Colonizing the roof of the world: Humans only settled permanently on the Tibetan plateau about 3600 years ago. Chen et al. examined archaeological crop remains unearthed in northeastern Tibet, which elucidate the timing of agricultural settlement. Although much earlier traces of humans in Tibet have been dated to 20,000 years ago, year-round presence at the highest altitudes appears to have been impossible until the advent of suitable crops, such as barley. Surprisingly, these prehistoric farming communities expanded onto the plateau at the same time as climate was cooling. Science , this issue p. 248

Based on radiocarbon dating and our analysis of plant and animal remains from Buziping, a Majiayao (5300–4300 BP) and Qijia (4200–3800 BP) period site located in Dingxi, Gansu Province, China, and our review of archaeobotanical studies in the Western Loess Plateau and adjacent areas, we discuss subsistence strategies during the Majiayao and Qijia periods. We also discuss the development of agriculture in the Western Loess Plateau and its influence on cultural expansion during the late Neolithic period. Humans settled at Buziping for the first time during the Majiayao period (4890–4710 cal. yr BP by ¹⁴C dating). Charred seeds from the site indicate that people engaged in millet-based agricultural production. People continued this type of agriculture during a second phase of occupation (4130–3880 cal. yr BP by ¹⁴C dating) during the Qijia period, but the proportion of foxtail millet to broomcorn millet increased from the Majiayao to Qijia period. Raising domestic animals was another aspect of subsistence during the Qijia period. The main domestic animals were likely pigs and dogs, although hunting of wild animals also took place. Subsistence at Buziping site was affected by the rapid development of intensive agriculture that diffused across eastern Gansu Province during the late Neolithic. Our work suggests that millet-based agriculture spread from east to west across the Western Loess Plateau and likely promoted the expansions of those two cultures in the area during the Majiayao period and early–mid Qijia period. Climate change might have also promoted Majiayao and Qijia expansions and probably facilitated the adoption of rain-fed agriculture in this region.

We studied the mid-Holocene climate change in eastern Qinghai Province, China and its impact on the evolution of Majiayao (3980–2050 BC) and Qijia (2183–1635 BC) cultures, near the important Neolithic site of Changning. The investigation focused on analyses of grain size, magnetic susceptibility, ratios of elemental contents, and pollen assemblage from a loess-paleosol sequence. The results indicate that the climate was wet during 5830–4900 cal yr BP, which promoted the development of early-mid Majiayao culture in eastern Qinghai Province. However, 4900–4700 cal yr BP were drought years in the region, responsible for the decline and eastward movement of prehistoric culture during the period of transition from early-mid to late Majiayao culture. The climate turned wet again during 4700–3940 cal yr BP, which accelerated the spread of Qijia culture to the middle reaches of the Huangshui River, including the Changning site.

Despite the proposed climate–human connection in the West Liao River Basin during the Bronze Age, the question of how climate change could have affected the subsistence strategies, and consequently, the cultural transformation from the Lower Xiajiadian to the Upper Xiajiadian periods, has never been systematically explored. Based on radiocarbon dating and the analysis of plant remains recovered by flotation, as well as the spatial distribution of archaeological sites, this study investigates the subsistence strategies of ancient people and their influence on cultural development in the West Liao River Basin during the Lower Xiajiadian (3900–3400 cal. yr BP) and Upper Xiajiadian periods (3000–2500 cal. yr BP). Carbonized seeds collected from 13 archaeological sites reveal that people engaged in millet-based agriculture in this area throughout the Bronze Age. Favorable climate during the Holocene Optimum promoted millet farming among the Lower Xiajiadian Culture. The end of the Holocene Optimum and its associated climate deterioration led to agricultural shrinkage in the Upper Xiajiadian period, which is revealed by the reduced amount of carbonized millet seeds and the ratio between foxtail millet and broomcorn millet. Climate deterioration led to diverse subsistence strategies, resulting in the dispersal of human settlements and the differentiation of the spatial distributions of different groups. People with millet-based subsistence strategies retreated southward, while people with animal husbandry and hunting-based subsistence strategies migrated westward. The above findings may offer insights in comprehending how climate deterioration could have affected the multi-facets of human societies in the West Liao River Basin, which is a climatically sensitive region, in Chinese prehistory.