Friday 23 December 2022

Investigating a Bronze Age cemetery in Gansu Province, China.

Northwestern China was an important part of Eurasian migration and trade routes in the middle of the second millennium BC, with technologies such as crop cultivation and metalworking techniques passing through the area in both directions. However, while the importance of this area for cultural interchange between China and Central Asia has long been understood, little attention has been paid to the people who lived here at this time, how they lived their lives, or their social and political structures.

The Mogou (磨沟) Cemetery is a Bronze Age funerary complex that has been dated to between 1750 and 1100 BC, located at the eastern perimeter of the Eurasian Steppe, on a terrace above the Tao River in Lintan County in southern Gansu Province. The site covers about 300 000 m², and is considered to be the best known example of a Qijia Culture (Early Bronze Age) cemetery discovered to date. 

The site was excavated by the Gansu Provincial Institute of Cultural Relics and Archaeology and the School of Cultural Heritage at Northwest University between 2008 and 2012. These excavations uncovered over 1700 burials, containing more than 6000 individuals. Artefacts recovered from the site included items from the Central Plains of northern China, and gold artefacts associated with the Andronovo culture of western Siberia and the central Eurasian Steppes.

The majority of the burials can be confidently attributed to the local Early Bronze Age Qijia Culture, although about 100 graves attributed to the later Siwa Culture. The graves are laid out in rows, with few overlapping one-another, suggesting an intentional layout. Two types of graves are present, simple shaft-graves, and graves with a side chamber. Both types of grave are found throughout the cemetery, with no partitioning. Almost all of the graves have multiple occupancy, with between two and twenty individuals in each, with individuals of all ages mixed together. The graves do not appear to have been sealed completely between burials, but covered with a stone or wooden board, until the final occupant was placed within.

In a paper published in the journal Antiquity on 1 December 2022, Xiaoying Ren of the Institute of Archaeological Science at Fudan University, Ruilin Mao and Guoke Chen of the Gansu Provincial Institute of Cultural Relics and Archaeology, and Edward Allen, Yao Yu, Michael Storozum, Jing Yuan, and Shaoqing Wen, all also of the Institute of Archaeological Science at Fudan University, present the initial results of a study by the Mogou Multidisciplinary Investigation Project, a collaboration between the Institute of Archaeological Science at Fudan University and the Gansu Provincial Institute of Cultural Relics and Archaeology, which aims to use a combination of ancient DNA, strontium isotope analysis and radiocarbon dating on individuals from the Mogou Cemetery, in order to shed light on inheritance rules, marriage practices and questions such as whether social status was related to a specific paternal/maternal lineage or a specific genetic structure in the Qijia culture.

Map showing north-west China and the location of the Mogou site. Xiaoying Ren in Ren et al. (2022).

Ren et al. selected three areas within the Mogou Cemetery for more detailed analysis, chosen to include both single and multiple burials, burials with and without grave goods, grave goods of different styles, and examples of both the Qijia and Siwa cultures. 

(a) Panoramic view of the Mogou site (blue area) and the Tao River; (b) east section of Mogou Cemetery. Ruilin Mao in Ren et al. (2022).

Ren et al.'s preliminary study focuses on a grave identified as M80. This is a Qijia burial with two niche chambers, one above the other, connected by a common shaft. The grave contains a variety of grave goods, as well as twelve Human individuals, which presumably indicates a long period of use. The Human remains are sorted into four groups. The first group comprises a single skull, identified as Individual 1, buried close to the entrance of the tomb. The second comprises four skeletons, identified as Individuals 2-5, buried at the bottom of the shaft connecting the two niche chambers. The third group comprises a single skeleton, Individual 6, placed in the upper niche chamber. The final group comprises another six skeletons, Individuals 7-12, placed in the lower niche chamber. Radiocarbon dates were obtained from two of the skeletons, Individual 5, who was dated to between 3456 and 3364 years before the present, and Individual 8, who was dated to between 3569 and 3411, dates which fit with the Qijia culture interpretation of the tomb.

(a) Plan of the Mogou Cemetery (excavated in 2008 and 2009) and the three sample areas; (b) schematic diagram of spatial structure of M80; (c) middle of the tomb passage (Zone A) and upper chamber (Zone B) of M80; (d) lower chamber (Zone C) of M80. Xiaoying Ren & Yao Yu in Ren et al. (2022).

Ren et al. were able to extract sufficient DNA to establish the mitochondrial haplogroups of ten of the individuals in the tomb, as well as the Y-chromosome haplogroups of three of those individuals. Because mitochondrial DNA is found in the mitochondria, organelles outside the cell nucleus, it is passed directly from mother to child without being sexually recombined each generation, enabling precise estimations of when individuals shared common ancestors, at least through the female line, forming a mitochondrial  haplogroup. It is also possible to trace direct ancestry through the male line, using DNA from the Y chromosome, which is passed directly from father to son without sexual recombination, forming a Y-chromosome haplogroup.

Four separate mitochondrial haplogroups were present within the tomb; R11 (Individual 2), F1 (Individuals 3 and 7), M11 (Individuals 4, 5, 8, 9, and 10), and B4 (Individuals 6 and 11), but only a single Y-chromosome haplogroup, O2 (Individuals 4, 5, and 7). The mitochondrial haplogroups are all fairly widespread in Asia, but the male haplogroup is more specifically Chinese, and is thought to derive from the Neolithic farmers of the Yellow River Basin, a group considered to have contributed a significant proportion of the DNA of the modern Han Chinese population.

The haplogroups can also tell something about the relationships of the individuals in the tomb to one-another. Individuals 8 and 9, female skeletons with estimated ages of 13-17 and 26-35 and identical haplogroups, were buried together in the lower chamber, along with individual 10, another female skeleton with an estimated age of 12, who (probably) had the same haplogroup. This haplogroup was shared with Individual 5, a male infant buried in the passage outside the chamber (burial goods were found in both the niche chambers and the passage, possibly indicating that both were seen as equally acceptable places to be buried), which is likely to indicate a close relationship between all these individuals, possibly with Individual 9 being the mother of the others. Another skeleton, Individual 11, interpreted as a male aged 35-39 buried in the lower niche chamber, shared a mitochondrial haplogroup with a skeleton in a neighbouring tomb (M90).

The Mogou Multidisciplinary Investigation Project aims to expand this study across more of the cemetery to establish relationships between the people in the cemetery, and with the wider world, to better understand migration routes, trade networks, political, and family structures in the Bronze Age of northwest China.

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