In the world's "Third Pole" of the Qinghai-Tibet Plateau, domestic yaks, wild yaks, and their hybrid descendants - dzo, hold significant importance for human settlement in extreme high-altitude environments. They serve not only as the mainstay for high-altitude agriculture, plowing, and transportation but also possess multifaceted value: yak meat and dairy products such as butter and yogurt are vital food resources, yak wool woven into tents provides resilience against fierce winds and harsh cold, and yak dung serves as a primary fuel indispensable in every household.
For a long time, questions regarding the origins and domestication of yaks and wild yaks on the Qinghai-Tibet Plateau, as well as the utilization of dzo, have been of great interest in genetics and archaeology. Recently, a research paper on the prehistoric domestication of yaks and the utilization of wild yaks on the Qinghai-Tibet Plateau was jointly completed by the Archaeological Science Center of Sichuan University and the research team of Northwest A&F University, and published in "Science Advances".
The research integrated traditional animal archaeology identification methods with ancient DNA sequencing technology, analyzing the bovine bones unearthed from the Bangga site in Qiongjie County, Shannan City, Tibet Autonomous Region. The results indicate that 2500 years ago, pastoralists on the Qinghai-Tibet Plateau had already begun extensive breeding of yaks, wild yaks, and dzo.
A slice of early pastoral development history on the Qinghai-Tibet Plateau has now been unveiled.
Four Years of Excavation and Screening
Situated at an altitude of 3750 meters, the Bangga site, dating back 3000 to 2000 years, is one of the few high-altitude prehistoric sites in Tibet that has been systematically excavated.
Since 2015, Professor Lü Hongliang's team from the Archaeological Science Center of Sichuan University, in collaboration with the Tibet Autonomous Region Institute of Cultural Relics Protection and the Shannan City Museum, has conducted four years of archaeological excavations at Bangga. The sorting and analysis of tens of thousands of unearthed relics, including pottery shards, stone artifacts, animal bone specimens, and plant seeds, were primarily led by the Archaeological Science Center of Sichuan University.
During the excavation process, in addition to the conventional method of handpicking, researchers also extensively used refined screening and flotation to collect artifacts.
"Due to the long period of use of the Bangga site and the frequent and diverse activities of ancient people at the site, there are vast amounts of tiny pottery fragments, bone fragments, and carbonized plant seeds within the site. In response to this situation, we used screening throughout the excavation of early strata and remains," explained Zhang Zhengwei, a postdoctoral fellow at the Archaeological Science Center of Sichuan University. The mesh size of the screen was adjusted according to the situation of the unearthed items, with a main aperture size of 6mm * 6mm.
To fully collect smaller artifacts such as plant seeds that are not easily identifiable by the naked eye in the site, researchers employed flotation. "By adding water to the fill, the lighter carbonized seeds will float up."
For specimens with relatively good preservation or special burial methods, researchers used total stations and RTK equipment to record their three-dimensional coordinates on-site, facilitating accurate reconstruction of their excavation positions in the site. "When excavating early remains, we also divided larger features such as stone structures into 1-square-meter grids, collecting different artifacts such as pottery shards, stone tools, and bones in different zones to identify their spatial distribution patterns in the features, thereby exploring the functions of the features and the ancient people's use plans for them," said Zhang Zhengwei.
After screening, researchers classified the unearthed items. Zhang Zhengwei was mainly responsible for the analysis of animal bones. He first selected suspected portions and then used comparative morphology to identify species. In the end, the team collected more than 180 cow bones in total.
"After detailed morphological analysis, we found that these cow bones may contain both wild yaks and domestic yaks," he explained, emphasizing the importance of first positioning the bones to determine which part they belong to, and then identifying the species based on the different bone characteristics of each type of cow.
At the same time, researchers found that the age at death of Bangga cows was over four years old, similar to the strategies for the utilization and management of domestic cattle by pastoralists in modern times as recorded in ethnographic literature. Information on the body parts and surface traces of the excavated cow bones also indicates that the slaughtering and consumption of these cows occurred within the site area.
Archaeological Site at Bangga: Insights from Genetics
After reaching initial conclusions, the team sought validation through molecular biology techniques.
Lü Hongliang promptly reached out to Professor Lei Chuzhao, an expert in the field of cattle and yak breeding from Northwest A&F University. They sent five well-preserved cow bones unearthed from the Bangga site to Professor Lei's laboratory to conduct ancient DNA analysis. The reason for choosing to collaborate with Professor Lei's team was simple: they had been deeply involved in the field of Chinese local yellow cattle for over two decades.
