Field Sparrows from 1906 (Top) and 1996 (Bottom). The Top Bird is Coated in Soot. (IMAGE)

Proceedings of the National Academy of Sciences

Field Sparrows from 1906 (Top) and 1996 (Bottom). The Top Bird is Coated in Soot.

Caption

These are field sparrows from 1906 (top) and 1996 (bottom). The top bird is coated in soot.

Credit

PNAS

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