The plague is apparently a lot older than we thought. Scientists says the disease was responsible for a massive migration of people across Europe and Asia during the Bronze Age—approximately 3,000 years earlier than it was believed to have existed, according to a study published Thursday in Cell. Nature reports that scientists discovered a mass exodus from what is now Russia and the Ukraine between 3,000 and 5,000 years ago and were looking for what caused it. To that end, they studied 89 billion DNA fragments from 101 Bronze Age skeletons. “Plague was just a long shot,” researcher Dr. Eske Willerslev tells the New York Times.
DNA from the plague-causing Yersinia pestis bacteria was found in the teeth of seven of the Bronze Age skeletons, the oldest having lived nearly 5,000 years ago in what is now Russia, according to Nature. “To my mind, this leaves little doubt that [the plague] has played a major role in those population replacements,” Willerslev tells the Times. According to Nature, the Bronze Age plague strain is similar to the infamous Black Death and modern bubonic plague, though it probably didn't spread as easily. That's because researchers found it lacked the gene allowing it to live inside fleas, which are helpful when transporting the disease between rodents and humans. The ancient plague was still fatal in 90% of cases, and the Times reports humans may have helped it along by hunting infected rodents for food. (This year, the US saw a first-of-its-kind case involving an infectious dog.)