On the trail of early epidemics: Plague outbreaks may have severely affected Europe’s Neolithic farming communities, according to a study. It is based on the paleogenetic examination of the remains of over a hundred people who lived in southern Scandinavia around 5,000 years ago. The researchers have found that 18 people were infected with the plague pathogen. The bacterium Yersinia pestis may have developed a stronger infectious and disease-causing potential earlier than previously assumed, the researchers explain.
It is considered the worst infectious disease of all time and is deeply rooted in the memory of Europeans: millions of people fell victim to the plague, especially in the 14th century. In the most intense phase of the epidemic, the so-called Black Death is estimated to have killed at least a third of the European population. It is now known that this was not the first time that the plague pathogen appeared in Europe. In paleogenetic studies, researchers have also found infections with early forms of the bacterium Yersinia pestis in people from the late Neolithic period. However, it has so far remained unclear to what extent these were isolated cases and whether the pathogen already caused life-threatening disease courses. This is because the early plague strains did not yet have at least certain genetic “killer factors” of the later versions.
Weren’t the early versions that bad?
That is why a research team did not see any evidence of a Stone Age pandemic in the case of an infected person who was buried about 5,000 years ago in what is now Latvia. Scientists who found a plague infection in a Neolithic farmer from what is now Sweden came to a different conclusion. They interpreted this discovery as an indication that a plague epidemic could have contributed to the so-called Neolithic Decline. This is a mysterious population collapse that became apparent in farming societies in some parts of Europe between 5,300 and 4,900 years ago. Various causes are being discussed as the reason for this: in addition to conflicts and crop failures, there were also diseases that could have spread via the already well-developed network of connections between communities.
The current study by researchers led by Frederik Seersholm from the University of Copenhagen now supports the assumption that the early forms of the plague played a role in the Neolithic decline. The results are based on the analysis of DNA that the team obtained from the remains of 108 people who were buried around 5,000 years ago in various megalithic tombs in Sweden and Denmark. The genetic material preserved in their relics allowed conclusions to be drawn about the family relationships and generational sequences of those buried in the respective tombs. In the DNA obtained, the team also found genetic material from the pathogens that infected the individuals at the time of their death.
Plague diagnosis in 17 percent of the dead
As the team reports, they found genetic traces of the plague pathogen Yersinia pestis in 18 of the 108 Neolithic people from the burial sites, some of which were far apart from each other. Since detection is only possible in some cases, a significant number of unreported cases is to be expected, the researchers emphasize. It is therefore likely that the pathogen caused very frequent infections among the Neolithic inhabitants of southern Scandinavia at times. In one of the families studied, whose members were buried in one of the graves over six generations over the course of around 120 years, at least three different plague outbreaks were evident. There are indications that the third and final wave in particular spread widely among the communities in southern Scandinavia.
In some cases, the DNA traces obtained also provided insights into the genetic characteristics of the Neolithic plague strains. It was again shown that they did not have a characteristic that is considered an important “killer factor” in the medieval versions: they still lacked the genetic features that enabled the bacteria to survive in fleas. In the case of the bubonic plague, these ensured the very effective transmission of the disease from rats to humans. But according to the researchers, it is also conceivable that the Neolithic strains had characteristics that could have enabled transmission from person to person or via lice. “In the case of the most recent plague strain we identified, there are also certain genetic indications that it may have had epidemic potential,” says Seersholm.
The researchers therefore see strong evidence in the results that the plague was involved in the Neolithic decline: “Since a significant proportion of the population appears to have been infected with the plague, excess mortality associated with the disease may have undermined the long-term viability of the affected communities, possibly leading to the collapse of some Neolithic societies,” the authors write. Seersholm concludes: “We cannot yet prove that this is what happened. But we have at least shown that it is possible,” says Seersholm.
Source: University of Copenhagen, Nature, doi: 10.1038/s41586-024-07651-2