Sunday 5 January 2020

Patterns of stone tool use among the earliest herders at Lake Turkana, northern Kenya.

Past societies around the world repeatedly reconfigured their technologies to accommodate the challenges and opportunities of novel food-production strategies. In Africa, mobile lifestyles that focused on herding livestock emerged before plant agriculture. Mobile herding facilitated the expansion of Human, animal and plant populations, contributing to the development of social and economic diversity in sub-Saharan Africa. Broad geographic patterns were shaped by the specific solutions adopted by herders as they confronted new climatic and social situations. Stone-tool technologies were a primary component of early herder strategies, reflecting the ways in which these groups interacted with their environments. The lithic record provides a means of connecting regional archaeological patterns to broader trajectories of African food production. African pastoralism emerged in the Early Holocene Sahara, during a period of high rainfall and associated expansion of rivers, lakes and grasslands. Initially, people integrated herding into extant fisher-forager lifeways, while maintaining the widespread use of wavy-line pottery, barbed bone points and microlithic and bifacial toolkits. As herding became more important, groups gradually increased their investment in systematic lithic raw-material acquisition, and reorganised their lithic methodologies. Aridity in the early Middle Holocene pushed herders southward. In eastern Africa, domesticated Cattle, Bos taurus,Sheep, Ovis aries, and Goats, Capra hircus, first appear at Lake Turkana in northern Kenya by 5000 years ago. Northern Kenya proved an important staging ground for the southward expansion of pastoralism. As herders ventured farther from resource-predictable river valleys such as the Nile in search of grazing, they encountered unpredictable and drought-prone environments already occupied by hunter-gatherers. Herders responded to these conditions by developing new social institutions, including the unprecedented tradition of constructing monumental ‘pillar-site’ cemeteries. Despite evidence for climatic and social change on this moving frontier, many aspects of herder economic strategies remain unclear. This is due predominantly to the challenge of differentiating herder and hunter-gatherer toolkits, and identifying meaningful variation within or between assemblages.

In a paper published in the journal Antiquity on 10 December 2019, Steven Goldstein of the Department of Archaeology at the Max Planck Institute for the Science of Human History, explores the lithic technological organisation of the earliest herders in northern Kenya, with the am of demonstrating the viability of lithic analyses in answering questions of local and regional significance: 

Debates concerning the origins of the earliest herders in Turkana have largely overshadowed discussion of how these economies operated. Due in part to the ephemeral nature of mobile herders on the landscape, only two habitation sites with domesticated Cattle and Caprines securely dated to 4500–4000 years ago are currently known. Faunal evidence indicates that the inhabitants of these sites were diversified pastoralists who balanced herding with fishing. The continuity in use of both aquatic resources and microlithic toolkits (made from local basalt and chert) through the Early to Middle Holocene has been argued to show that local hunter-gatherer-fishers were integrating livestock into their subsistence economies.

Nderit herder sites and obsidian sources. Goldstein (2019).

A combination of new ceramic styles, burial traditions and patterns of obsidian transport however, may suggest a more substantial economic shift in association with the first domesticated animals/ At Dongodien, evidence for early livestock is associated with a new, highly decorated style of ceramics, termed ‘Nderit ware’ that differs from the plain and wavy-line pottery traditions of local fisher-foragers. Nderit ceramics are also present at several of, but not all, the monumental cemeteries marked by natural basalt pillars that appear around Turkana after 5300 years ago. The construction of large burial mounds marked with rows of translocated natural basalt pillars at Lothagam North and Jarigole is attributed to early herders, based on material culture similarities with Dongodien. In addition, Caprines have been identified in the faunal assemblage from Lothagam North and clay Cattle figurines have been recovered from Jarigole.

Lothagam North pillar site, view facing east towards Lake Turkana, Kenya. Goldstein (2019).

Other, smaller pillar sites, such as Lothagam West and Kalokol have yielded no clear connections to herders, and differ from the Nderit sites in their organisation and material culture. Extant samples of lithics from such sites are too small to be statistically significant, and preliminary analysis suggests that a few of these assemblages are heavily weathered Middle Stone Age (approximately 250 000  to 25 000 year old) artefacts. Whatever these other, smaller, sites may represent, the tradition(s) of pillar-site construction and associated Nderit pottery use disappeared from Turkana after 4000 years ago. This coincides with another retreat of lake water levels and a prolonged shift towards more arid conditions across the Turkana Basin. The few known post-Nderit sites attest to some continuation of mixed small-scale herding, fishing and foraging.

Three-dimensional scan of fired-clay cow figurine from Jarigole. Goldstein (2019).

