Where did the Black Death start? DNA detectives find a key clue
Where and when was the Black Death born? The question has been asked for centuries and has sparked heated debate among historians.
Now a group of researchers report that they have found the answer in the pulp of the teeth of people buried in the 14th century.
Based on their analysis of preserved genetic material, the researchers report that the Black Death arrived in 1338 or 1339 near Issyk-Kul, a lake in a mountainous region just west of China in present-day Kyrgyzstan. . The plague first infected people in a small nearby trading colony eight years before devastating Eurasia, killing 60% of the population.
The survey was led by Wolfgang Haak and Johannes Krause of the Max Planck Institutes for Evolutionary Anthropology and the Science of Human History in Germany as well as Philip Slavin of the University of Stirling in Scotland, who described their findings on Wednesday in Nature.
What used to be called the Black Death – named after the black spots that appeared on the bodies of victims – is caused by a bacterium, Yersinia pestis, which is carried by fleas that live on rodents. The disease is still present today, carried by rodents on all continents except Australia. But infections are rare because hygiene is better. Infections are easily cured with antibiotics.
The 14th-century plague was actually the second major outbreak of Yersinia pestis — the first was the Plague of Justinian in the 6th century, said Mary Fissell, a medical historian at Johns Hopkins University. But the Black Death is the best known and is considered one of the deadliest epidemics in human history.
Its terrors were chronicled by Giovanni Boccaccio, an Italian writer and poet who lived through the plague when it hit Florence. The disease, he wrote, “showed its first signs in both men and women by means of swellings either in the groin or in the armpits, some of which reached the size of an ordinary apple and others the egg size, and people called them buboes”, which became known as “signs of impending death”.
Historians have traced the path of the epidemic – it apparently started in China or near China’s western border and moved along trade routes to Europe, North Africa and the Middle East. East.
But Monica Green, a medical historian and independent researcher who was not involved in the new paper, noted that historians will never be able to answer the question they have been asking: was it really Yersinia pestis that caused this massive pandemic?
“We hit a wall. We are historians and we deal with documents,” Green said.
She vividly remembers meeting a paleopathologist 20 years ago who was studying leprosy, which leaves visible marks on skeletons.
“When will you plague?” Green asked. She said the paleopathologist replied that they couldn’t study the plague because a disease that kills people so quickly leaves no marks on the bones.
Now this impasse is overcome.
Finding the origin of the plague “is like a detective story,” said Fissell, who was not involved in the new study. “Now they have very good evidence from the crime scene.”
The hunt goes back more than a decade, when the group that carried out the latest study stunned archaeologists with their report that they could find plague bacteria DNA in the teeth of skeletons.
This study involved plague victims in London.
Fourteenth-century Londoners knew the Black Death was coming, so they dedicated a cemetery ahead of time to prepare for its victims. The bodies were exhumed and are now kept in the Museum of London. The situation was ideal because not only did these victims come from a plague-stricken cemetery, but the date of their death was known.
“As an epidemiological case study, it’s perfect,” Green said. “The technical skill that has gone into this work has been nothing short of amazing.”
Since the London study, the group has analyzed the genetic material of plague victims at other sites, building a DNA family tree of variants of the plague bacterium. She and other researchers reported that the tree had a trunk and then suddenly seemed to explode into four branches of strains of Yersinia pestis whose descendants are found in rodents today. They called the event the Big Bang and began a quest to find out when and where it happened.
Historians have offered various dates, ranging from the 10th to the 14th century.
Slavin, a latecomer to the group that analyzed plague victims in Kyrgyzstan, said one of his dreams was to solve the riddle of the origins of the Black Death.
“I was aware of two Christian cemeteries in Kyrgyzstan and started digging,” he said.
To his delight, he discovered that hundreds of tombstones were precisely dated. Some bore inscriptions saying, in an ancient language, Syriac, that the person had died of “plague”. And the death rate of the population had skyrocketed the year these people died.
“It caught my attention because it wasn’t just any year,” Slavin said. It was in 1338, “just seven or eight years before the Black Death arrived in Europe”.
“We can’t ask for much more than to have headstones with the year,” he said.
Researchers found plague DNA in the teeth of three people whose headstones said they had died of “plague”.
The group also reports that the rodents that spread the bacteria to these victims were groundhogs. The marmots of this region today have fleas carrying a type of Yersinia pestis which seems to derive directly from the ancestral stock.
And researchers report that the stump in Kyrgyzstan comes from the trunk that exploded into four stumps. It’s the beginning of the Big Bang, the group proposes.
If they’re right, Fissell said, it appears the Big Bang happened just before the Black Death in Eurasia, indicating that the spread of the plague was most likely via trade routes and not, as some historians have suggested it, by military actions a century earlier.
Green and other historians have proposed that the Big Bang happened when the Mongols of the early 13th century spread the bacteria. But if that had been the case, the bacterium in Kyrgyzstan would have been from one of the branches and not the ancestral strain.
“These battles in the 1200s are pretty irrelevant,” Fissell said.
Green said she was convinced the group had found plague victims in Kyrgyzstan. But she said the evidence now available was insufficient to substantiate her bold claims.
“Stay tuned,” Green said, adding that she expected more evidence to emerge.
So far, she says, detective work has unearthed an important clue.
The artwork, she added, “puts a pin on the map, with a date.”
[This article originally appeared in The New York Times.]