Exploring Late Pleistocene hominin dispersals, coexistence and extinction with agent-based multi-factor models

Toward the end of the Pleistocene, archaic humans in Eurasia such as the Neanderthals and Denisovans were completely replaced by anatomically modern humans dispersing from Africa. The causes underlying the replacement and extinction processes remain controversial, especially regarding the relative importance of random events, and anthropogenic and environmental factors. Here, we use the most comprehensive agent-based modeling framework to date for exploring Late Pleistocene human population dynamics under realistic time-evolving environmental conditions. Model simulations suggest multiple out-of-Africa dispersals. Most of these resulted in only partial replacement of Eurasians and long-term coexistence of spatially structured archaic and modern populations in Eurasia. Moreover, a comparison of empirical and model data suggests that the best-documented extinction process – that of the Neanderthals – did not have a single overarching cause, but spatially and temporally diverse causes and mechanisms, such as environmental fluctuations, and asymmetry in resource exploitation efficiency and reproductive rates. When viewed in isolation, various population properties have central importance for replacements, but their true importance can only be understood in comparison and with interactions with other properties.