Major leaps forward in understanding rice both in genetics and archaeology have taken place in the past decade or so-with the publication of full draft genomes for indica and japonica rice, on the one hand, and with the spread of systematic flotation and increased recovery of archaeological spikelet bases and other rice remains on early sites in China, India and Southeast Asia. This paper will sketch a framework that coherently integrates the evidence from these burgeoning fields. This framework implies a reticulate framework in the phylogeny of early cultivated rice, with multiple starts of cultivation (two is perhaps not enough) but with the key consolidations of adaptations that must have been spread through hybridisation and therefore long-distance cultural contacts.Archaeobotanical evidence allows us to document the gradual evolutionary process of domestication through rice spikelet bases and grain size change. Separate trends in grain size change can be identified in India and China. The earliest centre of rice domestication was in the Yangtze basin of China, but a largely separate trajectory into rice cultivation can be traced in the Ganges plains of India. Intriguingly, contact-induced hybridisation is indicated for the early development of indica in northern India, ca. 2000 BC. An updated synthesis of the interwoven patterns of the spread of various rice varieties throughout Asia and to Madagascar can be suggested in which rice reached most of its historical range of important cultivation by the Iron Age. The distribution of wild rice and genetic diversity in domesticated ricesRice is a highly diversified crop, being grown from the equator to over 40°N, from sea-level ca. 2,700 m in parts of the Himalayas and in a wide ecological range of cultivation systems. Although there is much less ecological variation found within its wild progenitor complex (Oryza rufipogon and Oryza nivara), these are nonetheless distributed over a wide geographical range and a spectrum of ecological niches from permanent to seasonal wetlands. As the origins of cultivation must have developed in places where hunter-gatherers were utilising wild populations, the distribution of the wild progenitor, in the past when cultivation began, is a key element in identifying the origins of rice. There are three lines of approach to inferring this without archaeological evidence, including (1) the Electronic supplementary material The online version of this article (

We review the origins and dispersal of rice in Asia based on a data base of 443 archaeobotanical reports. Evidence is considered in terms of quality, and especially whether there are data indicating the mode of cultivation, in flooded ('paddy' or 'wet') or non-flooded ('dry') fields. At present it appears that early rice cultivation in the Yangtze region and southern China was based on wet, paddy-field systems from early on, before 4000 bc, whereas early rice in northern India and Thailand was predominantly dry rice at 2000 bc, with a transition to flooded rice documented for India at c. 1000 bc. On the basis of these data we have developed a GIS spatial model of the spread of rice and the growth of land area under paddy rice. This is then compared with a review of the spread of ungulate livestock (cattle, water buffalo, sheep, goat) throughout the Old World. After the initial dispersal through Europe and around the Mediterranean (7000-4000 bc), the major period of livestock expansion is after 3000 bc, into the Sub-Saharan savannas, through monsoonal India and into central China. Further expansion, to southern Africa and Southeast Asia dates mostly after 1000 bc. Based on these two data sets we provide a quantitative model of the land area under irrigated rice, and its likely methane output, through the mid to late Holocene, for comparison to a more preliminary estimate of the expansion of methane-producing livestock. Both data sets are congruent with an anthropogenic source of later Holocene methane after 3000 bc, although it may be that increase in methane input from livestock was most significant in the 3000-1000 bc period, whereas rice paddies become an increasingly significant source especially after 2000 bc.

We have compiled an extensive database of archaeological evidence for rice across Asia, including 400 sites from mainland East Asia, Southeast Asia and South Asia. This dataset is used to compare several models for the geographical origins of rice cultivation and infer the most likely region(s) for its origins and subsequent outward diffusion. The approach is based on regression modelling wherein goodness of fit is obtained from power law quantile regressions of the archaeologically inferred age versus a least-cost distance from the putative origin(s). The Fast Marching method is used to estimate the least-cost distances based on simple geographical features. The origin region that best fits the archaeobotanical data is also compared to other hypothetical geographical origins derived from the literature, including from genetics, archaeology and historical linguistics. The model that best fits all available archaeological evidence is a dual origin model with two centres for the cultivation and dispersal of rice focused on the Middle Yangtze and the Lower Yangtze valleys.

