The evolution of modern human diversity in Africa
All evidence shows that Homo sapiens evolved in Africa towards the end of the Middle Pleistocene (790,000 – 130,000 years ago), and dispersed throughout the continent during the Upper Pleistocene (130,000 – 11,000 years ago). The African fossil record for both these periods is extremely small, but Upper Pleistocene archaeological sites are revolutionising our understanding of early human behaviour.
INFORMATION ON: Middle Pleistocene sub-Saharan African hominin fossils
INFORMATION ON: Late Middle-early Upper Pleistocene African human fossils
The period that followed the MIS6 glacial-arid phase is known as MIS5a-e (130,000-71,000 years ago), and corresponds to an interglacial period. In the tropics, interglacials were often accompanied by periods of extreme precipitation (pluvials) and thus expansion of lakes, rivers and biomass in general. MIS5e (130,000 -1115,000 years ago) was one such pluvial period, when the African biome bridged the Sahara into northern Africa and the Middle East. The evidence for this biogeographic expansion is both environmental (the ‘Green Sahara’) and biogeographic – the presence of Ethiopian faunas in MIS5 cave deposits in Israel, such as Qafzeh1,2.
Humans would have had the same response to the improving environmental conditions as the faunas, so we expect that the modern human populations in Africa who survived the extreme challenges of MIS6 would expand demographically and geographically at this time3,4. Although fossil evidence of that moment of human expansion and diversification within Africa remains limited, the presence of modern humans at the edge of Africa, in the caves of Skhul and Qafzeh in the Levant, shows the extent of early human geographic (and presumably, demographic) expansion at this time5-9. These fossils, some of which played an important role in the history of research into late human evolution, share key morphological traits with both the earlier Omo Kibish/Herto Homo sapiens remains from Ethiopia and all living humans. These features are very few, but so unique to humans that they represent the signature of the morphological evolution of the lineage10-16.
In contrast to the small number of human fossils, African archaeological sites dating to the last interglacial are numerous, especially in South and North Africa. The main aspect of the lithic industries at these sites does not differ significantly from earlier Middle Stone Age (MSA) assemblages, which continue to be characterised by a predominance of flakes, often struck from facetted platforms on Levallois, discoid or radial cores, and often standardised into triangular or blade-like shapes with convergent dorsal scars. There is, however, greater regional patterning created by an increase in innovative tool forms and technological strategies of tool manufacture17-19.
Because MSA stone tools were made by both modern humans and other hominins, and because it is not known when those other hominin populations became extinct in Africa, the distribution of MSA sites per se does not necessarily correspond to the distribution of modern humans, even after 195,000 years ago when we know the first members of the Homo sapiens lineage lived in southern Ethiopia. However, the occasional association of post-130,000 year old MSA sites with early human fossils (for example at Klasies River20, Border Cave21, Blombos22 and Equus Cave23 in South Africa; and Mugharet el-Aliya24, Dar-es Soltan25, El Harhoura26, Témara27, Haua Fteah28 and Taramsa Hill29 in North Africa; and Mumba Shelter30, Aduma31 and Diré-Dawa32 in East Africa) allows the attribution of these sites and their material cultural remains to early populations of Homo sapiens.
The wide geographic distribution of these sites maps the geographic expansion of modern humans in Africa during the last interglacial (130,000-71,000 years ago). The overall number of archaeological sites throughout Africa increases significantly at this time and in the subsequent period (MIS4, 71,000 – 60,000 years ago), when the classic African MSA becomes widespread and abundant.
This phase of modern human evolutionary history – from 130,000 to 60,000 years ago (MIS5 and MIS4) marks a moment of significant change in behaviour – the first evidence for personal ornaments33-36, for the non-functional use of pigments37,38, for the decoration of objects39, for the use of carefully chosen plants for bedding40, and for technological innovations, such as the range of use of bone as raw material, tangs on lithic points, or the development of true microliths and composite tools18,41-43. These behaviours show that early human populations developed material means of expressing social traditions and symbolic thoughts.
