For millennia, communities in the Argentinian Andes have survived on water heavily contaminated with naturally occurring arsenic – a substance lethal to most people. Recent genetic research confirms that natural selection has equipped these populations with a remarkable adaptation: a genetic variant enabling them to safely metabolize high levels of arsenic. This discovery highlights the extraordinary capacity of humans to evolve resistance to even the most toxic environmental hazards.
The Silent Threat of Arsenic
Arsenic contaminates groundwater in many regions due to volcanic bedrock leaching toxic compounds into the water supply. The World Health Organization recommends a limit of 10 micrograms per liter in drinking water. In the remote Argentinian town of San Antonio de los Cobres, water once contained over 200 micrograms per liter – twenty times the safe level – yet the area has been inhabited for 7,000 to 11,000 years. This longevity in the face of extreme toxicity puzzled scientists for decades.
How Adaptation Works
When arsenic enters the body, it transforms into intermediate forms, one of which, monomethylated arsenic (MMA), is highly toxic. The body ideally converts arsenic into dimethylated arsenic (DMA), which is easier to excrete. Residents of San Antonio de los Cobres displayed an unusual ability to produce more DMA and less MMA, suggesting an efficient processing mechanism.
Identifying the Genetic Basis
Researchers at Uppsala University led by Carina Schlebusch and Lucie Gattepaille analyzed DNA from 124 women in San Antonio de los Cobres. Comparing their genomes with those of populations in Peru and Colombia, they identified a cluster of genetic variants near the AS3MT gene. These variants were significantly more common in the Argentine population and appear to enhance the body’s ability to convert arsenic into safe, excretable forms.
The key is efficiency: The genetic variants allow faster conversion to DMA, minimizing the buildup of toxic intermediates. This aligns with previous studies on arsenic metabolites found in the urine of affected populations.
Long-Term Exposure Drives Evolution
While arsenic contamination is widespread, few communities have endured such prolonged exposure. The people of San Antonio de los Cobres have lived with arsenic in their water for thousands of years, giving natural selection ample time to favor traits that mitigate its effects.
Further research suggests similar genetic adaptations may exist in other Andean populations, indicating the adaptation could be broader across the region. The researchers conclude that carrying the arsenic-tolerance genetic variant provides a significant survival advantage in high-arsenic environments, potentially explaining its prevalence.
This adaptation is a stark reminder of human resilience: Given enough time, life finds ways to overcome even the most dangerous conditions.
