In wagons and on horses, Yamnaya pastoralists left their genetic mark from Ireland to China
Nomadic herders living on western Asia’s hilly grasslands made a couple of big moves east and west around 5,000 years ago. These were not typical, back-and-forth treks from one seasonal grazing spot to another. These people blazed new trails.
A technological revolution had transformed travel for ancient herders around that time. Of course they couldn’t make online hotel reservations. Trip planners would have searched in vain for a Steppe Depot stocked with essential tools and supplies. The closest thing to a traveler’s pit stop was a mountain stream and a decent grazing spot for cattle. Yet, unlike anyone before, these hardy people had the means to move — wheels, wagons and horses.
Here’s how the journeys may have played out: At a time when rainfall dwindled and grasslands in western Asia turned brown, oxen-pulled wagons loaded with personal belongings rolled west, following greener pastures into central and northern Europe. Other carts rumbled east as far as Siberia’s Altai Mountains, where Russia, China, Mongolia and Kazakhstan meet today. Families of men, women and children may have piled on board. Or travelers may have been mostly men, who married women from farming villages along the way. Cattle, sheep and goats undoubtedly trailed along with whoever made these trips, under the watchful guidance of horse riders. Wagons served as mobile homes while on the move and during periodic stops to let animals graze.
These journeys, by people now known as the Yamnaya, transformed human genes and cultures across a huge swath of Europe and Asia. Yamnaya people left their mark from Ireland to China’s western border, across roughly 4,000 kilometers.
Two pioneering studies of ancient DNA, published in Nature in 2015, unveiled the Yamnaya people’s big moves. Getting those results was a pivotal moment for researchers who study the Eurasian Bronze Age, which stretched from around 5,000 to 3,000 years ago. Those two millennia witnessed the rise of metalworking, writing systems and other signature features of urban civilizations.
Now new papers try to explain how Yamnaya DNA made major inroads into Bronze Age Europe during the first 200 to 300 years of that key period. The two studies differ on whether the Yamnaya influenced European cultures and languages in one big sweep or over an extended period.
A mobile web
Researchers have often overlooked these Yamnaya nomads and other herding cultures as early forces of globalization. But archaeological evidence increasingly portrays Bronze Age pastoralists — who moved their cattle and campsites from one seasonal grazing spot to another — as a web of mobile societies that formed an intercontinental communication system. Research at sites across Asia’s grasslands, foothills and mountain ranges indicates that these herders forged extensive trade networks crucial to the rise of agricultural states. Herders still thrive in several parts of the world today, providing a variety of services to towns across remote, mountainous parts of Asia.
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Follow the herd
The road from early farming villages to the first large-scale civilizations in Europe and Asia intersected with the continent-spanning travels of Asian nomadic herders. Genetic studies have highlighted the role of pastoralists known as the Yamnaya, who influenced European and Asian cultures at least 5,000 years ago.
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C. Chang; T. Tibbitts
Granting special status to ancient pastoralists as civilization builders is not a new idea. In the 1950s and 1960s, prominent archaeologists argued that horse-riding pastoralists launched a series of migrations out of their homeland, the Pontic-Caspian steppe region north of the Black Sea, from roughly 6,000 to 3,000 years ago. Those archaeologists saw these pastoralists as fierce nomadic warriors who spread the lifestyle, beliefs and language of what is known as Kurgan culture to farmers and foragers in Europe and parts of Asia. Kurgan groups, which included the Yamnaya, were known for burying their people in graves covered by dirt mounds. These groups had no writing system but spoke an early version of modern Indo-European languages, some archaeologists have argued. Indo-European tongues today include English, Spanish, Russian and Bengali, among more than 400 others.
By the 1980s, a different perspective took hold. Researchers proposed that Bronze Age European cultures and languages changed as ideas passed from one group to another. Europeans didn’t form families with wayfaring, or marauding, pastoralists. Instead, locals adopted outsiders’ practices as needed, but the natives kept their genes to themselves.
