Ancient farmers, foragers kept genes to themselves

Modern Europeans’ genetic roots took a surprising turn after farming’s introduction to the continent around 7,500 years ago, two studies suggest.

Farmers and hunter-gatherers lived alongside each other in Central Europe for 2,000 years without mating outside their own groups, according to one of the studies. Until now, researchers have primarily thought that farmers entering Europe from the east either drove out hunter-gatherers or quickly drew nomadic groups into a lifestyle of crop growing and animal raising.

Instead, at least one group of hunter-gatherers clung to its culture for a surprisingly long time despite regularly crossing paths with farmers, paleogeneticist Ruth Bollongino of the University of Mainz in Germany and her colleagues report October 10 in Science. It’s not known whether these hunter-gatherers eventually took up farming, left Central Europe or died out.

Her team analyzed mitochondrial DNA from 25 individuals buried in a German cave: five who died a few thousand years before agriculture’s onset and 20 from between about 6,000 and 4,900 years ago. Mitochondrial DNA is inherited only from mothers. Chemical compositions of the later skeletons revealed that 11 individuals had eaten primarily animals typical of early farmers, whereas nine had subsisted largely on freshwater fish.

Unlike the farmers, the fish-eaters shared some of their mitochondrial DNA profile with the earlier hunter-gatherers excavated in the cave. That suggested to Bollongino’s team that hunter-gatherers had continuously lived in the area since farmers had arrived but had not mated with them. 

“The surprise is that foragers and farmers had separate ways of life for 2,000 years even though they clearly interacted with one another, as their use of the same burial cave shows,” remarks archaeologist Stephen Shennan of University College London.

An extended, side-by-side coexistence of Central European farmers and hunter-gatherers fits with mitochondrial DNA evidence from the second study, published in the Oct. 11 Science. It analyzed DNA from 364 individuals who lived in what’s now Germany between 7,500 and 3,550 years ago.

A team led by University of Mainz graduate student Guido Brandt — working independently of Bollongino’s team — concludes that Central European farmers remained genetically distinct until about 5,000 years ago. Groups from other cultures and regions, including hunter-gatherers from southern Scandinavia, altered Central Europeans’ mitochondrial DNA profiles over the next 1,000 years, the researchers say.

Members of different Central European cultures from that time, previously identified by pottery styles and other material remains, possessed distinct mitochondrial DNA profiles, the researchers find. Entrants into Central Europe between 5,000 and 4,000 years ago, including early Bronze-working cultures, contributed substantially to the mitochondrial DNA of Europeans today, Brandt’s group proposes.

It’s not yet clear whether mitochondrial DNA patterns uncovered in Brandt’s study are consistent with those of ancient farmers and hunter-gatherers who lived elsewhere in Europe, comments evolutionary biologist Mattias Jakobsson of Uppsala University in Sweden. Mitochondrial DNA results also need to be compared with as-yet-unrecovered ancient DNA from cells’ nuclei, Jakobsson says, which makes up “the overwhelming part of the human genome.”