which is ~39 thousand years old, suggesting an early settlement after the dispersal of modern humans across Eurasia.
Second, their Y-chromosomes are dominated by Y-haplogroup D, the sister clade of African haplogroup E, which links in some (unspecified, but I'm guessing old) time depth with such diverse peoples as the Andaman Islanders and the Ainu. Mongolians also share haplogroup D, but this is perhaps not surprising given the well-known links between Mongolia and Tibet. One might attribute the high Tibetan D frequency to drift, but drift acts randomly, and I don't think it's a coincidence that it acted in the same way in three quite different and fairly isolated corners of Eurasia to produce the Tibetan/Andaman/Ainu local peaks in an otherwise rather barren haplogroup D landscape.
There are other interesting details, such as the presence of R1a*(xM17) in Tibet, a haplogroup that has a patchy distribution in Asia. In a sample size of ~2,354 it's possible to get one of these less successful relatives of mega-groups like R-M17, and their systematic study may help root in space the earliest history of these lineages.
Genetic evidence of Paleolithic colonization and Neolithic expansion of modern humans on the Tibetan Plateau
Xuebin Qi et al.
Tibetans live on the highest plateau in the world, their current population size is nearly 5 million, and most of them live at an altitude exceeding 3,500 meters. Therefore, the Tibetan Plateau is a remarkable area for cultural and biological studies of human population history. However, the chronological profile of the Tibetan Plateau's colonization remains an unsolved question of human prehistory. To reconstruct the prehistoric colonization and demographic history of modern humans on the Tibetan Plateau, we systematically sampled 6,109 Tibetan individuals from 41 geographic populations across the entire region of the Tibetan Plateau and analyzed the phylogeographic patterns of both paternal (n = 2,354) and maternal (n = 6,109) lineages as well as genome-wide SNP markers (n = 50) in Tibetan populations. We found that there have been two distinct, major prehistoric migrations of modern humans into the Tibetan Plateau. The first migration was marked by ancient Tibetan genetic signatures dated to around 30,000 years ago, indicating that the initial peopling of the Tibetan Plateau by modern humans occurred during the Upper Paleolithic rather than Neolithic. We also found evidences for relatively young (only 7-10 thousand years old) shared Y chromosome and mitochondrial DNA haplotypes between Tibetans and Han Chinese, suggesting a second wave of migration during the early Neolithic. Collectively, the genetic data indicate that Tibetans have been adapted to a high altitude environment since initial colonization of the Tibetan Plateau in the early Upper Paleolithic, before the Last Glacial Maximum, followed by a rapid population expansion that coincided with the establishment of farming and yak pastoralism on the Plateau in the early Neolithic.