Eastern African Stone Age
Abstract and Keywords
The Stone Age record is longer and better documented in eastern Africa. Archaeological and fossil evidence derives particularly from sites within the Rift Valley of the region, often with secure radiometric age estimates. Despite a relatively late start and disproportionate focus on earlier periods and open-air sites within the rift, scientific research into the region’s Stone Age record continues to play a central role in our understanding of human evolution.
Putative stone tools and cutmarked bones from two Late Pliocene (3.6–2.58 million years ago or Ma) contexts are exclusive to eastern Africa, as is conclusive evidence for these by 2.5 Ma. The earliest indisputable technological traces appear in the form of simple flakes and core tools as well as surface-modified bones. It is not clear what triggered this invention, or whether there was a more rudimentary precursor to it. Neither is it certain which hominin lineage started this technology, or if it hunted or only scavenged carcasses. Well-provenienced archaeological occurrences predating 2.0 Ma are limited to sites in Ethiopia and Kenya, becoming more common across eastern Africa and beyond only later.
By 1.75 Ma, lithic technologies that included heavy-duty and large cutting tools appeared in Ethiopian and Kenyan localities. Several details about this technological tradition are still inadequately understood, although its appearance in eastern Africa roughly coincides with that of Homo erectus/ergaster. By far the longest-lived Stone Age tradition, hominins with such technologies successfully inhabited high-altitude environments as early as 1.5 Ma, and expanded within and beyond Africaeven earlier. Hunting and use of fire probably started in the earlier part of this technological tradition.
Small-sized and highly diverse tool forms gradually and variably started to replace heavy-duty and large cutting tools beginning c. 300 thousand years ago (ka). Conventional wisdom associates this technological and behavioral shift with the rise of Homo sapiens, although the oldest undisputed representatives of our species continued to use large cutting tools in eastern Africa after 200 ka. In addition to small retouched tools, often on products from prepared cores, significant innovations such as hafting and ranged weaponry emerged during the length of this technological tradition. Increasingly complex sociocultural behaviors, including mortuary practices, mark the later part of this period in eastern Africa. The consolidation of such skills and behaviors, besides ecological/demographic dynamics, may have enabled the ultimately decisive Out-of-Africa dispersal of our species, from eastern Africa, 50–80 ka.
Even smaller and more diverse stone tool forms and other sociocultural innovations evolved in many areas of eastern Africa by 50 ka. Miniaturization and diversification allowed for the adoption of more complex technologies, including intentional blunting and microlithization. Some of these were used as parts of sophisticated composite implements, such as the bow and arrow. Complex behaviors involving personal ornamentation, symbolism, and rituals that resembled the lifeways of ethnographically known hunter-gatherer populations were similarly adopted. These dynamics eventually led to the development of new technological and socioeconomic systems marked by the inception of agriculture and attendant lifeways.
Introduction: Geography and Environment
Eastern Africa is most commonly recognized as comprising two distinct regions: East Africa (Kenya, Uganda, and Tanzania) and the Horn of Africa (Eritrea, Ethiopia, Djibouti, and Somalia). Rwanda and Burundi are sometimes considered a part of this region, although they are more often categorized under Central Africa.
Eastern Africa can be best described as a region of great geographic contrasts, with distinctive physical features that range from massive mountains to plateaus, lowlands, and Rift Valley depressions (fig. 1).1
With elevations reaching up to 5,895 meters above sea level in Mount Kilimanjaro, and 5,199 m in Mount Kenya, the region contains Africa’s highest points. Dubbed the roof of Africa,2 the Ethiopian highlands alone account for much of the continent’s high ground. Kenya, Tanzania, and Uganda similarly contain remarkably high mountain ranges and massifs, albeit far less extensive. The East African Rift system (EARs) divides most of the highlands and plateaus in the region, stretching from the Red Sea coast in the north all the way to the southern border of Tanzania. A part of the Great Rift Valley—which extends further north to Jordan and south to the Indian Ocean through Malawi and Mozambique—the EARs is considered one of the planet’s most extensive geographic features and geologic wonders. In its oldest and widest section, known as the Afar Rift, lie the continent’s lowest points, measuring 155 m and 125 m below sea level at Djibouti’s Lake Assal, and Ethiopia’s Dallol locality, respectively. Further south, the rift system bifurcates into the eastern and western branches. The former bisects Kenya longitudinally before splaying out in northern Tanzania, while the latter forms the western borders of Uganda, Rwanda, Burundi, and Tanzania, before continuing farther into Mozambique across Lake Malawi.
The rift floor contains vast plains dotted with numerous volcanic cones, and elongated lakes aligned along the rift axis. Some of the most prominent rift lakes include Tanganyika, Malawi, Rukwa, Albert, and Turkana. The plateau between the two rift branches contains Africa’s largest freshwater lake, Lake Victoria. Major rivers within the region rise from the plateaus and highlands and include the White Nile, Blue Nile, Tana, Omo, Juba, and Shebelle. Some of the longest records of human evolution are preserved in a few eastern African basins, namely the Omo-Turkana, Awash, and Olduvai. Vast lowlands and coastlines along the Horn of Africa mark the continent’s peninsular extension across much of Somalia, Djibouti, and the eastern parts of Ethiopia and Eritrea.
Eastern Africa’s tropical climatic conditions are ameliorated in the highlands and plateaus, while amplified in the lowlands, depressions, and coastal environments. Coupled with such major climatic regulators as convergence zones, eastern Africa’s diverse topographies and hydrology isolate it as a region with some of the most spectacular wildlife and ecosystems, but also with the most complex climatic patterns on the continent from prehistoric times to the contemporary period.3
The vegetation biomes of eastern Africa largely correspond to the rainfall and relief patterns, where open grassland with scattered trees and shrubland—collectively referred to as the savanna—accounts for much of the natural vegetation from the rift floor to the vast lowlands adjoining the plateaus. Hot and dry semi-deserts and desertic regions with meager rains, such as parts of the Afar Rift, Turkana depression, Somali lowlands, and the Eritrean Sahel belt, are rather sparsely covered by xerophytic plants. Where such regions are drained by major rivers and wadis, they are covered by riparian forests. Much of the eastern African plateaus are dominated by mixed forest and shrublands. Montane forests are variably available throughout the region, while only southwestern Ethiopia and Uganda contain closed evergreen forests. The Afromontane woodland zone gradually transitions to an Afroalpine one in higher elevations (>3000 m), with the highest of such concentrations found in the Ethiopian highlands, followed by margins of the western branch of the rift, and patchy pockets in central Kenya.
