The Holocene 1–10 © The Author(s) 2016 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0959683616641742 hol.sagepub.com Introduction There are many factors involved in decision-making regarding the adoption or rejection of a new crop variety. These driving mechanisms include environmental constraints and phenotypi- cal adaptive traits of available landraces, cultivation and pro- cessing technology, nutritional and agronomic qualities, social relationships between source and receiving regions, and cultural associations of status, ritual, and appropriateness to the local cuisine, including concepts of taste. In this article, we assess some of the factors that played a role in the acceptance of broomcorn (Panicum miliaceum) and foxtail (Setaria italica) millet as a key component in an array of different productive economies across the Old World, focusing on their early spread out of East Asia a little over four millennia ago. Both Panicoid species are well known as warm-season, drought-resistant crops, for they require relatively little water and have a short growing season. It is, therefore, paradoxical that they are often grown under irrigation over much of West and Central Asia today, where the prevailing climatic regime is Mediterranean in nature – characterized by cold wet winters and hot dry summers. While we acknowledge that cultural factors played an important role in the spread of these two millets, in this paper we investigate how climatic constraints changed over time. (Here, we use the term ‘millet’ to refer only to broomcorn and/or foxtail millet.) Our approach maps the archaeobotanical data in relation to seasonal climate and vegetation. Origins of broomcorn and foxtail millet The Chinese evidence The origins of broomcorn and foxtail millet have long been a topic of debate. The earliest evidence for domesticated broom- corn millet from charred seed remains comes from the site of Dadiwan (c. 5900 cal. BC) in northeastern China (Liu et al., 2004). The earliest remains of foxtail millet grains that show the morphological changes associated with domestication come from the Yuezhuang site and date to 6000–5700 cal. BC (Crawford et al., 2013). Directly dated grains from the Early Neolithic site of Xinglonggou, Inner Mongolia, produced a date of 5670–5610 cal. BC (Zhao, 2011). In the Neolithic layers at Xinglonggou, 1400 charred grains of broomcorn millet and about 60 grains of foxtail Millet cultivation across Eurasia: Origins, spread, and the influence of seasonal climate Naomi F Miller, 1 Robert N Spengler 2 and Michael Frachetti 3 Abstract The two East Asian millets, broomcorn (Panicum miliaceum) and foxtail millet (Setaria italica), spread across Eurasia and became important crops by the second millennium BC. The earliest indisputable archaeobotanical remains of broomcorn millet outside of East Asia identified thus far date to the end of the third millennium BC in eastern Kazakhstan. By the end of the second millennium BC, broomcorn millet cultivation had spread to the rest of Central Eurasia and to Eastern Europe. Both millets are well suited to an arid ecology where the dominant portion of the annual precipitation falls during the warm summer months. Indeed, the earliest sites with millet remains outside of East Asia are restricted to a narrow foothill ecocline between 800 and 2000 m a.s.l., where summer precipitation is relatively high (about 125 mm or more, from May through October). Ethnohistorically, millets, as fast- growing, warm-season crops, were commonly cultivated as a way to reduce agricultural risk and were grown as a low-investment rain-fed summer crop. In Eurasian regions with moist winters and very low summer precipitation, the prevailing agricultural regime had long depended on winter wheat (Triticum aestivum) and barley (Hordeum vulgare) cultivated with supplemental irrigation. We propose that the secondary wave of millet cultivation that spread into the summer-dry regions of southern Central Asia is associated with an intensification of productive economies in general, and specifically with the expansion of centrally organized irrigation works. Keywords agriculture, irrigation, Panicum miliaceum, plant domestication, seasonality, Setaria italica Received 12 December 2015; revised manuscript accepted 20 February 2016 1 University of Pennsylvania Museum of Archaeology and Anthropology, USA 2 Deutsches Archäologisches Institut (German Archaeological Institute), Germany 3 Washington University in St. Louis, USA Corresponding author: Naomi F Miller, University of Pennsylvania Museum of Archaeology and Anthropology, 3260 South Street, Philadelphia, PA 19104, USA. Email: nmiller0@sas.upenn.edu 641742HOL 0 0 10.1177/0959683616641742The HoloceneMiller et al. research-article 2016 Research paper at UNIV OF PENNSYLVANIA on April 21, 2016 hol.sagepub.com Downloaded from