Peppered Proof

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Peppered proof published in Biology. Letters, online 8 Feb 2012, doi: 10.1098/rsbl.2011.1136. The various coloured peppered moths living on trees which had been heavily polluted during the industrial revolution around Manchester UK, have been used as an example of evolution in many biology textbooks for around 60 years. The story has been that birds preyed on moths that rested on trees during the day. Moths whose colour matched the trees, e.g. black peppered moths on soot blackened trees, survived, whist those whose colour contrasted with the trees, e.g. black moths on lichen covered trees, were eaten by birds. As the colour of trees changed the numbers of light and dark moths changed. The increase in the percentage of black moths in regions where trees were blackened by soot from factories was called “industrial melanism” and this was claimed to be proof of natural selection, and therefore, evolution in action.

For decades biology textbooks have used results obtained by a series of moth release and recapture experiments done by Bernard Kettlewell in the 1950s but Kettlewell’s experimental method came in for much criticism in the late 1990s. In response to this criticism Cambridge University entomologist Michael Majerus repeated the experiment in clean unsooted Cambridgeshire, but correcting the experimental design. Majerus found that birds were preying on moths that were less camouflaged, and this was enough to change the relative numbers of dark and light forms in succeeding generations. The combination of camouflage and bird predation on moths was therefore proven to be a real example of natural selection.

Majerus died in 2009, but his colleagues have now published his results. They conclude their report with: “The new data, coupled with the weight of previously existing data convincingly show that ‘industrial melanism’ in the peppered moth is still one of the clearest and most easily understood examples of Darwinian evolution in action”.

Editorial Comment: Since these moths have still only been observed to remain moths of exactly the same species, and since all that has changed is the number of light and dark forms of the same species, all of which existed prior to both Majerus’ and Kettlewell’s observations, what has been observed may be a genuine example of natural selection, but it is definitely not an example of evolution. When Majerus started this project he admitted his real motivation was to campaign against creationism. He claimed: “To have people believe the biology of the planet is controlled by a Creator, I think that’s dangerous”. (Science, 25 June 2004) Now that Majerus has departed this planet he has discovered how much more dangerous it was to reject the Creator of both moths and men. (insects, ecology, Britain)

Evidence News 13 June 2012