Due to its geology, hydrology, and biogeography, the Rift Valley appears to have, across the last several million years, supported the longest and most continuous hominin existence. Extensive tectonics and volcanism across such a long time span not only provided rich habitats, but also allowed for the quick burial and exceptional preservation of paleontological and archaeological remains, often with intercalated volcanic ashes suitable for some of the most reliable radiometric age determinations. Ensuing tectonics and erosion expose extensive sedimentary deposits with invaluable paleoanthropological resources, sampling different time slices. From the fossil evidence for emergence of the hominin lineage, to the evolution of bipedalism, paleobiological conditions leading up to the evolution of our genus, and later our species, the beginning of toolmaking, and the coevolution of the environment, culture, behavior, and anatomy, eastern Africa offers unparalleled windows into the past.
Background to Eastern African Stone Age
Research Framework and Nomenclature
Stone Age studies are fast-paced; new lines of evidence and methodological advances persistently change prevailing understanding. This is particularly the case in eastern Africa, owing to the richness of its Stone Age record and growing research attention it continues to receive. Central to current knowledge of the Stone Age are research framework and nomenclature.
The eastern African Stone Age has been variously recognized, organized, and interpreted, often conditioned by the theoretical and methodological backgrounds of researchers. From the definition of specific concepts to the organization of analytical units, interpretation of the region’s Stone Age record is marked by a myriad of controversies that feature prominently in paleoanthropology.4 The naming and classification of technological and hominin taxonomic units is, for example, problematic at best. For eastern Africa, classifications such as the “Earlier,” “Middle,” and “Later Stone Age” (“ESA,” “MSA,” “LSA”) often fail to accurately reflect the evident technological and contextual diversity witnessed in the region.5 The uncritical use of the term “transition,” and the frame or mindset that it engenders, add further to the failings of the Stone Age trichotomy. This is particularly so with the current realization that shifts in technological patterns were by and large processes rather than events, and contain numerous exceptions to generalizations. Similar problems persist as the rigid biological classificatory labels fail to adequately express dynamic changes in hominin anatomy and behavior.6 In the interest of providing a comprehensive and balanced treatment, relevant controversies are cautiously summarized in the present article. Where possible, technological and anatomical changes are treated in tandem with the available ecological data to provide the bigger picture, rather than simple outlines, of processes of change.
Notwithstanding its shortcomings, the Stone Age trilogy is currently widely adopted in sub-Saharan prehistory.7 Clearly, the simplistic schemata of this system masks the variability in the eastern African archaeological record. In this article, the technological and behavioral features of each assemblage of interest is presented in its own right, with the Stone Age categories used only for general organizational purposes. Similarly, controversial taxonomic classifications are presented here only generically.
Temporal control via various methods of age determination (i.e., dating) is indispensable for accurate inferences about evolutionary change. Since different dating techniques offer different levels of accuracy, this article will indicate, wherever necessary, dating techniques and stratigraphic readings of contexts of interest for a meaningful treatment.
Brief Research History
The unique archaeological and paleontological potential of a few sub-regions within eastern Africa was recognized early on. Pioneering archaeological exploration and sample collection started as early as the late 19th century, although systematic and long-term field programs became common only after the mid-20th century.8 By the 1930s, the famous Olduvai Gorge sequence in Tanzania was discovered, becoming the center of long-term archaeological and paleoanthropological research since the 1950s.9 Newly discovered sites in the Omo-Turkana basin across the Ethio-Kenyan border, and the Awash Valley, over the following few decades, have since positioned eastern Africa at the forefront of human evolution research worldwide.
Research into the eastern African Stone Age has been largely focused on open-air Plio-Pleistocene sites with fossils of early hominins, and evidence of early toolmaking. Well-studied archaeological sites sampling the later Middle and Late Pleistocene are to date few and far between. The small number of cave sites with deep sequences in the region similarly limit detailed understanding of technological and other behavioral changes across the origin and spread of our species. This stands in stark contrast to some regions on the continent. Likewise, research bias toward older periods has meant that several interesting aspects of the Stone Age—such as shifts to complex lifeways and food production—remain as yet inadequately probed in the subcontinent (M’Mbogori 2016).
The Eastern African Stone Age Record
Notwithstanding controversial claims for a much older beginning in the last decade, uncontested evidence for toolmaking and use comes only after the Pliocene. This evidence marks the widely accepted beginning of the Stone Age in eastern Africa, and worldwide.
