War, space, and the evolution of Old World complex societies
Proceedings of the National Academy of Sciences
National Academy of Sciences
Freely available online through the PNAS open access option
How did human societies evolve from small groups, integrated by face-to-face cooperation, to huge anonymous societies of today, typically organized as states? Why is there so much variation in the ability of different human populations to construct viable states? Existing theories are usually formulated as verbal models and, as a result, do not yield sharply defined, quantitative predictions that could be unambiguously tested with data. Here we develop a cultural evolutionary model that predicts where and when the largest-scale complex societies arose in human history. The central premise of the model, which we test, is that costly institutions that enabled large human groups to function without splitting up evolved as a result of intense competition between societies-primarily warfare. Warfare intensity, in turn, depended on the spread of historically attested military technologies (e.g., chariots and cavalry) and on geographic factors (e.g., rugged landscape). The model was simulated within a realistic landscape of the Afroeurasian landmass and its predictions were tested against a large dataset documenting the spatiotemporal distribution of historical large-scale societies in Afroeurasia between 1,500 BCE and 1,500 CE. The model-predicted pattern of spread of large-scale societies was very similar to the observed one. Overall, the model explained 65% of variance in the data. An alternative model, omitting the effect of diffusing military technologies, explained only 16% of variance. Our results support theories that emphasize the role of institutions in state-building and suggest a possible explanation why a long history of statehood is positively correlated with political stability, institutional quality, and income per capita.
Support for this work was provided by Economic and Social Research Council Grant REF RES-060-25-0085, “Ritual, Community, and Conflict”; European Research Council Grant “The Evolution of Cultural Norms in Real World Settings”; National Institute for Mathematical and Biological Synthesis and University of Tennessee (S.G. and P.T.); the National Science Foundation (NSF); the US Department of Homeland Security; and US Department of Agriculture NSF Award EF-0832858.
This is the author accepted manuscript. The final version is available from the National Academy of Sciences via the DOI in this record
Vol. 110 (41), pp. 16384 - 16389
Place of publication