This discovery challenges the idea that the plague required dense agricultural villages to become deadly.
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The oldest known traces of plague, around 5,500 years old, were discovered in hunter-gatherer burials in Siberia.
Found at one of four ancient burial sites, the discovery predates the earliest signs of the plague by hundreds of years. This also indicates that hunter-gatherers were threatened by plague epidemics several centuries before the invention of agriculture and sedentary villages, researchers report June 17 in Nature.
“We didn’t expect this result at all,” says archaeologist Ruairidh Macleod of the University of Oxford. “It was expected that these big epidemics wouldn’t really happen among prehistoric hunter-gatherers. [but only] with people living in high-density settlements.
Macleod and his colleagues had discovered an unusually high number of children’s graves at hunter-gatherer burial sites near Lake Baikal, but initially the reason was unclear. The team collected and analyzed DNA from the remains, hoping that family ties between those buried could help explain the mystery.
Their analysis of 46 people from four burial sites determined that at least 18 of them had been infected with the virus. Yersinia pestis — the bacteria that causes the plague — when they are dead. They had also been buried in mass graves alongside others, indicating that they had been buried in haste; and the burial sites had only been used once, suggesting that they had been killed by a deadly outbreak of the disease.
Until now, the oldest traces of plague came from only one grave in Latvia and of a mass grave at a Neolithic agricultural site in Swedenboth about 5,000 years ago. These findings support the hypothesis that plague became a virulent danger to human communities only after they began farming and living in confined spaces, leading to the spread of large numbers of rats and fleas that spread the disease.
Evidence from Lake Baikal indicates otherwise.
The most likely source was marmots, large burrowing rodents that lived alongside hunter-gatherers and are a natural reservoir of Y. pestis. Macleod notes that it is possible that the plague first infected another animal that people interacted with, such as a bird.
The Siberia strain had genes that made it deadly and virulent, the researchers found – a finding that had not been possible with previous findings. The analysis also suggests that the plague moved away from a less deadly relative at least 5,700 years ago, probably in Central Asia. It is the oldest and most original form of plague discovered so far – older than the Latvian strain, which appeared later as the disease spread.
Nicolás Rascovan, a molecular biologist at the Pasteur Institute in Paris who led research into ancient Y. pestis infection in Swedenstates that the discovery of Lake Baikal is “clear evidence of an epidemic in prehistoric times that argues against agricultural lifestyles being a major factor in the emergence of plague.”
He warns that it may be difficult to determine exactly which species or strain of bacteria caused the ancient outbreak. “There are still several thousand years left Y. pestis evolution and spread” that have been neglected, he said. “I believe there are still many surprises to come in the history of plague.”