Peppered moths and a pinch of salt

With the aid of the Clean Air Acts and the decline of heavy industry, nature then completed the story. Pollution decreased, and so did the black moths. The textbooks celebrated this example of "evolution in action".

Evolutionists had a trophy case-study that they could brandish at creationists, and at other scientists who considered them inferior because they could only interpret things that had already happened. For once in nature, the story was simple and the case was closed.

As with human celebrities, though, the moths look chequered in hindsight. Revisionists have pointed out anomalies in the evidence, such as the prevalence of black moths in unpolluted East Anglia. They have scrutinised the design of Kettlewell's experiments and found them sadly wanting - not least because the moths don't actually sit on tree trunks during daytime. They have failed to reproduce his neat results, and some believe that these were too neat: sloppy procedure may have allowed unconscious bias to massage the figures. Some scientists now feel that the peppered moth should be suspended from the textbooks. For creationists, as Judith Hooper observes in this absorbing account, it is like capturing the enemy flag.

It is certainly a posthumous humiliation for Kettlewell, who in life never quite managed to attain the standards Oxford demanded - one day he found his nameplate annotated "He's not really a doctor", meaning that he had a medical degree rather than a scientific doctorate. Hooper depicts him as a gifted amateur naturalist who made a poor scientist; outwardly a bluff cove, inwardly a tormented soul who paced his camp at night like an office-bound executive, trying to douse his anxieties with gin and cigars.

She suggests that he was the cat's-paw of the geneticist EB "Henry" Ford, an arrogant and egregious figure who makes a natural villain for her tale. But she tells her story with sensitivity and grace, and Ford insidiously turns himself into a sympathetic character. He was a virtuoso of high-table high camp, and therefore fluent in irony. The inveterate namedropper acknowledged his peccadillo by referring to "my friend the Pope"; the notorious detester of "female women" would raise his bowler to the Kettlewells' nanny and inquire "How is your pussy?" Perhaps this kind of thing plays better in the land of Kenneth Williams than in the States, from whose perspective this skilful synthesis of scientific and human detail is written. The moth story certainly did.

Britain has sustained a can-do attitude among evolutionists: many of them have been singularly ready to believe that natural selection can and does do everything interesting in nature. Much of the cold water poured over peppered moths, and other putative examples of selection, has come from the US. American moths take the contrarian stance too, dark varieties commonly populating unpolluted regions.

Somewhat to Hooper's surprise, though, the scientific consensus holds.

"All of us in the peppered moth debate agree that the moth story is a sound example of evolution produced by natural selection," affirms Jerry Coyne, one of the evolutionists co-opted against their will by creationists. It's just that, as Coyne puts it, we have seen the footprint of natural selection, but we may not yet have seen the foot.

The peppered moth is no longer a neat textbook illustration, dark moth and pale side by side, but normal science, phlegmatically reviewing its shortcomings and striving to untangle nature. And, with the appearance of a creationist specimen in the north of England, it bears an urgent load on its wings. Of Moths and Men merits far more attention than its title suggests.

? Marek Kohn's A Reason for Everything will be published by Granta next year.