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The Tibetan plateau, often called the “roof of the world”, is one of the most hostile climatic regions in the world.
Yet people have made the world’s highest and largest plateau--covering some 250,000 sq km and at a mean elevation of over 4,000 metre—their home. Human settlement in this area far predates the Buddhist culture that it is now associated with. Today, barley is the most prevalent crop in the plateau. However, the earliest crops of the region were millets.
A recent study published in the journal Proceedings of the National Academy of Sciences (PNAS) shows that global cooling, which began around the late 3rd millennium BC, created a situation in which cultivation of millet became impossible for the people living in the eastern fringes of the Tibetan Plateau. This may have led to the abrupt collapse of this ancient civilisation around 2000 BC.
The study, which was led by Jade D’Alpoim Guedes of the Washington State University, finds a transition to wheat and barley after an interval of around 300 years.
Guedes says apart from millet agriculture, the early inhabitants of this area reared pigs. They lived in small but permanent villages and used a characteristic form of pottery which is known in China as the Majiayao type.
The study presents archaeobotanical evidence from the Ashaonao, Haimenkou and other archaeological sites in Tibet about the use of wheat and barley from around 1700 BC. An abundance of ancient wheat and barley seeds found at the sites suggested the crops rapidly replaced millet as the staple food source of the region during the second millennium BC, according to a news release of Washington State University. The study says the ability of these crops to tolerate frost and their lower heat requirements helped them survive in the cooler temperatures that prevailed in this period. These crops became an important part of subsistence living and may have later spread to other parts of East Asia to become the staple crops of the region. Wheat and barley not just helped people adapt to these cooler conditions but probably also helped them spread to a wider area and to higher elevations.
Collapse or adaptation?
Guedes says, “We are not sure what happened to the people that occupied this region between 2000-1700 BC and this is something further research in the area needs to resolve. All we know now is that continuing with farm millet would have been challenging for them.”
John Belezza, a scholar in Tibetan prehistory, agrees with this assessment and calls the phase between 2000 and 1700 BC as “an intriguing period when middle Bronze Age civilizations in the greater region seemed to have collapsed”.
Guedes says collapse of the civilisation seems a distinct possibility because the material culture and settlement patterns of those who practised wheat and barley cultivation was very different from those who practised millet agriculture, which has led many archaeologists to believe that the people who grew wheat and barley may have migrated from elsewhere. But she adds it is also possible that people migrated to areas of lower altitude, or that they simply changed their strategies to include wheat, barley and pastoralism. Guedes and John say archaeological studies in the area are still in the early phase and several questions remain unanswered.
However, the fact that people adapted to this cold, low-oxygen climate, undertook agriculture and made permanent settlements in the area is itself a testament to human fortitude and skill in the face of adversities.
Full circle
But now the Tibetan plateau is once again experiencing change in climate. There are some areas in the south-eastern plateau where temperatures are 6°C higher than they were 200 years ago.
This increase in temperature is now making it difficult for the inhabitants of Tibet to grow cold weather crops and raise and breed yaks, says the Washington State University press release.
“So now we have a complete reversal, and climate warming is having a big impact on the livelihood of smaller farmers on the Tibetan Plateau,” Guedes says.