A rare Stone Age cemetery on a Swedish island reveals that some of Europe's last hunter-gatherers were buried not with their extremely close relations but with more distantly related people, according to a new DNA analysis.
However, some burials had close biological family members, including that of a teenage girl whose father's jumbled bones had been placed on top and next to her, the researchers found.
Since the site was first excavated in 1983, Ajvide on the western Swedish island of Gotland has yielded 85 graves from the Pitted Ware culture, a hunter-gatherer society that lived in the area 5,500 years ago. Although agriculture had spread across Europe along with farming communities at this time, some hunter-gatherer groups continued to live in Scandinavia, primarily hunting seals and fishing.
Ajvide was occupied for at least four centuries, and archaeologists have found tons of pottery and animal bones, in addition to a cemetery. Excavation of the cemetery revealed that eight graves contained more than one person. Researchers originally assumed that the people in the graves were closely related. But advances in ancient DNA analysis raised the possibility of fully investigating familial relationships in the Ajvide cemetery.
"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," Tiina Mattila, a population geneticist at Uppsala University, said in a statement. Mattila led the genetic analysis of four of the burials, and the study was published Wednesday (Feb. 18) in the journal Proceedings of the Royal Society B.
In one grave, excavators had found an adult female skeleton along with the skeletons of two young children. The researchers' DNA analysis revealed that the children were a boy and a girl who were full siblings. The woman, however, was not their mother and may have been their father's sister or their half-sister.
A second grave contained the skeletons of a boy and a girl buried together. DNA analysis showed that they were third-degree relatives – who share one-eighth of their DNA – and likely cousins. In the third grave, DNA analysis of the skeletons of a girl and a young woman revealed they were also third-degree relatives, likely cousins or a great-aunt and great-niece.
And in the fourth grave, there was a young teenage girl buried on her back in an outstretched position, with a pile of bones on top and next to her. Using DNA analysis, the researchers discovered that the bones were those of the girl's father. His death probably predates hers, and his bones had likely been dug up and moved to his daughter's grave from elsewhere, the researchers said.
"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," study co-author Helena Malmström, an archaeogeneticist at Uppsala University, said in the statement. "This suggests that these people had a good knowledge of their family lineages and that relationships beyond the immediate family played an important role."
This study of the Ajvide burials is the first to explore family relationships among Scandinavian Neolithic hunter-gatherers, according to the statement. But more work is planned, as the researchers will now analyze all the skeletons recovered from the cemetery to learn more about ancient hunter-gatherer social structure, life history and burial rites.
