The Middle Period of the Atacama oases, North Chile, has been characterized as a time of peace, uniform abundance, and widespread access to exotic materials. In the present work, we test this notion through a comparison of Middle Period human isotopic data (δ13Cco, δ15Nco, and δ13Cap) representing two distinct ayllus, Solcor and Tchecar, in the San Pedro de Atacama oases. We employ Bayesian mixture modeling of individual-level isotopic data to quantify and compare dietary composition within and between the cemetery populations of these two contemporary locales. Ultimately, our research shows that dietary diversity, which we take as a proxy for differential levels of participation in long-distance exchange or the access to the products thereof, was unequally distributed, and that the supposedly uniform richness of the Middle Period was similarly discontinuous. While average isotopic values for the two ayllus were similar, variance within each differed significantly, as did variance in dietary composition arrived at through modeling. By all measures, the individuals interred in Solcor 3 had more varied diets, particularly in terms of carbohydrate-rich plants, than their contemporaries interred at Tchecar Túmulo Sur, suggesting that more individuals from Solcor 3 had greater participation in/access to long-distance exchange networks. Besides providing novel insights into the lived experience of the Middle Period residents of far northern Chile, this work also demonstrates the power of Bayesian mixture modeling for the reconstruction of individual paleodiet.
