Family relationships identified in Stone Age graves on Gotland

(Press-News.org) A woman was buried with two children, but they were not her own. In another grave, two children were placed. They were not siblings and were more distantly related, perhaps cousins. In a new study, researchers at Uppsala University have clarified family relationships in four graves from a 5,500-year-old hunter-gatherer culture at Ajvide on Gotland. DNA analyses suggest that the people were well aware of family lineages and that relationships beyond the immediate family played an important role.

Ajvide is one of the most important Stone Age sites in Scandinavia and is known for its well-preserved graves and rich archaeological finds. Around 5,500 years ago, hunter-gatherers lived there, supporting themselves primarily by hunting seals and fishing. By this time, agriculture had spread across Europe, but in the north, hunter-gatherer cultures persisted and remained genetically distinct from the farmers.

The large burial site contains 85 known graves. Among the findings here, eight graves have been discovered that hold two or more individuals. Researchers at Uppsala University have now analysed DNA from the remains that lay in four these shared graves to investigate the kinship between the individuals. 

“Surprisingly enough, the analysis showed that many of those who were buried together were second- or third-degree relatives, rather than first-degree relatives – in other words, parent and child or siblings – as is often assumed. This suggests that these people had a good knowledge of their family lineages and that relationships beyond the immediate family played an important role,” says archaeogeneticist Helena Malmström, who was responsible for the design of the study.

At least one child in most graves

In one of the graves, a 20-year-old woman was found lying on her back. Two children lay on either side of her, one of them was a four-year old and the other a one-and-a-half years old. The DNA analysis shows that the children – a boy and a girl – are full siblings, but that the woman is not their mother. She is most likely their father’s sister or their half-sister.

In the second grave, a young individual was discovered. Lying alongside were the remains of an adult man that had probably been moved to the grave from somewhere else. The analysis shows that the young person was a girl and that the man is her father.

In the third grave, two children – a boy and a girl, were buried together. Their relationship was a little more distant and was measured as third-degree, which likely means they were cousins.

In the fourth grave, there was a girl and a young woman. The analysis showed that they were third-degree relatives, with one of them probably being the other’s great-aunt or cousin.

“As it is unusual for these kinds of hunter-gatherer graves to be preserved, studies of kinship in archaeological hunter-gatherer cultures are scarce and typically limited in scale,” says population geneticist Tiina Mattila, who had lead responsibility for the genetic analyses.

“The analyses provide insight into social organisation in the Stone Age,” says Paul Wallin, Professor of Archaeology and an expert on the Ajvide burial ground.

The archaeogenetic analysis of the co-burials in Ajvide burial ground is the first pilot study exploring family relationships among Scandinavian Neolithic hunter-gatherers. The researchers will now continue with interdisciplinary studies of the remains of more than 70 individuals from the burial ground. In this way, they hope to learn more about the social structure, life histories and burial rites of the ancient hunter-gatherer cultures.

Facts: How sex and kinship were determined

The researchers were able to find out sex and kinship by analysing DNA from teeth and bones from the ten individuals. The children’s sex cannot be seen from the skeletons but could be determined by investigating whether the deceased had two X chromosomes (girl) or one X and one Y chromosome (boy). Kinship could be identified by looking at how large a proportion of the DNA the individuals share. Individuals who are first-degree relatives, such as parents and children or full siblings, share half of their DNA. Second-degree relatives, such as grandparents and grandchildren or half-siblings, share a quarter of their DNA. Cousins or great-grandparents and great-grandchildren are third-degree relatives and share an eighth of their DNA.

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