Functional mastery of percussive technology in nut-cracking and stone-flaking actions: experimental comparison and implications for the evolution of the human brain

Reconstructing hammerstone size flake by flake: an experimental approach

Understanding force application in flake production is essential for reconstructing hominin behaviour, technological advancements and biomechanics. Extensive research has examined stone tool production, focusing on the intended material outcomes such as the cores, tools and flakes. Analyzing force application in this process requires knowledge of hammerstone selection and use. Despite progress made in understanding hammerstone selection and use, linking specific knapping outcomes to hammerstone use remains challenging. This difficulty stems from the complex relationship between fracture mechanics and material signatures in lithic artifacts. Key variables related to hammerstone use and their influence on flaking outcomes remain poorly understood. We draw on fracture mechanics to explore factors driving flake ring crack size-the circular region where the Hertzian cone, a feature of conchoidal flaking, intersects with the platform. Our experiment systematically examines how hammerstone size, velocity and strike angle-factors influencing strike force-affect ring crack and flake size under controlled conditions. We validate our findings with previously reported controlled and replicative experiments. Results show that flake ring crack size can estimate hammerstone size. Our findings mean that we can reconstruct the flaking process and particularly variability in the application of force at a level of detail previously unavailable.

Higher order affordances

Affordances are opportunities for action for a given animal (or animals) in a given environment or situation. The concept of affordance has been widely adopted in the behavioral sciences, but important questions remain. We propose a new way of understanding the nature of affordances; in particular, how affordances are related to one another. We claim that many - perhaps most - affordances emerge from non-additive relations among other affordances, such that some affordances are of higher order relative to other affordances. That is, we propose that affordances form a continuous category of perceiveables that differ only in whether and how they relate to other affordances. We argue that: (1) opportunities for behaviors of all kinds can be described as affordances, (2) some affordances emerge from relations between animal and environment, whereas most affordances emerge from relations between other affordances, and (3) all affordances lawfully structure ambient energy arrays and, therefore, can be perceived directly. Our concept of higher order affordances provides a general account of behavioral phenomena that traditionally have been interpreted in terms of cognitive processes (e.g., remembering or imagining) as well as behavioral phenomena that have traditionally been interpreted in terms of cultural rules, such as conventions, or customs.

Neural plasticity in early potters: Shape analysis and TMS-EEG co-registration trace the rise of a new motor skill

In this study, we explored the biocultural mechanisms underlying ancient craft behaviours. Archaeological methods were integrated with neuroscience techniques to explore the impact on neuroplasticity resulting from the introduction of early pottery techniques. The advent of ceramic marked a profound change in the economy and socio-cultural dynamics of past societies. It may have also played a central role in developing new craft skills that influenced the neural plasticity of the potters. Coiling, one of the most widespread neolithic techniques, requires precise hand movements and the ability to regulate finger pressure to shape the clay without deformation. In a pilot study involving intensive training in neolithic pottery, we used TMS-EEG co-registration to monitor a group of participants and we examined the shape of the artefacts they made before and after training. Our findings suggest changes in the functional properties of the primary motor cortex (M1) responsible for the control and execution of actions. We also observed an improvement in symmetry and consistency of the artefacts and a significant reduction in errors. This multidisciplinary approach sheds light on the mechanisms of material culture's variation in the archaeological field and provides promising insights into the co-evolution of technology and human skill.

"How handy was early hominin 'know-how'?" An experimental approach exploring efficient early stone tool use

OBJECTIVES

The appearance of early lithic industries has been associated with the gradual development of unique biomechanical and cognitive abilities in hominins, including human-like precision grasping and basic learning and/or communicating capacities. These include tools used for activities exclusively associated with hominin contexts (cutting flakes) and hammerstones utilized for behaviors shared with non-human primates (e.g., nut-cracking). However, no previous experimental research has focused on comparing the factors affecting efficiency between these two key behavioral patterns and their evolutionary implications.

MATERIALS AND METHODS

Here, we address this gap with an experimental design involving participants with varying tool-related experience levels (i.e., no experience, theoretical-only experience, and extensive practical knapping expertise) to monitor their success rates, biometrics, and surface electromyography (sEMG) recordings from eight important hand and forearm muscles.

RESULTS

Our results showed that practical experience had a substantial impact on flake-cutting efficiency, allowing participants to achieve greater success rates with substantially less muscle effort. This relationship between success rates and muscle effort was not observed for the nut-cracking task. Moreover, even though practical experience did not significantly benefit nut-cracking success, experts exhibited increased rates of self-improvement in that task.

DISCUSSION

Altogether, these experimental findings suggest that the ability to practice and retain tool-using knowledge played a fundamental role in the subsistence strategies and adaptability of early hominins, potentially providing the cognitive basis for conceptualizing the first intentional tool production strategies.

