Biometric variables predict stone tool functional performance more effectively than tool‐form attributes: a case study in handaxe loading capabilities

Both the form of a stone tool and the anatomy of the individual using it have potential to influence its cutting performance. To date, however, the selective pressures acting on stone‐tool form and hominin biometric/biomechanical attributes have been investigated in isolation and their relative influence on performance have never been compared directly. This paper examines the influence of both tool‐form attributes and biometric variation on the functional performance of Acheulean handaxes. Specifically, it investigates the impact of 13 tool attributes and eight biometric traits on the working forces applied through the edge of 457 replica tools. The relative contribution of tool‐form and biometric attributes to handaxe loading levels were examined statistically. Results identify that both tool‐form attributes and biometric traits are significantly related to loading; however, tool–user biometric variation has a substantially greater impact relative to tool‐form attributes. This difference was demonstrated by up to a factor of 10. These results bear directly on the co‐evolutionary relationships of stone tools and hominin anatomy, and the comparative strength of selective pressure acting on each. They also underline why handaxe forms may have been free to vary in form across time and space without necessarily incurring critical impacts on their functional capabilities.     

Could woodworking have influenced variation in the form of Acheulean handaxes?

The relationship between tool form and function is fundamental to hominin behaviour and evolution. Acheulean handaxes are known for their general consistency across more than a million years and three continents, albeit with some variation in size and shape. However, the influence of this variation on cutting has only rarely been studied, mostly in either butchery or generalized cutting tasks. Yet evidence indicates that handaxes were used for woodworking by at least 1.5 mya. Here, we experimentally tested whether woodworking could have exerted selective pressures on handaxe form. Additionally, these data were compared with a previous experiment that tested flakes during woodworking. For handaxes, no significant relationships were detected in woodworking efficiency. Accordingly, woodworking likely did not exert strong selective pressures on handaxe variability. However, the effectiveness shown by handaxes further demonstrates the functional flexibility of this technology, which is likely a factor contributing to their use over broad temporal, geographical and ecological spans. When comparing handaxes with flakes, only the smallest flakes were found to be significantly less efficient than handaxes. Therefore, the functional demands of woodworking were likely influencing hominin technological decisions about flake morphology, or the selection of flakes for woodworking, more than they were handaxe morphology.     

Technology based evolution? A biometric test of the effects of handsize versus tool form on efficiency in an experimental cutting task

The use of stone cutting tools opened a novel adaptive niche for hominins. Hence, it has been hypothesised that biomechanical adaptations evolved to maximise efficiency when using such tools. Here, we test experimentally whether biometric variation influences the efficiency of simple cutting tools (n = 60 participants). Grip strength and handsize were measured in each participant. 30 participants used flint flakes, while the other 30 used small (unhafted) steel blades. Variations in basic parameters of tool form (length, width, thickness, cutting edge length) were recorded for the 30 flint flakes. It was ensured that mean handsize and strength in each participant group were not significantly different to investigate the effect of tool variation. The experimental task required cutting through a 10 mm-diameter hessian rope. Cutting efficiency was measured using both ‘Number of cutting strokes required’ and ‘Total time taken’. Results show that both efficiency measures were significantly correlated with handsize using all 60 participants. However, no significant differences were found between the flake and blade groups in terms of mean efficiency. Nor was any significant relationship found between tool form parameters and efficiency in the flint flake group. We stress that our results do not imply that tool form has no impact on tool efficiency, but rather that – all other things being equal – biometric variation has a statistically significant influence on efficiency variation when using simple cutting tools. These results demonstrate that biomechanical parameters related directly to efficiency of use, may plausibly have been subject to selection in the earliest stone tool-using hominins.     

