Agricultural origins in North China pushed back to the Pleistocene-Holocene boundary.

T wo grains, common (proso or broomcorn) millet (Panicum miliaceum) (Fig. 1) and foxtail millet (Setaria italica), were fundamental to the development of agricultural societies that eventually evolved into the first urban societies of China between 4500 and 3800 calibrated years (cal.) B.P. (1). Today, these grains are important mainly in parts of Russia, South Asia, and East Asia. How, when, and in what settings these millets initially evolved is not well known (2). One hypothesis holds that common millet was domesticated rapidly in the central Wei river basin shortly after ca. 8000 cal. B.P. (3). Another hypothesis proposes that common millet was domesticated in the Northeast China Liao river basin around the same time (4). In reality, archaeological data have simply not been adequate to resolve the issues surrounding the domestication of millet and the development of the first agricultural communities in North China. Complicating the problem, common millet is also present in Europe ca. 8000–7500 cal. B.P. (2), so this timing opens the possibility that the crop was domesticated more than once. Otherwise, its origins must predate 8000 cal. B.P. The Early Holocene Cishan site in North China is one of several sites considered key to understanding millet domestication and the origin of dry-land agriculture in China, yet the dating and identity of the crops recovered there have never been adequately documented. The study published in this issue of PNAS (5) revisits Cishan, located on a terrace on the western edge of the North China Plain 9 km from where the Nanming river emerges from the Taihang mountains. Two outstanding issues regarding the early archaeological record of millet at Cishan first reported nearly 30 years ago (6, 7), their dating and identification, are resolved in the new study. Cishan, a Neolithic village at least 400 m square, has an exceptionally-rich pottery, stone, plant, and animal bone assemblage. The pottery consists of plates, bowls, and pots decorated by cord-wrapped paddle and incising/ trailing; none of it is painted. No specific precursors are known. The houses and pits are divided into 2 occupations, periods I and II. Excavations revealed 476 pits, among which 376 are rectangular in plan view. Some of the large, oval pits are houses. Most of the pits belong to period II (7). Many of these characteristics are still unique to the Cishan culture but it was the large quantity of silicified millet remnants in 88 of the pits, nearly 80% from period I, that was so surprising. When the millet was first exposed, it decomposed rapidly, leaving some grains that were too fragile to be recovered and the tough chaff whose cells are composed mainly of silica. At first, the grain was thought to be foxtail millet (S. italica) but details of the morphology were never reported and the identification has not been universally accepted. The age of the site was also surprising considering its complexity: 8000 cal. B.P. Archaeologists were uncertain how long the site was occupied, if the millet was as old as the charcoal that provided the radiocarbon dates, or if, indeed, the site was as old as they surmised. Lu et al. (5) report that some of the pits are at least 2,000 years older than previously thought and the plant remains are composed primarily of common millet rather than foxtail millet. To make an incontrovertible case for the age and association of crops, archaeologists require secure dating, welldocumented identifications, and proper documentation of the context from which the dates and the crops were obtained. Lu et al. (5) obtained 46 new samples of plant remains and 9 accelerator mass spectrometry (AMS) radiocarbon dates directly on the millet. Two of the AMS dates are younger and 7 are older than the non-AMS radiocarbon dates on charcoal from the original excavations. The structure and contents of the site appear to be consistent with the extended chronology. Archaeologists suspected that the site has a longer history, and in 2008 Lu et al.’s team reviewed the stratigraphy at Cishan and learned that the opening of pit CS-I was just at the bottom of the Holocene soil layer, while the mouth of the younger CS-II pit was excavated into slightly shallower Holocene soil. The stratigraphy structures of the site appear to be consistent with the extended chronology (Lu et al., personal communication). Three of the older dates extend the occupation to 10,400–10,100 cal. B.P. The dates also show for the first time that the community spanned a period of 3,000 years (ca. 10,400 to 7500 cal. B.P.). How were the crops identified? The remains are extremely fragmentary, being the remnants of chaff. Identification is relatively straightforward when the actual grains are present but in this case Lu et al. (5) needed some ingenuity to identify the specimens. They used 3 techniques to clarify that broomcorn millet was the only crop in period I and the primary crop in period II. A small quantity of foxtail millet is present in period II, indicating that it was a later addition to the crop assemblage and was not a significant crop there. The first identification method, an examination of the epidermal cells of the husks, involved measuring the amplitude of the undulations of the long cells and statistically testing for significant differences. The measurements have a bimodal distribution, indicating that, indeed, the epidermal cell measurements form 2 clusters, 1 for common millet and 1 for foxtail millet. Furthermore, the morphology of silica bodies (phytoliths) in chaff epidermal cells have been used to