The First Modern Human Dispersals across Africa

Teresa Rito,Viktor Cerny,Luísa Pereira,Pedro Soares,Verónica Fernandes,Martin B Richards,Farida Alshamali,Tom Gilbert

doi:10.1371/journal.pone.0080031

Abstract

The emergence of more refined chronologies for climate change and archaeology in prehistoric Africa, and for the evolution of human mitochondrial DNA (mtDNA), now make it feasible to test more sophisticated models of early modern human dispersals suggested by mtDNA distributions. Here we have generated 42 novel whole-mtDNA genomes belonging to haplogroup L0, the most divergent clade in the maternal line of descent, and analysed them alongside the growing database of African lineages belonging to L0’s sister clade, L1’6. We propose that the last common ancestor of modern human mtDNAs (carried by “mitochondrial Eve”) possibly arose in central Africa ~180 ka, at a time of low population size. By ~130 ka two distinct groups of anatomically modern humans co-existed in Africa: broadly, the ancestors of many modern-day Khoe and San populations in the south and a second central/eastern African group that includes the ancestors of most extant worldwide populations. Early modern human dispersals correlate with climate changes, particularly the tropical African “megadroughts” of MIS 5 (marine isotope stage 5, 135–75 ka) which paradoxically may have facilitated expansions in central and eastern Africa, ultimately triggering the dispersal out of Africa of people carrying haplogroup L3 ~60 ka. Two south to east migrations are discernible within haplogroup LO. One, between 120 and 75 ka, represents the first unambiguous long-range modern human dispersal detected by mtDNA and might have allowed the dispersal of several markers of modernity. A second one, within the last 20 ka signalled by L0d, may have been responsible for the spread of southern click-consonant languages to eastern Africa, contrary to the view that these eastern examples constitute relicts of an ancient, much wider distribution.

Highlights

There is a broad consensus that Africa was the birthplace of Homo sapiens – and what have been referred to as “anatomically modern humans” (AMH)
A minority lineage in most populations in terms of frequencies, phylogenetically L0 represents half of the mitochondrial DNA (mtDNA) variation observed in extant African populations – and worldwide
The modern human mtDNA tree split first at ~180 ka into L0 and a second branch comprising L1-L6, including the L3 branch that migrated out of Africa 60–70 ka [22] (Figure 1). This L1’6 branch is much more frequent than L0 throughout Africa and has a likely eastern or central African origin, since L5, L6 and L4 are all virtually restricted to eastern Africa while L1 is found in maximum likelihood (ML) whole-mtDNA ρ whole-mtDNA age ρ synonymous age

Summary

Introduction

There is a broad consensus that Africa was the birthplace of Homo sapiens – and what have been referred to as “anatomically modern humans” (AMH). The Omo 1 cranium found in south-western Ethiopia and dating to ~190–200 ka (thousand years ago) is the oldest known fossil agreed to display AMH features [3] and alongside crania from Herto (in northern Ethiopia), dating to ~154–160 ka [4,5], and remains from Sudan and Tanzania [6], provide the palaeoanthropological case for an eastern African origin. The oldest agreed AMH fossil known in southern Africa is from the Klasies River caves and dates to ~65–105 ka [9], again its status as AMH has been contested [10]; there are more archaic remains (notably from Florisbad, South Africa) dating to 190–330 ka [9], indicating that a southern origin is a possibility. The fossil record is extremely patchy, but tends to point to a northern rather than southern, and in particular an eastern African, origin for AMH

Methods

Results

Conclusion