Martinez L, Criado-Boado F, Müeller J, Clark A. A computational approach to selective attention in embodied approaches to cognitive archaeology

This article proposes a novel computational approach to embodied approaches in cognitive archaeology called computational cognitive archaeology (CCA). We argue that cognitive archaeology, understood as the study of the human mind based on archaeological findings such as artefacts and material remains excavated and interpreted in the present, can benefit from the integration of novel methods in computational neuroscience interested in modelling the way the brain, the body and the environment are coupled and parameterized to allow for adaptive behaviour. We discuss the kind of tasks that CCA may engage in with a narrative example of how one can model the cumulative cultural evolution of the material and cognitive components of technologies, focusing on the case of knapping technology. This article thus provides a novel theoretical framework to formalize research in cognitive archaeology using recent developments in computational neuroscience.

Design and development of a sensorized hammerstone for accurate force measurement in stone knapping experiments

The process of making stone tools, specifically knapping, is a hominin behaviour that typically involves using the upper limb to manipulate a stone hammer and apply concentrated percussive force to another stone, causing fracture and detachment of stone chips with sharp edges. To understand the emergence and subsequent evolution of tool-related behaviours in hominins, the connections between the mechanics of stone knapping, including the delivery of percussive forces, and biomechanics and hominin anatomy, especially in the upper limb, are required. However, there is an absence of direct experimental means to measure the actual forces generated and applied to produce flakes during knapping. Our study introduces a novel solution to this problem in the form of an ergonomic hand-held synthetic hammerstone that can record the percussive forces that occur during knapping experiments. This hammerstone is composed of a deformable pneumatic 3D-printed chamber encased within a 3D-printed grip and a stone-milled striker. During knapping, hammer impact causes the pneumatic chamber to deform, which leads to a change in pressure that is measured by a sensor. Comparisons of recorded pressure data against corresponding force values measured using a force plate show that the synthetic hammer quantifies percussion forces with relatively high accuracy. The performance of this hammerstone was further validated by conducting anvil-supported knapping experiments on glass that resulted in a root mean square error of under 6%, while recording forces up to 730 N with successful flake detachments. These validation results indicate that accuracy was not sensitive to variations up to 15° from the vertical in the hammer striking angle. Our approach allows future studies to directly examine the role of percussive force during the stone knapping process and its relationship with both anatomical and technological changes during human evolution.

Linking primatology and archaeology: The transversality of stone percussive behaviors

Since the launch of the Journal of Human Evolution fifty years ago, the archaeology of human origins and the evolution of culture have witnessed major breakthroughs with the identification of several new archaeological sites whose chronology has been slowly pushed back until the discovery of the earliest evidence of stone tool making at Lomekwi 3 (West Turkana, Kenya), at 3.3 Ma. Parallel to these discoveries, the study of wild primates, especially chimpanzees (Pan troglodytes), allowed the development of models to understand key aspects of the behavior of extinct hominin species. Indeed, chimpanzees possess an impressive diversity of tool-aided foraging behaviors, demonstrating that technology (and culture) is not exclusive to humans. Additionally, current research has also shown that wild capuchin monkeys (Sapajus libidinosus) and long-tailed macaques (Macaca fascicularis) also rely on stone percussive foraging behaviors. The investigation of these primates is boosting new interpretative models to understand the origins of stone flaking and the archaeological signature left by these primates. This review aims to present an examination of the state-of-the-art and the current advances made in the study of the earliest hominin technology and primate percussive behaviors. Overall, we argue that while it has been shown that extant primates can generate unintentional flakes, early hominins exhibited skills in the production and use of flakes not identified in primates. Nonetheless, we stand up to continue developing interdisciplinary approaches (i.e., primate archaeology) to study extant primates, as these endeavors are essential to move forward toward a detailed understanding of the technological foraging behaviors beyond the genus Homo. Finally, we discuss future challenges for the study of the emergence of stone technology.

Evidence for an internal model of friction when controlling kinetic energy at impact to slide an object along a surface toward a target

Although the role of an internal model of gravity for the predictive control of the upper limbs is quite well established, evidence is lacking regarding an internal model of friction. In this study, 33 male and female human participants performed a striking movement (with the index finger) to slide a plastic cube-like object to a given target distance. The surface material (aluminum or balsa wood) on which the object slides, the surface slope (-10°, 0, or +10°) and the target distance (25 cm or 50 cm) varied across conditions, with ten successive trials in each condition. Analysis of the object speed at impact and spatial error suggests that: 1) the participants chose to impart a similar speed to the object in the first trial regardless of the surface material to facilitate the estimation of the coefficient of friction; 2) the movement is parameterized across repetitions to reduce spatial error; 3) an internal model of friction can be generalized when the slope changes. Biomechanical analysis showed interindividual variability in the recruitment of the upper limb segments and in the adjustment of finger speed at impact in order to transmit the kinetic energy required to slide the object to the target distance. In short, we provide evidence that the brain builds an internal model of friction that makes it possible to parametrically control a striking movement in order to regulate the amount of kinetic energy required to impart the appropriate initial speed to the object.

