This paper investigates the factors contributing to the emergence and persistence of large, complex human societies in Afro-Eurasia. Using spatially explicit statistical analyses of the geographical and temporal distribution of large human groups over 3000 years, the study finds strong support for two hypotheses: (i) longer duration of agriculture fostered the development of norms and institutions for large-scale organization, and (ii) proximity to the Eurasian steppe, a region characterized by intense warfare, created selection pressure for societies to scale up. The hypothesis that naturally high agricultural productivity promotes large societies was not supported.

Thomas E. Currie, Peter Turchin, Edward Turner, Sergey Gavrilets