DNA from 5,500-year-old graves shows Stone Age hunter-gatherers buried extended kin, not parents

The graves at Ajvide on Gotland are among the best-preserved Stone Age burial sites in all of Scandinavia. Situated on a windswept island in the Baltic Sea, the site contains at least 85 known graves from a hunter-gatherer culture that thrived roughly 5,500 years ago - a group known as the Pitted Ware culture, who survived primarily by hunting seals and fishing while agricultural practices had already spread across much of Europe to the south.

Among those 85 graves, eight contain two or more individuals buried together. That co-burial practice has long fascinated archaeologists, but understanding the relationships between those individuals required a tool unavailable to earlier researchers: ancient DNA analysis. Uppsala University scientists have now analyzed genetic material from 10 individuals across four of those shared graves, and the results challenge a common assumption about who was buried with whom.

Extended kin, not immediate family

The assumption, natural enough, is that people buried together would be the people closest to them in life - a parent and child, or perhaps siblings. The DNA tells a different story. In the four graves analyzed, the individuals were typically second- or third-degree relatives: grandparents and grandchildren, half-siblings, cousins, or great-aunts and nieces. First-degree relationships - parent and child or full siblings - were the exception rather than the rule.

The most striking example is the first grave examined. A woman in her early twenties was found lying on her back with two young children - a boy of about four and a girl of about 18 months - positioned on either side of her. The children are full siblings, sharing both parents. But the woman is not their mother. Genetic analysis indicates she is most likely their paternal aunt - their father's sister - or possibly a half-sister.

In the second grave, a young girl was buried alongside the remains of an adult man who appears to have been moved to the grave from somewhere else - his remains showed signs of prior burial. The man was her father. In the third grave, a boy and a girl buried together were found to be cousins rather than siblings. The fourth grave held a girl and a young woman who were third-degree relatives, with one likely being the other's great-aunt or cousin.

"Surprisingly enough, the analysis showed that many of those who were buried together were second- or third-degree relatives, rather than first-degree relatives - such as parent and child or siblings - as is often assumed," said archaeogeneticist Helena Malmstrom of Uppsala University, who designed the study. "This suggests that these people had a good knowledge of their family lineages and that relationships beyond the immediate family played an important role."

What kinship knowledge implies about social structure

Tracking family relationships beyond the nuclear household requires social memory that persists across generations. Knowing that two children share a father's sister, or that two individuals are cousins, means maintaining genealogical knowledge across multiple family lines. For a small, mobile hunter-gatherer group in the Neolithic Baltic, that level of kinship tracking implies a sophisticated social organization - one where extended family networks were not just recognized but actively meaningful.

The presence of children in most of the shared graves is also notable. At least one child was found in three of the four graves. Whether children were specifically chosen to accompany older relatives in death, or whether child mortality rates and the social significance of young children drove this pattern, cannot be determined from the genetic analysis alone. But the pattern is consistent enough to suggest intent rather than coincidence.

Methods and limitations

Sex determination was performed by analyzing whether individuals carried two X chromosomes (female) or one X and one Y chromosome (male) - a method particularly useful for children, whose skeletal features do not yet show adult sex differences reliably. Kinship was determined by calculating the proportion of shared DNA: first-degree relatives share approximately half their DNA, second-degree relatives share a quarter, and third-degree relatives share an eighth.

The study analyzed only 10 individuals from 4 of the 8 co-burial graves at Ajvide. The full burial ground contains 85 graves, with most holding single individuals. Whether the kinship patterns observed in the shared graves are representative of broader social structures at the site - or reflect specific circumstances like epidemic mortality, ritual practices, or family tragedies - cannot be determined from this pilot study alone.

The researchers plan to continue with interdisciplinary analysis of the remains of more than 70 individuals from the entire burial ground, combining genetic data with archaeological evidence about grave goods, body positioning, and site stratigraphy to build a more complete picture of Pitted Ware social organization.