Hi all,
I hate to point out a flaw in your usually explemplary
website, but a section in the "Are Mutations Harmful?" FAQ
is 'bugging' me (ouch, sorry about the pun):
Regarding peppered moths, Richard Harter writes,
"Kettlewell's explanation (which makes for an appealing
story) has not stood the test of time. Peppered moths
seldom rest on exposed areas of the trunks of trees.
Moreover the distribution of dark moths might not be well
correlated with tree color except in the areas which
Kettlewell studied. Some more recent studies indicate that
peppered moth melanism is very well correlated with the
amount of SO2 (sulfur dioxide) in the air. [5]"
...and he cites an article by none other than Discovery
Institute Fellow Jonathan Wells, author of the recently
infamous book Icons of Evolution".
Footnote 5 continues:
[5] Johnathan Wells has written an excellent summary
article on the peppered moth which should not be taken as
being definitive. The topic is the subject of considerable
controversy. For dissenting commentary see:
Peppered Moths - round 2 (part 1 of 2) and
Peppered Moths - round 2 (part 2 of 2).
...citing Wells' article at trueorigins, talkorigins'
arch-nemesis!
(It's spelled JONATHAN, BTW)
Now, it is laudable to cite one's opponents if they do
indeed succeed in making a legitimate point. However, my
sense of it is that Wells has succeeded only in taking the
mistakes of some scientists (namely Jerry Coyne's misguided
review of Majerus' Melanism: Evolution in
Action in Nature) and then further exaggerating the
plight of the moth story via the usual tactics of selective
quotation and condemnatory allusion.
Fortunately the footnote cites the alternative view
posted (if I recall correctly) by Donald Frack on the
Calvin listserv. Based on the helpful discussion there, I
read Majerus' book, the review of the book Coyne (upon
which Wells built his case), and subsequent commentary by
the moth experts on the situation. My points follow:
1) Here is Jerry Coyne (Nature) review:
Not black and white
...and I can confirm Frack's opinion that there is very
little relation between Coyne's review of Majerus and the
actual chapters of Majerus' book. For example, Coyne says
in his review:
"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."
...but, Coyne completely fails to mention that in the
very next paragraph of Majerus' book, Majerus cites his own
data on the natural resting places of moths -- some 47
moths -- not alot, but far more than two. This alone, in an
article in Nature, furgoodnesssakes, is
sufficient reason to discount Coyne's review (let alone
Wells' further exaggerations of the issue). Of the 47
moths, Majerus found:
6 on exposed trunks 6 on unexposed trunks 20 on
trunk/branch joints 15 in branches
...which indicates that, in fact, some 68% of the
available natural sample actually does rest on trunk of
some sort, contra Coyne and Wells. It is hard to see how
Coyne missed this dataset, as Majerus also mentions it in
the first lines of his preface (he's been collecting for
his whole career -- peppered moths are not easy to find,
because, well, they're camoflagued, which is the whole
point).
(Frack lists the numbers here:
Peppered Moths - round 2 (part 1 of 2) )
Now, sure, it may be that the moths rest in branches as
well as trunks, and the relative proportions are somewhat
debatable given the limited dataset (although, the much
more extensive 'moths found near traps' data of Majerus has
at least comparable proportions, which would suggest that
the near-traps data is at least somewhat representative as
well -- some 136 out of 156 moths were found on trunks of
some sort, and 48/156 on exposed trunks in this case,
although the attraction of the traps doubtlessly biases
this data somewhat). And even if you ignore the data and
imagine that moths are found entirely in tree branches, as
Wells implies, well, lichens and birds (being known flying
creatures) are also often found in tree branches, so it
seems that the bird predation hypothesis at least remains
quite reasonable.
I suspect that either Coyne was just having an off-day
when he wrote the review, or he was influenced by Sargent
et al.'s review hypothesizing other causes (but apparently
without any supporting evidence, unlike the
selective-predation-by-birds hypothesis) and by his 'higher
goal', namely communicating his concluding point: "We must
stop pretending that we understand the course of natural
selection as soon as we have calculated the relative
fitness of different traits."
...which may be true in other cases, but almost
certainly not in the case of peppered moths. I've read
several recent scientific articles by actual professional
entomologists, and none of them seem to think that the
natural-selection-by-differential-bird-predation hypothesis
is anything like the "peppered myth" that Wells
asserts.
Numerous additional points could be made about Wells'
scholarship (see: Icons of
Anti-Evolution and the thread on the ARN design
forum which references Frack's critiques of Wells, here:
Topic: Wells not incompetent on peppered moths ). The
whole thing is really deserving of a very long FAQ, given
the multitude of creationist and ID webpages trumpeting the
death of the peppered moth. [After this page was originally
posted, Nic wrote the first of this Archive's Icons of Evolution FAQs. See it for
more details.] Frack says:
The bottom line is this: not only is the peppered moth
scenario not dead, it isn't even sick; it is still
considered to be an example of "evolution in action" even
though the scenario is not as simple as it is frequently
portrayed to be.
