Dual-tier approach to societal evolution and types

• The dual-tier approach to societal evolution involves comparisons within and between regions.
• Societal types play an essential role guiding the selection of appropriate cases for comparison.
• Chiefdoms in the prehistoric Polynesia and the U.S. Southeast and Southwest varied.
• Exceptionally complex cases were located in optimal locations and experienced similar trends.
• Organizational transformations were produced by distinctive “Goldilocks” moments.

The dual-tier approach to studying societal evolution aims to identify both specific and general processes of prehistoric change that produced greater organizational complexity. The approach involves diachronic comparisons of archaeological sequences that represent typologically similar cases. Initial comparisons are done of historically related societies within world regions so as to define each region’s organizational variability for the type and time period being considered. This variability provides important contextual information for identifying exceptionally complex cases and understanding the reasons why they developed. Next, comparisons are done of different regions’ singularly complex cases to identify similar, but historically independent, processes of societal evolution. Societal types guide the selection of appropriate world regions and exceptionally complex societies to compare. Focusing on chiefdoms, a classic evolutionary type that we define by polity population size, we illustrate the dual-tier approach with late prehistoric sequences from Polynesia and the North American Southeast and Southwest. We show that the different regions’ exceptionally complex cases were located in optimal environments where they experienced population growth, intensified resource procurement, expanded political economy, and formalized religious ideology. However, the relative importance and details of these trends varied considerably. Documenting the “Goldilocks moments” that made organizational transformation possible offers a productive means for future evolutionary studies.