Portrait of Dr Alastair Key

Dr Alastair Key

British Academy Postdoctoral Research Fellow

About

Dr Alastair Key is a Palaeolithic archaeologist and palaeoanthropologist specialising in the interplay between cultural and biological aspects of our evolutionary history. Recent research of his has addressed questions relating to how stone tool production and use may have influenced the evolution of the human hand, how modern mechanical and ergonomic principles may further our understanding of early stone tool design, and whether Lower Palaeolithic stone tools were optimised with regards to their functional performance.  

Currently Dr Key is working on the British Academy funded project ‘In the palm of your hand: A biomechanical study of stone tool design, use, and ergonomics throughout early human evolution’. Using a combination of electromyography, grip analyses and geometric morphometrics, this project will investigate the functional consequences of variable Lower Palaeolithic tool forms and the extent to which early tool design choices were influenced by ergonomic principles.

Prior to undertaking his Postdoctoral Fellowship with the British Academy, Dr Key was a Lecturer in Biological Anthropology at the University of Kent. Previous to this Alastair received his PhD in Biological Anthropology from the University of Kent and MSc in Palaeoanthropology and Palaeolithic Archaeology from University College London.

Publications

Article

  • Key, A. et al. (2018). Comparing the use of meat and clay during cutting and projectile research. Engineering Fracture Mechanics [Online] 192:163-175. Available at: https://doi.org/10.1016/j.engfracmech.2018.02.010.
    Diverse disciplines investigate how muscular tissue (i.e. ‘meat’) responds to being cut and deformed, however, large-scale, empirically robust investigations into these matters are often impractical and expensive. Previous research has used clay as an alternative to meat. To establish whether clay is a reliable proxy for meat, we directly compare the two materials via a series of cutting and projectile tests. Results confirm that the two materials display distinct cutting mechanics, resistance to penetration and are not comparable. Under certain conditions clay can be used as an alternative to meat, although distinctions between the two may lead to experimental limitations.
  • Key, A., Merrit, S. and Kivell, T. (2018). Hand grip diversity and frequency during the use of Lower Palaeolithic stone cutting-tools. Journal of Human Evolution [Online]. Available at: https://doi.org/10.1016/j.jhevol.2018.08.006.
    The suite of anatomical features contributing to the unique gripping capabilities of the modern human hand evolved alongside the proliferation of Lower Palaeolithic flaked tool technologies across the Old World. Experimental studies investigating their potential co-evolution suggest that the use of flakes, handaxes, and other stone tools is facilitated by manipulative capabilities consistent with the evolutionary trajectory of the hominin hand during this period. Grip analyses have provided important contributions to this understanding. To date, however, there has been no large-scale investigation of grip diversity during flaked stone-tool use, empirical comparative analyses of grip use frequencies, or examination of ergonomic relationships between grip choice and stone tool type and form.

    Here, we conduct four experimental studies, using replica Lower Palaeolithic stone tools in a series of actualistic and laboratory-based contexts, to record grip type and frequency of grip use during 1067 stone tool-use events by 123 individuals. Using detailed morphometric data recorded from each tool, we demonstrate how grip choice varies according to the type and form of stone tool used, and how these relationships differ between tool-use contexts. We identify 29 grip types across all tool-use events, with significant differences recorded in their frequency of use dependent on tool type, tool form, and the context of use. Despite the influence of these three factors, there is consistency in the frequent use of a limited number (≤4) of grip types within each experiment and the consistent and seemingly forceful recruitment of the thumb and index finger. Accordingly, we argue that there are deep-rooted, ergonomically-related, regularities in how stone tools are gripped during their use, that these regularities may have been present during the use of stone tools by Plio-Pleistocene hominins, and any subsequent selective pressures would likely have been focused on the first and second digit.
  • Key, A., Fisch, M. and Eren, M. (2018). Early stage blunting causes rapid reductions in stone tool performance. Journal of Archaeological Science [Online] 91:1-11. Available at: https://doi.org/10.1016/j.jas.2018.01.003.
