Chimpanzees use social information to acquire a skill they fail to innovate.

Cumulative cultural evolution has been claimed to be a uniquely human phenomenon pivotal to the biological success of our species. One plausible condition for cumulative cultural evolution to emerge is individuals' ability to use social learning to acquire know-how that they cannot easily innovate by themselves. It has been suggested that chimpanzees may be capable of such know-how social learning, but this assertion remains largely untested. Here we show that chimpanzees use social learning to acquire a skill that they failed to independently innovate. By teaching chimpanzees how to solve a sequential task (one chimpanzee in each of the two tested groups, n = 66) and using network-based diffusion analysis, we found that 14 naive chimpanzees learned to operate a puzzle box that they failed to operate during the preceding three months of exposure to all necessary materials. In conjunction, we present evidence for the hypothesis that social learning in chimpanzees is necessary and sufficient to acquire a new, complex skill after the initial innovation.

Chimpanzees engage in competitive altruism in a triadic ultimatum game.

Partner choice promotes competition among individuals to be selected as a cooperative partner, a phenomenon referred to as competitive altruism. We explored whether chimpanzees engage in competitive altruism in a triadic Ultimatum Game where two proposers can send offers simultaneously or consecutively to a responder who can only accept one of the two competing offers. In a dyadic control condition only one proposer at a time could send an offer to the responder. Chimpanzees increased their offers across trials in the competitive triadic, but not in the dyadic control condition. Chimpanzees also increased their offers after being rejected in previous triadic trials. Furthermore, we found that chimpanzees, under specific conditions, outcompete first proposers in triadic consecutive trials before the responder could choose which offer to accept by offering more than what is expected if they acted randomly or simply offered the smallest possible amount. These results suggest that competitive altruism in chimpanzees did not emerge just as a by-product of them trying to increase over previous losses. Chimpanzees might consider how others' interactions affect their outcomes and engage in strategies to maximize their chances of being selected as cooperative partners.

TANGO: A reliable, open-source, browser-based task to assess individual differences in gaze understanding in 3 to 5-year-old children and adults.

Traditional measures of social cognition used in developmental research often lack satisfactory psychometric properties and are not designed to capture variation between individuals. Here, we present the TANGO (Task for Assessing iNdividual differences in Gaze understanding-Open); a brief (approx. 5-10min), reliable, open-source task to quantify individual differences in the understanding of gaze cues. Localizing the attentional focus of an agent is crucial in inferring their mental states, building common ground, and thus, supporting cooperation. Our interactive browser-based task works across devices and enables in-person and remote testing. The implemented spatial layout allows for discrete and continuous measures of participants' click imprecision and is easily adaptable to different study requirements. Our task measures inter-individual differences in a child (N = 387) and an adult (N = 236) sample. Our two study versions and data collection modes yield comparable results that show substantial developmental gains: the older children are, the more accurately they locate the target. High internal consistency and test-retest reliability estimates underline that the captured variation is systematic. Associations with social-environmental factors and language skills speak to the validity of the task. This work shows a promising way forward in studying individual differences in social cognition and will help us explore the structure and development of our core social-cognitive processes in greater detail.

Direct and Observed Joint Attention Modulate 9-Month-Old Infants' Object Encoding.

Sharing joint visual attention to an object with another person biases infants to encode qualitatively different object properties compared to a parallel attention situation lacking interpersonal sharedness. This study investigated whether merely observing joint attention amongst others shows the same effect. In Experiment 1 (first-party replication experiment), N = 36 9-month-old German infants were presented with a violation-of-expectation task during which they saw an adult looking either in the direction of the infant (eye contact) or to the side (no eye contact) before and after looking at an object. Following an occlusion phase, infants saw one of three different outcomes: the same object reappeared at the same screen position (no change), the same object reappeared at a novel position (location change), or a novel object appeared at the same position (identity change). We found that infants looked longer at identity change outcomes (vs. no changes) in the "eye contact" condition compared to the "no eye contact" condition. In contrast, infants' response to location changes was not influenced by the presence of eye contact. In Experiment 2, we found the same result pattern in a matched third-party design, in which another sample of N = 36 9-month-old German infants saw two adults establishing eye contact (or no eye contact) before alternating their gaze between an object and their partner without ever looking at the infant. These findings indicate that infants learn similarly from interacting with others and observing others interact, suggesting that infant cultural learning extends beyond infant-directed interactions.

Testing Causal Effects of Empathy on Children's Prosociality in Politeness Dilemmas - An Intervention Study.

