Modern humans first evolved sometime around 200,000 years ago in the grasslands of East Africa. But evolution is not a static process and continues to occur in the background even in recent times. It now seems likely that people living in the harsh environment of the Atacama Desert may have even evolved to be able to drink water laced with arsenic within the last few thousand years.
The Atacama Desert, sandwiched between the Pacific on one side and the Andes the other, is one of the driest environments on Earth. In fact, it is so arid that some parts of the landscape have never received rain in recorded history. Water is obviously hard to come by, and those sources that do exist are contaminated with massive levels of arsenic.
And yet, for some reason, humans settled this region some 7,000 years ago.
The levels of arsenic in some wells are almost 100 times greater than the safe limit set by the World Health Organization, and are thought to cause health problems among people who drink from such sources. However, the survival of people living in the region could be down to the natural selection of those who possess a genetic mutation that allows their body to break arsenic down into a less toxic compound, as reported in the American Journal of Physical Anthropology.
The genetic mutation revolves around a gene known as AS3MT, which codes for an enzyme that is used by the body to take toxins and incorporate them into two compounds, one of which is easily expelled by the body in urine. It turns out that there is a genetic mutation in this gene that pushes the body towards making more of the compound that can be peed out, efficiently detoxifying the body of arsenic as it does so. And it is this mutation that is more prevalent in those groups of people who consume the contaminated water.
While this is not the first time that scientists have looked into how the high levels of arsenic present in the region have seemingly shaped the evolution of those who settled there and called it home, this latest study compared those living in areas with high concentrations of the element in the drinking water to those with lower levels. They found that two populations living far apart, both of which consume contaminated water, had an increased prevalence of the mutation responsible for conferring protection, compared to another population whose water is clean.
The researcher discovered that 68 percent of those from a region called Camarones had the genetic variance, and 48 percent of people from Azapa, while only 8 percent of people from San Juan de la Costa had the genetic tweak. This heavily suggests that there has been a fair amount of selection pressure on those who have been drinking the arsenic-laden water, driving their evolution.
[H/T New Scientist]