Genetics traces 10,000 years of evolution of our immunity

A recently published study traces the evolution of genetic mutations over the past 10,000 years, from the Neolithic period, when hunter-gatherers abandoned their nomadic lifestyle to develop farming and animal husbandry.

Scientists analyzed the ancient DNA of 2,300 Europeans, found during various archaeological excavations and already stored in the database. They combined these samples with 500 modern genomes and developed a method to detect and date genetic variations that have evolved over time. An approach based on paleogenomics, the discipline that won the 2022 Nobel Prize in Medicine for the Swedish biologist Svante Paabo.

Of the hundreds of thousands of mutations retrieved, they found some that are “useful in fighting infections.” These mutations are located in 89 genes, explains Luis Quintana-Mursi, leader of the study, published in the journal Cells Genomics. To their “great surprise,” the scientists found an increased frequency of these 89 genes involved in our immune response against pathogens, adds this professor at the Pasteur Institute and the College de France.

Both the OAS genes that act on antiviral functions and the genes responsible for the ABO blood types, the Pasteur Institute clarifies in a press release.

Yamna peoples

These mutations beneficial to our survival have been amplified over the centuries by “positive” selection for human adaptation to the environment.

The second discovery: “We were able to date from the moment when they became profitable, namely from the last 4500 years, from the Bronze Age,” Professor Quintana-Murchi says enthusiastically.

A date coinciding with “the arrival of the great migration from the steppes of Central Asia of the peoples of the Yamnaya culture, who were to bring the Indo-European languages ​​and from which today all Europeans bear genetic traces,” says it. population geneticist.

This migration led to a significant increase in the population of Europe and created fertile ground for the spread of disease-causing microbes.

The study rules out new pathogens brought by the Yamna peoples. Proof ? “Genetic mutations were already there before this migration, they were “sticking out”, but they were neutral, because there were not so many diseases. It was with the growth of the population that they became beneficial for fighting infections, ”the author explains.

The price to be paid

But there was a price to pay for this. As our defenses against infectious diseases increased, those same mutations made us “increasingly vulnerable” to autoimmune diseases such as Crohn’s disease, lupus or rheumatoid arthritis, as well as inflammatory diseases.

Pathologies that kill much less than infectious diseases, which would explain the adaptation of our immunity to the most serious danger.

“We knew that our system had become less resistant to autoimmune and inflammatory diseases, but we did not know that this dates back to the beginning of the Bronze Age,” says Professor Quintana-Murchi.

This refutes the hygienic hypothesis that it was the advent of vaccines and antibiotics in the 20th century that contributed to the development of autoimmune and inflammatory diseases in exchange for a decrease in the prevalence of infectious diseases.

Due to the lack of sufficient samples on continents other than Europe, the authors of the study could not know if this evolution was the same all over the world.

But their discovery could open up opportunities for medical research by developing treatments that target specific genes.

Juliet COLLEN/AFP