The authors next built mathematical models that describe how ancient populations might have interacted as they moved from place to place.
The models show that for each of the three regions included in the study, the arrival of farmers prompted interbreeding with local hunter-gatherers. This trend was seen repeatedly over time, with the liaisons leaving distinct genetic signatures in each geographical region.
“I think, by nature, groups of people are more likely to mix and interact than not, regardless of cultural differences,” Lipson said. “We do find, though, that the admixture continued over an extended period, so it wasn’t all immediate.”
The liaisons appear to have been particularly consistent, however, in Hungary, the region in which the researchers had the most number of ancient DNA samples.
The data also suggest that farmers tended to travel a lot, while hunter-gatherers were more apt to stay fairly close to home.
“High population densities among farmers led them to expand to additional arable land,” Lipson said. “During this period, it seems likely that hunter-gatherers were not migrating such long distances, but our knowledge is not complete.”
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It would appear to be equally challenging to distinguish hunter-gatherers from farmers in the archaeological record and from DNA. Lipson indicated that the differences between the two are surprisingly not too difficult to tease apart.
He explained that artifacts and remains left behind by farmers and hunter-gatherers are distinctive to each group.
“On an individual level, differences in diet can also be detected by isotope ratios in bones and teeth,” he said. “And in places where farmers and hunter-gatherers are genetically differentiated, we can measure that by comparing their relationships to other populations.”
The DNA evidence further sheds light on the origins of the Neolithic farmers. Most appear to have been migrants from Anatolia, an area that today falls within Turkey. In geographic terms, this is the area bounded to the north by the Black Sea, to the east and south by the Southeastern Taurus Mountains and the Mediterranean Sea, and to the west by the Aegean Sea and the Sea of Marmara.