George Busby went to hear Harvard professor David Reich speak about his latest research on European ancestry in Oxford on 9 February 2015
Archaeologists who have dated the earliest stone tools, pots, and agricultural implements found in Europe tell us that agriculture spread across the continent from its Middle Eastern origin slowly over the period 10,000 to 4,000 years ago. Most European, and many non-European languages, have a common origin and belong to a large language group known as Indo-European. Based on the distribution of Indo-European languages today, linguists believe that they probably spread into Europe from the east at some point in the last 10,000 years.
But big questions remain. Did people move with culture? And where, geographically, did various innovations first arise? These questions are now being addressed with genetics, specifically by the sequencing of DNA from people alive thousands of years ago. By understanding the genetic code of people alive at different times, in different places, associated with different archaeological material, researchers can gain unprecedented insight into historical movements in Europe.
To a packed auditorium, David Reich of Harvard Medical School described how he and his colleagues are attempting to do just this by generating and analysing genetic data from almost 100 people who were alive in and around Europe 10,000 to 2,000 years ago. DNA degrades over time, making isolating and sequencing genetic material from ancient samples particularly tricky. Typically, researchers have tried to reconstruct the whole of an ancient human’s genetic sequence, aiming to cover each part of the genome at least once, a process that requires a large amount of DNA.
Reich’s team has developed a new technology that targets a small number of specific genetic loci, meaning that they need a far smaller amount of DNA to get meaningful genetic data from ancient samples. In the first of many surprises, he told us that this allowed them to generate comparable genetic information from almost double the total number of ancient humans previously available.
They sequenced people from five European countries: Spain, Germany, Hungary, Sweden, and Russia. Crucially, they were associated with a range of archaeological contexts, from the early Neolithic (~8000 BCE; before the common era) to the late Bronze Age (~2000 BCE), linking the people’s genes to their lifestyles and cultural artefacts.
Europe was originally populated by hunter-gatherers. Because the ancient farmers were more closely related to Middle Easterners than ancient hunter-gatherers, we heard, the people who farmed must have come later, bringing agricultural technologies from the Middle East with them.
He next told us that the spread of these farmers was not smooth, and that after the initial influx of farming DNA, there was a rebound in hunter-gatherer ancestry across most, but not all, Middle Neolithic groups. Surprisingly, this meant that some people had forebears from the same place who had more farming ancestry than themselves. In contrast, individuals from a Russian group known as the Yamnaya showed a reduction in hunter-gatherer ancestry, as well as an affinity to populations from the Caucasus and South Asia, a relationship that Reich did not see in any of the ancient farmers. He followed this with the most intriguing result of the night: all individuals analysed from within Europe who were alive after this time (during the Late Neolithic and Bronze Age), as well as almost all contemporary European populations, show evidence of shared ancestry with the Yamnaya.
Within Europe, this “steppe” ancestry is seen for the first time at around 2500BCE in individuals associated with Corded Ware culture – a large suite of related artefacts found across northern Europe. Out of all the ancient populations analysed in the study, the Corded Ware were most genetically similar to the Yamnaya, a strange result given the large geographical distance between the two groups. This key, novel, insight suggests that there was a considerable pulse of steppe ancestry into Europe between 4000 and 5000 years ago.
It is the identification of this second mass migration of individuals into Europe that makes this work enormously significant. One hypothesis on the origins and expansion of Indo-European languages into Europe proposes a spread out of Anatolia (modern day Turkey) roughly 8000 years ago. A competing hypothesis suggests that the first Indo-Europeans came from the eastern European steppe roughly 4500 years ago, with people who first tamed horses and invented the wheel. A large turnover in the population of Europe around 5000 years ago is incompatible with the Anatolian hypothesis, and the ubiquitous Yamanaya ancestry across many ancient and contemporary populations provides compelling, if not incontrovertible, evidence for a steppe origin.
It appears then that Indo-European languages were unlikely to have spread with agriculture, but instead with the Corded Ware. An archaeologist present cautioned that the Corded Ware is unlikely to represent an homogeneous unified group, but recognised that genetic evidence of a mass migration from the steppe does have support within the field. Reich’s team is still unable unambiguously to link the spread of Indo-European languages to the spread of Corded Ware, but this important work has shown the utility of sequencing multiple ancient individuals across multiple time points, in uncovering fresh insight into our past.