Welcome Article on Natural Selection in Peppered Moths

| 25 Comments

David W. Rudge (2005), assistant professor of biological sciences at Western Michigan University, has published a very welcome addition to the literature regarding Bernard Kettlewell’s classic experiments on natural selection in peppered moths. Here are some of his comments regarding his concerns about creationists’ misuse of industrial melanism and of Judith Hooper’s charges of fraud against Kettlewell:

As one might imagine, advocates of creation and intelligent design have misinterpreted these long-recognized problems as undermining the continued use of the example in science textbooks (Wells 2000; but see also Rudge 2002). The motive in these attacks is transparent: if one can knock down the poster child of evolution, the entire theory will thereby become suspect. As noted above, the continued inclusion of the phenomenon of industrial melanism in textbooks should not be interpreted as an indication of its theoretical importance to evolutionary biology. Moreover, no one should be surprised that there are differences between the explanations given in popularizations and introductory textbooks, which are intended for children and the lay public, and what is actually known about the phenomenon as it is discussed in journal articles intended for scientists. The existence of ongoing questions about the phenomenon is indicative of an active area of research. That scientists continue to believe the explanation we associate with Kettlewell does not imply they are being dogmatic in the face of overwhelming contradictory evidence. Biologists don’t abandon well-supported theories simply because they run into problems applying an idealized explanation to a particular example, particularly when no better alternative theory is available. Moreover, even if we threw out Kettlewell’s experimental work on bird predation entirely, it wouldn’t threaten in any way the enormous genetic evidence for natural selection in the evolution of melanism, nor the eight or so follow-up predation studies on the mechanism that qualitatively support Kettlewell’s original conclusions (Cook 2000, 2003).

Similar discrepancies surround our current understanding of Kettlewell’s work on the phenomenon. In the first book-length popularization of this episode, Judith Hooper (2002) portrays Kettlewell as a bumbling amateur and all but accuses him of committing fraud. The latter charge is entirely baseless (Grant 2002, Rudge 2005). No one would deny that, judged by contemporary standards, the design and conduct of Kettlewell’s experiments are problematic (Shapiro 2002). Nor would even Kettlewell deny that his work on the subject involved a number of false steps and errors of interpretation: his first scientific publication of the results of his study is remarkably candid about the numerous problems he encountered in the field (Kettlewell 1955). But do these considerations imply that Kettlewell’s experiments should no longer be used in science classrooms? The answer, I believe, is a decided no. Discrepancies between the textbook accounts of Kettlewell’s work and what scientists now know about it represent a beautiful opportunity for science instructors to help students appreciate a variety of issues associated with the nature of science, such as the tentative nature of scientific conclusions (Rudge 2000, 2004a, 2004b).

Professor Rudge promises an additional article, ‘Did Kettlewell Commit Fraud? Re-examining the Evidence’ (Rudge, 2005b).

References.

Rudge, David, 2005a, ‘The Beauty of Kettlewell’s Classic Experimental Demonstration of Natural Selection,’ BioScience, 55(4), 369-375, http://www.rednova.com/news/display[…]ce=r_science, accessed 1 May 2005.

Rudge, David, 2005b, ‘Did Kettlewell Commit Fraud? Re-examining the Evidence,’ Public Understanding of Science, forthcoming.

Additional bibliography.

Young, Matt, 2005, ‘Why the Peppered Moth Remains an Icon of Evolution,’ The Panda’s Thumb, http://www.pandasthumb.org/pt-archi[…]/000886.html, accessed May 1, 2005.

Young, Matt, and Ian Musgrave, 2005, ‘Moonshine: Why the Peppered Moth Remains an Icon of Evolution,’ Skeptical Inquirer, March-April, pp. 23-28, http://www.csicop.org/si/? (not available on the Web as of this writing).

Further references may be found in (Rudge 2005a).

25 Comments

I personally would like to see more of this type of article.

there have been legitimate scientific criticisms of various articles in support of evolutionary theory in the past.

