A review of Denisovans

Abstract

In 2010, geneticists reported the mitochondrial DNA and nuclear DNA sequences of a fragment of hominin phalanx found in Denisova cave, in the Altai Mountains in Russia, and the discovery of a new archaic human group which they named “Denisovans”. Subsequently, significant progress has been made in research on Denisovans. This paper reviews and summarizes recent achievements and advances in Denisovan studies, especially in chronology, archaeology, anthropology and genetics, over the past decade, with the aim of encouraging in-depth research in related fields in China. Comprehensive geochronological studies in Denisova cave suggest that Denisovans and Neanderthals may have occupied the cave during the interval of 287−55 ka (thousand years ago) and during 193−97 ka. Direct dating of hominin fossils, or of strata containing hominin fossils, indicates that Denisovans occupied the cave during 195−52 ka, while there is evidence of Neanderthals occupying the cave during 14.7−9.1 ka. These results reflect the long occupation history of Denisovans and Neanderthals in Denisova cave. In addition, the dating of the Xiahe mandible, from Baishiya karst cave (Xiahe County, Gansu Province, China) in the northeastern Tibetan Plateau, indicates that this is the first Denisovan fossil discovered outside Denisova cave, and suggests that Denisovans occupied the Tibetan Plateau at least at 160 ka, in the late Middle Pleistocene. This extends the spatial distribution of Denisovans from the Altai Mountains to the Tibetan Plateau and indicates that the Xiahe Denisovans may have been adapted to the extremely cold and hypoxic environment of the plateau. Lithic assemblages from Denisova cave include both Levallois and blade technologies produced by either Denisovans or Neanderthals, or both, who coexisted in the cave for a long time. However, preliminary analysis of lithic artifacts collected from Baishiya Karst cave indicates the dominance of simple core and flake technology. In consideration of long coexistence of two archaic humans in Denisova cave, and the archeological work in Baishiya Karst cave is still in its infancy stage, the cultural connotation of Denisovans needs further comprehensive study. Considering the long coexistence of the two archaic humans in Denisova cave, and that archeological work in Baishiya karst cave is still at a preliminary stage, the cultural connotations of the Denisovans require further comprehensive study. The fragments of Denisovan fossils found in Denisova cave provide limited evidence of the morphological characteristics of the phalanx and teeth, while the Xiahe mandible provides more extensive and important evidence of the morphological characteristics of the mandibles of Denisovans. The present study shows that the overall morphological characteristics of the phalanx are closer to those of modern humans than to Neanderthals, although the size of the molars is much greater than that those of Neanderthals and modern humans; in addition, the mandible has several features similar to those of archaic Homo sapiens in East Asia. However, due to the limited fossil evidence, the morphological differences between Denisovans and other archaic humans remain to be comprehensively documented. In addition, in contrast to the Neanderthals’ wide genetic contribution to modern humans, Denisovans only genetically contributed to modern populations in Oceania, East Asia, South Asia and America, and they exhibit a gene flow from superarchaic humans. In addition, multiple deeply differentiated branches may exist within the Denisovan population. These findings imply that Denisovans may have been more widely distributed in Asia than was previously thought and that they possess a more complex evolutionary history. At present, only one high-coverage Denisovan genome has been discovered in Denisova cave and no ancient DNA is preserved in the Xiahe mandible, which limits our understanding of other Denisovan branches. Although we still know little about Denisovans, we anticipate that future in-depth archaeological studies at Baishiya karst cave will provide additional important information on the physical morphology of Denisovans, their genetic characteristics and behavioral culture, and will elucidate the adaptation mechanism of Denisovans to high-altitude environments. In addition, we expect that an increasing number of new discoveries and multidisciplinary endeavors will shed additional light on the Denisovans and thus contribute to the study of human evolution in East Asia.