Within a nondescript Bronze Age cemetery first discovered by Swedish archaeologists in 1934 and rediscovered by the Xinjiang Archaeological Institute in 2000, researchers have found the oldest and best-preserved mummies in the Tarim Basin area of China. Their skeletal remains, along with unprecedented artifacts, are helping solve the longstanding question of the origins of human settlement in a politically contested area of China.
Contemporary occupants of the Tarim Basin, a geographical area in the Xinjiang Uyghur autonomous region of northwest China, are both biologically and culturally diverse. The region borders numerous countries and was historically a part of the Silk Road trade route between the West and the East, so people and artifacts have moved through the Tarim Basin for thousands of years. But the origins of the inhabitants of the basin have been questioned.
One hypothesis suggests that the earliest settlers of this part of Asia were nomadic herders from the steppes of Russia and Kazakhstan, while the other suggests that people came first from the oases of Bactria, or modern Uzbekistan, Afghanistan, and Turkmenistan. While both hypotheses have support in archaeological findings such as burial customs, clothing styles, and animal bones, previous genetic evidence from human remains, which came from a cemetery called Gumugou on the eastern edge of the Tarim Basin, was inconclusive.
Writing in the journals BMC Genetics and BMC Biology, Chunxiang Li, an ancient DNA specialist at Jilin University, and colleagues report on their analysis of human remains from the Xiaohe tomb complex also on the eastern edge of the basin. Dating to about 4000 years before present, the site boasts notable artifacts like “numerous large phallus and vulva posts made of poplar, striking wooden human figurines and masts, well-preserved boat coffins, leather hides,” as well as grain and other preserved organic material, they write. More importantly, Xiaohe has produced the oldest, best-preserved mummies in the Tarim Basin, ideal for testing hypotheses about the origins of these people, and the site spans a millennium, making it ideal for looking into population interaction after initial settlement.
From the earliest layer of burials, Li and colleagues tested 20 individuals who produced affinities with 5 different mitochondrial DNA haplogroups, or major branches on the female side of the genetic family tree. “The dominant haplogroup,” they write, “in the Xiaohe people was the East Eurasian lineage C” which corresponds with a likely origin in South Siberia. But there were also “two West Eurasian mtDNA haplogroups H and K.” In looking more closely at the lineages and mutations, however, Li and colleagues noted that several of the samples had mutations that are either rare in modern people or are not found in modern gene banks. They further analyzed Y chromosome haplogroups to attempt to identify major branches of the male line. But all seven males in the study belonged to a haplogroup that is widely distributed throughout Eurasia.
“Considering the presence of haplogroups H and K in the Xiaohe people and the geographical distribution of shared sequences, we conclude that the west Eurasian component observed in the Xiaohe people originated from western Europe, and maternal ancestry of the Xiaohe people might have close relationships with western Europeans,” Li and colleagues note. By the Bronze Age, the people buried at Xiaohe cemetery were already “admixed,” coming together millennia earlier in Siberia and Mongolia.