Long before the two deadliest pandemics in history – The Plague of Justinian and the Black Plague – an ancient strain of the bacterium responsible for these scourges Yersinia pestis – may have caused devastation among Neolithic European communities, according to a controversial new study more than 5,000 years ago.
New Research published today in Cell describes a newly identified strain of Yersinia pestis the bacterium causing the plague. The DNA of the new tribe was obtained by a woman who lived 4,900 years ago in a Neolithic farming community in present-day Sweden. The bacterium is unique in that it is the oldest genome of Y. pestis and, at the genetic level, the earliest ever discovered disease strain.
More controversial are the authors of the new study led by Metagenomics researcher Simon Rasmussen of the Technical University of Denmark and the University of London. Copenhagen says this bacterium could have spread to the late Neolithic European communities where it became pest – like Conditions that contributed to the decline of these settlements and created the conditions for the subsequent Bronze Age. In addition, the plague was not introduced by settlers from the Eurasian steppe, the researchers argue, but had an Eastern European origin. Other experts are not convinced, however, that further archaeological and genetic evidence is needed for the claim.
At the heart of this study Yersinia pestis is the bacterium responsible for an indescribable level of human suffering. This pathogen, which spreads to humans through bites of infected fleas, caused Justinian's plague in the sixth century AD, killing between 30 million and 50 million people – almost half of the population at that time. The plague would return 800 years later and manifest as a Black Death – a threat that killed 50 million Europeans from 1347 to 1351.
Long before these episodes, however, the bacterium had already shaped human communities. In 2015, a research team led by Rasmussen led the plague between 3000 and 1000 BC. Back to the Bronze Age. Rasmussen's latest work pushes the origin of the disease even further back to the late Neolithic.
Rasmussen and his colleagues discovered the ancient strain in a publicly accessible database of ancient DNA taken from the teeth of people buried in the Swedish tomb of Fralsegarden. While screening for specific sequences of the bacterium, the researchers came across the previously unidentified strain in the genetic material of a 20-year-old woman who died in Sweden between 5,040 and 4,867 years. The Gok2 strain, as it is now called, was compared to bacteria that came before and after it. There were slight differences and some obvious similarities. Gok2 differs from Y. Pseudotuberculosis the strain originating from the plague in order to justify the declaration of a new bacterial species. At the same time, the newly discovered strain is very similar to the version of Y. pestis is already known to us and contains the genes responsible for the lethality of modern lung pneumonia. The disease manifests itself in two different forms, the bump and the pneumonia, the former being an infection of the lymphatic system and the lymphatic system. The latter is an infection of the respiratory system.
Interestingly, the researchers found traces of the Gok2 strain in another person buried at the same tomb – a 20-year-old man who lived at the same time as the woman. This could mean that both individuals died of the plague and that an epidemic had seized this agricultural community, the researchers speculate.
As already mentioned, the Gok2 strain is the oldest ever discovered, but it is also the most basic. Using the term basal, the researchers mean that they are closest to the genetic origin of Y. pestis – From a genetic point of view, this is the earliest plague that occurs on a different evolutionary branch than other tribes. The Gok2 strain, according to the authors, originated about 5,700 years ago, the strain that would plague the Bronze Age was created 5,300 years ago, and the current strain occurred 5,100 years ago. At least three different versions of the plague circulated in Eastern and Northern Europe in the late Neolithic, not to speak of new research, of those we do not know yet.
This observation, the researchers say, could solve a continuing mystery of the decline of late Neolithic communities. For reasons that are not completely clear, about 5,500 years ago, Neolithic settlements – some with 10,000 to 20,000 inhabitants – began to disappear. The decline may have been caused by Neolithic peasants overfishing the environment, or by incoming settlers (or invaders, depending on your historical beliefs) bringing the plague from the Eurasian steppe.
But the authors of the New Studies say they have a better explanation: a late Neolithic plague, fueled by the Gok2 strain that originated in Eastern Europe and not in the Eurasian steppe.
"These mega-settlements were the largest settlements in Europe at this time, ten times larger than anything else. They had people, animals and food close to each other and probably very poor sanitation. This is the textbook example of what you need to develop new pathogens, "said Rasmussen in a statement. "We believe that our data fits. If plague developed in the mega settlements, the settlements would have been abandoned and destroyed when people died. This is exactly what was observed in these settlements after 5,500 years.
The Y. pestis bacterium would also have begun to migrate along all the trade routes made possible by the transport of wheels, which had spread throughout Europe at that time, he explained. Through these trade routes, the Neolithic plague finally reached Sweden and infected the farmers of Fralsegarden.
Analysis of the 20-year-old woman's DNA showed that she was not genetically related to the Eurasian steppe migrants – an observation suggesting that the Gok2 strain was making its rounds before arriving in Europe Steppe Eurasians were not responsible for introducing the plague in Europe.
It certainly makes sense, but more work will be needed to validate this theory. As the authors themselves acknowledge, they have not really identified the specific version of the plague that could have terrorized the mega-settlements.
"We did not really find the smoking weapon, but that's partly because we have not looked yet," Rasmussen said. "And we would really like to do that, because if we could find a plague in these settlements, that would be a strong support for this theory."
Boris Valentijn Schmid, a biologist at the University of Oslo, described the New Study as technically sound.
"This group has already published [a paper] on these very early disease strains, and they have a good methodology to check whether the bacterium they are looking at is actually an early form of the disease than the ancestral bacteria , from which the plague went out, Y. Pseudotuberculosis "said Schmid to Gizmodo.
Johannes Krause, a geneticist at the Max Planck Institute, did not like the new work and said that the authors did not really identify the oldest genome.
"You've made a mistake in your study," he told Gizmodo. Krause refers to a strain that dates back to the same time – about 4,900 years ago – and was found in the population of Yamanya (now in Ukraine and parts of Russia), as described in a study from 2017, whose Krause is co-author. It's a fussy complaint and likely role of competing research teams.
Krause, however, found it interesting that the new strain was found in a person that has "no steppe genes" and that the stem belongs to another branch in the evolutionary history of Y. Pestis .
"Not just a new branch, but a more basic branch, so closer to the original split of Y. Pestis of Y. Pseudotuberculosis ," explained Schmid. "That's a nice find for me."
The claim that the plague originated in Eastern Europe "is highly speculative and is not supported by any data," said Krause. Schmid agreed and said, "It is indeed so highly speculative that I would not burden that."
However, the scientists found that scientists were an interesting new option – and now it's time for other archaeologists, geneticists, microbiologists. and pathologists to do their part.
"Much depends on numbers – how often did humans die of this early form of plague? And was that enough to influence the total? In their earlier work, Rasmussen and his colleagues found traces of the bacterium in seven out of 101 samples, an impressive amount, and only slightly less than the percentage of deaths caused today by all infectious diseases, "said Schmid. "However, I do not know if this percentage is enough to counteract population growth and cause a decline."
The discovery of an ancient form of plague in two Neolithic Swedish individuals is interesting, but certainly not enough to guarantee the explanation of a comprehensive European epidemic during the late Neolithic. This is certainly a compelling possibility and consideration that is now appropriate for future investigations.
Regardless, the plague seems to have suffered in the human ass for a long time.