Functional fixedness in chimpanzees.

Differences in the tool use of non-human primates and humans are subject of ongoing debate. In humans, representations of object functions underpin efficient tool use. Yet, representations of object functions can lead to functional fixedness, which describes the fixation on a familiar tool function leading to less efficient problem solving when the problem requires using the tool for a new function. In the current study, we examined whether chimpanzees exhibit functional fixedness. After solving a problem with a tool, chimpanzees were less efficient in solving another problem which required using the same tool with a different function compared to a control group. This fixation effect was still apparent after a period of nine months and when chimpanzees had learned about the function of a tool by observation of a conspecific. These results suggest that functional fixedness in our closest living relatives likely exists and cast doubt on the notion that stable function representations are uniquely human.

Protracted development of stick tool use skills extends into adulthood in wild western chimpanzees.

Tool use is considered a driving force behind the evolution of brain expansion and prolonged juvenile dependency in the hominin lineage. However, it remains rare across animals, possibly due to inherent constraints related to manual dexterity and cognitive abilities. In our study, we investigated the ontogeny of tool use in chimpanzees (Pan troglodytes), a species known for its extensive and flexible tool use behavior. We observed 70 wild chimpanzees across all ages and analyzed 1,460 stick use events filmed in the Taï National Park, Côte d'Ivoire during the chimpanzee attempts to retrieve high-nutrient, but difficult-to-access, foods. We found that chimpanzees increasingly utilized hand grips employing more than 1 independent digit as they matured. Such hand grips emerged at the age of 2, became predominant and fully functional at the age of 6, and ubiquitous at the age of 15, enhancing task accuracy. Adults adjusted their hand grip based on the specific task at hand, favoring power grips for pounding actions and intermediate grips that combine power and precision, for others. Highly protracted development of suitable actions to acquire hidden (i.e., larvae) compared to non-hidden (i.e., nut kernel) food was evident, with adult skill levels achieved only after 15 years, suggesting a pronounced cognitive learning component to task success. The prolonged time required for cognitive assimilation compared to neuromotor control points to selection pressure favoring the retention of learning capacities into adulthood.

Left anterior supramarginal gyrus activity during tool use action observation after extensive tool use training.

The advanced use of complex tools is considered a primary characteristic of human evolution and technological advancement. However, questions remain regarding whether humans possess unique underlying brain networks that support advanced tool-using abilities. Specifically, previous studies have demonstrated the presence of a structurally and functionally unique region in the left anterior supramarginal gyrus (aSMG), that is consistently active during tool use action observation. This region has been proposed as a primary hub for integrating semantic and technical information to form action plans with tools. However, it is still largely unknown how tool use motor learning affects left aSMG activation or connectivity with other brain regions. To address this, participants with little experience using chopsticks observed an experimenter using chopsticks to perform a novel task while undergoing two functional magnetic resonance imaging (fMRI) scans. Between the scans, participants underwent four weeks of behavioral training where they learned to use chopsticks and achieve proficiency in the observed task. Results demonstrated a significant change in effective connectivity between the left aSMG and the left anterior intraparietal sulcus (aIPS), a region involved in object affordances and planning grasping actions. These findings suggest that during unfamiliar tool use, the left aSMG integrates semantic and technical information to communicate with regions involved with grasp selection, such as the aIPS. This communication then allows appropriate grasps to be planned based on the physical properties of the objects involved and their potential interactions.

Stone tools improve diet quality in wild monkeys.

