Dark moths by Prof Matthew J. James

Industrial soot

Biston betularia

Quo vadis dark moths?


The Peppered Moth (Biston betularia) is a classic example of evolution in action, yet in recent years Darwin’s Finches seem to have eclipsed the Peppered Moth as the textbook example of natural selection.

This sciku, written by Professor Matthew J. James, celebrates the Peppered Moth as an example of rapid natural selection and asks where the dark moths are going, Quo vadis in Latin meaning “Where are you going?”. The question refers to both the population change in moth colouration from dark to light and also implies a nostalgic deeper meaning asking where the Peppered Moth explanation of natural selection has gone in light of the present-day dominance of Darwin’s Finches.

The wild-type Peppered Moth has light wing patterns that act as effective camouflage against its common environmental background. Industrial smog from 19th century coal burning in the United Kingdom resulted in the trees upon which they rested becoming blackened by soot, making the moths stand out. As a result the population of light-winged moths plummeted due to increased predation, however numbers of the melanic mutant form (black in colour) of the species rose – this process has been termed Industrial Melanism. As the Industrial Revolution waned and levels of pollution decreased, numbers of the light-winged form of the moth rose once again. Cook & Saccheri (2013) present an interesting review of the Peppered Moth as a natural selection case study.

Original research: https://dx.doi.org/10.1038%2Fhdy.2012.92

Professor Matthew J. James is Chair in the Department of Geology at Sonoma State University, California. His recent book, Collecting Evolution, examines a scientific collecting expedition to the Galapagos Islands in 1905-06 that resulted in the concept of Darwin’s Finches being developed by David Lack in his 1947 book by that same name.

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