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The oldest known plague victims date back about 5,000 years ago in Europe, but there are two cases One in Latvia and In Sweden There were isolated, sporadic outbreaks or evidence of a more widespread epidemic.
A new study based on ancient DNA recovered from 108 prehistoric people excavated from nine graves in Sweden and Denmark suggests that an ancient form of plague may have been widespread among early European farmers and may explain why this population mysteriously declined over a 400-year period.
“Despite some pretty big differences in archaeology, it’s pretty consistent across Scandinavia, France and Sweden, and you see the same patterns, they just fade away,” said Frederik Thiersholm, a postdoctoral researcher at the Lundbeck Foundation Centre for Geogenetics, Globe Institute, University of Copenhagen in Denmark, and lead author of the study. study The findings were published Wednesday in the journal Nature.
This group, known as the Neolithic Farmers, migrated from the eastern Mediterranean and replaced small groups of hunter-gatherers, first bringing agriculture and settled life to northwestern Europe around 6,000 to 7,000 years ago. Their legacy lives on in the continent’s many megalithic tombs and monuments, the most famous of which is Stonehenge.
Archaeologists are fiercely debating what caused the group’s disappearance between 5,300 and 4,900 years ago. Agricultural crisis Climate change is believed to be the cause, but disease is also suspected to be the culprit.
“Suddenly there’s no one left to be buried at (these monuments), and the people who built these megaliths are (gone),” Mr Searsholm said.
Seersholm said it was unlikely that violence played a role, and the next wave of newcomers Known as YamnayaThey arrived from the Eurasian steppes after a gap in the archaeological record.
The study found that a form of the bacterium that causes the plague was present in one in six ancient samples, suggesting that transmission of the disease was not uncommon.
“These plague cases date back to exactly the same time period as the Neolithic population collapse, providing very strong circumstantial evidence that the plague may have been involved in this collapse,” he said.
Genetic information about pathogens can be stored in human DNA, allowing scientists to time travel and study ancient diseases and their evolution.
Yersinia pestis, the bacterium that causes the plague, was the most common of the six pathogens identified in the new study, being present in 18 of the 108 people sampled, or 17 percent.
But the study suggests that the true prevalence of the plague at the time may have been much higher, given that ancient DNA can only be extracted from well-preserved human remains (it’s impossible to know for sure whether the people studied died from the plague, only that they were infected).
Karl Goran Sjogren
Archaeologists excavated a grave in Frelsegarden, Sweden, in 2001. DNA extracted from some of the bones revealed the presence of the bacteria that causes the plague.
Still, the study authors said their findings don’t necessarily suggest a rapid and deadly plague epidemic: The bacteria was found in remains from four out of six generations buried in some cemeteries.
“We expected that finding that the plague was only present in the last generation would be evidence that it killed them all, and that’s exactly what happened,” said Searsholm, who used ancestral information contained in ancient DNA to piece together family trees from the graves.
“I also expected the plague to be exactly the same, with all of the DNA base pairs exactly the same, because that’s what you’d expect if a disease spreads rapidly. But that’s not what we found,” he said.
Instead, the team found evidence of three separate instances of infection and different mutants of the bacteria that causes the plague.
“So the big question is, why didn’t the plague just kill everyone in the first place? This was puzzling even to us, so we started looking at genetics to see if we could find some explanation,” he said.
The team found instances of plague genetic shuffling — where DNA sequences were lost, added or moved — that could have affected the pathogen’s virulence over the course of a single generation.
“This is in a genomic region that we know encodes virulence, and that’s why we hypothesized that it became more virulent[over generations],” says Searsholm, “but of course this is very difficult to test, because you can’t culture ancient[bacteria].”
Given that the bodies were carefully buried in graves, the genetic data from the study could have captured the beginning of a plague outbreak, said Searsholm, and it’s possible the disease was milder than the bubonic plague epidemic of the 1940s. Black DeathIt was the world’s most devastating plague pandemic, estimated to have killed half of Europe’s population over a seven-year period during the Middle Ages.
What’s more, the variants detected in the samples lacked genes that geneticists know are essential for the bacteria to survive in the flea’s digestive tract, so the resulting disease is likely not identical to the bubonic plague that is spread by rodent-carrying fleas, the study said. Bubonic plague still existsSymptoms include painful, swollen lymph nodes called buboes in the groin, armpits, or neck, fever, chills, and cough.
Mark Thomas, professor of evolutionary genetics at University College London, said the study suggests that the plague probably spread from person to person in Scandinavia at the time, rather than as a sporadic infection from animals, but it is impossible to know how deadly or chronic the disease was.
But the first, who was not involved in the latest study, Identified the decline of the NeolithicHe said he was not convinced the plague was the main cause of the population decline, saying it had occurred at different times in Europe and was more likely the result of a combination of factors, including poor agricultural practices that exhausted the soil and widespread health problems.
“Neolithic people were very weak in terms of their overall health. Their bones are in terrible condition,” Thomas said.
“It’s possible that there was an overall increase in pathogen load,” he added, but “from a DNA perspective,” Y. pestis is one of the more visible diseases to archaeologists, making it easier to identify and study.
