Wells' Icons of Evolution - Peppered Moths

Wells' complaints about the peppered moth relate mostly to their natural resting places. Some photographs that were used to illustrate the contrast between light/dark moths and light/dark tree trunks were actually photos of dead moths pinned to tree trunks. There have been claims that moths do not naturally rest on exposed (and photogenic) tree trunks and therefore the idea that the average population color changed (via bird predation leading to natural selection) in the direction of better camouflage against those tree trunks is false.These claims are hooey. Wells wrote that "peppered moths in the wild don't even rest on tree trunks" which is a flat-out lie. It's difficult to measure precisely what percentage of the time moths rest where; the little boogers are freakin' camouflaged and hard to see. Most measurement techniques (e.g. traps in various locations and counting how many moths are trapped) have at least the possibility of some bias. However, it's clear that moths rest on tree trunks a significant percentage of the time (and on what is equivalent as far as the question of this camouflage is concerned, tree trunks and tree branches and branch-trunk junctions a large percentage of the time), and it's clear that natural selection caused by some factor or factors has changed the average population color in the direction of better camouflage.The open question is exactly how much of the natural selection that's involved is predation by birds and how much is other factors.IMHO the best summary up to five years ago is FINE TUNING THE PEPPERED MOTH PARADIGM (a PDF document), which concludes with:

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Even if all of the experiments relating to melanism in peppered moths were jettisoned, we would still possess the most massive data set on record documenting what Sewall Wright (1978) called the clearest case in which a conspicuous evolutionary process has been actually observed. Certainly there are other examples of natural selection. Our field would be in mighty bad shape if there weren’t. Industrial melanism in peppered moths remains one of the best documented and easiest to understand.

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There's a good but slightly out-of-date discussion of Wells' treatment of the peppered moth story at Icon of Obfuscation: Chapter 7: Peppered Moths, which includes some nice pie charts showing where moths have been found to rest. Remember that in reference to the natural selection claim, trunks (exposed and unexposed) and branches and branch-trunk junctions are equivalent.In 2002, Judith Hooper rekindled the controversy in Of Moths and Men: Intrigue, Tragedy and the Peppered Moth, in which she chracterized Kettlewell's original experiments as a flagrant scientific fraud. Of course the creationists love this. Her claims are refuted in many places, including Moonshine: Why the Peppered Moth Remains an Icon of EvolutionSome good current references are The peppered moth: a black and white story after all (PDF) (which includes some of the infamous "posed" pictures), and Recent History of Melanism in American Peppered Moths (PDF).

Not according to Wells. Both of those two statements by Wells are incorrect.YWells also wrote:: "Pictures of peppered moths camouflaged on tree trunks are used as evidence for natural selection, but biologists have known since the 1980s that the moths don’t normally rest on tree trunks, and in any event all the pictures have been staged." (as quoted at http://www.nmsr.org/text.htm#moth). Majerus' pictures were not staged. 47 is a small, but statistically significant, number.Only 25% of them rested on trunks. 100% of them rested on parts of trees in which the camouflage offered by appropriate coloration is relevant. Do you think that birds can't find moths on branches or trunk-branch junctions?Of the 203 moths observed near traps, 76.9% of them were on parts of trees in which the camouflage offered by appropriate coloration is relevant."The peppered moths in the wild do not even rest on tree trunks" "peppered moths do not NORMALLY rest on tree trunks" are bald-faced lies ... you might argue that the data is inconclusive because of different results by different researchers, but Wells is totally ignoring Kettlewell's and Majerus' data. As acknowledged earlier, the question of the importance of bird predation is stil open.{added in edit} That's pretty bizarre. You acknowledge that the population was selected ... do you think it was some un-natural agency doing the selection? Do you think that the change was a random fluctuation? (hint: it wasn't, the statistics are pretty clear).Sounds to me as if you are acknowledging natural selection but refusing to call it that.{end addition in edit} There are still some mystries. There is no mystery about the overall effect; natural selection changed the population.I suggest you read the T.O. article.[This message has been edited by JonF, 04-27-2004]

"Branches" is unnecessarily restricting. (I mention it only because of the stink that has been made about exactly where the little boogers rest, even though that's not crucial).You left out:--The lighter phenotype then increased in the population in correlation with decreased pollution and lightening of tree trunks and branches.

