DNA techniques unravel a prehistoric mass murder
Fifteen women, children and young men, each killed by blows to the head. Presumably in a massacre. But who were they? Many questions needed to be answered when archaeologists and genetic researchers collaborated in trying to understand the origins of a 5000-year-old mass grave in southern Poland. The results provide a unique perspective on a Europe affected by mass migration and violent conflicts.
Dramatic images are available of mass graves from recent massacres such as those in Bosnia and Herzegovina or Iraq. The bodies are often thrown into the graves like cattle – randomly and on top of each other. However, the mass grave archaeologists discovered near the village of Koszyce in southern Poland looked completely different. The skeletons were not randomly laid out. The 15 bodies had been carefully arranged, with some lying in pairs and some in groups. This intrigued the researchers so much that they decided to investigate who the 15 people were and why they were positioned as they were.
“We used radiocarbon dating and DNA techniques to unravel a family tragedy from the late Neolithic period. There is a mother with her children. A grandmother with her two sons. And two younger brothers together. The bodies were also flanked by grave goods, which indicates that those who buried the dead knew them well. The DNA also shows that the bodies were from Europe’s Neolithic population and not the people from the Pontic steppe who were expanding westward into Europe at that time,” explains a main author, Morten Allentoft, Associate Professor, Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen.
Three missing fathers
The bodies were buried 5000 years ago. Obtaining these exciting results would not have been possible a few years ago given the limited amount of DNA available because it degrades with time. This required the use of highly optimized ancient DNA technology combined with powerful next-generation sequencing machines to map the complete genome of each of the 15 skeletons.
“Previous studies have shown that we should try to take samples from the petrous bone inside the cranium. This is very hard, which means that the DNA is often extremely well preserved and not contaminated by other DNA such as that from soil bacteria. We extracted DNA from the right petrous temporal bone of all the skulls and successfully sequenced the genomes of the 15 skeletons in the grave.”
The researchers combined modern gene-sequencing methods with archaeological methods, including carbon-14 dating, and determined not only when the 15 people had lived and how they died but also whether the people buried in the grave had been related.
“We concluded that they had been murdered, because they all had massive trauma to the head, but a real eye-opener was that the DNA analysis revealed that this was a large extended family comprising four nuclear families.”
Although this was mass murder, the bodies had been buried very carefully, and painstaking genetic analysis enabled the researchers to determine exactly how the 15 people were related and how this influenced where they were positioned in the grave.
“They were not randomly positioned in the grave. An adult was next to a child. They turned out to be mother and daughter, and two young men lying next to each other turned out to be brothers. Everyone in the grave was a woman, a child or a young man. However, three fathers were missing. So our theory is that the fathers were absent at the time of the murders, discovered their murdered relatives when they returned to the settlement and then buried them.”
DNA: our new history books
Besides the kinship among the 15 people in the grave, the researchers also determined the culture of these people. Archaeologically, they belong to the Globular Amphora culture that existed around 5000 years ago in Europe during the late Neolithic period. Genetically, they are also part of the typical Stone Age population in Europe.
“These murders occurred during a violent era in European prehistory. Five thousand years ago, the people of Europe experienced a reduction in Neolithic genomic ancestry as Yamnaya cultures migrated from the Pontic steppe. We demonstrated this in previous studies. But the DNA shows that the 15 people in the mass grave were Stone Age farmers with no steppe ancestry. Of course, we can never find out who killed them, but this extended family in Koszyce might very well have been killed as a result of territorial conflict during this dramatic time.”
Niels Nørkjær Johannsen from the Department of Archaeology and Heritage Studies of Aarhus University came up with the idea of carrying out the DNA study of the mass grave in Poland. One goal was to reveal some of the prehistory of the European peoples, which was not particularly well known. The skeletons in the mass grave played a very special role in this.
“DNA analysis is helping to determine our prehistory, and typically we can only make general conclusions about the scale of population migration. But this grave reflects a specific event in a specific village and family and therefore provides us with a snapshot of an important and very violent time of transition in Europe,” says Niels Nørkjær Johannsen.
”Unraveling ancestry, kinship, and violence in a Late Neolithic mass grave” has been published in Proceedings of the National Academy of Sciences of the United States of America. Co-author Simon Rasmussen is Associate Professor, Novo Nordisk Foundation Center for Protein Research, University of Copenhagen.