Toxic Avengers: Pollution Drove Fish Evolution
Tomcod fish found in rivers in New York and New Jersey evolved to handle dangerous chemicals that were dumped in the river between 1947 and 1976, a study finds. The fish aren't mutants, though ? some had genetic resistance that allowed them to tolerate the PCBs and dioxins that entered the water.
Source: http://www.npr.org/2011/02/17/133842089/toxic-avengers-pollution-drove-fish-evolution?ft=1&f=1007