I think it would be a good idea if we spent a bit more time publicizing how the criticisms were addressed, and why the conclusions ended up supporting evoltuionary theory, rather than rejecting it.

that way, it would seem even more apparent that there is no “dogmatism” involved with supporting evolutionary theory.

make it VERY clear the theory has been tested thousands of times, and come out a winner.

cheers

Is there anything more to the Peppered Moth example than the fact that the lighter moths got eaten, and therefore, there were more darker moths producing offspring?

I have not read Wells Icons, but I’m not sure what his complaint could be. The above seems to be a fairly uncontroversial instance of “evolution” qua “change in alleles of a population over time.”

It doesn’t seem to be related to the more contentious issues of neo-Darwinian evolution at all. What am I missing here?

Is there anything more to the Peppered Moth example than the fact that the lighter moths were eaten at a much higher rate, and therefore, there were more darker moths producing offspring?

I have not read Wells Icons, but I’m not sure what his complaint could be. The above seems to be a fairly uncontroversial instance of “evolution” qua “change in the alleles of a population over time.”

It doesn’t seem to be related to the more contentious issues of neo-Darwinian “evolution” at all. What am I missing here?

The Peppered Moth is a good example of natural selection. Natural selection is a part of evolutionary theory. Hence, anyone who goes to a university to ‘destroy Darwinism’ may see it as a valid target. Too bad that Wells, nor Hooper really did their homework. Wells’ treatment of the peppered moth suggests an unfamiliarity with the actual data and research in this area. Not that other ‘icons’ show a better understanding of science.

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@finley:

well, obviously read Wells icons to see what the specific objections he raises are, but also read the objections listed under the section:

“Problems with the textbook depiction “

in the article by Rudge linked to first above.

“but I’m not sure what his complaint could be. “

do a little work, man.

cheers

[ot]I have to apparently post a “bump” to get the thread to update for me.

plz ignore.

Finley

Is there anything more to the Peppered Moth example than the fact that the lighter moths were eaten at a much higher rate, and therefore, there were more darker moths producing offspring?

I think Wells considers the moth data evidence of a Great Scientific Conspiracy to snowball children with respect to evolution.

Surely you knew that creationists held totally nutball and asinine positions about the “scientific community”. That is just one way that Wells and his ilk try to mock scientists but end up making of mockery of their religion. Of course, Wells belongs to an exceptionally strange and extreme cult, bordering on personality worship. You’ve heard of Moonies? The Washington Times? Anti-gay vitriol of the ugliest sort? Google it.

I remember seeing the moth pictures when I was very young – maybe 6 years old – in a book about animals and camouflage.

Of course, the creationists will spout some garbage about how a black moth is still a moth, a snow-shoed hare is still a hare, a flounder is still a fish, blah blah blah blah blah designer blah blah mysterious blah blah blah Jesus.

Camouflage is a great example of natural selection. That book was so cool – one of the inspirations to become a biologist for sure, along with my beloved pets. And another book I remember called “How Big is Big” is what got me interested in chemistry and in astronomy.

Theocrats should be aware: I found those books in our library and read them long before we discussed the topics in our science classes.

The reality-based world won’t be as easy to sterilize as the fundamentalists think.

Pim wrote:

Too bad that Wells, nor Hooper really did their homework. Wells’ treatment of the peppered moth suggests an unfamiliarity with the actual data and research in this area.

Actually, reading Well’s bibliography and refferences, it is clear that Well’s had enough information to form a true picture of the situation. However, he very selectively uses his refferences to create a false impression. Given that, in a direct debate with his major source (Majerus), he ended up directly calling Majerus a liar for clearly stating the facts,and given that he later accused Kenneth Miller of using false statistical arguments in direct contradiction of Majerus (when Majerus had used precisely the argument used by Miller in the debate with Wells); I can only conclude that this is an example of deliberate deceit rather than overwhelming bias.

why are you using the “at” symbol to mean “In regard to”? As far as I know, that’s not correct.

Too bad that [neither] Wells, nor Hooper really did their homework. Wells’ treatment of the peppered moth suggests an unfamiliarity with the actual data and research in this area. Not that other ‘icons’ show a better understanding of science.

Oh, it’s much funnier and dirtier than their just “not doing homework.”

