Stable isotope and dental caries data reveal abrupt changes in subsistence economy in ancient China in response to global climate change

Abstract

Prior to the introduction of wheat and barley from Central Asia during the Neolithic period, northern Chinese agricultural groups subsisted heavily on millet. Despite being the focus of many decades of intensive interest and research, the exact route(s), date(s), and mechanisms of the spread and adoption of wheat and barley into the existing well-established millet-based diet in northern China are still debated. As the majority of the important introduced crops are C3 plants, while the indigenous millet is C4, archaeologists can effectively identify the consumption of any introduced crops using stable carbon isotope analysis. Here we examine published stable isotope and dental caries data of human skeletal remains from 77 archaeological sites across northern and northwestern China. These sites date between 9000 to 1750 BP, encompassing the period from the beginning of agriculture to wheat's emergence as a staple crop in northern China. The aim of this study is to evaluate the implications of the spread and adoption of these crops in ancient China. Detailed analysis of human bone collagen δ13C values reveals an almost concurrent shift from a C4-based to a mixed C3/ C4- based subsistence economy across all regions at around 4500-4000 BP. This coincided with a global climatic event, Holocene Event 3 at 4200 BP, suggesting that the sudden change in subsistence economy across northern and northwestern China was likely related to climate change. Moreover, the substantially increased prevalence of dental caries from pre-to post-4000 BP indicates an increase in the consumption of cariogenic cereals during the later period. The results from this study have significant implications for understanding how the adoption of a staple crop can be indicative of large-scale environmental and socio-political changes in a region.

Fig 1. A map showing all sites analysed in this study and the major geological features of northern and northwestern China.

A key to site IDs is provided in the Table 2. The map was created using QGIS Version 2.12.0 for OSX (www.qgis.org). All maps used are in the public domain (CC0), sourced from Natural Earth (www.naturalearthdata.com).

Fig 2. Bone collagen δ¹³C values of humans from all sites discussed in this study, organized by province groups.

Note that due to the 1000-year gap between the last two groups of data from the GQ region, the smooth line was not extended to the last group.

Fig 3

Boxplots showing changes in the prevalence of dental caries before and after 4000 BP in the three regions: a) changes in prevalence of dental caries in NCP; b) changes in prevalence of dental caries in QJ; c) changes in prevalence of dental caries in GQ.