Spatial analysis of a geo-referenced radiocarbon database for Early Iron Age sites in sub-Saharan Africa.

We report on the compilation of a geo-referenced database of Early Iron Age dates for the regions associated with the expansion of Bantu-language speaking peoples in Sub-Saharan Africa. Parallels can be drawn between the African Early Iron Age and the spread of the Neolithic in Europe (e.g. Diamond and Bellwood 2003; Gronenborn 2004; Mitchell 2004). In the case of Neolithic Europe there is now a substantial literature evaluating radiocarbon evidence for the rate of spatial spread of the Neolithic transition (e.g. Russell 2004, Pinhasi et al. 2005, Davison et al. 2006, Davison et al. 2009). Whereas in Europe the debate has revolved around the degree to which cultural innovations diffused by adoption amongst pre-existing hunter-gatherer populations as opposed to by the invasive spread of growing and fissioning farmer groups, in Africa there has been little opposition to the idea that this was wholly a process of demic expansion. We see the database’s potential to provide us with an opportunity to unravel the Early Iron Age package so as to explore its complexity (see Phillipson 1969, Chami 2001, Ehret 2001, Robertson & Bradley 2000, Vansina 1994-95 who question, to different degrees, the extent to which biological, linguistic, and cultural traits should be seen as dispersing in a tightly-coupled package). This paper reports on our initial spatial analysis of the database. We examine the evidence for gradients in radiocarbon age of the earliest archaeological records of the EIA package at different locations, and we compare the empirical rates of spread of EIA cultural markers with those predicted from a demographic model of demic expansion.