Asynchronicity of dietary transformation in different regions along the Bronze Age Eastern Silk Road

The eastern ancient Silk Road (EASR)—an area critical in linking Central China with the pastoralist societies of the eastern Eurasian Steppe and Central Asia—was a key component to trans-Eurasian exchange since the Bronze Age. Despite the area's importance, not much is known regarding the spatio-temporal variation of human diets and the associated subsistence practices during the Bronze Age. This dearth of information is largely due to the absence of key evidence from the EASR during 3000–2200 years before present (yr B.P.). In this study, we report new carbon and nitrogen isotopic data, including radiocarbon dates of human and animal bones unearthed from the Shijia-Yucun (SJ-YC) site in the EASR, dated between ∼2700 and 2500 yr B.P. During our target period of study, the humans, pigs and dogs living in SJ-YC mainly consumed C4 foods (millets and millet by-products), while herbivorous livestock consumed a mix of C3 and C4 plants. Combined with published isotopic and archaeobotanical data, we detected an asynchronous transformation of dietary patterns in different regions of the EASR during the Bronze Age. Between 3500 and 2200 yr B.P., staple foods for most western EASR humans shifted from C4 to mixed C3 and C4 foods. In the eastern EASR, C4 foods remained dominant in human diets throughout the Bronze Age. Patterns in dietary changes are not completely consistent with the various trajectory of crop cultivation. We propose that, in the context of Bronze Age trans-Eurasian exchanges, humans adopted different livelihoods throughout the EASR to deal with the survival pressures and social customs associated with variations in climate, population, and geopolitical factors. Our work provides vital evidence for dietary and subsistence variation in the EASR and explores the complicated relationship between Bronze Age humans and their environment.