Scientists Reconstructed Genetic Origins and Population History of Tibetan Highlanders
Authors:Dr.XU Shuhua’s group Time:2016-08-31 Read:187
Current knowledge of the origin and population history of Tibetan highlanders is still very much in its infancy and controversial. Who are the Tibetans? How long have they been living at the Tibetan Plateau, the “Roof of the World”? Who were the early highlanders? Were they modern human or non-modern human species? Whether is there a genetic continuity, or just some continuity of culture, between the pre-historical populations and present-day Tibetans? These questions remain the most contentious puzzles in history, anthropology, and genetics.
A research team led by Dr. XU Shuhua from CAS-MPG Partner Institute for Computational Biology (PICB),Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences analyzed deep-sequenced genomes of 38 Tibetan highlanders together with available data on archaic and modern humans, and comprehensively characterized the ancestral makeup of Tibetans and uncover their origins.
Their analysis showed that Tibetans arose from a mixture of multiple ancestral gene pools, in particular, analysis of ~200 contemporary populations showed that Tibetans share ancestry with populations from East Asia (~82%), Central Asia and Siberia (~11%), South Asia (~6%), and western Eurasia and Oceania (~1%). The Tibetans and Sherpas show closest affinities to the surrounding highland groups such as Yizu, Tu and Naxi, followed by lowland Han Chinese. The divergence time between Tibetan and Han Chinese populations was estimated to be ~15,000 to ~9,000 years.
The team applied state-of-the-art methods and also developed a new method (ArchaicSeeker) to search for ancient ancestries in the genomes of Tibetan highlanders. The team identified elevated archaic ancestry in Tibetans, and they dated the most recent common ancestors of the surviving archaic lineages in the Tibetan genomes back to ~60,000 – 40,000 years ago, predating the Last Glacial Maximum (LGM). Their results indicate that plateau colonization and the altitudinal adaptation of human beings were considerably earlier and more complicated than had previously been suspected.
This study provides compelling evidence for the co-existence of both Paleolithic and Neolithic ancestries on a genome-wide scale in the modern Tibetan gene pool, which supports a genetic continuity between pre-LGM highland-foragers and present-day Tibetans. The Paleolithic ancestries in the modern Tibetan gene pool entangle Denisovan-like, Neanderthal-like, ancient- Siberian-like, and unknown archaic sequences, indicating that Tibet remained a human melting pot where interbreeding occurred among different hominine groups before the LGM. The team suggested that the highly differentiated sequences harbored in highlanders’ genomes were most likely inherited from pre-LGM settlers of multiple ancestral origins, a genetically admixed group which was named SUNDer, and maintained in high frequency by natural selection. The team further proposed a two-wave “Admixture of Admixture” (AoA) model to help explain the ancestral make-up and pre-history of Tibetans and Sherpas.
This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, by National Natural Science Foundation of China grants, and by the Science and Technology Commission of Shanghai Municipality.
Prof. Dr. XU Shuhua, Group Leader & Principal Investigator
Max Planck Independent Research Group on Population Genomics,
CAS-MPG Partner Institute for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences,
A sketch-map for the origins and demographic history of Tibetans and Sherpas. A simplified model for the origins and evolutionary history of Tibetans and Sherpas based on the observations and estimations from this study. MRCA0: most recent common ancestor of modern human and archaic hominoids; MRCA1: most recent common ancestor of Eurasians; MRCA2: most recent common ancestor of HAN and TIB; MRCA3: most recent common ancestor of TBN and SHP. SUNDer: a tentative label for the early settlers who contributed ancient or archaic ancestry to present-day Tibetan highlanders. The two dashed lines connecting HAN and TBN, and TBN and SHP represent possible gene flow occurred between populations. (Image provided by Dr.XU Shuhua’s group)