Bridging Paleolimnology And Archaeology Through Human Biomarkers In Lake Sediment

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Understanding human population levels over time is fundamentally important for answering numerous questions about the deep past. For instance, were rising population levels responsible for spurring major social transformations, like the adoption of agriculture, more complex social and political hierarchies, or intensified warfare? How were population levels affected by major events like the colonization of new areas, environmental crises, or the collapse of states? Traditionally, archaeologists arrive at estimates of past demography through archaeological survey, but this is not always possible (e.g., for phases of human settlement with low population densities and high mobility, or in regions with poor surface visibility of sites due to thick vegetation or alluvial deposition). This interdisciplinary project aims to establish whether recently defined biochemical markers in ancient lake sediment can serve as reliable proxies for human population levels over time. P.I. Dr. Elizabeth Arkush, Co-P.I. Dr. Josef Werne, and Co-PI Dr. Mark Abbott will use National Science Foundation support for a pilot season of coring and analysis of lake sediments from the Titicaca Basin of southern Peru. If successful, this technique will hold major potential for reconstructing the demographic histories of regions. In addition, because lake core sequences also have other significant information such as precipitation levels, this technique holds promise for investigating the relationship between human populations and environmental change by reducing the chronological uncertainty that comes from matching separate climate and population records.Recent research shows that fecal 5-Ò-stanols, organic compounds deriving from feces of higher mammals, are present in measurable amounts in lake sediments. The presence and quantity should reflect human population levels in the lake watershed, particularly coprostanol, which is the major 5-Ò-stanol in human feces. This project aims to evaluate and expand the utility of this biomarker for archaeological research by comparing 5-Ò-stanols in two lake cores in the south-central Andes with sequences of population levels derived from two already completed full-coverage archaeological surveys. In addition to advancing new methodology for the reconstruction of past demography, the resulting dataset has the potential to make significant advances on questions about the connection between pre-Columbian sociopolitical change and paleoclimate. The project's broader impacts include significant training and research opportunities for undergraduate and graduate students.