Stable Isotopes in Archaeological Research: An Experimental Study of Diet-Tissue Fractionation

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With National Science Foundation support Drs. Matt Sponheimer and Thure Cerling will conduct a series of experiments designed to improve our ability to reconstruct the diets and environments of ancient populations. In recent years chemical techniques such as stable isotope analysis have become an important tool for investigating our predecessors. The idea behind this method is that "you are what you eat," enabling researchers to provide information about an individual's diet and environment through analysis of their soft or hard tissues. Importantly, one must know the proper relationship between dietary chemical compositions and those of tissues such as bone collagen, enamel mineral, or hair that are often preserved at archaeological sites. At present, however, there is considerable controversy with regard to the exact nature of these diet-tissue relationships, which can significantly complicate interpretation of archaeological stable isotope data. The goal of this project is to investigate these diet-tissue relationships, and in so doing, increase the ability of archaeologists to research humanity's recent and distant past.To this end, the team will raise four mammalian species on identical diets. Tissues will be obtained at intervals throughout the experiment, and the team will collect data on urine, feces, methane, and respired carbon dioxide production. The study will specifically test hypotheses put forward by archaeologists about the effects of age, diet, and physiology on mammalian stable isotope compositions. For instance, it has been suggested that the consumption of milk by infants significantly alters their stable isotope compositions relative to their mothers, and that weaning leaves an observable isotopic "fingerprint" in their bones, teeth, and hair. This study will investigate these and other questions for the first time in multiple species, and in so doing, increase the accuracy of paleodietary and paleoenvironmental reconstructions. Moreover, the samples obtained during the experiment will also be shared with colleagues both in the U.S. and overseas in an effort to foster greater scientific collaboration and develop new techniques for investigating the past. The project will also train graduate and undergraduate students in stable isotope analysis and animal nutrition. Stable isotope analysis can be used on tissues of virtually any age, so this study can contribute to our understanding of the origin of humanity, as well as the rise and fall of civilizations. Furthermore, stable isotope analysis has become an important tool in paleontology, ecology, wildlife conservation, physiology, and forensic science, so this study will make an important contribution above and beyond its archaeological significance. Thus, the project will train young researchers, foster inter-university and international cooperation, and make broad contributions to archaeology and other disciplines.