The Bronze Age came to Europe and Asia 5000 years ago, leaving a trail of metal tools, axes, and jewelry that stretches from Siberia to Scandinavia. But was this powerful new technology an idea that spread from the Middle East to European and Asian people, or was it brought in by foreigners? Two of the largest studies of ancient DNA from Bronze Age and Iron Age people have now found that outsiders deserve the credit: Nomadic herders from the steppes of today's Russia and Ukraine brought their culture and, possibly, languages with them—and made a relatively recent and lasting imprint on the genetic makeup of Europeans and Asians.

In the studies, published online today in Nature, two rival teams of geneticists analyzed the DNA from 170 individuals who lived at key archaeological sites in Europe and Asia 5000 to 3000 years ago. Both teams found strong evidence that a wave of nomadic herders known as the Yamnaya from the Pontic-Caspian, a vast steppeland stretching from the northern shores of the Black Sea and as far east as the Caspian Sea, swept into Europe sometime between 5000 and 4800 years ago; along the way, they may have brought with them Proto-Indo-European, the mysterious ancestral tongue from which all of today’s 400 Indo-European languages spring. These herders interbred with local farmers and created the Corded Ware culture of central Europe, named for the twisted cord imprint on its pottery. Their genes were passed down to northern and central Europeans living today, as one of the teams posted on a preprint server earlier this year and published today.

But in a new twist, one of the studies also found that the Yamnaya headed east from their homeland in the Eurasian steppelands, moving all the way to the Altai Mountains of Siberia, where they replaced local hunter-gatherers. This means that this distinctive culture of pastoralists, who had ox-driven wagons with wheels and whose warriors rode horses, dominated much of Eurasia, from north-central Europe to central Siberia and northern Mongolia. They persisted there until as recently as 2000 years ago. “Now we see the Yamnaya is not only spreading north into Europe; they’re also spreading east, crossing the Urals, getting all the way into central Asia, all the way into the Altai, between Mongolia, China, and Siberia,” says evolutionary biologist Eske Willerslev of the University of Copenhagen, author of one study.

Archaeologists have long noticed connections between the steppe cultures such as the Yamnaya and Bronze Age people to the east, who lived in the Minusinsk Basin and the Altai Mountains of southern Siberia and Mongolia about 5500 to 4500 years ago. Like the steppe people, these eastern cultures, such as the Afanasievo of the Altai, buried their high-status people in a supine flexed position, covered in ochre with animal remains in their graves, beneath mounds (or stone kurgans in the steppe). They also made pointed-based pots, censers (circular bowls on legs), and were among the first people to drive carts with wheels and tame horses. All of these traits also link them to people in central and eastern Europe, including the Yamnaya and Corded Ware people, who are thought to have spoken early Indo-European languages.

In one of the new studies, Willerslev’s international team sequenced the genomes of 101 ancient people from across Europe. They found that the Yamnaya of the Samara Valley in the northern steppe of Russia were genetically indistinguishable from the Afanasievo of the Altai in the Yenesey region of southern Siberia, which confirms archaeologists’ suggestions that there was a vast migration of steppe pastoralists to the east. But unlike in Europe where the Yamnaya interbred with local farmers, the Yamnaya moving east completely replaced the local hunter-gatherers—perhaps because this region was only sparsely populated, Willerslev says.

This eastern branch of the Yamnaya (or Afanasievo) persisted in central Asia and, perhaps, Mongolia and China until they themselves were replaced by fierce warriors in chariots called the Sintashta (also known as the Andronovo culture). These people from the Urals and Caucuses, who were genetically related to central Europeans, persisted in central Asia until 2000 years ago, which means that people in central Asia were actually more like Europeans than living Asians. It wasn’t until relatively recently—just 2000 years ago—that these “Caucasians” were replaced by immigrants from eastern Asia, such as the Karasuk, Mezhovskaya, and other Iron Age cultures that today make up the ancestry of people in central Asia.

The implications of these genetic links between the Asian and European Bronze Age cultures are far-reaching: A few closely-linked groups from the steppe dominated a huge area from Europe to Asia and shaped major parts of the genetics of Europeans and Asians. “We now have samples all the way from Spain and the Atlantic Ocean to central Siberia,” says population geneticist Iosif Lazaridis of Harvard University and a co-author of the second study led by David Reich, also of Harvard. “The genetics of a lot of temperate Eurasia was completely unknown until a few years ago. Now it is almost completely known for this Bronze Age–Neolithic period.”

Both studies found that these people brought genes for light skin and brown eyes with them, although northern hunter-gatherers already had light skin as well, Willerslev’s team found. In one surprising twist, it appears that even though the Yamnaya and these other Bronze Age cultures herded cattle, goats, and sheep, they couldn’t digest raw milk as adults. Lactose tolerance was still rare among Europeans and Asians at the end of the Bronze Age, just 2000 years ago. “The lack of lactose tolerance is very surprising, because most people would have assumed that the ability to drink raw milk that you see in present-day Europeans was selected for and fixed at least by the beginning of Bronze Age,” Willerslev says.

This massive migration from the steppe also may have spread the Indo-European languages that have been spoken across Europe and in central and southern Asia since the beginning of recorded history, including Italic, Germanic, Slavic, Hindi, and Tocharian languages, among others. If the genetic affinities do mirror linguistic families, this would be strong evidence against a rival hypothesis that farmers from the Middle East spread early Indo-European languages.

Although geneticists think the correlation is remarkably strong, the issue is far from resolved for linguists, who are following the new ancient DNA work closely. “There is a real sense that after more than 2 centuries of linguistics trying to solve the Indo-European question, it's ancient DNA that is suddenly moving us fast toward a possible resolution,” says linguist Paul Heggarty of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. But it is not enough just to have data from northern Eurasia, where the Yamnaya’s movements may reflect only one part of the spread of Indo-European languages. Heggarty adds: “We need key data from the majority of the Indo-European-speaking world in the Mediterranean and south of the Black Sea-Caspian-Himalayas.”

Other researchers say that the combined power of the two studies shows that it was people—not just pots or ideas—that spread the Bronze Age culture and genes. The studies “provide additional evidence for a mass migration at the end of the Neolithic from the Pontic steppe region into central Europe,” says paleogeneticist Johannes Krause of the Max Planck Institute for the Science of Human History in Jena, Germany.