Whether it's the genome of modern Chinese yellow cattle, ancient yellow cattle unearthed from the 3,900-year-old Shimao site in northwest China, or genetic data of yaks and various cattle species from abroad, the team possesses a large genomic database that is relatively advanced domestically. Moreover, they had conducted previous research on cattle species in the Qinghai-Tibet Plateau.
By extracting ancient DNA from the samples and comparing them with the genetic data of yellow cattle unearthed from the Shimao site 3,900 years ago and modern Tibetan cattle, the team fully supported the previous morphological identification results, confirming that the unearthed yellow cattle bones from Bangga belonged to domesticated yellow cattle. "Simultaneously comparing them with the genetic data of modern domesticated yaks and wild yaks, we found that the Bangga yak bones have a very close genetic relationship with modern domesticated yaks, also supporting the fact that the yak bones unearthed from Bangga belong to domesticated yaks," said Associate Professor Chen Ning from the College of Animal Science and Technology at Northwest A&F University.
Researchers also discovered that the yellow cattle from Bangga had a high genetic similarity with the ancient yellow cattle unearthed from the Shimao site and modern Tibetan yellow cattle genomes, indicating a close genetic relationship and genetic continuity. It is speculated that the yellow cattle on the Qinghai-Tibet Plateau during prehistoric times were likely directly introduced from northwest China.
Such genetic continuity also suggests the successful adaptation of prehistoric livestock populations represented by Bangga yellow cattle to the extreme environments of high altitudes. "Because if they were not adapted, the population of these cattle would have significantly decreased and would have been replaced by other cattle species that could adapt, leading to significant genetic changes," explained Lei Chuzhao.
Furthermore, genetic testing showed that Bangga yellow cattle possessed 12.1% to 19.5% domestic yak ancestry, indicating that hybridization between yaks and yellow cattle had occurred at least 2,500 years ago.
In the Qinghai-Tibet Plateau, the fur of hybrid cattle is shorter, they grow faster, and they have higher milk and meat production as well as better draft performance than yaks. "Perhaps the pastoralists in Bangga already knew the benefits of hybrid offspring between yaks and yellow cattle, known as hybrid cattle, and promoted their use," noted Chen Ning, suggesting that this study also provides genetic evidence for investigating the domestication of yaks and the adaptation of yellow cattle to high altitudes.
Slices of History
The achievements of this study are inseparable from the long-term accumulation of researchers.
To answer questions such as which animal the bones belong to and the differences between the same parts of different cattle breeds, it is necessary to rely on the comparison and analysis of a large amount of sample data.
Over the past decade, Zhang Zheng has been specializing in archaeological research on animals in the Qinghai-Tibet Plateau. During this time, he has continuously collected and examined bone information from various common cattle species in the Qinghai-Tibet Plateau from museums, animal research institutes, archaeological institutes, etc. "I have basic information on over a dozen samples of almost every cattle breed, enough to support the identification work this time."
Similarly, Lei Chuzhao has been devoted to the construction of a genetic variation database for Chinese local yellow cattle and has been deeply involved in the field of the origin and evolution of Chinese local yellow cattle for over twenty years, particularly in the systematic study of the genetic diversity of Chinese local yellow cattle.
"This study combines the work of two teams very well," said Lü Hongliang, marking the beginning of a deep fusion of archaeological and ancient DNA research on prehistoric animal remains in the high-altitude regions of the Qinghai-Tibet Plateau. "In the past, perhaps we only obtained ancient DNA information from a bone, but its background information such as site location, age, and morphology was unclear. But this time, we can have a more in-depth understanding, confirmation, and tracing, and vice versa."
Lei Chuzhao also expressed a similar view. "In the past, we might have only drawn a segment of history. But through accumulation, we have mastered modern cattle data and gradually found some information about ancient cattle. This line will be drawn longer, and the process of origin and evolution will become clearer."
However, there are still countless mysteries to be solved in the future. "Questions like the purposes of the cattle at the Bangga site and how they were domesticated, we currently cannot answer," said Zhang Zheng, emphasizing the need for stricter and more detailed archaeological morphology screening of target sites before discussing the next steps. He has also been establishing regional standards for animal bone morphology to improve identification accuracy.
"We are only seeing a slice of history right now," said Lü Hongliang. "Currently, we can only conclude that 2,500 years ago, there were already domesticated yaks on the Qinghai-Tibet Plateau, as well as hybrid breeds of yaks and yellow cattle. But this time point can definitely be pushed further back, and as for how long ago it began, we still need to continue searching."
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