Selection could well be ongoing within the mountain communities that we studied because they still have high levels of arsenic in their drinking water. In turn, I would not expect to find such strong genetic selection amongst communities with access to good healthcare systems.
Professor Karin Broberg
A study has revealed that Argentinean villagers living in the Andes have developed genetic protection against the high levels of arsenic that are present in their water. Scientists from Lund University
and Uppsala University
in Sweden discovered that a high proportion of these villagers were able to metabolise arsenic unusually efficiently.
Their findings show evolution’s continuing relevance for modern humanity. The researchers compared Atacameño Indian villagers in San Antonio de los Cobres, who have lived in the mountains for generations, with other indigenous groups from South and Central America. A gene variant that enables the more efficient metabolism of arsenic was found to be much more prevalent amongst the villagers than it was in the other groups.
To find out more about the implications of these findings, I spoke to co-author of the study Professor Karin Broberg from Lund University’s Faculty of Medicine. I began by asking Professor Broberg how drinking water containing high levels of arsenic might affect somebody without this particular gene variant.
"Arsenic in drinking water is a known carcinogen," she replied. "It is also a potent toxicant that is associated with cardiovascular disease, diabetes and liver problems. I should state that the gene variant we identified is not completely protective. The health of those who have developed this protection can still be adversely affected. These people are simply able to more effectively metabolise the arsenic in their water.
"We have published two papers concerning pre-malignant changes in these communities," Professor Broberg continued. "We found that in most cases, people who did not carry the genetic variant – those who were less capable of metabolising arsenic – exhibited more DNA damage than those who did. Whilst certain types of DNA damage are associated with cancer, the participants that we tested did not have cancer. We have not been able to conduct any research into whether individuals with the variant are at lower risk of cancer because this would require a much larger group of participants. Even so, we did collect anecdotal evidence from physicians, who told us that cancer is rarer amongst the villagers than it is amongst populations living in the jungle area. Spanish descent is more common amongst these communities and they do not tend to possess the protective variant that is prevalent amongst the mountain villagers. Again, this is anecdotal; we have not conducted a truly scientific study into cancer prevalence."
The villagers’ development of this genetic variant is a tangible example of evolution’s relevance to modern humanity. Humans have lived in these mountains for thousands of years and the findings suggest that those most capable of metabolising arsenic have thrived. As Professor Broberg explained, adaptation is context sensitive.
"Selection could well be ongoing within the mountain communities that we studied because they still have high levels of arsenic in their drinking water," she said. "In turn, I would not expect to find such strong genetic selection amongst communities with access to good healthcare systems."
The residents of San Antonio de los Cobres have had millennia to develop genetic protection to arsenic. In many places, however, the presence of this chemical element represents a comparatively new problem. Arsenic contamination of certain water supplies in Bangladesh, for example, has been linked to the drilling of new wells, and communities within these areas have not had sufficient time to develop genetic protection. I concluded our conversation by asking Professor Broberg whether her findings might be used to help such individuals.
"A comprehensive understanding of genetic history is important if we wish to learn more about arsenic susceptibility," she replied. "Knowledge of a community’s genetic background can help scientists to more accurately estimate the risk that arsenic poses to its people. First and foremost, however, we need to curtail the exposure of these communities to arsenic. This is the most effective way to help their inhabitants."