People living in Chile's Atacama Desert have different versions of a gene that allow them to cope with the region's naturally high levels of arsenic.

Arsenic from rocks seeps into the desert's scarce water sources, exposing people in the Camarones Valley to levels 100 times higher than the safe limit of 10 micrograms per litre set by the World Health Organization. Mauricio Moraga at the University of Chile in Santiago and his colleagues compared the DNA of 50 people from this region with that of 92 individuals from other areas of the country that have lower levels of arsenic. They identified mutations that increased the efficiency with which the arsenic methyltransferase enzyme processes the element, and found these to be more common in the people of the Camarones Valley.

Nearly 70% of the Camarones people carried the most protective variant, considerably more than in other populations. These people have evolved over just 7,000 years under natural selection to tolerate arsenic, the authors say.

Am. J. Phys. Anthropol. (2017)