study and find, to their horror, that it is flawed or downright wrong… Until now, however, the prize horse in our stable of examples has been the evolution of 'industrial melanism' in the peppered moth, Biston betularia, presented by most teachers and textbooks as the paradigm of natural selection and evolution occurring within a human lifetime… Depressingly, [Michael Majerus's book, Melanism: Evolution in Action]shows that this classic example is in bad shape, and, while not yet ready for the glue factory, needs serious attention.
…Criticisms of this story have circulated in samizdat for several years, but Majerus summarizes them for the first time in print in an absorbing two-chapter critique (coincidentally, a similar analysis [Sargent et al., Evol. Biol. 30, 299-322; 1998] has just appeared). Majerus notes that the most serious problem is that B. betularia probably does not rest on tree trunks -- exactly two moths have been seen in such a position in more than 40 years of intensive search. The natural resting spots are, in fact, a mystery. This alone invalidates Kettlewell's release-recapture experiments, as moths were released by placing them directly onto tree trunks, where they are highly visible to bird predators. (Kettlewell also released his moths during the day, while they normally choose resting places at night.) The story is further eroded by noting that the resurgence of typica occurred well before lichens recolonized the polluted trees, and that a parallel increase and decrease of the melanic form also occurred in industrial areas of the United States, where there was no change in the abundance of the lichens that supposedly play such an important role.
Finally, the results of Kettlewell's behavioural experiments were not replicated in later studies: moths have no tendency to choose matching backgrounds. Majerus finds many other flaws in the work, but they are too numerous to list here. I unearthed additional problems when, embarrassed at having taught the standard Biston story for years, I read Kettlewell's papers for the first time.
… 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.
… It is also worth pondering why there has been general and unquestioned acceptance of Kettlewell's work. Perhaps such powerful stories discourage close scrutiny. Moreover, in evolutionary biology there is little payoff in repeating other people's experiments, and, unlike molecular biology, our field is not self-correcting because few studies depend on the accuracy of earlier ones. Finally, teachers such as myself often neglect original papers in favour of shorter textbook summaries, which bleach the blemishes from complicated experiments.” (Nature 396, 35 - 36 1998)
Coyne confessed that the realization gave him the same feeling as when he found out that Santa Claus was not real. He added that Dr Kettlewell's widely quoted experiments are essentially useless. "There is a lot of wishful thinking and design flaws in them, and they wouldn't get published today”.[Did he say the dreaded “D” - "design" word?]
Richard Dawkins, the professor of the public understanding of science at Oxford University and author of "The Selfish Gene", tried to put a positive spin on the matter: "The details of any experiments done 40 years ago are bound to be vulnerable to detailed criticism. But, in any case, nothing momentous hangs on these experiments."
The story was broken in the scientific community by Michael Majerus but it was Robert Matthews, the Science Correspondent of the London "Sunday Telegraph" who broke the story to the wider public (March 14 1999) exposing the fundamental flaws in one of the most popular illustrations of the theory of evolution, one which is repeated frequently in textbooks on science, and on television programs. But now the whole story is as suspect as the Piltdown Man hoax.
So where did all the pictures in textbooks and shots on the Net of peppered moths on different colored tree trunks come from? They were all staged. Dead moths were glued, pinned, or placed onto tree trunks and their pictures taken. Peppered moths do not rest on tree trunks during the day; they hide in the shadows under branches and where the branch joins the tree. Birds do not see the moths on the tree trunks because the moths are not there. Pictures of the moths on tree trunks are misleading. Even Kettlewell who first studied this nocturnal moth put them onto those parts of the trees during the day where the birds could easily see them. The scientists who used these pictures in their books to prove evolution all conveniently forgot to tell their readers this fact. If the BEST example of evolution that has been believed and used as proof by eminent evolutionary biologists for over 40 years is not true, should we be suspicious of other examples, as well?
