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‘Darwin’s Moth’ example confirmed by scientists

1:59 pm, 17th August 2018

The peppered moth exists in two forms – pale and dark – and the relative success of these forms provided an early example of Darwin’s theory of evolution by natural selection.

According to the study, the pale and dark forms of the moth are explained by how well camouflaged they are to birds in clean and polluted woods.

During the industrial revolution, the levels of pollution in the UK were so high that the light-coloured lichen on trees was killed and the bark was darkened by soot, causing a darker form of the moth to emerge.

But when laws were introduced to ensure the air was cleaner and soot levels dropped, the lichen began to recover – causing the pale peppered moths to surge.

The textbook example of evolution through the development of peppered moths had been supported by a number of studies.

However, scientists hadn’t tested how well camouflaged the moths actually were when it came to the vision of their key predators, and thus how directly their colouring influenced their survival.

The scientists from the University of Exeter have examined how the vision of birds means that pale moths are much more camouflaged against lichen-covered trees than dark moths.

As such, pale moths were much less likely to be eaten by birds in unpolluted woodland, giving them an evolutionary advantage.

“This is one of the most iconic examples of evolution, used in biology textbooks around the world, yet fiercely attacked by creationists seeking to discredit evolution,” said Professor Martin Stevens.

“Remarkably, no previous study has quantified the camouflage of peppered moths, or related this to survival against predators in controlled experiments.

“Using digital image analysis to simulate bird vision and field experiments in British woodland, we compared how easily birds can see pale and darker moths, and ultimately determine their predation risk.

“Our findings confirm the conventional story put forward by early evolutionary biologists – that changes in the frequency of dark and pale peppered moths were driven by changes in pollution and camouflage.”

The research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and published in the journal Communications Biology.