Baligang is a Neolithic site on a northern tributary of the middle Yangtze and provides a long archaeobotanical sequence from the Seventh Millennium BC upto the First Millennium BC. It provides evidence for developments in rice and millet agriculture influenced by shifting cultural affiliation with the north (Yangshao and Longshan) and south (Qujialing and Shijiahe) between 4300 and 1800 BC. This paper reports on plant macro-remains (seeds), from systematic flotation of 123 samples (1700 litres), producing more than 10,000 identifiable remains. The earliest Pre-Yangshao occupation of the sites provide evidence for cultivation of rice (Oryza sativa) between 6300–6700 BC. This rice appears already domesticated in on the basis of a dominance of non-shattering spikelet bases. However, in terms of grain size changes has not yet finished, as grains are still thinner than more recent domesaticated rice and are closer in grain shape to wild rices. This early rice was cultivated alongside collection of wild staple foods, especially acorns (Quercus/Lithicarpus sensu lato). In later periods the sites has evidence for mixed farming of both rice and millets (Setaria italica and Panicum miliaceum). Soybean appears on the site in the Shijiahe period (ca.2500 BC) and wheat (Triticum cf. aestivum) in the Late Longshan levels (2200–1800 BC). Weed flora suggests an intensification of rice agriculture over time with increasing evidence of wetland weeds. We interpret these data as indicating early opportunistic cultivation of alluvial floodplains and some rainfed rice, developing into more systematic and probably irrigated cultivation starting in the Yangshao period, which intensified in the Qujialing and Shijiahe period, before a shift back to an emphasis on millets with the Late Longshan cultural influence from the north.

Abstract

28Agricultural origins and dispersals are subjects of fundamental importance to archaeology as 29 well as many other scholarly disciplines. These investigations are world-wide in scope and 30 require significant amounts of paleobotanical data attesting to the exploitation of wild 31 progenitors of crop plants and subsequent domestication and spread. Accordingly, for the past 32 few decades the development of methods for identifying the remains of wild and domesticated 33 plant species has been a focus of paleo-ethnobotany. Phytolith analysis has increasingly taken its 34 place as an important independent contributor of data in all areas of the globe, and the volume of 35 literature on the subject is now both very substantial and disseminated in a range of international 36 journals. In this paper, experts who have carried out the hands-on work review the utility and 37 importance of phytolith analysis in documenting the domestication and dispersals of crop plants 38 around the world. It will serve as an important resource both to paleo-ethnobotanists and other 39 scholars interested in the development and spread of agriculture. 40

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The archaeology of rice has made important methodological advances over the past decade that have contributed new data on the domestication process, spread and ecology of cultivation. Growing evidence from spikelet bases indicates that non-shattering, domesticated forms evolved gradually in the Yangtze basin and that there were at least two distinct processes around the Middle Yangtze region pre-dating 6000 BC, and the in the Lower Yangtze region between 6000 and 4000 BC. Early rice cultivation in these areas was based on wet field ecologies, in contrast to rainfed rice that is indicated among the earliest systems in India. When rice first spread north it was not entirely suited to shorter temperate summer growth seasons, and we are able to infer from high levels of apparently green-harvested spikelets that genetic adaptations to temperate conditions evolved after 2000 BC. When rice first spread south, to mainland Southeast Asia, after 2500 BC, it was grown in rainfed, dry ecologies that were less labourdemanding and less-productive. More productive and intensive irrigated rice then redeveloped in Southeast Asia around 2000 years ago, supporting growing population densities and social complexity. IntroductionRice is one of the world's most widely eaten and most productive cereals. Over the past decade archaeobotanical research based at the UCL Institute of Archaeology and involving a wide range of collaborators in east, south, and southeast Asia has been seeking new insights into the processes by which rice evolved and rice cultivation systems evolved, and how these relate to cultural change and long-distance cultural relationships across Monsoon Asia. While this research began with critical reflections and debate surrounding the initial cultivation of rice in China (Fuller, Harvey and Qin 2007) and India (Fuller 2006),