Two small bone shaft fragments from Dikika (Afar Rift, Ethiopia) were interpreted as bearing evidence of stone-tool-assisted butchery ~3.4 million years ago (Ma).10 However, the absence of associated stone tools, small sample size, and equifinality associated with the modification marks render this exceptional claim extremely untenable.11 More recently, a small number of modified stones from Lomekwi (West Turakana, Kenya) were proclaimed as evidence of early hominin lithic technology at ~3.3 Ma.12 The Lomekwi assemblage was suggested to have been produced by passive hammer as well as bipolar percussion. Less knapping control and more knapping error in this assemblage apparently compare to accidental flaking from chimpanzee nut-cracking using stone hammer and anvil.13 A challenge to the Lomekwi claim pertains to the possibility of the artifacts deriving from a slope deposit that is younger by an unknown age than the actual mid-Pliocene beds.14
The notion that stone tools were made and used by hominins much earlier than is widely accepted is not new. In fact, the suggestion for possible use of unmodified stones as tools in the Pliocene receives ostensible support from living primates using rocks for pounding.15 However, it remains controversial whether extant apes and monkeys can be used as behavioral referents for early hominins; nor is it certain how such tools can be recognized in Pliocene contexts. The abrupt and ubiquitous appearance of the world’s unquestionably oldest tools has for the last two decades raised speculations that there would be an even earlier, more rudimentary form. However, there has to date been no convincing evidence for this from numerous rigorously investigated contexts dating to 2.6–3.4 Ma.16
The First Tools, Their Makers, and Contexts
The earliest recognized stone tools derive from four excavated localities at Gona, in the Lower Awash Valley of Ethiopia, dating to 2.6–2.5 Ma, 2003.17 Large pebbles and fist-sized cobbles were knapped in order to detach small flakes with sharp edges; the unifacially and bifacially flaked cores also provided sharp edges suitable for heavy-duty use, such as chopping. Several hundred flakes with prominent bulb of percussion as well as smooth flake release surface suggest handheld, hard-hammer percussion as the main technique of production for the very earliest tools. The Gona tools also attest to the complex knapping skills of their makers, including knowledge of the flaking properties (i.e., the mechanics of conchoidal fracture) of rocks.18 The presence and anatomical placement of bone modification marks suggest that the earliest stone tools at Gona were used, among other functions, to assist in the acquisition of animal soft tissue.19
Localities in the Hatayae Member at Bouri (~100 kilometers south of Gona) have yielded ~2.5-Ma-old faunal remains with surface modification, some inferred to be the result of stone-tool-assisted carcass processing.20 Stone tools were found lying on the surface nearby, but subsequent excavations could not recover artifacts from in situ contexts. The presence of crocodile-bitten bones here similarly highlights the need for further work to resolve the Bouri inference.21 More conclusive evidence of early stone tools comes from a few eastern African sites between 2.3 and 2.4 Ma. At Hadar, just east of Gona, excavations have yielded simple flakes and cores.22 Sites in Member-F of the Shungura Formation (Lower Omo Valley, Ethiopia) as well as from excavations at Lokalalei (West Turkana Basin) contain artifacts of similar antiquity from in situ contexts.23
Taken together, artifact assemblages from the oldest archaeological sites are characterized by a high proportion of flakes and cores, and the lack of retouched tools, standardized forms, and core preparation. Recurrent exploitation of cores from unprepared and cortical platforms is most common, with unifacial flaking more dominant than bifacial and multifacial ones. Evidence for raw material selectivity and transport, and consistent and controlled core exploitation, attests to the sophisticated knapping skills of the first toolmakers. The concentration of sites with evidence of early toolmaking in a few contexts in the Awash and Omo-Turkana basins of the rift in Ethiopia and Kenya was long considered an artifact of our patchy sampling of contexts predating 2.3 Ma. However, exhaustive field research in the 21st century has proven that such data are indeed sporadic.
A significant, but as yet unresolved, question pertains to the evolutionary processes and hominin species responsible for the earliest technological breakthrough. Unlike the contested claims for Pliocene tool use, for which Au. afarensis would be an obvious maker/user, several hominins are considered candidates for authorship of the earliest recognized lithic technology. No hominin remains have been recovered from 2.6–2.5 Ma at Gona, leaving the identity of the earliest toolmaker there enigmatic. Chronologically and geographically proximal, Au. garhi—a species considered intermediate between afarensis and early Homo—was discovered at Bouri.24 However, the absence of directly associated stone tools renders this assumption only tentative. More recently, a hemi-mandible from the Ledi-Geraru study area near Hadar has been interpreted as representing early Homo at 2.75 Ma,25 although this attribution has been questioned,26 and no sign of Pliocene tool use has been identified there. Strong evidence comes only at 2.33 Ma, where a maxilla of early Homo appears in very close association with excavated stone tools at Hadar.27 Further support for early Homo derives from Lokalalei, with an isolated molar assigned to this genus recovered ~100 m from the 2.34-Ma-old stone tools.28 In addition to garhi and early Homo, robust australopithecines such as aethiopicus and boisei are known from the Omo-Turkana basin, variously spanning the critical period between 2.6 and 2.3 Ma. Although some researchers suggest these robust lineages to be equally plausible candidates for early toolmaking and use, direct evidence for this is yet to come.
There is little agreement on what triggered the beginning of toolmaking and use. Suggestions range from the emergence of the genus Homo with relatively bigger brain size and different anatomy, to the impact of climate change and tectonics on faunal communities in eastern Africa across the Plio-Pleistocene boundary.29 Unraveling precisely how each or a combination of these and other factors resulted in the beginning of toolmaking and use is extremely difficult, particularly considering the dearth of archaeological sites and paleoenvironmental data from contexts sampling the time period of interest. Similarly, understanding whether the earliest technology was a cumulative process of improvisation whose sporadic and isolated outburst is best evidenced first 2.6–2.5 Ma, or a rather abrupt invention with no precursor, requires irrefutable lines of evidence from the Late Pliocene, which are currently lacking anywhere.
“Earlier Stone Age”
Conventionally bookended by the beginning of stone tool technology after 2.6 Ma and the appearance of core preparation for convergent flaking by 300 thousand years ago (ka), the ESA is further classified into two recognizable technological traditions (also variously known as industries or techno-complexes): the Oldowan and the Acheulean. Like the Stone Age trilogy, these lower-level aggregations of the ESA are made based on technological-typological traits considered generally shared, and variable only according to ecological and idiosyncratic factors.30
Introduced based on early work in the Olduvai, the Oldowan was defined as a technological tradition involving the simple flaking of large pebbles to produce flakes as well as a jagged sharp edge on the core (fig. 2). At Olduvai, this pebble-based tradition was recognized consistently underlying the “handaxe cultures” above Bed I.31 Despite its limitations, such cultural-historical sequence of reference based on the typology and anticipated function of tool forms still continues to be used by archaeologists worldwide.
The widely accepted temporal range for the Oldowan is ca. 2.6–1.76 Ma—although some researchers posit that the very earliest Stone Age sites predating ~2.0 Ma should be distinctly classified as pre-Oldowan.32 By about 2.0 Ma, the Oldowan is evidenced in more eastern African sites, including at Fejej in Ethiopia,33 and Koobi Fora and Kanjera in Kenya.34 The number of Oldowan sites increases after 2.0 Ma, with higher artifact density and better evidence of animal carcass processing, both in the subcontinent and beyond. By far the most exhaustively studied and complete Oldowan assemblages sampling the period between 2.0 Ma and 1.7 Ma derive from Olduvai and Koobi Fora.