In his chapter on moths, Wells cites Majerus, Coyne and Grant. He cited them in a contretemp in a little town in Kansas in 1998 or 1999. All three wrote letters saying Wells had cited them exactly the opposite of what their research showed, and in relatively polite terms they called Wells a prevaricator.

In her book, of course, Hooper noted that scientists kept telling her that creationists like Wells would cite her book as evidence against evolution. She spent a couple of paragraphs noting just how dishonest that would be. In 2003, in Texas, Wells added a citation to Hooper’s book, claiming she said exactly the opposite of what she said, claiming her support for a proposition she had already labeled dishonest. When I pointed that out in testimony, I was asked by staffers and at least one board member for the citation. Fortunately, I had Hooper’s book with me.

There are eight members of the Texas board who might be classed as creationist. But only four of them voted the creationist line. The other four voted to leave ID out, and keep evolution in. I cannot say for certain that the dishonesty was the deciding factor, but I think it played a role.

Michael Finley:

I have not read Wells Icons, but I’m not sure what his complaint could be. The above seems to be a fairly uncontroversial instance of “evolution” qua “change in the alleles of a population over time.”

It doesn’t seem to be related to the more contentious issues of neo-Darwinian “evolution” at all. What am I missing here?

Mr. Finley or anyone else who might be interested, can get the gist of what Wells was getting at in his chapter on peppered moths in Icons by reading his earlier article on same (a version of which was published as an opinion piece in The Scientist): Second Thoughts about Peppered Moths

Michael Finley wrote:

I have not read Wells Icons, but I’m not sure what his complaint could be. The above seems to be a fairly uncontroversial instance of “evolution” qua “change in alleles of a population over time.”

It doesn’t seem to be related to the more contentious issues of neo-Darwinian evolution at all. What am I missing here?

Mr. Finley, or anyone else who might be interested, can get the gist of what Wells was getting at in his peppered moth chapter in Icons by reading his earlier article on the same subject (which was published as an opinion piece in The Scientist in 1999): Second Thoughts about Peppered Moths.

Michael Finely Wrote:

It doesn’t seem to be related to the more contentious issues of neo-Darwinian “evolution” at all. What am I missing here?

What you are missing is that Wells’ intention (and by extention, that of the entire ID movement which vigorously promoted him) was to smear biologists as being dishonest and untrustworthy. Indeed, the fact that almost no IDists dispute that natural selection happens in the wild (and there are far better examples than the peppered moths) is a good indication that Wells’ target was not natural selection itself, but rather the scientific community.

The evolution of color in peppered moths is microevolution by anyone’s definition. Creationists claim to believe in microevolution. Does Wells see divine intervention extending to microevolution in some cases?

Everytime I hear the name Jonathan Wells I think of Rev. Moon which makes me think of the anti-gay bigotry espoused by Moon and other ignorant individuals walking the planet.

The following is a link to an awesome little pre-history lesson found at Washington Monthly relating to some anti-gay literature legislation currently being pursued in good ol’ Alabama (a former slave-holding state, if you can imagine that).

http://lawandpolitics.blogspot.com/[…]586671576091

and the hits just keep comin’

Is it just that the baby boomers are losing their minds, or what? what explains this overwhelming urge towards complete idiocy that seems to be gripping the country?

This Kettlewell stuff is even more complicated that it first seems. Let me first quote Stephen J. Gould on Richard Goldschmidt, and then Goldschmidt himself.

First Gould:

(Goldschmidt) also elucidated the genetics of industrial melanism and proposed scenarios that sought the adaptive value of dark color not directly in crypsis against visual predators, but indirectly as the by-products of metabolic change that permitted the caterpillars to feed upon plants loaded with industrial chemicals.

