A plague related to the mysterious disappearance of Europe’s first farmers

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The oldest known plane victims go about 5,000 years ago in Europe. But it was never clear whether two cases, one in Latvia and one in Sweden, were isolated and sporadic or evidence of a wider outbreak.

A new study, based on ancient DNA obtained from 108 prehistoric people found in nine graves in Sweden and Denmark, suggests that an ancient form of the plague may have been widespread among Europe’s first farmers and could have explain why this population mysteriously fell through space. of 400 years.

“It’s pretty consistent across Northern Europe, France and it’s in Sweden, although there are some big differences in the archaeology, we still see the same pattern, they disappear,” said Frederik Seersholm, a postdoctoral researcher at the Lundbeck. GeoGenetics Center Foundation, Globe Institute, University of Copenhagen in Denmark and lead author of the 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 a settled lifestyle to northwestern Europe for the first time around 6,000 to 7,000 years ago . Their legacy lives on in the continent’s many tombs and megalithic monuments, the most famous of which is Stonehenge.

Archaeologists debate the cause of this population between 5,300 and 4,900 years ago. Some attribute their deaths to the agricultural crisis caused by climate change and others suspect disease.

“Suddenly, nobody is being buried (at these monuments) anymore. And the people who were responsible for building these megaliths are (gone),” Seersholm said.

Violence is unlikely to have played a role, Seersholm said, as the next wave of newcomers, known as the Yamnaya, arrived from the Eurasian steppe after a gap in the archaeological record.

​​​​The study found that 1 in 6 ancient samples contained forms of the bacteria that cause plague, suggesting that infection with the disease was not rare.

“These cases of plague, they are dated exactly to the time frame that we know the Neolithic decline took place so this is very strong circumstantial evidence that the plague may have had something to do with this collapse of the population,” he said.

Genetic time travel

Genetic information about pathogens can be preserved in human DNA, allowing scientists to travel through time to learn about 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, in 18 people, or 17% of the 108 sampled.

However, according to the study, the true prevalence of the plague at that time could be much higher since 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 of the plague – just that they were infected.)

Archaeologists excavate a grave in Frälsegården, Sweden, in 2001. DNA extracted from some of the bones revealed the presence of the bacterium that causes plague.  - Karl-Göran Sjögren

Archaeologists excavate a grave in Frälsegården, Sweden, in 2001. DNA extracted from some of the bones revealed the presence of the bacterium that causes plague. – Karl-Göran Sjögren

However, the study’s authors said their findings did not necessarily imply a rapid and deadly epidemic of plague. The bacterium was detected in remains from four out of six generations buried at some of the grave sites.

“I was hoping 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’s it,” said Seersholm, who planted generated trees together from the graves using the ancestral knowledge. is in the ancient DNA.

“I also expected the plague to be exactly the same, like every DNA base pair would be the same, so that’s what you’d expect if you saw a rapid outbreak of the disease, but that’s not what we got ,” he said. said.

Instead, the team found evidence of three separate infection events, as well as different versions of the bacterium that causes plague.

“The big question is, then, how come the plague didn’t just kill everyone in the first place? And that was amazing to us as well, so we started looking at the genes to see if we could find some kind of explanation,” he said.

The team found cases where plague genes had been rearranged – lost, added or moved around in the DNA sequences – which could possibly affect the genetics of the pathogen through generations.

“It’s in an area of ​​the genome where we know that virulence is coded, and (that’s) the reason why we hypothesized that it was more virulent (over the generations),” Seerholm said. “But of course, this is, this is very, very difficult to test, because you can really only grow ancient (bacteria).”

Transmission of the prehistoric plague

Since the remains were carefully buried in a grave, Seersholm said the genetic data examined in the study could have started a plague epidemic. It is also likely that the disease was not as severe as the bubonic plague that caused the Black Death, the world’s most devastating plague outbreak which is estimated to have killed half of Europe’s population in seven years during the Middle Ages.

Furthermore, because the variants detected in the samples lacked a gene that geneticists know is essential for the survival of the bacterium in the flea’s digestive tract, it is unlikely that the resulting disease was identical with bubonic plague, which is spread by fleas carried by rodents, according to the study. Bubonic plague still exists today, and symptoms include painful, swollen lymph nodes, called buboes, in the groin, armpit or neck areas, as well as fever, chills and cough.

The study suggests that the plague in Scandinavia at that time was probably spread from person to person rather than through rare animal transmission, although it is not possible to know how fatal or chronic the disease was, which said Mark Thomas, professor of evolutionary genetics at University College London.

However, Thomas, who was not involved in the latest research but was part of the team that first identified the Neolithic decline, said he is not so convinced that the plague was the main cause of the wider population boom. , which he said happened at different times i. Europe and was probably the result of a combination of factors, including poor farming practices that left the soil and widespread poor health.

“Neolithic people were very dangerous in terms of general health. Their bones look bad,” said Tomás.

“There could be a more general increase in pathogen load,” he said. However, “from a DNA perspective” Yersinia pestis turns out to be one of the most visible diseases to archaeologists and therefore easier to identify and study.

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