Kettlewell's experiment

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In Great Britain during the late 1940s through the 1950s, it was noticed that there was a reduced number of light colored European peppered moths (Biston betularia) (light color was most common) and an increased number of the darker colored moths in the industrial areas. This led British ecologist Bernard Kettlewell to search for an explanation.

The experiment[edit]

During the late 1950s, Kettlewell began raising populations of light and dark peppered moths in his laboratory so he could perform his experiment. He marked all the moths with a drop of paint on the wings, so they could be recognized later. Next he released the light and dark moths in two separate wooded areas of England. One of the wooded areas was Birmingham wood near the city of Birmingham, which was very polluted. The other wooded area was Dorset wood, which was in a farm area that was not polluted. At the end of this, Kettlewell set traps around the woods to catch the moths and see which populations survived in the two different areas. Peppered moths with the color of the trunks survived; in the polluted areas where the trees were black the black moths thrived, and in the woods where the trees were light the light moths thrived.


Kettlewell concluded that the pollution from the factories in Birmingham created industrial melanism, which darkened the color of the woods. This in turn caused the moths with the recessive traits to have a better chance of survival because of the camouflage. So Kettlewell concluded that natural selection from industrial melanism caused the moths to adapt to their changing environment.


Johnson and Raven, George B. and Peter H. Biology Principles and Exploration, Austin: Holt, RineHart and Winston, 1997, 290-291.