Tool use is a fundamental feature of human evolution. Stone tools are in the archaeological record from 3.4 Ma, even before Homo,1 and the use of stone tools probably predated the split between hominins and panins.2 Using tools (hereafter, tooling cf Fragaszy and Mangalam3) is hypothesized to have improved hominins' foraging efficiency or access to high-quality foods.4-7 This hypothesis is supported if feeding with tools positively contributes to diet quality in extant non-human primates or if foraging efficiency is increased by tooling. However, the contribution of tooling to non-human primates' foraging success has never been investigated through a direct analysis of nutritional ecology.8,9 We used multi-dimensional nutritional geometry to analyze energy and macronutrients (nonstructural carbohydrates, lipids, and protein) in the diets of wild capuchin monkeys (Sapajus libidinous) that routinely crack palm nuts with stone hammers.10,11 We show that eating nuts obtained through tooling helps monkeys to achieve more consistent dietary intakes. Tooling increased the net energy gain by 50% and decreased the proportion of fiber ingested by 7%. Tooling also increased the daily non-protein energy intake. By contrast, protein intake remained constant across foraging days, suggesting a pattern of macronutrient regulation called protein prioritization, which is also found in contemporary humans.8,9 In addition, tooling reduced dispersion in the ratio of protein to non-protein energy, suggesting a role in macronutrient balancing. Our findings suggest that tooling prior to tool making could have substantially increased the nutritional security of ancestral hominins, sowing the seeds for cultural development.5,7 VIDEO ABSTRACT.

Experimental investigation of orangutans' lithic percussive and sharp stone tool behaviours.

Early stone tools, and in particular sharp stone tools, arguably represent one of the most important technological milestones in human evolution. The production and use of sharp stone tools significantly widened the ecological niche of our ancestors, allowing them to exploit novel food resources. However, despite their importance, it is still unclear how these early lithic technologies emerged and which behaviours served as stepping-stones for the development of systematic lithic production in our lineage. One approach to answer this question is to collect comparative data on the stone tool making and using abilities of our closest living relatives, the great apes, to reconstruct the potential stone-related behaviours of early hominins. To this end, we tested both the individual and the social learning abilities of five orangutans to make and use stone tools. Although the orangutans did not make sharp stone tools initially, three individuals spontaneously engaged in lithic percussion, and sharp stone pieces were produced under later experimental conditions. Furthermore, when provided with a human-made sharp stone, one orangutan spontaneously used it as a cutting tool. Contrary to previous experiments, social demonstrations did not considerably improve the stone tool making and using abilities of orangutans. Our study is the first to systematically investigate the stone tool making and using abilities of untrained, unenculturated orangutans showing that two proposed pre-requisites for the emergence of early lithic technologies-lithic percussion and the recognition of sharp-edged stones as cutting tools-are present in this species. We discuss the implications that ours and previous great ape stone tool experiments have for understanding the initial stages of lithic technologies in our lineage.

The measurement, evolution, and neural representation of action grammars of human behavior.

Human behaviors from toolmaking to language are thought to rely on a uniquely evolved capacity for hierarchical action sequencing. Testing this idea will require objective, generalizable methods for measuring the structural complexity of real-world behavior. Here we present a data-driven approach for extracting action grammars from basic ethograms, exemplified with respect to the evolutionarily relevant behavior of stone toolmaking. We analyzed sequences from the experimental replication of ~ 2.5 Mya Oldowan vs. ~ 0.5 Mya Acheulean tools, finding that, while using the same "alphabet" of elementary actions, Acheulean sequences are quantifiably more complex and Oldowan grammars are a subset of Acheulean grammars. We illustrate the utility of our complexity measures by re-analyzing data from an fMRI study of stone toolmaking to identify brain responses to structural complexity. Beyond specific implications regarding the co-evolution of language and technology, this exercise illustrates the general applicability of our method to investigate naturalistic human behavior and cognition.

DNA barcoding identifies cryptic animal tool materials.

Some animals fashion tools or constructions out of plant materials to aid foraging, reproduction, self-maintenance, or protection. Their choice of raw materials can affect the structure and properties of the resulting artifacts, with considerable fitness consequences. Documenting animals' material preferences is challenging, however, as manufacture behavior is often difficult to observe directly, and materials may be processed so heavily that they lack identifying features. Here, we use DNA barcoding to identify, from just a few recovered tool specimens, the plant species New Caledonian crows (Corvus moneduloides) use for crafting elaborate hooked stick tools in one of our long-term study populations. The method succeeded where extensive fieldwork using an array of conventional approaches-including targeted observations, camera traps, radio-tracking, bird-mounted video cameras, and behavioral experiments with wild and temporarily captive subjects-had failed. We believe that DNA barcoding will prove useful for investigating many other tool and construction behaviors, helping to unlock significant research potential across a wide range of study systems.