Please show your calculations. Please show your data and statistical calculations. Lack of large numbers of observed moths on trees is not data. The data we have indicates large percentages of moths on trees. I already noted the difficulties involved in collecting unbiased data in the message to which you replied. Nonetheless, the data is indicative. A significant understatement of the areas involved (there's several more in England, and American areas have been studied too) and an unwarrented extrapolation. The statistics belie your claim.{Aded in edit} I just came across Mallet's excellent article on teh Web; I though it was only up in PDF. I suggest your read The peppered moth: a black and white story after all. It has some good data and pointers to more.[This message has been edited by JonF, 04-28-2004]

Nothing is ever proved in science.The best explanation that we have, which fits all the data and does not fail to fit any of the data, is natural selection. We have enough data to be virtually certian (though not absolutely certain) that natural selection is operating. Note that the article to which I pointed you contains data which refutes your claim that there's not enough time for natural selection.There is the possibility of other contributory factors, and research is ongoing.When you or Wells come up with a theory that fits the data, does not fail to fit any of the data, and explains the data better than nautural selection, we'll talk. Or, when you or Wells come up with data, not just incredulity, that falsifies natural selection in this case, we'll talk. Unti then, we'll continue to point to the peppered moth changes as natural selection at work.If you want to discuss this further, let's see your data and your calculations. Personal incredulity just doesn't cut it.

A reasonable question.I don't think that the actual mutations or genes have been identified. I could be wrong.There have been lots of breeding experiments (in the 60's and 70's by Clarke, Sheppard, Lees, Creed and Steward) with the peppered moth that have established that the difference between light and dark forms follows classic Mendelian genetic rules (with the dark form having a dominant allele that controls the expression of melanin in the wings) and three different alleles of the same gene that control variations of color in the lighter moths (if the dominant form is not present). (Somebody, I forget who, even tested for Lamarkian inheritance and failed to find any).The experiments indicate that, whatever the mutation actually is, it's a fairly common and recurring one.The fascinating thing is that the black form is a dominant allele; if a moth has it from either parent the moth is black. In the absence of strong selective pressure the black form would be common and maybe even dominate. But no black moths were observed before 1800 or so (and I know that there's a lot of possible effects there, but one way or another the black form was rare).The difference between light and dark moths is genetic, and whatever has caused the population color distribution to change is affected the hereditability of particular genes. Sounds like NS to me.

You can read an earlier version of Wells' treatment of the peppered moth at Second Thoughts about Peppered Moths. I doubt that he chaned his conclusion much in the book. It appears to me that his major problem is with the staged photographs. At that URL, he writes:

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This does not mean that the same explanation applies to peppered moths, but it clearly indicates that cryptic coloration and selective predation are not the only possible explanations for industrial melanism. Some biologists continue to believe, like Harrison (1920), that melanism might be directly induced by environmental factors (reviewed in Sargent et al. 1998). Most biologists, however, believe that natural selection is responsible, though no one knows what traits are being selected or what factors in the environment are doing the selecting.

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The very prominence of the peppered moth story in the teaching of evolution requires that it be scrupulously accurate. According to Grant and Howlett, as Biston betularia has served as a paradigm of evolution, it demands the closest possible scrutiny (Grant and Howlett 1988, p. 231). Yet this classical story of evolution by natural selection, as it continues to be retold in many textbooks, is seriously flawed. In particular, the illustrations which typically accompany the story (like the photographs in Figure 1) mislead students by portraying peppered moths on tree trunks where they do not normally rest. Unknown to Kettlewell, his experiments had less to do with natural selection than with unnatural selection, and the true causes of industrial melanism in peppered moths remain largely unknown.

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Note that date of his Harrison reference.IMHO he doesn't make his case that "the true causes of industrial melanism in peppered moths remain largely unknown". But others might disagree, incredible as that seems.

