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The oldest known plague victims date back to around 5,000 years ago in Europe. But it was never clear whether two cases, one in Latvia It is one in Sweden, were isolated and sporadic or evidence of a broader outbreak.
A new study, based on ancient DNA recovered from 108 prehistoric individuals unearthed in nine graves in Sweden and Denmark, suggests that an ancient form of the plague may have been widespread among Europe’s early farmers and could explain why this population mysteriously collapsed in space. 400 years old.
“It’s pretty consistent across northern Europe, in France and Sweden, although there are some big differences in the archaeology, we still see the same pattern, they just disappear,” said Frederik Seersholm, postdoctoral researcher at Lundbeck. Foundation GeoGenetics Centre, Globe Institute, University of Copenhagen in Denmark and lead author of to study published in the journal Nature on Wednesday.
This group, known as Neolithic farmers, migrated from the eastern Mediterranean, replacing small bands of hunter-gatherers and bringing agriculture and an established way of life to northwestern Europe for the first time around 6,000 to 7,000 years ago. His legacy lives on in the continent’s many megalithic tombs and monuments, the most famous of which is Stonehenge.
Archaeologists intensely debate the cause of this population’s disappearance between 5,300 and 4,900 years ago. Some attribute his death to a agricultural crisis caused by climate change and others suspect disease.
“Suddenly, there are no more people being buried (in these monuments). And the people responsible for building these megaliths (are gone),” Seersholm said.
It’s unlikely that violence played a role, Seersholm said, with the next wave of newcomers, known as Yamnayaarriving from the Eurasian steppe after a gap in the archaeological record.
The study found that forms of the bacteria that cause plague were present in 1 in 6 ancient samples, suggesting that infection with the disease was not rare.
“These plague cases are dated to exactly the period in which we know the Neolithic decline occurred, so this is very strong circumstantial evidence that plague may have been involved in this population collapse,” he said.
Genetic time travel
Genetic information about pathogens can be preserved in human DNA, allowing scientists to travel through time to discover ancient diseases and how they evolved.
Yersinia pestis, the bacteria that causes plague, was the most prevalent of the six pathogens identified in the new research, present in 18 individuals, or 17% of the 108 sampled.
However, according to the study, the true prevalence of plague at that time could have been much higher, given that ancient DNA can only be extracted from well-preserved human remains. (It is also not possible to know for sure whether the people studied died from the plague – only that they were infected.)
However, the study authors said their findings do not necessarily suggest a rapid and deadly plague epidemic. The bacteria was detected in remains from four of the six generations buried in some of the tombs.
“I expected to find that the plague was only present in the last generation, which would be evidence that the plague is killing them all, and that was it,” said Seersholm, who pieced together the tomb family trees using the ancestry information. contained in ancient DNA.
“I also expected the plague to be exactly the same, like every DNA base pair was exactly the same, because that’s what you would expect if you saw a rapid disease outbreak, but that’s not what we found,” he said. .
Instead, the team found evidence of three distinct infection events, as well as different variants of the bacteria that cause plague.
“The big question is, then, how did the plague not kill everyone at the beginning? And that was intriguing to us too, so we started looking at genes to see if we could find some kind of explanation,” he said.
The team found cases in which plague genes were rearranged – lost, added or moved in DNA sequences – which could perhaps have affected the pathogen’s virulence within a generation.
“It’s in an area of the genome where we know virulence is encoded, and (that’s) why our hypothesis is that it was more virulent (across generations),” Seersholm said. “But of course this is very, very difficult to test, because you can’t just grow an old (bacteria).”
Prehistoric plague transmission
Given that the remains were carefully buried in a grave, Seersholm said it is possible that the genetic data examined in the study captured the beginning of a plague epidemic. It is also likely that the disease was less serious than the bubonic plague that caused the Black Deaththe world’s most devastating plague outbreak, estimated to have killed half of Europe’s population within seven years during the Middle Ages.
What’s more, because the variants detected in the samples lacked a gene that geneticists know is crucial for the bacteria’s survival in a flea’s digestive tract, it was unlikely that the resulting disease was identical to bubonic plague, which was transmitted by fleas carried by rodents, according to the study. Bubonic plague still exists todayand symptoms include swollen and painful lymph nodes, called buboes, in the groin, armpit, or neck areas, as well as fever, chills, and cough.
The study suggests that at that time in Scandinavia, the plague was probably spreading from human to human rather than through sporadic transmission from animals, although it is not possible to know how lethal or chronic the disease was, said Mark Thomas, professor of evolutionary genetics at the University. University College London.
However, Thomas, who was not involved in the most recent research but was part of the team that first identified the Neolithic declinesaid he was less convinced that the plague was the main reason behind the overall population drop, which he said happened at different times in Europe and was likely the result of a combination of factors, including poor agricultural practices that depleted the soil and widespread health problems.
“Neolithic people were very compromised in terms of general health. His bones look bad,” Thomas said.
“There could have been a more general increase in pathogen load,” he added. However, “from a DNA point of view”, Yersinia pestis is one of the most visible diseases for archaeologists and, therefore, easier to identify and study.
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