5,500 years ago, during the prehistoric era, the plague was already an unrelenting killer among humans. An international team of researchers analyzed DNA extracted from human remains in hunter-gatherer cemeteries near Lake Baikal in eastern Siberia and discovered early strains of the Yersinia pestis bacteria.
The results, published in the journal Nature, show that nearly 40% of the individuals studied showed evidence of infection. This even surpasses the rates detected at some medieval burial sites associated with bubonic plague.
These ancient strains proved to be highly lethal, even without the flea and rodent transmission mechanisms known in later times.
The scientists reconstructed bacterial genomes from genetic material preserved in ancient teeth. They combined this genetic information with archaeological data and radiocarbon dating to reconstruct what happened in those small communities.
Devastating family outbreaks
In the two largest cemeteries, an unusually high number of children and adolescents were found among the deceased. For decades, archaeologists struggled to explain this pattern. Now, the presence of plague DNA solves the mystery.
The datings indicate that many burials occurred within a short period of time. In several cases, siblings or parents and children died almost simultaneously and were buried together, suggesting rapid outbreaks within families.
"Finding that the plague was the cause is extraordinary, but it makes a lot of sense," said archaeologist Andrzej Weber, principal investigator of the Baikal Archaeological Project.
The outbreaks particularly affected the youngest, leaving a devastating impact on these groups of hunter-gatherers who lived in close contact with nature.
A unique genetic factor
The researchers identified a distinctive superantigen in the ancient strains, a genetic factor that produces toxins and is not found in later historical variants. This element can trigger very strong immune reactions, increasing the severity of the infection.
Eske Willerslev, a professor at the University of Copenhagen and Cambridge, explained that this demonstrates that early forms of the plague were already highly virulent. This changes the traditional understanding of the origins and lethality of the disease.
It was previously thought that the initial strains were milder because they lacked certain genetic features for efficient transmission by fleas. The new findings indicate the opposite: the plague could be just as deadly in its early stages.
The hunter-gatherers in the area had frequent contact with marmots, large rodents that still carry the bacteria today. It is believed that transmission may have occurred directly from these animals to humans.
Implications for the origin of the plague
The study reinforces the idea that the plague emerged in Central or Northeast Asia before spreading across Eurasia through populations of wild rodents. This places the origin much further back in time than was commonly imagined.
The results provide a clearer picture of how infectious diseases impacted human societies even in very early stages, without the need for large urban concentrations or intensive agriculture.
This work not only solves a long-standing archaeological mystery but also enriches the understanding of the evolution of pathogens and their interaction with humans over millennia.
The research combines advanced genetics, archaeology, and precise dating, demonstrating the power of interdisciplinary techniques to reconstruct prehistoric events. Ancient outbreaks of plague were as lethal as later ones, particularly for the children and youth of those Siberian communities.
