RE: Peppered Moths again

Pim van Meurs (
Mon, 5 Apr 1999 23:54:47 -0700

The following was posted on the CARM group where I posted the peppered moth articles. It is unclear who the author of the email is, although it might not be to hard to guess.


Helen: When there are posts as long as this series of yours, I like to print them off and then read them. I have not had the time to do that with yours this evening,
so the following may be in agreement with some of it or not -- I don't know. But this is from an email I received regarding the peppered moth ruckus that is
going on right now and at least I think it might add significantly to the conversation. I'll try to read all your material tomorrow.


I have just re-read Kettlewell's classic article "Darwin's Missing Evidence" in the Scientific American of March 1959 (Vol. 201, No. 3, pp48-53),
concerning the alleged example of Darwinian "evolution in action" (p48) evidenced by a change in the relative preponderance of light and dark variants of
the peppered moth (Biston betularia) in England.

While the peppered moth example would be no problem even for the strictest special creationist, since even if true it would only show natural selection
operating in a conservative sense, it seems to me that Kettlewell's article has a number of major flaws which cast doubt on whether his Darwinian
conclusions were warranted from the evidence. Since Kettlewell's peppered moth studies in general, and this article in particular, are cited uncritically in
many books on evolution (both technical and popular), as virtually the conclusive piece of evidence for Darwinian natural selection in action, such flaws
would, if sustained, point to serious deficiencies in Darwinist thinking over the space of four decades.

These claimed flaws include the following:

1) The tone of the article. Kettlewell's article reads more like a piece of Darwinian propaganda than a scientific article. He hypes the significance of his
study, as virtually the experimentum crucis that establishes Darwinism. For example, he claims that the change of the "peppered moth Biston betularia from
"predominantly light coloration" to "predominantly dark" coloration in "less than a century" in England was "the most striking evolutionary change ever
witnessed by man" and that this constitutes "Darwin's Missing Evidence" (pp48-49). Indeed, Kettlewell actually states that: "Had Darwin observed industrial
melanism...He would have witnessed the consummation and confirmation of his life's work." (p53).

Kettlewell's Darwinian apologetical intent is clear in his summary dismissal as "Lamarckian", British biologist Heslop Harrison's 1926 experiments which
showed that industrial melanism in moths was related to their ingestion of industrial pollutants. (p48).

2) The unnatural positioning of the moths. Kettlewell notes that Biston betularia is one of those moths that "fly at night and spend the day resting against a
background such as a tree trunk." (p48). He expands this to include also "the underside of the boughs." (p49). But as University of Chicago biologist Jerry
Coyne points out in a recent NATURE article, "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." (Coyne J.A., "Not black and white," Nature 396, 1998, pp35-36).

Indeed Kettlewell's article has photographs showing peppered moths on tree trunks, with the following comment: "Both the light and dark forms appear in
each of the photographs at right and on the next page." (p49). Moreover, Kettlewell draws an important conclusion from the fact that they are resting on a
tree trunk:
"The background of each photograph is noteworthy. In the
photograph on the next page the background is a lichen-encrusted oak trunk of the sort that today is found only in unpolluted rural districts. Against this
background the light form is almost invisible and the dark form is conspicuous. In the photograph at right the background is a bare and blackened oak trunk
in the heavily polluted area of Birmingham. Here it is the dark form which is almost invisible, and the light form which is conspicuous." (p49). But if Coyne's
claim above is true, then Kettlewell's photographs are artificially contrived, and his conclusions based on them are misleading, if not actually fraudulent.

Furthermore, Kettlewell admitted four years before this article that placing the moths on the trunks of trees produced an unnaturally high concentration of
moths: "I admit that, under their own choice, many would have taken up position higher in the trees, and that since the surface area of a tree increases
proportional to the distance up the trunks or boughs, in so doing they would have avoided concentrations such as I produced...Others have shown the
importance to cryptic [camouflaged] insects of avoiding too high a density, but this is no argument against the findings for the relative advantages of the
three forms." (Kettlewell H.B.D. "Selection experiments on industrial melanism in the Lepidoptera" Heredity, Vol. 9, 1955, p340, in Bowden M., "Science
vs Evolution," 1991, p197). But this ignores what Kettlewell must have known that if he placed the moths in the boughs, his recapture rate, though still
relatively the same, might have been so small as to be statistically insignificant. For example, instead of 34 dark moths out of a total of 96 recaptured in his
first experiment, he might have only recaptured 3 out of a total of 9!

3) The experiments' conclusions are unjustified. It is not clear that Kettlewell's experiments tested what they purported to, or justified the Darwinian
conclusions reached. He writes: "We decided to test the rate of survival of the two forms in the contrasting types of woodland. We did this by releasing
known numbers of moths of both forms...In an unpolluted forest we released 984 moths: 488 dark and 496 light. We recaptured 34 dark and 62 light,
indicating that in these woods the light form had a clear advantage over the dark. We then repeated the experiment in the polluted Birmingham woods,
releasing 630 moths: 493 dark and 137 light. The result of the first experiment was completely reversed; we recaptured proportionately twice as many of
the dark form of the light." (p49). Thus this first experiment rests on only 9.8% of the released moths and extrapolates from this sample what happened to
the other 90.2%! And this second reverse experiment seems odd in that a much larger number of dark moths were released, and the results are not given.

