Scientists have uncovered what is believed to be the oldest known evidence of a plague outbreak, a discovery that is reshaping understanding of one of humanity’s deadliest diseases and challenging long-held beliefs about its origins.
The groundbreaking findings, published in the journal Nature, emerged from the analysis of prehistoric graves in Siberia dating back approximately 5,500 years. Researchers discovered DNA from the plague-causing bacterium, Yersinia pestis, in nearly 40 percent of the skeletons examined, providing the earliest direct evidence of a plague outbreak affecting human communities.
The burial sites, located along the Angara River near Lake Baikal in modern-day Siberia, contained the remains of multiple generations of hunter-gatherers. Genetic testing conducted on teeth recovered from the graves revealed traces of the deadly bacterium in numerous individuals, including several children buried together.
According to lead researcher Ruairidh Macleod, one of the most striking discoveries involved groups of young children who appeared to have died around the same time.
“We see three very young girls, all buried at the same time, having presumably died at the same time,” Macleod said. “It’s clearly having a very tragic impact on the children in particular in these communities.”
Researchers believe the evidence points to at least two separate plague outbreaks among prehistoric hunter-gatherer populations. The findings challenge the long-standing theory that plague and other major epidemic diseases primarily emerged after humans adopted agriculture and began living in larger, denser settlements alongside domesticated animals.
Instead, the study suggests that plague was already circulating among hunter-gatherer groups thousands of years before the rise of large farming societies.
Ancient DNA expert Nicolás Rascovan, who was not involved in the study, said the discovery provides compelling evidence that significant outbreaks occurred in prehistoric communities and weakens the argument that agricultural lifestyles were the primary trigger for the emergence of plague.
Researchers believe the ancient disease likely spread among family members and close-knit groups living near wild animals carrying the bacterium. DNA analysis revealed biological relationships among some of the victims, including siblings and half-siblings buried together.
The strain identified in the graves belonged to the same species responsible for later catastrophic pandemics, including the Black Death that devastated Europe beginning in 1347. However, scientists say the prehistoric version of the bacterium had not yet evolved key traits that made later outbreaks so destructive.
Unlike later forms of plague that spread through infected fleas and caused bubonic plague, the ancient strain likely caused pneumonic plague, a severe respiratory infection transmitted through coughing and close human contact.
“It’s spread by coughing. It’s an infection of the lungs, but it’s extremely severe, and it’s extremely deadly,” Macleod explained.
The research was based on skeletal remains excavated by Russian archaeologists during the 1980s and preserved for future study. Several graves contained multiple individuals buried simultaneously, leading researchers to conclude that entire family groups may have succumbed during outbreaks.
Contributing researcher Eske Willerslev said the findings overturn romanticized assumptions that prehistoric hunter-gatherer life was largely free from infectious disease.
“Now we can see, well, it wasn’t that easy to be a hunter-gatherer either,” Willerslev said. “You got hit by plague again and again.”
While plague remains rare today, cases still occur in some parts of the world. Modern medicine can effectively treat the disease with antibiotics when detected early. However, the discovery highlights that humanity’s battle with plague stretches back thousands of years further than previously documented.