Darwin Day and the Peppered Moths
This article first appeared in
the Independent on Sunday 'Talk
of the Town' London section, 29 February 2004.
Richard Dawkins was looking magisterial, his demeanour and his dark
suit apt for an occasion devoted to an eminent Victorian. This was Darwin Day, February 12, the
anniversary of the great scientist's birth in 1809. The international
Darwin Day Program urges its celebration around the world; the British Humanist
Association, for whose event Dawkins was acting as chair, wants it
to be a public holiday. It feels that if believers have saints' days,
non-believers should have a ceremonial day off too.
How should we spend such a day, though? There are no obvious
traditions, like maypole-dancing and marches for May Day. Over in Shrewsbury, Darwin's birthplace,
they were having "a night of fine food and revelry" on the grounds that
as a Cambridge student, Darwin had belonged to a 'Glutton Club' devoted
to dining on "strange flesh". At the London School of Economics, by
contrast, the atmosphere was more chapel than feast. Darwin Day was an
occasion for sober dress and righteous ire.
Dawkins did make one concession to levity, noting that Newton's
birthday is December 25, "so you'll all have been sending your Newton
Day cards". Darwin Day certainly won't be complete without cards; and
no set of Darwin cards would be complete without a design featuring a
pair of moths, one speckled and one black.
These are the two main forms of the peppered moth, emblems and textbook
examples of evolution in action. The dark form appeared in Victorian
Manchester, described at the time as "the chimney of the world", and
had almost taken over from the speckled by the century's end. An
entomologist named J.W. Tutt suggested that the dark ones were better
concealed from birds in industrial districts, where pollution had
stripped the lichen from the trees and covered them in soot. Half a
century later, experiments by Bernard Kettlewell, of Oxford University,
supported Tutt's hypothesis and made the peppered moths famous as a
demonstration of evolution at a pace humans could observe. Then the
dark forms duly went into decline along with smokestack industries and
coal fires, making the textbook story complete. Yet in the past few
years, Creationists and other anti-evolutionists have taken up the
peppered moth as a stick with which to beat Darwinians. The LSE event
was a rally in defence of the peppered moths' tarnished reputation.
And it was personal - relentlessly, vehemently, entirely personal. The
speaker was Dr Michael Majerus, who leads the Evolutionary
Genetics group at Cambridge University. Some years ago, he
published a book in which he reviewed the studies done on the peppered
moths. There were some anomalies, such as the appearance of dark moths
in unpolluted areas, and it remained infernally difficult to do
experiments which did not distort the untidy reality of life in the
wild. These difficulties did not, however, shake his confidence in the
story that Tutt had started a century before. But reviewing the book in
the journal Nature, Jerry Coyne, an American evolutionist, compared his
reaction to Majerus's discussion with the dismay he had felt when he
discovered the truth about Santa Claus. He considered that the moth
should be discarded as "a well-understood example of natural selection
in action".
An entirely predictable selective process then occurred, as
Creationists seized upon these words, disregarding his comment that
plenty of better examples remained available. For opponents of
evolutionary theory, it was like capturing the other side's mascots.
The moths had become celebrities, early stars of natural history films
(and well adapted to black and white television screens). They were
easily grasped and memorable. Two moths side by side were enough to
make the point, and the industrial background gave the story human
interest.
There was plenty of the latter in a subsequent book, Of Moths and Men,
by Judith Hooper, an American author. Hooper seemed to have started out
with the idea - possibly acquired from the writings of the Harvard
palaeontologist Stephen Jay Gould - that English evolutionists are
upper-class, eccentric and excessively fixated on the idea of natural
selection, and sought to add imputations of dishonesty against some of
the deceased ones. At the end of her account, she appeared bemused to
have found that every scientist involved with peppered moths, either
side of the Atlantic, is sure that the story is indeed one of natural
selection in action.
Given a platform, Majerus took his revenge. For an hour he refuted,
denounced and mocked. He closed with an impassioned invocation of over
forty years' experience, man and boy: "I have caught literally millions
of moths in moth traps. And I have found in the wild more peppered
moths than any other person alive or dead. I know I'm right, I know
Kettlewell was right, I know Tutt was right."
But, he acknowledged, anyone else needs scientific proof. He described
the slow and difficult field studies he is undertaking in search of it.
"If I get that proof, and splash it over every front page I can get,"
and the moth-bothering Darwin-baiters read it, "will they be
convinced?". He stopped, and in that moment of quiet, you could see why
he was so angry.
Michael Majerus has posted the text
on which his lecture was based, and the Powerpoint presentation,
on his lab
homepage.