A recently analyzed ancient cemetery in southeast Siberia has provided new insights into the early history of plague, challenging long-held assumptions about the origins and spread of this disease. Excavations at the site, known as Ust’-Ida I, along with nearby burial grounds, revealed a high number of children and adolescents among the deceased, prompting researchers to investigate the cause of death.

Genetic analysis of dental remains from 46 individuals found fragments of Yersinia pestis, the bacterium responsible for plague, in the teeth of nearly a third of those studied at Ust’-Ida I. This discovery marks the earliest known evidence of plague outbreaks, dating back more than 5,700 years. Researchers theorize that the infection was initially transmitted from marmots, a type of wild rodent native to the region, likely through the consumption of undercooked meat or exposure to blood droplets during hunting and skinning.

The pattern of deaths—where closely related family members perished around the same time—suggests that after zoonotic transmission, the disease spread directly from person to person, possibly through caregiving interactions. However, because plague DNA degrades over time, its absence in some remains does not rule out widespread infection. Comparable modern analyses of medieval plague pits, such as one found in London, detect the pathogen in only about 20% of victims, despite strong evidence that all died from plague.

This ancient strain of Yersinia pestis lacked later evolutionary adaptations that allowed transmission via blood-feeding insects such as fleas, which contributed to the devastating pandemics like the Black Death in medieval Europe. The findings complicate the established view that large-scale infectious disease outbreaks arose predominantly after the advent of agriculture, which brought humans into closer quarters with domesticated animals and each other. Instead, plague appears to have affected hunter-gatherer communities long before the development of farming societies.

Anne Stone, an anthropological geneticist at Arizona State University not involved in the research, noted that these results provide a valuable perspective on how the plague impacted early human populations who often have been underrepresented in ancient DNA studies due to the fragility of their remains. The study underscores the continuity of infectious disease impacts throughout human history, even among mobile, small-scale populations.

Eske Willerslev, an evolutionary geneticist at the University of Copenhagen and one of the lead researchers, reflected on how the findings challenge idyllic views of prehistoric life. “You get a result like this, and it just rocks the boat. You’re happy you’re born when you are, you know?” he said, highlighting the enduring and complex relationship between humans and infectious pathogens over millennia.