Humans in The Andes Appear to Have Evolved a Strange Genetic Ability

Why It Matters

The finding provides concrete evidence of recent human evolution driven by environmental toxins, informing public‑health strategies and genetic research on contaminant resistance. It also highlights the need to consider local genetic adaptations when assessing risk from polluted water sources.

Key Takeaways

• High‑arsenic water in Andes exceeds WHO limits twentyfold.
• Residents show unique AS3MT gene variants enhancing arsenic metabolism.
• Genetic adaptation reduces toxic MMA, increases excretable DMA.
• Study compared 124 women to 1000 Genomes data.
• Findings suggest broader Andean tolerance and evolutionary insight.

Pulse Analysis

Arsenic contamination is a global public‑health challenge, but few communities have endured such extreme exposure for thousands of years. In northern Argentina’s Puna de Atacama plateau, natural leaching of volcanic bedrock has pushed arsenic concentrations in drinking water to roughly 200 µg L⁻¹—twenty times the World Health Organization’s safe threshold. Residents have historically relied on this water, exposing generations to a toxic metalloid linked to cancer, skin lesions, and developmental defects. The prolonged exposure created a unique natural experiment for evolutionary biologists seeking evidence of human adaptation to chemical stressors.

A 2015 study led by Carina Schlebusch and Lucie Gattepaille collected cheek‑swab DNA from 124 women in San Antonio de los Cobres and analyzed millions of genetic markers. The researchers identified a haplotype near the arsenic (+3 oxidation state) methyltransferase (AS3MT) gene that was markedly more common than in comparable South‑American populations from the 1000 Genomes Project. These variants enhance the conversion of ingested arsenic into dimethylated arsenic (DMA), a form the body can readily excrete, while limiting the buildup of the highly toxic monomethylated intermediate (MMA). Metabolite profiling of urine samples confirmed that carriers produce less MMA and more DMA, directly linking genotype to a protective biochemical phenotype.

The discovery underscores that human evolution can operate on relatively short timescales when selective pressures are intense and persistent. It offers a template for integrating genomic surveillance with environmental health assessments, potentially guiding targeted screening in other high‑arsenic regions. Moreover, understanding the molecular mechanisms behind natural arsenic tolerance could inform therapeutic approaches or engineered bioremediation strategies, extending the relevance of this Andean case far beyond its geographic borders.