A genetic perspective on African prehistory

The various genetic systems (mitochondrial DNA, the Y chromosome and the genome-wide autosomes) indicate that Africa is the most genetically diverse continent in the world and the most likely place of origin for anatomically modern humans. However, where in Africa modern human arose and how the current genetic makeup within the continent was shaped is still open to debate. Here, we summarise the debate and focus especially on the maternallyinherited mitochondrial DNA (mtDNA) and a recently revised chronology for the African mtDNA tree. We discuss the possible origin of modern humans in southern, eastern or central Africa; the possibility of a migration from southern to eastern Africa more than 100 ka, carrying lineages within mtDNA haplogroup L0; the evidence for a climate-change-mediated population expansion in eastern Africa involving mtDNA haplogroup L3, leading to the “out-of-Africa” migration around 70–60 ka; the re-population of North Africa from the Near East around 40–30 ka suggested by mtDNA haplogroups U6 and M1; the evidence for population expansions and dispersals across the continent in the onset of the Holocene; and the impact of the Bantu dispersals in central, eastern and southern Africa within the last few millennia. There is a consensus across the fields of genetics, archaeology and palaeoanthropology that Africa is the cradle of Homo sapiens. Genetically, across the genome-wide autosomal variation and the uniparental markers, the mitochondrial DNA (mtDNA) and Y-chromosome, Africa is the continent with by far the highest genetic diversity (Torroni et al. 2006; Behar et al. 2008; Li et al. 2008; Cruciani et al. 2011). However, with a few exceptions, this is where the consensus ends. A whole range of crucial questions remain highly controversial. These include: where in Africa modern humans first appeared; when each part of Africa was first colonized by modern humans; the impact of climate change on human populations; and how cultural and technological innovations helped shape the current genetic diversity in the