Age-depth model for uppermost Ndutu Beds constrains Middle Stone Age technology and climate-induced paleoenvironmental changes at Olduvai Gorge (Tanzania).

Olduvai Gorge in northern Tanzania is part of a globally important archeological and paleoanthropological World Heritage Site location critical to our understanding of modern human evolution. The Ndutu Beds in the upper part of the geological sequence at Olduvai Gorge represent the oldest unit to yield modern Homo sapiens skeletal material and Middle Stone Age technology. However, the timing of the deposition of the Ndutu Beds is poorly constrained at present, which limits our understanding of the paleoenvironments critical for contextualizing H. sapiens and related technologies in the Olduvai Basin. Using a suite of 15 luminescence ages of sedimentary core samples, combined with Bayesian statistics, this study provides a new higher-resolution age-depth model for the deposition of the uppermost Upper Ndutu and Naisiuiu Beds cored by the Olduvai Gorge Coring Project. The luminescence and modeled ages are presented as ±1 σ uncertainties. The Ndutu Beds intersected by the Olduvai Gorge Coring Project cores are dated to between 117.1 ± 17.9 and 45.3 ± 4.2 ka (between 125.9 ± 26.5 and 45.8 ± 8.2 ka modeled ages), while a probable overlying layer of Naisiusiu Beds dates to 23.7 ± 10.9 to 12.1 ± 1.7 ka (25.7 ± 18.9 ka and 12.0 ± 3.4 ka modeled age). Time-averaged accretion rates are derived during this time: (1) initially low rates (<5 cm ka-1) from the bottom of the core at 117.1 ± 17.9 ka up to 95.3 ± 11.1 ka (125.9 ± 26.5 to 95.5 ± 23.3 ka modeled ages); (2) the middle section spanning between 95.3 ± 11.1 and 62.7 ± 5.7 ka (95.5 ± 23.3 to 61.9 ± 10.4 ka modeled ages) with mean rates above 15 cm ka-1; and (3) the last 62.7 ± 5.7 ka (61.9 ± 10.4 ka modeled age) where the accretion rate reduces to below 5 cm ka-1. This reduction can be explained by the evolution of the gorge system that was likely driven by subsidence of the Olbalbal depression and changes in climate, particularly precipitation and resulting lake and base level changes. Older Upper Ndutu and Lower Ndutu Beds are contained within proto-gorges within the modern gorge system.

Olduvai's oldest Oldowan.

Previously, Olduvai Bed I excavations revealed Oldowan assemblages <1.85 Ma, mainly in the eastern gorge. New western gorge excavations locate a much older ∼2.0 Ma assemblage between the Coarse Feldspar Crystal Tuff (∼2.015 Ma) and Tuff IA (∼1.98 Ma) of Lower Bed I, predating the oldest eastern gorge DK assemblage below Tuff IB by ∼150 kyr. We characterize this newly discovered fossil and artifact assemblage, adding information on landscape and hominin resource use during the ∼2.3-2.0 Ma period, scarce in Oldowan sites. Assemblage lithics and bones, lithofacies boundaries, and phytolith samples were surveyed and mapped. Sedimentological facies analysis, tephrostratigraphic and sequence stratigraphic principles were applied to reconstruct paleoenvironments and sedimentary processes of sandy claystone (lake), sandstone (fluvial), and sandy diamictite (debris flow) as principal lithofacies. Artifacts, sized, weighed, categorized, were examined for petrography, retouch, and flake scar size. Taxonomic classifications and taphonomic descriptions of faunal remains were made, and phytoliths were categorized based on reference collections. Lithics are dominantly quartzite, mainly debitage and less frequently simple cores, retouched pieces, and percussors. Well-rounded spheroids and retouched flakes are rare. Identifiable taxa, Ceratotherium cf. simum (white rhinoceros) and Equus cf. oldowayensis (extinct zebra), accord with nearby open savanna grasslands, inferred from C3 grass, mixed and/or alternating with C4 grass-dominated phytolith assemblages. Palms, sedges, and dicots were also identified from phytoliths. Diatoms and sponge spicules imply nearby freshwater. The assemblage accumulated at the toe of a Ngorongoro Volcano-sourced fan-delta apron of stacked debris flows, fluvials, and tuffs, preserving fossil tree stumps and wooded grassland phytoliths farther upfan. It formed after the climax of Ngorongoro volcanic activity during a Paleolake Olduvai lowstand and was then buried and preserved by lacustrine clays, marking the first of two lake transgressions, signifying wetter climates. Orbital precessional lake cycles were superposed upon multimillennial (∼4.9 kyr) lake fluctuations.

The evolution and cultural transmission of percussive technology: integrating evidence from palaeoanthropology and primatology.

We bring together the quite different kinds of evidence available from palaeoanthropology and primatology to better understand the origins of Plio-Pleistocene percussive technology. Accumulated palaeoanthropological discoveries now document the Oldowan Complex as the dominant stone tool making culture between 2.6-1.4 Ma, the earlier part of this contemporaneous with pre-Homo hominins. The principal types of artefacts and other remains from 20 Early Stone Age (Oldowan and earliest Acheulean) localities in Africa and elsewhere are reviewed and described. To better understand the ancestral behavioural foundations of this early lithic culture, we examine a range of recent findings from primatology. In particular, we attempt to identify key shared characteristics of Homo and Pan that support inferences about the preparedness of our common ancestor for the innovation of stone tool culture. Findings of particular relevance include: (i) the discovery of an expanding repertoire of percussive and other tool use based on directed use of force among wild chimpanzees, implicating capacities that include significant innovatory potential and appreciation of relevant causal factors; (ii) evidence of material cultural diversity among wild chimpanzees, indicating a readiness to acquire and transmit tool use innovations; and (iii) experimental studies of social learning in chimpanzees and bonobos that now encompass the acquisition of nut cracking through observation of skilled use of hammers and anvils by conspecifics, the diffusion within and between groups of alternative styles of tool use, and the adoption of free-hand stone-to-stone percussion to create useful flakes for cutting to gain access to food resources. We use the distributions of the inferred cultural traits in the wild to assess how diffusion relates to geographic distances, and find that shared traits drop by 50% from the approximately eight characteristic of close neighbours over a distance of approximately 700 km. This pattern is used to explore the implications of analogous processes operating in relation to Early Stone Age sites.

Neural correlates of Early Stone Age toolmaking: technology, language and cognition in human evolution.

Archaeological and palaeontological evidence from the Early Stone Age (ESA) documents parallel trends of brain expansion and technological elaboration in human evolution over a period of more than 2Myr. However, the relationship between these defining trends remains controversial and poorly understood. Here, we present results from a positron emission tomography study of functional brain activation during experimental ESA (Oldowan and Acheulean) toolmaking by expert subjects. Together with a previous study of Oldowan toolmaking by novices, these results document increased demands for effective visuomotor coordination and hierarchical action organization in more advanced toolmaking. This includes an increased activation of ventral premotor and inferior parietal elements of the parietofrontal praxis circuits in both the hemispheres and of the right hemisphere homologue of Broca's area. The observed patterns of activation and of overlap with language circuits suggest that toolmaking and language share a basis in more general human capacities for complex, goal-directed action. The results are consistent with coevolutionary hypotheses linking the emergence of language, toolmaking, population-level functional lateralization and association cortex expansion in human evolution.