When, where and how anatomically modern humans originated and migrated remains a controversial topic. While fossil evidence seems to favour eastern Africa (e.g. Omo and Herto), archaeological evidence seems to indicate the origin of certain types of behaviour in southern Africa (e.g. Blombos). Genetic and palaeoclimatic evidence add additional levels of complexity. A recent study by Rito and colleagues published in PlosOne tries to pull together these different lines of evidence although the main focus of their study is on human mitochondrial DNA (mtDNA).
The study suggests that the ‘mitochondrial Eve’ possibly arose in central Africa around 180,000 years ago. L0 phylogeography further implies a number of very early dispersals between eastern, central and southern Africa. By ca. 130,000 years two distinct groups of modern humans co-existed in Africa: a southern group and a central/eastern African group. This latter event can be correlated with climate changes, particularly the “megadroughts” of MIS 5, which resulted a thinning of the rainforest in central Africa. This period witnesses the expansion of mode 3 technological industries throughout Africa and ‘archaic’ Homo sapiens fossils seem to disappear from the record.
Subsequent dispersals from southern towards eastern Africa occurred around 100,000 years ago, perhaps involving the spread of personal ornaments, as seen by the occurrence of beads and incised ochre. The successful dispersal within, and out of, Africa around 60,000 years ago of haplogroup 3 and the associated wider dispersal of mtDNA lineages attest to a larger and more interconnected human population. The authors stipulate that the establishment of broad-scale social networks could have provided a method for better retaining cultural innovations, resulting in the ‘human revolution’ claimed in the archaeological record.
Overall this study highlights both the complexity and the potential of the phylogeographic study of African mtDNA lineages and indicates that both climate and culture were main factors shaping early modern human dispersals. Further genetic data and a finer chronological resolution are essential to more comprehensively understand the complexities occurring throughout this time period.
Full reference: Rito T, Richards MB, Fernandes V, Alshamali F, Cerny V, et al. (2013) The First Modern Human Dispersals across Africa. PLoS ONE 8(11): e80031.