Denisovan DNA in Tibetan Cave Changes History of Early Humans in Asia
An international team has found evidence that could change our understanding of a mysterious species of early humans, the Denisovans. They have found DNA from these humans in a Buddhist cave on the Tibetan Plateau in China. These finds are adding to experts’ knowledge of the mysterious Denisovans and how they interacted with modern humans as they migrated into Asia.
The Baisiya Karst Cave is approximately 10,400 feet (3,200 m) high on the rugged Tibetan Plateau. For the local Buddhist monks, the cave is a sacred site. Many years ago, a mysterious lower jawbone (mandible) was found in the cave and it has recently been re-examined. In 2019 researchers proposed it belonged to a Denisovan, but this was disputed.
The Xiahe mandible is the first Denisovan fossil to have been discovered outside of the Denisova Cave in Siberia. Unearthed in the Baishiya Karst Cave by a Tibetan monk in 1980, scientists used protein analysis in 2019 to identify the ancient human from this ancient jawbone. (Dongju Zhang / CC BY-SA 4.0 )
Denisovans: Relatives of Modern Humans
About 40,000 years ago, this species of archaic human lived across Asia. A close relative of Neanderthals, the Denisovans even interbred with our ancestors. Many modern Australasians and Asians have Denisovan ancestry. Almost no remains of the hominins have been found outside of the Denisova Cave in Siberia, after which the species is named.
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Because of the scarcity of remains, the jawbone could provide precious insights into the extinct archaic human species. However, the only evidence that it was Denisovan was “based on a single amino acid position,” reports Cosmos. Archaeologist Dongju Zhang of Lanzhou University and her colleagues wanted to prove once and for all that the jawbone was from a Denisovan and sought DNA which would be used as conclusive proof.
The Baishiya Karst Cave on the Tibetan Plateau in China has been exceptionally challenging for archaeologists. A sacred Buddhist site, the team was forced to work at night so as not to disturb worshipers. (Han Yuanyuan / Chinese Academy of Sciences Headquarters )
Excavations in Sub-Zero Temperatures
In the winter of 2018, they worked with an international team on an intensive investigation of the cave. This excavation was terribly challenging. Because the cave is sacred to local Buddhists, the team could only work at night so as not to disturb the faithful during the day. They also had to remove all traces of their work before the morning and often worked in temperatures as low as –18°C (-0.4°F).
The experts dug deep into the soil of the cave. While they did not find any hominin bones, they found something even better: traces of mitochondrial DNA. This is a hugely important discovery. According to Science “Zhang’s team reports the first Denisovan ancient DNA found outside the Denisova Cave : mitochondrial DNA (mtDNA) gleaned not from fossils, but from the cave sediments themselves.” This is the first time that genetic evidence for the Denisovans has been found outside Siberia. The DNA was extracted from human remains in the topsoil. This was probably left behind in the poop and urine of the Denisovans.
In September 2019 scientists used epigenetics to work out the possible physical makeup of a Denisovan face. Their reconstruction won the 2019 Science magazine’s People’s Choice for Breakthrough of the Year. ( Maayan Harel )
Early Humans in Tibet
Bo Li of the Australian University of Wollongong told Cosmos that they have “detected ancient human fragments that matched mitochondrial DNA associated with Denisovans in four different layers of sediment deposited.” The sediment where the DNA has been dated to around 100,000 and 60,000 years ago and possibly as “recently as 45,000 years back, the time when modern humans were migrating to the eastern part of Asia,” reports News Click .
These findings change the history of early humans in Asia. The researchers wrote in Science that the DNA “extends the time of occupation of the Tibetan plateau by hominins.” Li and his colleagues were able to date the finds by using optical dating, which works by showing when they had been exposed to light. By showing that DNA and dates can be gathered from sediment, this groundbreaking research is paving the way for “a new era of molecular caving,” explains Katerina Douka of the Max Planck Institute in Science.
The find is important because it is the first DNA to have been found outside the Denisovan Cave in Siberia. Unearthed some 1200 km from Siberia, the discoveries in the soil of the cave end a long search for Denisovan DNA outside of Siberia. They also provide further evidence that Denisovans were once widespread across Asia.
Scientists analyze sediment samples from the Baishiya Karst Cave at the lab. Their research has identified Denisovan DNA from as far back as 100,000 years ago. (WANG Xiao / Chinese Academy of Sciences Headquarters )
Denisovan “Superathlete” Gene
But DNA wasn’t all they found. The team also unearthed several artifacts and other remains in the holy cave, as well as a great deal of charcoal which proves that the Denisovans used fire. Moreover, the experts found over 1,300 rudimentary tools and many animal bones, including some from hyenas and rhinos, both of which once roamed Tibet. It has also been speculated that they used the cave as a lookout from which to watch out for prey on the meadows below.
Finding the remains of Denisovans at such an altitude shows that the ancient species could cope with a range of environments and that they were highly adaptable. This ability was inherited by modern Tibetans, allowing them to survive in one of the world’s toughest environments. Modern Tibetans inherited from the Denisovans “a ‘superathlete’ variant of a gene, called EPAS1,” explains Science. However, it only spread widely in the last 5,000 years and may indicate that the extinct archaic humans only lived seasonally in the cave.
More finds are expected to be made at the Baishiya Karst Cave site. Li told Cosmos that their “next target is to date more samples from the cave and try to answer when Denisovans started to occupy the cave and when they ‘disappear’ from the cave.” This could be crucial in understanding modern humans’ interactions with the archaic hominins and perhaps even solve the mystery of their extinction.
Top image: Yao Juanting and Chen Xiaoshan collecting sediment samples inside the Baishiya Karst Cave on the Tibetan Plateau in China. Thanks to the discovery of Denisovan mitochondrial DNA, the team has been able to definitively conclude that Denisovans lived in the area as far back as 100,000 years ago. Source: Han Yuanyuan / Chinese Academy of Sciences Headquarters
By Ed Whelan