A population of shepherds who arrived in northern Europe 5,000 years ago introduced a genetic variant that protected them against livestock infections but increased the risk of multiple sclerosis. This explains why northern Europe is the region in the world with the highest prevalence of the disease, a phenomenon that until now had no explanation, according to an international research project that has reconstructed the genetic history of European populations since the Mesolithic.
The research, presented today in the journal Nature, reveals how the transition from hunter-gatherer societies towards agriculture and pastoralism modified the genome of the ancient inhabitants of Europe in a way that affects the risk of diseases of their current descendants. as well as personality traits and physical characteristics.
The difference in average height between people from northern and southern Europe, for example, is not because northern people have evolved to be taller by natural selection. It is explained because the same shepherds who introduced the genetic variant of multiple sclerosis, who came from the Pontic steppe, between the Black Sea and the Caspian Sea, also introduced variants related to altitude.
Other genetic variants related to the propensity for irritability, anxiety and feelings of guilt come from Neolithic agricultural communities that already lived in Eurasia before the arrival of the shepherds from the Pontic steppe. This would explain why people who have more genetic heritage from these agricultural communities may have a greater risk of certain psychiatric disorders.
The hunter-gatherers who populated Eurasia before agriculture was introduced, and who have also left their genetic imprint on current populations, have left behind an important genetic variant related to an increased risk of Alzheimer’s – the so-called ApoE4 allele of apolipoprotein E. -. This allele is more common in northeastern Europe, where there is greater genetic inheritance from ancient hunter-gatherers, than in Mediterranean countries.
These discoveries are the result of a scientific project in which 1,664 genomes obtained from bones and teeth of ancient inhabitants of Eurasia have been analyzed. The project, which began five years ago, has been led by Eske Willerslev, a specialist in ancient DNA at the universities of Copenhagen and Cambridge.
Other findings are related to the adaptation to a diet with more vegetables and less meat after the introduction of agriculture, which has left its mark on a group of genes related to fat metabolism. Or with greater protection against sexually transmitted diseases at the cost of a greater risk of psoriasis, which is an autoimmune disease like multiple sclerosis.
“What we see is that there has been a constant genetic selection according to the pathogens that populations have encountered throughout human history,” Astrid Iversen, a neuroscientist at the University of Oxford and co-author of the research, explained in a press conference yesterday.
This has caused, according to Iversen, that “now our immune system is a little unbalanced” and that “in some people it is activated excessively.” According to this interpretation, immune responses that in the past protected humanity from infections are now responsible for autoimmune diseases, which occur when the immune system attacks the body itself after being activated in response to a virus or some other stimulus. In the case of multiple sclerosis, in which the immune system attacks the myelin of neurons, it is an infection with the Epstein-Barr virus that usually triggers the disease.
The high prevalence of multiple sclerosis in northern Europe is explained by a genetic variant of chromosome 6 introduced by the shepherds of the Yamna culture. These shepherds lived with their herds of cattle, so their immune system adapted to avoid infections of animal origin.
Researchers have shown, from the analysis of ancient genomes, which agree with archaeological evidence, that the Yamna culture expanded 5,000 years ago from the Pontic steppe to northern Europe. In Denmark, to which a specific part of the project has been dedicated, the Yamna culture completely replaced the previous settlers, so there is no genetic trace of hunter-gatherers or Neolithic farmers in the native population.
“If you want to treat a disease, you have to understand what you’re dealing with,” Eske Willerslev declared at the press conference. The project director explained that his two main objectives have been to understand the history of populations and the history of human diseases.