The Plague Was Already Killing Humans 5,500 Years Ago

A study published in June 2026 has pushed back the history of one of humanity's most feared diseases by thousands of years. By analysing ancient DNA extracted from the remains of hunter-gatherers buried in Siberian cemeteries approximately 5,500 years ago, researchers discovered evidence of Yersinia pestis — the bacterium responsible for the plague — in a period long before the conditions usually associated with epidemic disease: cities, dense populations and rats.

The ancient form of the plague bacterium found in these hunter-gatherers was not identical to the strain that caused the Black Death in the fourteenth century, which killed up to a third of Europe's population. It lacked some of the genetic features that make the medieval plague so extraordinarily lethal and contagious. Nevertheless, it was capable of infecting humans, and the discovery suggests that Yersinia pestis was already circulating in human populations during the Neolithic period.

The finding has significant implications for our understanding of prehistoric human societies. Population declines that archaeologists have previously attributed to climate change, migration or social collapse may in some cases have been caused — at least in part — by infectious disease. The plague may have been shaping human history even before the invention of writing.

The study adds to a growing body of research that uses ancient DNA to trace the deep history of infectious diseases in human populations. From tuberculosis to hepatitis B, scientists are discovering that many diseases have been part of human life far longer than previously realised, raising fundamental questions about co-evolution between humans and the microorganisms that infect them.