A newly-published genetic study of ancient DNA obtained from prehistoric human remains in Sweden has provided a fresh insight into the transition to agriculture in Scandinavia.
The ability to obtain DNA from the remains of prehistoric people has in recent years added a new dimension to the long-running quest to understand the demographics of the transition from hunter-gathering to farming in Neolithic Europe. Studies based on living populations have been unable to provide definitive answers, as ancient genetic signals are often blurred by far more recent events.
Researchers at Stockholm University and Uppsala University obtained genetic material from the remains of six hunter-gatherers and four farmers from the Scandinavian Neolithic, dating to around 5,000 years ago, together with a late Mesolithic hunter-gatherer from 7,500 years ago. The samples were obtained from mainland Sweden and the Swedish island of Gotland.
It was found that the genetic diversity of the hunter-gatherers was far lower than that of the farmers and of any present-day Eurasian populations, suggesting that their population sizes were very small. Fluctuating climatic conditions and/or restricted carrying capacities might have affected hunter-gatherer population sizes. It is also possible that the genetic diversity of the hunter-gatherers never recovered from population crashes occurring during the Last Glacial Maximum when European populations were confined to a few ice-free refugia.
A significant finding was that the hunter-gatherer and farming populations were genetically distinct from one another, confirming the view that agriculture was spread across Europe by migrating farmers, rather than by indigenous hunter-gatherers simply taking up farming. In other words, it was farmers and not just farming that spread.
The researchers also found evidence for genetic admixing between the hunter-gathering and farming communities – but it was one way. Hunter-gatherers apparently married into the farming communities, but not the other way round. Thus the expanding farming communities assimilated indigenous hunter-gatherers.
The study, published in the journal Science, is part of a recently-launched initiative to investigate ancient human remains in Scandinavia. Known as the Atlas project, it is being conducted by researchers at Stockholm University and Uppsala University.
1. Skoglund, P. et al., Genomic Diversity and Admixture Differs for Stone-Age Scandinavian Foragers and Farmers. Science (2014).