On the psychological origins of tool use

The ubiquity of tool use in human life has generated multiple lines of scientific and philosophical investigation to understand the development and expression of humans' engagement with tools and its relation to other dimensions of human experience. However, existing literature on tool use faces several epistemological challenges in which the same set of questions generate many different answers. At least four critical questions can be identified, which are intimately intertwined-(1) What constitutes tool use? (2) What psychological processes underlie tool use in humans and nonhuman animals? (3) Which of these psychological processes are exclusive to tool use? (4) Which psychological processes involved in tool use are exclusive to Homo sapiens? To help advance a multidisciplinary scientific understanding of tool use, six author groups representing different academic disciplines (e.g., anthropology, psychology, neuroscience) and different theoretical perspectives respond to each of these questions, and then point to the direction of future work on tool use. We find that while there are marked differences among the responses of the respective author groups to each question, there is a surprising degree of agreement about many essential concepts and questions. We believe that this interdisciplinary and intertheoretical discussion will foster a more comprehensive understanding of tool use than any one of these perspectives (or any one of these author groups) would (or could) on their own.

Biomechanical demands of percussive techniques in the context of early stone toolmaking

Recent discoveries in archaeology and palaeoanthropology highlight that stone tool knapping could have emerged first within the genera Australopithecus or Kenyanthropus rather than Homo. To explore the implications of this hypothesis determining the physical demands and motor control needed for performing the percussive movements during the oldest stone toolmaking technology (i.e. Lomekwian) would help. We analysed the joint angle patterns and muscle activity of a knapping expert using three stone tool replication techniques: unipolar flaking on the passive hammer (PH), bipolar (BP) flaking on the anvil, and multidirectional and multifacial flaking with free hand (FH). PH presents high levels of activity for Biceps brachii and wrist extensors and flexors. By contrast, BP and FH are characterized by high solicitation of forearm pronation. The synergy analyses depict a high muscular and kinematic coordination. Whereas the muscle pattern is very close between the techniques, the kinematic pattern is more variable, especially for PH. FH displays better muscle coordination and conversely lesser joint angle coordination. These observations suggest that the transition from anvil and hammer to freehand knapping techniques in early hominins would have been made possible by the acquisition of a behavioural repertoire producing an evolutionary advantage that gradually would have been beneficial for stone tool production.

Identifying animal complex cognition requires natural complexity

The search for human cognitive uniqueness often relied on low ecological tests with subjects experiencing unnatural ontogeny. Recently, neuroscience demonstrated the significance of a rich environment on the development of brain structures and cognitive abilities. This stresses the importance to consider the prior knowledge that subjects bring in any experiment. Second, recent developments in multivariate statistics control precisely for a number of factors and their interactions. Making controls in natural observations equivalent and sometimes superior to captive experimental studies without the drawbacks of the latter methods. Thus, we can now investigate complex cognition by accounting for many different factors, as required when solving tasks in nature. Combining both progresses allows us to move toward an “experience-specific cognition”, recognizing that cognition varies extensively in nature as individuals adapt to the precise challenges they experience in life. Such cognitive specialization makes cross-species comparisons more complex, while potentially identifying human cognitive uniqueness.

How bearded capuchin monkeys (Sapajus libidinosus) prepare to use a stone to crack nuts

Bearded capuchin monkeys crack nuts with naturally varying stone hammers, suggesting they may tune their grips and muscular forces to each stone. If so, they might use discrete actions on a stone before lifting and striking, and they would likely use these actions more frequently when the stone is larger and/or less familiar and/or when first initiating striking. We examined the behavior of (a) four monkeys (all proficient at cracking nuts) with two larger (1 kg) and two smaller (0.5 kg) stones, (b) 12 monkeys with one 1 kg stone, and (c) one monkey during its first 100 strikes with an initially unfamiliar 1 kg stone. Bearded capuchin monkeys used three discrete actions on the stone before striking, all more often with the larger stones than the smaller stones. We infer that the first discrete action (Spin) aided the monkey in determining where to grip the stone, the second (Flip) allowed it to position the stone on the anvil ergonomically before lifting it, and the third (Preparatory Lift) readied the monkey for the strenuous lifting action. The monkey that provided 100 strikes with one initially unfamiliar stone performed fewer Spins in later strikes but performed Flip and Preparatory Lift at consistent rates. The monkeys gripped the stone with both hands along the sides to lift it, but usually moved one or both hands to the top of the stone at the zenith of the lift for the downward strike. The findings highlight two new aspects of the capuchins' nut-cracking: (a) Anticipatory actions with the stone before striking, especially when the stone is larger or unfamiliar, and when initiating striking and (b) shifting grips on the stone during a strike. We invite researchers to investigate if other taxa use anticipatory actions and shift their grips during percussive activity.