Broadly speaking, the technologies, tool forms, as well as inferred adaptive and ecological contexts of the very earliest archaeological occurrences at Gona persist throughout the Oldowan. Pebbles are used for producing simple flakes as well as core-tools, while evidence of retouched tools, standardized forms, and striking platform preparation remain limited. Common artifact forms of the Oldowan include core-tools (choppers, polyhedrons, heavy-duty scrapers), flakes, scrapers, borers, and pounded pieces (hammerstones, battered spheroids) (fig. 2). Direct hard-hammer percussion was used in most cases where small cobbles were available to the knappers; the bipolar technique was more common in contexts with pebble-sized raw materials, such as at Omo. Oldowan hominins in eastern Africa selected and transported raw materials for their tool production (Semaw et al. 2003).35 Adaptation was almost always near water, with animal carcass processing as the most likely function for which tools were used.
There is little technical change across the Oldowan, so much so that some researchers consider it as a period of relative technological stasis;36 others argue for more diachronic change.37 In sites with well-stratified and relatively continuous stratigraphy, such as Olduvai, technological nuances have led to the proposed assignment of younger Oldowan sites, with a higher number of “scrapers” and spheroids and a lower frequency of choppers, to a new, site-specific category called the Developed Oldowan.38 Whether inter-assemblage variability across the entire length of the Oldowan in eastern Africa was significant enough to suggest distinct technological, temporal, and/or cultural nuances, and whether differential ecological traits and distinct hominin species had an impact on the nature of Oldowan assemblages, remains unanswered. For instance, the widely accepted view that the limited Oldowan variation represents differential raw material constraints—such as type, distance, and abundance—remains to be rigorously tested.
By 1.7 Ma, the Oldowan tradition in eastern Africa was already starting to show nuances. For example, standardized small tools on obsidian made up a good portion of the 1.7-Ma-old Oldowan assemblages at Melka Kunture in the Ethiopian plateaus.39 Similarly, increased technological complexity has been suggested for the late Oldowan assemblages from Peninj (Tanzania) at ~1.6 Ma.40 Among several places where the Oldowan persisted after 1.5 Ma are Nyabusosi in Uganda, and Chisowanja in Kenya, where flake production shows signs of advanced skills in the form of decortication and radial exploitation of cores, all in the absence of true bifaces.41
The evidence shows that hominins in eastern Africa produced large flake blanks (~10–20 cm long) by 1.75 Ma, which they modified into what are commonly called heavy-duty and large cutting tools. In addition to large flakes, cobbles of suitable size were used for the manufacture of both tool categories. Large cutting tools (LCTs) comprise handaxes, cleavers, and knives, and are more generically called bifaces; heavy-duty tools include picks and core-axes (fig. 2). The production of these tool classes marks the known onset of a new technological tradition conventionally known as the Acheulean.
The earliest known Acheulean assemblages are from Kokiselei (West Turkana) and Konso (southern Ethiopia), both dating to ~1.75 Ma.42 In both areas, the very earliest Acheulean is mostly unifacially worked, relatively crude in form with minimal flake-removal scars, and dominated by heavy-duty forms such as picks (fig. 2). The main focus of tool production was the attainment of large and heavy tools with somewhat consistent morphologies; potential functional requirements are reflected in the attention paid to the shaping of sides and tips into pointed forms and flat working edges. The recurrent production of unifacially shaped tools and crude forms on large flake blanks often detached from boulder cores suggests that ecological and functional factors, rather than raw material constraints, influenced these technologies.
A precocious sophistication of early Acheulean knapping has been proposed based on the co-occurrence of a single relatively well-shaped handaxe at FLK West (Olduvai) with otherwise crudely shaped forms mostly on tabular quartz slabs dating to 1.66 Ma. This and additional claims for butchery based on an extremely small sample size, in which carnivore tooth marks account for the most damage, necessitate cautious treatment of the FLK West evidence.43 At Gona, unifacial and bifacial LCTs as well as heavy-duty tools co-occur with Oldowan cores and débitage ~1.6 Ma.44 The comparable use of large flake blanks and cobbles for making crudely shaped bifaces here has been attributed to the abundant choice of proximally available raw material.
Assemblages with typical Acheulean characteristics are documented at a number of eastern African sites after about 1.6 Ma. The Gadeb and Melka Kunture Acheulean occurrences at >2,000 m indicate successful adaptation to high altitude by ~1.5 Ma.45 At Gadeb, retouched tools were relatively well represented from early on. Long-distance raw material transport suggested for the Gadeb obsidian handaxes requires reconsideration, as do the suggestions for fire use and butchery there. At Melka Kunture, extensive excavations have yielded multiple Acheulean occurrences with some of the richest lithic and faunal assemblages. The early Acheulean assemblage from the Garba IV locality here (probably as old as 1.6 Ma) is interpreted as showing the same focus on small débitage reduction methods as the late Oldowan, although with better knapping skills.46 At Koobi Fora, assemblages dated to ~1.4 Ma contain mostly crudely worked flake blanks and flaked cobbles, often with pointed tips and/or steep lateral retouches. Although described recently as LCTs,47 the Koobi Fora early Acheulean tools bear more similarity to Oldowan core-scrapers, and are considered to lack true LCTs.48 Claims for the use of fire at Koobi Fora ~1.5 Ma,49 much like at Gadeb and Chesowanja (Kenya), will be one of the earliest instances if proven reliable. Uniquely preserved footprints recovered from the Ileret locality at Koobi Fora hint at erectus foraging behavior ~1.5 Ma (Hatala et al. 2017).
With a general diachronic trend already evident in the earliest Acheulean assemblages from Konso and Kokiselei, the organization of Acheulean production and resultant finished products clearly involved standardization and refinement of form. Specifically, a clear trend is exhibited in the planning and organization of the lithic reduction process, with progressively higher flake scar counts, retouch invasiveness, tip thinning, and regularization of edges or plan–form symmetry. Such gradual enhancements were chiefly evident in LCTs rather than in heavy-duty forms such as picks. One explanation can be that LCTs required more predetermination of form and elaboration relative to functional specialization, while heavy-duty tools remained suitable for relatively similar functions requiring a pointed end and heavy weight. By 1.0 Ma, LCT production had become intensive and widespread, with typically symmetrical and invasively worked handaxes and cleavers dominating most Acheulean assemblages.
