Late Middle Pleistocene Denisovan mandible from the Tibetan Plateau
Nebert, Daniel (nebertdw)
Wed 6/12, 12:53 PM
Denisovans are an extinct hominin (human-like) group related most closely to Neanderthals (another extinct hominin); Denisovans are known only from fossil fragments that were identified at Denisova Cave (in Altai, Russia). However, their genomic legacy (i.e. distinct DNA sequence haplotypes, ‘patterns’) has been detected in several Asian, Australian and Melanesian populations — suggesting they once might have been widespread.
“Introgression” [also known (in genetics) as ‘introgressive hybridization’, this is the transfer of genetic information from one species to another as a result of hybridization between them and repeated backcrossing] was a term just used in a recent GEITP email, to describe killifish in the Gulf of Mexico. Denisovan introgression into present-day Tibetans, Sherpas and neighboring populations includes positive selection for the Denisovan allele of the endothelial PAS domain-containing protein-1 gene (EPAS1); this allele provides high-altitude adaptation to hypoxia (i.e. low O2) in present-day humans inhabiting the Tibetan Plateau. This Denisovan-derived adaptation is currently difficult to reconcile — given the low altitude of Denisova Cave (700 m altitude), combined with earliest evidence of a high-altitude presence of humans on the Tibetan Plateau “only” ~30–40 thousand years before present.
Furthermore, relationships of various Middle Pleistocene (781,000 to 126,000 years ago) and Late Pleistocene (126,000 to 5,000 years ago) hominin fossils in East Asia with Denisovans are difficult to resolve — owing to limited morphological information on Denisovans and lack of paleogenetic data on Middle Pleistocene hominin fossils from East Asia and tropical Oceania. Authors [see attached article] describe a Denisovan mandible (jaw bone), identified by ancient protein analysis, found on the Tibetan Plateau in a cave in Xiahe (Gansu, China); they determined the mandible to be at least 160,000 years old (via radioisotope-dating analysis). This bone provides direct evidence of Denisovans existing outside the Altai Mountains, and this specimen offers unique insights into Denisovan mandibular and dental morphology.
These findings thus confirm that archaic hominins occupied the Tibetan Plateau in the Middle Pleistocene Epoch, and that the genome of these hominins had adapted successfully to high-altitude hypoxic environments — lo-o-o-o-ong before the arrival of modern Homo sapiens in that region. 😊