n the Maya, whose ancestors lived in iodine-poor soils, the researchers found strong evidence of genetic changes in iodine metabolism. In parts of South Asia with unusually high magnesium levels, they identified two genes suggesting adaptation to prevent magnesium toxicity. The findings suggest that across continents and millennia, genes responded to the quiet but persistent tug of local geology.
A Mosaic of Human Diets
Before agriculture, people already depended on their environment for trace elements. But farming and settlement likely intensified the problem. Soil depletion, monoculture, and new diets amplified shortages and sometimes created surpluses. Over thousands of years, these pressures influenced which gene variants thrived.
“This paper is a first step in understanding which populations might be most at risk,” Rees said. “We hope with more studies, the findings can eventually help inform public health going forward.”
Why It Matters for the Present
Modern human populations are not starting from scratch. Each carries a legacy of past adaptations. As climate change and industrial farming continue to strip soils of nutrients, understanding these inherited vulnerabilities could help predict who is most at risk for deficiency-related disease.
Anthropologists and geneticists are now asking how deep this pattern runs. Did micronutrient pressure shape not just physical health but also cognition or reproductive patterns? Could mineral deficiencies explain aspects of migration, settlement, or even myths about sacred springs and salt? These are open questions, but the Rees team’s data lay a foundation.
ur knowledge of the genetic basis of their biology15,20,21,22,23,24,25,26,63,93,94,95,96,97,98,99,100,101,102,103,104: calcium, chloride, copper, iodine, iron, magnesium, manganese, molybdenum, phosphorus, potassium, selenium, sodium, and zinc. This includes all trace metals and macrominerals (Table S1), with the exception of fluoride and sulfur, which were omitted due to limited knowledge of their functionally associated genes in humans. For similar reasons, this study does not investigate the role of the 13 essential vitamins in human adaptation.
micronutrients may have been an important selective force driving genetic adaptation in modern humans.
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An excess of iodine, not sodium chloride, is linked to an increased risk of thyroid tumors. Sodium chloride is common table salt, but iodine is only present in fortified versions called iodized salt. A high intake of iodized salt can cause too much iodine, which may promote the development of thyroid cancer and nodules in susceptible individuals
molybdenum show an excess of Relate and FST significant SNPs in many populations (Figure 2), but this appears to be driven by the high number of significant SNPs in two genes, GPHN and MOCS2, in this very small gene set (n = 5). The SNPs in these two genes have high allele frequencies in Yoruba (
these, only the SUMSTAT values of phosphorus in the American Pima population and selenium in the East Asian Xibo-Mongolian population fall in the 1% tail of the background distribution (Table 1).
High rates of goiter, a swelling of the thyroid gland caused by extreme iodine deficiency, is common among contemporary populations across Central America,113,114 indicating iodine deficiency as a pervasive environmental pressure in this region (albeit perhaps exacerbated by socioeconomic inequalities). Given that contemporary populations in this locality likely have substantial recent European and African ancestry, this is not an evaluation of the response to iodine deficiency in the Maya, and it remains possible that this population has evolved genetic adaptations to mediate the risks of dietary iodine deficiency.Interestingly, four iodine-associated candidate genes in the Maya are also candidates in the Mbuti population of Central Africa, three of which are part of the thyroid hormone pathway: THRA (MIM: 190120), THRB (MIM: 190160), and TRIP4115 (the latter identified as a target of positive selection16). Rainforest environments, such as those where the Mbuti live, often have iodine-deficient soils,35,45,116 and it has been previously suggested that this may drive adaptations in local populations.16 Thyroid receptors also play an important role in regulating growth, development, and metabolism,25,117,118 and it is feasible that adaptations in these genes, driven by low dietary iodine, underlie the distinctive short stature of Maya and Mbuti (height < 160 cm113,119).
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