Isotopic evidence for the expansion of wheat consumption in northern China

Abstract

Flotation and carbon dating indicate that wheat was introduced into northern China, where millet agriculture had existed for thousands of years, around 3000–2000BC. Wheat eventually replaced millet as the staple of northern Chinese diets, but it is still unclear how it was added to the established agricultural system and when millet finally lost its staple role to the imported crop. Because wheat and millet have distinct δ13C values, stable isotope analysis offers an opportunity to answer these questions. Here, we review published stable isotope data for 645 human samples from 36 sites in northern China, dating from 3000 to 2000BC to the sixth century AD, summarizing the current evidence for dietary changes since the appearance of wheat. The results indicate that wheat had little influence on human nutrition at its first appearance. The first possible evidence for wheat consumption is seen in Xinjiang about 1800BC. Further east in Qinghai and Gansu, a shift from C4-based diets to mixed C4/C3-based diets occurred between 2000 and 1500BC. In areas further east, millet continues to dominate human diets for the following two millennia, although wheat has been widely recovered in archeological contexts and its importance in agriculture was recorded in contemporary documents. It was only in the sixth century AD that C3 crops became important in human diets in the east of northern China. This is quite different from the scenario depicted by palaeobotanical studies, and illustrates the need for further stable isotope analysis of human and faunal remains to better characterize the millet-wheat transition in northern China.