Plague in Siberia upends timeline of outbreaks

Ancient DNA from hunter-gatherer burials near Lake Baikal shows that Yersinia pestis struck at least 18 people around 5,500 years ago—hundreds of years earlier than the previous oldest evidence. The findings suggest lethal plague outbreaks were possible long b

The first hint came from something that looked, at the time, like a separate mystery: unusually large numbers of children’s graves at hunter-gatherer burial sites near Lake Baikal.

Archaeologist Ruairidh Macleod of the University of Oxford and colleagues weren’t sure what they were seeing. The team gathered and analyzed DNA from the remains, hoping that family relationships between the buried individuals might explain why so many children were there.

But the results turned that expectation on its head. The researchers reported June 17 in Nature that their analysis of 46 people from four burial sites determined that at least 18 had been infected with Yersinia pestis—the bacterium that causes plague—when they died. The evidence also pointed to sudden. brutal circumstances: the individuals were buried in mass graves alongside others. suggesting they were put to rest in a hurry. and the burial sites had been used only once. consistent with deaths from a fatal outbreak.

Until now. the oldest-known traces of plague had been linked to two finds roughly 5. 000 years old: a single grave in Latvia and a mass grave at a settled Neolithic farming site in Sweden. Those earlier cases aligned with a widely held hypothesis. Plague. the thinking went. became a more virulent danger only after farming expanded and people lived in close quarters—conditions that could boost the rat and flea networks that spread the disease.

Lake Baikal doesn’t fit neatly into that story.

The traces found in Siberia date to around 5,500 years ago, and they predate the previously oldest signs of plague by several hundred years. In other words: the outbreak appears to have struck hunter-gatherers centuries before the farming-and-settlement era could plausibly explain everything.

If plague was traveling through animals rather than humans clustering in villages, the landscape near the graves still offers clues. The researchers say the most likely source was marmots. large burrowing rodents that lived alongside the hunter-gatherers and act as a natural reservoir of Y. pestis. Macleod also said it’s possible the plague may have first infected another animal the people interacted with. such as a bird.

The genetic details added another jolt to the timeline. The team found that the Siberia strain had genes that made it deadly and virulent—a feature that researchers say hadn’t been possible to identify with earlier plague finds. Their analysis also suggests that plague diverged from a less lethal relative at least 5,700 years ago, probably in Central Asia. That oldest. most original form of plague identified so far would be older than the strain from Latvia. which emerged later as the disease spread.

Nicolás Rascovan, a molecular biologist at Institut Pasteur in Paris who led the research into the ancient Y. pestis infection in Sweden. called the Lake Baikal discovery “clear evidence of an outbreak in prehistoric times that argues against agricultural lifestyles as a major driver of plague emergence.”.

At the same time, the scientists caution against overconfidence in pinning down the exact chain of events. Rascovan warned that it can be difficult to determine precisely which species or strain of bacteria caused a specific ancient outbreak because “there are still several thousands of years of Y. pestis evolution and spread” that have been overlooked. He said, “I believe there are still many surprises to come in the history of the plague.”.

The emotional punch of the discovery is hard to miss. Evidence of a lethal disease is now placed firmly in a world that did not rely on fields and crowded settlements. The graves near Lake Baikal show a one-time. high-fatality event—one that struck hard enough to leave behind mass burials and enough children’s graves to catch the team’s attention in the first place.

And if plague was already capable of deadly outbreaks among prehistoric hunter-gatherers, then the familiar timeline for how and when Y. pestis became dangerous to humans just got longer—and more complicated.

plague Yersinia pestis ancient DNA hunter-gatherers Siberia Lake Baikal marmots Nature archaeology