March 02, 2015
The new study reports genome wide data from more than twice as many samples of ancient Eurasians as the preceding literature. “This reflects a sea change in ancient DNA studies, in which it has now become possible to collect whole genome data from dozens of individuals at once,” says David Reich of Harvard Medical School, the Broad Institute, and the Howard Hughes Medical Institute, who led the study. “We isolated parts of the genome that are most informative about history and only sequenced those.” This technique makes it practical to screen and study large numbers of ancient samples.
By studying genome-scale data from more than 90 ancient European individuals ranging from 3,000 to 8,000 years old, the study documents two major population replacements:
The first was the arrival of Europe’s first farmers, who had expanded from Near East more than 9,000 years ago and had reached Central Europe and the Iberian Peninsula in the West by 7,500 years ago. The pottery they made looked very different, and some archaeologists have suggested that they were unrelated to each other and came from two separate migration waves. But the genetic data suggests otherwise. Wolfgang Haak, a geneticist at the University of Adelaide, and co-first author of the new study, observes: “The first farmers, whether from Hungary, Germany or Spain, are genetically almost identical: they are from the same origin.”
Remarkably, the hunter-gatherers that lived in Europe before the first farmers did not disappear. “By 6,000-5,000 years ago, a resurgence of hunter-gatherer ancestry had occurred in agricultural populations across Europe,” says Iosif Lazaridis, a postdoctoral fellow at Harvard Medical School, and the other co-first-author of the new study. “This shows that populations with substantial hunter-gatherer ancestry persisted in parts of Europe even after the arrival of the first farmers.” “This also shows that hunter-gatherers had been slowly but steadily integrated into farming communities”, adds co-author Professor Kurt Alt from the Danube Private University Krems and University Basel, Switzerland.
In earlier studies, several of the same authors had shown that Europeans today are a mixture of three very different ancestral populations: hunter-gatherers, first farmers, and a population with eastern affinities that was not yet present in Europe at the time of the first farmers. It was unclear when and how this eastern component arrived in Europe. “When we first looked at the new data, it was a Eureka moment,” says Lazaridis. “The eastern ancestry was present in every single sample starting at around 4,500 years ago, and absent in every single one before that time.”
Haak goes even further: “The great power of the genetic data can be seen from the fact that we could go almost as far as to genetically date samples based on whether they have one, two or all three of the components. Indeed, three individuals were assigned based on their archaeological context to a period older than 4,500 years ago and yet the genetics revealed that all had eastern ancestry. The team then decided to commission radiocarbon dates: “The noticeable similarity of Corded Ware and Yamnaya cultures is also seen in their material remains. This affinity could now also be testified scientifically.”, adds co-author Professor Harald Meller, director of the State Museum of Prehistory in Halle, which provided a substantial number of prehistoric specimens.
“People associated with the Corded Ware culture are the first group with evidence of the eastern ancestry and also have the most, suggesting a major genetic turnover around this time” says Dr Haak. “We estimate that around 75% of the ancestry of the Corded Ware people in Germany came from a population related to the Yamnaya people who were steppe pastoralists from Russia expanding westwards,” says Lazaridis, adding that “the Corded Ware and the Yamnaya are genetically very similar despite living 2,600 km apart”.
This large migration from the east almost certainly had lasting effects on the languages people spoke. “Our results make a strong case that the Corded Ware people, who were overwhelmingly of steppe origin, also spoke a steppe language,” says Lazaridis. ”Since the people that succeeded the Corded Ware in northern Europe also trace more of their ancestry to the steppe than to the first farmers, it seems likely that the steppe migrants contributed at least some of the Indo-European languages”, concludes Haak. Reich adds: “These results challenge the theory that all Indo-European languages in Europe today owe their origin to the arrival of the first farmers from Anatolia more than eight thousand years ago.”
“The combination of archaeology, linguistic and genetic data is highly controversial and has been treated like a hot potato”, adds co-author Professor Johannes Krause, director Max Planck Institute for the Sciences of Human History in Jena. “But these are very exciting times and we’ve already scheduled a workshop later this year to tackle old and newly arising questions with experts from all three disciplines”.
For example, the new study doesn’t solve the centuries-old problem of the location of the homeland of all Indo-European languages, which are distributed widely not only in Europe but in Asia. However, Reich, Haak and the team are optimistic that a solution to the problem of Indo-European origins may be within reach, despite the magnitude of the task: “The priority now is to carry out similar ancient DNA studies to understand how the people of Europe 3,000-6,000 years ago were linked with those in Turkey, the Caucasus, Iran and India.”
The study is a joint international effort involving leading researchers from German universities in Mainz and Tübingen, the State Museum of Prehistory in Halle (Saale), as well as the newly established Max-Planck Institute for the Science of Human History in Jena, with substantial funding from the German Research Foundation. About half of the samples came from excavations in Saxony-Anhalt, where a huge number of new finds had been recovered due to major roadworks.