The Origins and Dispersal of Maize Agriculture: A Review and Critical Assessment of the Isotopic Evidence

The application of stable isotope analysis of human skeletal remains to reconstructing ancient diet has now been in practice for two decades. Initial studies focused on interpreting carbon isotope ratios, which primarily reflect differences between C3 and C4 plants in human food chains, through the analysis of bone collagen. In the Americas, the typical application has been documenting the dietary importance of maize, generally the only significant C4 crop exploited by Native Americans. Most research efforts now also include the measurement of nitrogen isotope ratios, which are ultimately dependent on how plants obtain their nitrogen (by symbiotic bacterial fixation or from soil nitrates) but are also affected by rainfall and other local conditions. The combined analysis of both carbon and nitrogen isotopes is especially critical for sorting out the consumption of marine foods in areas where C4 crops such as maize also were available. It is also necessary to establish the isotopic values for both marine and riverine/lacustrine resources on a local basis in order to interpret properly the human bone isotope data. Most recently, it has been established that collagen carbon and nitrogen is derived primarily from the protein portion of the diet, while bone apatite/tooth enamel carbon appears to be derived from all dietary components. Since maize contains only 10% protein, small contributions of meat or seafood to Native American diets would dominate the isotopic signal in bone collagen, thus requiring the analysis of both bone collagen and apatite (or tooth enamel) to reconstruct ancient diet.

In this paper, a critical synthesis of the isotopic data accumulated in the last two decades for Native American diets will be presented, based on evidence from countries including the United States, Canada, Mexico, the Caribbean, Belize, Honduras, Guatemala, Panama, Venezuela, Ecuador, Peru and Argentina, and including isotopic data from the author's own as yet unpublished research. In combination with traditional faunal, botanical, palynological and other data (e.g. pottery residues, phytoliths) relevant to prehistoric maize use, a chronological and spatial model of the origins of maize agriculture and its dispersal throughout the Americas will be formulated. Specific pathways of maize dispersal, as well as diverse local patterns of consumption, will be presented. Lastly, areas for future research which will explicitly test these hypotheses will be suggested.