Monday, 27 April 2009

Millet Watch: Even earlier dates for Chinese Panicum

Published on-line last week in PNAS was a major new archaeobotanical study of the site of Cishan in central China, which utilized husk phytolith identification methods-- recently developed (published in PLoSone in February)-- and chemical differentiation between foxtail millet and broomcorn millet-- newly developed in this paper. Cishan is well-known site names, generally dated to sometime around 6000 BC, and regarded as type sites one of the early Neolithic cultures of northertn China. There has long been confusion over exactly what sort of millet remains were preserved there, based on the report from previous excavations in the early 1980s, of large storage pits full of 'millet' which variously been interpreted as Panicum or Setaria, but which never were studied or published within any real basis for identification (see for example the recent Cantab. review on early millets). Now this paper by Lu Houyuan and colleagues from the Institute of Geology at the Chinese Academy of Sciences, have cleared this matter up: broomcorn millet was the basic staple at Cishan, at least at its earliest period, and Setaria italica, therefore appears to be a later addition to the crop repertoire, at least in this region. Indeed, this also appears to be the case fruther west at the later Dadiwan, where Panicum cultivation, and especially consumption (by people and their dogs), goes back to 5900 BC or so (work by Barton et al., on which I blogged previously - and with a reply from Barton).

The other major bit of exciting evidence from this new Cishan study are the radiocarbon dates that put the earliest storage pits and millet at the site back to 8000-8500 BC. This would seem to push millet back about 2000 years! (Giving it an even bigger head-start, over rice, as a crop). Other dates are as late as 5500 BC, suggesting a very long (but continuous ?) occupation at Cishan. As any archaeologist will feel, the long span of time covered by the Cishan dates raises many questions about the nature of settlement, society, and site formation over this period.

This study has many strengths (especially with regards to the careful and innovative lab methodologies) but it also has a few weaknesses. These include the unstated/unquestioned assumptions about the ecology of the wild progenitor-- points I raised earlier in relation to Dadiwan-- although I tend to agree that large grain stores imply a regularly cultivated stock. There is also a lack of comparably detailed archaeological work: what is the settlement pattern and material culture that goes with these early millet cultivators and how does it change over the millennia between 8500 and 5500 BC? The latter is, of course, not a question aimed at the authors of this study, but at Chinese archaeological colleagues. Prof. Lu and colleagues have provided some powerful new tools for finding and identifying early millets, but the next step is to deploy these methods in some joint projects with archaeologists so that open excavations, ceramic and lithic toolkits can be assessed alongside the phytoliths. In short, we need more archaeobotany like this to be part of archaeological projects.

My final quibble, as is so often the case, is that we need to be cautious with use of the term 'domestication'. Was the millet at Cishan cultivated? Probably, for the reason that it was stored in large quantities as a staple food. Had it undergone morphological domestication, for non-shattering, larger grain sizes, possible changes in dormancy?... More research that links phytolith morphologies to the domestication process (selection pressures) and domestication traits is needed (this is true of most cereal crops, not just millets!). It seems unlikely that phytoliths will answer all the questions about domestication (like non-shattering). Where on the pathway to domestication was the Cishan millet, and how did it change and move along that evolutionary trajectory over the 3000 years the site was occupied? (Or are we to infer the process was all finished?) The lesson of Tianluoshan is that early crops were still evolving, and this is a protracted process that we should be able to see and track, once we develop the right tools with which to see this-- somes lesseon might be drawn from other crops like wheat and barley for which it is just becoming possible to track the mode and rate of domestication [Ann. Bot. paper]. These new phytolith and chemical criteria, developed in this Cishan study, are an important part of the tool kit that we need for domestication studies in millets. We need more data and integration together with additional methods (macro-remains, isotopes). So the fun begins, the quest for millet domestication.

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