Tuesday, March 6, 2012

Industrial Strength Natural Selection

White-bodied Pepper Moth
A new study confirms what has been long suspected, that natural selection favors dark pepper moths* (Biston betularia) where the environment is sooty.  If you happen to be a beautiful white-bodied pepper moth minding your own business while clinging to a dark sooty surface of a tree, you stand out like a giraffe on the Branson strip.  A hungry bird is more likely to turn you rather than your darker cousin into breakfast .

The dark version of the pepper moth, called melanism, was first noticed in industrial Manchester England in 1848 and by 1895, 98% of the local pepper moths were dark.  More evidence of natural selection appeared when clean air regulations cleared the air and the dark form frequency declined.
Black-bodied Pepper Moth

Some authors have challenged these studies based on their methodology.  In the new study reviewed in sciencenews.org/, Michael Majerus carried out six years of rsearch in the relatively unpolluted area in Cambridge where he lived.  Every spring and summer day he climbed a ladder and placed both varieties of pepper moth on his backyard trees and then watched as predatory birds grabbed them.  He showed that the dark forms had only a 91% survival rate compared to the white forms.

While this doesn't necessarily indicate "evolution" with a capital "E" over 50 years, it does show how rapidly populations can change coloration in response to environmental change.  From there it is only a short step in time to the development of a new species.


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