The Hudson River has been one of the most polluted in America, but because of that pollution, it’s now the site of evolution happening at a breakneck pace.

The furiously evolving species is the bottom-feeding Atlantic tomcod, which lives in areas of the Hudson that were contaminated by PCBs through much of the 20th century.

PCBs, or polychlorinated biphenyls, were first introduced in 1929 and were used in hundreds of industrial and commercial applications, mostly as electrical insulators. They were banned 50 years later, but they don’t simply degrade. Partly because of PCB contamination, a 200-mile stretch of the Hudson River is the nation’s largest Superfund site. [National Geographic]

Despite swimming in PCB-polluted waters and accumulating the chemicals in their systems, the tomcods are alive and well in the river. In a study in Science this week, Isaac Wirgin and colleagues show that this is because in the span of just a few dozen generations, the fish have evolved a resistance to PCBs.

The resistance is provided by a variant in a single gene that prevents the chemical from binding ...