The increasing variability of the Acheulean has begun to receive greater appreciation. For example, by ~1.0 Ma, Acheulean assemblages from Peninj, Tanzania attest to the raw material selectivity and knapping prowess of their makers, with symmetrical biface production well documented.50 A rich assemblage of crudely worked LCTs and choppers in the Buia basin (Dandiero, Eritrea) is reported from mostly surface contexts and in stratigraphic association with fossils of H. erectus ~1.0 Ma.51 Acheulean assemblages of similar antiquity from the Dakanihylo Member at Bouri, also associated with a H. erectus calvaria, on the other hand, show more refinement.52
It is not clear what led to the shift from the pebble-based, simple flake/core Oldowan technologies to the more structured Acheulean tradition. The available evidence for foraging range expansion, raw material transport and use, as well as organized lithic manufacture suggests that the Acheulean was a rather abrupt and considerably nuanced innovation over the Oldowan, one that was as much cognitive and adaptive as it was technological.53 Long and continuous sequences that document this technological shift are limited, which restricts (sub)regional understanding of the development of the Acheulean. The discovery of fossils attributed to Homo erectus/ergaster at some of the eastern African early Acheulean sites suggest that the beginning of this technological tradition may be linked to the appearance of this early Homo lineage.54 However, beyond this broad temporal association, the details of the apparent relationship between technological innovations and the appearance of derived anatomical features remain enigmatic. It remains equally unclear whether robust australopiths such as boisie, which overlapped briefly with H. erectus/ergaster at Konso, Olduvai, and West Turkana, made and used early Acheulean tools. A more controversial taxon called H. habilis similarly appears at Ileret in Koobi Fora,55 raising the expectation that hominins besides erectus/ergaster probably produced and used early Acheulean tools.
Some researchers identify the pre-1.0 Ma eastern African Acheulean record as the early Acheulean.56 In general terms, most eastern African Acheulean assemblages after ~1.0 Ma show considerably advanced LCT production, with a high prevalence of standardized, bifacially worked LCTs. For example, LCTs account for >80 percent of the youngest (~850 ka, KGA20) assemblage at Konso, with the frequency of picks showing a gradual but relatively steady fall across the sequence. In much of eastern Africa, Acheulean assemblages after this show strong emphasis on thinner flake blanks, sometimes produced using prepared core techniques. Such advance in flake production, coupled with shallow, intensive, and invasive flaking, gradually resulted in the pervasiveness of handaxes and cleavers with straight (as opposed to sinuous) edges, standardized shape, biconvex/semi-biconvex cross sections, thinned tips, and symmetrical plan form. From Olorgesailie, in Kenya, to Melka Kunture and the Middle Awash area, assemblages from several eastern African sites attest to this pattern of flaking and elaboration in the late Acheulean.
Attaining thin and large flake blanks and applying shallow and highly invasive biface thinning removals were possible, perhaps, due to the adoption of the soft-hammer technique (fig. 2). More sophisticated blank acquisition and tool shaping techniques were combined with increased diversity of raw materials to produce smaller and finely worked LCTs. There is no convincing ground to link such technological developments within the Acheulean to emergent anatomical changes in what has been described as H. heidelbergensis/rhodesiensis.
Various tool forms began to appear within the Acheulean broadly after ~500 ka. For example, blades and prepared core reduction methods were described from localities in Kenya’s Kapthurin Formation.57 The broader period similarly witnessed the persistence of crude tool forms into the otherwise advanced Acheulean toolkit. For example, heavy-duty tools and small denticulates collectively termed as Sangoan appeared, presumably as a technological adaptation to wooded environments. Enhanced technical skill is implied from the adoption of platform preparation and more varied core exploitation and blank trimming methods, which later on grade into full-fledged prepared core techniques. Major final Acheulean assemblages from eastern Africa come from sites at Melka Kunture, Bodo, and Meiso in Ethiopia; Olorgesailie, and Kapthurin in Kenya; and Isimila in Tanzania. Some of these sites, such as Bodo and Ndutu (Olduvai), have also yielded hominin fossils with progressively more human-like features. Gombore II, at Melka Kunture, provides a rare glimpse of past hominin group behavior in the form of 700-ka-old footprints.58
From the ecological and adaptive contexts of the early Acheulean, to the function of specific tool forms, and the biological and behavioral adaptations of its makers and users across time, there remain a number of unresolved questions about this longest-lived technological tradition in eastern Africa. Although the sporadic data suggest a wide range of paleoecological settings for the early Acheulean, ranging from near lake and stream water contexts at Konso, Kokiselei, Gona, and Olduvai, to drier, savanna environments at Peninj, and high-altitude ones at Melka Kunture and Gadeb, the details of what led to the emergence, endurance, and later replacement of this technological tradition are as yet to be closely investigated.
“Middle Stone Age”
Several eastern African sites (fig. 3) document evolutionary processes marking the final Acheulean, but none sample in detail the transition to the MSA. Between ~300 and 250 ka, new production techniques, toolkits, as well as adaptive and sociocultural behaviors were ushered in.
The appearance of smaller and more diverse tool forms, and most notably true prepared core (or Levallois, fig. 4) technology from which flakes of the desired size and shape were detached, marks the onset of this new technological tradition conventionally recognized as the MSA. The Levallois reduction strategy differs from other prepared core technologies in the hierarchical preparation of the core to obtain truly predetermined final products for predictable functions. Preparation and predetermination, coupled with the continuous alternation of knapping systems (namely the débitage and façionnage), make the Levallois a technology often considered cognitively demanding.59 The wide recognition of an African origin of our species has since recently attracted more research attention on this period and the subcontinent, although it remains as yet largely unclear whether or how the beginning of the MSA is associated with the emergence of H. sapiens (fig. 4).
The earliest securely dated assemblages described as MSA derive from contexts dated to ~305 ka in the Olorgesailie basin.60 These contain pointed pieces and Levallois technologies, while lacking LCTs in the excavated assemblages. The transport of lithic raw material up to 50 km distances on the ancient landscape and the potential use of ochre at Olorgesailie further suggest behavioral advances early on. Assemblages from younger layers at Olorgesailie, as well as from other areas such as Kapthurin, and Gademotta (Ethiopia), firmly establish the emergence in this region of distinctive technologies and behaviors across the broader period between 300 and 250 ka.
