Dissertation
Reconstructing Summer Temperatures in the Southwestern US Over the Last Five Millennia: Effects on Prehispanic Farmers and the Spread of Maize Farming
Washington State University
Doctor of Philosophy (PhD), Washington State University
2022
DOI:
https://doi.org/10.7273/000005020
Abstract
The Neolithic Demographic Transition (NDT) was a consequential demographic shift in human history, providing the prologue for widespread appearance of pervasive social inequality and the rise of the state. I develop a low-frequency (multi-decadal to millennial-scale) temperature reconstruction for the southwestern United States (SWUS) for the last 5,000 years, where temperature was modulated by ENSO phase and intensity. Further, I show how this temperature record, and an ENSO record that can be inferred from it, affected the rate of uptake and intensity of maize farming. Depending on the phase, ENSO contributes to cooler-wetter conditions (El Niño) or warmer-drier conditions (La Niña). Maize was domesticated in Mexico and arrives in southern Arizona around 3600 BC—a few thousand years prior to the NDT. However, maize does not move quickly north from Arizona, but rather arrives in New Mexico around 2300 BC. Temperature, ENSO, and adaptational constraints affected the rate at which maize moved north. Maize dependence increases substantially in southeastern Utah during Basketmaker II (500 BC – AD 500). The slow movement north from the southern SWUS is due to latitudinal constraints. Maize was under selective pressure to reduce time to flowering under the novel day-length and cooler temperature regimes encountered as it moved north and often up in elevation. The ability to grow maize in cooler conditions expanded where people could live and farm, contributing to major increases in population sizes and densities (the NDT). As a result, people navigated an increasingly complicated landscape in new ways. Tattooing was one way that people showed group affiliation, helping to negotiate relationships between individuals during the NDT. The temperature and ENSO reconstruction suggest that conditions were favorable for maize production and population expansion during the first millennium AD, when El Niño-like conditions prevailed, but turned less favorable in the second millennium AD under the influence of La Niña-like conditions, contributing to the demise of the Chacoan regional system and depopulation of the northern Southwest. I bring together a variety of methods and information through computational and reproducible approaches and a suite of other tools to better understand coupled human and natural systems.
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Details
- Title
- Reconstructing Summer Temperatures in the Southwestern US Over the Last Five Millennia
- Creators
- Andrew Gillreath-BrownAndrew Gillreath-Brown
- Contributors
- Timothy A Kohler (Advisor)Andrew I Duff (Committee Member)Shannon Tushingham (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Anthropology
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 256
- Identifiers
- 99901019638801842
- Language
- English
- Resource Type
- Dissertation