Proponents of that “migrating ideas” perspective take a cautious view of Yamnaya DNA in Europe. Genetic signatures of past migrations raise more questions than they answer, these researchers argue. DNA can’t comment on why, say, Yamnaya people moved in the first place. The size of westward and eastward migrations and ways in which each passage unfolded over several centuries also remain mysterious. Perhaps most crucially, sets of genes shared by distant populations can’t explain how ancient cultures and languages changed over time.
Despite the uncertainties, the Yamnaya’s wandering DNA makes one thing clear, says Eske Willerslev, an evolutionary geneticist at the University of Copenhagen. “Bronze Age pastoralists moved long distances for a long time and had an important impact on European and central Asian civilizations.” Willerslev directed one of the 2015 Yamnaya investigations. A team led by Harvard Medical School geneticist David Reich conducted the other study. Efforts to flesh out how ancient herders became movers and shakers in the rise of civilization are now in full swing, as evidenced by a range of new papers.
Willerslev’s and Reich’s ancient DNA investigations, conducted independently in collaboration with different sets of archaeologists, reached the same conclusion: Yamnaya people reshaped central and northern Europeans’ DNA within a couple of hundred years after starting the journey west as early as 5,100 years ago. That came as a surprise to both research groups.
The smoking gun: DNA extracted from a total of 195 skeletons of Bronze Age northern and central Europeans in the two studies showed that those who lived between 4,900 and 4,400 years ago possessed a remarkably large amount of Yamnaya DNA. Yamnaya people contributed about 75 percent of the ancestry of those farmers, the scientists concluded.
“We never would have known that Yamnaya people produced two distinct cultures by looking at archaeological finds alone,” says Anthony, who coauthored the 2015 paper by Reich’s group. Absent a genetic link, it would look like the Yamnaya, who previously had made nothing resembling Corded Ware pottery or battle-axes, had no hand in Corded Ware culture.
Population declines among European farmers and foragers around 5,000 years ago (SN: 11/2/13, p. 12), possibly due to epidemics (SN: 11/28/15, p. 7), may have enabled incoming Yamnaya to exert such influence. First, migrating herders sent war bands of teenage boys as advance forces to settle European territories (SN Online: 8/7/17), a team led by Kristian Kristiansen of the University of Gothenburg in Sweden proposed in the April Antiquity. The rest of the migrants arrived soon after, the researchers suspect. Yamnaya men then married women from local groups, possibly by abducting them. Kristiansen coauthored the 2015 paper by Willerslev’s group.
Corded Ware culture emerged as a hybrid way of life that included crop cultivation, breeding of farm animals and some hunting and gathering, Kristiansen argues. Communal living structures and group graves of earlier European farmers were replaced by smaller structures suitable for families and single graves covered by earthen mounds. Yamnaya families had lived out of their wagons even before trekking to Europe. A shared emphasis on family life and burying the dead individually indicates that members of the Yamnaya and Corded Ware cultures kept possessions among close relatives, in Kristiansen’s view.
“The Yamnaya and the Corded Ware culture were unified by a new idea of transmitting property between related individuals and families,” Kristiansen says.
Yamnaya migrants must have spoken a fledgling version of Indo-European languages that later spread across Europe and parts of Asia, Kristiansen’s group contends. Anthony, a longtime Kristiansen collaborator, agrees. Reconstructed vocabularies for people of the Corded Ware culture include words related to wagons, wheels and horse breeding that could have come only from the Yamnaya, Anthony says.
As Indo-European languages spread, the Yamnaya’s genetic impact in Europe remained substantial, even after the disappearance of Corded Ware culture around 4,400 years ago, Reich’s team reported online May 9 at bioRxiv.org. About 50 percent of the ancestry of individuals from a later Bronze Age culture, dubbed the Bell Beaker culture for its pottery vessels shaped like an inverted bell, derived from Yamnaya stock. Such pottery spread across much of Europe starting nearly 4,770 years ago and disappeared by 3,800 years ago. Migrations of either people or ideas may have accounted for that dispersal.
Even today, DNA from modern western, central and northern Europeans carries close to a 50 percent genetic contribution from the Yamnaya, Reich’s team reported in 2015.
