New advances in the study of prehistoric human activity on the Tibetan Plateau

Abstract

The origin, nature and timing of prehistoric human activity on the Tibetan Plateau has become a major research topic in recent years, and great progress has been made in the study of the earliest human activity on the plateau and in the origin of modern Tibetans. The earliest human presence on the plateau has been updated by two important new studies. Rich blade assemblages found in the excavation of the Nwya Devu site shows that modern humans occupied the interior region of the Tibetan Plateau, above 4600 m a.s. l., some 30−40 thousand years ago. Recently, a study of a human mandible fossil found in Xiahe County, Gansu Province, in the northeastern Tibetan Plateau, indicated that Denisovans occupied the Tibetan Plateau at least 160000 years ago, much earlier than the arrival of modern humans to the region. The latter study also implies that the high-altitude adaptation gene, which occurs widely among modern Tibetans and Sherpa, was probably contributed by local archaic humans, like the Xiahe Denisovans. These two studies not only point to the long and complex human history in the Tibetan Plateau, but they also indicate the complexity of human evolution in the Middle and Late Pleistocene in East Asia. Whether early Holocene hunter-gatherers had already permanently settled on the Tibetan Plateau before the arrival of millet and barley agriculture after the middle Holocene, has become another major research topic in the study of the prehistoric human history of the Tibetan Plateau. However, due to the current lack of reliable evidence for the seasonality of Paleolithic site occupations in the Tibetan Plateau, the issue remains difficult to resolve. The origin of modern Tibetans has been debated for decades. A new linguistic study of the phylogeny and the time depth of the original divergence of the Sino-Tibetan language, based on Bayesian phylogenetic analysis of 109 languages, indicates that Sino-Tibetan languages diverged during some 4200 to 7800 years ago, which points to Neolithic population dispersals to the Tibetan Plateau and their close relationship with modern Tibetans. In addition, a new genetic study, based on mitochondrial DNA (mtDNA) analyses of 8277 Tibetans and 58514 individuals from the surrounding populations, has traced the genetic legacy of modern Tibetans to the historical or even Neolithic periods. Calculation of the time depth of the two common haplogroups in modern Tibetans found in this study, implies that these two groups of populations originated in northern China between 6000 and 10000 years ago and differentiated between 4000 and 5200 years ago. Both of these studies are consistent with previous archaeological studies which propose that Neolithic and Bronze Age populations moved to the Tibetan Plateau from a substantial considerable of areas in North China. More importantly, the two studies further confirm the close relationships between Neolithic millet farmers and modern Tibetans, clarifying the origin of modern Tibetans. There have also been several new Paleolithic archaeological studies of the regions surrounding the Tibetan Plateau. A deeper understanding of the Initial Upper Paleolithic in North China, Mongolia and Siberia, and new findings of the Levallois technology in the Jinsitai and Tongtian cave sites in North China, indicate a dispersal route of Paleolithic populations from the north to the Tibetan Plateau. Other studies also propose possible population migration routes in the southeastern and southwestern plateau, although archaeological evidence is currently lacking. Together with the new Paleolithic archaeological findings for the Tibetan Plateau, it appears that different human groups, including Denisovans, Neanderthals and modern humans, were living in or around the Tibetan Plateau during the Middle to Late Pleistocene. Although recent studies provide new clues for understanding their inter-relationships, additional questions have arisen, and more multidisciplinary studies are needed in the future to address them. Above all, these new studies are crucial for understanding the mechanisms by which prehistoric humans spread to and in the Tibetan Plateau, and their adaptation to the high elevation environments. In addition, they shed new light on the origin of modern humans, as well as on human evolution in East Asia during the Middle and Late Pleistocene.