What were the genetic effects of Europe's first farmers settling down and mixing with local hunter-gatherers? This is the question that a recent study done by the Francis Crick Institute, a biomedical research center in London, sought to answer.
The researchers found that diversity in genetic coding for immunity may have facilitated adaptation to farming lifestyles in prehistoric periods.
Arrival in Europe
The peer-reviewed study published in the scientific journal Current Biology looks at genome-wide DNA from 677 individuals, who belonged to the early Neolithic groups from Anatolia that spread and settled across Europe in the period from 10,000 to 5,000 years ago and became the first European farmers.
“When farming groups expanded from the Near East into Europe and mixed with local hunter-gatherers, the natural prediction would be that the farmers’ immunity genes would be best adapted to the farming lifestyle and thus selected for."
Potus Skoglund, research team member
Throughout the course of their research, they found support for the previous view that the transition to farming had increased natural selection and improved immunity against diseases - but discovered that diversity in genes associated with immunity may have been just as important.
After settling down in their new surroundings, the groups of Neolithic farmers inevitably began mixing with the local population, which until then was made up of groups of Mesolithic hunter-gatherers. By around 4,000 BCE, the farmers derived 20%–30% of their ancestry and genes from hunter-gatherers.
The new cultural and geographical surroundings along with higher population density and higher proximity to domesticated animals would increase the chance of sickness and disease, raising the question of what effects this new landscape had on the mixed genetics of the population.
“It was really exciting to see for the first time that immunity is important for the transition to farming in a prehistoric population. The later Neolithic people had far more farmer ancestry in general, so we expected to see the same at the MHC region, especially as many diseases have been linked to Neolithic periods," said Tom Davy, PhD student at the Francis Crick Institute.
"But we saw about 50:50 ancestry from Neolithic farmers and Mesolithic hunter-gatherers here, showing that natural selection favored genes from the hunter-gatherers already in Europe."
Evolution and preferential treatment
Looking at the major histocompatibility complex (MHC), a genetic region responsible for immune responses to diseases, the researchers found evidence of rapid evolution, as expected. But they found more Mesolithic hunter-gatherer ancestry than they originally would have thought, which means that genetic variants that were present in the local population were passed down preferentially.
“The shift to farming was an important transition all over the world, resulting in changing diets and exposure to infectious disease," Potus Skoglund, a member of the research team said.
“When farming groups expanded from the Near East into Europe and mixed with local hunter-gatherers, the natural prediction would be that the farmers’ immunity genes would be best adapted to the farming lifestyle and thus selected for."
Attempting to explain this phenomenon, the research team speculated that the local population may have already been adapted to bacteria and viruses that were present in Europe, or that it was simply advantageous to have many different forms of genes.
“At the moment we’re not quite sure why this happened, but a proposal is that the European hunter-gatherers had genetic variations which allowed them to fight Europe-specific diseases," Skoglund said. "Or picking up a variety of genes from both hunter-gatherers and farmers was beneficial because it resulted in lots of diversity at this major group of genes, allowing people to better fight off disease.”
He added: “This study revealed natural selection during the agricultural transition in one region of the world, Europe, but other regions are not well understood. Future ancient-DNA studies will also be able to address to what extent immunity was a key target also in other periods of environmental and lifestyle change during human evolution.”