| Intercontinental cultural exchanges between communities living in different parts of Eurasia during the late prehistoric period are important and interesting topics in archaeological research. For example, it is important to study Trans-Eurasia cultural communication for understanding the formation process of Chinese Bronze Age. Furthermore, the two important agriculture origin centers, Southwest Asia (or Near East) and China, are also connected by these communications. This culture exchange could be characterized by long-distance movements of various elements, including metallurgy, livestock, crops, diseases, and so on. In the second millennium BC, the exchange was more intensive and frequent than earlier times. And the large-scale intercontinental exchanges had been observed based on the strong archaeobotanical evidence for novel crop combinations in several regions of the Old World. However, the temporal and spatial maps of these exchanges are highly debated for the lack of archaeological evidence in those regions connecting the west and the east. Considerable interest is focused on the pathway offered by the Hexi Corridor (between the Tianshan Mountain and Gobi desert) and the articulation of this pathway with the Hehuang region (the upper reaches of the Yellow River and its tributaries in Gansu and Qinghai province) before and after 2000BC. Therefore, we choose the Hehuang and contiguous regions to study the relate questions about the intercontinental exchanges. In this dissertation, we focus on the direct evidence of the crop plants that could be moved and then were consumed. The skeletal collections in the Hehuang region provide us an opportunity to explore central elements of Trans-Eurasian culture exchange:cereals, such as millets first domesticated in East Asia and wheat and barley first domesticated in Southwest Asia.. These two groups of cereals have contrasting photosynthetic pathways and consequently have very different stable carbon isotope signatures in the bones of their consumers.In this study, we analysed the carbon isotopes and nitrogen isotopes of human (n=180) and faunal (n=72) skeletal and teeth remains during C.2000BC-1000BC and reconstructed their diets. To get an idea of the age of our materials, we chose eight human bones and one charcoal sample to date. Then the variation of human diets and the development of prehistory agriculture in the study region were discussed. Finally, we estimated the possible reasons of dietary changes and their influences on the evolution of prehistory cultural systems in the study area. The main conclusions are as follows.(1) During C.2000BC-1600BC, the range of δ13C values of the Machang and Qijia human remains were from -9.3‰ to-7.3‰(n=16, mean=-8.6±1.0%o) and from -9.7%o to -7.3‰ (n=41, mean=-8.9±1.1‰), respectively. The δ13C values of omnivores ranged from -22.7%o to -6.8‰ (n=25, mean=-10.0±3,8‰),which suggests that most of the omnivorous animals and all humans had diets dominated by C4 foods from c.2000BC to 1600BC. We infer that the C4 signal in human and omnivore diets comes from the consumption of millet and/or animals fed on millet, since the millet grains dominate in Qijia and Machang archaeobotanical assemblages. It illustrates that humans and omnivores from c.2000BC to 1600BC relied upon millet-based agriculture and consumed little or none wheat or barley.(2) The wheat and barley-based agriculture occurred post-1600BC at several sites in Hehuang region, accompanying with the millet-based agriculture. The strong evidence is the mixed C3 and C4 signals from human bone collagen (n=44,-18.5‰～-11.1‰, mean=-14.7±1.8‰) at the Mogou site dated to 1640-1250 BC. The stronger C3 signals were observed from Kayue population at the Lajigai site (n=5,-17.4‰～-13.1‰, mean=-14.9±1.8%o) at around 1300BC. The difference between the mean 815N values of the human and the herbivore samples from the two sites are 1.7‰ and 2.1‰, respectively, which are less than the generally stated tropic level offset of 3-5‰. We, therefore, could exclude that these C3 signals derived from animal protein by comparing human isotope data with animal data. It shows that wheat and barley probably contributed to human diets in a certain degree. Moreover, this result is supported by other archaeological evidence, such as archaeobotanical assemblages and starch grain analysis from human teeth.(3) The mean human δ13C values of Hupo, Sanheyi and Xiahaishi site are -8.7±0.4%o(n=6), 9.1±0.5‰ (n=5) and-7.6±0.4‰ (n=10), respectively. There are statistical differences in human δ13C lues from the three sites (P=0.001), suggesting that the consumption of millet varied among humans from these sites. Although all of them depended on millet agriculture then. No statistical differences are observed between Mogou and Lajigai human δ13C values (P=0.869), but the mean human δ13C values derived from the Mogou (n=44, mean=-14.7±1.8%o) and Shangsunjia (n=18, mean=-16.1±1.3%o) are significantly different (P=0.002). These results suggest the spatial differences in human dietary patterns in the Hehuang region. The dietary patterns are possible relative to their local landscapes around the sites. It is because that various environments could provide resources of different quantities and qualities to human. And human utilization of these resources could also be very different. All these factors could affect human diets. Therefore, local environment might play an important role in human diets.(4) A group of new social relationship might be introduced to the study region with the appearance of the wheat and barley-based agriculture. Because the wheat and barley-based agriculture is quite different from the millet-based agriculture. In addition, people might response to the new culture elements (e.g., wheat and barley) very differently in a wide spatial region. The reorganized social relationship and the local community’s different responses might crucially impact the establishment of the multi-cultures in the Bronze Age system in Gan (su)-Qing (hai) region.(5) The establishment, development and spread of millet-based agriculture are closely related to the optimal environmental conditions in middle Holocene. In contrast, the wheat and barley-based agriculture appeared in the dryer and cooler climate context in the study region after 1600BC, indicating that prehistoric humans may adjust their agricultural strategy in order to adapt the dryer and cooler climate and/or population growth. However, it should be noticed that social factors could also play an important role in the development and adjustment of prehistoric agriculture system.This study enlarges and supplements the human and animal isotopic data set for prehistoric societies in the Hehuang region and provides more evidence for prehistoric subsistence strategy study. It also provides the direct evidence for frequent wheat and barley consumption of humans and the evidence of first appearance of the wheat and barley-based agriculture in Hehuang region. Finally, we find a new insight on studying the Bronze Age culture system in Gan (su)-Qing (hai) region, which is the introduction of new social relationships and the local community’s different responses. |