    Palaeolithic stone technologies have never been investigated in terms of how sharpness influences their ability to cut. In turn, there is little understanding of how quickly stone cutting edges blunt, how past populations responded to any consequent changes in performance, or how these factors influenced the Palaeolithic archaeological record. Presented here is experimental data quantitatively detailing how variation in edge sharpness influences stone tool cutting performance. Significant increases in force (N) and material displacement (mm) requirements occur rapidly within early stages of blunting, with a single abrasive cutting stroke causing, on average, a 38% increase in the force needed to initiate a cut. In energetic terms, this equates to a 70% increase in work (J). Subsequent to early stages of blunting we identify a substantial drop in the impact of additional edge abrasion. We also demonstrate how edge (included) angle significantly influences cutting force and energy requirements and how it co-varies with sharpness. Amongst other conclusions, we suggest that rapid reductions in performance due to blunting may account for the abundance of lithic artefacts at some archaeological sites, the speed that resharpening behaviours altered tool forms, and the lack of microscopic wear traces on many lithic implements.
  • Dunmore, C., Patemen, B. and Key, A. (2018). A citation network analysis of lithic microwear research. Journal of Archaeological Science [Online] 91:33-42. Available at: https://doi.org/10.1016/j.jas.2018.01.006.
    The introduction of lithic microwear research into the wider archaeological community by Keeley (1980) was concurrent with the development of the processual paradigm and the adoption of the scientific method. Subsequently, lithic microwear research has benefited from over 35 years of innovation, including the introduction of novel methodological and analytical procedures. The present study employs a citation network to objectively analyse the development of microwear research. Given developments in technology, as well as the institutional isolation of early microwear research, the present analysis considers the citation network that stems from Keeley's seminal 1980 volume. The 363 papers identified as having cited Keeley (1980) in the subsequent 35 years were treated as individual nodes within the citation network. Before analysis, nodes were assigned attributes, including the type of research published and whether they were supportive of three key aspects of Keeley's experimental program: the ability to determine the function of the tool and to ascertain the type of worked material from microwear, as well as the use of high-powered microscopy techniques. Emergent properties of the papers, including closeness centrality, indegree and betweenness centrality, are used to test for significant differences between paper attributes. Similarly a clustering algorithm is used to objectively define distinct clusters of important papers within the discipline. Results indicate that a small number of nodes in the network maintain statistically significant influence on the form of the citation network. These important nodes and the distinct ‘schools of thought’ identified are discussed in the context of Keeley's initial contribution to the sub-field.
  • Key, A. and Lycett, S. (2018). Biometric variables predict stone tool functional performance more effectively than tool‐form attributes: a case study in handaxe loading capabilities. Archaeometry [Online]. Available at: https://doi.org/10.1111/arcm.12439.
    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.
  • Key, A. and Dunmore, C. (2018). Manual restrictions on Palaeolithic technological behaviours. PeerJ [Online] 6:e5399. Available at: http://dx.doi.org/10.7717/peerj.5399.
    The causes of technological innovation in the Palaeolithic archaeological record are central to understanding Plio-Pleistocene hominin behaviour and temporal trends in artefact variation. Palaeolithic archaeologists frequently investigate the Oldowan-Acheulean transition and technological developments during the subsequent million years of the Acheulean technocomplex. Here, we approach the question of why innovative stone tool production techniques occur in the Lower Palaeolithic archaeological record from an experimental biomechanical and evolutionary perspective. Nine experienced flintknappers reproduced Oldowan flake tools, ‘early Acheulean’ handaxes, and ‘late Acheulean’ handaxes while pressure data were collected from their non-dominant (core-holding) hands. For each flake removal or platform preparation event performed, the percussor used, the stage of reduction, the core securing technique utilised, and the relative success of flake removals were recorded. Results indicate that more heavily reduced, intensively shaped handaxes with greater volumetric controls do not necessarily require significantly greater manual pressure than Oldowan flake tools or earlier ‘rougher’ handaxe forms. Platform preparation events do, however, require significantly greater pressure relative to either soft or hard hammer flake detachments. No significant relationships were identified between flaking success and pressure variation. Our results suggest that the preparation of flake platforms, a technological behaviour associated with the production of late Acheulean handaxes, could plausibly have been restricted prior to the emergence of more forceful precision-manipulative capabilities than those required for earlier lithic technologies.
