The bacterium Yersinia pestis has caused devastating plagues throughout human history, including the Plague of Justinian, the Black Death, and the Third Plague. For a long time, the prevailing theory was that the development of agriculture, while providing a stable food source, also facilitated the spread of plague by attracting pests that carried the bacteria. Archaeologists believed that nomadic hunter-gatherer societies, with their smaller groups and constant movement, were less susceptible to widespread outbreaks.
However, new research published in Nature challenges this long-held idea. A study of prehistoric hunter-gatherers in Siberia has revealed evidence of plague outbreaks occurring approximately 5,500 years ago, predating the Justinian Plague by thousands of years and making it the earliest known outbreak in the archaeological record. Lead author Ruairidh Macleod, a postdoctoral research fellow at the University of Oxford, stated that the discovery in an isolated hunter-gatherer group is remarkable and fundamentally alters epidemiological understanding. This finding is particularly significant as these groups had no contact with agricultural or pastoral communities.
Unraveling the Mystery of Child Deaths
The region around Lake Baikal in Siberia is rich in archaeological finds, with numerous cemeteries dating back to the late Mesolithic and early Bronze Age. One particular burial site has puzzled researchers for decades due to a disproportionately high number of graves belonging to children and adolescents. Skeletal analysis at Ust’-Ida indicated that these young individuals did not die from violence and perished within a short timeframe.
Recent DNA analysis of teeth from individuals at Ust’-Ida and other nearby cemeteries has provided a groundbreaking explanation: plague. DNA testing revealed that Yersinia pestis was present in the remains of 18 out of 46 children and adolescents, strongly suggesting that the disease was the cause of their deaths. Macleod collected samples from the teeth, a part of the body where DNA can be preserved, and found a significant prevalence of the plague bacterium. This rate is notably higher than that found in the East Smithfield plague pit in London, an emergency burial site from the 14th-century Black Death.
Two Outbreaks, Centuries Apart
The earliest plague outbreak identified near Lake Baikal occurred between 5,520 and 5,265 years ago, affecting individuals buried at Ust’-Ida and the nearby Shumilkha site. While these cemeteries belonged to distinct family groups, radiocarbon dating and genomic analysis showed similar patterns, indicating a single widespread outbreak. Macleod suggests that these groups, while separate, likely interacted due to their nomadic lifestyles.
Further analysis of specimens from cemeteries at Bratskii Kamen and Serovo, further up the Angara River, revealed evidence of a second plague outbreak approximately 300 years after the first. Although radiocarbon dating varied at these sites, the presence of Yersinia pestis in some of the child and adolescent burials pointed to a subsequent epidemic. For instance, one grave contained three young girls, believed to be sisters and their cousin, all of whom tested positive for the plague bacterium.
Researchers theorize that children were particularly vulnerable due to prehistoric strains of the plague carrying a superantigenic toxin absent in later versions. This toxin could have triggered an extreme immune response, potentially similar to Kawasaki syndrome, which is more commonly seen in young children. The discovery of multiple siblings dying simultaneously and buried together underscores the devastating impact of these outbreaks.
Marmots as the Likely Source
Marmots, large ground squirrels that were hunted by Siberian hunter-gatherers, are believed to have been the reservoir for Yersinia pestis. The researchers suspect that zoonotic transmission from marmots initiated both outbreaks, which then spread among human populations.
These findings also refute the theory that prehistoric plague strains were less lethal than those that appeared later in history. The evidence from Lake Baikal demonstrates that Yersinia pestis was highly virulent and contagious even in ancient times. The idea that hunter-gatherer lifestyles offered immunity from plague is now disproven, especially considering how infectious diseases can decimate animal populations. The universal threat of infectious disease, impacting humans and animals throughout history, including ancient hominins like Neanderthals, is a constant in the human story.