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Inferring the evolutionary history of cognitive abilities requires large and diverse samples. However, such samples are often beyond the reach of individual researchers or institutions, and studies are often limited to small numbers of species. Consequently, methodological and site-specific-differences across studies can limit comparisons between species. Here we introduce the ManyPrimates project, which addresses these challenges by providing a large-scale collaborative framework for comparative studies in primate cognition. To demonstrate the viability of the project we conducted a case study of short-term memory. In this initial study, we were able to include 176 individuals from 12 primate species housed at 11 sites across Africa, Asia, North America and Europe. All subjects were tested in a delayed-response task using consistent methodology across sites. Individuals could access food rewards by remembering the position of the hidden reward after a 0, 15, or 30-second delay. Overall, individuals performed better with shorter delays, as predicted by previous studies. Phylogenetic analysis revealed a strong phylogenetic signal for short-term memory. Although, with only 12 species, the validity of this analysis is limited, our initial results demonstrate the feasibility of a large, collaborative open-science project. We present the ManyPrimates project as an exciting opportunity to address open questions in primate cognition and behaviour with large, diverse datasets.

Ant workers are often specialized in specific tasks, and it is well‐established that the main task an ant performs in the colony can be used to predict its sensitivity and responses to task‐associated stimuli. An often‐overlooked aspect of ants' task specialization is that individuals often switch tasks throughout the day and are not always engaged in functional tasks. Furthermore, the tasks individuals engage in are often correlated with other context‐specific factors, such as worker density, which can independently influence individuals' behaviour. Given this intra‐individual variation in task engagement and its correlation with density, it is currently unknown how these two factors interact to modulate ants' sensitivity and responses to stimuli. To address this question, we built a robotic manipulation system that allowed us to teleoperate a dummy inside ant colonies and to provide simulated antennations to ants when performing different tasks in areas with different worker densities. We coupled this manipulation system with a custom‐built automated tracking system (FORT) that allowed us to track individual identities and locations as well as to record the ants' responses to the dummy stimulation. We found independent effects of task and worker density on ants' responsiveness and alarm towards the dummy. Ants were less likely to respond and be alarmed by the dummy when stimulated in areas with high worker density. Responsiveness but not alarm was further influenced by the task being performed, with ants doing broodcare being the least responsive. Our results suggest that ants' behaviour is density‐dependent and that ants experience a process of habituation to tactile stimulation. Additionally, ants' responsiveness is modulated by the task they are performing at a given time, showing that sensitivity to stimuli is context‐dependent. Our robotic set‐up constitutes a valuable tool to systematically investigate social insect behaviour under unprecedented experimental control to unravel the individual‐level behavioural rules that underpin the organization of social insect colonies. The integrated system presented here opens new research avenues to empirically investigate the effects of more complex stimuli on social insect behaviour and has the potential to significantly further our understanding of decentralized collective systems.

Urban environments expose animals to abundant anthropogenic materials and foods that facilitate foraging innovations in species with opportunistic diets and high behavioral flexibility. Neophilia and exploration tendency are believed to be important behavioral traits for animals thriving in urban environments. Vervet monkeys (Chlorocebus pygerythrus) are one of few primate species that have successfully adapted to urban environments, thus making them an ideal species to study these traits. Using a within-species cross-habitat approach, we compared neophilia and exploration of novel objects (jointly referred to as “object curiosity”) between semi-urban, wild, and captive monkeys to shed light on the cognitive traits facilitating urban living. To measure “object curiosity,” we exposed monkeys to various types of novel stimuli and compared their approaches and explorative behavior. Our results revealed differences in the number of approaches and explorative behavior toward novel stimuli between the habitat types

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.

Extant primates, especially chimpanzees, are often used as models for pre-modern hominin (henceforth: hominin) behaviour, anatomy and cognition. In particular, as hominin behaviour cannot be inferred from archaeological remains and artefacts alone, extant primates (including modern humans) are used as a ‘time machine’ to reconstruct the technological repertoires of our early ancestors. Whilst many continue to use primates to approximate hominin tool behaviours, others have questioned the value of these comparisons. The aim of this review is to critically examine how previous studies have compared various primate species to hominins with regards to stone percussion and flaking, as well as to discuss the limitations and strengths of these comparisons. Evidence is presented to support the view that certain monkey species, alongside non-primate animal species, might provide important insights when reconstructing hominin stone tool culture, despite being phylogenetically further removed from our lineage. In conclusion, whilst some studies may inflate the value of primates as models for early hominins, data from extant primates, alongside the archaeological record and anthropological reports, can help create a more comprehensive picture of hominin stone tool culture.