In the Kapthurin Formation (Fm), the earliest MSA at >284 ka co-occurs with LCTs, some made on Levallois flakes.61 True blade production is also documented, along with possible ochre processing, from the oldest MSA here. Younger assemblages from the Koimilot locality within the same formation show considerable variability in Levallois production methods, and the absence of LCTs, by ~200–250 ka.62 At Gademotta, the earliest MSA dated to >279 ka similarly shows a high frequency of retouched tools, as well as highly diverse tool production methods and forms, all from excavations devoid of Acheulean elements.63 Such a pattern continues into younger sites within the Gademotta Fm, leading to the suggestion that ecological stability due to ecotonal location and locally available obsidian may have contributed to the “precocious” technological variability and tool diversity here.64 Use of some of the Gademotta obsidian points as spear tips has been inferred from functional analyses,65 although contested on typological grounds.66
Few other sites sample the earlier part of the MSA. In the Kibish Fm of the Omo basin, excavated assemblages broadly dated to 154–195 ka exhibit the exploitation of diverse siliceous raw materials for the production of tools using Levallois as well as discoidal methods;67 LCTs and heavy-duty tools were also recovered from these sites, although rarely from excavated contexts.68 Dated to a broadly similar age (154–160 ka) are assemblages from Upper Herto, Bouri, that contain a mix of artifacts recognizable as MSA as well as Acheulean, including from recently revisited in situ contexts (fig. 4).69 Kibish and Upper Herto contain the earliest securely dated fossils universally accepted as representatives of our species (fig. 4).70 Poorly dated assemblages and fragmentary cranial remains from Garba III at Melka Kunture have been interpreted as early MSA and early H. sapiens, respectively.71
The emergent picture from early MSA sites in eastern Africa is that “transitions” marking the later Middle Pleistocene were complex and spatio-temporally highly variable. Olorgesailie and Gademotta suggest stratigraphically sharply defined transitions 305–280 ka; the Kapthurin Fm, on the other hand, suggests a gradual and cumulative development of the MSA after initial interstratification with the Acheulean.72 At Omo Kibish and Upper Herto, too, Acheulean artifacts occur alongside MSA assemblages and the earliest H. sapiens fossils ~154–195 ka (figs. 3 and 4). At Mieso, within the Awash basin, on the contrary, exclusively final Acheulean assemblages persist after 212 ka.73 The paucity of continuous sequences leaves the beginning of adaptive technologies and other behaviors often associated with emergent H. sapiens a subject of perennial debate. Poor chronological control and insufficient paleoecological data similarly limit inferences on the timing, nature, and trajectories of this shift. Recently suggested “drivers” of the MSA and events leading up to H. sapiens origins range from climatic shift and faunal turnover to regional volcanism.74 Such assumptions are currently difficult to assess, pending directly associated and compelling data.
A series of Kenyan localities, namely Cartwright’s Site, Malewa Gorge, and Prospect Farm, contain poorly dated assemblages, mostly from selective surface collections described for their bifacial points with invasive retouch and thinned base (Waweru 2007).75 Further south in Tanzania, sites in the Lake Eyasi Beds contain MSA assemblages tentatively dated to ~132–88 ka and associated with fossils exhibiting a mosaic of primitive and derived anatomical features, probably representing early H. sapiens.76 Also in Tanzania, MSA assemblages in the Ngaloba Beds at Laetoli co-occur with cranial remains of early H. sapiens broadly dated to ~120 ka.77
The latter part of the MSA is recognized for its increasingly variable technological and stylistic features, as well as increased frequency of behaviors considered complex (fig. 5). Indications of some form of mortuary practice appear on multiple H. sapiens idaltu fossils from Herto by 154 ka (fig. 4).78 The multiplicity of polish- and cutmarks on the well-preserved adult and juvenile idaltu crania, and the absence of any postcranial remains, strongly suggest perimortem deflashing and curation of the head. The Herto early humans also exploited obsidian from sources as far as 289 km away,79 indicating extensive knowledge of the distribution of resources, complex social networks, and/or mobility/migration. An even earlier long-distance (166 km) transport of obsidian is reported from Sibilo, Kenya at 222 ka.80 After 100 ka, obsidian transport across greater distances becomes more common in the archaeological record of the region, together with greater diversity of sources. Some of these obsidian sources are shared between sites of distinct ages, hinting at ancient connections through shared knowledge of resource distribution.81 At Prolonged Drift, in the Kenyan highlands, most of the MSA artifacts are made on obsidian from the most distant sources, albeit only ~50 km away.82
Ecological factors arguably played a significant role in shaping adaptive and other behaviors during the MSA.83 Assemblage variability in the Kapedo Tuff MSA (~135–123 ka) of Kenya may be strongly linked to raw material availability, rather than behavioral variability.84 Coastal adaptation at Abdur, in the Eritrean Red Sea littoral, is inferred from a small number of MSA tools co-occurring with Acheulean bifaces ~125 ka, although the dating and context require reevaluation.85 Additional surface occurrences in the same reef formation from the nearby Asfet locality, and Ethiopia’s Danakil depression, show MSA features.86 A long sequence with MSA material at its base has been reported from the Kenyan coast. With estimated OSL dates of >67 ka, the Panga ya Saidi MSA is characterized by Levallois cores and large pointed pieces.87 Late Pleistocene coastal occurrences particularly in the Horn region of the subcontinent are frequently interpreted in relation to the hypothesized Out-of-Africa dispersal of modern humans, although a robust understanding requires more detailed investigation and widespread data.
