Wild monkeys flake stone tools

Proceedings of the Royal Society B: Biological Sciences, 2016

Stone tool transport leaves long lasting behavioural evidence in the landscape. However, it remains unknown how large scale patterns of stone distribution emerge through undirected, short term transport behaviors. One of the longest studied groups of stone tool using primates are the chimpanzees of the Taï National Park in Ivory Coast, West-Africa. Using hammerstones left behind at chimpanzee Panda nut-cracking sites, we tested for a distance-decay effect, in which the weight of material decreases with increasing distance from raw material sources. We found that this effect exists over a range of more than 2 km, despite the fact that observed, short term tool transport does not appear to involve deliberate movements away from raw material sources. Tools from the millennia-old Noulo site in the Taï forest fit the same pattern. The fact that chimpanzees show both complex short term behavioural planning, and yet produce a landscape-wide pattern over the long term, raises the question of whether similar processes operate within other stone tool using primates, including hominins. Where hominin landscapes have discrete material sources, a distance-decay effect, and increasing use of stone materials away from sources, the Taï chimpanzees provide a relevant analogy for understanding the formation of those landscapes.

Biology letters, 2018

We analysed the patterns of coordination of striking movement and perceptuomotor control of stone hammers in wild bearded capuchin monkeys, Sapajus libidinosus as they cracked open palm nut using hammers of different mass, a habitual behaviour in our study population. We aimed to determine why these monkeys cannot produce conchoidally fractured flakes as do contemporary human knappers or as did prehistoric hominin knappers. We found that the monkeys altered their patterns of coordination of movement to accommodate changes in hammer mass. By altering their patterns of coordination, the monkeys kept the strike's amplitude and the hammer's velocity at impact constant with respect to hammer mass. In doing so, the hammer's kinetic energy at impact-which determines the propagation of a fracture/crack in a nut-varied across hammers of different mass. The monkeys did not control the hammer's kinetic energy at impact, the key parameter a perceiver-actor should control while k...

Biological Theory, 2021

It is widely thought that causal cognition underpins technical reasoning. Here we suggest that understanding causal cognition as a thinking system that includes theory of mind (i.e., social cognition) can be a productive theoretical tool for the field of evolutionary cognitive archaeology. With this contribution, we expand on an earlier model that distinguishes seven grades of causal cognition, explicitly presenting it together with a new analysis of the theory of mind involved in the different grades. We then suggest how such thinking may manifest in the archaeological or stone tool record and techno-behaviors of the last three million years or so. Our thesis is threefold: (a) theory of mind is an integral element of causal cognition; (b) generally speaking, the more advanced causal cognition is, the more it is dependent on theory of mind; and (c) the evolution of causal cognition depends more and more on mental representations of hidden variables. Ultimately, the final or seventh ...

Open Research Europe

Background: Despite substantial research on early hominin lithic technologies, the learning mechanisms underlying flake manufacture and use are contested. To draw phylogenetic inferences on the potential cognitive processes underlying the acquisition of both of these abilities in early hominins, we investigated if and how one of our closest living relatives, chimpanzees (Pan troglodytes), could learn to make and use flakes. Methods: Across several experimental conditions, we tested eleven task-naïve chimpanzees (unenculturated n=8, unknown status n=3) from two independent populations for their abilities to spontaneously make and subsequently use flakes as well as to use flakes made by a human experimenter. Results: Despite the fact that the chimpanzees seemed to understand the requirements of the task, were sufficiently motivated and had ample opportunities to develop the target behaviours, none of the chimpanzees tested made or used flakes in any of the experimental conditions. Con...

Cambridge Archaeological Journal, 2018

Although it is sometimes suggested that modern-day chimpanzee nut-cracking behaviour is cognitively similar to early stone-tool-knapping behaviour, few systematic comparative studies have tested this assumption. Recently, two further techno-behaviours were reported that could both represent intermediary phases in hominin cognitive evolution pertaining to our ultimate technological astuteness. These behaviours are that of bearded capuchin monkeys pounding rocks and very early stone-tool knapping from Lomekwi 3. Here we use a multi-model approach to directly compare cognitive aspects required for 11 techno-behaviours, ranging from the simplest capuchin pounding behaviour to the most complex chimpanzee nut-cracking and Lomekwi 3 knapping behaviours. We demonstrate a marked difference in broad-spectrum cognitive requirements between capuchin pounding on the one hand and Lomekwian bipolar knapping on the other. Whereas the contrast is less pronounced between chimpanzee nut-cracking scena...

