DNA analysis reveals source of Black Death

A view of the Tian Shan mountains in Kyrgyzstan, where scientists have identified the origins of the plague outbreak that caused the Black Death in the Middle Ages, is shown.

(CNN)Tombstones in what's now Kyrgyzstan have revealed tantalizing details about the origins of the Black Death, the world's most devastating plague outbreak that is estimated to have killed half of Europe's population in the space of seven years during the Middle Ages.

The source of that pandemic has been debated by historians for centuries, but the inscribed tombstones -- some of which referred to a mysterious pestilence -- and genetic material from bodies exhumed from two grave sites that date back to the 13th century have provided some concrete answers to this long-standing question.
Researchers first excavated the burial sites in the 1880s. The tombstone inscriptions, written in the Syriac language, were painstakingly reexamined in 2017 by historian Phil Slavin, an associate professor at the University of Stirling in Scotland. He noticed that of the 467 burials that were precisely dated, a disproportionate number -- 118 -- were from just two years: 1338 and 1339. It's a revelation he described as "astonishing."
    "When you have one or two years with excess mortality, it means that something was going on. But another thing that really caught my attention is the fact that it wasn't any year -- because it was just seven or eight years before the (plague) actually came to Europe," Slavin told a news briefing.
      Inscriptions on the tombstones referred to a mysterious pestilence.
      "I've always been fascinated with the Black Death. And one of my dreams was to actually be able to solve this riddle of its origins," he added.
      Slavin and his collaborators discovered the remains of 30 of the individuals buried in the Kyrgyzstan grave sites had been taken to the Peter the Great Museum of Anthropology and Ethnography in St. Petersburg, Russia. The research team was able to get permission to attempt to extract DNA from the skeletons to understand how they had died.
      For seven of the individuals, the researchers were able to extract and sequence DNA from their teeth. In this genetic material, they found the DNA of the plague bacterium -- which scientists call Yersinia pestis -- in three of the individuals, who all had the death year 1338 inscribed on their tombstones.
        This confirmed that the pestilence mentioned on the tombstones was indeed the plague, which is spread from rodents to humans via fleas