Rapid Evolution in Response to Pollution

Last time in class we swiftly went over the process of Microevolution, changes in frequency of certain traits within a population. A kind of fish called the Atlantic Tomcod, which is a small bottom-feeder in the Hudson river, has undergone a dramatic change in just the past 50 years. In the 1950s, the tomcods in the Hudson river suffered an onslaught of chemical pollution caused by Electric companies dumping toxic PCBs into the river. Young fish that ate the toxins died of heart defects. However, a small portion of the fishies had a mutation which allowed them to tolerate PCBs. You can imagine that prior to 1950 there would be no real advantage to having such a tolerance, and mutated fish were just as likely to survive and reproduce as the others, and so the trait remained rare. Once PCBs were introduced into the ecosystem, the rare mutation that allowed some fish to survive became very important, because only the baby fish that inherited that trait from their parents could survive in the polluted river. Today, all of the tomcods in the Hudson River are PCB-tolerant, so even though today's tomcods look just like the tomcods from 50 years ago, microevolution has changed this species and its ability to survive in a disrupted habitat.

This article explains the whole thing.