Royal Society open science, 2018

Habitual reliance on tool use is a marked behavioural difference between wild robust (genus ) and gracile (genus ) capuchin monkeys. Despite being well studied and having a rich repertoire of social and extractive foraging traditions, sp. rarely use tools and have never been observed using stone tools. By contrast, habitual tool use by is widespread. We review theory and discuss factors which might explain these differences in patterns of tool use between and . We then report the first case of habitual stone tool use in a gracile capuchin: a population of white-faced capuchins () in Coiba National Park, Panama who habitually rely on hammerstone and anvil tool use to access structurally protected food items in coastal areas including seeds, hermit crabs, marine snails, terrestrial crabs and other items. This behaviour has persisted on one island in Coiba National Park since at least 2004. From 1 year of camera trapping, we found that stone tool use is strongly male-biased. Of the 205...

Journal of Human Evolution, 2022

When and how human ancestors first used tools remains unknown, despite intense research into the origins of technology. It has been hypothesized that the evolutionary roots of stone flake technology has its origin in percussive behavior. Before intentional stone flaking, hominins potentially engaged in various percussive behaviors resulting in accidental flake detachments. We refer to this scenario as the ‘by-product hypothesis.’ In this scenario, repeated detachments of sharp stone fragments eventually resulted in intentional flake production. Here, we tested the circumstances of accidental flake production as a by-product of percussive foraging in wild capuchin monkeys (Sapajus libidinosus) from Brazil, the only nonhuman primate known to habitually produce sharp-edged flakes through a percussive behavior. We conducted field experiments where we tested the potential for accidental flake production during nut cracking. We provided three different types of stone with varied material properties as anvils to assess the circumstances in which accidental production of sharp-edged flakes occurs during nut cracking. A further freehand knapping experiment, with the raw material that exhibited accidental flake detachments, allows a direct comparison of flakes that have been intentionally produced by an expe- rienced knapper and flakes produced during nut cracking by capuchin monkeys. Our results show that raw material quality and morphology significantly affect the rate of sharp-edged flake production as well as the resulting lithic signature of this behavior. In addition, accidental flakes produced during capuchin nut cracking on highly isotropic raw material are similar in many respects to intentionally produced flakes by a human knapper. Our field experiments highlight the fact that nut-cracking behavior can lead to the unintentional production of substantial quantities of sharp-edged flakes and therefore supports the ‘by-product hypothesis’ as a potential mechanism for the emergence of hominin flake technology.

Biological Theory, 2020

Recent field studies have broadened our view on cultural performances in animals. This has consequences for the concept of cumulative culture. Here, we deconstruct the common individualist and differential approaches to culture. Individualistic approaches to the study of cultural evolution are shown to be problematic, because culture cannot be reduced to factors on the micro level of individual behavior (methodological individualism, “atomism”) but possesses a dynamic that only occurs on the group level and profoundly affects the individuals (“holism”). Naive individuals, as a prerequisite of an atomistic perspective, do not exist. We address the construction of a social approach to (cumulative) culture by introducing an inevitable social embedding of the individual development of social beings. The sociological notion of “habitus” as embodied cultural capital permits us to understand social transmission of behavioral components on a very basic level, resulting in a cumulative effec...

Antiquity

Lithic technologies dominate understanding of early humans, yet natural processes can fracture rock in ways that resemble artefacts made by Homo sapiens and other primates. Differentiating between fractures made by natural processes and primates is important for assessing the validity of early and controversial archaeological sites. Rather than depend on expert authority or intuition, the authors propose a null model of conchoidally fractured Antarctic rocks. As no primates have ever occupied the continent, Antarctica offers a laboratory for generating samples that could only have been naturally fractured. Examples that resemble artefacts produced by primates illustrate the potential of ‘archaeological’ research in Antarctica for the evaluation of hominin sites worldwide.

