Peppered Moths again

Arthur V. Chadwick (
Wed, 31 Mar 1999 07:44:36 -0800

I post the following from another listserve:

British geneticist Michael Majerus (whose responded by email to Don Frack's
questions) has been a major player in the peppered moth business for years,
and in 1998 he wrote an important book reviewing the topic (M.E.N. Majerus,
MELANISM: EVOLUTION IN ACTION, Oxford University Press).

Majerus's book includes a chapter entitled "The peppered moth story
dissected." Surprisingly, on the first page (117) of that chapter appear
both of the following statements:

"...the basic peppered moth story is wrong, inaccurate, or incomplete, with
respect to most of the story's component parts."


" my view....differential bird habitats affected by
industrial pollution to different degrees, is the primary influence on the
evolution of melanism in the peppered moth."

A careful reading of the chapter reveals that this second statement is not
based on evidence, but rather on Majerus's conviction that natural
selection MUST be the cause of evolution.

Here are the essential facts:

(1) 150 years ago most peppered moths in the U.K. and U.S. were light with
dark spots (hence "peppered"); with the advent of industrialization, moth
populations became predominantly black ("melanic" - hence "industrial
melanism"); once pollution-control measures were introduced in the 1950's,
the proportion of light-colored moths increased again in most areas.

(2) In the 1950's, British physician and amateur lepidopterist Bernard
Kettlewell performed a series of experiments to test the idea that
industrial melanism was due to cryptic coloration and selective bird
predation. Kettlewell released captive moths (including light and dark
forms) onto nearby tree trunks in the morning and watched through
binoculars as predatory birds picked them off and ate them; he also
recaptured moths that evening and compared the proportion of light- and
dark- colored ones with their pre-release proportions. Kettlewell did
parallel experiments in polluted and unpolluted woodlands, and found
convincing evidence that (a) light- and dark- colored moths differed
dramatically in the effectiveness of their camouflage on polluted (dark)
and unpolluted (light, because lichen-covered) tree trunks; (b) birds were
more likely to eat the more conspicuous moths; and (c) the recapture
proportions showed that better-camouflaged moths were more likely to
survive the day.

(3) Subsequent studies in both the U.K. and U.S. showed, unexpectedly, that
the rise and fall of industrial melanism was not correlated with lichen
cover on tree trunks.

(4) In the 1980's, several researchers showed independently that peppered
moths do not rest on tree trunks in the wild. The moths normally fly only
at night, and before dawn they apparently take up positions high in the
canopy, underneath horizontal branches. In 40 years of field work, only
one peppered moth was found resting on a tree trunk in the wild. Although
some uncertainty remains about where the moths actually do rest during the
day, it is absolutely clear that they do not rest on vertical tree trunks.

Facts (3) and (4) show beyond a doubt that Kettlewell's experiments did not
reflect natural conditions. He released night-flying moths in daylight;
apparently disoriented, they settled on nearby tree trunks, where surprised
birds picked them off and ate them. As far as I can tell from the
literature, though, Kettlewell himself was an honest and careful
experimenter; he had no idea at the time that his experimental conditions
did not reflect natural ones. When other experimenters subsequently glued
dead moths to tree trunks to test the selective predation theory,
Kettlewell objected that this was not good science.

Until the 1980's, then, it seemed empirically justified to believe that
industrial melanism was due to cryptic coloration and selective predation.
Even now, though it is clear that peppered moths do not normally rest on
tree trunks, it is theoretically possible that industrial melanism was due,
at least in part, to these factors; but evidence is lacking.

An older hypothesis -- that melanism was induced directly by environmental
pollutants -- was rejected years ago for lack of evidence, and because
Kettlewell supposedly found evidence for the true cause. Of course, the
discrediting of Kettlewell's evidence does not mean that environmental
induction must be the cause; but the two hypotheses are now at least on a
par, in the sense that they are equally unsupported. In other words,
natural selection is no longer the only reasonable hypothesis -- unless one
is a dogmatic Darwinist.

This, unfortunately, appears to be the case with Majerus, American
geneticist Bruce Grant, American textbook writer Ken Miller, and certain
other defenders of the classic peppered moth story. Technically, they have
not been proved wrong, since removing empirical support does not falsify a
hypothesis. But it does leave Darwinists out on a limb, so to speak.

There is a much more serious issue here, however -- the issue of deliberate
scientific fraud. ALL of the photographs in biology textbooks which show
peppered moths resting on tree trunks have been staged. I have
corresponded with several of the lepidopterists who made these photographs;
they either (a) glued dead specimens on tree trunks in order to photograph
them, or (b) placed living specimens on tree trunks in bright light (which
makes them quite torpid, so they stay whereever they're put). Most such
photographs were made before the 1980's, so this approach was quite
reasonable; as Majerus writes in his email response to Don Flack (which
Phil posted to Phylogeny), "as long as the behaviour film is what actually
happens in true life,... there is nothing wrong with this approach." So I
see no reason to accuse the original photograph-makers of fraud.

MOTHS DO NOT REST ON TREE TRUNKS IN THE WILD. This means that every time
those staged photographs have been knowingly re-published since the 1980's
constitutes a case of deliberate scientific fraud. Michael Majerus is
being dishonest, and textbook-writers are lying to biology students. The
behavior of these people is downright scandalous.

Fraud is fraud. It's time to tell it like it is.

Jonathan Wells, Ph.D.
Department of Molecular & Cell Biology
University of California, Berkeley
Senior Fellow
Discovery Institute Seattle