It’s not called the Third pole for nothing. The Tibetan Plateau forms the bulk of a vast mountain range of ice and glaciers that covers some 100,000 square kilometers of the Earth’s surface.
It’s a cold, barren and unforgiving landscape that couldn’t be more different from the warm plains and valleys from which our species sprang.
Yet the Tibetan Plateau has been occupied by for thousands of years homo sapiens. It has seen the establishment of agrarian societies and the growth of religions, kingdoms and even empires.
How humans managed to not only survive but thrive in this high-altitude landscape is a question that has challenged researchers for decades—and one that has enthralled us, too.
We know that part of the answer lies in Tibetan genes, and a unique adjustment that enables people living in the region to use oxygen more efficiently, avoiding the potentially deadly effects of hypoxia (the condition that comes from a lack of oxygen).
But just as important as avoiding hypoxia was finding sufficient food in the plateau’s unpredictable, frigid and hyper-arid environment.
Our research, published today in Science Advances, to take a closer look at early Tibetan diets. To do this, we examined ancient dental plaque, a rich source of nutritional information.
Our results show that one food item in particular may have been crucial to sustained human occupation and expansion across the Tibetan plateau: milk.
The benefits of not brushing
Without dentists, people in ancient times often accumulated thick layers of plaque – also known as tartar – on their teeth. Using a new method called paleoproteomics, scientists can examine the food proteins that became trapped and preserved in the dental plaque of ancient humans.
Palaeoproteomics allows us to look at types of food, such as milk, that are not visible through traditional archaeological approaches, and identify specific individuals that consumed them.
Our study analyzed all available human skeletal remains on the plateau: a total of 40 individuals, dating between 3500 and 1200 years ago, from 15 widely distributed sites.
Our work produced fascinating results. Fragments of proteins derived from dairy products were preserved in the teeth of many of these people. The protein sequences showed that the milk came from domesticated herd animals: sheep, goats and probably yak.
We could see that dairy products were consumed by a large part of the Tibetan Plateau society, including adults and children, elites and commoners. Dairy was even present in the earliest Tibetan Plateau skeletons we looked at.
In fact, we found that dairy was consumed as far back as 3,500 years ago – evidence for dairy on the plateau was traced back 2,000 years earlier than in historical sources, such as the 8th and 9th centuries. Tongdian Encyclopedia.
Evidence for dairy farming now matches the earliest evidence for domesticated herd animals on the Tibetan Plateau, suggesting that dairy farming and cattle ranching co-existed in this region.
Across the crop border
Our results showed another interesting pattern: all the milk peptides we identified originated from ancient individuals in the highest parts of the plateau. These were the most inhospitable areas, where growing crops was difficult.
In the south-central and southeastern valleys, where farmland was available, we did not find dairy proteins from human tartar.
Dairy, it seems, was vital to human habitation of the parts of the plateau beyond the reach of even frost-resistant crops. This is a vast area as less than 1% of the Tibetan plateau supports crop cultivation.
Long-term habitation has been maintained in the lower areas by growing plant foods. But on most of the plateau, ranching was the main livelihood.
Dairy free? No option
While dairy would eventually become central to Tibetan cuisine and culture, our results suggest that it was initially adopted out of necessity. It enabled people in the most extreme environments of the Tibetan Plateau to convert the energy locked up in alpine meadow grasses into a protein-rich, nutritious food that was endlessly renewable – because no animals were killed to obtain it.
Dairy farming opened up the Tibetan plateau to the dispersal and continued growth of human population, ultimately allowing the emergence of substantial cultural complexity.
In one of the harshest environments on Earth, dairy-free doesn’t seem like an option.
Future work on the plateau will be vital to understanding how human adoption of animal husbandry and dairy farming has reshaped Tibetan landscapes. And just as critically, it will shed light on what human-induced climate change means for the future of the ecosystems today’s pastoralists rely on.
Read more: How midnight tombs in a sacred Tibetan cave opened a window to prehistoric humans who lived on the roof of the world