Journal of Archaeological Science, 2023

The production of sharp-edged stone flakes is often viewed as a unique adaptation specific to the hominin lineage. The discovery of large stone cores and flakes dated to 3.3 Ma has shown that the earliest evidence of hominin stone flake production differs from the later Oldowan (dated to 2.6 Ma) record. Recent discoveries have shown that capuchin monkeys (Sapajus libidinosus) can unintentionally produce sharp-edged flake assemblages as a by-product of percussive behaviour. Capuchin monkeys are the only wild primate to intentionally strike two stones together (stone-on-stone percussion) to produce quartz powder. In doing so, they unintentionally produce high frequencies of sharp-edged flakes. It has been suggested that these possess the same technological attributes commonly used to describe intentional hominin stone flakes. Here we directly compare the basic morphometric descriptions, technological and 3D morphometric properties of unintentional capuchin flakes with experimen- tally produced flakes derived from two intentional flaking techniques employed during the Plio-Pleistocene, freehand and passive hammer knapping and a sample of Oldowan freehand flakes from Olduvai Gorge (Tanzania). Our results show that unintentional stone-on-stone flakes overlap in terms of their shape, size and technological attributes with those produced through intentional knapping techniques. We, however, identify attributes that may be critical for differentiating between intentional knapping techniques documented in the early archaeological record and unintentional flakes. Using these data we show that Oldowan flakes more closely resemble intentional freehand techniques.

2017

We have learned much about tool use in nonhumans since the discovery of Oldowan stone tools. Despite the ongoing debate over whether tool use in other animals requires cultural transmission, it seems clear that, today, humans show a quantitative, if not qualitative, difference in our ability to transmit information socially through cultural transmission. This ability makes cumulative culture possible. Although comparative studies provide relevant insights, we must look to the Paleolithic archaeological record to address when, where, and ultimately why this shift to high-fidelity social learning occurred. Yet here the frequent assumption that even the earliest stone tools serve as evidence of high-fidelity cultural transmission hinders investigation more than it helps. We pragmatically suggest resetting the null hypothesis for the processes underlying early stone tool production. The null hypothesis that we prefer is that early stone tools might have been so-called latent solutions rather than cultural material that derived from—and depended upon—modern human- like high-fidelity cultural transmission. This simple shift in perspective prioritizes the systematic investigation of more parsimonious potential explanations and forces us to demonstrate, rather than presume, that stone tools could not have existed without high-fidelity cultural transmission.

2022

The earliest stone tool types, sharp fakes knapped from stone cores, are assumed to have played a crucial role in human cognitive evolution. Flaked stone tools have been observed to be accidentally produced when wild monkeys use handheld stones as tools. Holding a stone core in hand and hitting it with another in the absence of faking, free hand hitting, has been considered a requirement for producing sharp stone fakes by hitting stone on stone, free hand percussion. We report on fve observations of free hand hitting behavior in two wild western gorillas, using stone‑like objects (pieces of termite mound). Gorillas are therefore the second non‑human lineage primate showing free‑hand hitting behavior in the wild, and ours is the frst report for free hand hitting behavior in wild apes. This study helps to shed light on the morphofunctional and cognitive requirements for the emergence of stone tool production as it shows that a prerequisite for free hand percussion (namely, free hand hitting) is part of the spontaneous behavioral repertoire of one of humans’ closest relatives (gorillas). However, the ability to combine free hand hitting with the force, precision, and accuracy needed to facilitate conchoidal fracture in free hand percussion may still have been a critical watershed for hominin evolution.

2021

Humans possess a perhaps unique type of culture among primates called cumulative culture. In this type of culture, behavioural forms cumulate changes over time, which increases their complexity and/or efficiency, eventually making these forms culture-dependent. As changes cumulate, culture-dependent forms become causally opaque, preventing the over- all behavioural form from being acquired by individuals on their own; in other words, culture-dependent forms must be copied between individuals and across generations. Despite the importance of cumulative culture for understanding the evolutionary history of our species, how and when cumulative culture evolved is still debated. One of the challenges faced when addressing these questions is how to identify culture-dependent forms that result from cumulative cultural evolution. Here we propose a novel method to identify the most likely cases of culture-dependent forms. The ‘Method of Local Restriction’ is based on the premise that as culture-dependent forms are repeatedly transmitted via copying, these forms will unavoidably cumulate population-specific changes (due to copying error) and therefore must be expected to become locally restricted over time. When we applied this method to our closest living relatives, the great apes, we found that most known ape behavioural forms are not locally restricted (across domains and species) and thus are unlikely to be acquired via copying. Nevertheless, we found 25 locally restricted forms across species and domains, three of which appear to be locally unique (having been observed in a single population of a single species). Locally unique forms represent the best current candidates for culture-dependent forms in non-human great apes. Besides these rare exceptions, our results show that overall, ape cultures do not rely heavily on copying, as most ape behaviours appear across sites and/or species, ren- dering them unlikely to be culture-dependent forms resulting from cumulative cultural evolution. Yet, the locally restricted forms (and especially the three locally unique forms) identified by our method should be tested further for their potential reliance on copying social learning mechanisms (and in turn, for their potential culture-dependence). Future studies could use the Method of Local Restriction to investigate the existence of culture-dependent forms in other animal species and in the hominin archaeological record to estimate how widespread copying is in the animal kingdom and to postulate a timeline for the emergence of copying in our lineage.

