Early residents of the Tibetan Plateau, one of the least hospitable places on earth, survived in large part by consuming large amounts of dairy products, according to a new study that chipped away at ancient teeth.

Sometimes referred to as the world’s Third Pole, the Tibetan Plateau is beset by dry, cold, unpredictable conditions that would have made life tough for the humans who lived there some 3,600 years ago. Conditions would have stymied efforts to raise crops, such as the barley raised in warmer Tibetan valleys and lowlands. And they would have lowered oxygen levels far enough to cause potentially fatal hypoxia.

To survive the Third Pole, the third snowiest place on earth behind the North and South poles, early Tibetans evolved genetic resistances to high altitudes. They also turned to goats and sheep and potentially yaks, according to a new study, animals that had the power to turn the plateau’s rough pastures into life-sustaining milk.

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Ancient Dairy

World dairy history extends back thousands of years: Cultivation first spread from Asia Minor to Europe about 8,000 years ago and into Mongolia some 5,000 years ago. This new study peered back to some 3,600 years ago by analyzing the dental remains of 40 people from 15 different sites and found clear evidence of milk consumption.

How could the researchers tell? Not by the strength of their teeth but by the dental calculus attached to them. Better known as tartar, dental calculus is “a hard, calcified deposit” formed from plaque that is so hardy, in fact, that it can survive thousands of years buried in the ground.

To learn what these ancient humans chewed on while alive, the researchers chipped off the calculus with razor blades and analyzed the proteins preserved inside using the burgeoning field of proteomics. Out of nine high-altitude sites, they found seven with intact oral proteins, and six of those contained dairy proteins.

Nearly half (47 percent) of the individuals found at the seven sites contained the proteins, in contrast to the lower, more arable sites. There, the researchers found no evidence of dairy consumption, suggesting the residents had relied more on farming. (This doesn’t necessarily mean these farmers lived dairy-free; they may have just consumed fewer products.)

Protein Patterns

“We were excited to observe an incredibly clear pattern,” says Li Tang, an archaeologist and lead author of the study, in a press release. “All our milk peptides came from ancient individuals in the western and northern steppes, where growing crops is extremely difficult. However, we did not detect any milk proteins from the southern-central and south-eastern valleys, where more farmable land is available.”

Further analysis determined that the milk had come from goats, sheep and potentially yaks, which produce especially nutritious milk. Modern herders rely upon them to produce butter, cheese and yogurt but rarely meat. Today, pasture still accounts for 68 percent of the Tibetan Plateau, as compared to the 1 percent dedicated to farmland.