The peppered moth has evolved significantly during the last two centuries. Peppered moths rest during the day on trees and need camouflage to prevent predators seeing them. Before the Industrial Revolution in Britain and North America most peppered moths were light coloured. The trees where they rested were also light coloured and covered with lichens. During that time light forms flourished. Later when pollution darkened trees darker coloured moths developed which could hide better on darker trees.

The rise of the dark form of the moths

During the Industrial Revolution pollution from factories killed many of the lichens and darkened the bark of trees where the insects rested. Light coloured moths stood out against the dark background so birds easily saw them and ate them. A dark coloured or, “melanic” form of the peppered moth was then better adapted and better able to survive. Naturalists observed and recorded how the melanic form became more common in polluted areas. By 1895 98% of the peppered moth population in Manchester were the dark form. It was first suggested in 1896 that predation by birds was causing the changes in colouration of the moths which had been noted before.

Partial return of the light forms of the moth

From the second half of the 20th Century to the present there have been legal pollution controls. Therefore the light form of the moth was better able to hide from birds that eat insects. Light coloured moths are now more frequent but have not replaced the dark moths totally. Mathematical models were developed which were consistent with observations. Parallel evolution happened in North America where a dark form of the peppered moth also became more frequent during industrialization.

Predation experiments

Experiments were done to check the simple hypothesis, that bird predation was causing the changes in the colouration of the moths. One experiment involved releasing moths into a large aviary where an insect eating bird, the Great Tit fed on them. Another experiment involved releasing and recapturing marked moths of both types in polluted woodland in industrial Birmingham, England. This experiment confirmed that in polluted woodland the light coloured moths were more likely to be eaten. The experiment was repeated in unpolluted woodland in Dorset, England to compare results. All experiments have confirmed that bird predation was causing the change in colour frequency of the moths.

We don't need God to explain life. Evolution explains it.

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