The Tibetan Plateau, also known as the “roof of the world,” is one of the most extreme environments on Earth. With an average elevation of over 4,500 meters, this inhospitable region presents significant challenges to human habitation, including a lack of arable land and limited resources.
Despite these obstacles, ancient Tibetans managed to survive and even thrive in this remote area. A new study, published in the journal Science Advances, has shed light on how they managed to accomplish this staggering feat: by consuming dairy products.
A high-altitude mystery solved
Although positive natural selection at several genomic loci enabled early Tibetans to better adapt to high elevations, obtaining sufficient food from the resource-poor highlands would have remained a challenge.
Li Tang of the Max Planck Institute of Geoanthropology, the lead author of the new study, has always been fascinated by the lifestyle of Tibetan nomads. Previously, she conducted research to learn more about how growing crops in the Tibetan Plateau contributed to the early occupation of the region. However, he rather quickly found out that crops didn’t help much at all as agriculture is only viable in a few rare valleys that account for less than 1% of the total area.
Yet despite these enormous challenges, the ancient Tibetans managed somehow — and it all had something to do with milk.
Tang and colleagues analyzed ancient proteins from the dental calculus of 40 individuals from 15 sites across the Tibetan Plateau and found evidence indicating that dairying was introduced onto the hinterland plateau at least 3,500 years ago.
The adoption of dairy pastoralism helped revolutionize people’s ability to occupy much of the plateau, particularly the vast areas too extreme for crop cultivation.
The study, which is the first to detect direct evidence of ancient dairying on the Tibetan Plateau, shows that dairy products were consumed by diverse populations, including females and males, adults and children, as well as individuals from both elite and non-elite burial contexts.
Tibetan highlanders made use of the dairy products of goats, sheep, and possibly cattle and yaks, with early pastoralists in western Tibet having a preference for goat milk. Even to this day, dairy products are still a huge part of the lives of modern-day Tibetans.
“Pastoralism is vital for modern Tibetans, particularly the highlanders, ruminants provide almost all the daily necessities they need, milk, meat for food, hair and wool for clothing and tents, and fuel from dung, as well as transportation,” Tang told ZME Science.
The impact of dairying on early Tibetan populations
These findings throw a wrench in the so-called “barley hypothesis”, which suggests that agriculture was the critical adaptation that enabled the permanent occupation of the plateau. Instead, dairy seems to have played an equal role — if not more important — in this achievement.
Tang first learned about paleoproteomics, the study of ancient proteins, during her doctoral research and has been hooked ever since. This novel method allows scientists to glean intimate details about the lives of ancient people by studying proteins trapped in the calcified dental plaque from very old human teeth.
Tracing dairying in the deep past has long been a challenge for researchers. Traditionally, archaeologists analyzed the remains of animals and the interiors of food containers for evidence of dairying, however, the ability of these sources to provide direct evidence of milk consumption is often limited. This is why paleoproteomics can be so powerful.
But since the method is novel, the young researcher also experienced pushback from her supervisors and had to do some convincing work in order to receive funding. To make matters more difficult, on top of these challenges came the COVID-19 pandemic.
“The lab work started at the beginning of the lockdown. We didn’t know when we could continue the extraction as usual. The most memorable moment must be when I first got milk signs from my samples.”
“I was checking the amino acid sequence, and found it’s unique to sheep milk. I texted my collaborators and supervisors immediately: ‘IT WORKS!’. It gave me huge motivation to move forward with the testing of the samples,” Tang recounted.
The researchers were excited to observe an incredibly clear pattern: all the milk peptides came from ancient individuals in the western and northern steppes, where growing crops is extremely difficult. However, they did not detect any milk proteins from the southern-central and southeastern valleys, where more farmable land is available.
Furthermore, all the individuals with evidence of milk consumption were recovered from sites higher than 3,700 meters above sea level, with almost half recovered above 4,000 meters, and the highest at the extreme altitude of 4,654 meters.
These findings indicate that dairying was crucial in supporting early pastoralist occupation of the highlands. Ruminant animals could convert the energy locked in alpine pastures into nutritional milk and meat, fueling the expansion of human populations into some of the world’s most extreme environments.
Next, the researchers would like to use the same method in combination with ancient DNA to find out more about the oral health of ancient populations in the hinterland plateau, as well as explore dairying on the eastern plateau and other parts of China.