Edge Angle as a Variably Influential Factor in Flake Cutting Efficiency: An Experimental Investigation of Its Relationship with Tool Size and Loading

Simple flake cutting tools were utilized across broad chronological and geographical ranges during prehistory. Fundamental to their functional utility is the presence of a relatively acute working edge. The acuteness of this ‘edge angle’ is widely hypothesized to be a primary determinant of cutting efficiency and, subsequently, of potential consequence to prehistoric peoples. However, the influence of the cutting edge angle in flake tools on the ability (efficiency) of tool users to cut through objects has not been empirically investigated under explicitly stated experimental conditions. Moreover, no consideration has been given to whether this relationship is dependent upon the size of the tool. Here, the influence that edge angle exerts on human stone tool users is examined experimentally in terms of efficiency during a cutting task, while also considering the relationship between edge angle, loading (i.e., the force applied) and overall flake size. The results demonstrate that there is a highly significant relationship between more acute working edges and increased cutting efficiency in the smallest flake tools tested. Above a certain flake‐size threshold, however, the working edge angle has no influence on cutting efficiency because larger flakes appear to facilitate the application of greater working loads by tool users. These results have important implications for potential flake selection criteria by prehistoric peoples, especially in relation to utility, function and the changing effects of edge angle through a sequence of retouch.     

Influence of Handaxe Size and Shape on Cutting Efficiency: A Large-Scale Experiment and Morphometric Analysis

Handaxes represent one of the most temporally enduring and geographically widespread of Palaeolithic artifacts and thus comprised a key technological strategy of many hominin populations. Archaeologically observable variation in the size (i.e., mass) and shape properties of handaxes has been frequently noted. It is logical to ask whether some of this variability may have had functional implications. Here, we report the results of a large-scale (n?=?500 handaxes) experiment designed to examine the influence of variation in handaxe size and shape on cutting efficiency rates during a laboratory task. We used a comprehensive dataset of morphometric (size-adjusted) shape variables and statistical methods (including multivariate methods) to address this issue. Our first set of analyses focused on handaxe mass/size variability. This analysis demonstrated that, at a broad-scale level of variation, handaxe mass may have been free to vary independently of functional (cutting) efficiency. Our analysis also, however, identified that there will be a task-specific threshold in terms of functional effectiveness at the lower end of handaxe mass variation. This implies that hominins may have targeted design forms to meet minimal (task-specific) thresholds and may also have managed handaxe reduction and discard in respect to such factors. Our second set of analyses focused on handaxe shape variability. This analysis also indicated that considerable variation in handaxe shape may occur independently of any strong effect on cutting efficiency. We discuss how these results have several implications for considerations of handaxe variation in the archaeological record. At a general level, our results demonstrate that variability within and between handaxe assemblages in terms of their size and shape properties will not necessarily have had immediate or strong impact on their effectiveness when used for cutting, and that such variability may have been related to factors other than functional issues.     

Experimental assessment of plan-view and profile-view gross-edge curvature on stone flake slicing efficiency

Separating two or more aspects of an object via cutting was likely an important factor in the origin and evolution of flaked stone technology. In recent years experiments have demonstrated that several stone tool attributes can influence different kinds of cutting behaviour: slicing, cleaving, scraping, sawing, drilling, piercing and abrading. Here we experimentally assessed the role of stone flake plan- and profile-view gross-edge curvature in a controlled slicing task. We also assessed the role of edge length. A total of 21 participants, using 252 stone flakes with distinct gross-edge curvatures and edge lengths, were asked to cut through a standardized substrate, and their efficiency in the task was measured over time. Flakes with longer edge lengths increased the efficiency of the cutting task, but increasing either plan- or profile-view edge curvature decreased the efficiency of the cutting task. These results have implications for the emergence of particular tool forms or reduction sequences throughout the Pleistocene, and may in part explain why certain forms were favoured by Paleolithic people, leading to their convergent evolution or widespread transmission.     

The oldowan reassessed: A close look at early stone artifacts

Early Stone Age assemblages called “Oldowan” and early “Developed Oldowan” are discussed, based on the results of a long-term study of Plio-Pleistocene sites at Koobi Fora, Kenya and an extensive experimental research program of replicating and using early stone artifact forms. Five major conclusions are drawn from this investigation: (1) many Oldowan core forms (“core-tools”) are probably simple by-products of flake manufacture rather than representations of stylistic norms; (2) flakes and retouched flakes - were essential tools in Oldowan technology, particularly for activities involving cutting; (3) this simple technology does not necessarily reflect the cognitive abilities of the early hominids that manufactured the stone artifacts; (4) there is evidence to show that Oldowan technology can be viewed as a simple curated one, in which raw material was intentionally carried from place to place for future use; (5) early hominid populations that made and used stone implements were not necessarily dependent upon them for their survival.     

