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) . . .