Learning curves and teaching when acquiring nut-cracking in humans and chimpanzees

Humans are considered superior to other species in their tool using skills. However, most of our knowledge about animals comes from observations in artificial conditions with individuals removed from their natural environment. We present a first comparison of humans and chimpanzees spontaneously acquiring the same technique as they forage in their natural environment. We compared the acquisition of the Panda nut-cracking technique between Mbendjele foragers from the Republic of Congo and the Taï chimpanzees from Côte d'Ivoire. Both species initially acquire the technique slowly with similar kinds of mistakes, with years of practice required for the apprentice to become expert. Chimpanzees more rapidly acquired the technique when an apprentice, and reached adult efficiency earlier than humans. Adult efficiencies in both species did not differ significantly. Expert-apprentice interactions showed many similar instances of teaching in both species, with more variability in humans due, in part to their more complex technique. While in humans, teaching occurred both vertically and obliquely, only the former existed in chimpanzees. This comparison of the acquisition of a natural technique clarifies how the two species differed in their technical intelligence. Furthermore, our observations support the idea of teaching in both species being more frequent for difficult skills.

Behavioral Repertoire Influences the Rate and Nature of Learning in Climbing: Implications for Individualized Learning Design in Preparation for Extreme Sports Participation

Extreme climbing where participants perform while knowing that a simple mistake could result in death requires a skill set normally acquired in non-extreme environments. In the ecological dynamics approach to perception and action, skill acquisition involves a process where the existing repertoire of behavioral capabilities (or coordination repertoire) of a learner are destabilized and re-organized through practice—this process can expand the individuals affordance boundaries allowing the individual to explore new environments. Change in coordination repertoire has been observed in bi-manual coordination and postural regulation tasks, where individuals begin practice using one mode of coordination before transitioning to another, more effective, coordination mode during practice. However, individuals may also improve through practice without qualitatively reorganizing movement system components—they do not find a new mode of coordination. To explain these individual differences during learning (i.e., whether or not a new action is discovered), a key candidate is the existing coordination repertoire present prior to practice. In this study, the learning dynamics of body configuration patterns organized with respect to an indoor climbing surface were observed and the existing repertoire of coordination evaluated prior to and after practice. Specifically, performance outcomes and movement patterns of eight beginners were observed across 42 trials of practice over a 7-week period. A pre- and post-test scanning procedure was used to determine existing patterns of movement coordination and the emergence of new movement patterns after the practice period. Data suggested the presence of different learning dynamics by examining trial-to-trial performance in terms of jerk (an indicator of climbing fluency), at the individual level of analysis. The different learning dynamics (identified qualitatively) included: continuous improvement, sudden improvement, and no improvement. Individuals showing sudden improvement appeared to develop a new movement pattern of coordination in terms of their capability to climb using new body-wall orientations, whereas those showing continuous improvement did not, they simply improved performance. The individual who did not improve in terms of jerk, improved in terms of distance climbed. We discuss implications for determining and predicting how individual differences can shape learning dynamics and interact with metastable learning design.

An earlier origin for stone tool making: implications for cognitive evolution and the transition to Homo

The discovery of the earliest known stone tools at Lomekwi 3 (LOM3) from West Turkana, Kenya, dated to 3.3 Ma, raises new questions about the mode and tempo of key adaptations in the hominin lineage. The LOM3 tools date to before the earliest known fossils attributed to Homo at 2.8 Ma. They were made and deposited in a more C3 environment than were the earliest Oldowan tools at 2.6 Ma. Their discovery leads to renewed investigation on the timing of the emergence of human-like manipulative capabilities in early hominins and implications for reconstructing cognition. The LOM3 artefacts form part of an emerging paradigm shift in palaeoanthropology, in which: tool-use and tool-making behaviours are not limited to the genus Homo; cranial, post-cranial and behavioural diversity in early Homo is much wider than previously thought; and these evolutionary changes may not have been direct adaptations to living in savannah grassland environments.This article is part of the themed issue 'Major transitions in human evolution'.

