I’ve recently been discussing stable isotope analysis as a way to directly determine dietary practices from skeletal evidence, and that is certainly a powerful tool in learning about past societies, but there are some drawbacks to it. Like all complicated laboratory procedures, it’s expensive, and it has the additional problem of being destructive. If it’s done right, it only requires a small amount of bone, but it does involve destroying that bone in the course of analysis, which puts it in tension with recent political trends away from invasive and destructive types of research. It is therefore good to have additional ways of evaluating dietary practices, despite the enormous potential of isotope studies.
One such line of evidence is much more low-tech, and quite simple, as well as being non-destructive. It starts from the widespread recognition that different types of diets have different and readily detectable effects on teeth. Specifically, diets high in carbohydrates tend to result in significantly more dental caries (cavities) than diets higher in proteins and fats. A variety of factors are involved in determining the rate of caries in a given individual, including the form of the teeth and the presence of caries-resistant minerals such as fluoride in the environment, but diet is one important factor and the one that can most easily account for differences between populations and societies in the rate of caries. The way this works is that diets rich in carbohydrates, especially refined carbohydrates such as ground meal or flour which stick to the teeth more easily, result in buildup of plaque that certain bacteria in the mouth feed on. Those bacteria then release waste products including lactic acid, which eats away at tooth enamel can causes caries. Fats and proteins also cause plaque buildup, but the bacteria don’t feed on this plaque, and it tends to be less acidic and therefore less conducive to caries formation.
The implication, then, is that societies that are dependent on agriculture, in which people eat large amounts of carbohydrates, will show much higher rates of caries than hunting and gathering societies in which people eat more fats and proteins. This has indeed been confirmed by observation of caries rates in numerous contemporary and prehistoric populations. There are some cases in which hunting and gathering populations can have relatively high rates of caries, such as a heavy dependence on gathered resources that are high in carbohydrates, such as acorns and pine nuts, but in general the difference between foragers and farmers is quite clear and can be used to determine to what extent a given prehistoric population depended on agriculture just by looking at their teeth.
One relatively recent study looking at this issue in the context of the Southwest is by Karen Gust Schollmeyer and Christy Turner. Turner is best known in the Southwest for his controversial ideas about cannibalism, but he has also had a longstanding interest in dental studies which I’ve discussed before. This paper looks specifically at the dispute over the timing of agricultural dependence in the Southwest and whether it arose at the same time as the “Pithouse to Pueblo Transition” between the Basketmaker III and Pueblo I periods, generally dated to around 750 AD. The hypothesis Schollmeyer and Turner tested is that the Basketmakers had a mixed farming and foraging economy with relatively little dependence on agriculture but that later Pueblo populations were heavily dependent on farming. This predicts that Pueblo populations should have substantially more caries than Basketmakers. The sample they used to test this was a large collection of human remains from various sites in southwestern Colorado, mostly in the Durango area and the La Plata Valley, in the collections of the Harvard Peabody Museum and the American Museum of Natural History. Since these were mostly excavated before 1930 and information on their exact origin and time period is often vague, Schollmeyer and Turner grouped them into just two groups, Basketmaker and Post-Basketmaker, and ran a series of statistical tests on the number and placement of caries in each group.
They found that there was basically no difference. Both groups had very high rates of caries, whether measured as total number of carious teeth, total number of carious teeth and teeth that fell out during life (which often results from caries), or total number of individuals with carious teeth. Statistically most of these were indistinguishable from each other, although it’s important to note that this can’t be considered a truly random sample and statistics drawn from it shouldn’t be taken too literally. Comparisons of caries on specific types of teeth and on different parts of teeth also showed high rates in both groups. There were no significant differences regarding types of teeth. There was a significant but weak difference in parts of teeth, with the later individuals having more caries on the parts of the teeth facing other teeth rather than facing outward. There was also a similarly significant but weak difference in the number of individuals with caries, which was lower in the later group, implying more caries per person with caries than in the Basketmaker period, since the overall number of carious teeth was not different. I don’t think too much should be made of either of these differences, given the nonrandom nature of the sample, and Schollmeyer and Turner are properly cautious in interpreting them. They do make the interesting suggestion, however, that if there is anything to these differences they may imply differences in processing of maize over time, with later groups processing it more efficiently and intensively, using more effective tools, perhaps in response to increased populations. They further suggest that this may be behind some of the dispute in the literature over the timing of dependence on agriculture, since some of the evidence put forth as showing a late date, coincident with the Pithouse to Pueblo Transition, is based on the use of larger and more efficient grinding tools. This is all pretty speculative, and I don’t think it’s really any more likely than the alternative explanation that the significant differences are just statistical noise, but it’s an interesting thought.
Overall, this evidence supports the other recent studies showing that Southwestern populations seem to have been dependent on agriculture by at least as early as the Basketmaker II period. It’s therefore not exactly groundbreaking, but it is useful to have as many lines of evidence as possible brought to bear on important questions like this, especially when most of them seem to point in the same direction.
Schollmeyer, K., & II, C. (2004). Dental Caries, Prehistoric Diet, and the Pithouse-to-Pueblo Transition in Southwestern Colorado American Antiquity, 69 (3) DOI: 10.2307/4128407