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The peppered moth (Biston betularia) is a moth that was drastically affected by soot pollution in England in the 1800's and is a classic demonstration of natural selection.

In England in the 1880's, soot covered much of the landscape, following the advent of the Industrial Revolution. Previous to the soot problem, the light-colored variety of the moth (called typis) was common in England. Its speckled coloration helped camouflage the moth when perched on birch tree trunks (this nocturnal moth rests on birch tree trunks during the day). This type of camouflage is called cryptic coloration. After pollution covered many of the trees with a dark layer of soot and killed the light, whitish-gray colored lichens that lived on the tree trunks, a dark form of the moth (called carbonaria) was observed (presumably since the light-colored variety was no longer camouflaged when at rest on trees, and they were caught by birds - the dark-colored variety were now better camouflaged and more likely to survive and reproduce). The dark form of the peppered moth was first observed in 1848, and by 1895, 95 percent of the peppered moths were of the darker type. This phenomenon is called "industrial melanism."

An Unpolluted Birch Forest
The light variety of the peppered moth on a birch tree trunk.	The dark variety of the peppered moth on a birch tree trunk.
A Polluted Birch Forest
The light variety of the peppered moth on a soot-blackened tree trunk.	The dark variety of the peppered moth on a soot-blackened tree trunk.

Recently, as cleaner-burning fuels have been used in England, the light-colored variety has returned to prominence.

For more on the peppered moth, click here for a page from Tulane University.

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