But apart from that, later in the article Kettlewell notes that the natural habitat of melanic forms of moths is dark forests: "I recently turned my attention
away from industrial centers and collected moths in one of the few remaining pieces of ancient Caledonian pine forest in Britain: the Black Wood of
Rannoch...Here I found no fewer than seven species of moths with melanic forms." (p53). So it is hardly surprising that Kettlewell recaptured more dark
moths in polluted forests and more light moths in unpolluted forests! Each form could simply have been disoriented in an unfamiliar environment, and most
of them may have set off trying to find a more familiar environment. Kettlewell mentions at page 53 how another species of melanic moth, C. repandata,
does just this.

In fact, he states on the previous page that peppered moths suffer "contrast conflict", when on the opposite background to their colour, and "move off
again": "Another difference between the behavior of B. betularia and that of its dark form carbonaria is suggested by our experiments on the question of
whether each form can choose the 'correct' background on which to rest during the day. We offered light and dark backgrounds of equal area to moths of
both forms, and discovered that a significantly large proportion of each form rested on the correct background... the behavior of both forms could be
explained by the single mechanism of "contrast appreciation." segment of-the eye of a moth senses the color of the background and that another
segment senses the moth's own color; thus the two colors could be compared. Presumably if they were the same, the moth would remain on its
background; but if they were different, 'contrast conflict' would result and the moth would move off again. That moths tend to be restless when the colors
conflict is certainly borne out by recent field observations."(p52) Moreover, Bowden cites an earlier article in which "Kettlewell carried out some tests of
just how far a Peppered Moth usually travelled over a period of time. He came to the conclusion that the moth
'frequently flies a mile per night, probably much further.'" (Kettlewell H.B.D., "A survey of the frequencies of Biston Betularia (L) (Lep.) and its melanic
forms in Great Britain," Heredity, Vol. 12, 1958, p60, in Bowden M., 1991, p204).

4) Bird predation as a major factor was not demonstrated. Kettlewell assumes that the main reason he captured more dark moths in polluted forests and
more light moths in unpolluted forests was due to birds seeing and eating more dark moths against a light background and more light moths against dark
background, despite the fact that there was little evidence for birds eating peppered moths in the wild: "For the first time, moreover, we had witnessed birds
in the act of taking moths from the trunks.... there had been absolutely no record of birds actually capturing resting moths. Indeed, many ornithologists
doubted that this happened on any large scale. The reason for the oversight soon became obvious. The bird usually seizes the insect and carries it away so
rapidly that the observer sees nothing unless he is keeping a constant watch on the insect. This is just what we were doing in the course of some of our
experiments. When I first published our findings, the editor of a certain journal was sufficiently rash as to question whether birds took resting moths at all.
There was only one thing to do, and in 1955 Niko Tinbergen of the University of Oxford filmed a repeat of my experiments. The film not only shows that
birds capture and eat resting moths, but also that they do so selectively." (pp49-50).

But the simpler explanation is that the moths that Kettlewell placed unnaturally on tree trunks in day-time were, disoriented and not surprisingly, eaten by
birds which saw what was going on! This proves nothing about what happened to the vast majority of moths, both light and dark, which were not

5) Bird predation is contradicted by the facts. Kettlewell's Darwinian conclusion that: "First, when the environment of a moth such as Biston betularia
changes so that the moth cannot hide by day, the moth is ruthlessly eliminated by predators unless it mutates to a form that is better suited to its new
environment" (p50), is not borne out by either his experiments or the facts. The fact is that as Kettlewell's own article says, the dark form is not "ruthlessly
eliminated by predators" but rather flourishes as a 90% majority "far outside" the "British industrial areas" (p49). On the next page Kettlewell admits that:
"...though the counties of eastern England are far removed from industrial centers, a surprisingly high percentage of the dark form is found in them." (p50).
Indeed, towards the end of the article, Kettlewell admits that it is unlikely the light form will be eliminated:

"Indications so far suggest, however, that complete removal is unlikely, and that a balance of the two forms would probably occur. In this balance the light
form would represent about 5 per cent of the population." (p53).

The geographic distribution of the dark form of the peppered moth revealed in Kettlewell's article does not support his bird predation theory. The article
states that "The dark form of the peppered moth was first recorded in 1848 at Manchester in England." (p49), but had spread well beyond the industrial
areas of England: "Of 621 wild moths caught in these Birmingham woods in 1953, 90 per cent were the dark form and only 10 per cent the light. Today this
same ratio applies in nearly all British industrial areas and far outside them." (p49). As previously stated, elsewhere in the article Kettlewell says:
"...though the counties of eastern England are far removed from industrial centers, a surprisingly high percentage of the dark form is found in them." (p50).

