Testing Assumptions on the Relationship between Humans and Their Environment: Case Studies from Cahokia Mounds, Illinois
A WashU dissertation by: Caitlin Rankin
Abstract: Many archaeologists argue that studying past human response to climate change can be helpful in informing future strategies to adapt to modern effects of climate change; however, archaeological research is rarely utilized in climate change policy. Much of archaeological research involves forming hypotheses to explain observations of past phenomena. However, the advancement of knowledge requires a back and forth between hypothesis forming and hypothesis testing. I argue that a lack of engagement in hypothesis testing has stalled the advancement in archaeological knowledge on the relationship between humans and their environment. Ultimately, it is this stall in the advancement of knowledge that makes archaeological research irrelevant to the fast paced and evolving demands of climate change policy. In this dissertation, I use Cahokia Mounds as a case study of an archaeological site where untested hypotheses related to the relationship between humans and their environment have persisted in academic literature and public discourse for decades. First, I address a hypothesis that deforestation caused increased flooding at the end of Cahokia’s occupation. I use stratigraphic analysis of archaeological excavations conducted in the floodplain of Cahokia Creek to demonstrate that geomorphic conditions were stable from Mississippian occupation (AD 1050 – 1400) until the Industrial Era (mid-1800s). The presence of a stable ground surface from Mississippian occupation to the Industrial Era does not support the expectations of the deforestation hypothesis. Ultimately, this research demonstrates that pre-Colombian ecological change does not inherently cause geomorphic change, and narratives of ecocide related to geomorphic change need to be validated with the stratigraphic record. Second, I address a hypothesis that regional trends of drought caused food insecurity at the end of Cahokia’s occupation. I rely on stable carbon isotope data of buried soil horizons as a proxy of dominant vegetation ground cover changes through time. These data show local ecological resilience to regional trends of drought, demonstrating that the assumed ecological effects of climate change are not universally inherent. Third, I address the hypothesis that the North Plaza complex was drier than modern times during the construction and utilization of this space. The hypothesis that the North Plaza was dry during Mississippian occupation is generally accepted because it fits into preconceived notions about the use of plaza space. I rely on stratigraphic and stable carbon isotope datasets to demonstrate that the North Plaza was a wetland during the construction and utilization this space. Ultimately, the North Plaza hypothesis is great example of how preconceived notions in archaeology can give leeway to accept untested hypotheses. Moving forward, I suggest archaeologists need to be more conscious of the assumptions that are built into explanations of past phenomena and that we should continue to develop research agendas capable of testing these assumptions.
Citation: Rankin, Caitlin G. “Testing Assumptions on the Relationship between Humans and Their Environment: Case Studies from Cahokia Mounds, Illinois.” PhD diss., Washington University in St. Louis, 2020. https://search.proquest.com/openview/b3d0d14b953bb77aa1e42a8f7d36927f/1?pq-origsite=gscholar&cbl=18750&diss=y