Milk fueled Bronze Age expansion of ‘eastern cowboys’ into Europe

More than 5000 years ago, nomads known today as the Yamnaya rumbled out of the grasslands of modern-day Russia and Ukraine in heavy, ox-drawn wagons. Within just a few centuries they had expanded across Eurasia, leaving a genetic signature in populations from Mongolia to Hungary. Now, fossilized plaque from the teeth of more than 50 Bronze Age skeletons suggests an unlikely weapon powered their expansion: milk.

“It’s great to see this type of evidence finally there,” says Wolfgang Haak, an archaeogeneticist at the Max Planck Institute for Evolutionary Anthropology who was not involved in the research. “It’s a convincing argument as far as dairy is concerned.”

Researchers have long speculated that a combination of wagons, dairying, and horseback riding might have made it possible for the Yamnaya—whom Haak refers to as “eastern cowboys”—to develop a new, more mobile way of life, unleashing their unprecedented expansion. But there was little direct evidence to back that up that idea, aside from a few wagon burials and pottery sherds.

To see what might have fueled the Yamnaya’s success, researchers from the United States, Europe, and Russia looked for milk proteins trapped and preserved in the dental calculus, or plaque, of people living on the steppes of modern-day Russia between 4600 and 1700 B.C.E. They examined 56 skeletons from more than two dozen sites north of the Caspian Sea. The team separated the preserved proteins from the mineral matrix of the plaque and then used mass spectrometry to identify individual proteins.

Prior to 3300 B.C.E., calculus from the teeth of people living in settlements along the Volga and Don rivers contained virtually no milk proteins. Instead, these pre-Yamnaya groups likely consumed lots of freshwater fish, wild game, and the occasional meal of domesticated cow, sheep, or goat meat, as suggested by previous analysis of isotopes in their skeletons and animal bones at the sites.  

Then, around 3300 B.C.E., something changed. Samples scraped from the teeth of people living after that date were full of cow, sheep, and goat milk proteins—direct evidence they were eating dairy products. A few even had trace amounts of preserved horse milk. “There’s a cultural switch,” says lead author Shevan Wilkin, a biomolecular archaeologist at the University of Zurich Institute of Evolutionary Medicine. “It’s a huge change of perspective from ‘we eat these animals sometimes’ to ‘we milk them all the time.’”

The proteins suggest the adoption of dairying and herding was key to the rapid transformation of hunter-gatherers into nomadic herders—and their expansion across Eurasia in the space of just 300 years, the researchers write today in Nature. “Horses, cattle, sheep, and goats turned grass into food, clothing, and shelter,” says Hartwick College archaeologist and co-author David Anthony. “The Yamnaya invented a new economy.”

Hard, mineralized dental calculus can preserve evidence of diet and disease for thousands of years.Egor Kitov/Samara Valley Project

But dairy didn’t do it alone: The introduction of wagons around the same time made carrying water and following grazing animals to distant pastures possible. Meanwhile, early domesticated horses might have enabled the newly nomadic Yamnaya to manage bigger herds. Together, the innovations opened up a vast new landscape. “Milk is a contributing factor, but not the only factor,” says University of Helsinki archaeologist Volker Heyd, who was not involved in the research. “It’s a new economy and a new way of life, and the origins are the invention of the wheel, horse riding, and dairying.”

One mystery remains. Previous analyses of ancient DNA have shown the Yamnaya lacked the genetic ability to metabolize milk sugars—in other words, they were lactose intolerant. It’s possible, Wilkin says, that—much like modern Mongolians—the Yamnaya consumed fermented dairy products like yogurt or hard cheeses, which contain virtually no lactose. Whatever form of dairy they consumed, she adds, “I don’t know how you would have moved that far that fast [without it].”

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