How the Peppered moth proved
Darwin’s theory of evolution
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In the early 19th century the peppered moth was known to most Naturalists as well as Charles Darwin as a predominantly white moth speckled with black.
It’s a rather ordinary creature flying at night and hiding during the day on twigs and tree trunks where it uses its colouring to good effect camouflaging itself against the lichen covered tree bark.
Back in 1848, as the ‘dark satanic mills’ of the industrial revolution started to cover swathes of the North of England with dark soot, a black version of the moth was discovered in Manchester. Within only 50 years the peppered moth population changed. In 1895 95% of the Mancunian moths were found to be black.
This characteristic 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 the fact that it escaped being eaten by birds because it was better camouflaged on the dark sooty surfaces than the lighter variant.
In 1956 Parliament passed the clean air act. What did this piece environmental changing legislation do for the peppered moth?
Sure enough, within a few years, the black peppered moths began to decline and the white variety increased.
This was used as an easily understood example of the mechanism that drives evolution. It’s a story involving things we are familiar with: vision and predation and birds and moths and pollution and camouflage and lunch and death.
However in 1998 a book appeared criticising the original research done by Bernard Kettlewell in the 1950’s throwing doubt upon the theory. This was siezed on by opponents of the theory of evolution as evidence that the experiments on peppered moths were flawed or fraudulent and if this example didn’t add up then neither did the theory of Darwinian evolution.
But now this evolutionary example has been vindicated. Mike Majerus, Professor of Evolution at Cambridge University spent seven years repeating the studies on predation of the peppered moth.
In 2007 he presented his research findings and, whilst concluding that there were some failings in Kettlewell’s original experiment, he was able to show that the peppered moth was after all, an example of Darwinian evolution. His study of visual sightings of birds eating peppered moths showed that in rural Cambridgeshire, the black form was significantly more likely to be eaten that the white.
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