Then Goldschmidt (who worked with the “gypsy moth”):

(T)he same phenomenon was simultaneously observed in a number of other moths, and that in all these cases the centers of distribution were found in the areas of high industrialization, both in England and in Germnay. Hence the term, “industrial melanism.” The genetic analysis in this case showed that this melanism was the result of at least three mutational steps uf unequal vale, but all of them dominant. … All these genes are additive in action and their different combinations produced the complete series of gradations from white with black bands to completely black. … We tried to see whether the dark individuals were larger or stronger, but with negative ressults, though these individuals were more viable in breeding, an experience also reported by Harrison (1920) for British melanic moths. Thus we concluded that the difference must be a phsyiological one. … The idea arose, therefore, that the melanic forms wer in some way chaned in regard to their metabolism, and that this enabled them to feed on the poisoned food of the industrial districts. … An interesting account of the formation of local forms … has been given by J.W. H. Harrison (1920) for local races of the geometrid moth Oporabia autumnata. In the short time between 1885 and 1919 a certain region in England changed its character completely in regard to the food trees of the species and corresponding microclimatic conditions. Two very different ecological habitats were formed, separated by a half mile of heather, one a coniferous wood, the other a birch wood with some alder. The two habitats now actually contain separate races distinguished by size, choice of food, color and markings, time of emergence. Breeding experiments showed the differences to be hereditary. … A mutant or a combination of mutants with similar effect had actually changed the species in such a way as to give to the new type a physiological advantage under proper environmental conditions. When, in the case of the nun moth, these were furnished by the chemical effects of industrial smoke upon food plants, the mutant began to replace the original form. The result is that a white nun moth has become a more or less black one.

Doesn’t this completely undermine Kettlewell?

no. Rather, these experiments simply build on Kettlewell contribution.

1. In the first case (your Gould quote), there is nothing preventing multiple selective pressures from maintaining a trait. All the article is saying is that the trait might be maintained by a selective mechanism other than predation. this does not a-priori exclude predation as still being a selective mechanism involved in maintaining the trait, especially since the mechanisms do not counter one another in their predicted effects.

2. In the second case, you are now talking about an entirely different species, in an entirely different habitat, which could have a whole new set of traits that might be linked to melanin production, and a whole different potential set of selection pressures.

bottom line, your post implies you are arguing from the perspective that alternative selective mechanisms affects our presumption about whether selection took place or not, which is rather like saying (to borrow an analogy) that since a fiat is not a porsche means that neither of them are cars.

no, if anything the fact that evolution still works just fine to explain circumstances where many different selective pressures might be involved actually strengthens the value of evolutionary theory’s predictive value.

or was your question simpler than that?

cheers

This is not a question of whether or not selection is taking place or not. Rather the question is: What is being selected?

Gould (1) acknowledges that it was Godlschmidt who worked out the genetics regarding industrial melanism–the issue at hand, and (2) does not disagree with Goldschmidt’s “elucidation.”

Goldschmidt acknowledges the work of Harrison (1920) upon which Kettlewell presumably built. What Goldschmidt seems to imply is that “selection” is a direct result of “industrial chemicals” and not, in the words of Gould, “crypsis”. Thus, if we’re dealing with a “phsyiological”, rather than a “predatory”, basis for the movement from white to black, then Kettlewell is on the wrong-footing (remember his methodology is at question here).

But again, this isn’t an argument about “if” selection takes place; it’s simply one of “what” was selected. In other words: what’s the need of defending Kettlewell?

NO NO NO.

you missed my first point entirely:

the two selection mechanisms proposed are NOT mutually exclusive.

let’s say you accept the physiological selection mechanism proposed; what predictions would you make from it?

now let’s say you accept the predation selection mechanism proposed; what predictions would you make from that?

essentially, they end up make the same predictions about population ratios of the color variants.

Now, can you think of a way to run an experiment that would distinguish between the two?

Has that experiment been done?

if not, there ya go. apply for a grant and get to it.

Sir_Toejam:

It seems you’ve missed my point completely. My point: either (a) industrial melanism is due to “predation”, or (b) it is due to chemically induced physiological changes. Either way, the mechanism is the same: selection of an expressed genotype. You’re point: There’s a third option: The expressed genotype is mutually selected by BOTH mechanisms: (a) and (b).

Again, if “industrial melanism” is PROVED to be due entirely to chemical agents related to industrial byproducts, selection is still seen to be at work. So, again, what need is there to defend Kettlewell?

Hmm, not being totally convince you are just a creationist troll, I will assume you are just a bit confused.

1. selection acts on phenotypes, NOT genotypes.

