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

For thousands of years, people living high in the Argentine Andes were dependent on drinking water that would make most people deathly ill.

There, naturally occurring arsenic in volcanic bedrock leaches into groundwater, contaminating the local water supply at high levels. toxic metalloid this would pose serious health risks to most human populations.

But for one group in northern Argentina, natural selection may have provided an unusual genetic advantage.

A population in the Argentinian Andes carries a gene variant that likely helps them, according to DNA analysis of people in western South America. metabolize arsenic more trustworthy.

“Adaptation drives genomic changes, but evidence for specific adaptations in humans remains limited,” wrote a team led by evolutionary biologists Carina Schlebusch and Lucie Gattepaille of Uppsala University. In a 2015 article.

“Our data suggest that adaptation to tolerate the environmental stressor arsenic likely leads to an increase in the frequency of protective variants of AS3MT, providing the first evidence of human adaptation to a toxic chemical.”

Given enough time and mildly enough exposure to a hazard, life has shown a remarkable ability to adapt to all kinds of wild conditions, from extreme heat to cold weather. complete lack of oxygen to dangerous radiation levels

But relatively little is known about how human populations adapt to toxic chemicals in their environment. Arsenic is highly toxicassociated with cancerskin lesions, birth defects and premature death. It is also widespread and occurs naturally at high levels in the groundwater of many regions around the world.

The current recommended limit for arsenic in drinking water is World Health Organizationlike that 10 micrograms per liter.

much filtering system A remote, high-altitude town in 2012 San Antonio de los CobresArgentina’s Puna de Atacama plateau had drinking water containing approximately 200 micrograms of arsenic per liter; this was nearly 20 times the recommended limit.

However, the region has been inhabited for thousands of years. at least 7,000 yearsand perhaps as long as 11,000.

This apparent ability to shrug off dangerously high levels of arsenic has baffled scientists for decades. in 1995 scientists noted It turns out that women in the Argentinian Andes have a “unique” ability to metabolize arsenic, as evidenced by metabolites in their urine.

When arsenic enters the body, enzymes transform it. various chemical forms. One of these intermediate forms, called monomethylated arsenic (MMA), is particularly toxic. A later form, dimethylated arsenic (DMA), is easier to eliminate from the body in the urine.

People in San Antonio de los Cobres tended to produce less toxic intermediates and more easily excreted forms; This suggests that their bodies are unusually effective at processing arsenic.

Intrigued, Schlebusch, Gattepaille and their colleagues wanted to solve the puzzle at the genetic level.

Using cheek swabs, the team collected DNA from 124 women in San Antonio de los Cobres; The women’s urine samples showed the same arsenic metabolite profile as in the 1995 study. They then analyzed millions of genetic markers in the genome.

To determine whether the gene variant was specific to the Argentinian population, the researchers compared their results with publicly available genome data from Peru and Colombia from international sources. 1000 Genomes Project.

Previous research has shown that an enzyme called arsenic (+3 oxidation state) methyltransferase (AS3MT) may play an important role in arsenic metabolism; so that’s where the researchers focused their efforts.

What they found was a group of genetic variants close to the AS3MT gene that strongly affected how the body processes arsenic. These variants were much more common in people in San Antonio de los Cobres than in genetically similar populations in Peru and Colombia.

The variants appear to make the body more efficient at converting arsenic into forms that can be safely excreted in the urine, reducing the formation of the most toxic intermediate compounds; This result is in clear agreement with previous studies of arsenic metabolites in urine.

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Although arsenic contamination is widespread worldwide, few communities have lived with such high levels of arsenic exposure for long periods of time.

In San Antonio de los Cobres, people have been living with arsenic in groundwater for thousands of years; this is long enough for natural selection to favor traits that reduce susceptibility to the toxic effects of arsenic.

Later research suggests that similar genetic signals may occur in humans. other Andean populations Generations of arsenic exposure support findings that long-term exposure may increase genetic tolerance and suggest that adaptation may be more widespread across the region.

“Given the serious detrimental effects of arsenic on health in both children and adults” researchers wrote“Individuals carrying the arsenic tolerance haplotype…may have a very strong selective advantage in high-arsenic environments.”

The research was published on: Molecular Biology and Evolution.

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