First, I put forward a number of suggestions regarding the initial cultivation and eventual domestication of Oryza sativa (subspecies japonica) and the consequent spread of the human populations who exploited and consumed it. Current genetic evidence suggests only one domestication of Oryza rufipogon, the ancestral perennial species for japonica, in or close to the Yangzi BasinFootnote 1 (Molina et al. 2011; Zhao 2010; in this paper, I do not discuss the separate domestication of O. sativa subspecies indica from annual forebears in South Asia). This domestication occurred gradually between 7,000 and 4,000 BC, commencing at the same time that summer monsoon rainfall and temperatures increased rapidly to levels that encouraged the growth of O. rufipogon northwards to Shandong (Zong et al. 2007). In addition, early Holocene global sea level rose 60 m, between 9,650 and 5,000 BC, as a result of glacial melt water release (Smith et al. 2011), converting the wide coastal plain of eastern China into a much steeper coastline fringed with many offshore islands (see Fig. 1 for the former extent of this coastal plain). This rather phenomenal rate of climatic warming and coastal drowning was part of the transition from the Younger Dryas subglaciation of the terminal Pleistocene (c.10,800 to 9,500 BC) into the Holocene epoch of modern interglacial climate. Perhaps it is no coincidence that the oldest evidence for actual rice exploitation in the Yangzi Valley and its northern tributaries dates from this time span.
Prior to the Younger Dryas, wild rice had only a very tenuous presence in certain caves to the south of the Yangzi (Nakamura 2010). But fairly soon after the Younger Dryas, by at least 7,000 BC, the inland basin archaeological site of Shangshan in northern Zhejiang contained a small settlement of wooden pile dwellings with rice husk tempered red-slipped pottery, polished stone axes, and grindstones (Jiang and Liu 2006). The rice was morphologically wild, but for the first time, we witness the possibility of human cultivation of rice and its deliberate threshing—the pottery contained chaff, not unprocessed whole grains (Zhao 2010). Similar evidence, also dating back to about 7,000 BC and including residue analysis in pottery as well as stable isotope dietary analysis of human bone, indicates rice consumption at the site of Jiahu in the Huai Valley, a northern tributary of the Yangzi in Henan Province (McGovern et al. 2004; Hu et al. 2006; Liu et al. 2007). On comparative Austroasiatic linguistic grounds, Ferlus (2010) suggests that rice was eaten first as a gruel of crushed and roughly husked grain. Only later was it boiled in loose grain form with a calculated amount of water to produce the “dry” dietary mainstay that so many people consume today. Diffloth (2011) also presents a strong case for a word meaning “husked rice” as a Proto-Austroasiatic reconstruction.
The idea that rice cultivation began close to the contemporary northern edge of the range of the wild plant, as a reaction to periodically adverse climatic circumstances, was to my knowledge first presented by Yan (1991: 125). It makes good sense, and a slight cooling of climate in central China at about 6,000 BC was possibly a further stimulus to the development of domestication, by inducing humans to actually plant the rice to ensure a continuing and reliable supply. For instance, at the site of Baligang, on the Han tributary of the middle Yangzi in Henan Province, there is evidence for a rice and acorn economy in the pre-Yangshao archaeological phase at c.6,000 BC, followed by a shift to millet in the Yangshao itself (c.5,000 BC), and then a return to rice in the subsequent Longshan phase (Deng Zhenhua, Peking University, personal communication 2011). Such fluctuations in the presence of rice might have reflected issues of availability and supply on the northern edge of its range.
