"Christianity Today" September/October 2002, Vol. 8, No. 5, Page 11
The Peppered Myth. Of moths and men: An evolutionary tale.
by Jonathan Wells
Open almost any textbook dealing with biological evolution and you'll probably find photographs of
peppered moths resting on tree trunks—illustrating the classic story of natural selection in action.
A friend of mine says those photographs are all he remembers about evolution from his
undergraduate days.
Before the mid-1800s, almost all peppered moths were light-colored, but during the industrial
revolution dark-colored ("melanic") moths became more common—a phenomenon called "industrial
melanism." In theory, industrial melanism was due to survival of the fittest: Dark moths were
better camouflaged on pollution-darkened tree trunks, and thus more likely to avoid being eaten
by predatory birds. For a long time, however, the theory lacked evidence.
In the early 1950s, British physician and amateur moth-collector Bernard Kettlewell released light
and dark peppered moths onto nearby tree trunks and watched as birds ate the less camouflaged
ones. He then released moths that had been marked on the underside with a tiny spot of paint.
When he later recaptured some, the proportion of moths matching the color of nearby tree trunks
was significantly higher than in the batch he had released, consistent with the
camouflage-predation theory. Kettlewell called this "Darwin's missing evidence," and it quickly
became standard fare in biology textbooks.
Most textbooks fail to mention, however, that the peppered moth story began to unravel in the
1960s, when biologists noticed that dark moths were unexpectedly plentiful in some unpolluted
locations. When anti-pollution legislation led to cleaner air in the 1970s, light-colored moths made
a comeback; but, contrary to theory, the comeback occurred without corresponding changes in
tree trunks. Then, in the 1980s, biologists realized that peppered moths almost never rest on tree
trunks (as Kettlewell wrongly supposed when he initially released the moths onto tree trunks,
creating atypical conditions). Instead, these night-flying insects probably spend their days hiding
underneath horizontal branches high up in the trees, where they can't be seen.
In 1998, University of Chicago evolutionary biologist Jerry Coyne wrote: "From time to time,
evolutionists re-examine a classic experimental study and find, to their horror, that it is flawed or
downright wrong." According to Coyne, the fact that peppered moths rarely rest on tree trunks
"alone invalidates Kettlewell's release-and-recapture experiments, as moths were released by
placing them directly onto tree trunks." Coyne concluded that this "prize horse in our stable of
examples" of natural selection "is in bad shape, and, while not yet ready for the glue factory,
needs serious attention" (Nature, Nov. 5, 1998).
Tipped off by a 1999 article in Whole Earth, author Judith Hooper decided to investigate the
peppered moth story. The result is a fascinating book, Of Moths and Men: An Evolutionary Tale.
Hooper deftly portrays the two men largely responsible for producing the classic story, E. B. Ford
and Bernard Kettlewell—and one man who took the lead in debunking it, Ted Sargent.
Oxford geneticist Edmund Brisco Ford wanted to study evolution under natural conditions, and
peppered moths seemed a good test case. Ford obtained grant support for Kettlewell, who was
then able to do what he loved most—traipsing around the woods surrounded by moths. Strangely,
Kettlewell's field notes were never found; since he usually worked alone, there was no
independent verification of his data. Ford helped Kettlewell compile and interpret his results, but
according to Ford's biographer the fit between theory and data was too good to be true.
In addition to the fundamental false assumption that prompted Kettlewell to release moths onto
nearby tree trunks, where they don't normally rest, Hooper lists various other problems with his
experiments; for example, (1) Kettlewell's moth densities were too high, "in effect, creating a
feeding tray," with the intensity of predation recorded in his experiments simply being "a learned
response by the local birds"; (2) Kettlewell measured camouflage by his own eye, even though
bird vision is quite different from human vision; (3) he and Ford disregarded evidence that
selection might operate on caterpillars (through differential mortality when exposed to pollution)
instead of on adult moths; and (4) the two men ignored the fact that the main predators of
peppered moths are night-flying bats.
Despite problems with the classic story, critics have been notably scarce. One of the few has
been University of Massachusetts biology professor Ted Sargent, now retired—the third major
protagonist in Hooper's book, and the real hero of the story. A lepidopterist, Sargent has been
critical for decades of the camouflage-predation explanation for industrial melanism in peppered
moths. In 1998 he and two colleagues wrote in Evolutionary Biology that "there is little persuasive
evidence, in the form of rigorous and replicated observations and experiments, to support this
explanation at the present time."
For his efforts, Sargent has been "marginalized" and even "demonized" by what Hooper calls "the
industrial melanism establishment." (His principal protection, it seems, was that he resisted the
modern trend among scientists to get research grants, so he remained free of the political
entanglements that muzzled so many of his contemporaries.)
Why was Sargent treated so badly? One reason may simply be the tendency of scientists to cling
to theories that are mainstays of their careers. I suspect, though, that something more is
involved: a desire to protect the classic story as an icon of Darwinian evolution in action.
Although Jerry Coyne is an outspoken evolutionist, and Ted Sargent is no creationist, the
evolution-creation controversy fosters a climate in which many Darwinists regard criticism of
supposed evidence for evolution as giving aid and comfort to the Enemy.
Ironically, though, the truth or falsity of the peppered moth story is largely irrelevant to the
evolution-creation controversy. If the story were true, it would show only a reversible shift in the
proportions of two varieties in a preexisting species—a result that even the most uncompromising
creationist could accept. And its falsity poses no threat to the most uncompromising evolutionist,
because there are now other, better examples of natural selection within existing species.
Nevertheless, many defenders of Darwinian evolution rush to protect the peppered moth icon as
though their religion depended on it. In 2000, I wrote a book pointing out that the peppered moth
story—though of limited significance in itself—is part of a larger pattern of systematic
misrepresentation serving to prop up Darwin's theory. Kevin Padian, a Berkeley professor and
president of the National Center for Science Education, a militantly pro-Darwin advocacy group,
responded by likening me to the sociopathic antihero of the film The Talented Mr. Ripley.
According to Padian, "a particularly egregious example of Mr. Wells's talents is his treatment of
the peppered moth." Padian then went on to defend the classic story by claiming that peppered
moths "rest on tree trunks 26% of the time" (The Quarterly Review of Biology, March 2002).
Padian bases his astonishing claim (which contradicts the published scientific literature) on the
fact that 47 moths were found resting in the wild between 1964 and 1996, and that one quarter
of these were on tree trunks. During the same period, however, many thousands of moths were
caught in nighttime traps, so the 47 found in natural resting positions were less than 1 percent of
the moths studied, and much less than 1 percent of all peppered moths living in the wild. Padian
might as well claim that a quarter of all ocean fish are visible to predatory birds because he did
statistics on the few that can be spotted from a boat.
Character assassination supported by transparently bogus statistics—how does a highly placed
scientist end up indulging in such tactics? Obviously, the peppered moth story involves more than
objective science.
So, what about those textbook photographs that impressed my college professor friend? If
peppered moths don't normally rest on tree trunks, how were the photographs obtained? It turns
out that they were staged—often by pinning or gluing dead moths in place.
Jonathan Wells is a Senior Fellow at the Seattle-based Discovery Institute and the author of "Second
Thoughts About Peppered Moths" (The Scientist, 1999) and Icons of Evolution (Regnery, 2000).
Copyright © 2002 by the author or Christianity Today International/Books & Culture magazine.
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