FECAL STEROL BIOMARKERS AS INDICATORS OF POPULATION CHANGE: AN EXAMPLE FROM THE CAHOKIA ARCHAEOLOGICAL COMPLEX, MADISON COUNTY, ILLINOIS

Demographic inferences in archaeology often rely on models using indirect data, such as midden volume, to infer population change. Fecal sterols, such as coprostanol and epicoprostanol, are cholesterol derivatives found in human waste. Due to their lasting stability in sediment, these molecular biomarkers may provide a direct record of population change within a region’s watershed. Despite several recent applications, this method has not been previously attempted in a North American archaeological context and no direct tests of the efficacy of this method have been conducted. This study attempts to verify that fecal sterol biomarkers can, and do, track changes in prehistoric populations.

We analyzed sediment from the watershed of Cahokia, one of the largest prehistoric population centers in the United States, to identify changes in fecal sterol amount over time. Lacustrine sediment was collected from Horseshoe Lake, located approximately 1 km north of Cahokia, and alluvial sediment was collected from borrow pits within the Cahokia archaeological complex. Fecal sterols were extracted from the sediment by soxhlet extraction, followed by derivatization with N,O-Bistrifluoroacetamide (BSTFA) into their trimethlysilyl (TMS) ethers, and analysis on a gas chromatograph-mass spectrometer (GC-MS). Lake sediment was obtained from locations of varying distances to the Cahokia population center to determine the effect of distance on recovered fecal sterol amount.

High fecal sterol concentrations are interpreted as population maxima corresponding to regional congregation and low fecal sterol concentrations are interpreted as population minima corresponding to regional depopulation. The timing of Cahokia’s population maximum and subsequent demographic collapse are poorly defined through traditional archaeological methods. Through fecal sterol biomarker analysis, this project aims to provide new insight into the timing and reasons for Cahokia’s population rise and collapse and confirm the utility of a nascent geoarchaeological method.