Many contacts, not one
Like many of his colleagues, archaeologist Volker Heyd of the University of Bristol in England was jolted by the 2015 reports of a close genetic link between Asian herders and a Bronze Age culture considered native to Europe. But, Heyd says, the story of ancient Yamnaya migrations is more complex than the rapid-change scenario sketched out by Kristiansen and Anthony.
No evidence exists that Yamnaya people rapidly developed practices typical of the Corded Ware culture in one part of Europe, Heyd argues in the April Antiquity. Cultural shifts in Europe around 5,000 years ago must have emerged from an extended series of small-scale dealings with Yamnaya and other pastoralists, which was then capped off by a large influx of steppe wagon travelers, he says.
For instance, individual graves and other signs of contact with the Yamnaya people and even earlier Asian pastoralists appear in Europe 1,000 to 2,000 years before DNA-transforming migrations occurred. Consider that the Yamnaya account for 5 percent of the ancestry of Ötzi the Iceman, who lived in southeastern Europe roughly 300 years before the Yamnaya’s big move (SN: 5/27/17, p. 13). Little is known about those earlier encounters.
Efforts to decipher ties between Yamnaya and Corded Ware culture are complicated by the fact that DNA is available from just a few people from each group, says Heyd, who is currently excavating Yamnaya graves in Hungary. Ancient DNA samples analyzed in the 2015 papers come from only a handful of Yamnaya and Corded Ware culture sites in a few parts of Europe and Russia.
Heyd suspects that Yamnaya travelers had even earlier contacts, perhaps by 5,400 years ago, with central and eastern Europeans known for making globe-shaped pots with small handles. Individuals from that culture, excavated at two sites in Poland and Ukraine, possess no Yamnaya genes, a team affiliated with Reich’s lab reported online May 9 at bioRxiv.org. But Heyd thinks mating between members of that European culture and Yamnaya migrants may have occurred a bit farther east, where cross-cultural contacts probably occurred at the boundary of European forests and Asian grasslands.
Other genetic clues point to a long history of Asian pastoralists crossing into parts of Europe. Small amounts of DNA from steppe herders, possibly the Yamnaya, appeared in three hunter-gatherer skeletons from southeastern Europe dating to as early as around 6,500 years ago.
Heyd’s skepticism of the Yamnaya’s singular contribution to Corded Ware culture makes sense, says archaeologist Ursula Brosseder of the University of Bonn in Germany. “Cultural phenomena, such as the Corded Ware culture, cannot be linked one-to-one to ethnic groups, genetic population groups or languages,” she says. Brosseder, who studies ancient European cultures, also doubts that the rise of Indo-European languages, which are so dominant in much of the world today, can be attributed to one population of migrating herders.
Brosseder and other critics of major Yamnaya migrations as game changers paint a different, two-pronged picture of what might have happened in Bronze Age Europe.
The story begins in the Middle East when farmers who spoke Indo-European languages domesticated goats and other animals 6,000 years ago or earlier. Animal breeding quickly gave rise to pastoralists, including the Yamnaya.
Around 5,000 years ago, a plague wiped out many farmers and foragers in upper parts of Europe. Herders migrated west to find better grazing pastures as a hotter, drier climate parched the central Asian steppes. In central and northern Europe, travelers encountered sparse populations struggling to survive. Natives adopted the newcomers’ early Indo-European language and married them.
But a second wave of influence came from the south, at the same time or perhaps a bit earlier. Related Indo-European languages spread via farmers moving out of Mediterranean areas and Anatolia (now Turkey) to lower parts of Europe and to southern Asia. Those cultivators had nothing to do with the Yamnaya’s big move and rarely mated with the herders.
Support for this scenario comes from 19 Bronze Age farmers found in Crete, Greece and Turkey. These people’s DNA was largely inherited from earlier farmers in western Anatolia and the Aegean, a team led by Harvard Medical School geneticist Iosif Lazaridis reported in the Aug. 10 Nature. Low amounts of Yamnaya ancestry, from 9 to 32 percent, appeared among these individuals.
