A group of researchers from France, Sweden and Denmark discovered a new strain of Yersinia pestis, a bacteria that causes pestilence in DNA derived from 5000-year human remains.
Their analysis, published on December 6 in the magazine Celica, show that this strain is the closest one ever found in genetic origin of the plague. Their work also suggests that merchants in Neolithic European settlements spread with plague, which contributed to the decline of settlements at the dawn of the Bronze Age.
"The plague is perhaps one of the deadly bacteria that ever existed for humans. And if you think of the word" plague, "it may mean infection with Y. pestis, but due to the trauma in our history, there has also been a general orientation to any epidemic The kind of analyzes we are doing here should come back over time and let's see how this pathogen, which had such a big impact on us, developed, "says Simon Rasmussen, senior author (@simonrasmu), a metagenomic researcher at the Technical University Denmark and the University of Copenhagen.
In order to better understand the evolutionary history of plague, Rasmussen and his colleagues passed through the publicly available genetic data of old people, examining sequences similar to modern ball-like strains. They found that in the genetic material of a 20-year-old woman who died some 5,000 years ago in Sweden, they have never been seen. The source had the same genes that today cause a lethal pulmonary disease, and traces were also found with another individual on the same grave, indicating that a young woman is likely to die due to illness.
This plague is the oldest that has ever been discovered. It is particularly interesting that by comparison with other strains, researchers found that this is also the most basic, which means that it is the closest source of genetic origin of Y. pestis. It probably differs from other strains about 5 700 years ago, while the plague, which was common in the Bronze Age, and the plague, which is the ancestor of existing strains today, has been between 5,300 and 5,100 years old. This suggests that at the end of the Neolithic period there were several types of plague.
Rasmussen also believes that this finding offers a new theory about how the plague spreads. It is well known that mass human migration from the Eurasian steppe to Europe occurred some 5,000 years ago, but it was still debating how these cultures could be replaced by the culture of the Neolithic peasant culture that was then present in Europe. Earlier researchers suggested that the attackers brought with them plagues that on the occasion of the destruction of large settlements of farmers of Stone Age.
If, however, the strain of researchers found in a Swedish woman was different from the rest of Y. Pestis 5 700 years ago, that is, he probably developed before the beginning of these migrations and around the time when Neolithic European settlements were already started Decline.
At that time, a total of 10,000-20,000 inhabitants in Europe became joint mega settlements, which enabled specialization, new technologies and trade. But there may have been plagiarists. "These mega settlements were the largest settlements at that time, ten times larger than anything else. They had people, animals and stored foods close together, and probably very poor sanitation. This is a learning example of what you need to develop new pathogens," says Rasmussen.
"We believe that our data is appropriate. If the plague developed in mega settlements, after people began to die from it, the settlements would be abandoned and destroyed. This was found in these settlements 5,500 years ago. so it began to migrate across all the trade routes provided by bicycle transportation, which at this time quickly spread across Europe, "he says.
Over time, he suggests that the plague would come through these trade interactions in a small settlement in Sweden, where the woman studied by his team lived. Rasmussen argues that women's own DNAs also offer additional evidence for this theory – it is not genetically linked to people who have attacked Europe from the Eurasian steppe, supporting the idea that this strain of swine came from mass migrations. Archeology also supports this hypothesis, because by the time she died, there were still no signs of invaders.
Of course there are some limitations on what the data from this study can tell us. Most importantly, researchers have not yet recognized the plague in individuals from mega settlements where it may have developed. "We have not found a smoking gun, but it's partly because we have not seen it yet. And I really want to do it because if violence was found in these settlements, this would be a strong support for this theory," says Rasmussen.
Nevertheless, he believes this study is a step towards understanding how plague and other pathogens have become fatal. "We often think that these superpatogens were always nearby, but that's not the case," she says. "The plague developed from an organism that was relatively harmless, and recently the same has happened with the big gods, malaria, Ebolo and Ziko. This process is very dynamic and is always happening. I think it's really interesting to try to understand how we go from something that is harmless to something extremely virulent. "
Picture of the head – This picture shows the remains of a 20-year-old woman (Gokhem2) of about 4900 BP killed by the first pandemic plague. She was one of the victims of the plague of pandemics, which probably led to the collapse of Neolithic societies in Europe. Credit: Karl-Göran Sjögren / University of Göteborg