Eleanor Kingwell-Banham

The contribution of rice agriculture and livestock pastoralism to prehistoric methane levels An archaeological assessment

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.

Early agriculture in South Asia

This introduction traces the origins of agriculture and the character of early agricultural communities across the world and surveys the development of the more complex social structures and cultural forms that agriculture enabled. Like modern scientists, however, some experimenters either unwittingly or intentionally manipulated the genetic make-up of plant and animal populations, selecting for traits and characteristics that were more productive or more pleasing and thus preferred. Food production has been linked to significant changes in landscapes and populations that eventually supported the rise of urbanism and enabled human populations to expand from 6 million to over 7 billion today. Alan Outram describes how, whether keeping a few livestock within a mixed farming system or maintaining large herds and flocks in systems of specialized pastoralism, the key limiting factors that have to be solved are access to grazing land and, for times of the year when the natural grazing is insufficient, adequate supplies of fodder.

A tale of two rice varieties: Modelling the prehistoric dispersals of japonica and proto-indica rices:

We model the prehistoric dispersals of two rice varieties, japonica and proto-indica, across Asia using empirical evidence drawn from an archaeobotanical dataset of 400 sites from mainland East, Southeast and South Asia. The approach is based on regression modelling wherein goodness of fit is obtained from log–log quantile regressions of the archaeologically inferred age versus a least-cost distance from the origin(s) of dispersal. The Fast Marching method is used to estimate the least-cost distances based on simple geographical features. We explicitly test three hypotheses for the arrival of japonica rice to India where, it has been proposed, it hybridized with the indigenous proto-indica, subsequently spreading again throughout India. Model selection, based on information criteria, highlights the role of the Inner Asia Mountain Corridor in introducing japonica rice into northeast India, followed closely by a ‘mixed-route’ model, where japonica was also almost simultaneously introduced via Assam, Bangladesh and Myanmar. Finally, we estimate the impact of future archaeological work on model selection, further strengthening the importance of the Inner Asia Mountain Corridor.