Research suggests that the enhanced immune system of the descendants of Stone Age farmers who settled in Europe was due to an unusually high percentage of immunity genes inherited from local hunter-gatherers. This finding indicates that the development of farming alone was not the sole reason for the increased pathogen resistance seen in early humans.
The commonly held belief was that ancient farmers had better immune systems than hunter-gatherers because of their living conditions, which were more densely populated and involved closer contact with animals, thus increasing exposure to pathogens. As farming populations grew and expanded, their immunity genes were thought to have been best adapted and inherited by their offspring.
However, the situation is more intricate than initially thought. According to Pontus Skoglund at the Francis Crick Institute in London, who conducted the research, early farming groups brought their lifestyle and technology to Europe, but the presence of hunter-gatherers in Europe meant that the two populations mixed, leading to the transfer of immunity genes.
Skoglund and his team analyzed the genomes of 677 ancient individuals from western Eurasia, dating back from about 12,000 to 5,000 years ago, in order to investigate further. The genomes were divided into three groups: early farmers who had migrated from the region now known as Turkey and the Balkans, European hunter-gatherers, and later individuals with mixed ancestry.
Skoglund notes that "fast forward a few millennia, and the remaining farming groups now have about 20 percent of their ancestry that can be traced back to hunter-gatherers." However, in the major histocompatibility complex (MHC) region of the genome, where many genes for adaptive immunity are located, the split was closer to 50:50, indicating that selection processes favored the hunter-gatherer genes in this area. The reason behind this selective advantage remains unclear, according to Skoglund.
According to Mark Thomas from University College London, who did not participate in the research, the simplest explanation for the higher share of immunity genes from hunter-gatherers in European farmers is that the former was better adapted to the pathogens in western Europe.
However, there is another possibility due to a unique evolutionary characteristic of groups that typically pass on a minority of their genes, such as hunter-gatherers. These groups can provide more genes for functions that require diversity, such as immunity, where the most successful offspring will be those that can withstand a range of diseases.
The major histocompatibility complex (MHC), which contains many genes for adaptive immunity, plays a crucial role in determining our ability to survive a specific infection. Therefore, it makes sense that we are highly diverse for MHC from an evolutionary standpoint, as this allows us to defend against a wider range of pathogens.
Journal reference: DOI: 10.1016/j.cub.2023.02.049