Er, no. I don't remember all the details, and I can't locate anything conclusive on the Web right now, but I'm pretty sure that data incdicates that the mutation is one that happens over and over again. That's what keeps the black phenotype in the population in times when it's so strongly selected against.I'm not enough of a geneticist to understand why a particular mutation would be common. Perhaps there's a particular point in the DNA that's unstable?

Well, then, no problem ... we've got it.

Er, yes, they have. Wells just didn't quote them. Consult the primary literature. Just for example, from The peppered moth: a black and white story after all (which I have recommended several times .. have you read it?), with emphasis added:

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JBS Haldane calculated long ago that the melanics must have had about 50% higher survival than typical mottled forms to explain the rapid rise in melanic gene frequency. In the last half of the last century, field experiments at 35 sites were performed by a number of scientists. These experiments directly demonstrated how bird predation affected the survival of adult moths, and demonstrated that the strength of natural selection was of the same order as that required by Haldane's calculations ...

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{Figure 3 caption} Relative fitness of adult typica (normal, pale form) compared with carbonaria (melanic form) in 35 field experiments with the peppered moth, Biston betularia. The survival data are plotted against the frequency of typica in the population, and the trend shows that adults of each form tend to have higher survival in areas where its own form is most abundant, as expected under the industrial melanism hypothesis. The equation for the best-fitting line is y = 0.83 + 0.65x; r2 = 0.20, P=0.007). The data are from Cook (2000); see also Lees (1981). Laurence Cook has told me he doesn't believe the simple regression analysis performed here is sensible, as different groups of experiments were done in very different ways and with different sample sizes. However, I am merely using this regression as a conservative heuristic tool to display the data, because I believe it shows the results clearly. Cook's own (2000) sample-size-weighted analysis of the data after log-transforming the relative fitness values gave similar results (P <0.001).

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There certainly is. It may not be conclusive enough for you or Wells, but it's conclusive enough for most people (and, of course, Wells wouldn't believe it unless God or Sun Myung Moon told him it was so). When a better alternative theory arises, or when NS is disproven, or even when somebody proposes a viable alternative hypothesis, scientists will listen.

I haven't done an exhaustive, or maybe not even thorough, survey of the primary literature, and it's been a few years since I did it. I found the data and calculations in the primary literature to conclusively support the thesis that natural selection is operating in the color changes in the peppered moth population. There's still room for argument about what the selective mechanisms are, and the relative importance of each, and there are questions which are unanswered. But NS is there, as proven as anything is in science.

You are making a totally unwarranted assumption.You are assuming (without justification) that there were thousands of moths not resting on tree trunks that Majerus could have observed but did not observe. Your "12 out of thousands" betrays a lack of knowledge of statistical sampling.Majerus sampled a set of observations from the set of all possible observations. There are well-established techniques for assessing the reliability of extrapolating the set of actual observations to the set of all possible observations. By those techniques Majerus' observations are "significant", meaning that the probability of a major error in assuming that about 25% of all peppered moths rest on tree trunks in the wild is insignificant. Combining this result with others by Grant and other researchers indicates without any doubt that a significant percentage of peppered moths rest on tree trunks in the wild.And you have promulgated the tired old creationist misdirection of counting only resting on tree trunks. Peppered moths resting on branches and peppered moths resting on branch-trunk junctions are subject to differential predation, and possibly peppered moths resting on leaves are subject to differential predation. The moths resting on branches and branch-trunk junctions must be counted in the percentage subject to selection by differential predation, and we must bear in mind that the percentage we get by counting them is probably an underestimate. From the Merriam-Webster dictionary:

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Experiment
1. a. A test under controlled conditions that is made to demonstrate a known truth, examine the validity of a hypothesis, or determine the efficacy of something previously untried.
b. The process of conducting such a test; experimentation

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Majerus's observations are experiments.You also missed looking at Grant's and others studies. IOW, he's not a scientist, and he's lying. Why is it better? And why should he ignore resting on branches, trunk-branch junctions, and leaves? Now, that's outright false. Your claim of thousands of unobserved moths is just a fairy tale.

