Wells' Icons of Evolution - Peppered Moths

Well I don't doubt that speciation occurs. Creationists since the time of Karl von Linne knew that the Created Kind was at least at the Genus level (Linne being a Creationist). However it could be that the definition of species is somewhat ambiguous... (OK, OK a new thread)As far as the moths and NS I don't see where it wouldn't be an example of that. The environment changed and when it changed those organisms better suited to that new environment thrived (and became the majority) and those that thrived in the old environment were now the minority. Looks like I will have to go back and read that chapter in "Icons..." again to see what Wells really says. I'll be back...

You might also take a look at Message 6 where Cromwell makes a lengthy argument and concludes that whatever the cause, it isn't NS. Cromwell draws upon arguments from Wells, but having not read Wells myself I don't know if Cromwell's conclusion agrees with him.--Percy

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.

Hi, JonF!Can I assume that your mentions of mutation did not mean to imply that repeated and relatively contemporary mutations were the source of the color changes. A recent mutation would surprise me as a source of the changes, since I would have thought it far more likely that NS was operating on preexisting alleles already in the peppered moth genome, even though of course they originally arose, who knows when, by mutation.You mention that the changes were found to follow "classic Mendelian genetic rules", and this would seem fairly conclusive for NS to me. Actually finding the gene on a chromosome doesn't seem necessary, though it would provide an additional level of confirmation.--Percy

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?

I guess I'd be surprised to learn that's the case. If you happen to run across more info let us know.--Percy

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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?

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Some mutations occur more often than others because certain DNA sequences lend themselves to being miscopied or for substitutions to occur. Its primarily due to the physical structure of the DNA at those points and its interactions with molecules such as DNA polymerase, and others.In the case of the peppered moth, however, the rise in the melanic form is NOT due to recurring mutations, simply because the rate of recurrent mutation is nowhere near enough to account for the increase.KC

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Some mutations occur more often than others because certain DNA sequences lend themselves to being miscopied or for substitutions to occur. Its primarily due to the physical structure of the DNA at those points and its interactions with molecules such as DNA polymerase, and others.

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In the case of the peppered moth, however, the rise in the melanic form is NOT due to recurring mutations, simply because the rate of recurrent mutation is nowhere near enough to account for the increase.

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May I ask for a minor clarification?Are you simply saying that the transition from ~0% dark moths to 98% dark is not accounted for by a recurring mutation that made each individual dark? Or do you mean that the rate of recurrence is so low that the dark moths were all likely the descendents of one dark mutant born in the 1800's?

My understanding is that there are always some dark in the population. I don't know why. It may be that it is linked to something that is of some other benefit. It would be interesting to have more of the details.

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May I ask for a minor clarification?
Are you simply saying that the transition from ~0% dark moths to 98% dark is not accounted for by a recurring mutation that made each individual dark? Or do you mean that the rate of recurrence is so low that the dark moths were all likely the descendents of one dark mutant born in the 1800's?

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The former.KC

http://www.arn.org/docs/wells/jw_pepmoth.htmIt looks like all Wells is saying that IF this story is an Icon of evolution scientists had better get the conclusion straight.

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It looks like all Wells is saying that IF this story is an Icon of evolution scientists had better get the conclusion straight.

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Too bad Wells can't get even the data or methods straight, let alone the conclusion.KC

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

What conclusion have we come to?Majerus and the studies in the U.S (Michigan,Pennsylvania e.t.c.)of the peppered moths are only observations of quantity sightings of the peppered moths.I was asked earlier to provide calculations on my assumptions that there wasn't enough "material" evidence... Quantity of moths predated upon,known number of polluted trees e.t.c.To show my reasons as to why i believe that natural selection was not the mechanism behind the melanic dominance due to a cryptic background.Resulting in one proliferation of a variant over another.I have no substantial calculations,because my assumptions were based on the observations of the Majerus,U.S. data and other data mentioned by Wells.They have not provided calculations either.
I have admittedly surmised that this does not look like natural selection,but i'm not the only one surmising.Without indepth evidence is not everyone else surmising?The data by the scientists consists of only the number of observations and a pie chart by Majerus.There are NO calculations provided by these observers giving an indication of how many moths were victims of predation,amount of polluted trees,and yes the moths landed on the open parts of the trees(very rarely),but a major factor would be for how long they rested on the trees,time of day,weather conditions,observations of predators present and other insects seen on the tree trunks at the time and many other factors.This is hardly an indepth study.
Surely as intelligent scientists you would want to know the whole picture before assuming that this is natural selection at work?I originally contested that this was not an icon of evolution.Is it really an icon? Is there really evidence that the mechanism behind variant changes in the peppered moth is by natural selection? Do the field studies truly bare this out?