The researchers have studied DNA samples from stone age graves. The samples come from 19 people who were hunters and gatherers and lived in Scandinavia until about 4,000 years ago.
The DNA has then been compared with common DNA sets collected from contemporary residents of the region.
“They differ very substantially. The gene pool that we have today could not have evolved by chance alone from that which existed then. Something else must have been added. Either a complete population replacement or gene flow,” said Anders Götherström, who led the study at Uppsala University.
Götherström explains that the gene pool must have been mixed.
“We have not quantified the results so we do not know that much, but my initial conclusion is that it is a mix. But there has to have been an immigration. The gene pool among the hunters and gatherers is not sufficient,” he said.
Götherström led the study which has involved researchers from Denmark and the UK.
According to the researchers the hunters and gatherers lived side by side with groups that began to till the soil. These farmers started to turn up in Scandinavia during the so-called new (Neolithic) stone age, from around 4,000-1,800 BC.
The study, which has been presented in the scientific journal Current Biology, also included analysis of DNA samples taken from three farmers buried at around the same time.
Among the hunters and gatherers there was no trace of the DNA sets common in the region today.
“But we found them in the farmer group,” Götherström revealed.
Götherström said that the researchers have concluded that there is only one direction from where the presumed wave of immigrants could have come.
“That is from the south. But from where and how far they have travelled, is difficult to say.”
The study will now continue and will include the collection and analysis of more samples collected from individuals belonging to the farmer group.
The purpose is to discern from where the immigrants may have come, Götherström said.
“Now want to know more exactly where they may have come from.”