A new and cutting-edge genomic study has uncovered surprising new details about the prehistoric origins of the plague. This tripartite research team consists of leaders in the field from Harvard University and the Max Planck Institute. The study suggests a surprising link between livestock—particularly sheep—and the bacterium Y. pestis, which causes plague. This bacterium has been a perennial menace to human settlement for millennia. Those conclusions come from a 4,000-year-old sheep tooth found on the Eurasian Steppe, which had the complete Y. pestis genome isolated from it.
Fortunately, researchers like Dr. Christina Warinner, Landon T. Clay Professor of Scientific Archaeology at Harvard University, and Dr. Felix M. Key from the Max Planck Institute for Evolutionary Anthropology (MPI-EVA) have been hard at work. She and her team revealed how domesticated animals were key players in the rapid spread of this ancient pathogen. Yersinia pestis’s toll on human populations. Their findings reconstruct Y. pestis’s impact on human populations for nearly 3,000 years. This particular lineage probably became extinct by the Late Neolithic Bronze Age (LNBA).
The Discovery of the Ancient Genome
The linchpin for this study was that analysis of a single sheep tooth. Our find while excavating in a part of the world that abounds with archaeological wonders, the Eurasian Steppe. This area produced many thousands of animal bones from Bronze Age domesticates, supplying an extremely rich source of data for this work. One of the most surprising things about the analysis was how consistent the ancient lineage of Y. pestis was. This predictability spanned an amazing 6,000 kilometer swath at any point in time.
The researchers speculate that widespread, large-scale sheep herding during the Bronze Age led to intimate contacts between pastoralist societies and the forest reservoirs of Y. pestis. This raised the risk of spillover events into humans.
“We can show that the ancient lineage evolved under elevated pressure, which is in contrast to the Y. pestis still found today. Moreover, the ancient [sheep] as well as human infections are likely isolated spillovers from the unknown reservoir, which remains at large. Finding that reservoir would be the next step.”
Also discovered in Russia, the site of Arkaim, a component of the Sintashta cultural complex, acted as a central point for this research. Arkaim provides a rare opportunity to explore the connections between early pastoral societies and plague infections. Its lack of human grain storage keeps them free from rodents and their fleas that are the usual carriers of Y. pestis.
Insights from Arkaim and Early Pastoralism
Dr. Taylor Hermes, an Assistant Professor of Anthropology at the University of Arkansas and co-author of the study, remarked on the significance of this location:
The Sintashta-Petrovka culture’s long-range herding is likely achieved through dynamic horse technologies. This close contact with wild animals then may have put their livestock at risk of infection, which in turn may have transmitted to humans.
“Arkaim was part of the Sintashta cultural complex and offered us a great place to look for plague clues: they were early pastoralist societies without the kind of grain storage that would attract rats and their fleas—and prior Sintashta individuals have been found with Y. pestis infections. Could their livestock be a missing link?”
This research highlights how fascinating ancient diseases spread and change through unique interactions between humans and animals. It underscores a fatal flaw in our collective understanding of where these disruptive pathogens come from and how they jump between species.
Ian Light-Maka, a Ph.D. candidate and lead author of the study, emphasized the importance of uncovering these origins:
“The Sintashta-Petrovka culture is famous for their extensive herding over vast pastures aided by innovative horse technologies, and this provided plenty of opportunity for their livestock to come into contact with wild animals infected by Y. pestis. From then on it is just one more short hop into humans.”
Implications for Understanding Disease Spread
Dr. Warinner further underscored this point, noting that if researchers had not identified the source as sheep, many would have assumed it was merely another human infection:
This research provides fascinating new context to the historical effects of the plague. It’s a wonderful story, but it underscores urgent and timely questions about how these novel diseases are spreading due to human-animal interactions. By learning about these dynamics, we can better tailor contemporary public health strategies to be successful.
“One of the first steps in understanding how a disease spreads and evolves is to find out where it’s hiding, but we haven’t done that yet in the ancient DNA field.”
Dr. Warinner further underscored this point, noting that if researchers had not identified the source as sheep, many would have assumed it was merely another human infection:
“If we didn’t know it was from a sheep, everyone would have assumed it was just another human infection—it’s almost indistinguishable.”
The findings from this research not only contribute to our comprehension of plague’s historical impact but also pose critical questions about modern disease transmission routes stemming from animal interactions. Understanding these dynamics can inform contemporary public health strategies.