NEW YORK (GenomeWeb News) – A new study of ancient DNA suggests modern-day Scandinavians do not belong to an unbroken line linked to ancient hunter-gatherers, but instead are likely descendents of a group that arrived in the region with the advent of agriculture.
Researchers from Sweden, Denmark, and the UK assessed genetic sequences from 4,000 to 5,500-year-old human remains found in Sweden and a neighboring island. The samples represent individuals from two groups: one that had a hunter-gather lifestyle and another that was agricultural. The research, which appeared online yesterday in Current Biology, suggests individuals living in Scandinavia today are more closely related to the immigrant agricultural group than to the hunter-gather group.
"The hunter-gatherers who inhabited Scandinavia more than 4,000 years ago had a different gene pool than ours," co-senior author Anders Götherström, an evolutionary biologist at Sweden's Uppsala University, said in a statement.
Although much of northern Europe had moved from a foraging, hunter-gather lifestyle to a more agricultural lifestyle by around 6,700 years ago, the researchers explained, this transition was slower in Scandinavia, where hunter-gather groups existed until around 4,000 years ago.
Past research suggests a group known as the Funnel Beaker Cultural (Trichterbecher Kultur), or TRB, complex arrived in Scandinavia roughly 6,000 years ago, apparently co-existing with foragers — including those in the Pitted Ware Culture, or PWC, the last known hunter-gatherers in the region — for at least 1,000 years.
But the origin of the hunter-gather PWC group and their relationship to modern-day Scandinavians, if any, is poorly understood. Because the oldest archeological evidence for the PWC group, found in coastal parts of Sweden and the nearby Baltic islands, is from around 5,300 years ago, some suspect they arrived after the agricultural TRB group. Others have speculated that the PWC were descendents of older hunter-gatherer groups or were individuals from TRB group who reverted to a hunter-gather lifestyle.
"The driving force behind the transition from a foraging to a farming lifestyle in prehistoric Europe (Neolithization) has been debated for more than a century," Götherström and his co-authors wrote. "Of particular interest is whether population replacement or cultural exchange was responsible."
To explore this further, the researchers used a Roche Genome Sequencer FLX to sequence 316 base pairs of ancient mitochondrial DNA from 22 Stone Age skeletons. They also evaluated the total amount of human DNA in each sample with quantitative real-time PCR.
Three of the samples are 4,500 to 5,500-year-old skeletal remains from TRB individuals found in Gökhem, Sweden, and the other 19 are 4,000 to 4,800-year-old samples collected on the Baltic island of Gotland, representing PWC individuals.
The team's subsequent analyses of the mtDNA showed that individuals from the hunter-gatherer PWC belong to mitochondrial haplogroups rarely detected in modern-day Scandinavians. Instead, the genetic patterns in PWC samples more closely resemble those found today in the eastern Baltic areas, such as Latvia and Lithuania, suggesting the PWC may have been ancestral to these populations instead.
"[T]he data analyses are consistent with a view that the eastern Baltic area remained a genetic refugia for some of the European hunter-gatherer populations," the authors noted. "Although the hunter-gatherer lifestyle was culturally replaced here, as in Scandinavia, the populations of the eastern Baltic area may have kept a certain level of population continuity."
While they did not rule out the possibility that the PWC descended from another hunter-gather group in northern Europe, the team concluded that it's very unlikely, based on the evidence so far, that there was a continuous lineage from the PWC and other hunter-gatherer populations to the populations in Scandinavia today. Rather, they say, agricultural groups seem to have migrated into the area and replaced the existing populations.
"[S]ome form of migration to Scandinavia took place, probably at the onset of the agricultural Stone Age," co-author Petra Molnar, a researcher at Stockholm University's Osteoarchaeological Research Laboratory, said in a statement. "The extent of this migration is as of yet impossible to determine."