In fact the article on page 51 has a map which shows the distribution of the dark and light forms of peppered moths in England: "The present status of the
peppered moth is shown in the map on the opposite page...The map makes the following points. First, there is a strong correlation between industrial centers
and a high percentage of the dark form of the moth. Second, populations consisting entirely of the light form are found today only in Western England and
northern Scotland. Third, though the counties of eastern England are far removed from industrial centers, a surprisingly high percentage of the dark form is
found in them. This, in my opinion, is due to the longstanding fallout of smoke particles carried from central England by the prevailing south-westerly winds."

This last point appears to be an astonishing blunder which suggests how much Kettlewell's need to fit the facts into his Darwinian paradigm has led him
astray. His map shows an equal number (if not the majority) of the dark peppered moths are actually found on the map in the unpolluted south-east corner
of England. And since the industrial centres are shown on the map as being to the northwest, there is no way that "smoke particles" could be "carried from
central England by "south-westerly winds"! So obvious is this blunder that I thought maybe I was missing something, until I read what another Englishman,
Bowden said about it: "there is a fairly high percentage (46) of dark moths recorded at Folkstone, and for this to have been due to a soot laden atmosphere
borne by the prevailing south-westerly wind would have required an industrial centre somewhere in the English Channel!" (Bowden M., 1991, p204).

But even if Kettlewell simply got his directions wrong and smoke particles were blown from the polluted north and west industrial areas to the unpolluted
south east, it would only help his case if the south east corner became polluted and the trees became darkened. But this has not happened as Bowden, who
lives in the south-east, verifies: "In a similar way, the high 89% of dark forms recorded for Bromley [Kent] could not be due to any polluted industrial
atmosphere, as can vouch for both present and in the past." (Bowden M., 1991, p204). A more likely explanation is that the dark moths themselves, perhaps
under the influence of north-westerly winds, have migrated from the industrialised north and west to the non-industrialised south and east, or have originated
independently in the latter. But this would of course seriously weakens Kettlewell's bird-predation theory, because these same dark moths should get picked
off by birds in the unpolluted forests.

6) Other possible factors are ignored. Kettlewell mentions other factors which would seem to explain the preponderance of dark peppered moths in England
as well (if not better), than his bird-predation theory. For starters, he points out the melanic gene is dominant: "The mutant gene of a melanin moth is
inherited as a Mendelian dominant; that is, the effect of the mutant gene is expressed and the effect of the other gene in the pair is not. Thus a moth that
inherits the mutant gene from only one of its parents is melanic." (p51).

Not only that but the melanic forms are hardier in their larval stage: "The mutant gene, however, does more than simply control the coloration of the moth.
The same gene (or others closely linked with it in the hereditary material) also gives rise to physiological and even behavioral traits. For example, it appears
that in some species of moths the caterpillars of the dark form are hardier than the caterpillars of the light form....Caterpillars of the dark form may be
hardier in the presence of such pollution than caterpillars of the light form. In that case natural selection would favor light-form caterpillars which mature
early over light-form caterpillars which mature late. For the hardier caterpillars of the dark form, on the other hand, the advantages of later feeding and
longer larval life might outweigh the disadvantages of feeding on increasingly polluted leaves. Then natural selection would favor those caterpillars which
mature late." (pp51-52).

This latter interpretation is supported by Kettlewell's observation that the peppered moth's "larvae feed on the foliage of such trees from June to late
October; its pupae pass the winter in the soil." (p49). This is significant because Kettlewell also notes that "the [industrial] smoke particles not only pollute
foliage but also kill vegetative lichens on the trunks and boughs of trees. Rain washes the pollutants down the boughs and trunks until they are bare and
black. In heavily polluted districts rocks and the very ground itself are darkened." (p48).

Indeed, Kettlewell states: "Melanism is not a recent phenomenon but a very old one. It enables us to appreciate the vast reserves of genetic variability
which are contained within each species, and which can be summoned when the occasion arises." (p53). If such is the case, then there seems no reason
why the peppered moth may not have originated, under the influence of pollutants (not necessarily industrial, e.g. pesticides), in several centres in England
since 1848.

There are other, more serious allegations against Kettlewell and his methods in Bowden's book, which draws on the criticisms of Kettlewell's scientific
articles by Italian non-Darwinist biology professor Sermonti. I will summarise these in a later post.
Suffice it to say that if this is the best evidence of Darwinian natural selection in action, and yet it is obviously flawed in both its methodology and its
conclusions, but those flaws have not been noticed by Darwinists for over 40 years, then it must cast doubt on other claimed examples of evidence for
The peppered moth has had immense public relations value for Darwinism because it can be easily grasped by school children and the general public. If it
turns out to be flawed, it will be a public relations nightmare for Darwinism, apart from the problem of removing it from all the textbooks and popular
Darwinist apologetics, and then finding something else to take its place.