Big Lessons From Little Moths
OF MOTHS AND MEN
An Evolutionary Tale: The Untold Story of Science and the Peppered Moth
by Judith Hooper
W.W. Norton
378 pp., $26.95
“Of Moths and Men” can serve as an elegant introduction to the method of science and the ways of scientists. Judith Hooper tells the intricate tale of how a British scientist’s supposed “proof” of Charles Darwin’s theory of evolution was a staple of natural science for years until an American scientist looked again and found the proof wanting.
The subject is the blackening of the peppered moth in the industrial areas of Britain. The moth was seen, starting in about 1850, to become blacker than its dominant color of gray/white in parts of Britain blackened by industrial smoke. The change toward the darker color is called melanism.
Was this an example of Darwinian natural selection at work? H.B.D. (Bernard) Kettlewell, an English doctor for whom catching and studying moths and butterflies was a passion bordering on the obsessive, thought so and tried to prove it. In 1953 he studied peppered moths in two locations, a smoke-blackened wood near Birmingham and in an unspoiled wood in Dorset.
He found, or thought he found, a higher incidence of blackened moths among the smoke-blackened trees and a lower incidence in the unpolluted ones. He discovered further, or thought he discovered, that the blackened moths near Birmingham escaped being eaten by birds by resting during daylight hours, when they are inactive, on the darker parts of trees. Hence, he reasoned, the blacker moths were evolving before his very eyes. The blacker the moths in the blackened woods, the more easily they would survive to perpetuate the species.
What Kettlewell presented to the world in scientific journals was believed to be of great importance, because Darwin’s great theory is easier to infer from what has happened than to observe what is happening now. Before long, photographs of Kettlewell’s peppered moths were being widely published in textbooks as a neat example of Darwinism caught in the act.
Alas for Kettlewell’s experiment, but fortunately for science, which lives by self-correction, Theodore David Sargent, now a professor emeritus of biology at the University of Massachusetts at Amherst, tried from 1965 to 1969 to replicate the part of Kettlewell’s experiment that showed how moths choose on which part of a tree trunk to alight. Sargent couldn’t do it. He found that the moths’ resting places were not matters of individual choice, as Kettlewell believed, but were genetically determined. Other naturalists showed that birds do not pick moths from tree trunks.
Sargent went on to examine records of Kettlewell’s experiment closely, as few others had done. Sargent found, essentially, that Kettlewell fiddled with his experiments until he got the results he--consciously or subconsciously--wanted. Was it fraud?
“It doesn’t have to be fraud,” Sargent told Hooper. “There are subtle ways to seduce yourself,” he said, describing one of the traps inherent in scientific inquiry: The scientist can fool himself into seeing what he wants to see, finding what he hopes to find.
Hooper’s tale is engrossing. Contemporary scientists increasingly do not work alone, and she describes with finesse the milieus in which Kettlewell especially and also Sargent did their work. Kettlewell’s was that of snobbish, high-table Oxford, in which, as a gifted amateur, he never felt quite at home. He was dominated by the powerful and haughty scientist E.B. Ford. An unhappy child, Kettlewell lived a troubled life and committed suicide in 1979. Despite the doubts about his major experiment, no one doubted that he was a brilliant field naturalist in the British tradition of ardent amateurs.
Sargent, also a natural in the fields and woods, was also a kind of odd man out, in part because he challenged the supremacy of the peppered moth doctrine, Hooper says. She makes it clear that in science as in other endeavors, the person who questions the conventions of the day runs the risk of isolation.
No creationist herself, Hooper regrets that those who to this day discount, in the name of religion or from obscurer motives, the Darwinian theory of natural selection, have seized upon the peppered moth story as evidence for their causes. But she believes in the scientific method, and, in that spirit, presents in “Of Moths and Men” an illuminating story of men and science always groping toward a better understanding of nature.
