A mysterious form of plague that spread across Eurasia thousands of years before the Black Death has finally revealed a crucial clue. Scientists analyzing ancient DNA discovered the bacterium Yersinia pestis in a 4,000-year-old domesticated sheep from a Bronze Age settlement in the Ural Mountains— the first time the pathogen has ever been found in a non-human host from that era. Because this early strain couldn’t spread through fleas like the medieval plague, researchers have long puzzled over how it traveled so widely. ...read more read less