And Majerus himself (who replied to Frack) confirms:
Evidence of selective predation in the peppered moth is
not lacking. It is just not provided in the quick text book
descriptions of the peppered moth. How can it be. I have
read some 500 papers on melanism in the Lepidoptera. In
total, these papers probably amount to about 8000 pages, ad
the story is condensed into a few paragraphs in most
textbooks for schools. Even in my own book, I could only
give a review of the case covering about 60 pages including
illustrations.
The older hypothesis that melanism was induced by
pollutants was discredited because eslop Hassison's
experiments lacked appropriate controls, and his results
could not be replicated, despite several attempts.
Furthermore, the levels of mutagenesis that he recorded are
several times higher than those produced by doses of
radiation that induce complete sterility in fruit flies
(see E.B. Ford (1964) Ecological Genetics for full critical
review).
Finally, I agree with Dr Wells that photographs of two
peppered moths staged on backgrounds for effect should say
they have been done purely for illustrative purposes. I
have many times, in undergraduate lectures, pointed out
that photographs of the type that appear in so many text
books are faked. However, I would point out that none of
the photographs of live peppered moths taken by myself,
which appear in the book were staged. All show peppered
moths where they were found in the wild.
End-note: It is difficult to have an informed discussion
of a complicated ecological system with those who have
little or no experience of the system. My advice to anyone
who wishes to obtain a fully objective view of this case is
to a) read the primary papers that I based my review upon,
and any other relevant papers, and b) gain some experience
of this moth and its habits in the wild. Of all the people
I know, including both amateur and professional
entomologists who have experience of this moth, I know of
none who doubts that differential bird predation is of
primary importance in the spread and decline of melanism in
the peppered moth.
I hope that this is some use to you, Donald, and that it
encourages more people to look at the case of the peppered
moth with an open mind. If it can help interest a few more
people in moths and butterflies, that is all to the
good.
Best wishes, and Happy Easter.
Mike Majerus
Anyhow, hopefully you'll print this letter, or get
Donald Frack's permission to repost his discussion on your
website, or get a FAQ up on this topic. At the very least,
perhaps you can reference several recent publications from
Actual Moth Researchers which defend the essential elements
of the peppered moth 'story' -- namely, that differential
bird predation (and migration) are the primary factors
accounting for the rise and fall of the melanic form of the
peppered moth over the past 150 years. Here those are:
Bruce Grant's
webpage
Grant, Bruce S. 1999. Fine
tuning the peppered moth paradigm. Evolution 53:
980-984.
(a brief treatment of Grant's work:
Back and Forth, and Back Again: Biologist makes an
unprecedented discovery about one of the most noted
examples of evolution in nature.)
And a specific recent review defending the conclusion
that differential bird predation is the selective force
that is acting on moths:
Cook, L. M. 2000. Changing views on peppered moths.
Biological Journal of the Linnean Society, 69: 431-441.
This last article is not about how moth researchers are
ditching the conventional view of peppered moths; it is
*about* the odd fact that 'conventional wisdom' on the
peppered moths has been changing in the public and even
with scientists like Coyne, despite the fact that the
actual researchers like Grant, Majerus, and Cook, do not
think that any radical change is necessary.
The abstract:
The rapid rise in frequency of melanic morphs in several
moth species, especially the peppered moth Biston
betularia, in industrial regions during the 19th century,
and the subsequent rapid decline, indicate the action of
strong selection. There has recently been a tendency to
criticise and question all aspects of research on
industrial melanism, including the experiments which
suggest that selective predation plays an important part in
the changes. These experiments are reexamined, together
with evidence for changes in appearance of tree surfaces
and for relation of initial melanic frequency to subsequent
rate of decline. It is suggested that intense pollution may
have been required to drive the carbonaria morph to a high
frequency, with frequency patterns over a mosaic
environment smoothed by migration. Improvements in these
extreme locations then triggered the decline, with little
indication of the environmental changes in areas of
moderate pollution. Reasons for criticism of past work are
discussed. Industrial melanism continues to provide an
exceptional opportunity to analyse a pattern of selection
and change in gene frequency.
...and some quotes:
Work by H. B. D. Kettlewell suggested that selective
predation was the main determining factor in B. betularia,
and probably in a wide range of other examples as well. His
evidence consisted of surveys which put the correlation
between melanic frequencies and urbanization on a
quantitative basis (Kettlewell, 1958, 1965), demonstration
that wild birds would eat the moths if they found them
(Kettlewell, 1955), and the now famous demonstration that
birds discovered most readily the forms least like the
daytime backgrounds on which they rested (Kettlewell, 1973;
Rudge, 1999). Colour of resting background and
heterogeneity due to epiphyte cover, appeared to aVect
relative visibility. Selective predation became the
accepted explanation for the rise in morph frequency
(Majerus, 1998).