The long developmental trajectory of body representation plasticity following tool use.

Humans evolution is distinctly characterized by their exquisite mastery of tools, allowing them to shape their environment in more elaborate ways compared to other species. This ability is present ever since infancy and most theories indicate that children become proficient with tool use very early. In adults, tool use has been shown to plastically modify metric aspects of the arm representation, as indexed by changes in movement kinematics. To date, whether and when the plastic capability of updating the body representation develops during childhood remains unknown. This question is particularly important since body representation plasticity could be impacted by the fact that the human body takes years to achieve a stable metric configuration. Here we assessed the kinematics of 90 young participants (8-21 years old) required to reach for an object before and after tool use, as a function of their pubertal development. Results revealed that tool incorporation, as indexed by the adult typical kinematic pattern, develops very slowly and displays a u-shaped developmental trajectory. From early to mid puberty, the changes in kinematics following tool use seem to reflect a shortened arm representation, opposite to what was previously reported in adults. This pattern starts reversing after mid puberty, which is characterized by the lack of any kinematics change following tool use. The typical adult-like pattern emerges only at late puberty, when body size is stable. These findings reveal the complex dynamics of tool incorporation across development, possibly indexing the transition from a vision-based to a proprioception-based body representation plasticity.

The ontogeny of termite gathering among chimpanzees in the Goualougo Triangle, Republic of Congo.

OBJECTIVES: Acquiring tool-assisted foraging skills can potentially improve dietary quality and increase fitness for wild chimpanzees (Pan troglodytes). In contrast to chimpanzees in East and West Africa, chimpanzees in the Congo Basin use tool sets and brush-tipped fishing probes to gather termites. We investigated the ontogeny of these tool skills in chimpanzees of the Goualougo Triangle, Republic of Congo, and compared it to that for chimpanzees at Gombe, Tanzania. We assessed whether chimpanzees acquired simple tool behaviors and single tool use before more complex actions and sequential use of multiple tool types. MATERIALS AND METHODS: Using a longitudinal approach, we scored remote video footage to document the acquisition of termite-gathering critical elements for 25 immature chimpanzees at Goualougo. RESULTS: All chimpanzees termite fished by 2.9 years but did not manufacture brush-tipped probes until an average of 4.3 years. Acquisition of sequential tool use extended into juvenility and adolescence. While we did not detect significant sex differences, most critical elements except tool manufacture were acquired slightly earlier by females. DISCUSSION: These findings contrast with Gombe, where chimpanzees learn to both use and make fishing probes between ages 1.5-3.5 and acquire the complete task by age 5.5. Differences between sites could reflect tool material selectivity and design complexity, the challenge of sequential tool behaviors, and strength requirements of puncturing subterranean termite nests at Goualougo. These results illustrate how task complexity may influence the timing and sequence of skill acquisition, improving models of the ontogeny of tool behavior among early hominins who likely used complex, perishable technologies.

Kinetics of stone tool production among novice and expert tool makers.

OBJECTIVES: As is the case among many complex motor tasks that require prolonged practice before achieving expertise, aspects of the biomechanics of knapping vary according to the relative experience/skill level of the practitioner. In archaeological experiments focused on the production of Plio-Pleistocene stone tools, these skill-mediated biomechanical differences have bearings on experimental design, the interpretation of results, and lithic assemblage analysis. A robust body of work exists on variation in kinematic patterns across skill levels but less is known about potential kinetic differences. The current study was undertaken to better understand kinetic patterns observed across skill levels during "Oldowan," freehand stone tool production. MATERIALS AND METHODS: Manual pressure data were collected from 23 novice and 9 expert stone tool makers during the production of simple stone flakes using direct hard hammer percussion. RESULTS: Results show that expert tool makers experienced significantly lower cumulative pressure magnitudes and pressure-time integral magnitudes compared with novices. In expert knappers, digits I and II experienced similarly high pressures (both peak pressure and pressure-time integrals) and low variability in pressure relative to digits III-V. Novices, in contrast, tended to hold hammerstones such that pressure patterns were similar across digits II-V, and they showed low variability on digit I only. DISCUSSION: The similar and consistent emphasis of the thumb by both skill groups indicates the importance of this digit in stabilizing the hammerstone. The emphasis placed on digit II is exclusive to expert knappers, and so this digit may offer osteological signals diagnostic of habitual expert tool production.

