Staple of Evolutionary Teaching May Not Be Textbook Case
By NICHOLAS WADE
New York Times, June 18, 2002

A leading example of evolution given in biology textbooks has 
come unglued, evoking jeers and jubilation in the camp of 
creationists, who have been trying for years to expel Darwin from 
the classroom.

The case is that of the peppered moth, which over the course of a 
few decades has changed its wing color from pale-peppered to 
black and back to peppered again in parallel with the rise and fall 
of industrial pollution.

The moth, a furtive citizen of Britain and the United States, flies 
only at night. During the day, it supposedly hides on the trunks of 
lichen-encrusted trees, where the normal pale form is almost 
invisible. 

Textbook writers have long held that the dark form of the moth 
grew much more common when soot from industrial activity 
blackened the trees and killed the lichens, making the pale form 
more conspicuous to birds. But with the passage of clean air laws, 
the lichens returned, the pale form regained its camouflage, and 
the black form reverted to rarity.

This account of events became an instant hit with Darwinian 
advocates. The story caught evolution in unusually speedy action, 
and flagged bird predation as the mechanism of natural selection 
that drove it. The moths made a striking illustration because in a 
typical pair of photographs, one with lichen covering a tree trunk 
and the other with soot, the reader could hardly spot the pale moth 
in the first or the dark form in the second, and it was easy to 
imagine a bird being similarly deceived.

For generations of biologists reared on the peppered moth story as 
perfect proof of Darwin's theory, it came as a shock to learn of 
certain problems the textbooks ignored and which a new book is 
interpreting in sinister light. For one thing, the moths in the famous 
photos were not alive. Like the parrot in the Monty Python skit, 
they were ex-moths, winged members of the choir invisible, firmly 
glued or pinned to their perches.

And they were glued in place for good reason: the peppered moth 
almost never rests on tree trunks, its preferred hideaway probably 
being under twigs in the high canopy of trees.

"My own reaction resembles the dismay attending my discovery, 
at the age of 6, that it was my father and not Santa who brought 
the presents on Christmas Eve," wrote Dr. Jerry A. Coyne, an 
evolutionary biologist at the University of Chicago, in a 1998 
review of a book, "Melanism: Evolution in Action," which noted 
the moth photos were staged. 

But not everyone sees the peppered moth story as a black-and-
white case of deception. Dr. Michael Majerus, a moth man at 
Cambridge University in England and the author of the book 
reviewed by Dr. Coyne, is a staunch supporter of the textbook 
version, despite all the flaws he laid out. So too are American 
moth experts like Dr. Bruce S. Grant of the College of William 
and Mary.

The moth's defenders concede that there were serious design 
problems with the original peppered moth experiments, conducted 
from the mid-1950's onward by Dr. Bernard Kettlewell of Oxford 
University. But they say that he and his successors have tried in 
good faith to correct the problems and that the basic story holds 
up. 

True, many biologists who tested Dr. Kettlewell's findings, though 
not Dr. Kettlewell himself, used dead moths to test birds' feeding 
preferences, but it was not done with intent to deceive, and the 
textbook writers who omitted the detail are at fault for 
oversimplifying, Dr. Majerus said. "Many of Kettlewell's 
experiments were not perfect," he said, "but I think they were 
right qualitatively."

Dr. Theodore D. Sargent of the University of Massachusetts has 
a less-forgiving interpretation. He believes that Dr. Kettlewell's 
experiments created an entirely artificial situation, with moths in 
an unnatural position and birds that quickly learned they were 
being served a free lunch in the woods.

Dr. Sargent is a central figure in "Of Moths and Men," by Judith 
Hooper, to be published by Norton in August. Ms. Hooper 
portrays the poisonous relationship between Dr. Kettlewell and his 
eccentric supervisor at Oxford, E. B. Ford, known as Henry.

"Sensitive to slights and always desperately insecure, Bernard 
became increasingly intimidated by Henry's basilisk gaze and his 
nuanced but lacerating put-downs," she writes on evidence from 
Dr. Kettlewell's son David. Both Dr. Kettlewell and Dr. Ford, like 
the moths in the pictures, are departed.

Reflecting Dr. Sargent's deep skepticism, Ms. Hooper suggests 
Dr. Kettlewell may have fudged his peppered moth counts so as 
to please his overbearing mentor. "I wouldn't want to go on record 
as saying he cooked his results," she said in an interview, but the 
failure by others to confirm some of Dr. Kettlewell's findings was 
"quite damning."

But Dr. Majerus rejected the notion that the two biologists had 
ever fudged their experiments, noting that he had trained with 
their students and never heard any suggestion of improper 
scientific behavior. 

Creationists have not been downcast at the confusion in the 
evolutionists' ranks, assailing the peppered moth story as another 
typical myth from the fairy tale book of evolution.

And Dr. Jonathan Wells, who belongs to the "intelligent design" 
school, which sees a designer giving a helping hand to evolution, 
argued that the case should no longer be presented as a textbook 
example of evolution in action. "Part of my gripe with evolutionary 
biologists is that they make their case sound so much stronger 
than it really is, and I would prefer to see a good deal more 
agnosticism," said Dr. Wells, a member of the Discovery Institute 
in Seattle with doctorates in biology and religious studies.

Perhaps the present truth about the peppered moth is too 
complicated for textbook treatment. The famous photographs are 
certainly misleading without mention that they are staged. But the 
creationists are crowing too early.

The pale form of the peppered moth clearly gave way to the dark, 
or melanic, form as industrialization and air pollution increased in 
England and the United States. Biologists agree that one form of 
the moth's color-determining gene became more common than the 
other. The process then reversed in the two countries, a 
compelling example of evolution in action, after clean air laws 
reduced pollution. But in some areas the pale moths returned to 
prominence before the lichens that Dr. Kettlewell argued were 
their camouflage.

Both Dr. Majerus and Dr. Grant remain convinced that the 
principal mechanism whereby natural selection acts on the 
peppered moth is predation by birds, and the two are working hard 
to prove it before the melanic form disappears altogether.

Dr. Majerus is spending 100 days this year on a bird and peppered 
moth feeding experiment. Dr. Grant, though now retired, is also in 
pursuit. From a phone booth in Alaska, where he is hunting for 
peppered moths, he said the role of lichens had been 
overemphasized and that grime alone had probably been enough 
to give the black form of the moth its transient advantage.

In retrospect, biologists may have accepted the simple version of 
the peppered moth story too eagerly. The Kettlewell experiments 
on lichen camouflage may have been just an enormous diversion. 
But the melanic form of the moth did rise and fall, for whatever 
reason. The moth is no myth, and the moth men's continuing 
efforts may one day get it ready for evolutionary prime time again.

Oryginal:
http://www.nytimes.com/2002/06/18/science/life/18MOTH.html

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