  • Williams-Hatala, E. et al. (2018). The manual pressures of stone tool behaviors and their implications for the evolution of the human hand. Journal of Human Evolution [Online] 119:14-26. Available at: https://doi.org/10.1016/j.jhevol.2018.02.008.
    It is widely agreed that biomechanical stresses imposed by stone tool behaviors influenced the evolution of the human hand. Though archaeological evidence suggests that early hominins participated in a variety of tool behaviors, it is unlikely that all behaviors equally influenced modern human hand anatomy. It is more probable that a behavior's likelihood of exerting a selective pressure was a weighted function of the magnitude of stresses associated with that behavior, the benefits received from it, and the amount of time spent performing it. Based on this premise, we focused on the first part of that equation and evaluated magnitudes of stresses associated with stone tool behaviors thought to have been commonly practiced by early hominins, to determine which placed the greatest loads on the digits. Manual pressure data were gathered from 39 human subjects using a Novel Pliance® manual pressure system while they participated in multiple Plio-Pleistocene tool behaviors: nut-cracking, marrow acquisition with a hammerstone, flake production with a hammerstone, and handaxe and flake use. Manual pressure distributions varied significantly according to behavior, though there was a tendency for regions of the hand subject to the lowest pressures (e.g., proximal phalanges) to be affected less by behavior type. Hammerstone use during marrow acquisition and flake production consistently placed the greatest loads on the digits collectively, on each digit and on each phalanx. Our results suggest that, based solely on the magnitudes of stresses, hammerstone use during marrow acquisition and flake production are the most likely of the assessed behaviors to have influenced the anatomical and functional evolution of the human hand.
  • Key, A. and Lycett, S. (2017). Form and function in the Lower Palaeolithic: history, progress, and continued relevance. Journal of Anthropological Sciences [Online] 95:67-108. Available at: http://dx.doi.org/10.4436/jass.95017.
    Percussively flaked stone artefacts constitute a major source of evidence relating to hominin behavioural strategies and are, essentially, a product or byproduct of a past individual’s decision to create a tool with respect to some broader goal. Moreover, it has long been noted that both differences and recurrent regularities exist within and between Palaeolithic stone artefact forms. Accordingly, archaeologists have frequently drawn links between form and functionality, with functional objectives and performance often being regarded consequential to a stone tool’s morphological properties. Despite these factors, extensive reviews of the related concepts of form and function with respect to the Lower Palaeolithic remain surprisingly sparse. We attempt to redress this issue. First we stress the historical place of form–function concepts, and their role in establishing basic ideas that echo to this day. We then highlight methodological and conceptual progress in determining artefactual function in more recent years. Thereafter, we evaluate four specific issues that are of direct consequence for evaluating the ongoing relevance of form–function concepts, especially with respect to their relevance for understanding human evolution more generally. Our discussion highlights specifically how recent developments have been able to build on a long historical legacy, and demonstrate that direct, indirect, experimental, and evolutionary perspectives intersect in crucial ways, with each providing specific but essential insights for ongoing questions. We conclude by emphasising that our understanding of these issues and their interaction, has been, and will be, essential to accurately interpret the Lower Palaeolithic archaeological record, tool-form related behaviours of Lower Palaeolithic hominins, and their consequences for (and relationship to) wider questions of human evolution.
  • Key, A. et al. (2017). Flake morphology as a record of manual pressure during stone tool production. Journal of Archaeological Science: Reports [Online] 12:43-53. Available at: http://dx.doi.org/10.1016/j.jasrep.2017.01.023.
