ANDEAN TOWN DRANK ARSENIC WATER FOR THOUSANDS OF YEARS

San Antonio de los Cobres sits about 3,775 meters up in the Puna de Atacama, where arsenic leaches out of volcanic bedrock and into the groundwater. Until a filtration system went in back in 2012, the local water carried roughly 200 micrograms of arsenic per liter. The World Health Organization's guideline is 10. People drank it anyway, for generations, because the other option was not drinking. Scientists clocked something strange in 1995. Women there were handling arsenic unusually well, producing less of the nastier intermediate form and more of the version the body can just pee out. So a Swedish-led team took DNA from 124 women in town and scanned millions of genetic markers. The signal landed on chromosome 10, near AS3MT, the gene behind the enzyme that processes arsenic. Those protective variants turned up far more often in San Antonio de los Cobres than in genetically similar people from Peru and Colombia. The mechanism here is bleak and simple. The people whose enzymes worked lived long enough to have kids, over and over, for a very long time. Mummies in the region from around 7,000 years ago have arsenic in their hair, so the exposure clock has been running a while. The work was published in Molecular Biology and Evolution and billed as the first known case of humans adapting to a toxic chemical, which is a hell of a trophy to win.

Why you should give a shit: Biology can solve a poisoned water supply given seven thousand years and an enormous number of funerals, or a government can install a filtration system, which is what finally happened in 2012.