Dongodien, Jarigole and Lothagam North are the only herding sites that have yielded large lithic assemblages and Nderit pottery securely dated to this early phase of herding (5000–4000 years before the present). Similarities between the sites in ecological settings and known distances to obsidian sources permit reconstructions of lithic technological strategies, and thus the broader economies, of the earliest herders in the Lake Turkana Basin.

Confusion over the variability of Middle Holocene lithic signatures across eastern Africa may result from a legacy of identifying industries based on tool types and ratios, rather than technological strategies. Approaches focused on site ecologies, quantitative morphologies and reduction sequences among herders and foragers are better developed in southern Kenya, where they have helped to clarify culture-history and economic variability. The present research operates within a theoretical framework that considers stone-tool assemblages to reflect intentional systems of manufacture, maintenance and discard. Patterns of flake production and tool use are structured by decisions weighing cultural, economic and environmental considerations within a cost-benefit framework. Choices about flake shape, striking-platform size and intensity of tool use reflect raw-material conservation strategies as related to mobility. In general, highly mobile groups favour more formal industries that maximise the utility of the stone-tool supply that they carry with them; less mobile groups not under such curation pressures expediently reduce local raw materials. Variety in tool types and morphological variation within type-categories reflect ongoing and anticipated tool needs (i.e. craft production, hunting or other subsistence tasks). In summary, technological organisation reflects the degrees to which people were planning for, and investing in, different activities, such as herding, fishing, hunting and gathering across the landscape.

To understand the conditions that structured the lithic choices of ancient herders around Lake Turkana, I analysed lithic material from all three early herding sites that, to date, have yielded large, securely dated, tool and debitage assemblages. These are the single habitation site of Dongodien and the pillar-cemetery sites at Jarigole and Lothagam North. Assessment of the cemetery assemblages demonstrates that they reflect construction, maintenance and mortuary activity, rather than being secondary deposits brought in as fill. Comparing assemblages from habitation and special-purpose sites is necessary given the lack of comparative assemblages from dated sites, but also presents an opportunity to identify social dimensions in technological variation.

Raw material selection is the basis for the development of technological strategies. It has implications for group mobility in terms of more mobile societies with less predictable access to stone sources tending to favour high-quality raw materials that allow for greater utility of tool production per unit of stone. Cobbles of high-quality chert can be found in nearby stream beds around Jarigole and Dongodien, and there are pockets of tabular chert eroding from the western side of the Lothagam ridge, adjacent to Lothagam North. Geochemical sourcing shows that primary obsidian sources are distributed along the north-eastern lake basin. Early Holocene hunter-gatherer-fishers across northern Kenya made ample use of abundant, local lavas and cherts. Obsidian, if present at all, typically constitutes only a small percentage of assemblages, and is often restricted to heavily deflated and reworked surface or near-surface contexts. Hunter-gatherer-fishers produced a highly diverse range of lithic industries, with sites exhibiting expedient flake technologies, diverse microlithic toolkits and sometimes mixes of both.

Tabular chert eroding from the western ridge of Lothagam, near Lothagam North. Goldstein (2019).

In contrast to the Early Holocene patterns, obsidian constitutes the vast majority (72–92%) of the lithic material at Middle Holocene sites in the Lake Turkana Basin associated with early herding. This signals a shift from down-the-line or incidental access to obsidian, to systematic or even semi-formalised acquisition systems. It is possible that newly formed obsidian exchange networks facilitated the movement of obsidian around, or across, Turkana after about 5000 ago. Investment in new social systems to access high-quality raw material highlights the importance of predictable flake production and microlithisiation. While these features were certainly present across Late Stone Age (roughly 25 000 to 5000 years ago) eastern Africa, their intensification at this time reflects major shifts in economic organisation. In other case studies around the world, similar shifts in raw-material selection are associated with pressure to maximise the efficiency of reducing a limited stone supply stemming from increased group mobility.

People at all three early herding sites used obsidian in the same way: i.e. the manufacture of blade blanks for formal tools, following a single operational sequence. Other raw materials were flaked expediently, without a preference for any flake shape. Roughly 92% of obsidian blades across all three assemblages exhibit parallel flake-scars, indicating maintenance of single-platform pyramidal blade cores. Identical distributions for blade curvatures across the sites reflect further consistency in the morphology of core release surfaces, and thus core design. Striking platforms are consistently small and intensively prepared through abrasive grinding to remove loose material before subsequent flaking.

Lithics from Dongodien: (A)–(B) backed crescents; (C)–(D) oblique truncations; (E) awl; (F) core-tablet; (G)–(L) representative bladelets; (M) lateral or ‘flanc’ removal from a pyramidal core. Goldstein (2019).