Investigating experimental knapping damage on an antler hammer: a pilot-study using high-resolution imaging and analytical techniques

Organic (bone, antler, wood) knapping tools were undoubtedly a component of early human tool kits since the Lower Palaeolithic. Previous studies have identified pitting and the occasional presence of embedded flint flakes as important features for recognizing archaeological bone and antler percussors. However, no systematic protocol of analysis has been suggested for the study of this rare archaeological material. Here we present qualitative and quantitative results of a preliminary analysis of an experimental knapping hammer, using a novel combination of microscopy (focus variation optical microscope and scanning electron microscope), micro-CT scanning and energy dispersive X-ray spectroscopy. These imaging and analytical techniques are used to characterize use-damage from the manufacture of handaxes. This paper highlights the strengths and weakness of each technique. Use-wear on the working area included attritional bone loss, micro-striations and compaction of the outer layer of the antler matrix from repeated hitting of the beam against the sharp edge of the handaxe during knapping. Embedded flint flakes were also identified in the pits and grooves. This combination of high-resolution imaging techniques is applicable to fragile archaeological specimens, including those encrusted by sediment or encased in matrix.     

A geometric morphometric relationship predicts stone flake shape and size variability

The archaeological record represents a window onto the complex relationship between stone artefact variance and hominin behaviour. Differences in the shapes and sizes of stone flakes—the most abundant remains of past behaviours for much of human evolutionary history—may be underpinned by variation in a range of different environmental and behavioural factors. Controlled flake production experiments have drawn inferences between flake platform preparation behaviours, which have thus far been approximated by linear measurements, and different aspects of overall stone flake variability (Dibble and Rezek J Archaeol Sci 36:1945–1954, 2009; Lin et al. Am Antiq 724–745, 2013; Magnani et al. J Archaeol Sci 46:37–49, 2014; Rezek et al. J Archaeol Sci 38:1346–1359, 2011). However, when the results are applied to archaeological assemblages, there remains a substantial amount of unexplained variability. It is unclear whether this disparity between explanatory models and archaeological data is a result of measurement error on certain key variables, whether traditional analyses are somehow a general limiting factor, or whether there are additional flake shape and size drivers that remain unaccounted for. To try and circumvent these issues, here, we describe a shape analysis approach to assessing stone flake variability including a newly developed three-dimensional geometric morphometric method (‘3DGM’). We use 3DGM to demonstrate that a relationship between platform and flake body governs flake shape and size variability. Contingently, we show that by using this 3DGM approach, we can use flake platform attributes to both (1) make fairly accurate stone flake size predictions and (2) make relatively detailed predictions of stone flake shape. Whether conscious or instinctive, an understanding of this geometric relationship would have been critical to past knappers effectively controlling the production of desired stone flakes. However, despite being able to holistically and accurately incorporate three-dimensional flake variance into our analyses, the behavioural drivers of this variance remain elusive.     

A Statistical Examination of Flake Edge Angles Produced During Experimental Lineal Levallois Reductions and Consideration of Their Functional Implications

