For decades, the peppered moth was the textbook example of evolution in action, unassailable proof that Darwin got it right. Generations of students learned how, during the industrial revolution in England, a dark-coloured mutant appeared and in polluted areas quickly replaced the normal light-coloured form because it was better camouflaged against bird predation. "It is the most simple to understand, visually attractive story of evolution in action," says Michael Majerus, a geneticist at the University of Cambridge.

Recently, though, the peppered moth's status as an icon of evolution has been under threat. Emboldened by legitimate scientific debate over the fine details of the peppered moth story, creationists and other anti-evolutionists have orchestrated a decade-long campaign to discredit it - and with it the entire edifice of evolution. These days you're less likely to hear about the peppered moth as proof of evolution than as proof that biologists cannot get their story straight.

The peppered moth now counts among the anti-evolutionists' most potent weapons. In the past few years it has helped them get material critical of evolution added to high-school science lessons in Ohio and Kansas, although the material has now been removed. In 2000, the authors of the widely used school textbook Biology reluctantly dropped the peppered moth in direct response to creationist attacks. "It would be really easy to say it is a fraud, and it would take a long explanation to respond to that," says co-author Kenneth Miller of Brown University in Providence, Rhode Island. The latest edition features the beaks of Galapagos finches instead.

Now, though, biologists are fighting back. Majerus recently finished an exhaustive experiment designed to repair the peppered moth's tattered reputation and reverse the creationists' advances. The preliminary results are out, and Majerus says they are enough to fully reinstate the moth as the prime example of Darwinian evolution in action.

[...]

Meanwhile, Majerus was steadily working through his experiment in his own garden in Cambridge. He started by identifying 103 branches that were suitable resting places for peppered moths, ranging in height from 2 to 26 metres, many of them covered in lichen. For seven years, every night from May to August, he placed nets around 12 randomly chosen branches and released a single moth into each net. Around 90 per cent were light-coloured to reflect the natural frequencies of the two forms around Cambridge.

The moths took up resting positions overnight, usually on the underside of the branch. At sunrise the next morning Majerus removed the nets and 4 hours later checked to see which moths were still there. His assumption was that, as peppered moths spend the whole day in their resting position, any that disappeared between sunrise and mid-morning had almost certainly been spotted and eaten by birds.

Because he was able to watch some of the branches from his house through binoculars, he also observed the moths being eaten by many species of bird - including robins, blackbirds, magpies and blue tits. As expected, the birds were better at spotting the dark moths than the camouflaged light ones, he says.

Majerus says his design addresses all the flaws in Kettlewell's experiments. He let moths choose their own resting positions, he used low densities, he released them at night when they were normally active, and he used local moths at the frequencies found in nature.

This August, Majerus presented his [link|http://www.gen.cam.ac.uk/Research/Majerus/SwedenPepperedmoth2007.ppt|preliminary results] at a meeting of evolutionary biologists at the University of Uppsala in Sweden. He said that over the seven years, 29 per cent of his melanic moths were eaten compared with 22 per cent of light ones. This was a statistically significant difference.

[...]