In the light of these findings Professor Kenneth R Miller (author of “Finding Darwin’s God”) has altered the textbook he co-authored. His explanation is:
“For years the story of the peppered moth, Biston betularia, has provided one of the best-known examples of natural selection in action… However, a recent book by Michael Majerus (Melanism -Evolution in Action) makes it clear that the peppered moth story will need to be rewritten…
Well, the best way to put it is that what we are seeing is the scientific process at its best. Majerus and other ecologists have carefully examined the details of Kettlewell's work and found them to be lacking. As Majerus explains, to be absolutely certain of exactly how natural selection produced the rise and fall of the carbonaria form, we need better experiments to show that birds (in a natural environment) really do respond to camoflage in the ways we have presumed, that the primary reason the dark moths did better in polluted areas was because of camoflage (and not other factors like behavior), and that migration rates of moths from the surrounding countryside are not so great that they overwhelm the influence of selection in local regions by birds. Until these studies are done, the peppered moth story will be incomplete. Not wrong, but incomplete.”
As Jason D. Browning points out the change in colour of the peppered moths is indeed “NATURAL SELECTION in action. The problem is that there is NO EVOLUTION occurring (no increase in complexity)! At the start of the story there are both light and dark colored moths present. At the end of the story there are both light and dark colored moths present. No new trait has been acquired. The only difference is a shift in the color distribution in the population…
Evolution is an important theory and gives the appearance of having great explanatory value, but when it comes right down to understanding the mechanism of what has happened in nature, evolutionary explanations too often deteriorate into "just-so" stories.”
Emerson Thomas McMullen has written:
"Even though the peppered moth never changed into anything else, it became a cherished icon of Darwin's idea of the origin of species, and the story appeared in textbooks and venues popularizing science. In reality, the story demonstrates adaption in action, not evolution in action, and even then it is flawed. University of Massachusetts biologist Theodore Sargent helped a NOVA documentary on the subject by gluing dead moths on trees for the cameras. Commenting on the textbooks and films about the peppered moth, he said "There have been a lot of fraudulent photographs." …
In retrospect, there were warnings that the peppered moth was a poor example for evolution. As early as 1937, E.B. Ford postulated that other factors besides coloration that were more important for moths like Biston. There was an excellent 1974 study by Lees and Creed, with great pictures of both colors of moths on tree trunks, and later a report, "Exploding the Myth of the Melanic Moth," in the 1986-7 New Scientist. These warnings were not heeded and, as a result, many evolutionists and their popularizers have put themselves and gradualistic evolution out on a limb.
"It may be that what caused the peppered moth to change color was its diet while in the larval stage - T.R. Sargent and his coworkers have found that this applies to a different nocturnal moth.Whatever caused the change, it was not according to the story that was told to the public for forty years. We have had philosophers of science propose that there exists in science theory-laden interpretation, observation, and recollection. Here is an example of theory-laden data doctoring. Consciously or unconsciously, researchers manipulated the data to fit the theory - but is there more to the story than just this?
…If we were dealing with pure science, the formulation and testing of ideas about nature, then biologists would be cautious about teaching their students that the peppered moth story is evolution in action. The crux of the story is that birds eat those moths that visually stand out as they rest on tree trunks. However, the fact is that the peppered moth prefers to rest high up in the tree canopy. This preference was known to Kettlewell at least by 1958. Mikkola wrote about the peppered moth's preference in separate articles in 1979 and 1984 Sir Cyril Clarke reported in 1985 that all he and his coworkers had found in twenty-five years of observations is where the peppered moths do NOT spend the day on the tree trunks.
Surely biologists … stayed current and knew all of the above. Yet they continued to teach the peppered moth story to their students as an example of evolution in action. And, over a decade later, nothing seems to have changed. There has been a lot more research showing additional weaknesses in the original story. For example, it had been assumed that birds see like us, but they do not. They have an ultraviolet capability that we do not have, and they may see colors better too. Also, simplifying assumptions were made to make mathematical calculations easier, but it turns out these cannot be made for the peppered moth. Nevertheless, the peppered moth story as an example of uniformitarian evolution in action continues to be taught. For instance, it can be found in the 1991 edition of George Gaylord Simpson's classic textbook (I studied the first edition as an undergraduate and still own the book); or in Raven and Johnson's Biology, 4th ed. (1996). The initial 'hyping' of the peppered moth story as an example of evolution in action, and not adaption in action, and the subsequent refusal to modify or drop it in the light of new data, fits the contention that uniformitarian evolution is not science, but a social construct, divorced from reality. So we are facing something that is more than just theory-ladeness, it is driven by a completely naturalistic worldview."
Is it time to mothball the peppered moth story?