Investigating the dental toolkit of primates based on food mechanical properties: Feeding action does matter

Although conveying an indisputable morphological and behavioral signal, traditional dietary categories such as frugivorous or folivorous tend to group a wide range of food mechanical properties together. Because food/tooth interactions are mostly mechanical, it seems relevant to investigate the dental morphology of primates based on mechanical categories. However, existing mechanical categories classify food by its properties but cannot be used as factors to classify primate dietary habits. This comes from the fact that one primate species might be adapted to a wide range of food mechanical properties. To tackle this issue, what follows is an original framework based on action-related categories. The proposal here is to classify extant primates based on the range of food mechanical properties they can process through one given action. The resulting categories can be used as factors to investigate the dental tools available to primates. Furthermore, cracking, grinding, and shearing categories assigned depending on the hardness and the toughness of food are shown to be supported by morphological data (3D relative enamel thickness) and topographic data (relief index, occlusal complexity, and Dirichlet normal energy). Inferring food mechanical properties from dental morphology is especially relevant for the study of extinct primates, which are mainly documented by dental remains. Hence, we use action-related categories to investigate the molar morphology of an extinct colobine monkey Mesopithecus pentelicus from the Miocene of Pikermi, Greece. Action-related categories show contrasting results compared with classical categories and give us new insights into the dietary adaptations of this extinct primate. Finally, we provide some possible directions for future research aiming to test action-related categories. In particular, we suggest acquiring more data on mechanically challenging fallback foods and advocate the use of other food mechanical properties such as abrasiveness. The development of new action-related dental metrics is also crucial for primate dental studies.

Nut Cracking Tools Used by Captive Chimpanzees (Pan troglodytes) and Their Comparison with Early Stone Age Percussive Artefacts from Olduvai Gorge

We present the results of a series of experiments at the Kumamoto Sanctuary in Japan, in which captive chimpanzees (Pan troglodytes) performed several nut cracking sessions using raw materials from Olduvai Gorge, Tanzania. We examined captive chimpanzee pounding tools using a combination of technological analysis, use-wear distribution, and micro-wear analysis. Our results show specific patterns of use-wear distribution across the active surfaces of pounding tools, which reveal some similarities with traces on archaeological percussive objects from the Early Stone Age, and are consistent with traces on other experimental pounding tools used by modern humans. The approach used in this study may help to stablish a framework with which to interpret archaeological assemblages and improve understanding of use-wear formation processes on pounding tools used by chimpanzees. This study represents the first direct comparison of chimpanzee pounding tools and archaeological material, and thus may contribute to a better understanding of hominin percussive activities.

The development of plant food processing in the Levant: insights from use-wear analysis of Early Epipalaeolithic ground stone tools

In recent years, the study of percussive, pounding and grinding tools has provided new insights into human evolution, more particularly regarding the development of technology enabling the processing and exploitation of plant resources. Some of these studies focus on early evidence for flour production, an activity frequently perceived as an important step in the evolution of plant exploitation. The present paper investigates plant food preparation in mobile hunter-gatherer societies from the Southern Levant. The analysis consists of a use-wear study of 18 tools recovered from Ohalo II, a 23 000-year-old site in Israel showing an exceptional level of preservation. Our sample includes a slab previously interpreted as a lower implement used for producing flour, based on the presence of cereal starch residues. The use-wear data we have obtained provide crucial information about the function of this and other percussive tools at Ohalo II, as well as on investment in tool manufacture, discard strategies and evidence for plant processing in the Late Pleistocene. The use-wear analysis indicates that the production of flour was a sporadic activity at Ohalo II, predating by thousands of years the onset of routine processing of plant foods.

How similar are nut-cracking and stone-flaking? A functional approach to percussive technology

Various authors have suggested similarities between tool use in early hominins and chimpanzees. This has been particularly evident in studies of nut-cracking which is considered to be the most complex skill exhibited by wild apes, and has also been interpreted as a precursor of more complex stone-flaking abilities. It has been argued that there is no major qualitative difference between what the chimpanzee does when he cracks a nut and what early hominins did when they detached a flake from a core. In this paper, similarities and differences between skills involved in stone-flaking and nut-cracking are explored through an experimental protocol with human subjects performing both tasks. We suggest that a 'functional' approach to percussive action, based on the distinction between functional parameters that characterize each task and parameters that characterize the agent's actions and movements, is a fruitful method for understanding those constraints which need to be mastered to perform each task successfully, and subsequently, the nature of skill involved in both tasks.

A new type of anvil in the Acheulian of Gesher Benot Ya'aqov, Israel

We report here on the identification and characterization of thin basalt anvils, a newly discovered component of the Acheulian lithic inventory of Gesher Benot Ya'aqov (GBY). These tools are an addition to the array of percussive tools (percussors, pitted stones and anvils) made of basalt, flint and limestone. The thin anvils were selected from particularly compact, horizontally fissured zones of basalt flows. This type of fissuring produces a natural geometry of thick and thin slabs. Hominins at GBY had multiple acquisition strategies, including the selection of thick slabs for the production of giant cores and cobbles for percussors. The selection of thin slabs was carried out according to yet another independent and targeted plan. The thinness of the anvils dictated a particular range of functions. The use of the anvils is well documented on their surfaces and edges. Two main types of damage are identified: those resulting from activities carried out on the surfaces of the anvils and those resulting from unintentional forceful blows (accidents de travaille). Percussive activities that may have been associated with the thin anvils include nut cracking and the processing of meat and bones, as well as plants.