That and other genetic studies of southeastern Europeans “suggest that some, but not all, branches of Indo-European [languages] came from steppe peoples,” says linguist Paul Heggarty of the Max Planck Institute for the Science of Human History in Jena, Germany. Indo-European speakers past and present display a variety of genetic patterns over a huge geographic area, raising doubts about any simple explanation for the spread of this language family, Heggarty holds.
The scenario above, although not confirmed, conveys the complexity of Eurasian population movements and cultures that spread Indo-European languages, says archaeologist Colin Renfrew of the University of Cambridge. Renfrew proposed 30 years ago that Anatolian farmers carried an early Indo-European tongue into Europe starting perhaps 9,000 years ago. His influential argument rejected the idea that waves of migrating herders had reshaped language and culture.
In line with his ideas, genetic data in the 2015 reports indicated that farming groups from southeastern Europe and Anatolia had moved into the heart of Europe more than 6,000 years ago, where hunter-gatherers already lived. When Yamnaya DNA arrived, sets of gene variants typical of those farmers and hunter-gatherers plummeted.
But the 2015 Yamnaya papers also shifted Renfrew’s thinking. He now accepts that Asian pastoralists reached central and northern parts of Europe around 5,000 years ago. What happened next, especially in southern Europe where the Yamnaya didn’t leave a big mark, is unclear. “The genetic origins of Bronze Age people in Anatolia, which was a royal road into Europe, are almost a complete blank,” he says. The same goes for the origins of members of the Bronze Age Indus Valley Civilization in southern Asia, where an early form of Indo-European languages may have been spoken.
Even with all the questions surrounding the Yamnaya’s western migration, perhaps the biggest mystery of all concerns what happened when these people moved east to central Asia’s Altai Mountains.
Willerslev’s team reported in 2015 that ancient DNA from early Bronze Age individuals who belonged to a poorly understood culture in the Altai region was virtually 100 percent identical to 5,000-year-old Yamnaya DNA. Yamnaya migrants may have developed that southern Siberian culture, known as Afanasievo culture, entirely on their own, making an even bigger impact than Yamnaya peers did on Europe’s Corded Ware culture, the team concluded.
From southern Siberia, ancient people with Yamnaya roots may have brought one of the oldest and most poorly understood Indo-European languages, Tocharian, to inhabitants of what’s now western China, the researchers speculated.
Whatever happened, central Asia was a hotbed of Bronze Age population movements, Willerslev and colleagues emphasized. After emerging around 4,000 years ago, western Asia’s horse-breeding Sintashta people gave rise to a distinct culture in the Altai region a few hundred years later, the team reported based on DNA from 40 Bronze Age Asians. Ancient DNA similarities indicated that mating had occurred between Sintashta migrants and Altai people they encountered. Around 3,500 years ago, several eastern Asian cultures reached the Altai region and became dominant, genetic findings further suggested.
Archaeologist Michael Frachetti of Washington University in St. Louis doesn’t doubt that different populations of Bronze Age herders continually moved through the heart of Asia. Research directed by Frachetti indicates that herders’ seasonal migrations through mountainous regions starting 4,000 years ago created key Silk Road routes over the next two millennia (SN: 4/15/17, p. 9).
But researchers still know little about the genetic structure and daily lives of ancient Asian people such as the Yamnaya and various Altai communities, Frachetti cautions. It’s not even clear whether excavated remains of Yamnaya people represent one culture or several cultures, he contends.
“From the Caspian Sea to China, many questions remain about Bronze Age pastoralists,” Frachetti says. He is now collaborating with Reich’s team on an analysis of DNA from individuals previously excavated at Bronze Age sites in central and eastern Asia dating to around the time of Europe’s Bronze Age.
Herders without borders
One thing is for sure: Ancient nomadic pastoralists are shedding their reputation as “barbarians” obsessed with raiding and warfare. That generalization got its start in early agricultural societies exposed to herders’ raids and conflicts in border regions. Armed with writing systems, farming civilizations recorded one-sided accounts of nomadic groups as mounted savages.
