Mitochondrial Genome Study Of Ancient Populations On The Tibetan Plateau And Some Surrounding Areas

The Tibetan Plateau is known as the "Third Pole of the World".Its harsh natural environment constantly poses a serious challenge to human survival.Therefore,questions about prehistoric human activities on the Tibetan Plateau have received widespread attention from academics.Recent archaeological evidence and genetic studies have greatly improved our understanding of the prehistory.But,at the same time,when faced with the two sides of the debate on "when did humans first move onto the plateau" and "when did humans first settle on the Tibetan Plateau",we can't help but be caught in a maze.The growing field of ancient DNA research provides us with another perspective on the genetic structure and migration of ancient populations and their relationship to present-day populations on the Tibetan Plateau.Thus,in this dissertation,we investigated the matrilineal inheritance of populations in and around different regions of the Tibetan Plateau and across different time periods.To this end,we successfully extracted mitochondrial DNA(mtDNA)from 75 ancient individuals from the Tibetan Plateau that date between 5200 and 300 years ago.We also extracted mtDNA from four ancient individuals from the Danyin Cave site in Yunnan,dating more than 3400 years ago.We obtained the following findings:First,we found genetic differences between high-altitude and low-altitude ancient populations on the Tibetan Plateau,as well as a close genetic relationship between them than other present-day populations.Second,we found two dispersals of ancient populations on the Tibetan Plateau.The first was a more recent population expansion associated with haplogroup M9alalclbla,which was in the high-altitude populations from about 2125 to 1100 years ago.Second,the population of haplogroup D4j lb spread from lower to higher altitudes between 4750 to 2125 years ago.Third,we used simulations to demonstrate that ancient and present-day populations on the Tibetan Plateau have genetic continuity.The ancient populations at high and low altitudes have a partial maternal genetic contribution to present-day Tibetans,but that is insufficient to fully explain the ancestral origin of present-day Tibetans.Lastly,we found that the ancient population from the 3400-year-old Dayin Cave site located in Yunnan is not closely related genetically to the ancient population on the Tibetan Plateau.Other ancient populations in Yunnan(e.g.,the hanging coffin burial population)also do not show a close genetic relationship with ancient populations on the Tibetan Plateau.