Since then, further evidence has been collected. Over
the last two decades industrial environments have become
cleaner and melanic frequencies lower (Clarke et al., 1990;
Mani & Majerus, 1993; Grant et al., 1998; Cook et al.,
1999). There has also been some revision of interpretation.
It has been shown that experiments designed to detect and
measure selective predation were carried out in places
where moths were not usually likely to rest if left to
their own devices (Mikkola, 1979, 1984; Liebert &
Brakefield, 1987; Grant & Howlett, 1988; Majerus,
1998). There is by no means a one-to-one relation between
reversion of morph frequency and reversion of epiphyte
pattern (Bates et al., 1990; Grant et al., 1998). These
findings cause us to reexamine the story, but they do not
obviously require a radical revision. Estimations of
selection appear to show a correspondence between fitness
and frequency. The correlation between the condition of the
sites used in experimental studies and those actually used
by the insects is likely to be high. Further lines of
experimentation are suggested, but no previously held view
has been overturned.
The general tone of commentary on Biston studies has,
however, altered. From being treated as a vivid
demonstration of natural selection (Luria, Gould &
Singer, 1981, provide an excellent example) and good field
experimentation (Hagen, 1999), the work concerned has come
to be viewed with suspicion (Sermonti & Catastini,
1984; Cherfas, 1987). In a recent review by Sargent et al.
(1998) almost every reference to past work is predicated by
expressions of doubt, reworking ground covered by Lambert
et al. (1986). When discussing predation experiments they
conclude ". . . there seems to be no clear and consistent
relationship between the relative survivorship of diVerent
morphs . . . and the frequencies at which the morphs
naturally occur in diVerent environments". Coyne (1998)
adopts a similar tone, saying that the flaws in the work
are too numerous to list. This has led to some alarming
reporting, such as Matthews (1999) in the Daily Telegraph
newspaper in Britain, who refers to a "series of scientific
blunders" and states that the experiments are "now thought
to be worthless". This article in turn was linked in its
electronic web version to the Creation Science home page.
Recent commentaries are quoted on more than one
anti-evolution web site. A balanced account, which shows
the strength of the data in the face of recent criticism,
has been provided by Grant (1999). I propose here to
illustrate the predation results, which Sargent et al. did
not do when they criticized them, and to consider why a
radical change in view should have occurred.
[...]
CONCLUSION
In industrial melanism of Biston betularia, both the
original increase and recent decline in frequency of
melanics are striking examples of natural genetic change
closely related to change in the environment. They must
have a selective basis. The experiments demonstrate
selective removal. There is a general correspondence of
morph frequency and appearance of backgrounds likely to be
adult resting sites. None of this is in doubt. The evidence
is, however, limited in two ways. First, non-visual
components of selection have not been investigated directly
in this species. Analysis of segregating progenies suggests
pre-adult survival diVerences (Creed et al., 1980) with
carbonaria homozygotes having an advantage over other
morphs. Non-visual selection is certainly indicated in
studies of other melanic moths (Bishop & Cook, 1980),
but we have little more idea than Leigh (1911) how it may
operate. [Next is Cook's summary of "why a radical change
in view should have occurred"] Secondly, the experimental
and observational evidence cannot on its own carry the
burden of a particular view of evolution, such as found in
Oxford ecological genetics. Smocovitis (1996) describes how
the view of the Synthesis with which it was associated came
to seem ‘constricted’ to many students of
evolution, and to generate a reaction in favour of more
complex models; the last three decades have been a period
of lively debate and controversy. Distrust of the evidence
of industrial melanism may sometimes arise from a wish to
question how the example relates to more complex levels of
evolutionary theory. Criticism on these grounds is
misplaced, and can attract the attention of advocates of
creationism who see an evolutionary field in apparent
disarray. The Biston story continues to provide an
exceptional opportunity to analyse a pattern of selection.
It should be pursued, along with study of other species
with related but different responses to environmental
change.
...which just about does Wells in, IMO. The essential
points of the classical peppered moth story remain firm.
Keep it in the textbooks.
Thanks, Nic Tamzek
PS: While I'm at it, the FAQ "Bombardier Beetles and the
Argument of Design" has the line "Creationists have
argued for an appearance of design in everything from
bacteria cilia to butterfly metamorphosis." I suspect that
"bacterial flagella" was meant.
OK, I'm done. Those are literally the only two
corrections I could find, so now you're clean :-) .
Seriously, keep up the good work.