    Relative to the hominin fossil record there is an abundance of lithic artefacts within Pleistocene sequences. Therefore, stone tools offer an important source of information regarding hominin behaviour and evolution. Here we report on the potential of Oldowan and Acheulean flake artefacts to provide a record of the biomechanical demands placed on the hominin hand during Lower Palaeolithic stone tool production sequences. Specifically, we examine whether the morphometric attributes of stone flakes, removed via hard hammer percussion, preserve correlates of the pressures experienced across the dominant hand of knappers. Results show that although significant and positive relationships exist between flake metrics and manual pressure, these relationships vary significantly between subjects. Indeed, we identify two biomechanically distinct strategies employed by knappers; those that alter their hammerstone grip pressure in relation to flake size and mass and those who consistently exert relatively high manual pressures. All individuals experience relatively high gripping pressure when detaching particularly large flakes. Amongst other results, our data indicate that the distinctive large flake technology associated with the Acheulean techno-complex may be demonstrative of an ability to withstand, and by extension, to exert higher manual pressures. However inferences from smaller flake artefacts, especially, must be treated with caution due to the variable biomechanical strategies employed.
  • Key, A. and Lycett, S. (2016). Investigating interrelationships between Lower Palaeolithic stone tool effectiveness and tool user biometric variation: implications for technological and evolutionary changes. Archaeological and Anthropological Sciences [Online]. Available at: http://dx.doi.org/10.1007/s12520-016-0433-x.
    Lower Palaeolithic hominins are thought to have been dependent upon stone tools during the acquisition and processing of food resources. Hence, it is hypothesized that the evolutionary advantages provided by efficient stone tool use may have selected for anatomical changes observed in the hand during this period. Similarly, hominin manipulative capabilities are suggested to have been of consequence to Lower Palaeolithic technological choices and tool-use capabilities. The extent and character of these relationships are not, however, fully understood and it is not known whether these hypothesized co-evolutionary and co-dependent relationships are consistent across varying technological and task-type conditions. Here, six key biometric parameters of the hand are investigated in terms of their statistical relationship with cutting efficiency using both flakes and handaxes over extended periods of use and in multiple types of cutting task. Results indicate that (1) both handaxe and flake cutting efficiency is significantly related with biometric variation of individual tool-users, (2) relationships between biometric parameters and efficiency are consistent across extended durations but vary dependent upon task-type conditions, (3) manipulative strength is the most significant biometric trait in terms of predicting flake efficiency, while (4) hand size is the strongest predictor of handaxe cutting efficiency. These results demonstrate the long-term impact that stone tool use likely had on the evolution of hominin biometric variation during the Lower Palaeolithic, while also highlighting the variable influence of different tool use contexts. Most notably, results indicate that the onset of the Acheulean may have been dependent, a priori, upon hand dimensions that are close to the modern human range, and that prior to the appearance of this anatomy, handaxe use would have been an impractical (i.e. inefficient) tool use behaviour compared to the use of flakes.
  • Key, A. et al. (2016). Looking at handaxes from another angle: Assessing the ergonomic and functional importance of edge form in Acheulean bifaces. Journal of Anthropological Archaeology [Online] 44:43-55. Available at: http://dx.doi.org/10.1016/j.jaa.2016.08.002.
    Edge angle is widely considered to be a morphological attribute that influences the functional performance of lithic technologies. However, the comparative performance capabilities of handaxes that vary in terms of edge angles has never been investigated under experimental conditions. Similarly, detailed accounts of Acheulean handaxe angle variation from archaeological examples have not been reported in the literature. Consequently, it has not previously been possible to assess the extent to which Palaeolithic individuals adhered to specific edge angle ranges during handaxe production or whether resultant artifactual properties may have been in response to varying rates of utility. Here, using a substantial experimental program (n = 500 handaxes), we investigate the impact that edge angle variation has on the cutting efficiency of handaxes at a “whole tool” and “edge-point localized” level. We then examine edge angles in a temporally and geographically wide range of handaxes (n = 643) and assess the extent to which hominins were likely altering tool production choices in response to functional pressures. Our experimental results demonstrate that, up to a certain value, higher edge angles in handaxes can actually increase functional performance. Furthermore, results indicate that edges in the proximal portion of handaxes have the greatest influence over efficiency rates. Combined with examination of archaeological specimens, these results suggest that hominins actively pursued the production of more obtuse edges in the proximal (butt) portion of handaxes in order to increase ergonomic features that facilitated greater efficiency during use. Edge angle values in the proximal portion of the archaeological handaxes were, however, consistently found to be below an efficiency threshold identified at ∼70 degrees, above which, an edge’s ability to effectively be applied to cutting tasks decreases markedly. This further suggests that the proximal edges of handaxes, at least occasionally, were required as a functional working edge.