Recent studies have indicated that Levallois-style core reduction offered potential practical benefits to hominin populations. However, none of these studies have yet considered one of the most important functional attributes of flake tools, which is edge angle. To address this shortcoming, we statistically examined flakes produced experimentally during “classic” or “lineal” Levallois core production and reduction. The primary aim of our analyses was to statistically test the null hypothesis of “no difference” between the edge angles of “Levallois” products and the flakes involved in their production. We employ existing edge angle analytical techniques and develop new comparative methodologies to assess flake blank standardization through the case of Levallois core reduction. Having determined the statistical properties of our experimental Levallois reductions, we thereafter evaluated to what extent edge angles produced may, or may not, have been useful to prehistoric hominins. Our analyses demonstrated that the experimentally produced Levallois edge angles were indeed statistically different from the flakes involved in their production. These differences were evident both in terms of relatively higher (i.e., more obtuse) edge angles than debitage flakes and in being significantly less variable around their higher mean edge angles compared to debitage flakes. However, based on current knowledge of how flake edge angle properties relate to issues of functionality, such differences would not have been detrimental to their functionality. Indeed, the edge angle properties they possess would have provided distinct benefits to hominins engaged in their manufacture. Most notably, Levallois-style core organization and reduction would have provided hominins with a reliable means of consistently producing flakes (i.e., “Levallois flakes”) possessing average flake angles that are beneficial in terms of providing a viable cutting edge yet not being so acute as to be friable upon application. Hence, edge angle properties join an array of other features that provide logical motive for why hominins may have organized core production and reduction around Levallois-style patterns at various times and places during the Mid-Late Pleistocene.     

Taphonomic resolution and hominin subsistence behaviour in the Lower Palaeolithic: differing data scales and interpretive frameworks at Boxgrove and Swanscombe (UK)

The identification of human butchery-signatures on fauna from Lower Palaeolithic sites is well documented and readily identifiable. Such bone surface modifications have the potential to provide not only information about past hominin meat-procurement behaviour but address the wider issue of competition for resources with other carnivore species. To understand and discuss these broader issues both hominin and natural bone surface modifications must be understood and contextualised within a site-specific spatial and temporal framework. This paper presents new results from faunal analysis at two key British Lower Palaeolithic localities: Boxgrove and Swanscombe. It illustrates that different depositional environments and excavation histories have resulted in different scales and resolutions of available data and hence in varying interpretive potentials. At Swanscombe the archaeological record has been disturbed by both fluvial activity and excavation history providing a coarser-grained record of anthropogenic behaviour than previously acknowledged. Conversely, at Boxgrove, a finer-grained, higher resolution record of human behaviours has been preserved; this, combined with both an extensive and intensive excavation strategy, has allowed for a broader discussion of hominin landscape use, resource competition and meat-procurement behaviour. This paper highlights that assessing the specific depositional environment at each site is crucial to understanding Palaeolithic faunal assemblage formation and, consequently, the available data-resolution and behavioural interpretation.     

The technology of Stone Age colonization: an empirical,regional-scale examination of Clovis unifacial stone tool reduction,allometry, and edge angle from the North American Lower Great Lakes region

There is now broad consensus that the appearance of Clovis in Northeastern North America (Great Lakes, New England) represents a colonization pulse into recently deglaciated landscapes. Due to the increased resource uncertainty that comes with colonizing unfamiliar landscapes, it was hypothesized that the majority tool component of Clovis assemblages, unifacial stone tools, should have been knapped on tool blanks possessing the design properties of longevity and functional flexibility to facilitate exploration mobility and guard against the absence of toolstone sources in the new landscape. These properties are optimized by large, flat flakes, possessing large surface area relative to flake thickness. Since discarded and, at times, exhausted unifacial stone tools do not preserve the original dimensions of the blank upon which they were created – necessary items for a true test of blank morphology selection – this study presents a set of predictions for inferring whether Clovis unifacial stone tool blanks were selected for the properties of longevity and functional flexibility based on evidence that Clovis people actually capitalized on those properties. Due to the nature of Clovis unifacial stone tools, tool size was of necessity used as a proxy for tool reduction, on the grounds that smaller tools are more likely to have been resharpened than larger tools, at least in the case of unifacial flake tools. The results showed that less resharpened tools possessed flatter, less spherical shapes than the more resharpened tools, which possessed more globular, spherical shapes, suggesting Clovis foragers exploited the retouch potential afforded by the larger, flatter blanks. Edge angles showed no relationship with tool reduction, suggesting that Clovis foragers exploited the functional flexibility afforded by flatter blanks by adjusting the edge angle to be either higher or lower as needed. These results are consistent with the notion that human colonizers, who did not know the abundance or location of stone outcrops prior to settling an unfamiliar territory, not only “geared up” before leaving a stone source, but geared up as efficiently as possible by carefully selecting the blanks they chose to carry. Broader implications for such careful unifacial stone tool blank selection are discussed.     