Experimental studies illuminate the cultural transmission of percussive technologies in Homo and Pan

The complexity of Stone Age tool-making is assumed to have relied upon cultural transmission, but direct evidence is lacking. This paper reviews evidence bearing on this question provided through five related empirical perspectives. Controlled experimental studies offer special power in identifying and dissecting social learning into its diverse component forms, such as imitation and emulation. The first approach focuses on experimental studies that have discriminated social learning processes in nut-cracking by chimpanzees. Second come experiments that have identified and dissected the processes of cultural transmission involved in a variety of other force-based forms of chimpanzee tool use. A third perspective is provided by field studies that have revealed a range of forms of forceful, targeted tool use by chimpanzees, that set percussion in its broader cognitive context. Fourth are experimental studies of the development of flint knapping to make functional sharp flakes by bonobos, implicating and defining the social learning and innovation involved. Finally, new and substantial experiments compare what different social learning processes, from observational learning to teaching, afford good quality human flake and biface manufacture. Together these complementary approaches begin to delineate the social learning processes necessary to percussive technologies within the Pan-Homo clade.

Experimental Insights into the Cognitive Significance of Early Stone Tools

Stone-flaking technology is the most enduring evidence for the evolving cognitive abilities of our early ancestors. Flake-making was mastered by African hominins ~3.3 ma, followed by the appearance of handaxes ~1.75 ma and complex stone reduction strategies by ~1.6 ma. Handaxes are stones flaked on two opposed faces (‘bifacially’), creating a robust, sharp-edged tool, and complex reduction strategies are reflected in strategic prior flaking to prepare or ‘predetermine’ the nature of a later flake removal that served as a tool blank. These technologies are interpreted as major milestones in hominin evolution that reflect the development of higher-order cognitive abilities, and the presence and nature of these technologies are used to track movements of early hominin species or ‘cultures’ in the archaeological record. However, the warranting argument that certain variations in stone tool morphologies are caused by differences in cognitive abilities relies on analogy with technical replications by skilled modern stoneworkers, and this raises the possibility that researchers are projecting modern approaches to technical problems onto our non-modern hominin ancestors. Here we present the results of novel experiments that randomise flake removal and disrupt the modern stoneworker’s inclination to use higher-order reasoning to guide the stone reduction process. Although our protocols prevented goal-directed replication of stone tool types, the experimental assemblage is morphologically standardised and includes handaxe-like ‘protobifaces’ and cores with apparently ‘predetermined’ flake removals. This shows that the geometrical constraints of fracture mechanics can give rise to what appear to be highly-designed stoneworking products and techniques when multiple flakes are removed randomly from a stone core.

Percussive tool use by Taï Western chimpanzees and Fazenda Boa Vista bearded capuchin monkeys: a comparison

Percussive tool use holds special interest for scientists concerned with human origins. We summarize the findings from two field sites, Taï and Fazenda Boa Vista, where percussive tool use by chimpanzees and bearded capuchins, respectively, has been extensively investigated. We describe the ecological settings in which nut-cracking occurs and focus on four aspects of nut-cracking that have important cognitive implications, namely selection of tools, tool transport, tool modification and modulation of actions to reach the goal of cracking the nut. We comment on similarities and differences in behaviour and consider whether the observed differences reflect ecological, morphological, social and/or cognitive factors. Both species are sensitive to physical properties of tools, adjust their selection of hammers conditionally to the resistance of the nuts and to transport distance, and modulate the energy of their strikes under some conditions. However, chimpanzees transport hammers more frequently and for longer distances, take into account a higher number of combinations of variables and occasionally intentionally modify tools. A parsimonious interpretation of our findings is that morphological, ecological and social factors account for the observed differences. Confirmation of plausible cognitive differences in nut-cracking requires data not yet available.

