Ancient DNA provides evidence of earliest known plague outbreak | Archaeology
Ancient DNA from Stone Age cemeteries in south-eastern Siberia reveals the earliest known plague outbreaks, according to researchers writing in Nature. The disease hit hunter-gatherer communities near Lake Baikal about 5,500 years ago, likely spreading from marmots to humans and decimating families, particularly young children.
An international team of researchers from Copenhagen, Alberta, Cambridge, and London analyzed dental pulp from 42 skeletons found at four cemeteries along the Angara River. They found Yersinia pestis DNA in 18 of the remains, a 39% positivity rate that exceeds some medieval plague pits.
The researchers suspect all those buried may have died from the plague, noting a high probability of false negatives due to degraded DNA. The evidence points to two distinct outbreaks: one starting 5,500 years ago and another 400 to 600 years later.
How did prehistoric hunter-gatherers contract the plague?
The hunter-gatherers likely became infected while butchering or eating raw marmots, which are the primary animal reservoir in the region. This practice remains a risk for plague deaths today.
Once the disease spilled over from the ground squirrels, it likely spread from person to person. Researchers believe the population most likely contracted pneumonic plague, a form of the disease that affects the lungs.
Ruairidh Macleod, a research fellow at the University of Oxford, noted that prehistoric hunter-gatherers had more contact with wild species than early farmers did. He stated that wild species, not domesticated animals, are the primary reservoirs of the disease.
Why were children more vulnerable to the ancient outbreak?
At the Ust-Ida cemetery on the bank of the Angara River, the shared graves predominantly contained the remains of children. In two of the studied cemeteries, at least two-thirds of the deceased were under 15 years old.
Researchers found that the Y. pestis strain carried a superantigen, a toxic protein that can trigger severe immune reactions. This likely made the disease particularly lethal for children, while older adults may have gained immunity from previous exposure.
Macleod described the discovery of plague in prehistoric hunter-gatherers as “extraordinary” and “super exciting,” as the team did not expect to find the disease in this specific population.
What does this discovery reveal about the history of Yersinia pestis?
The analysis shows that Y. pestis emerged at least 5,700 years ago. It evolved after splitting from an ancestor called Yersinia pseudotuberculosis, a bacterium known to cause vomiting, fever, diarrhoea, and abdominal pain.
Samuel Cohn, a professor of medieval history at the University of Glasgow, called the conclusions “groundbreaking.” He noted that identifying outbreaks in hunter-gatherers contrasts with the common belief that such diseases primarily affected agricultural settlements.
Cohn pointed out that isolated communities continued to suffer in later outbreaks, citing examples of mountainous villages in Tuscany and Snowdonia that were hit during the Black Death.
Future analysis of ancient remains could potentially reveal more about how the bacterium’s virulence evolved before it triggered the 14th-century pandemic that killed half of Europe’s population.
Frequently Asked Questions
What was the primary cause of the plague spillover in Siberia?
The infection likely began when hunter-gatherers butchered or ate raw marmots, which served as the primary animal reservoir for the bacterium.
How does the Siberian find compare to other ancient plague sites?
The Y. pestis DNA was found in 39% of the tested skeletons, which researchers say is a higher proportion than what is seen in some medieval plague pits.
What are the different forms of plague caused by Y. pestis?
The bacterium causes pneumonic plague (lungs), septicemic plague (blood infection), and bubonic plague (swollen lymph nodes or buboes).
How does this change your perspective on the origins of global pandemics?