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DNA analyses show the plague may have caused the downfall of Stone Age farmers

The plague may have caused the downfall of the Stone Age farmers
One of the complete skeletons found in the Frälsegården passage grave (Individual B/FRA043). The skeleton is that of a 30-40 years old woman, related only in the second degree to individuals in the kinship tree. According to strontium isotopes in her teeth she was born outside the sedimentary geology of Falbygden, probably in a neighboring region of western Sweden. The cranium was removed earlier during the excavation.  Credit: Karl-Göran Sjögren.

Ancient DNA from bones and teeth hints at a role of the plague in Stone Age population collapse. Contrary to previous beliefs, the plague may have diminished Europe's populations long before the major plague outbreaks of the Middle Ages, new research published in the journal Nature shows.

In the 14th century Europe, the ravaged the population during the so-called "Black Death," claiming the lives of nearly a third of the population.

But the plague arrived in Scandinavia several thousand years earlier, and despite several theories suggesting otherwise, the plague might have caused an epidemic, according to new research from the University of Copenhagen.

In collaboration with researchers from the University of Gothenburg in Sweden, researchers from the Globe Institute, have analyzed DNA from ancient teeth and bones of 108 individuals who died 5,000 years ago.

"The analyses show that 18 of these individuals, 17%, were infected with the plague when they died. Furthermore, our results suggests that the youngest plague strain we identify might have had epidemic potential," says postdoc Frederik Seersholm, who led the DNA analysis.

This means that the plague at that time may have been a contributing factor to the population collapse in the end of the Neolithic, known as the Neolithic decline. This population bust caused large parts of the farming population in Scandinavia and Northwestern Europe to disappear within just a few centuries, 5,000 years ago.

The plague may have caused the downfall of the Stone Age farmers
The skulls of the two second generation individuals in the right branch, FRA022 and FRA023, placed beside a limestone slab covering the ancestral individual, FRA021. Credit: Karl-Göran Sjögren.

"We cannot—yet—prove that this was exactly how it happened. But the fact that we can now show that it could have happened this way is significant. The cause of this , which we have known about for a long time, has always been subject of debate," says Seersholm.

The archaeological material analyzed comes mainly from passage graves in Sweden, but one of the individuals is from a stone cist in Stevns, Denmark.

Ancient DNA provides answers

The analyses were conducted using a method called "deep shotgun sequencing," which allows researchers to extract highly detailed information from , even though ancient DNA is often heavily damaged or degraded. The researchers examined DNA from tooth and bone material from the Neolithic time period, studying both familial relations and diseases in the individuals.

The plague may have caused the downfall of the Stone Age farmers
Excavation of the Frälsegården passage grave in 2001. The bones were labeled and measured individually with a total station.  Credit: Karl-Göran Sjögren

"We have been able to carry out a comprehensive mapping of plague lineages, and a detailed description of other microbes in the DNA data. At the same time, through these analyses, we have been able to look at the human DNA from a broad perspective to a local one—and right down to the individual level, getting a picture of the social organization that existed back then," says Associate Professor Martin Sikora at the Globe Institute, who is also behind the study.

The finding that 17% of the individuals whose DNA was analyzed had plague, indicates that the plague was common in Scandinavia during the late Stone Age.

In one of the analyzed families, at least three plague outbreaks were observed over the six generations in the family that researchers have been able to map.

"The question of possible kinship relations between individuals whose bones and teeth have been found in megalithic tombs has been debated for at least 200 years. There have been many theories and speculations, but now, thanks to DNA, we have data," says Karl-Göran Sjögren, Associate Professor of Archaeology at the University of Gothenburg, who was also involved in the new study.

The plague may have caused the downfall of the Stone Age farmers
Plague spread in Neolithic Scandinavia. Each individual in the study is represented by colored shapes. Only Neolithic individuals are show. Squares represent males and circles females; triangles represent a person of unknown sex. Colors indicate genetic ancestry, and black crosses designate individuals with the plague. Credit: Seersholm et al., Nature (2024)

Seersholm believes that the new results rule out previous theories suggesting that the population decline could not have been caused by plague.

"In connection with the population decline in the end of the Neolithic, both war and outbreaks of infectious diseases, including plague, have been suggested. There have been several theories involving the plague, and one of them suggested that the plague could not have caused an epidemic—but that assumption no longer holds," says Seersholm.

More information: Frederik Seersholm, Repeated plague infections across six generations of Neolithic Farmers, Nature (2024). DOI: 10.1038/s41586-024-07651-2. www.nature.com/articles/s41586-024-07651-2

Journal information: Nature

Citation: DNA analyses show the plague may have caused the downfall of Stone Age farmers (2024, July 10) retrieved 19 July 2024 from https://phys.org/news/2024-07-dna-analyses-plague-downfall-stone.html
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