Stable Isotopes

Stable isotope analysis refers broadly to a series of chemical methods used to study phenomena such as earth systems, the hydrological cycle, and ecology. The use of stable isotopes in anthropology traces its beginnings to the late 1970s. Originally focused on geological, hydrological, and ecological problems, stable isotope analysis now is a major component of the anthropologist’s toolkit. Current applications within anthropology draw from the core scientific disciplines but adapt these methods for specific research questions within archaeology, bioarchaeology, paleoanthropology, and forensic anthropology. One major area of study is dietary reconstruction, which focuses on isotope analysis of human skeletons to examine temporal and regional dietary patterns, as well as variation associated with sex, age, mortuary patterns, and social status. More specialized approaches examine weaning and childhood diet patterns using serial sections of tooth enamel and dentin. Another major area of isotope research in anthropology is the study of past residence patterns (e.g., migration and mobility). Some stable isotopes record information about the local water and geology, and thus provide information regarding the place of origin or travel history of an individual. By examining multiple isotopes in different tissues, anthropologists can reconstruct changes in residence patterns. For example, isotopes in enamel bioapatite (mineral fraction) do not change throughout life, so teeth provide a record of where a person lived when a particular tooth formed. Bone collagen (organic fraction) and bioapatite (mineral fraction), in contrast, are constantly replaced through remodeling; thus, if a person moved to a new geographic region, the isotope values in their bones will shift toward the new location over time. By comparing the isotopes in teeth versus bones, anthropologists can detect whether a person was local or nonlocal to the area where they died. In instances where hair or nails are preserved (e.g., mummies, modern forensic cases), serial sections of these tissues can be used to provide a detailed record of diet or travel history in the months prior to death. More recently, forensic anthropologists have begun to examine stable isotopes in modern human remains to aid with medicolegal identification. These methods are especially useful when a decedent is nonlocal to the area where they died (for example, a recent traveler or foreign-born individual).