The use of pigments dates to the beginnings of the MSA38, being present as modified chunks of ochre or other materials at Kapthurin44 , Twin Rivers45 and Saï Island46 before 200,000 years ago, while a number of pieces of differently coloured pigments were found at Pinnacle Point47. Pigments may have been used even earlier48, but the evidence remains inconclusive, and black pigments were clearly used by Neanderthals49. An argument has been made that the use of pigment in the early MSA was at least partly symbolic on the basis of colour choice – MSA hominins preferentially chose red rather than yellow colours37,50,51. However, the use of ochre as an adhesive for hafting52-55, specially red ochre, argues for at least some functional origin of the pigment pieces found in MSA sites56-58. The concomitant development of backing59 and of tanged points60 strongly suggests that good adhesive substances would have been needed.
However, personal ornaments carry an undisputable social and symbolic meaning, and they appear for the first time in the record of the early humans during MIS5. The earliest ornaments are perforated bivalve Glycymeris shells at Qafzeh (from layer XXIV of the Qafzeh sequence and below the human burials)33, while several perforated Nassarius shells have been found at the Grotte des Pigeons in Morocco34, in Oued Djebban in Algeria36, and at Blombos35 in South Africa. Other evidence of increasing material expression of social norms and shared symbolic and aesthetic meaning is in the form of burials with objects (such as Qafzeh 11)61, the decoration of domestic objects (such as the ostrich eggs from South Africa)39, or the enigmatic markings on soft stones (such as the geometric scratching of a chunk of ochre at Blombos62, at Klein Kliphuis63 and the engraved piece at Klasies River64, all in South Africa).
The end of this interglacial period is climatically and demographically dynamic. Recent programmes of dating and re-dating of particular groups of sites using a single method have revealed the fluctuating demography of MSA populations at the time, as observed for the Aterian of the Maghreb65 and the Stillbay and Howieson’s Poort assemblages of southern Africa66,67. In particular, the South African sites show the rise and fall of MSA traditions in the course of 5,000 years.
These demographic changes are reflected in the mtDNA diversity, and to some extent, the genomic structure of living African populations68. The entire framework of global human mtDNA diversity (all the existing stem lineages) appears to have evolved by the end of MIS5, including the population ancestral to Bantu-speakers in Africa and the small sub-branch that represents the ancestors of all non-African peoples of the world69. Except for a few groups of hunter-gatherers (such as the Hadza and Sandawe in Tanzania), the genetic history of the speakers of the major African linguistic groups today (Khoisan, Nilo-Saharan, Afroasiatic, Niger-Kordofanian) is marked by extensive population movement and admixture throughout the continent68. A few groups, mostly associated with food-producing economies, increased demographically in the last 5,000 years, and their geographic expansion let to the assimilation and/or replacement of hunter-gatherers throughout Africa. Africa went from being a continent where everyone hunted and gathered in relatively small groups over large areas 5,000 years ago, to one where >90% of the nearly 1,000,000,000 people live in settled or semi-settled communities that intensively use the land to produce food. Such overwhelming demographic change highlights the importance of archaeological and fossil remains to reconstruct the processes and events that shaped human diversity in Africa between 70,000-5,000 years ago. Archaeologically, that period records the continent-wide transition from MSA to Later Stone Age (LSA) industries, with blades and/or microliths of many sorts, the ubiquitous production of beads, and wider social and trade networks70-72.
The timing of this transition remains one of the most exciting issues in the evolutionary history of African populations. In many parts of Africa, LSA archaeological remains date to the postglacial period – between ca. 16,000 years ago and the present. In South Africa, sites such as Border Cave date the earliest LSA at ~40,000 years ago73, significantly before the last glacial maximum 18,000 years ago, and in East Africa, two sites – Mumba in Tanzania74 and Enkapune Ya Muto in Kenya70 – date the first LSA to even earlier, between 60,000-48,000 years ago, at a time when many populations in Africa still made their tools and organised their material culture in the same way as people 100,000 years earlier.