A functional approach to movement analysis and error identification in sports and physical education

In a hypothesis-and-theory paper, a functional approach to movement analysis in sports is introduced. In this approach, contrary to classical concepts, it is not anymore the "ideal" movement of elite athletes that is taken as a template for the movements produced by learners. Instead, movements are understood as the means to solve given tasks that in turn, are defined by to-be-achieved task goals. A functional analysis comprises the steps of (1) recognizing constraints that define the functional structure, (2) identifying sub-actions that subserve the achievement of structure-dependent goals, (3) explicating modalities as specifics of the movement execution, and (4) assigning functions to actions, sub-actions and modalities. Regarding motor-control theory, a functional approach can be linked to a dynamical-system framework of behavioral shaping, to cognitive models of modular effect-related motor control as well as to explicit concepts of goal setting and goal achievement. Finally, it is shown that a functional approach is of particular help for sports practice in the context of structuring part practice, recognizing functionally equivalent task solutions, finding innovative technique alternatives, distinguishing errors from style, and identifying root causes of movement errors.

Learning to tune the antero-posterior propulsive forces during walking: a necessary skill for mastering upright locomotion in toddlers

This study examines the process of learning to walk from a functional perspective. To move forward, one must generate and control propulsive forces. To achieve this, it is necessary to create and tune a distance between the centre of mass (CoM) and the centre of pressure (CoP) along the antero-posterior axis. We hypothesize that learning to walk consists of learning how to calibrate these self-generated propulsive forces to control such distance. We investigated this question with six infants (three girls and three boys) who we followed up weekly for the first 8 weeks after the onset of walking and then biweekly until they reached 14-16 weeks of walking experience. The infants' walking patterns (kinematics and propelling forces) were captured via synched motion analysis and force plate. The results show that the distance between the CoM and the CoP along the antero-posterior axis increased rapidly during the first months of learning to walk and that this increase was correlated with an increase in velocity. The initial small values of (CoM-CoP) observed at walking onset, coupled with small velocity are interpreted as the solution infants adopted to satisfy a compromise between the need to generate propulsive forces to move forward while simultaneously controlling the disequilibrium resulting from creating a with distance between the CoM and CoP.

Movement pattern variability in stone knapping: implications for the development of percussive traditions

The earliest direct evidence for tool-use by our ancestors are 2.6 million year old stone tools from Africa. These earliest artifacts show that, already, early hominins had developed the required advanced movement skills and cognitive capacities to manufacture stone tools. Currently, it is not well understood, however, which specific movement skills are required for successful stone knapping and accordingly it is unknown how these skills emerged during early hominin evolution. In particular, it is not clear which striking movements are indicative of skilled performance, how striking movement patterns vary with task and environmental constraints, and how movement patterns are passed on within social groups. The present study addresses these questions by investigating striking movement patterns and striking variability in 18 modern stone knappers (nine experienced and nine novices). The results suggest that no single movement pattern characterizes successful stone knapping. Participants showed large inter-individual movement variability of the elementary knapping action irrespective of knapping experience and knapping performance. Changes in task- and environmental constraints led knappers to adapt their elementary striking actions using a combination of individual and common strategies. Investigation of striking pattern similarities within social groups showed only partial overlap of striking patterns across related individuals. The results therefore suggest that striking movement patterns in modern stone knappers are largely specific to the individual and movement variability is not indicative of knapping performance. The implications of these results for the development of percussive traditions are discussed.

Tool use ability depends on understanding of functional dynamics and not specific joint contribution profiles

Researchers in cognitive neuroscience have become increasingly interested in how different aspects of tool use are integrated and represented by the brain. Comparatively less attention has been directed toward tool use actions themselves and how effective tool use behaviors are coordinated. In response, we take this opportunity to consider the mechanical principles of tool use actions and their relationship to motor learning. Using kinematic analysis, we examine both functional dynamics and joint contribution profiles of subjects with different levels of experience in a primordial percussive task. Our results show that the ability to successfully produce stone flakes using the Oldowan method did not correspond with any particular joint contribution profile. Rather, expertise in this tool use action was principally associated with the subject's ability to regulate the functional parameters that define the task itself.

How can ten fingers shape a pot? Evidence for equivalent function in culturally distinct motor skills

Behavioural variability is likely to emerge when a particular task is performed in different cultural settings, assuming that part of human motor behaviour is influenced by culture. In analysing motor behaviour it is useful to distinguish how the action is performed from the result achieved. Does cultural environment lead to specific cultural motor skills? Are there differences between cultures both in the skills themselves and in the corresponding outcomes? Here we analyse the skill of pottery wheel-throwing in French and Indian cultural environments. Our specific goal was to examine the ability of expert potters from distinct cultural settings to reproduce a common model shape (a sphere). The operational aspects of motor performance were captured through the analysis of the hand positions used by the potters during the fashioning process. In parallel, the outcomes were captured by the geometrical characteristics of the vessels produced. As expected, results revealed a cultural influence on the operational aspects of the potters’ motor skill. Yet, the marked cultural differences in hand positions used did not give rise to noticeable differences in the shapes of the vessels produced. Hence, for the simple model form studied, the culturally-specific motor traditions of the French and Indian potters gave rise to an equivalent outcome, that is shape uniformity. Further work is needed to test whether such equivalence is also observed in more complex ceramic shapes.

