Mysterious, now extinct, members of the human lineage called Denisovans have lived on the roof of the world for 100,000 years or more.
Denisovan mitochondrial DNA extracted from the sediment layers of the Baishiya Karst Cave on the Tibetan Plateau indicates that these humans inhabited the site about 100,000 years ago and again about 60,000 years ago, say geoarchaeologist Dongju Zhang of Lanzhou University (China) and his colleagues. . These are the first examples of Denisovan DNA found outside the Denisova cave in Siberia (SN: 16/12/19).
Cave sediments dating back 50,000 to 30,000 years ago also produced Denisovan mitochondrial DNA, scientists reported on Oct. 30. If further research confirms that age estimate, it increases the likelihood that Denisovans would have survived on the Tibetan Plateau long enough to meet the first humans to reach those heights 40,000 years ago.
In that case, the old new humans in the air of the region may have acquired genetic traits advantageous to that environment by mating with resident Denisovans. Today’s Tibetans carry a Denisovan gene variant that aids survival at high altitude (SN: 02/02/14), although it is unclear whether mestizos have occurred on the Tibetan plateau.
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Zhang's group previously identified a lower-jawed fossil from the Baishiya karst cave as coming from a Denisovan who lived at least 160,000 years ago (SN: 5/1/19). That analysis focused on the protein structure of the jaw, not the DNA, leaving questions about the evolutionary identity of the find.
In the new study, Denisovan mitochondrial DNA in the Baishiya karst cave – found in layers of sediment that also contained stone tools and pieces of animal bones – showed close links to mitochondrial Denisovan DNA in the Denisova cave, located about 2,800 kilometers northwest of the site of the Tibetan Plateau. Overall, the new findings suggest "that Denisovan populations were widespread in eastern Eurasia and had adapted to the Tibetan Plateau for a long time," Zhang says.
Yuanyuan Han, D. Zhang, Lanzhou Univ.
Mitochondrial DNA, usually inherited from the mother, provides a closer view of a population’s evolutionary past than nuclear DNA, which is inherited from both parents. Zhang's group has not yet found Denisovan's nuclear DNA in the sediment of the Baishiya karst cave.
Denisovan genetic evidence remains scarce, says paleogeneticist Carles Lalueza-Fox of the Institute of Evolutionary Biology in Barcelona. But evidence of people’s inherited Denisovan DNA today suggests that Denisovans ranged from the cold Tibetan plateau to tropical Southeast Asia, says Lalueza-Fox, who did not participate in the new study.
Given its wide Asian distribution, it is suspected that Denisovan populations developed a number of genetic traits and cultural behaviors.
A second study in the same issue of Science supports that idea. Nuclear DNA extracted from fossils of two ancient Asian Homo sapiens: one dated 34,000 years ago in Mongolia and the other about 40,000 years ago in China (SN: 21/1/13) – includes segments inherited from a specific line of Denisovans, says one team led by paleogeneticist Diiendo Massilani of the Max Planck Institute for Evolutionary Anthropology in Leipzig. These genetic segments are found in present-day continental Asians, but are different from the Denisovan DNA that modern Papuans and Aboriginal Australians apparently inherited from ancestors that mingled with another Denisovan population, scientists report.