When a group of thirty-something bones was excavated from tombs in northern Kyrgyzstan in the late 1880s, researchers had no idea that the remains would disclose fresh evidence regarding the Black Death's beginnings some 130 years later.
The Black Death was the initial wave of a 500-year-long epidemic that would become one of the worst in human history. The deadly bacteria Yersinia pestis was to blame, and it cast a long shadow over the Middle Ages, wiping off significant swaths of Europe's population.
Despite its enormous effect, the disease's roots have long eluded experts, who have recently traced long-buried ancient Y. pestis genomes across the continent.
This new study, which claims the Black Death originated in Central Eurasia, is only the latest in a long line of archeological and paleoecological discoveries that are slowly changing our perceptions of the disease.
"Our study puts to rest one of the biggest and most fascinating questions in history and determines when and where the single most notorious and infamous killer of humans began," according to University of Stirling historian Phil Slavin, who collaborated with lead author Maria Spyrou, an archaeogeneticist at the University of Tübingen, and biochemist Johannes Krause of the Max Planck Institute for Evolutionary Anthropology.
Spyrou and Krause had previously been able to trace the origins of the second plague epidemic back to a riverbank village in Russia by comparing ancient genomes from the remains of people who had died of the plague in England, France, Germany, and elsewhere.
Other teams have claimed to have discovered the earliest known plague victim, who died in what is now Latvia from a less transmissible, ancestral strain of Y. pestis thousands of years before the Black Death ripped around the world in the mid-14th century.
However, the roots of the second plague epidemic, which began with the Black Death and lasted five centuries, have long been contested, and efforts to trace it have been impeded, according to the scientists, by a dominant Eurocentric perspective.
With DNA evidence from the bones of seven victims excavated from two graves in modern-day Kyrgyzstan, this new discovery extends the likely origins of the Black Death even further east into Central Asia.
The cemeteries, which were discovered between 1885 and 1892 in the Chüy Valley near Lake Issyk-Kul, featured a cluster of burials identified by tombstones written with hazy descriptions of an unknown epidemic.
The local epidemic coincided with the start of the second plague pandemic, however the actual cause of mortality was never determined.
To find out more, the researchers extracted DNA from the found skeletons' teeth, sequenced the genetic material and compared it to modern and historical genomes of Y. pestis.
"Despite the risk of environmental contamination and no guarantee that the bacteria would have been able to be preserved, we were able to sequence [ancient] DNA taken from seven individuals," adds Spyrou.
They discovered evidence of old DNA of the plague bacteria, Y. pestis, in the molars of three of the seven corpses, and used historic diaries from the initial digs to connect these skeletons to their headstones.
"We could finally show that the epidemic mentioned on the tombstones was indeed caused by plague," explains historian Slavin.
Two of the ancient genomes rebuilt belonged to a single strain from the first half of the 14th century. This ancestral strain, according to genomic comparisons, caused a vast increase of various plague strains that branched out and spawned the pandemic.
"We found that the ancient strains from Kyrgyzstan are positioned exactly at the node of this massive diversification event," adds Spyrou. "In other words, we found the Black Death's source strain and we even know its exact date." The year 1338 is etched on the skeleton's headstones in the old Syriac language.
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| The headstone of one of the plague victims buried in the Chu Valley |
Of course, age estimations for ancient DNA samples retrieved from disintegrating corpses may vary greatly, and archaeological results are never conclusive, so there could be more to this story yet, particularly if additional plague victims' remains are discovered.
Based on the findings, the researchers discovered that the original strain was similar to present strains circulating in wild mouse populations surrounding the adjacent Tian Shan mountains, suggesting that the Black Death originated in the area rather than being imported from elsewhere.
"This points to an origin of Black Death's ancestor in Central Asia," Krause argues.
Another pressing topic was and is how the Black Death spread; conflict and trade networks are assumed to have been major factors in Y. pestis's rapid expansion in the 14th century.
The researchers believe the Chüy Valley was home to varied groups that relied on commerce with places across Eurasia based on additional investigations of tombstone inscriptions, burial items, currency hoards, and historical documents.
Those commerce channels may have picked up an unexpected passenger.
"An investigation of early-to-mid-fourteenth-century [trade] connections across Asia, interpreted alongside other genomic evidence, will be important for disentangling the bacterium's westward dispersals," the researchers write.
