Prehistoric Colonization and Demographic History of Modern Humans on the Tibetan Plateau

Abstract

Abstract Tibetans differ significantly from other human populations living at low elevations in terms of their superior physiological adaptation to hypoxia at high altitudes. These adaptations to hypoxic environments, such as those on the Tibetan Plateau, likely reflect a long history of colonisation in the area. Archaeologists have previously proposed the earliest human occupation of the Tibetan Plateau some 40 thousand years ago (ka) in the Upper Palaeolithic, but there is some controversy to this dating, as some researchers are sceptical of these Upper Palaeolithic autochthons surviving the harsh conditions of the Last Glacial Maximum (LGM, 22–18 ka), suggesting that modern Tibetans then descended from immigrants that settled the Plateau following the end of the LGM. Recent genetic evidence somewhat supports the earlier explanation of permanent colonisation of Tibetan Plateau likely 30 ka, during the early Upper Palaeolithic, followed by major migration(s) of Neolithic agriculturalists into the Plateau from the modern‐day northwestern China, eventually leading to the establishment of agriculture and pastoralism on the Plateau, which provided a sufficient and stable food supply necessary for the rapid population growth that occurred on the Plateau around 10–7 ka during the early Neolithic. Key Concepts: The Tibetan Plateau represents one of the most extreme environments for human settlement due to its severe hypoxia at high altitude, making it an ideal ‘natural laboratory’ for studying molecular mechanism of human adaptation to high‐altitude hypoxia. Modern Tibetans possess superior physiological adaptations to hypoxia at high altitudes, likely due to a long history of colonisation of the Tibetan Plateau by their ancestral populations. Researchers are divided on whether modern humans successfully settled on the Plateau during the Upper Palaeolithic and survived the harsh conditions of the Last Glacial Maximum (LGM, 22–18 ka), with sceptics arguing that Tibetans likely descended from postglacial immigrants that settled on the Plateau following the end of the LGM. Recent application of phylogeographic analysis of Y chromosome and mtDNA lineages of modern human populations have proven to be powerful tools in inferring the demographic history of human populations, though there can be marked differences in the resulting models due to different samples and markers. Genetic evidence supports the hypothesis of permanent colonisation of Tibetan Plateau approximately 30 ka in the early Upper Palaeolithic, with some portions of the population surviving the LGM and mixing with the later Neolithic immigrants, who introduced agriculture and pastoralism, which allowed for the rapid population expansion approximately 10–7 ka in the early Neolithic. Both the Upper Palaeolithic autochthons and Neolithic agriculturalists significantly contributed to the observed genetic diversity and adaptation of present‐day Tibetan populations inhabiting the Tibetan Plateau. Recent genetic findings provide novel insights into the prehistoric colonisation and human migration on the Tibetan Plateau, which may have implications to several different fields of study, as well as to genetic researchers in terms of subject selection for studies of genetic adaptation to high‐altitude hypoxia in Tibetan populations as well as others.