2. i thought i answered your question quite nicely.

your point in your original post was:

“Doesn’t this completely undermine Kettlewell?”

and i answered very clearly that it does not.

now that you agree that the mechanisms do not compete, you ask:

what need is there to defend Kettlewell?

well, there really isn’t any need, as i have shown, it was you who raised the question.

if you really mean: of what value is Kettlewell’s experiment?

I answered that one too.

we build on the experiments of those who came before us. Kettlewell’s experiment at the time was a good example of a basic experiment testing an hypothesis of natural selection. We don’t simply throw out old experiments that are essentially good examples, simply because we get new results. Kettlewell is a good example for a basic biology textbook. this is aside from the fact that nothing has demonstrated that he was wrong in concluding that predation acts as a selection pressure on this trait, since, as i pointed out, the other selection pressure you note does not make contradictory predictions.

I could also argue that all Goldschmidt has done is define a mechanism that causes the genetic diversity that selection then acts on. so rather than a random mutation, it was a non-random mutation (chemically induced) that produced the melanin variant to begin with. He proposed that the mutation was then maintained through compatibility with the new food source that may have caused the mutation to begin with (in other words, those that had the genes that caused the melanin mutant had better survival rates feeding on the “poisoned” plants). However, that selective pressure would only act on the larval stage, not the adult (adult moths no longer feed). Selection would still act on the variability in the population in the adult forms as well.

Moreover, there have been plenty of experiments demonstrating predation as a selective agent in moth morhphology since.

the value of kettlewell is that you have something to test against.

“either (a) industrial melanism is due to “predation”, or (b) it is due to chemically induced physiological changes.”

well, to correct your own interpretation (based on the article you are quote mining from), i think you mean in (b) that the changes are selected for by chemical changes in food supply that the larval stage feeds on, which is not the same thing as “induced physiological changes”

this could be corect, but as i pointed out, you would have to come up with a way to distinguish between the two mechanisms in the field (as well as any other potential mechanisms).

as it stands, you can’t distinguish between the two mechanisms by looking at distributions of melanic forms in the adult population. You would have to first figure out how to eliminate any possibility of predation acting as a selective pressure in the field (certainly possible; do you know how you would go about doing that?). Afterwards, you would then have to follow the population for several generations to see if you still get the same ratios.

Can you think of anything else you would have to rule out in order to say that chemical change in food source is the ONLY selection pressure affecting this trait?

it rarely is an either or thing. a trait is often affected by multiple selection pressures, and can also be linked to other traits (genetically) that have a completely different set of selection pressures.

my absolute favorite textbook example to illustrate this is the sickle-cell trait in humans. I won’t go into detail here, but here is a rather in depth coverage of it that shows how mutliple selective pressures work:

http://home.san.rr.com/denbeste/sickle.html

If this isn’t clear to you, i can certainly refer you to a primer that will explain how selection pressures work in the field, and another explaining what you need to know about genetics.

“if “industrial melanism” is PROVED to be due entirely to chemical agents related to industrial byproducts”

but that’s a big IF; what you have posted is a plausible mechanism, but i only see a hypothesis, not experimental data testing whether it the sole selective agent in melanin production.

so… read the rest of their paper (Goldschmidt). go to the science citation index and see if someone has done more recent research based on their hypothesis.

if nobody has yet, it would be an excellent graduate thesis topic to pursue. If you care about science, that is.

However, i suspect that since you are quoting Gould, who is talking about Goldschmidt, that this was quite some time ago (25 years or more). I’m sure if you do a search on the primary literature, someone has tested Goldschmidt’s hypothesis by now.

why don’t you do that and let us know what you find out?

Thanks for the extensive answer. About Goldschmidt’s work, do you have any idea where one begins to look for that online other than a google search?

I don’t think google will help you much with the primary literature search on this.

you will need to access a univeristy library to check on the original publication, then you might try using the science citation index to see if anyone has cited the original paper since.

the librarian at the university library of your choice should be able to direct you in how to use the science citation index.

alternatively, the library you choose may also have access to the Current Contents Database, which might be a quicker search.

try both if available.

good luck

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This page contains a single entry by Matt Young published on May 2, 2005 3:46 PM.

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