How human cultures have adapted to environmentally high levels of arsenic in drinking water

Darwin said it all, back in the mid-19th century. “As organisms live for many generations –– in the same environment with its various adversities, –– ‘survival of the fittest’ will occur.”  In other words, DNA sequence mutations or epigenetic effects will “spontaneously happen” that change the genome to produce offspring having better survival, fertility, ability to find food, fertility, and survival to reproductive age.

Arsenic is well known from animal studies (also from epidemiological studies of human populations) to have serious genotoxic and carcinogenic effects –– as well as ths capacity to increase child mortality rates. Quebrada Camarones, in the Atacama Desert (northern Chile and southern Peru), has the highest arsenic levels in the drinking water in the Americas (>1,000 mg/L). However, the Camarones people have subsisted in this adverse environment during the last 7,000 years and have not presented any epidemiological emergencies.

The AS3MT gene encodes arsenite methyltransferase, an enzyme that detoxifies arsenic and enhance excretion of the detoxified product. In the attached article, authors therefore compared the frequencies of four protective nucleotide variants of the AS3MT gene between populations of Camarones (N = 50) and (as controls) two other populations (N = 47; N = 45) historically exposed to lower levels of arsenic.

The nucleotide sequence of these four protective variants showed higher frequencies in the Camarones than in the other two populations: 68% compared with the Azapa (48%) and the San Juan de la Costa (8%). Statistical tests included χ2 analysis to evaluate the Hardy-Weinberg equilibrium, Fisher’s exact test to estimate significance of allelic differences for the three population samples, and the population differentiation index (Fst) of haplotype estimated frequencies calculated from the Expectation-Maximization algorithm (log EM).

Hence, although statistics of such small cohorts cannot be particularly robust (P <0.05) –– this study is consistent with Darwin’s conclusions of “survival of the fittest” from his 1859 book.

Am J Phys Anthropol  2o17; 1–8

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