  • Key, A. (2016). Manual Loading Distribution During Carrying Behaviors: Implications for the Evolution of the Hominin Hand. PLoS ONE [Online]. Available at: http://dx.doi.org/10.1371/journal.pone.0163801.
    The human hand is unparalleled amongst primates in its ability to manipulate objects forcefully and dexterously. Previous research has predominantly sought to explain the evolution of these capabilities through an adaptive relationship between more modern human-like anatomical features in the upper limb and increased stone tool production and use proficiency. To date, however, we know little about the influence that other manipulatively demanding behaviors may have had upon the evolution of the human hand. The present study addresses one aspect of this deficiency by examining the recruitment of the distal phalanges during a range of manual transportation (i.e. carrying) events related to hominin behavioral repertoires during the Plio-Pleistocene. Specifically, forces on the volar pad of each digit are recorded during the transportation of stones and wooden branches that vary in weight and size. Results indicate that in
    most instances, the index and middle fingers are recruited to a significantly greater extent than the other three digits during carrying events. Relative force differences between digits were, however, dependent upon the size and weight of the object
    transported. Carrying behaviors therefore appear unlikely to have contributed to the evolution of the robust thumb anatomy observed in the human hand. Rather, results suggest that the manual transportation of objects may plausibly have influenced the evolution of the human gripping capabilities and the 3rd metacarpal styloid process.
  • Key, A. (2016). Integrating mechanical and ergonomic research within functional and morphological analyses of lithic cutting technology: key principles and future experimental directions. Ethnoarchaeology [Online] 8. Available at: http://dx.doi.org/10.1080/19442890.2016.1150626.
    The functional value of a stone tool is principally in its ability to cut, split, or otherwise deform material. The relative efficiency with which stone tools undertake cutting processes has been a point of interest to lithic archaeologists for decades, with many linking aspects of tool morphology to functional performance. Many of the questions asked by stone tool research are, however, pertinent to other disciplines. This includes mechanical engineering and ergonomic sciences where there is a substantial amount of research dedicated to understanding the mechanics of cutting and the influence exerted by tool-form attributes during use. These investigations therefore have valuable insights for lithic archaeology and our understanding of the variables that would have been influencing stone tool use in past populations. Here, the value of mechanical and ergonomic research to lithic archaeology is analyzed, key morphological and mechanical principles central to the determination of a stone tool’s cutting efficiency are reviewed, and the need for future experiments that investigate these principles within archaeological contexts is highlighted.
  • Key, A. and Lycett, S. (2016). Influence of handaxe size and shape on cutting efficiency: a large-scale experiment and morphometric analysis. Journal of Archaeological Method and Theory [Online]:1-28. Available at: http://dx.doi.org/10.1007/s10816-016-9276-0.
    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.
  • Key, A. and Dunmore, C. (2015). The evolution of the hominin thumb and the influence exerted by the non-dominant hand during stone tool production. Journal of Human Evolution [Online] 78:60-69. Available at: http://dx.doi.org/10.1016/j.jhevol.2014.08.006.
    Modern humans possess a highly derived thumb that is substantially stronger and more robust than the fingers. Previous hypotheses concerning the evolution of such traits have focused upon the manipulation of hammerstones during stone tool production and of stone tools during their use. To date there has been no research on the manipulative pressures exerted by the non-dominant (core-holding) hand during stone tool production and its potential influence on the evolutionary history of the thumb. Here we provide the first investigation into the frequencies of digit recruitment and the relative manipulative forces experienced in the non-dominant hand during stone tool production. Eight experienced knappers produced flake cutting tools under four distinct conditions while pressure sensors, secured to the volar pads of the thumb, index and middle fingers of the non-dominant hand, recorded manipulative forces. Results indicate that relative to the fingers, the thumb was recruited significantly more frequently and experienced significantly greater manipulative forces during core repositioning events and the securing of the core during flake detachments. Our results support the hypothesis that the robust thumb anatomy observed in the hominin lineage was selected for, at least in part, as a result of more frequent and greater manipulative pressures acting upon the thumb relative to the fingers on the non-dominant hand during stone tool production.
