Denisovan

The Denisovans or Denisova hominins ( /dɪˈniːsəvə/ di-NEE-sə-və) are an extinct species or subspecies of archaic humans in the genus Homo. Pending its taxonomic status, it currently carries temporary species or subspecies names Homo denisova, Homo altaiensis, Homo sapiens denisova, or Homo sp. Altai. In 2010, scientists announced the discovery of an undated finger bone fragment of a juvenile female found in the Denisova Cave in the Altai Mountains in Siberia, a cave that has also been inhabited by Neanderthals and modern humans. The mitochondrial DNA (mtDNA) of the finger bone showed it to be genetically distinct from Neanderthals and modern humans. The nuclear genome from this specimen suggested that Denisovans shared a common origin with Neanderthals, that they ranged from Siberia to Southeast Asia, and that they lived among and interbred with the ancestors of some modern humans, with about three to five percent of the DNA of Melanesians and Aboriginal Australians and around six percent in Papuans deriving from Denisovans. Several additional specimens from the Denisova Cave were subsequently discovered and characterized, as was a single specimen from the Baishiya Karst Cave on the Tibetan Plateau in China. A comparison with the genome of a Neanderthal from the Denisova cave revealed local interbreeding with local Neanderthal DNA representing 17 percent of the Denisovan genome, and evidence of interbreeding with an as yet unidentified ancient human lineage, while an unexpected degree of mtDNA divergence among Denisovans was detected. The lineage that developed into Denisovans and Neanderthals is estimated to have separated from the lineage that developed into 'anatomically modern' Homo sapiens approximately 600,000 to 744,000 years ago. Denisovans and Neanderthals then significantly diverged from each other genetically a mere 300 generations after that. Several types of humans, including Denisovans, Neanderthals and related hybrids, may have each dwelt in the Denisova Cave in Siberia over thousands of years, but it is unclear whether they ever cohabited in the cave. Denisovans may have interbred with modern humans in New Guinea as recently as 15,000 years ago. The Denisova Cave is in south-central Siberia, Russia in the Altai Mountains near the border with Kazakhstan, China and Mongolia. It is named after Denis, a Russian hermit who lived there in the 18th century. The cave was originally explored in the 1970s by Russian paleontologist Nikolai Ovodov, who was looking for remains of canids. In 2008, Michael Shunkov from the Russian Academy of Sciences and other Russian archaeologists from the Institute of Archaeology and Ethnology of Novosibirsk investigated the cave. They found the finger bone of a juvenile hominin, originally referred to as the 'X woman' (referring to the maternal descent of mtDNA), or the Denisova hominin. Artifacts (including a bracelet) excavated in the cave at the same level were dated using radiocarbon and oxygen isotopes to around 40,000 BP. Excavations have since revealed human artifacts showing an intermittent presence going back 125,000 years. A team of scientists led by Johannes Krause and Svante Pääbo from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, sequenced mtDNA extracted from the fragment. The cool climate of the Denisova Cave preserved the DNA. The average annual temperature of the cave is 0 °C (32°F), which has contributed to the preservation of archaic DNA among the remains discovered. The analysis indicated that the Denisova hominin 'diverged from a common ancestor well before Neanderthals and modern humans did'—around 1 million years ago. The mtDNA analysis further suggested that this new hominin species was the result of an earlier migration out of Africa, distinct from the later out-of-Africa migrations associated with modern humans, but also distinct from the even earlier African exodus of Homo erectus. Pääbo noted that the existence of this distant branch creates a much more complex picture of humankind during the Late Pleistocene. This work shows that the Denisovans were actually a sister group to the Neanderthals, branching off from the human lineage 550,000 years ago, and diverging from Neanderthals, probably in the Middle East, 300,000 years ago. A second paper from the Svante Pääbo group reported the prior discovery of a third upper molar from a young adult, dating from about the same time (the finger was from level 11 in the cave sequence, the tooth from level 11.1). The tooth differed in several aspects from those of Neanderthals, while having archaic characteristics similar to the teeth of Homo erectus. They performed mtDNA analysis on the tooth and found it to have a sequence somewhat similar to that of the finger bone, indicating a divergence time about 7,500 years before, and suggesting that it belonged to a different individual from the same population. A team at the Max Planck Institute for the Science of Human History, led by Katerina Douka, have radiocarbon dated specimens from Denisova Cave, and estimate that the oldest group were present in the cave as early as 195,000 years ago (95.4% probability). These specimens from the Denisova cave in the Altai Mountains remained the only known examples of Denisovans until 2019, when a research group led by Fahu Chen, Dongju Zhang and Jean-Jacques Hublin described a partial mandible discovered in 1980 by a Buddhist monk in the Baishiya Karst Cave in Xiahe County on the Tibetan Plateau (China). The fossil became part of the collection of Lanzhou University, where it remained unstudied until 2010. It was determined by ancient protein analysis to contain collagen that by sequence was found to have close affiliation to that of the Denisovans from the Altai, while uranium decay dating of the carbonate crust enshrouding the specimen indicated it was more than 160 thousand years old.