Surprising discovery changes the picture of hunter-gatherers

New genetic evidence shows that devastating plague epidemics struck Siberian hunter-gatherer communities two centuries before the earliest known cases. The discovery contradicts the idea of a disease-free "golden age” and offers important clues about the origin of epidemics. The plague decimated hunter-gatherer communities in Siberia about 5,500 years ago, according to a study published in the journal Nature, which changes the perspective on the origin of one of the most devastating diseases in human history. The discovery was made around Lake Baikal, where archaeologists have been studying prehistoric cemeteries for decades. One of them caught their attention with an unusual mortality profile, characterized by a very large number of children and adolescents dying in a short period of time. "There were no signs of violence or trauma on the skeletons, and the causes of this catastrophe remained unknown,” explained Ruairidh Macleod, a paleogenomics researcher at the University of Oxford and one of the authors of the study.

• DNA from teeth revealed the presence of the plague bacteria

Scientists analyzed DNA preserved in the teeth of 46 individuals buried in four burial sites in the region and found that 18 of them were infected with Yersinia pestis, the bacteria responsible for the plague. The infection rate, of almost 40%, is remarkable and even exceeds the proportions observed in some mass graves during medieval epidemics. According to the researchers, almost all of the people buried in those cemeteries may have died as a result of two separate epidemic episodes, the oldest of which was dated to about 5,500 years ago. "It was a complete surprise,” confessed Macleod.

• Plague is older than previously thought

Until now, the oldest traces of the disease had been identified in farming communities in Northern Europe, dating back about 5,300 years. The new discovery pushes back the known origin of plague epidemics by two centuries and shows that the disease was not limited to sedentary societies. "The classical theory was that such epidemics should not have occurred in hunter-gatherers, who lived in small groups and were constantly moving," explained Danish paleogeneticist Eske Willerslev, a professor at the University of Copenhagen and the University of Cambridge.

• The myth of a disease-free "golden age" is being questioned

According to Willerslev, the idea that prehistoric people lived in a disease-free world has been popularized by authors such as Yuval Noah Harari and Jared Diamond. "In reality, the life of hunter-gatherers was not so idyllic. If plague occurred repeatedly, then it is likely that such epidemics were relatively frequent," the researcher said.

• Marmots would have been the first hosts of the disease

Unlike the medieval epidemics associated with rats, in prehistoric Siberia the main natural reservoir of the bacteria would have been the Siberian marmot (Marmota sibirica).

These rodents have a very ancient evolutionary relationship with the bacterium Yersinia pestis, and researchers believe that they are the original host in which the disease first developed. Cases of plague are still being reported in Siberia and Mongolia, where marmots are hunted for their meat and fur.

• An important lesson for future epidemics

According to virologist Astrid Iversen, of the Universities of Oxford and Copenhagen, the infection was initially transmitted from animals to humans, after which it spread between humans via the respiratory route. The researcher emphasizes that the phenomenon is still relevant today, because about 75% of new infectious diseases identified by the World Health Organization are zoonoses, that is, diseases transmitted from animals. "Understanding how pathogens passed from animals to humans in the past is essential for assessing future risks,” concluded Ruairidh Macleod. The discovery suggests that epidemics were not an exclusive consequence of crowded cities or agricultural civilizations, but accompanied humanity thousands of years before, even in small and mobile communities of hunter-gatherers.