At Mochena Borago rockshelter, Ethiopia, late MSA assemblages containing flakes produced from minimally prepared obsidian cores appear starting ~53 ka.88 This period is associated with harsh climatic conditions, thus leading to the hypothesis that such successful occupation may represent one of few refugia of modern human populations. A similar inference has been made for occupation >40 ka of Gud-Gud cave and Midhishi rockshelter, both on a northern Somalian ridge.89 Gorgora rockshelter in highland Ethiopia provides a long archaeological sequence with rich late MSA assemblages, albeit with no secure date to tie these to paleoenvironmental data from the nearby Lake Tana.90 At K’one in the Ethiopian rift floor, some of the richest MSA assemblages, characterized by the predominance of convergent pieces, are recovered from occupation around a rich obsidian source,91 which was also exploited by several other sites near and far.92
Some of the extensively studied late MSA assemblages from open-air context in eastern Africa come from the Aduma region in the Middle Awash Valley, where they occur in stratigraphic association with the remains of anatomically modern humans ~80–100 ka.93 Nuanced tool production methods, including from micro-Levallois cores, indicate a regional variant of the MSA developing in response to specific ecological, functional, and/or stylistic requirements. The progressive refinement and miniaturization of pointed artifacts at Aduma, along with their morphological and damage patterns, is interpreted as related to the innovation of complex projectile technologies (fig. 4).94 The large number of base-thinned points and scrapers of different types and sizes also suggests mounting of tools in shafts and handles for composite implements.
Complex projectiles are considered decisive innovations of the later MSA, although establishing their antiquity is extremely difficult as organic components of such systems do not preserve well. Because such technologies are suggested to have enabled the Out-of-Africa dispersal of modern humans, their discovery in the eastern African MSA will have significant implications.95 In addition to Aduma, point assemblages from Porc-Epic cave, also in Ethiopia, may represent early complex projectiles at ~50–77 ka, based on morphological and metric assessments.96 The strategic location of this cave overlooking the rift floor is inferred to be for controlling game movement.97 The excavated faunas suggest systematic accumulation of skeletal parts consistent with hunting.98
The presence in eastern Africa of a distinct lithic techno-complex, known as the Nubian, is considered important because of the view that this tradition originated in northeastern Africa and was diffused to Ethiopia and the Horn region. The Nubian complex sensu stricto entails a uniquely standardized production of convergent flakes, primarily via the preferential Levallois method on “beaked” (Nubian) cores that are prepared by two distal-divergent removals. Eastern African sites with Nubian cores/products include ETH-72-5 (<104 ka) in the Gademotta Fm (fig. 4);99 Aduma;100 K’one;101 and Asfet.102 The discovery in southern Arabia of ~105-ka-old Nubian cores and products, and its absence in the Levant as well as south of Ethiopia, is considered to be indicative of early human Out-of-Africa expansion across the Red Sea mouth.103 The possibility that technological innovations, such as the Nubian, may have appeared in different parts of Africa, Arabia, and the Levant as a result of independent innovation challenges strictly diffusionist views.
Evidence of non-utilitarian behavior is best evidenced in the form of personal ornaments, including smoothed, perforated, and/or engraved shells, worked ochre, and bone tools almost exclusively from cave sites and near the close of MSA. Mumba rockshelter in Tanzania contains MSA assemblages and a few isolated human molars at ~63 ka,104 although it is not clear if the rich ostrich eggshell beads are from this layer; nor are the direct amino-acid racemization dates on these beads considered accurate and reliable. At Nasera rockshelter northwest of Mumba, MSA assemblages are similarly recovered from contexts dating roughly to >56 ka.105 Loiyangalani in the wider region represents an open-air site with MSA assemblages comprising worked bone, ochre, and fauna, suggesting a seasonal, near water occupation ~65 ka.106 Unexpectedly young direct radiocarbon dates on ostrich eggshells from MSA layers at Loiyangalani attest to the presence of vertical reworking. Strong evidence for MSA beads comes from ~50 ka at Magubike, a rockshelter overhang site in southern Tanzania.107 The Porc-Epic late MSA similarly contains some of the largest concentrations of worked ochre, numbering in the thousands, as well as perforated ostrich eggshell and gastropod potentially worn as beads (fig. 4).108
Some of the latest instances of exclusively MSA materials come from the Wasiriya Beds on Rusinga Island, in the Kenyan Lake Victoria region, dating to 33–45 ka.109 Other undated sites from the region, such as Muguruk and Songhor, have yielded similar late MSA elements.110 The general proliferation of personal ornamentation and decorative artifacts can be considered a new technological entity fostering the expression of cultural identities and population interactions. The consolidation of such sociocultural behaviors, which flicker sporadically in the final MSA record of the region, coincides with a general shift toward new technological and sociocultural systems usually termed as the LSA.
“Later Stone Age”
Just like the MSA, the appearance of changes in technological and other behavioral aspects collectively recognized as marking the onset of the LSA was neither straightforward nor uniform across space and time. A number of late MSA sites in eastern Africa document technological and economic shifts primarily characterized by the production of small stone tools—microliths—from cores with plain, rather than prepared, platforms. A wide variety of unretouched and retouched microliths are manufactured on flakes produced using, among others, the bipolar technique of lithic reduction. Intentional blunting (or backing) of edges of microliths by abrupt retouching similarly began during this period, perhaps for more effective mounting of the pieces onto hafts as barbs for use as hunting weapons and other implements. The pervasiveness in the archaeological record of personal ornaments, utilized pigments, symbolic representations, and other innovative behavioral traits reminiscent of the lifeways of historic hunter-gatherers further characterize the LSA of eastern Africa, and the continent as a whole, albeit differently in different areas.
As the youngest phase of the Stone Age, the sub-Saharan LSA is often presumed to have some form of continuity into historic and ethnographic hunter-gatherer lifeways. This connection is most evident in archaeological data from the later phase of the LSA, such as rock art and personal ornamentation. As a result, some of the complex traits considered quintessentially human, such as language and symbolically mediated behaviors, can be securely considered to have evolved during the LSA. Similarly, LSA hominin fossils play an important role in our understanding of the evolution of modern anatomical morphology in H. sapiens as well as population histories that have shaped the regional and global modern demographic dynamics.111
The most relevant eastern African archaeological assemblages with some of the earliest instances of LSA elements come from cave/rockshelter contexts in southern Kenya and northern Tanzania, broadly dating to 65–30 ka (fig. 6).
