Millet consumption
All species of millet photosynthesize through the Hatch-Slack or C4 pathway. During photosynthesis, C4 plants discriminate against atmospheric 13CO2 less than C3 plants, yielding higher δ13C values than C3 plants (approximate mean values of -12.5‰ and -26.5‰ respectively), with no overlap.
In the northern latitudes of Eurasia the only indigenous domesticated C4 crops are broomcorn and foxtail millet. The consumption of millet grains consequently generates an isotopically characteristic C4 signature in human and animal bone collagen. Stable carbon isotopic measurements of human and animal skeletal samples can thus be used to infer levels of millet consumption across space and time.Systematic isotopic research was carried out in Chifeng. Human and animal skeletal specimens from a range of sites, including Xinglonggou i, ii, and ιιι, were selected for isotopic analysis.[732] The results indicate that substantial millet consumption by humans in Chifeng began at Xinglonggou I. Although the isotopic values do not directly inform us about the domestication process, of which we still have a limited understanding, the significant dietary input of millet in Xinglonggou i indicates that millet was certainly
used as a staple food. Throughout the Neolithic and into the Bronze Age in Chifeng, the proportion of C4 foods in the diet increased. The absence of strongly C4 isotopically labelled animals in the early Neolithic indicates that the C4 signal in humans of that period was not derived from the consumption of animals fed on millet, but from humans directly eating millet. In the Bronze Age, the C4 signal in humans may be interpreted as derived from increased consumption of either millet or animals fed on millet, since the contemporaneous animals also have a C4 signal.