Plague may have been claiming human lives thousands of years before cities, crowded settlements and medieval pandemics existed, according to new research led by an international team of scientists. The study, published in the journal Nature, analysed ancient DNA from prehistoric human remains and suggests the disease was already causing deadly outbreaks among hunter-gatherer communities around 5,500 years ago.
Researchers from institutions including the University of Cambridge, the University of Copenhagen, the University of Oxford and the University of Alberta examined genetic material preserved inside the teeth of people buried at four hunter-gatherer cemeteries near Lake Baikal in East Siberia. Their findings indicate that early forms of Yersinia pestis, the bacterium responsible for plague, were capable of causing severe disease long before the pathogen evolved into the flea-borne form associated with later pandemics.
The team reconstructed ancient bacterial genomes from 46 individuals and identified plague DNA in 18 of them, meaning almost 40% showed evidence of infection. According to the researchers, that proportion is higher than has been reported at some medieval plague burial sites.
The study also helps explain a long-standing archaeological mystery. At two of the largest burial grounds, an unusually high number of children and young teenagers had been buried within what radiocarbon dating showed was a relatively short period. Genetic evidence further revealed that some of those buried together were close relatives, including siblings and parents with children, suggesting outbreaks may have swept rapidly through families.
Scientists had previously believed the earliest strains of plague were less dangerous because they lacked key genetic features that later enabled efficient transmission by fleas carried on rodents. However, the newly identified strains appear to have possessed a unique toxin-producing superantigen that may have triggered an extreme immune response, potentially making infections highly lethal despite the absence of flea-borne spread.
The findings also strengthen the theory that plague first emerged in Central or North-East Asia before gradually spreading across Eurasia. Archaeological evidence suggests the hunter-gatherer communities studied had frequent contact with marmots, wild rodents that continue to harbour plague today, raising the possibility that direct transmission from infected animals sparked these prehistoric outbreaks.
The research reshapes scientists’ understanding of one of history’s most feared diseases, indicating that plague had already become a serious threat to human populations millennia before agriculture and urban civilisation transformed the way infectious diseases spread.
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