When does tool use become distinctively human? Hammering in young children

This study examines the development of hammering within an ontogenetic and evolutionary framework using motion-capture technology. Twenty-four right-handed toddlers (19-35 months) wore reflective markers while hammering a peg into a peg-board. The study focuses on the motor characteristics that make tool use uniquely human: wrist involvement, lateralization, and handle use. Older children showed more distally controlled movements, characterized by relatively more reliance on the wrist, but only when hammering with their right hand. Greater age, use of the right hand, and more wrist involvement were associated with higher accuracy; handle use did not systematically change with age. Collectively, the results provide new insights about the emergence of hammering in young children and when hammering begins to manifest distinctively human characteristics.

What limits tool use in nonhuman primates? Insights from tufted capuchin monkeys (Sapajus spp.) and chimpanzees (Pan troglodytes) aligning three-dimensional objects to a surface

Perceptuomotor functions that support using hand tools can be examined in other manipulation tasks, such as alignment of objects to surfaces. We examined tufted capuchin monkeys' and chimpanzees' performance at aligning objects to surfaces while managing one or two spatial relations to do so. We presented six subjects of each species with a single stick to place into a groove, two sticks of equal length to place into two grooves, or two sticks joined as a T to place into a T-shaped groove. Tufted capuchins and chimpanzees performed equivalently on these tasks, aligning the straight stick to within 22.5° of parallel to the groove in approximately half of their attempts to place it, and taking more attempts to place the T stick than two straight sticks. The findings provide strong evidence that tufted capuchins and chimpanzees do not reliably align even one prominent axial feature of an object to a surface, and that managing two concurrent allocentric spatial relations in an alignment problem is significantly more challenging to them than managing two sequential relations. In contrast, humans from 2 years of age display very different perceptuomotor abilities in a similar task: they align sticks to a groove reliably on each attempt, and they readily manage two allocentric spatial relations concurrently. Limitations in aligning objects and in managing two or more relations at a time significantly constrain how nonhuman primates can use hand tools.

Laterality and the evolution of the prefronto-cerebellar system in anthropoids

There is extensive evidence for an early vertebrate origin of lateralized motor behavior and of related asymmetries in underlying brain systems. We investigate human lateralized motor functioning in a broad comparative context of evolutionary neural reorganization. We quantify evolutionary trends in the fronto-cerebellar system (involved in motor learning) across 46 million years of divergent primate evolution by comparing rates of evolution of prefrontal cortex, frontal motor cortex, and posterior cerebellar hemispheres along individual branches of the primate tree of life. We provide a detailed evolutionary model of the neuroanatomical changes leading to modern human lateralized motor functioning, demonstrating an increased role for the fronto-cerebellar system in the apes dating to their evolutionary divergence from the monkeys (∼30 million years ago (Mya)), and a subsequent shift toward an increased role for prefrontal cortex over frontal motor cortex in the fronto-cerebellar system in the Homo-Pan ancestral lineage (∼10 Mya) and in the human ancestral lineage (∼6 Mya). We discuss these results in the context of cortico-cerebellar functions and their likely role in the evolution of human tool use and speech.

Coordination strategies used in stone knapping

Stone tool-use and manufacture is seen as an important skill during the evolution of our species and recently there has been increased interest in the understanding of perceptual-motor abilities underlying this skill. This study provides further information with respect to the motor strategies used during stone knapping. Kinematics of the striking arm were recorded in expert and novice knappers while producing flakes of two different sizes. Using Uncontrolled Manifold Analysis, the results showed that knappers structure joint angle movements such that the hammer trajectory variability is minimized across trials, with experts displaying significantly smaller variability compared with novices. Principal component analysis further revealed that a single component captures the complexity of the strike and that the strike is governed by movements of the elbow and the wrist. Analysis of movement velocities indicated that both groups adjusted movement velocities according to flake size although experts used smaller hammer, wrist, and elbow velocities in both flake conditions compared with novices. The results suggest that while the gross striking movement is easy to replicate for a novice knapper, it requires prolonged training before a knapper becomes attuned to the finer details necessary for controlled flaking.

From action to language: comparative perspectives on primate tool use, gesture and the evolution of human language

The papers in this Special Issue examine tool use and manual gestures in primates as a window on the evolution of the human capacity for language. Neurophysiological research has supported the hypothesis of a close association between some aspects of human action organization and of language representation, in both phonology and semantics. Tool use provides an excellent experimental context to investigate analogies between action organization and linguistic syntax. Contributors report and contextualize experimental evidence from monkeys, great apes, humans and fossil hominins, and consider the nature and the extent of overlaps between the neural representations of tool use, manual gestures and linguistic processes.