First Human Adaptation to Toxic Chemical Uncovered

For hundreds of years, people who live high in Argentina's Andes Mountains have been exposed to elevated levels of arsenic, which naturally occurs in their water. Arsenic is toxic, causing cancer and other health problems, and people vary in their ability to metabolize and get rid of it.

Researchers analyzed the genes involved in this detoxification process, comparing the genetic fingerprint of people whose descendants hail from this area with those from South American environs home to drinking water with lower levels of arsenic. The scientists found that people from the high-arsenic area have a genetic variation that is linked with an ability to more quickly metabolize and expel the substance.

"This is the first evidence of human adaptation to toxic material," says study author Karin Broberg, a researcher at the Karolinska Institutet in Sweden.

The scientists hypothesize that people with this genetic variation were better able to survive, Broberg says, and thus pass on this trait. Arsenic is particularly deadly to children and interferes with people's ability to reproduce, according to the study, published in the journal Molecular Biology and Evolution.

Previous studies have shown that people with this genetic fingerprint metabolize arsenic differently from others, getting rid of the metalloid more quickly by converting it into a substance called dimethylarsinic acid. Those without this genetically derived ability are more prone to metabolizing arsenic into a chemical called monomethylarsonic acid, which is more toxic and takes longer to purge from the body.

Different groups of people around the world may have evolved to metabolize other toxic substances, but this is the first such example of such to be found, Broberg says.

Arsenic is one of the world's major pollutants, she adds, and more than 100 million people are exposed to elevated levels of arsenic in their drinking water.