This is an unsupported assertion. You need to present evidence, and statistical analysis of that evidence, before you can make such a claim. Yes. And according to Majerus' measurements and the statistical analysis of those measurements, the best estimate of the percentage of the entire population of moths that landed on exposed areas where they were likely to be predated upon is well over 50%. Repeating your unsupported assertion. Where's your evidence? Where's your statistical analysis of what is or is not likely? It is absolutely deniable; the evidence collected by many researchers indicates that your claim is false. Let's see your evidence and analysis that supports your claim. Yup. And if he wants to claim that his viewpoint is scientific and should be considered by scientists and/or taught in U.S. public schools as science, then he'd better start acting like a scientist and stop telling lies.Apropos of nothing whatsoever in your posts, but relevant to this thread, Grant has published a review of "Creationism’s Trojan Horse: The Wedge of Intelligent Design" which opens with a lambasting of Wells, including:

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His ‘errors’ tend to be of selective omission and appear to be consistently crafted to support his arguments. I think this tactic is more common in the field of law in which the objective is to win the argument rather than to find the truth. To readers not intimately familiar with the primary literature in this field it might appear that [he] has assembled a strong indictment against the widely held view that natural selection is chiefly responsible for the temporal and geographic variations observed in peppered moth populations. [The] list of references cited in his essay is both long and impressive. But based on his account of this work in his essay, I am left wondering whether he has actually read the papers and books he cites, or whether he has read them carefully. Perhaps my impression is wrong; perhaps he has mastered the literature in this field. If so, then I am forced to entertain the disquieting notion that [his] distortions of the controversies in this field have been deliberate. Whatever the cause, ignorance or dishonesty, [his] essay certainly does not qualify as objective scholarship.

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Argumentum ad hominem. Address the facts, please. Of course not. If you believe that it is necessary to count every moth, or even a large percentage of all moths, in order to get an accurate estimate of the behavior of all moths, then you are sadly mistaken and need to learn some statistics and sampling theory before proceeding. Sorry, the exact size of the population is not required to do the statistics. We know that the population is much larger than Majerus's sample, and that's all we need to know. No. That is not one of the assumptions of the analysis. It's pretty likely that there were thousands of moths in the general area. Hand-waving. Present your statistical anlayis of the significance or lack thereof, or admit you have no idea what you are talking about. The number is sparse, yes, but statistically significant. You are still assuming, without evidence, that the moths Majerus did not observe act tremendously differently from the moths that Majerus did observe; whereas we have evidence (statistical analyses of Majerus' observations and others) that the percentages Majerus found are reasonably representative of the activities of the population at large.Yuo need evidence and analysis to support your claims, not just hand-waving. Perhaps; I'm not going to bother to look back. You said "25%" many times, and that's the number for moths resting on tree trunks. If you meant exposed part of the trees, the number should have been much larger. It was an experiment, one that was not intended to (and could not, by design) measure the results of predation of the peppered moths. I posted the definition of "experiment", and Majerus' actions fit that definition, therefore what Majerus did was an experiment. The evidence for differential predation is very strong. Other factors might also be significant, and research is continuing. The evidence for natural selection affecting the distribution of dark and light varieties through differential predation and/or other mechanisms is conclusive. You're the only one that's assuming, because you don't know statistics and sampling theory.I never claimed that thousands of moths could have been missed. It's virtually certain that Majerus did miss observing thousands of moths that he possibly could have observed. However, the statistical anlysis tells us that the small number of moths that he did observe are certainly close to being representative of all moths. Maybe only 20% of all moths rest on tree trunks, maybe 30% of all moths rest on tree trunks; but it is not possible that less than 5% of so of moths rest on tree trunks. Even if 5% of moths rest on places where their camouflage or lack thereof affect predation, that's plenty for natural selection to operate; those calculations have been done too.If you want to claim that an insignificant percentage of moths rest on exposed portions of trees, stop hand-waving and present observations and statistical analyses to support your claim.

We have a goodly portion of the how, maybe not most of it and certainly not all of it.I may be misinterpreting, but it appears to me that Cromwell is arguing that we can't conclude what happened (natural selection) because we haven't observed every moth and we don't know every detail of the process.He's certainly claiming that Majerus' statistics on moth resting places are wildly wrong as estimates of the behavior of the population at large, and in that he himself is wildy wrong.