Genomic Research Of The Early Bronze Age Populations From Xinjiang

As part of the Silk Road and located at the geographical confluence of Eastern and Western cultures,the Xinjiang Uyghur Autonomous Region(henceforth‘Xinjiang')has long served as a major crossroads for trans-Eurasian exchanges of people,cultures,agriculture and languages.Within and around the Dzungarian Basin,pastoralist Early Bronze Age(EBA)Afanasievo(3000-2600 BCE)sites have been plausibly linked to the Afanasievo herders of the Altai-Sayan region in southern Siberia(3150-2750 BCE),who in turn have close genetic ties with the Yamnaya(3500-2500 BCE)of the Pontic-Caspian steppe located 3,000 km to the west.Since the late 1990s,the discovery of hundreds of naturally mummified remains dating to ca.2000 BCE to 200 CE in the Tarim Basin has attracted international attention due to their so-called 'Western' physical appearance,their felted and woven woolen clothing,and their agropastoral economy that included cattle,sheep/goat,wheat,barley,millet,and even kefir cheese.Such mummies have now been found throughout the Tarim Basin,among which the earliest are those found in the lowest layers of the cemeteries at Gumugou(2135-1939 BCE),Xiaohe(1884-1736 BCE),and Beifang(1785-1664 BCE).These and related Bronze Age sites are grouped within the Xiaohe archaeological horizon based on their shared material culture.Two contrasting hypotheses have been suggested by scholars to explain the origins and 'Western' elements of the Xiaohe horizon,including the Yamnaya/Afanasievo steppe hypothesis(hereafter'steppe hypothesis'),the Bactrian oasis hypothesis(hereafter 'oasis hypothesis').The steppe hypothesis posits that the Afanasievo-related EBA populations in Altai/Sayan mountains spread via the Dzungarian Basin into the Tarim Basin and subsequently founded the agropastoralist communities making up the Xiaohe horizon ca.2000 BCE.In contrast,the 'oasis hypothesis' posits that the Tarim Basin was initially colonized by migrating farmers of the Bactria-Margiana Archaeological Complex(BMAC;ca.2300-1800 BCE)from the desert oases of Afghanistan,Turkmenistan and Uzbekistan via the mountains of Central Asia.Support for this hypothesis is largely based on similarities in the agricultural and irrigation systems between the two regions that reflect adaptations to a desert environment,as well as evidence for the ritual use of Ephedra at both locations.Recent archaeogenomic research has shown that Bronze Age Afanasievo of southern Siberia and BMAC populations of Central Asia have distinguishable genetic profiles,and that these profiles are likewise also distinct from those of pre-agropastoralist hunter-gatherer populations in Inner Asia.As such,an archaeogenomic investigation of Bronze Age Xinjiang populations presents a powerful approach for reconstructing the population histories of the Dzungarian and Tarim Basins and the origins of the Bronze Age Xiaohe horizon.Examining the skeletal material of Bronze Age individuals from sites in the Dzungarian(Nileke,Ayituohan,Songshugou)and Tarim(Xiaohe,Gumugou,Beifang)basins.Through analyzing the ancient genome extracted from earliest Bronze Age tombs in the Dzungaria Basin and the Tarim Basin,respectively,we mainly draw the following conclusions:First,the earliest indigenous populations in the Tarim Basin,including the ancient people from the 4th and 5th phases of the Xiaohe cemetery,the northern cemetery of the Keliya River,and the Gumugou cemetery are highly genetically similar,which is consistent with the similarity of their archaeological characteristics.By analyzing the genomic data of Xiaohe population,we found that they share the most genetic affinity with the AG3 individuals(ANE)from the Paleolithic Afontova Gora site in the Yenisei River 16,000 years ago,further carry significant ancestry components from the ancient Northeastern Asians(ANA).The date of this admixture event between ANE and ANA were estimated to 600010000 years ago.We found that the Xiaohe people do not carry any ancestry contributions from either the Afanasievo or BMAC-related