Nature Human Behaviour, 2017

Proceedings of the National Academy of Sciences, 2021

Significance Surviving challenging environments, living long lives, and engaging in complex cognitive processes are hallmark human characteristics. Similar traits have evolved in parallel in capuchin monkeys, but their genetic underpinnings remain unexplored. We developed and annotated a reference assembly for white-faced capuchin monkeys to explore the evolution of these phenotypes. By comparing populations of capuchins inhabiting rainforest versus dry forests with seasonal droughts, we detected selection in genes associated with kidney function, muscular wasting, and metabolism, suggesting adaptation to periodic resource scarcity. When comparing capuchins to other mammals, we identified evidence of selection in multiple genes implicated in longevity and brain development. Our research was facilitated by our method to generate high- and low-coverage genomes from noninvasive biomaterials.

American Antiquity

For at least three million years, knapping stone has been practiced by hominin societies large and small, past and present. Thus, understanding knapping, knappers, and knapping cultures is fundamental to anthropological research around the world. Although there is a general sense that stone knapping is inherently dangerous and can lead to injury, little is formally, specifically, or systematically known about the frequency, location, or severity of knapping injuries. Toward this end, we conducted a 31-question survey of modern knappers to better understand knapping risks. Responses from 173 survey participants suggest that knapping injuries are a real and persistent hazard, even though a majority of modern knappers use personal protective equipment. A variety of injuries (lacerations, punctures, aches, etc.) can occur on nearly any part of the body. The severity of injury sustained by some of our participants is shocking, and nearly one-quarter of respondents reported having sought ...

Reviews in Anthropology, 2017

Recent analyses of the preserved ancient genomes of the Mal'ta boy and Anzick infant have transformed our understanding of Native Americans' origins. The Mal'ta genome shows that about one-third of Native American genetic ancestry is derived from admixture, about fifteen to twenty thousand years ago, of East Asians with a now-vanished population of interior southern Siberia. Living Native Americans are demonstrably the direct descendants of the people who made and used Clovis tools and buried the Anzick infant in Montana ca. 12,800 cal B.P. The profound implications of these data for the origins of the first Americans should be obvious. However, as evidenced by the books reviewed here, archaeologists appear largely unaware of these data and their now-standard but unsubstantiated narratives of pre-Clovis coastal migrations remain unaffected.

International Journal of Primatology, 2017

Anthropogenic disturbances have a detrimental impact on the natural world; the vast expansion of palm oil monocultures is one of the most significant agricultural influences. Primates worldwide consequently have been affected by the loss of their natural ecosystems. Long-tailed macaques (Macaca fascilularis) in Southern Thailand have, however, learned to exploit oil palm nuts using stone tools. Using camera traps, we captured the stone tool behavior of one macaque group in Ao Phang-Nga National Park. Line transects placed throughout an abandoned oil palm plantation confirmed a high abundance of nut cracking sites. Long-tailed macaques previously have been observed using stone tools to harvest shellfish along the coasts of Thailand and Myanmar. The novel nut processing behavior indicates the successful transfer of existing lithic technology to a new food source. Such behavioral plasticity has been suggested to underlie cultural behavior in animals, suggesting that long-tailed macaques have potential to Int J Primatol

Royal Society Open Science, 2018

a new target for primate archaeological investigations, and opens new opportunities for comparisons between tool using primate species and with early hominin percussive behaviour, for which nutcracking has been frequently inferred.