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13 November 2014

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You are in: Manchester > Science > Science features > Darwin's moth: 'proof of evolution'

The peppered moth: [photo: Olaf Leillinger]

The peppered moth (c) Olaf Leillinger

Darwin's moth: 'proof of evolution'

There’s no hiding the fact: the moth is the dowdy relation of its prettier cousin, the butterfly. But one Manchester moth holds a special place above all 'God's creatures' as proof of evolution.

At first sight, the peppered moth (Biston betularia) is an unremarkable creature: a night flying moth which favours temperate climates hiding on twigs and tree trunks during the day.

Darwin rare book.

Charles Darwin's Origin of Species

Yet this humble insect found itself at the centre of a worldwide debate about the origins of life:

Did we evolve through a process of natural selection, as Charles Darwin proposed? Or is the peppered moth, and therefore all life including Man, the work of a divine Creator?

Evolution

In the early 19th Century, the peppered moth was known to most naturalists, including Charles Darwin, as a predominantly white-winged moth liberally speckled with black.

Then in 1848, as the dark satanic mills covered swathes of northern England in sooty black smoke, a black variant of the moth was discovered in Manchester.

Mill c. 1830 [courtesy of People's History Museum]

1830: industrial Manchester

By 1895, 95% of the Mancunian peppered moths were black. This dark form spread across industrial Britain until the Victorian entomologist JW Tutt suggested that the prevalence of the dark form of the moth was due to it being better camouflaged on dark sooty surfaces than the lighter variant.

Sure enough, following the 1956 Clean Air Act, the black form of the moth began to decline with the return of the white form which was bettered camouflaged on lichen-covered tree bark.

Creationism

To decades of schoolchildren, the adaptation of the peppered moth in response to changes in its environment has been held up as an example of evolution in action.

Not so, however, said critics of Darwin who claimed that the science was not as black and white as it seemed. 

"That is why the anti-evolution lobby attacks the peppered moth story. They are frightened that too many people will be able to understand."

Professor Mike Majerus

Seizing on a controversy surrounding a scientific study by Bernard Kettlewell on the peppered moth in the 1950s, anti-evolutionists began to question Darwin’s theory on the origin of species itself.

After criticisms of Kettlewell’s methods were mentioned in a 1998 book by Professor Mike Majerus, and further highlighted in a review in the science journal ‘Nature’ , creationists and counter-evolutionaries began to cite Majerus’ book as ‘evidence’ that the experiments on the peppered moth were ‘flawed’ or even ‘fraudulent.’

They even claimed that if this classic example of evolution didn't add up, then nor did Darwin’s theory. The moth was even withdrawn from school textbooks.

Garden science

But the peppered moth has been vindicated.

Prof Mike Majerus

'Proof': Professor Mike Majerus

Mike Majerus, Professor of Evolution at Cambridge University spent seven years repeating the studies on the predation of the peppered moth. In 2007, he concluded that, while there were some failings in Kettlewell’s original experiment, the peppered moth was, after all, ‘an example of Darwinian evolution.’

Professor Majerus compiled enough visual sightings of birds eating peppered moths to show that, in rural Cambridgeshire, the black form was significantly more likely to be eaten than the peppered.

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

Adding: "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. After all, it provides the proof of evolution."

last updated: 26/01/2009 at 16:02
created: 04/06/2008

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