Mothballed Science
The peppered moth story, for almost fifty years the prime textbook example of evolution by natural selection, is fast becoming biology’s greatest embarrassment. Before long, Biston betularia, to use the moth’s scientific name, will be famous only as the subject of a messy experiment whose faults were overlooked because the data were needed to support something that leading biologists and many other people badly wanted to believe.
Anybody who ever took a biology class has seen the photos of light and dark moths that all the textbooks use to illustrate this classic example. The official story is that the peppered moth in Britain, normally off-white with a freckling of black scales, was well camouflaged against a background of lichen-covered tree trunks until the Industrial Revolution. In 1848, a collector spotted a single dark (melanic) moth in the industrial midlands. Thereafter, the melanic variety quickly spread throughout polluted industrial districts.
Scientists theorized that smoke from the factories killed the lichen and darkened the tree trunks on which the moths were believed to rest during the day. Viewed against the newly blackened background, the melanic moths were virtually invisible to birds and so flourished uneaten, while the lighter variety became bird food and declined in number, until air pollution restrictions in the mid-twentieth century allowed the lichen to grow back on the tree trunks. Then the lighter-colored moths made a rapid comeback, or so the story goes.
Bernard Kettlewell, a medical doctor and skilled moth collector whose scientific training was minimal, performed allegedly “carefully controlled” experiments in the mid-1950s to verify the numbers of light and dark moths in polluted and unpolluted regions. Kettlewell thus confirmed, or so it seemed at the time, that differential bird predation had caused the back-and-forth shifts of the predominant coloring in the moth population.
Biologists acclaimed Kettlewell’s studies for providing what he called “Darwin’s missing evidence,” the first confirmation that natural selection had any effect whatever in the wild. Lacking such evidence, Darwin could only illustrate his theory with examples from domestic animal breeding, a process guided by human intelligence rather than by nature. Armed with Kettlewell’s evidence, and uninhibited by any reluctance to extrapolate wildly, the biologists had sufficient confidence, when they gathered in Chicago in 1959 to celebrate the centennial of Darwin’s masterpiece, The Origin of Species, to declare to a credulous world that the entire Darwinian story of biological creation had been proved beyond doubt.
Ever since, the peppered moth story has been Exhibit A in the Darwinists’ case, cited so often and with such emphasis that it came to seem the very embodiment of Darwin’s theory.
Nothing Proved
Anyone who can reason logically can see at once that the moth story, even taken at face value, proves nothing about how moths, trees, birds, and scientific observers came into existence in the first place.
One of the things that amazed me when I first began to study evolution was that most biologists vigorously dispute that fact, and insist that evolution, supposedly the creator of us all, requires no more than the accumulation over geological time of slight changes in gene frequencies of the kind illustrated by the peppered moth story. When Darwinism has passed into the dustbin of history, an event that surely will occur sometime in this century, historians will marvel at the spectacular power this ideology possessed in its heyday to cloud the minds of otherwise intelligent people, including the majority of scientists.
For years I avoided telling my lecture audiences about any of the defects in Kettlewell’s scientific practices, preferring not to distract them from contemplating the absurdity of using this trivial example to prove that natural selection is capable of creating such marvels as cells, wings, eyes, and brains. Now, however, the hilarious true story of the botched Kettlewell studies has leaked out to the general public, and the story is too good not to tell and retell. The Darwinists are stuck with an icon that they can’t afford to abandon and don’t know how to defend.
The trouble started in 1998 when a moth expert named Michael Majerus published a book that Oxford University Press had, ironically, commissioned to commemorate Kettlewell’s achievement. Majerus disclosed enough of Kettlewell’s many departures from proper scientific practice to inspire a reviewer to examine the original papers and then to write in Nature that the situation was even worse than Majerus had suggested, so that “for the time being we must discard the peppered moth as a well-understood example of natural selection in action.”
Phillip E. Johnson is Professor of Law (emeritus) at the University of California at Berkeley. He is the author of Darwin on Trial, The Wedge of Truth, The Right Questions (InterVarsity Press), and other books challenging the naturalistic assumptions that dominate modern culture. He is a contributing editor of Touchstone.
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