Tiny elements in the human diet, such as micronutrients, may have influenced human evolution in ways greater than previously recognised, according to a new study led by UCL researchers.
In the American Journal of Human Genetics, the scientists describe how human ancestors around the world developed various genetic adaptations in response to shortages and surpluses of minerals in their diets based on where they lived.
First author Dr Jasmin Rees, who led this study during her PhD at UCL before moving to the University of Pennsylvania, said: "This is the first study that looks at micronutrient-driven adaptation on a global scale and across this many micronutrients. Different human populations live in different environments, so they had to adapt to different kinds of environmental pressures, like disease and diet, that over time can drive trait differences."
Micronutrients play an important role in metabolism, development, immune system and other tissue functions in humans. But their availability in the diet depends on their content in the soil, so it varies widely across environments. Before dietary supplements were available, many populations lived with too little, and occasionally too much, of key dietary nutrients. For example, some populations living in African rainforests can develop goitre, a swelling in the neck from an enlarged thyroid, because the soil there is low in iodine.
When deficiencies are severe and long-lasting, they can act as selective pressure on human genes, say the academics. Prior studies have suggested that natural selection has acted on genes associated with selenium regulation in certain East Asian populations living on selenium-poor soils, possibly to increase selenium absorption in these populations. But it remained unclear if micronutrients as a whole had broadly influenced human evolution.
To investigate, Dr Rees, while jointly based at the UCL Genetics Institute and the UCL Great Ormond Street Institute of Child Health, and colleagues focused on 276 genes associated with how our bodies absorb, transport or use 13 essential minerals, including iron, calcium, zinc and selenium. They studied the evolution for these genes using the genetic data of more than 900 individuals from 40 different populations worldwide.
For every mineral studied, they found evidence for adaptation in the genes of at least one population, and the impact of these micronutrients was evident across the globe. This suggests that each of these micronutrients likely influenced human evolution at some point in history and in some population.
Among the 13 minerals analysed, some stood out. In Central America, the Maya who live in regions with iodine-poor soils show strong evidence of genetic changes in genes indicated in iodine regulation or metabolism, which could reflect adaptation to low levels of iodine in the diet. Similarly, the researchers found that the Mbuti population of central Africa, another population noted for their short stature and living in environments with iodine-poor soils, also bear signs of genetic adaptation in some of the same iodine-dependent thyroid receptors. Given that, in this same region, another short-statured population has previously been shown to have lower rates of goitre than their taller neighbours, the researchers speculate that shorter stature may be linked to an evolutionary adaptation to the risks of low iodine.
In some parts of South Asia, where the soil is very high in magnesium, the team found evidence for adaptation in two genes likely related to the level of magnesium uptake in the local populations, in a change that the authors speculate might have protected people from magnesium poisoning.
Understanding how pressure from micronutrient availability shaped human genes can help establish which populations may be most vulnerable to deficiencies as climate change and intense farming continue to deplete nutrients in soils, the researchers say.
For example, the NHS recommends that people with darker skin colour in the UK to take vitamin D supplements. This is because darker skin synthesises less vitamin D from the sun, and Britain gets little year-round sunshine.
Dr Rees said: "This paper is very much a first step in understanding which populations might be most at risk, focusing on understanding their evolutionary history rather than their vulnerabilities. We hope with more studies, the findings can eventually help inform public health going forward."
Senior author Professor Aida Andrés (UCL Genetics Institute) added: "Our findings demonstrate the importance of studying past genetic adaptations to understand human diversity and health, and could help to explain why people from certain groups may be more prone than others to certain micronutrient deficiencies."
The study was supported by the NIHR Great Ormond Street Hospital Biomedical Research Centre and Wellcome.
