Multiple waves of westward dry-land agriculture expansions along the East Silk Road during the Neolithic age.

The intersection between ancient agriculture, population, and language during the Neolithic is a widely researched topic across multiple disciplines. In East Asia, multiple waves of westward expansions of dry-land agriculture based on millet cultivation along the Eastern Silk Road (ESR) during the Neolithic have been identified; however, the timing and scope of these expansions remain unresolved. This is due to the uncertain timing of the earliest millet cultivation and a lack of research on the spatial-temporal patterns of this dry-land agriculture expansion. At the Dadiwan site, located in the ESR, abundant charred millet remains have been identified from associated materials in cultural layers between ∼7900 and 4800. Critically, however, direct radiocarbon dates of millet grains remain absent. Based on systematic archeobotanical analysis from the 2014-2015 excavation of the Dadiwan site, 29 samples of charred millet remains were collected and directly AMS radiocarbon dated. This yielded the earliest direct date of millet cultivation (∼7900 BP), both in the Dadiwan and across the ESR. Most of the new direct dates conflict with the previously assumed ages of the cultural strata from which the millet remains were unearthed. This highlights the importance of directly dating charred seed remains from archeological sites when exploring the chronologies of agricultural systems. We compare this new data with previously published dates, the stable isotope analysis of human diet, and archeological evidence, detecting four waves of westward expansion of dry-land agriculture along Neolithic ESR. These waves occurred approximately at 7800 BP, 6500 BP, 5500 BP and 4500 BP, broadly corresponding to cultural phases in the pre-Yangshao, early-mid Yangshao, late Yangshao-early Majiayao, and late Majiayao-Qijia periods, respectively. This work enhances our understanding of the timing and spatial patterns of dry-land agriculture, offering valuable data and insights into the connections between agricultural expansion, population growth, and language in the ancient Neolithic ESR and East Asia.