New experimental evidence on the relation between percussion flaking and flake variation

Controlled experiments in percussion flaking allowed for objective analysis of relationships between variables of flake production and those variables which are attributes of the final result. The independent variables, those controlled by the flintknapper in the production of stone tools, include force and angle of blow, platform thickness and exterior platform angle. The dependent variables are those attributes of the flakes which are often used in current lithic analyses and include interior platform angle, length, thickness and flake termination. The results clearly show that exterior platform angle is highly significant for understanding many aspects of flake production. These and other relationships between the independent and dependent variables are also discussed.     

Factors affecting Early Stone Age cut mark cross-sectional size: implications from actualistic butchery trials

Early Stone Age cut marks are byproducts of hominins' tool-assisted animal carcass consumption and provide a potential avenue of inference into the paleoecology of hominin carnivory. If diagnostic cut mark characteristics can be linked to flake and core tool use or the completion of distinct butchery actions, it may be possible to infer ancient tool preferences, reconstruct the consumption of specific muscular tissues, and illuminate landscape-scale stone resource use. Recently, diagnostic morphological criteria including cut mark width and depth have been used to identify marks made by different classes of experimental and archaeological stone tools (Bello, S.M., Parfitt, S.A., Stringer, C., 2009. Quantitative micromorphological analyses of cut marks produced by ancient and modern handaxes. Journal of Archaeological Science 36: 1869–1880; de Juana, S., Galan, A.B., Dominguez-Rodrigo, M., 2010. Taphonomic identification of cut marks made with lithic handaxes: an experimental study. Journal of Archaeological Science 37: 1841–1850; Dominguez-Rodrigo, M., de Juana, S., Galan, A. B., Rodriguez, M., 2009. A new protocol to differentiate trampling marks from butchery cut marks. Journal of Archaeological Science 36: 2643–2654). The work presented here adds to this experimental butchery database by using measurements of cut mark cross-section taken from bone surface molds to investigate how stone tool characteristics including flake versus core tool type, edge angle, and tool weight, influence cut mark width and depth, ultimately testing whether cut mark size is a useful indicator of tool identity. Additionally, these experiments investigate the influence of contextual factors, including butchery action, carcass size, and bone density on cut mark size. An experienced butcher used replicated Oldowan flakes and bifacial core tools in experimental trials that isolated skinning, bulk and scrap muscle defleshing, and element disarticulation cut marks on goat and cow skeletons. This sample explores cut mark traces generated under realistic butchery scenarios and suggests the following results: 1) Core and flake tools were equally efficient at completing all butchery tasks in size 1 and 3 bovid carcasses. 2) Samples of cut mark width and depth produced by core and flake tools were similar and cut marks could not be accurately classified to a known tool type. 3) Skinning and disarticulation activities produced significantly wider and deeper marks than defleshing activities. 4) Cut marks on cows tended to be wider and deeper than those on goats. 5) Cut mark width is negatively correlated with bone density when carcass size and bone portion are taken into consideration. These results suggest that a general quantitative model for inferring tool type or edge characteristics from archaeological cut mark size is not warranted.     

Acheulean variability and hominin dispersals: a model-bound approach

Understanding the pattern of hominin dispersal is a fundamental component of Palaeolithic archaeology and palaeoanthropology. A widely held assumption is that bifacial handaxe (i.e. Acheulean or ‘Mode 2’) technologies evolved in Africa and dispersed into northern and western Eurasia via subsequent hominin migrations. To date, however, few formal tests of this hypothesis have been presented. Here, we use a combination of morphometrics, cultural transmission theory, and a dispersal model drawn from population genetics in order to test this hypothesis. The iterative founder effect (repeated bottlenecking) model is assumed to be supported if a significant inverse relationship is found between geographic distance from source along an estimated dispersal route and within-assemblage variance. The results of our analyses support the hypothesis that Acheulean technologies evolved in Africa and dispersed with migrating hominin populations into northern and western Eurasia under the assumptions of this iterative founder effect model. Based on our results we suggest that the occurrence of certain Mode 1 technologies such as those east of the Movius Line, and some assemblages assigned to the Clactonian of Britain, plausibly represent instances where effective population sizes in colonising populations dropped below levels where Mode 2 technologies could be maintained.     

