Tuesday, September 16, 2008

Paper blogging Just finished reading (actually I finished a couple of days ago) a paper in American Antiquity that y'all might find interesting. Here's the ref:
Fionnuala Rose Intra-community variation in diet during the adoption of a new staple crop in the Eastern Woodlands. American Antiquity 73.3 (July 2008): p413(27).

Abstract: This study investigated intracommunity variation in diet during the introduction and adoption of a new staple crop (maize) into an indigenous horticultural system. Carbon and nitrogen isotopes of human bone collagen were analyzed from five sites in west-central Illinois, dating from the Middle Woodland to Mississippian periods, and the results contrasted with evidence from neighboring river valleys and the wider Eastern Woodlands area. Contrary to speculation, neither the initial adoption of maize nor subsequent intensification in its use were correlated with status, gender, or age. A striking bimodal distribution was observed in consumption of native and introduced crops; growing or eating small amounts of maize was apparently not practiced. Fluoride dating confirms the burials are contemporary, and the pattern persists over several hundred years. Possible explanations include issues related to the economics of maize growing, household requirements for storage, exchange, or levies, or individual taste. Also notable were earlier-than-expected dates for intensive exploitation of the maize in this area, in the early Late Woodland, possibly as early as A.D. 400. Nitrogen isotope ratios were higher for males at all sites and time periods; the cause may have been greater access to dietary protein, or could be the result of physiological differences.

She used stable carbon and nitrogen isotopes (δ13C and δ15N) (see here and here for way more detail than you probably need and here for something more succinct) to determine the amount of maize in the diet over the Middle Woodland (150 B.C.-A.D. 250) into the Mississippian (AD 900-1700). I'll skip right to the conclusions:

First, this study has confirmed that maize was not eaten in large quantities in the Middle Woodland. Maize consumption at that date has been linked to ritual activity, and it may have been a prestige food, but no differences in diet were identified between the low-status Joe Gay and high-status Lawrence Gay burials. This may reflect either no differences in diet, or that any differences were not substantial enough to have biological consequences, and an effect on bone collagen.

Pretty straightforward, no differences detected between low and high status burials, but it doesn't rule out minor consumption that may not be detectable.

Second, there is now clear evidence in this region for an early increase in utilization of maize and its adoption as a staple crop, in the early Late Woodland, and almost certainly prior to A.D. 800, the date commonly accepted for the rise in maize consumption in the Eastern Woodlands, and well before the appearance of Mississippian cultures. Markedly more enriched carbon isotope ratios, indicative of maize consumption, are recorded in the early Late Woodland at Knight and Joe Gay in the Central Mississippi River Valley. . .Maize consumption is not at this time as high a proportion of diet as is seen later in some areas, and indigenous crops and wild plant foods continued to be important.

Again, nothing earth shattering, but still note that maize didn't become a large part of the diet right at its introduction. It was gradually introduced into the regular array of locally domesticated plants.

This is the interesting part:
Third, as maize utilization took off, there was a widespread and long-lived pattern of striking variability in maize consumption within communities, varying from no maize, to quite a high proportion. This variability is so marked as to result in a bimodal pattern in carbon isotope ratios. Neither gender, status, nor age explain this variability. The ratio of maize consumers to non-maize consumers changes over time, as maize is adopted by more of the community, but the presence of two discrete consumption patterns does not, until the early Mississippian.

Odd that. Doesn't have any apparent relationship to sex, social status, or age. Why would some parts of the community eat a reasonable amount, but others did not? Or is it something chronological that just makes it look like contemporary differences? That is, are some burials really later than others and does this just reflect imperfect dating? She did deal with this in a way, though not in an ideal manner. Dating is a problem, as these are older excavated sites. She used fluoride dating, a relative method where bone absorbs fluoride from groundwater; thus, the longer a sample has been exposed the more fluoride it should contain. Unfortunately, this requires samples from similar contexts and only one site (Yokem) was amenable. Still, no patterns were found. Imperfect, yes, but it is suggestive and points out another area where work could be done.

Two reasons I like this thing. First, it is a good use of formerly excavated material, something I've highlighted before. Unfortunately, the problems of using this sort of material (poor dating in this case) are also displayed. Still, it shows the good use to which older collections can be put.

Second, it's an interesting examination of how maize didn't quickly replace local domesticates everywhere. It took several hundred years after its introduction to largely replace indigenous domesticated plants (squash, sumpweed, goosefoot, etc.) and still produced variation in its adoption.