Reconstruction of core-reduction strategies in the assemblages reflects a shared methodology. Obsidian cores begin with pyramidal shapes, with the single striking platform that retains cortex. Average blade curvatures at all three sites increase through the reduction sequence along a similar regression line, suggesting the consistent management of core shape Once reduced to lengths of about 20mm, cores were too small for continued bladelet production. At this stage, knappers switched to bipolar production techniques, producing chipped tools or splintered flakes. Expended bipolar pieces make up a greater proportion of cores abandoned at Jarigole and Lothagam North. Although pyramidal cores were more often abandoned before they reached the bipolar stage at Dongodien, differences in core proportions are not significant. Intensity of core reduction is reflected in the differences between the volumes of unworked obsidian nodules from a source outcrop and recovered cores.

Lithics from Jarigole: (A)–(D) backed crescents; (E)–(F) oblique truncations; G) utilised flake; (H)–(I) chipped tools/bipolar cores; (J)–(M) typical bladelets; (N) bipolar flake; (O)–(P) large flakes. (A)–(N) are obsidian, (O)–(P) are basalt. Goldstein (2019).

While the fundamental aspects of lithic technological strategies are consistent across early herder sites in Turkana, there is some variability in how these strategies were deployed. Blade lengths are significantly higher at Lothagam North compared to Dongodien and Jarigole, although the differences are not significant if several large refitting blades associated with a burial are removed from the analysis. Blade-width distributions display the opposite pattern, with lower values at Lothagam North. Taken together, the length and width patterns of obsidian blades do not demonstrate a clear relationship with distance from raw-material sources, as would be expected with simple down-the-line exchange. Instead, this non-linear metric variation is more consistent with more organised lithic-provisioning behaviours.

Lithics from Lothagam North: (A)–(D) typical bladelets; (E)–(F) utilised bladelets; (H) chipped tool/ bipolar core; (I) multidirectional core; (J) opposed platform removal; (K)–(L) oblique truncations; (M)–(O) backed crescents; (P) combination endscraper/burin; (Q)–(R) bipolar cores. All pieces are obsidian. Goldstein (2019).

Although striking platforms on obsidian blades are universally small, their relationships with blade metrics vary between sites. For pillar-site assemblages, platform size is a strong predictor of both blade width and thickness. At the Dongodien habitation site, there are no correlations between platform size and metrics.

Cores from Dongodien: (A)–(B) pyramidal bladelet cores with cortical platforms; (C) multi-directional bifacial core; (D) bipolar core; (E) bi-directional core. Goldstein (2019).

Tool use is the final relevant dimension of lithic variability. Goldsteim differentiates between formal, shaped tools and flakes with only casual retouch or edge damage. Lothagam North is the only site where these categories are equally represented. Informal modified pieces tend to be made from local raw-material sources, whereas obsidian blades are used as blanks in nearly all formal tool production. This reinforces the distinction between the structured and systematic use of obsidian by early herders, and the more opportunistic use of obsidian.

Formal assemblages from all three sites comprise a consistently narrow range of tool types. The toolkits from Dongodien are predominately backed microliths (75–92%). Crescents and truncations are the most common forms of backed tools. The average sizes of crescents, which were probably used in composite projectiles or cutting tools, are consistent with values for the earliest herders in southern Kenya. Crescents are twice as abundant at Dongodien, whereas scrapers and awls are more common at Jarigole. This difference is partially driven by the unusual presence of chert awls, presumably for bead production, in the Jarigole assemblage. Despite minor differences in ratios, the overall consistency in tool types, morphologies and sizes across all three sites suggest that they reflect the same toolkit and tool-use strategies.

A comparative analysis of lithic assemblages from three early pastoralist sites provides new and valuable insights for addressing major questions concerning the spread of herding into northern Kenya. First, this analysis demonstrates that communities who lived at Dongodien, and those who constructed and used the Jarigole and Lothagam North pillar sites, all shared a distinct technological tradition that set them apart from other Late Stone Age sites in the region. Early herders at all three sites employed the same chaîne opératoire to produce morphologically consistent blade cores and bladelet blanks for formal tools from obsidian, while local raw materials were reduced and used expediently for informal tools. This contrasts with Early Holocene hunter-gatherer-fisher assemblages, which attest the manufacture of diverse microlithic and large-flake toolkits on local chert and basalts.While earlier hunter-gatherers used obsidian occasionally, the high proportions of obsidian at early herding sites have no precedent in the Turkana Basin.

Refitting blade sequence from Lothagam North. Goldstein (2019).

