Moth study backs classic 'test case' for Darwin's theory

It was a classic experiment in the 1950s. Release moths of two different types in different environments -- unpolluted and polluted, and see which ones are subject to predation in which environments. Well, it's a bit more involved than that, and people have raised methodological issues with the original study, issues echoed with occasional accuracy in "Icons of Evolution".

Now researchers have re-done the experiment, fixing the problems identified with the original experiment. It retains its iconic status. Moth study backs classic "test case" for Darwin"s theory. Source: The Independent.

For more than a century it has been cited as the quintessential example of Darwinism in action. It was the story of the peppered moth and how its two forms had struggled for supremacy in the polluted woodlands of industrial Britain.

Every biology textbook on evolution included the example of the black and peppered forms of the moth, Biston betularia. The relative numbers of these two forms were supposed to be affected by predatory birds being able to pick off selectively either the black or peppered variety, depending on whether they rested on polluted or unpolluted trees.

It became the most widely cited example of Darwinian natural selection and how it affected the balance between two competing genes controlling the coloration of an organism. Then the doubts began to emerge.

Critics suggested that the key experiments on the peppered moth in the 1950s were flawed. Some went as far as to suggest the research was fraudulent, with the implication that the school textbooks were feeding children a lie.

Creationists smelt blood. The story of the peppered moth became a story of how Darwinism itself was flawed - with its best known example being based on fiddled data.
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In a seminal description of his results to a scientific conference this week in Sweden, Professor Majerus gave a resounding vote of confidence in the peppered month story. He found unequivocal evidence that birds were indeed responsible for the lower numbers of the black carbonaria forms of the moth. It was a complete vindication of the peppered month story, he told the meeting.

"I conclude that differential bird predation here is a major factor responsible for the decline of carbonaria frequency in Cambridge between 2001 and 2007," Professor Majerus said.

"If the rise and fall of the peppered moth is one of the most visually impacting and easily understood examples of Darwinian evolution in action, it should be taught. It provides after all the proof of evolution," he said.
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Professor Majerus compiled enough visual sightings of birds eating peppered moths in his garden over the seven years to show that the black form was significantly more likely to be eaten than the peppered.

A statistical analysis of the results revealed a clear example of Darwinian natural selection in action.

"The peppered moth story is easy to understand, because it involves things that we are familiar with: vision and predation and birds and moths and pollution and camouflage and lunch and death," he said. "That is why the anti-evolution lobby attacks the peppered moth story. They are frightened that too many people will be able to understand."

Natural selection in action

The peppered moth comes in two distinct, genetic varieties: the black, melanic form (carbonaria) and the mottled form (typica). Against the background of a lichen-covered tree growing in unpolluted countryside, the typica form is well camouflaged. But in polluted areas where lichens do not grow, it is the melanic form that is difficult to see.

The Victorian naturalist J W Tutt noted that 98 per cent of peppered moths caught near Manchester at the end of the 19th century were the melanic variety. He was the first to suggest that it was the result of higher predation of typica by birds. With cleaner air in the late 20th century, it was the turn of the melanic form to suffer from bird predation. Now it is the typica form that is more common in most areas of Britain.