populations,thus the currently ancient DNA results do not support previous hypotheses for the origin of the Tarim mummies.We additionally estimated quite a low level of the genetic differences within the Xiaohe people,suggesting the Xiaohe horizon belong to an ancient and isolated autochthonous people.They made cheese from ruminant milk using a kefir-like fermentation,perhaps learned from descendants of the Afanasievo,and they cultivated wheat,barley and millet,crops that were originally domesticated in the Near East and northern China and which were introduced into Xinjiang no earlier than 3500 BCE,likely via their Inner Mountains Corridor.They buried their dead with Ephedra twigs in a style reminiscent of the BMAC oasis cultures of Central Asia,and they also developed distinctive cultural elements not found among other cultures in Xinjiang or elsewhere,such as boat-shaped wooden coffins covered with cattle hides and marked by timber poles or oars,as well as an apparent preference for woven baskets over pottery.Taken together,although the harsh environment of the Tarim Basin may have served as a strong barrier to gene flow into the region,it was not a barrier to the flow of ideas or technologies,as foreign innovations,such as dairy pastoralism and wheat and millet agriculture,came to form the basis of the Bronze Age Tarim economies.Second,the Early Bronze Age and Cooper Age populations in the Dzungarian Basins are the earliest people in Xinjiang,currently,they derive a majority ancestry from Afanasievo,suggesting the Dzungaria population was formed in a large extent by the expansion of the western Eurasian steppe pastoralists both by the population movement and the transformation of ideas.The observation of Afanasievo-related ancestry in the Dzungaria population provide genetic evidence of that the Tocharian may have been plausibly introduced to the Dzungarian Basin by Afanasievo migrants during the Early Bronze Age.However,the Ayituohan people and Songshugou people(Dzungaria?EBA1),as well as the two Copper Age individuals from the Nileke G218 cemetery(Dzungaria EBA2)share most genetic affinity with the Early and Middle Bronze Age Xiaohe groups in the Tarim Basin,as well as multiple ANE-related populations,such as Botai?CA,West?Siberia?N,and AG3.Our qpAdm results show that with the except of Afanasievo-related ancestry,the remaining ancestry of the Dzungaria people in our study can be best modelled as a mixture of AG3/Tarim?EMBA1(19-36%)and Baikal?EBA(921%).Taken together,these results indicate that the early dispersal of the Afanasievo herders into Dzungaria was accompanied by a substantial level of genetic mixing with local autochthonous populations,a pattern distinct from that of the initial formation of Afanasievo in southern Siberia.Third,the earliest Tarim basin populations are among only a few known Holocene populations that derive the majority of their ancestry from Pleistocene ANE groups,who once made up the Hunter-Gatherer populations of southern Siberia,and which are represented by individual genomes from the archaeological sites of Mal'ta(MA-1)and Afontova Gora(AG3).Interestingly,we observe that most Bronze Age and pre-Bronze Age populations with substantial ANE ancestry,such as Botai?CA from Eneolithic northern Kazakhstan,Kumsay?EBA and Mereke?MBA from western Kazakhstan,West?Siberia?N from Neolithic southern Russia,Okunevo?EMB A from the Minusinsk Basin,Chemurchek from Altai mountains,and Aigyrzhal?BA,Dali?EBA,Kanai?MBA from the nearby region,show the highest genetic sharing with Tarim?EMBA1,suggesting that the Tarim mummies are currently the best representative of the pre-pastoralist ANE-related population that once inhabited Central Asia and southern Siberia,even though Tarim?EMBA1 postdates these populations in time.These results confirm that the genetic profile represented by the Tarim mummies is a good proxy for the ANE substratum that was once more widely distributed across pre-pastoralist Central Asia,and suggests that Dzungaria?EBA locally relayed Afanasievo ancestry into northern Xinjiang and its neighboring regions.