It is hypothesized that tool-assisted excavation of plant underground storage organs (USOs) played an adaptive role in hominin evolution and was also once considered a uniquely human behavior. Recent data indicate that savanna chimpanzees also use tools to excavate edible USOs. However, those chimpanzees remain largely unhabituated and we lack direct observations of this behavior in the wild. To fill this gap in our knowledge of hominoid USO extractive foraging, we conducted tool-mediated excavation experiments with captive chimpanzees naïve to this behavior. We presented the chimpanzees with the opportunity to use tools in order to excavate artificially-placed underground foods in their naturally forested outdoor enclosure. No guidance or demonstration was given to the chimpanzees at any time. The chimpanzees used tools spontaneously in order to excavate the underground foods. They exhibited six different tool use behaviors in the context of excavation: probe, perforate, dig, pound, enlarge and shovel. However, they still excavated manually more often than they did with tools. Chimpanzees were selective in their choice of tools that we provided, preferring longer tools for excavation. They also obtained their own tools mainly from naturally occurring vegetation and transported them to the excavation site. They reused some tools throughout the study. Our new data provide a direction for the study of variables relevant to modeling USO extractive foraging by early hominins.

Reliability assessments are a quality control protocol commonly employed in fields of research that deal with video-recorded behavioural data. During these assessments, the same sample of videos is coded (at least) twice by the same researcher (intrarater reliability), or - more often - by two different researchers independently (interrater reliability). Next, levels of agreement are quantified to assess how reliable the behavioural classification is. In this manuscript, we concentrate on interrater reliability, though our points hold generally true for both cases. Despite the importance of interrater reliability assessments to ensure research quality, to the best of our knowledge there is no guideline to date specifying how they should be conducted to avoid potentially detrimental effects of 'coders' degrees of freedom' (CDF) and 'questionable coder practices' (QCP). For instance, there is no consensus regarding how large the sample of behaviours evaluated should be, the sample composition, the inclusion of negative controls or what statistical measures should be used to compare the raters' classifications. To begin to fill this methodological gap, we provide a list of best practices to conduct reliability tests, which we term the BRAVO (Balanced Reliability Assessment of Video Observations) workflow. We complement these recommendations with a series of simulations highlighting the properties of BRAVO and its use-cases. BRAVO represents the first step in creating a methodological gold-standard that researchers can use to perform valid reliability assessments. Given the widespread use of behavioural data across fields, we hope that the BRAVO workflow will be implemented by researchers from a variety of disciplines such as psychology, ethology, behavioural economics, and anthropology to increase quality control and scientific transparency.

Digging for underground storage organs of plants has been reported in various populations of wild chimpanzees (Pan troglodytes). However, it is unknown so far whether chimpanzees display lateral biases in manual digging as direct observations of this behavior are still lacking. It was therefore the aim of the present study to assess, for the first time, hand preferences for digging in a group of nine captive chimpanzees. We found that with only one exception, all individuals engaged in manual digging for buried food. Five individuals displayed a significant right-hand preference, two a significant left-hand preference, and one was ambidextrous. No apparent differences between males and females were found with regard to the direction or strength of hand preferences for manual digging. Only one out of four parent–offspring pairs was congruent in their preferred hand for manual digging. Three of the eight chimpanzees who dug manually also used tools in order to excavate buried food. Among those three individuals, one displayed a significant right-, one a significant left-hand preference, and one was ambidextrous. Only one of these three chimpanzees was consistent in preferring the same hand for manual and tool digging. The present findings are in line with the notion that chimpanzees display significant hand preferences at the individual level for haptic-guided behaviors, with a tendency for the right hand.

To support their claim for technical reasoning skills rather than imitation as the key for cumulative technological culture (CTC), Osiurak and Reynaud argue that chimpanzees can imitate mechanical actions, but do not have CTC. They also state that an increase in working memory in human evolution could not have been a key driver of CTC. We discuss why we disagree with these claims.