DNA tracks ancient Mediterranean farmers to Scandinavia

Modern Europeans’ genetic profile may have been partly cultivated by early Mediterranean farmers who moved to what’s now Scandinavia, where they paired up with resident hunter-gatherers.

DNA taken from 5,000-year-old skeletons previously excavated in Sweden unveils a scenario in which agricultural newcomers from the south interbred with northern hunter-gatherers, say evolutionary genetics graduate student Pontus Skoglund of Uppsala University in Sweden and his colleagues. Their findings feed into a picture of many early migrations of farmers into Europe, which often would have included interactions with local hunter-gatherers.

Pieces of DNA extracted from an ancient farmer’s remains buried in southern Sweden display gene variants most like those found in people now living in Greece and Cyprus, the scientists report in the April 27 Science. DNA retrieved from the bones of three hunter-gatherers interred on an island off Sweden’s coast contains distinctive gene variants that most resemble those of native Finns.

Most Europeans today possess genetic arrangements in between those of the long-dead farmer and his hunter-gatherer neighbors, Skoglund’s team finds. Breeding between culturally discrete cultivators and foragers contributed to Europeans’ current genetic makeup, the researchers propose.

“Our data suggest that northern European farmers originated in Mediterranean Europe and were genetically distinct from northern hunter-gatherers some 5,000 years ago,” says study coauthor and evolutionary geneticist Mattias Jakobsson, also of Uppsala University.

Ancient DNA in the new analysis came from cell nuclei, a form of genetic material inherited from both parents. Researchers isolated and studied from 1 percent to 3 percent of the nuclear genome for each excavated individual.

Jakobsson  says the new nuclear DNA evidence challenges a 2010 investigation that traced genes extracted from the remains of members of a 7,000-year-old farming culture in Central Europe to current residents of Turkey and areas just to its east. That study, led by human paleobiologist Wolfgang Haak of the University of Adelaide in Australia, examined maternally inherited DNA from cell structures called mitochondria and the paternally inherited Y chromosome.

Archaeological finds point to several routes into Europe for early Middle Eastern farmers, Haak says. A Mediterranean-based farming group may have reached Scandinavia 1,000 to 2,000 years after an initial expansion of farmers from further east into Central Europe, he suggests.

Farming’s rise “was by no means a uniform process across Europe,” Haak says.

Investigators generally agree that farming originated about 11,000 years ago in the Middle East and reached Europe by around 7,000 years ago. Debate has long revolved around whether waves of advancing farmers chased off European hunter-gatherers or traded cultural practices with native groups that then took up agriculture (SN Online: 10/24/11).

DNA links between the ancient Swedish farmer and nearby hunter-gatherers show that agriculture spread across Europe with the aid of genetic as well as cultural exchanges, Jakobsson says.