What kind of hominin first left Africa?

Recent discoveries of stone tools from Jordan (2.5 Ma) and China (2.1 Ma) document hominin presence in Asia at the beginning of the Pleistocene, well before the conventional Dmanisi datum at 1.8 Ma. Although no fossil hominins documenting this earliest Out of Africa phase have been found, on chronological grounds a pre-Homo erectus hominin must be considered the most likely maker of those artifacts. If so, this sheds new light on at least two disputed subjects in paleoanthropology, namely the remarkable variation among the five Dmanisi skulls, and the ancestry of Homo floresiensis.

Suppression of mutually incompatible proprioceptive and visual action effects in tool use.

Movements of a tool typically diverge from the movements of the hand manipulating that tool, such as when operating a pivotal lever where tool and hand move in opposite directions. Previous studies suggest that humans are often unaware of the position or movements of their effective body part (mostly the hand) in such situations. It has been suggested that this might be due to a "haptic neglect" of bodily sensations to decrease the interference of representations of body and tool movements. However, in principle this interference could also be decreased by neglecting sensations regarding the tool and focusing instead on body movements. While in most tool use situations the tool-related action effects are task-relevant and thus suppression of body-related rather than tool-related sensations is more beneficial for successful goal achievement, we manipulated this task-relevance in a controlled experiment. The results showed that visual, tool-related effect representations can be suppressed just as proprioceptive, body-related ones in situations where effect representations interfere, given that task-relevance of body-related effects is increased relative to tool-related ones.

Rapid trial-and-error learning with simulation supports flexible tool use and physical reasoning.

Many animals, and an increasing number of artificial agents, display sophisticated capabilities to perceive and manipulate objects. But human beings remain distinctive in their capacity for flexible, creative tool use-using objects in new ways to act on the world, achieve a goal, or solve a problem. To study this type of general physical problem solving, we introduce the Virtual Tools game. In this game, people solve a large range of challenging physical puzzles in just a handful of attempts. We propose that the flexibility of human physical problem solving rests on an ability to imagine the effects of hypothesized actions, while the efficiency of human search arises from rich action priors which are updated via observations of the world. We instantiate these components in the "sample, simulate, update" (SSUP) model and show that it captures human performance across 30 levels of the Virtual Tools game. More broadly, this model provides a mechanism for explaining how people condense general physical knowledge into actionable, task-specific plans to achieve flexible and efficient physical problem solving.

The Lichtenberg Keilmesser - it's all about the angle.

The presence of the 'Keilmesser-concept' in late Middle Paleolithic assemblages of Central and Eastern Europe defines the eponymous 'Keilmessergruppen'. The site of Lichtenberg (Lower Saxony, Germany) was discovered in 1987 and yielded one of the most important Keilmessergruppen assemblages of the northwestern European Plain. At that time, researchers used the bifacial backed knives to define a new type, the 'Lichtenberger Keilmesser', which they characterized by an aesthetic form-function concept with a specific range of morphological variability on the one hand, and a standardized convex cutting edge one the other hand. Thereby, a shape continuum was observed between different form-function concepts in the Lichtenberg assemblage, from Keilmesser through to Faustkeilblätter and handaxes. In a contrasting view, it was recently suggested that the morphology of Keilmesser, including what is defined here as type Lichtenberg, is the result of solutions to establish and maintain edge angles during resharpening. With the intention to evaluate these contrasting hypotheses, I conducted a re-analysis of the Keilmesser from Lichtenberg and their relationship to central German late Middle Paleolithic knives, using 3D geometric morphometric analyses and an automatized approach to measure edge angles on 3D models. Despite a morphological overlap of the tools from both regions, I could show that the Lichtenberg Keilmesser concept refers to one solution to create a tool with specific functionalities, like potentially cutting, prehension, and reusability. To establish and maintain its functionality, certain angles where created by the knappers along the active edges. This behavior resulted in specific shapes and positions of the active parts and created what looks like a standardized or template morphology of this Keilmesser type.