The Lower Palaeolithic on the northern plateau of the Iberian Peninsula (Sierra de Atapuerca,Ambrona and La Maya I): a technological analysis of the cutting edge and weight of artefacts. Developing an hypothetical model

This article analyses the relationship between the weight and cutting edge of lithic artefacts from the main Lower Palaeolithic sites on the northern plateau (Meseta) of the Iberian Peninsula. The weight and cutting edge of a tool determine its cutting ability and the amount of force it is capable of, making them extremely important aspects of study to further our understanding of the potential capacity for human intervention in the environment. However, the analysis of these features has not received much attention in the ongoing debate on the Palaeolithic era in Europe. This study argues that the quantitative and qualitative technological analysis of these two aspects is of fundamental importance in determining the potential of lithic assemblages.     

The Palaeolithic of the Middle Son valley, north-central India: Changes in hominin lithic technology and behaviour during the Upper Pleistocene

The Middle Son valley in north-central India preserves extensive Quaternary alluvial deposits. A long history of archaeological and geological research in the valley has resulted in the discovery of lithic assemblages ranging from Lower Palaeolithic to microlithic, a rich corpus of fossilised faunal remains, and ash deposits from the 74,000 year-old Toba supereruption. This paper reviews the chronology and stratigraphy of the valley’s Quaternary sediments, and presents a model that hypothesizes the temporal sequence of important lithic assemblages from excavated and surface contexts. Artefacts in these assemblages are analysed and changes in lithic technology through time are described; this evidence is used to propose shifts in hominin behaviour and demographic structure in this region during the Upper Pleistocene. Recognising gaps in our understanding of the Middle Son record, future avenues of research are recommended that will build upon previous research and address questions of palaeoanthropological significance. The Middle Son valley preserves a long and rich record of hominin occupation from all periods of the Palaeolithic that is rarely paralleled by other sites in India.     

Assessing the distribution of African Palaeolithic sites: a predictive model of collagen degradation

In order to assess the distribution of African Palaeolithic sites and hominin remains, we need an understanding of the factors that may affect the preservation of archaeological material in the fossil record. One of the main factors that is thought to affect seriously the global distribution of fossil remains is taphonomy, but it would seem that taphonomic processes may themselves be overprinted by collagen degradation.The rate of collagen loss is highly temperature dependent, and it has been shown that bone is more likely to be preserved in areas of lower temperature and so lower collagen loss. Hence, it would be expected that fossil fauna remains would be distributed in areas of low collagen loss, i.e. low temperature. Conversely, lithics will not be subject to a temperature bias in their preservation. We have tested this hypothesis through the use of archaeological material.Our results show that the distributions of both lithic and faunal assemblages are non-random across the African continent, with all archaeological sites being found in areas of relatively low collagen degradation. This implies that bone collagen degradation is not the only factor affecting the distribution of African Palaeolithic sites and hominin remains. We suggest that the site distribution is not a reflection of bias in excavation history, but is a real phenomenon reflecting hominin habitat choice.     

The reality of reduction experiments and the GIUR: reply to Eren and Sampson

There is no ambiguity in the existing empirical support for a GIUR as a robust predictor of mass lost from flakes through unifacial retouching. We demonstrate why the GIUR is a reliable method for inferring mass loss, in appropriate circumstances, and why it is a more powerful predictor of mass loss than touted competitors. We explain why Eren, M.I., Sampson's, G. [2009. Kuhn's geometric index of unifacial stone tool reduction (GIUR): does it measure missing flake mass? J. Archaeol. Sci.] arguments are faulty and why researchers should use the GIUR in preference to other methods of estimating the extent of unifacial retouch.