After Jiahu and Shangshan, further archaeological evidence for the intensification of rice exploitation comes from Kuahuqiao in northern Zhejiang (ZPICRA 2004; Zong et al. 2007). Dating to c.6,000 BC, this site has yielded a waterlogged canoe, wooden paddles, foundations of pile dwellings, a small proportion of morphologically domesticated rice (most grains still have wild morphologies) that resembles the japonica subspecies, and a possibility of pig domestication (Liu et al. 2007). By 4,600 BC, rice had risen at Tianluoshan to perhaps 30% of a plant food diet that also included acorns, water chestnuts, and foxnuts (Fuller et al. 2009). By 4,000 BC, nonshattering spikelet bases of carbonized rice grains had increased sufficiently in percentage in lower Yangzi sites (to between 40% and 65%) for Fuller et al. (2009) to accept that rice had become fully domesticated, a process that had progressed continuously for more than 2,500 years from the incipient stage of (mainly wild) rice cultivation represented at Jiahu and Shangshan.
Movement of rice in the early days of its cultivation to new locations where water availability was seasonal, rather than perennial, appears to have been crucial for its eventual domestication as an annual cereal. Hill (2009) and Fuller et al. (2009) suggest that the wild ancestor of domesticated rice, the perennial grass O. rufipogon, was originally harvested continuously in perennial swamps by ratooning. This practice produces lower yields than fresh planting of seed, but requires far less labor. However, humans eventually would have planted rice seeds outside permanent wetlands, perhaps in seasonally wet terrain where the climatic regime would have imposed selection for the annual growth habit that characterizes O. sativa. Outplanting away from wild stands would also have allowed any selection towards nonshattering to be retained more easily with each successive monsoonal planting season (Allaby et al. 2008). The implication here is that the very process of radiation and migration on the part of humans was an essential part of the domestication process for rice right from the start.
Under what kind of cultivation system did rice cultivation initially spread? Fuller and Qin (2009) have suggested that it spread originally as a wet field crop and also suggest that it spread as a result of increasing social complexity and intensification. However, the labor and land tenurial demands of intensive wet rice production, and the nature of the early Holocene environments of coastal China and Southeast Asia render this mode of production rather unlikely in a pioneer colonization situation, however much it might have spread among established and demographically increasing rice-growing populations in later periods.
In an economic context, fully irrigated wet rice, as recorded (for instance) in colonial Java, had an enormous ability to absorb an increasing labor input and to feed an increasing population. Geertz (1963) referred to this process as “agricultural involution,” noting that wet rice intensification did not damage the environment because of the stability provided by terracing and field construction, and the constant renewal of nutrients by riverine flooding. Fully irrigated wet rice at this level can only spread slowly because of its need for high labor investment and stable tenurial arrangements in the establishment of new fields.
Kirch (1994) has noted a similar situation from a different perspective for wet taro (Colocasia esculenta) cultivation in the islands of Futuna and Hawai'i in Polynesia. Wet taro was a highly productive agricultural system in Polynesian prehistory that absorbed high quantities of labor and supported populous and powerful chiefdoms. However, predatory chieftainship and territorial expansion emanated not from such areas of plenty but from the dry and often overexploited landscapes on the leeward sides of many Polynesian islands. Shifting cultivation under conditions of periodic stress was the real recipe for expansion and land taking, not cropping from highly valuable and labor-intensive wet fields. Vayda (1961) made similar observations for groups such as the Iban of Borneo and the Tiv of Nigeria—shifting cultivation was often bound up with predatory and often very long distance expansion. The ethnographic rice swiddening Iban colonized river banks through perhaps 1,000 km of Borneo, from western Sarawak to Brunei, in under a century (see also Freeman 1970).
In the heartland of early rice cultivation in the middle and lower Yangzi Basin, it is likely that rice farming had already reached highly intensive levels by as early as 4,000 BC. Incipient wet rice field complexes date back to almost 5,000 BC at Tianluoshan (Zheng et al. 2009). Fuller et al. (2011) suggest that by 3,000 BC, the system was highly productive, capable of supporting the huge population of the Liangzhu phase in the lower Yangzi valley.Footnote 2 The elongated Liangzhu wet rice fields at Maoshan, for instance, dating from c.3,200–2,400 BC, were separated by long paralleled bunds of fired soil about 20 m apart and covered an area of at least 50 by 700 m, according to phytolith analysis (Qin Ling, Peking University, personal communication 2011). It seems unlikely that rice cultivation spread into Southeast Asia with the first farmers as a simple transplant of this Liangzhu intensive production system.