Frequent visits to various anvils during tool use by the graphic tuskfish Choerodon graphicus (Labridae).

This study investigated tool use by the graphic tuskfish Choerodon graphicus in New Caledonia. Anvils included rocks, a conical shell, flat dead corals and a concrete mooring. Sixteen tool-use events were observed in 10 h. A tool-use event often involved more than one anvil (44%). On average, C. graphicus struck prey six times and spent 84 s at an anvil. The only prey items brought to anvils were bivalve and gastropod molluscs. These results provide a foundation for future research on tool use in fishes.

Knowledge vs. know-how? Dissecting the foundations of stone knapping skill.

Stone tools provide some of the best remaining evidence of behavioral change over long periods, but their cognitive and evolutionary implications remain poorly understood. Here, we contribute to a growing body of experimental research on the cognitive and perceptual-motor foundations of stone toolmaking skills by using a flake prediction paradigm to assess the relative importance of technological understanding vs. accurate action execution in Late Acheulean-style handaxe production. This experiment took place as part of a larger, longitudinal study of knapping skill acquisition, allowing us to assemble a large sample of predictions across learning stages and in a comparative sample of experts. By combining group and individual-level statistical analyses with predictive modeling, we show that understanding and predicting specific flaking outcomes in this technology is both more difficult and less important than expected from previous work. Instead, our findings reveal the critical importance of perceptual motor skills needed to manage speed-accuracy trade-offs and reliably detach the large, invasive flakes that enable bifacial edging and thinning. With practice, novices increased striking accuracy, flaking success rates, and (to an extent) handaxe quality by targeting small flakes with acute platform angles. However, only experts were able to combine percussive force and accuracy to produce results comparable with actual Late Acheulean handaxes. The relatively intense demands for accurate action execution documented in our study indicate that biomechanical properties of the upper limb, cortical and cerebellar systems for sensorimotor control, and the cognitive, communicative, and affective traits supporting deliberate practice would all have been likely targets of selection acting on Late Acheulean toolmaking aptitude.

The dawn of the Middle Paleolithic in Atapuerca: the lithic assemblage of TD10.1 from Gran Dolina.

The Atapuerca localities present evidence of a long series of hominin occupations from the Early Pleistocene onward and are a key site for understanding the continuity and discontinuity of Western European technological and settlement dynamics. The TD10 unit from Gran Dolina is located in the upper part of the sequence and divided into four lithostratigraphic subunits (TD10.4 to TD10.1, from bottom to top) dated between ca. 450 ka and ca. 250 ka (Marine Isotope Stage 11 to Marine Isotope Stage 8). The technological analysis of the lithic assemblages belonging to the TD10.1 sequence aims to determine the trends among its archeological levels and check its relation to late Middle Pleistocene technological evolution and site functionality. Archeostratigraphic studies have identified several occupation events within its approximately 1.5 m of thickness, whose artifact densities and occupational models differ. However, no remarkable technical differences have been observed among them. Lithic assemblages from those events show more evolved features than other Atapuerca Mode 2 assemblages. These changes are reflected in the selective raw material management strategies; more hierarchized and predetermined reduction methods; and the progressive decrease of large cutting tools in the lithic assemblages with respect to flake tools, the latter defined by a greater typological diversification. These technological changes did not lead to a clear break with respect to previous technological models and were accompanied by other sporadic but significant changes in subsistence and behavioral strategies (bone tools and retouchers; lithic recycling, and so on), which were consolidated during the Middle Paleolithic. Hence, the archeological record from the TD10.1 subunit of Gran Dolina reflects a local stratigraphic transition from Mode 2 to Mode 3 technocomplexes, paralleling that observed in other sites in southwestern Europe.