Archaeological discoveries now suggest Bronze Age pastoralists specialized in intercontinental communication. Around 5,000 years ago, nomadic communities began to exchange knowledge, food and metalworking technology across increasingly vast stretches of Asia. Nomadic groups were the first engines of globalization, connecting agricultural civilizations in southwestern and eastern Asia via mountain valleys running across the continent, Frachetti says.
Herders moving through those valleys brought southwestern Asian crops into China and eastern Asian crops back the other way, says archaeologist Robert Spengler of the Max Planck Institute for the Science of Human History. While working their way across Asia through mountain valleys, pastoralists incorporated crops into their own way of life.
Seeds found at two herder campsites in Kazakhstan show that people there used bread wheat from southwest Asia and broomcorn millet from eastern Asia between 4,800 and 4,300 years ago (SN: 5/3/14, p. 15). These grains, found in small amounts, may have been eaten or employed in rituals of some kind.
Herders at 17 Kazakhstan sites dating to around 3,800 to 2,800 years ago ate fish as well as meat, and cultivated increasing amounts of millet over time. Archaeologist Emma Lightfoot of the University of Cambridge and colleagues analyzed chemical signatures of different types of food consumption in the bones of people from those Bronze and early Iron Age campsites. The results appeared in 2015 in Archaeometry.
Pastoralists also spread key ideas about life and death, as represented in burial practices across Bronze Age Asia, Frachetti contends. Graves of Bronze Age agricultural societies and pastoralist communities — stretching from south-central Asian deltas to central Asian steppes and western China’s Xinjiang desert region — display common ways of interring the dead that can’t be coincidental, he says. Those graves date to between around 4,200 and 3,500 years ago. Shared burial practices included placing dead bodies in a curled, sleeping position and providing the dead with special items for the afterlife, such as pottery vessels or baskets that contained food and various bronze objects, particularly jewelry, weapons and mirrors.
Ancient pastoralists moved complex settlements from one location to another while traveling with their herds between around 2,200 and 700 years ago, says archaeologist J. Daniel Rogers of the Smithsonian National Museum of Natural History in Washington, D.C. These steppe societies, which clustered in what’s now Mongolia and northwestern China, frequently built walled settlements in river valleys along seasonal herding corridors.
Groups moving among seasonal grazing sites assembled temporary tent communities inside these spacious walled areas, Rogers concluded in the September Archaeological Research in Asia. Mobile communities included rulers, craft workers and even administrative personnel, he proposes.
Pastoralist and agricultural civilizations traded goods and ideas, even if conflicts sometimes broke out along the borders of the routes herders traveled.Frachetti adds, “Pastoralists formed their own brand of civilization based on mobility to keep their economies growing and people fed.”
Few ancient or living pastoralists can be called classic nomads, moving constantly across the landscape. The number and length of annual migrations varies greatly from one group to another, says archaeologist Nikolay Kradin of the Far Eastern Branch of the Russian Academy of Sciences in Vladivostok. But herders today move at least once or twice a year to seasonal grazing spots.
Despite Soviet-era attempts to force Asian pastoralists to become farmers, about 40 million people currently engage in mobile herding in Asia, Africa and the Middle East, Kradin estimates. Dry grasslands and desert areas conducive to pastoralism cover about 25 percent of Earth’s land surface, he says.
Mountain pastoralists in central Asia maintain valuable herds, some worth hundreds of thousands of dollars, Frachetti says. In their treks along mountain valleys that still serve as an unofficial highway connecting remote towns, herders provide lambs to slaughter for weddings, act as couriers between settled regions and create widespread social and family networks through marriage, business deals and trade.
Asian herders continue to specialize in mobility and networking across vast areas. These groups represent “nerve centers” for town dwellers dotting Asian valleys and mountain ranges.
“Mountain pastoralists of inner Asia don’t need Artificial Intelligence to survive,” Frachetti says. “They’ll still be around when the major civilizations today melt into the ocean.” The Yamnaya, whose genes have outlasted a bevy of Bronze Age cultures, would undoubtedly agree.
This article appears in the November 25, 2017 Science News with the headline, “Big moves: How Asian nomadic herders built new Bronze Age cultures.”
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