The production of uniform, highly transportable blade blanks requires access to homogeneous raw materials with highly predictable fracture mechanics. Obsidian was preferred by many stone-tool-using societies around the world, both because it possesses these attributes and because it produces razor-sharp edges when flaked.

These properties of obsidian allow for the manufacture of formal, prepared blade cores, which are generally associated with more mobile societies. Uniform blanks produced from these blade cores can be used to make a wide variety of tools, offering increased flexibility to exploit a broader range of resources and environments. Being able to respond rapidly to changing climatic conditions would have been advantageous for communities whose livelihoods depended on their ability to move livestock within a heterogeneous and ever-changing distribution of rain-fed pasture. The coarse volcanic stones used by many Early Holocene groups do not have these qualities and cannot be used to produce consistently uniform blade blanks. Site-by-site variation among Early Holocene hunter-gatherer-fishers may indicate more localised problem-solving.

Maintaining access to obsidian that had to be transported around, or across, Lake Turkana required not only increased mobility to and from obsidian sources, but also social investment and community bonds. Even though groups were mobile, they could not guarantee access to obsidian within seasonal rounds organised around the location of grazing lands. Formal exchange relationships akin to historically documented stock-friend partnerships would have been an ideal solution, wherein individuals distribute livestock among kin and friends as an insurance policy against the catastrophic loss of a herd. Similar risk-reduction networks were also developed by early herders in southern Kenya. Indeed, the presence of identical lithic-reduction techniques across the three sampled sites indicates participation in a shared ‘community-of-practice’, wherein these skills and techniques were transmitted and maintained among spatially disparate groups. Evidence for social networks surrounding lithic production reflect one facet of broader landscape-level cooperation that first appeared with early herders in Turkana, and culminated with the construction of megalithic cemeteries.

While Dongodien, Lothagam North, and Jarigole share an identical lithic technological strategy, differences in tool ratios and reduction intensities signal subtle variations in how this strategy was deployed. Variation in core-reduction intensity between the mortuary sites of Lothagam North and Jarigole, for example, reflects differences in how material supply was managed during ritual/ceremonial activities at or around the monumental cemetery sites relative to domestic-use stone stockpiles at Dongodien. The variation in tool ratios is also a product of behavioural differences between sites. Activities involved in pillar-site construction, maintenance and human interment certainly differ from those expected for a herder habitation site. It is important to recognise that these minor differences within the early herding assemblages pale in comparison to the differences observed between herder assemblages and those of earlier hunter-gatherer-fishers.

The single greatest obstacle in exploring the relationships between herder and hunter-gatherer-fisher lithic assemblages continues to be the lack of published artifact inventories, measurements and technological descriptions from these site types. The present research establishes a clear and quantifiable lithic signature for the three sites with the best evidence for herding in northern Kenya. This can now be used to test this hypothesis in future analyses. Detecting, or failing to detect, local precedents for the mobility strategies that made herding lifeways possible in Turkana will add further lines of evidence for discussions about the processes by which pastoralism was first introduced into eastern Africa.

Technological strategies of the earliest herders in eastern Africa differ from those in regions where early food production entailed sedentary village agriculture. In the Lake Turkana region of northern Kenya, the earliest appearance of livestock and monumental mortuary complexes coincides with the adoption of obsidian as the dominant raw material, the development of consistent lithic reduction strategies and the formalisation of blade and tool morphologies. These changes reflect a reorientation and intensification of traits already present in Late Stone Age repertoires, highlighting the difficulty in disentangling lithic strategies based on qualitative attributes alone. Quantitative analyses reveal how herder assemblages deviate from those of hunter-gatherer-fishers, and that herder assemblages themselves exhibit a uniform technological strategy across the Lake Turkana area. This strategy appears to be oriented around preparing for heterogeneous environmental conditions and diverse economic tasks. If supported by further analyses, this would indicate that the introduction of herding fundamentally altered how certain peoples interacted with the landscape of the Turkana Basin.

The new technological strategies developed and employed by early herders were sustained by long-distance obsidian distribution networks. Exchange systems that appear after 5000 years ago appear to have been far more cohesive and consistent than any observed among earlier hunter-gatherers around Lake Turkana. Such systems formed only one component of a larger pattern of affiliation and cooperation among early herders. Strategic experiments in Turkana, whether successful or not, probably conditioned how herders responded to similar environmental, economic and social challenges as lifeways based on cattle, sheep and goats subsequently spread throughout eastern and southern Africa. Further comparative analyses of African archaeological data at the regional level will foster a more holistic understanding of how the spread of food production shaped population histories, social systems and human-environment interactions, both in Africa and around the world.

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