Subspheroids in the lithic assemblage of Barranco León (Spain): Recognizing the late Oldowan in Europe.

The lithic assemblage of Barranco León (BL), attributed to the Oldowan techno-complex, contributes valuable information to reconstruct behavioral patterning of the first hominins to disperse into Western Europe. This archaic stone tool assemblage comprises two, very different groups of tools, made from distinct raw materials. On the one hand, a small-sized toolkit knapped from Jurassic flint, comprising intensively exploited cores and small-sized flakes and fragments and, on the other hand, a large-sized limestone toolkit that is mainly linked to percussive activities. In recent years, the limestone macro-tools have been the center of particular attention, leading to a re-evaluation of their role in the assemblage. Main results bring to light strict hominin selective processes, mainly concerning the quality of the limestone and the morphology of the cobbles, in relation to their use-patterning. In addition to the variety of traces of percussion identified on the limestone tools, recurrences have recently been documented in their positioning and in the morphology of the active surfaces. Coupled with experimental work, this data has contributed to formulating hypothesis about the range of uses for these tools, beyond stone knapping and butchery, for activities such as: wood-working or tendon and meat tenderizing. The abundance of hammerstones, as well as the presence of heavy-duty scrapers, are special features recognized for the limestone component of the Barranco León assemblage. This paper presents, for the first time, another characteristic of the assemblage: the presence of polyhedral and, especially, subspheroid morphologies, virtually unknown in the European context for this timeframe. We present an analysis of these tools, combining qualitative evaluation of the raw materials, diacritical study, 3D geometric morphometric analysis of facet angles and an evaluation of the type and position of percussive traces; opening up the discussion of the late Oldowan beyond the African context.

Predicting surgical site infections following laparoscopic bariatric surgery: development of the BariWound tool using the MBSAQIP database.

BACKGROUND: Although bariatric surgery is a safe procedure for severe obesity, incisional surgical site infections (SSI) remain a significant cause of morbidity. Bariatric surgery patients are at high risk due to obesity and diabetes. The objective of this study was to develop a predictive tool for incisional SSI within 30 days of bariatric surgery. METHODS: Data were retrieved from the 2015 and 2016 MBSAQIP databases. This study included patients who underwent primary laparoscopic Roux-en-Y gastric bypass (LRYGB) or laparoscopic sleeve gastrectomy (LSG). The primary outcome of interest was incisional SSI occurring within 30 days. Surgeries performed in 2015 were used in a derivation cohort and the predictive tool was validated against the 2016 cohort. A forward selection algorithm was used to build a logistic regression model predicting probability of SSI. RESULTS: A total of 274,187 patients were included with 71.7% being LSG and 28.3% LRYGB. 0.7% of patients had a SSI in which 71.0% had an incisional SSI, and 29.9% had an organ/space SSI. Of patients who had an incisional SSI, 88.7% were superficial, 10.9% were deep, and 0.4% were both. A prediction model to assess for risk of incisional SSI, BariWound, was derived and validated. BariWound consists of procedure type, chronic steroid or immunosuppressant use, gastroesophageal reflux disease, obstructive sleep apnea, sex, type 2 diabetes, hypertension, operative time, and body mass index. It stratifies individuals into very high (> 10%), high (5-10%), medium (1-5%), and low risk (< 1%) groups. This model accurately predicted events in the validation cohort with an area under the receiver operating characteristic curve of 0.73. CONCLUSIONS: BariWound accurately predicted the risk of 30-day incisional SSI in individuals undergoing bariatric surgery. Stratifying low- and high-risk groups allows for customized SSI prophylactic measures for patients in various risk categories and potentially enables future research targeted at high-risk patients.