Pollution and evolution Waters of change

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http://www.economist.com/node/21534749

IT IS not often that biologists have a chance to watch natural selection in action. The best-known cases—the evolution of resistance to antibiotics in bacteria and to pesticides in insects—are responses to deliberate changes people have made in the environment of the creatures concerned. But mankind has caused lots of accidental changes as well, and these also offer opportunities to study evolution.

Recently, two groups of researchers, one at New York University (NYU) and the other at the Woods Hole Oceanographic Institute in Massachusetts, have taken advantage of one of these changes to look at how fish evolve in response to environmental stress. The stress in question is pollution by polychlorinated biphenyls (PCBs). These chemicals—widely used in the middle decades of the 20th century to manufacture electrical insulation, coolants, sealants and plasticisers—often ended up dumped in lakes, rivers and coastal waters. Eventually, such dumping was banned (in America, this happened in 1977). But PCBs are persistent chemicals, and their effects are felt even today. In particular, they disrupt the immune systems of animals such as fish, cause hormonal imbalances and promote tumours.

As is the way of evolution, however, some fish species have developed resistance to PCB poisoning. Isaac Wirgin, at NYU, and Mark Hahn, at Woods Hole, have been studying PCB-resistant fish, to see how they do it. After that, the two researchers will be able to look at how these populations evolve yet again as the environment is cleaned up.