The modern European and Central Asian gene pools are the result of mass migrations during the Bronze Age, according to a new analysis of ancient human remains.
In a collaboration between geneticists, archaeologists and linguists, the researchers conclude that the major cultural changes seen during the period 3,000 to 5,000 years ago are the result of the movement of large numbers of people into Eurasia, rather than a movement of ideas between existing Eurasians and outside populations.
Analysing the genomes of 101 people whose lives in Eurasia spanned the Bronze Age, palaeogenomicists Morten Allentoft and Eske Willerslev of the Natural History Museum of Denmark in Copenhagen were able to build up a picture of how the origins of the populations of Eurasia changed over time. Writing in Nature, they say that 'the European and Central Asian gene pools towards the end of the Bronze Age mirror present-day Eurasian genetic structure'.
At the beginning of the Bronze Age, Europeans appear to have a mixture between hunter-gatherers and late Stone Age farmers. This changed about 5,000 years ago to include a large genetic input from Caucasian populations originating in the area between the Black and Caspian seas. At the same time, the Yamnaya culture emerges in the archaeological record, bringing with it changes to burial rituals and family structure.
Beginning in 2,000 BC, the Sintashta culture also spread rapidly across Europe and into Asia, bringing with it skills in chariot-building and advanced weaponry. But the genetic analysis shows that these people were later completely replaced in Central Asia by people of East Asian origin.
The study also revealed the origins of specific genetic traits. Genes for lactose tolerance, which gives adults the ability to digest the sugars in milk, were rare in Europeans at the beginning of the Bronze Age but became widespread during this time - much later than was previously thought.
Similarly, genetic markers associated with light-skin pigmentation suggest that light skin became widespread in Europe over the 3,000 years leading up to the Bronze Age.
Although attempts have been made before to gather DNA from Bronze Age remains, this has been difficult because the chemical breaks down over the centuries. The team used a variety of techniques to obtain more intact samples, including collecting DNA from a different layer of tooth to that normally used.
This study was the first to investigate the genomes of ancient populations on such a large scale. Dr Greger Larson, an evolutionary biologist at the University of Oxford, told Nature News: 'In another five years, we'll be talking about tens of thousands of ancient genomes.'