Two distinct phases of plague outbreaks occurred among hunter-gatherer communities near Lake Baikal in southeast Siberia, beginning around 5,500 years ago, according to new research. The study analyzed ancient DNA from human remains, revealing a high prevalence of the plague-causing bacterium Yersinia pestis across four cemetery sites.
Early Plague Strains Identified
The findings indicate that these early plague strains, which predate those known to cause the bubonic form of the disease, were lethal. A 39% detection rate for plague infection was observed among the individuals studied. By reconstructing kinship pedigrees, scientists determined that small familial groups were impacted, suggesting human-to-human transmission. The first outbreak appears to have occurred within a single generation.
This period of outbreaks predates the emergence of key virulence factors required for bubonic plague, which were previously thought to have appeared around 3,800 years ago. The research also noted functional differences in the new strains, including at the ypm superantigen locus, which is also found in the present-day bacterium Yersinia pseudotuberculosis. These newly identified strains diverge ancestrally from known Y. pestis, pushing back the estimated timing of its emergence to before approximately 5,700 years ago.
Impact on Hunter-Gatherer Communities
The infections resulted in acute mortality, with a notable impact on children aged 8 to 11 years. The study challenges the notion that higher population densities and lifestyle changes associated with the Neolithic agricultural transition were prerequisites for plague epidemics. The occurrence of these outbreaks among mid-Holocene hunter-gatherer communities, situated outside the sphere of Late Neolithic Europe, suggests that plague could spread and cause significant mortality even in less densely populated, non-agricultural societies.
The two identified outbreaks were separated by an interval of four to six centuries. The first outbreak, dated between approximately 5,520–5,265 years ago, is associated with the Isakovo mortuary tradition. The second outbreak, occurring between 5,315–4,235 years ago, is linked to the Serovo mortuary tradition. Cases from the Bratskii Kamen cemetery were found in both phases.
These sites are located along the Angara River, a major watercourse flowing from Lake Baikal. Analysis of isotopic data from individuals at the Ust’-Ida I site indicated consumption of both local fish and terrestrial game, reflecting the hunter-gatherer lifestyle of these communities.
The research analyzed ancient DNA from 46 individuals, with Y. pestis being the most frequently detected pathogen. The findings provide crucial insights into the early evolution of plague and its devastating impact on prehistoric human populations.
Helene Elliott is the senior reporter for News Raise. She covers Science news. She also has a keen interest in photojournalism. Helene holds a nomination for the prestigious Red Smith Award. She is married to author Dennis D’Agostino, a former publicist with the New York Mets.
