Last Stone Age hunter-gatherers avoided inbreeding

A genetic study of some of western Europe’s last Stone Age hunter-gatherers has revealed a possible strategy in ancient societies to avoid inbreeding.

It is the first time the genomes of several Stone Age hunter-gatherers who lived near new Neolithic farming communities have been analysed.

Researchers sequenced and analysed the complete genomes of 10 individuals found in modern-day France. The ancient people lived between about 8,300 and 6,760 years ago. They were found in 3 burial sites: Champigny in north-east France, and Téviec and Hoedic in the north-west.

Map of europe with burial sites identified with coloured triangles
Location of individuals and graves discussed in the text. Credit: Proceedings of the National Academy of Sciences (2024).

They lived during the late Mesolithic (Middle Stone Age) – a period of human cultural development which in parts of France persisted until about 6,500 years ago.

The beginning of the Mesolithic came about after the end of the last Ice Age. Mesolithic humans were still hunter-gatherers, but more temperate climate conditions saw significant changes in human society. This included new settlement patterns and technologies as well as the emergence of subsistence toward its end, leading to farming and animal husbandry during the age known as the Neolithic (New Stone Age).

New research published in the Proceedings of the National Academy of Sciences shows bloodlines and kinship were not the only factors involved in shaping these ancient communities. And different families living together might have been a strategy to avoid inbreeding.

“This gives a new picture of the last Stone Age hunter-gatherer populations in Western Europe,” says senior author Professor Mattias Jakobsson from Uppsala University, Sweden. “Our study provides a unique opportunity to analyse these groups and their social dynamics.”

With the emergence of Neolithic farmers, their relationships and interactions with the last hunter-gatherer groups is relatively unknown.

Previous research based on isotope data has suggested that the last hunter-gatherer communities deliberately assimilated women from their Neolithic neighbours. But the new genetic study shows that they mixed with other hunter-gatherers.

“Our genomic analyses show that although these groups were made up of few individuals, they were generally not closely related,” says first author Luciana G. Simões, researcher at Uppsala University. “Furthermore, there were no signs of inbreeding. However, we know that there were distinct social units – with different dietary habits – and a pattern of groups emerges that was probably part of a strategy to avoid inbreeding.”

Other research has also shown even isolated Mesolithic groups avoiding inbreeding.

The sites are unusual among Mesolithic burials because it had previously been assumed that individuals buried together must have been related.

“Our results show that in many cases – even in the case of women and children in the same grave – the individuals were not related,” says co-author Dr. Amélie Vialet from the Muséum national d’Histoire naturelle in France. “This suggests that there were strong social bonds that had nothing to do with biological kinship and that these relationships remained important even after death.”

How these living arrangements came to develop in these societies remains a mystery.

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