The DNA of our ancestors has spoken again, recounting ten thousand years of evolution of our immune system. Where it appears that the yoke of microbes, especially since the Bronze Age, has shaped the genes that govern our immune defenses. Viruses and bacteria have thus been one of the most powerful engines of evolution.
It was a team from the Institut Pasteur, in Paris, who made this fossil DNA speak. His results were published on January 13 in the journal Cell Genomics. “ Our goal was to identify advantageous mutations, those whose frequency has increased as a result of natural selection. But also deleterious mutations, the frequency of which has dropped,” explains Lluis Quintana-Murci, professor at the College de France and the Institut Pasteur (CNRS, Paris Cité University), who coordinated this new study.
The authors examined the variability of the genomes of more than 2,800 individuals who had lived across present-day Europe for ten thousand years, during the Neolithic, the Bronze and Iron Ages, the Middle Ages and the current period. These genomes came from the database of David Reich, paleogenomics specialist at Harvard University (United States). In total, the Parisian team followed the evolution of 1.3 million DNA mutations or “variants”.
“This phenomenon is quite recent”
The authors first identified 89 genes whose beneficial mutations spread over time. Most of these genes are involved in our first lines of immune defense (the so-called “ innate”), such as the OAS genes (with antiviral functions) or those of the ABO blood group system (the frequency of groups A and B has increased over time).
The researchers also found other genes known to have been under positive selection in Europe, such as the lactase gene (which allows the digestion of lactose) or one of the genes associated with light skin pigmentation (which maximizes production of vitamin D by the body, in the event of low sunlight).
The second result is a surprise: most of the advantageous mutations, for fighting viruses and bacteria, appeared in the Bronze Age, around four thousand five hundred years ago, and then spread rapidly across Europe.
“ The great value of this study is to have established the chronology of the selection of immunity genesbelieves Simon Fillatreau, professor of immunology at the Necker-Enfants Malades Institute (AP-HP, Inserm, CNRS, Paris Cité University). And to have thus shown that this phenomenon is quite recent. »
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