Indeed, there is every reason to expect that early agricultural expansion into and through a landscape of hunter-gatherers would have tended to emphasize those systems of production that minimized labor input, especially in situations where manpower was limited. We can see a parallel here in the first human settlement of the islands of Polynesia, including New Zealand, in which agriculturalist settlers (without rice) spent the first few decades of their occupation in a fairly avid reduction, even extirpation, of easily accessible and naïve bird and sea mammal resources. Investment of labor in wet taro fields appears to have been a late prehistoric activity in most island groups, fueled by population increase and the need for intensification of production (Kirch 2010; Spriggs 2011).
Another factor that would have inhibited the export of full-scale intensive wet rice agriculture was the nature of the early Holocene coastal terrain of East Asia, following the very dramatic postglacial rise of sea level. This transformed the eastern coastline of China from a coastal plain up to 700 km wide into an archipelago (Nakamura 2010, see Fig. 1). Modern sea level was reached generally by about 5,000 BC, but in areas of shallow continental shelf, such as Sundaland (western Indonesia) and the eastern coastline of China, isostatic loading by the weight of sea water would have caused crustal sinking to continue until well after this dated. Proske et al. (2010) dates the highest sea level (+2.5 m) to between 4,000 and 3,000 BC in what is today the Mekong Delta, and Sathiamurthy and Voris (2006) recognize a +5-m-high stand for this area as recently as 2,200 BC. This means that rice cultivation was spreading southwards from central China at a time when the coastlines were maximally flooded by the Holocene sea level rise, and any perennial freshwater swamps beyond the range of tidal influence would have been of very limited extent. In the more fortunate situation of the Yangzi Delta, many of the early sites with rice appear to have been sheltered behind a series of chenier ridges that formed inland from Shanghai (Zong et al. 2007, Fig. 1; Zheng et al. 2009). But such favorable circumstances are unlikely to have been available along the more exposed coastlines of China, south of Hangzhou Bay.
Thus, Rolett et al. (2011) note that the Neolithic site of Tanshishan, in Fujian Province, now 75 km inland near Fuzhou city was located between 3,000 and 2,300 BC on an island in the inner and then estuarine Fuzhou Basin. No good deltaic land was available for wet rice agriculture, and the excavators think that the Tanshishan economy was still basically without reliance on rice. I have noted a similar situation for the coastline and rivers of Ilocos Norte in the northern Philippines (Bellwood et al. 2008); the Holocene sea level rise here drowned narrow incised valleys that were cut down to the last glacial maximum coastline over steep coastal terrain (the Philippines do not lie on a continental shelf), forming “fiords” flanked by steep slopes until human occupation and forest clearance allowed lowlands to accumulate alluvium and colluvium (cf. Spriggs 2011; Carson 2011, for identical situations in Oceanic islands at first colonization). Such coastal plain and valley sedimentation probably did not develop to any degree in Luzon until long after Neolithic farmers had impacted on the environment through burning and forest clearance, certainly long after 1,000 BC.
In mainland Southeast Asia, the only areas of alluvium that could have offered suitable areas for wet rice cultivation at 2,000 BC, without a considerable input of labor on the part of the farmers, were presumably on the fringes of the largest riverine basins like the Pearl, Red, and Mekong (Proske et al. 2010). Island Southeast has only small riverine basins, and many regions outside Java and Bali had very poor potential for wet rice production owing to unfavorable equatorial climates, soils, and terrain (Pelzer 1948; Geertz 1963; Spencer 1966). If wet rice production was involved in farming expansions out of central China, it was surely at a very basic level without major investment in wet field infrastructure.