  • Stemp, W., Morozov, M. and Key, A. (2015). Quantifying lithic microwear with load variation on experimental basalt flakes using LSCM and area-scale fractal complexity (Asfc). Surface Topography: Metrology and Properties [Online] 3. Available at: http://dx.doi.org/10.1088/2051-672X/3/3/034006.
    Working load is one factor that affects wear on stone tools. Despite the recognition of the importance of the relationship between working load and the development of microwear on stone tools, there have been few attempts to quantify differences in wear due to changes in load. In a controlled experiment, we used 30 basalt flakes knapped from raw material collected in Olduvai Gorge, Tanzania, Africa, to cut oak branches for the same number of strokes. For each flake, a different loading level was applied starting at 150 g and increasing by increments of 150 g to a maximum load of 4.5 kg. A laser scanning confocal microscope was used to mathematically document the surface texture of the flakes. The worn surface data were compared using area-scale fractal complexity (Asfc), calculated from relative areas, to determine the degree to which variation in loading significantly affected the amount of wear on the flake surfaces. Our results indicate that working load does play a role in the development of lithic microwear on these flakes and that discrimination of two worn flake surfaces, using mean square ratios of Asfc, based on variable load is consistently possible with load differences between ~100 g and 4.5 kg. However, discrimination of microwear on flake surfaces was not consistent for all load level differences and discrimination became less consistent when working load differences were below ~100 g.
  • Key, A. and Lycett, S. (2015). Edge angle as a variably influential factor in flake cutting efficiency: An experimental investigation of its relationship with tool size and loading. Archaeometry [Online] 57:911-927. Available at: http://dx.doi.org/10.1111/arcm.12140.
    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.
  • Key, A. and Lycett, S. (2015). Reassessing the production of handaxes versus flakes from a functional perspective. Archaeological and Anthropological Sciences [Online]:1-17. Available at: http://www.dx.doi.org/10.1007/s12520-015-0300-1.
    Bifacially flaked stone tools, traditionally referred to as “handaxes” were produced by Pleistocene hominins for over one million years over three different continents. This spatial and temporal prevalence raises questions about the factors that may have motivated their use as supplements to more simple flake tools. Hence, understanding the comparative functional performance capabilities of flakes and handaxes is essential to understanding factors that may have motivated the repeated production of handaxes during the Pleistocene. Here, we examine this question using a larger scale experimental approach than has previously been undertaken. We statistically assessed the comparative functional efficiencies of basic flake cutting tools and handaxes when undertaking a series of distinct cutting tasks. Furthermore, for the first time, we examined the functional capabilities of flake tools that are of equal size and mass to handaxes. Our results identify that the specific material context in which these tools are used is key to their relative functional efficiencies, with basic flake cutting tools being significantly more efficient than handaxes when undertaking relatively small, precise cutting tasks. Alternatively, we identify that handaxes are significantly more efficient than basic flake cutting tools when tasked with cutting relatively large, resistant portions of material. Thus, we conclude the adoption and widespread production of handaxes by Pleistocene hominins was motivated, at least in part, by requirements to undertake this specific type of task, rather than them being inherently superior to flakes in all cutting tasks. Indeed, interestingly, the comparative functional efficiencies of handaxes and flakes of equal size are far less pronounced than expected, with a number of tasks displaying no significant efficiency differences. Subsequently, we stress that a number of other hypothesized advantages of handaxes may have also been key to their widespread production and use by Pleistocene hominins.
  • Key, A. et al. (2015). Is loading a significantly influential factor in the development of lithic microwear? An experimental test using LSCM on basalt from Olduvai Gorge. Journal of Archaeological Method and Theory [Online] 22:1193-1214. Available at: http://dx.doi.org/10.1007/s10816-014-9224-9.
