By sequencing the genomes of ancient human skeletons, scientists finally have a likely explanation for how the Stone Age plague entered Europe. The same bacterium behind the Stone Age plague was also responsible for the 14th-century Black Death, which wiped out roughly half of Europe’s population at the time.
The bacterium is called Yersinia pestis. Researchers tested more than 500 ancient bone samples and ultimately recovered complete Yersinia pestis genomes from six human skeletons, dating from Late Neolithic to Bronze Age. The samples came from Russia and Croatia as well as Germany, Lithuania, and Estonia. Their analysis found that the Stone Age plague first came to Europe via large-scale migration from the Eurasian steppe approximately 4,800 years ago. A paper describing the work was published in the journal Current Biology.
"This suggests that the plague either entered Europe multiple times during this period from the same reservoir, or entered once in the Stone Age and remained there," co-author Aida Andrades Valtueña from the Max Planck Institute for the Science of Human History in Jena, Germany, told BBC News.
Co-author Alexander Herbig, also from Max Planck, told BBC News that the samples from Russia and Croatia are among the oldest plague-positive samples ever recovered. And despite their wide geographic range, all six were closely related genetically.
"This suggests that the plague either entered Europe multiple times during this period from the same reservoir, or entered once in the Stone Age and remained there," Valtueña told ScienceDaily.
Because the earliest evidence of the plague’s arrival in Europe coincided with the incoming populations from the steppe, the researchers believe it was a mass migration that brought the plague bacterium into Europe.
The period between the Late Neolithic and early Bronze Age was, as the authors described in the paper, “characterized by major transformative cultural and social changes that led to cross-European networks of contact and exchange.” It’s conceivable that the bacterium itself was the reason for the mass migration in the first place, as late Neolithic and early Bronze Age civilizations fled the Eurasian steppe to try to outrun the disease.
"It's possible that certain European populations, or the steppe people, may have had a different level of immunity," lead author Johannes Krause, director of the Department of Archaeogenetics at the Max Planck Institute for the Science of Human History, told ScienceDaily.
So basically, when the steppe peoples entered Europe in a bid to leave the plague behind, they would have unwittingly introduced the bacterium to entirely new populations which had never encountered it. The bacterium thrived and the Black Death plague would later kill an estimated 25 million people.
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