Extinct Human Species Once Thrived in Tibet
New research shows Denisovans lived in Tibet and what they ate to survive
You probably know our species is called Homo sapiens; perhaps you’ve heard that our close evolutionary cousins were the Neanderthals. A few years ago (2010), another species was added to the list of cousins with whom all humans (with genetic lineages outside sub-Saharan Africa) share some DNA: the Denisovans.
Our genetic evidence suggests that Denisovans, like Neanderthals with whom they share a recent common ancestor, were once widely distributed across Eurasia. This can be surmised by the amount of Denisovan DNA found in several populations, primarily those of South, East, and Southeastern Asian descent.
Neanderthal DNA percentages are often given in genetic tests; my grandfather had a little less than 2%. However, Denisovan DNA is not commonly reported in DNA tests, though I would love to know how much I may have in my genes.
Denisovan DNA in modern populations reflects their widespread distribution across Eurasia, with its varying biomes and climates. This shows that Denisovans could adapt to diverse environments with faunal and floral species.
Sadly, physical evidence to back up this claim has been scarce archaeologically.
However, PhD student Huan Xia and colleagues recently published new findings in Nature. The findings discuss the finding of a new Denisovan specimen and explain what animals Denisovans ate and how they adapted to fluctuating environments.
Denisova and Baishiya Karst Caves
In 2008, the first-ever Denisovan remains were found, a finger bone and a molar from Denisova Cave in Siberia, Russia. The cave had been home to Homo sapiens and Neanderthals for the past 300,000 years.
How did archaeologists determine this bone was unlike any they had found before?
Finger bones and teeth are unique to each species, and while variation occurs within each species, these bones are a bit too unique. But that was not enough to conclude the bones belonged to a separate species. It was, however, sufficient to promote further investigation.
As it turned out, the bones were well preserved so scientists could sequence their DNA. In 2010 this was done, and it was determined that the bones were not Neanderthal or Homo sapien.
So what could they be? A new hominin species was named Denisovan after the cave in which it was found.
After its discovery, Denisovan DNA was also identified in current populations across Europe and Asia (depending on the region you are from, you may have between 4–6% Denisovan DNA). This suggests that Denisovans once roamed widely across both continents, interbreeding with other hominin populations they encountered.
In 2019, more Denisovan remains were discovered, hinting at the widespread nature of Denisovans. The remains were collected by a monk who had gone to Baishiya Karst Cave (BKC) (Tibet) to meditate in 1980. When he returned, he brought a mandible and some teeth (Xiahe mandible).
However, he did not know then that these bones belonged to a unique hominin species.
The bones were dated and were found to be at least 160,000 years old.
Together with mitochondrial DNA (mtDNA) recovered from sediments from the BKC, it was shown that Denisovans occupied the high-altitude Tibetan cave from 167,000 to 40,000 years ago.
Analyzing the Animal remains at Baishiya Karst Cave
Archaeological excavations commenced at BKC and revealed stratigraphic layers (sediment deposit layers) with evidence of hominin occupation dating as far back as 190,000 years. Thousands of fragmentary bones belonging to various animal species, from birds and wolves to yaks and snow leopards and rodents (marmots), were recovered within the sediment.
The sheer number of animal remains presented a unique opportunity to study what the Denisovans ate in the harsh Tibetan Plateau.
Using a combination of traditional zooarchaeology (identifying animal species based on bones) and Zooarchaeology by Mass Spectrometry (ZooMS), which identifies animal species based on their unique protein signatures, the researchers were able to identify 2005 bone fragments taxonomically.
Most animals were bovids, specifically species belonging to the sub-family Caprinae (sheep, goats, antelopes, etc). More specifically, they identified (among others) Tibetan gazelle, Tibetan fox, red deer, musk deer, porcupine, groove-toothed flying squirrel, spotted hyena, snow leopard, wolf, and golden eagle.
The animal composition suggests that during the Middle (781,000 to126,000 years ago) and Late Pleistocene (126,000 to 11,700 years ago), the Tibetan plateau was grass-dominated with small forest-shrub areas.
Further analysis revealed hominin activity, such as cut marks, percussion notches, and other bone modifications that suggested marrow extraction and skinning.
These bone modifications were found in a wide range of species, from birds to carnivores to small mammals, suggesting that the hominins who made them relied on many species to survive the harsh conditions of their homes.
A New Denisovan Identified
A rib, broken in half during excavation, was identified and dated. It was around 48,000 to 32,000 years old. Sending the rib through ZooMS screening, the protein signature determined it belonged to a Homininae.
Sadly, the protein signature, despite having comparative sequences for each species, cannot tell us if the rib belonged to Homo sapiens, Neanderthal or Denisovan.
However, the scientists deduced since there is no evidence that other archaic hominins lived in northeastern Tibet at the time, the rib deposited at BKC had to belong to a Denisovan.
Denosivans were the only known Homininae species to have lived in the area then. This discovery extends the fossil evidence for the presence of Denisovans from the Middle Pleistocene into the Late Pleistocene at BKC.
This means that Denisovans had occupied the cave and the surrounding Tibetan Plateau since at least 167,000 years ago and remained there until their sudden disappearance from the area between 48,000 and 32,000 years ago.
The discovery of the Denisovan rib and animal remains gives us a unique insight into how our human cousins lived, what they ate, and how they survived in the Tibetan Plateau for thousands of years.
Slowly but surely, we are piecing together evidence of where Denisovans lived and when. This helps us narrow down the timeline of when they started interbreeding with other hominins, providing modern populations with a piece of their DNA.
The above results were based on findings from excavations pre-dating COVID-19. Now researchers are back at the cave excavating new material, and perhaps more insights into Denisovan life will be gleaned from these new finds.
Do you have any Denisovan DNA?
And what do you think we will learn about our extinct evolutionary cousins?
Let me know your thoughts, and if you’d like to support me further, why not Buy Me A Coffee?
References
- Callaway, E., How Denisovans thrived on top of the world: mysterious ancient humans’ survival secrets revealed. Nature.
- Ruder, D.B. (2012). Spelunking for Genes: A bone and a molar hold clues to a new branch of our family tree. [online] Harvard Medicine. Available at: https://magazine.hms.harvard.edu/articles/spelunking-genes [Accessed 13 Jul. 2024].
- Teague, R. and McRae, R. (n.d.). Ancient DNA and Neanderthals. [online] The Smithsonian Institution’s Human Origins Program. Available at: https://humanorigins.si.edu/evidence/genetics/ancient-dna-and-neanderthals [Accessed 13 Jul. 2024].
- Xia, H., Zhang, D., Wang, J., Fagernäs, Z., Li, T., Li, Y., Yao, J., Lin, D., Troché, G., Smith, G.M. and Chen, X., 2024. Middle and Late Pleistocene Denisovan subsistence at Baishiya Karst Cave. Nature, pp.1–6.