    Lithic microwear develops as a result of abrasive friction between a stone tool’s working edge and the surface of a worked material. Variation in the loading (i.e. force) applied to a stone tool during its use alters the amount of friction created between these two materials and should subsequently affect the level of any wear accrued. To date, however, no comprehensive account of the interaction between variable working loads and wear development has been undertaken. If such a relationship does exist, it may be possible to calculate the loading levels applied to stone tool artefacts during their use. Here, we use 30 basalt flakes knapped from raw materials collected in Olduvai Gorge, Tanzania, in a controlled experimental cutting task of standardized duration. Loading levels are recorded throughout with each flake being used with a predetermined load, ranging between 150 g and 4.5 kg. Laser scanning confocal microscopy (LSCM), coupled with the relative area (Srel) algorithm, is used to mathematically document the surface texture of the flakes to determine whether variation in loading does in fact significantly affect the amount of wear on the flake surfaces. Results indicate that working load does play a role in the development of lithic microwear; however, its interaction with other variables, including the naturally rough surface of basalt, may reduce the likelihood of its accurate determination on tools recovered from archaeological deposits.
  • Key, A. (2014). Are bigger flakes always better? An experimental assessment of flake size variation on cutting efficiency and loading. Journal of Archaeological Science [Online] 41:140-146. Available at: http://dx.doi.org/10.1016/j.jas.2013.07.033.
    Previous studies have indicated that the cutting efficiency of flake tools increases with increased tool size. Here, we undertook to examine the relationship between flake size and efficiency parameters using a larger and more variable flake dataset than used in previous analyses. Our analyses were specifically designed to assess whether there is an absolute relationship between ever-increasing flake size and increased efficiency and/or loading potential. An alternative hypothesis is merely that only the smallest flakes are inefficient, and it is this factor which has been driving previous statements linking increasing flake size with increased efficiency. Our first set of analyses, using all experimental flakes, determined that a statistically significant relationship existed between increased flake sizes and increased cutting efficiency, as measured by two different efficiency measures (‘Time taken’ and ‘Number of cutting strokes required’). This analysis also demonstrated a statistically significant positive relationship between flake size and loading forces. However, our second analysis, which excluded the smallest flakes in our sample, revealed a different pattern. In this second set of analyses, increasing flake size did not indicate a statistically significant relationship with our two measures of cutting efficiency. A statistically significant relationship between increased flake size and increased loading was, however, still evinced. In sum, these results suggest that there is not an unconditional or absolute relationship between increased flake size and increased cutting efficiency in all circumstances. Rather, there is a threshold below which flakes of a certain size will become markedly inefficient. Our results have particular implications relating to flake utility, optimality, and factors potentially influencing flake selection by hominins.
  • Key, A. (2013). Applied force as a determining factor in lithic use-wear accrual: an experimental investigation of its validity as a method with which to infer hominin upper limb biomechanics. Lithic Technology [Online] 38:32-45. Available at: http://dx.doi.org/10.1179/0197726113Z.0000000001.
    The advent of flake technology represented a fundamental shift in the capability of hominins to effectively access and process animal food sources. As such, the efficiency with which these tools were utilized is often widely implicated in palaeoanthropological debate, most pertinently, with regards to the evolution of upper limb biomechanics. Hence, it would then be of significance if the force, and by association efficiency, with which these tools were used is able to be determined. Presented here is the first attempt to correlate the force with which flaked tools are used to the associated microwear polish accrued on the lithics worked edge. This would potentially allow biomechanical inferences to be taken from stone artifacts and subsequently be applied to the populations that were using them. Twenty five participants of varying strength carried out a simple cutting task using small, unhafted flakes made from English chalk flint. Both maximum and mean applied force was recorded during these tasks by a sensor placed under the worked material while all other variables, including stroke count and flake size, were controlled for. Lithic polish was quantified through seven textural analyses of SEM micrographs. Results indicated that there were no statistically significant relationships between lithic polish and both maximum and mean applied force at low levels of variation. It is, however, suggested that given more archaeologically inferable experimental conditions then polish accrual may have displayed higher developmental distinctions, thus allowing lithic wear to differentiate between applied forces.
  • Key, A. and Lycett, S. (2011). Technology based evolution? A biometric test of the effects of handsize versus tool form on efficiency in an experimental cutting task. Journal of Archaeological Science [Online] 38:1663-1670. Available at: http://dx.doi.org/10.1016/j.jas.2011.02.032.
    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.