A demographic model for Palaeolithic technological evolution: The case of East Asia and the Movius Line

The Pleistocene record of East Asia continues to pose controversial questions for palaeoanthropology, especially with regard to Palaeolithic technological patterns. In recent years, an increased understanding of the effect of demography on cultural transmission has improved our understanding of the incidence, proliferation, and elaboration of technological traditions. Here, we present a generalised null model of Lower-Middle Palaeolithic technological evolution, which expressly links cultural transmission theory and demographic factors (i.e. population size, density, and social interconnectedness). Consistent with our model, Africa exhibits evidence of major technological innovations during the Early to Middle Pleistocene, due to a constant source of population and growth due to accumulation through time. In comparison, Pleistocene East Asian assemblages are dominated by Mode 1-type technologies, and only a few localized occurrences of bifacial technology are currently known. We detail evidence suggesting that during much of the Pleistocene a combination of biogeographical, topographical, and dispersal factors are likely to have resulted in relatively lower effective population sizes in East Asian hominins compared with western portions of the Old World, particularly Africa. Thus, the Movius Line - as is the case with its namesake 'Wallace's line' - must be examined in terms of its biogeographical context, if the divergent evolutionary trajectories of entities either side of it are to be understood. Most parsimoniously, the Movius Line sensu lato is thus a 'line' which represents the crossing of a demographic threshold. Under the parameters of our (testable) null model, geographically and temporally sporadic occurrences of bifacial technology in East Asia are the product of short-lived instances of technological convergence. As a consequence, the in situ evolution of Levallois (Mode 3) was inhibited in East Asia due to the constraints of relatively smaller effective population sizes.