At Panga ya Saidi, microlithization and bipolar techniques of reduction on cryptocrystalline materials appear alongside Levallois technology >63 ka—most distinctly ~50 ka—and continue throughout the sequence. Ostrich eggshell and marine shell beads, as well as worked ochre, appear early on and with increasing frequency across sequence. Such a pattern of technological and behavioral shift at the Panga ya Saidi costal site is presumably coincident with paleoecological changes from arid to forest–grassland-dominated ecotone.112 Similar shift is inferred to have occurred at Mumba, where previous work reported transitional assemblages with Levallois cores, retouched points, and knives persisting through to ~50 ka in Bed V,113 which is otherwise characterized by higher frequencies of bipolar reduction, microliths, and cryptocrystalline materials. By contrast, recent work reports that the MSA elements are limited only to the base of Bed V, hence hinting at a more abrupt shift to the LSA accomplished by 63 ka.114 A clearer picture of gradual technological shift is recognized at Nasera, where Levallois cores and retouched points show progressive decrease across sequence, along with general artifact dimension, between 50 and 25 ka.115 On the other hand, backed microliths and bipolar cores show a gradual increase in frequency. At Kisese II rockshelter (also in Tanzania), a securely dated sequence similarly documents a very gradual and incremental technological shift that spanned ~10 ka, beginning ~40 ka.116 Interestingly, the Kisese II evidence shows that changes in subsistence technologies, inferred from lithic artifacts, postdate those in other behavioral aspects, such as the production and use of beads. This pattern contrasts with other sites, such as Enkapune ya Muto and Nasera, that span the broader time period associated with this transition. There, backed pieces appear at least by 46 ka, and ostrich eggshell beads by 40 ka (Ranhorn and Tryon 2018).117 Interestingly, ostrich eggshell beadmaking at Magubike starts in the exclusively MSA layers dating to ~50 ka, reinforcing the view that most of the widespread and elaborate technological and social innovations of the LSA had their roots in the MSA.118
The similar timing and large number of beads at Enkapune ya Muto and other sites in the subcontinent, such as Nasera, may indicate the bourgeoning of sophisticated social systems in the sub-region, including reciprocity and group identity (fig. 6). At Prospect Farm, Kenya, tentative dates of ~32 ka mark the beginning of the LSA.119 Lukenya Hill, also in Kenya, contains several sites with a minimum age of ~30 ka for the earliest LSA that overlies a long and complex transition of >10 ka.120 Several other sites in the subcontinent sample the shift in subsistence technologies and other aspects of life. However, most suffer from poor chronological control, poor documentation, and lack of revisits.
It is not clear what led to the beginning of nuanced adaptive and sociocultural patterns conventionally considered as the LSA. Factors ranging from abrupt climate fluctuations to population surges, or decline, and biological changes are posited to have spurred these technological as well as social innovations.121 Nor is it certain how the persistence of remnant populations of “archaic” hominin groups into the early LSA may have affected the demographic, adaptive, and behavioral dynamics across this critical period with arguably significant continuity with recent hunter-gatherer populations.122 Extensive exchange networks and sharing of information, some argue, enabled successful adaptation and resilience, and ultimately modern human expansions within and beyond the continent.123
By 25 ka, most eastern African sites had lithic technologies dominated by microliths with a diverse selection of tools, both functionally and stylistically. Standardization into backed and geometric forms proliferated, while composite toolmaking added to the complexity of these technologies. Complex armature systems, perhaps developing in response to ecological as well as demographic eventualities, expanded the niches of LSA humans. Increased expression of individual and group identity is attested in the thriving of different social systems, including personal ornamentation and symbolism. The widespread use, for example, of ostrich eggshell beads and modified ochre in eastern Africa suggests ancient connections, effective technological organization, and resource exploitation in the face of major climate and demographic change during the last glacial period.124 Nuanced technologies and behaviors as well as enhanced connections/territoriality arguably conferred on terminal Pleistocene hunter-gatherers enhanced abilities to cope with ecological risk and better adaptability. Such behaviors continued with generally higher magnitude into the early Holocene (<12 ka) archaeological record of the region, albeit waxing and waning sporadically.125
The later part of the eastern African LSA remains spatio-temporally highly variable, perhaps due to the increasingly diverse responses of different populations across the region to different ecological necessities and eventualities. As technological and sociocultural innovations whose beginnings are witnessed across the MSA–LSA interface became even more complex, so did the distinctions between associated technologies, behaviors, and even economies. The attendant complications are best illustrated by the lack of consensus on what labels such as “hunter-gatherer,” “Neolithic,” or even “macrolith” stand for. The continuation of most of the LSA archaeological and behavioral elements well into the ethnographic record allows for better relational analogies, but at the same time blurs the distinctions and renders the identification of entities complicated.
The lithic components of the later phase of the LSA are variably dominated by backed microliths, burins, and various kinds of scrapers (Brandt 1986; Tryon et al. 2018).126 The dominance of scrapers, perforators, and other specialized tool forms in certain eastern African assemblages is particularly intriguing and hints at an increasing emphasis on specialized craft traditions, such as hideworking. Raw material transport increased not only in distance, but also in the complexity of exchange networks and exploitation patterns.
No sharp boundary can be demarcated as the end of the LSA in eastern Africa, as such lifeways continue into the early Holocene. With a humid period across eastern Africa at the onset of the Holocene came newer economic and sociocultural systems. Specialized foraging strategies are witnessed as fishing-hunting-gathering lifeways were adopted along river and lake margins, and with these a suit of economic and behavioral patterns that characterize the region’s Holocene prehistory.127 The earliest signs of food production appear in the region, with prehistoric humans still retaining their LSA technologies and sociocultural systems while domesticating animals and crops, including some indigenous to the region. These cultural and economic developments, some argue, should mark the end of the LSA and the beginning of a new phase in the region’s prehistory, although several details about the new phase remain highly controversial (M’Mbogori 2016).
Conclusion and Future Directions
The Stone Age of eastern Africa provides exceptional windows into the past. Its unique geography and geology make the subcontinent one of the richest in paleoanthropological resources. Long-term research projects, and redoubled fieldwork efforts, continue to unearth these resources, furnishing our knowledge of key technological, behavioral, anatomical, and paleoenvironmental processes that have shaped our evolutionary path. Heartening examples of ancient DNA studies on human remains from the region are just starting to promise unprecedented insights into population history. By contrast, substantial work is still needed in exploring the recent past of the region, including the dating and study of rock art. Perhaps most important of all, cultural heritage administration organs in the region must make every effort to promote capacity-building so that its rich Stone Age resources can be best studied, promoted, and conserved.
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