Empathy is commonly considered a driver of prosociality in child ontogeny, but causal assumptions regarding this effect mostly rely on correlational research designs. Here, 96 urban German children (5-8 years; 48 girls; predominantly White; from mid-to-high socioeconomic backgrounds) participated in an empathy intervention or a control condition before prosocial behaviors (polite lie-telling: rating the drawing as good; prosocial encouragement: utterances interpreted as cheering up the artist) were assessed in an art-rating task. Contrasting children's empathy at baseline with their empathy after the intervention indicated promoted empathy compared to the control group. Despite the intervention's effect on children's empathy, there were no simultaneous changes in prosocial behaviors. At the same time, children's empathy at baseline was associated with their prosocial encouragement. These results indicate conceptual associations between children's empathy and prosociality. However, they do not support strict causal claims regarding this association in middle childhood. Further applications of the novel short-time intervention to address causal effects of empathy on prosociality and other developmental outcomes are discussed.

Great ape cognition is structured by stable cognitive abilities and predicted by developmental conditions.

Great ape cognition is used as a reference point to specify the evolutionary origins of complex cognitive abilities, including in humans. This research often assumes that great ape cognition consists of cognitive abilities (traits) that account for stable differences between individuals, which change and develop in response to experience. Here, we test the validity of these assumptions by assessing repeatability of cognitive performance among captive great apes (Gorilla gorilla, Pongo abelii, Pan paniscus, Pan troglodytes) in five tasks covering a range of cognitive domains. We examine whether individual characteristics (age, group, test experience) or transient situational factors (life events, testing arrangements or sociality) influence cognitive performance. Our results show that task-level performance is generally stable over time; four of the five tasks were reliable measurement tools. Performance in the tasks was best explained by stable differences in cognitive abilities (traits) between individuals. Cognitive abilities were further correlated, suggesting shared cognitive processes. Finally, when predicting cognitive performance, we found stable individual characteristics to be more important than variables capturing transient experience. Taken together, this study shows that great ape cognition is structured by stable cognitive abilities that respond to different developmental conditions.

Simulating peers: Can puppets simulate peer interactions in studies on children's socio-cognitive development?

Interactions with peers are fundamental to socio-cognitive development, but assessing peer interactions in standardized experiments is challenging. Therefore, researchers commonly utilize puppetry to simulate peers. This Registered Report investigated urban German children's (AgeRange  = 3.5-4.5 years; N = 144; 76♀) mind ascriptions and social cognition to test whether they treat puppets like peers, adults, or neither. Children attributed less mind properties to puppets than peers or adults. However, children's social cognition (i.e., normativity, prosociality, and theory of mind) varied little across partners. Puppetry relies on children's ability for pretense, but can provide valid insights into socio-cognitive development. Implications for using puppets as stand-ins for peers in developmental research are discussed.

Copying fideliy of functional and non-functional features in ni-Vanuatu children: A transmission chain study.

Observational learning plays a key role in cultural transmission. Previous transmission chain experiments have shown that children are able to maintain information across multiple generations through observational learning. It still remains unclear how the transmission of functional vs. non-functional information and the effect of being observed unfold across age in different communities. Here, we examine children's copying fidelity in observational learning of 5- to 13-year-olds from five different communities in Vanuatu, both individually (n = 263, 144 boys) and throughout a transmission chain of five to six children (n = 324, 178 boys). We additionally varied the functionality of the feature being copied (shape vs. color) and the copying context (observed vs. unobserved). Further, we also study developmental and cultural variation in the interaction of features and conditions. We find that children transmit the functional feature shape more faithfully than the non-functional feature color, both in the dyadic transitions as well as the transmission chains with an increasing tendency to do so as they get older. The age patterns show greater variation between communities for color than for shape. Overall, we find that being observed shows no uniform effects but influences transmission differently across communities. Our study shows that children are prone to passing on a functional feature across multiple generations of peers. Children copy non-functional features as well, but with lower fidelity. In sum, our results show children's high propensity and developing abilities for observational learning, ultimately allowing for effective cultural transmission.

Children over-imitate adults and peers more than puppets.

Researchers commonly use puppets in development science. Amongst other things, puppets are employed to reduce social hierarchies between child participants and adult experimenters akin to peer interactions. However, it remains controversial whether children treat puppets like real-world social partners in these settings. This study investigated children's imitation of causally irrelevant actions (i.e., over-imitation) performed by puppet, adult, or child models. Seventy-two German children (AgeRange  = 4.6-6.5 years; 36 girls) from urban, socioeconomically diverse backgrounds observed a model retrieving stickers from reward containers. The model performed causally irrelevant actions either in contact with the reward container or not. Children were more likely to over-imitate adults' and peers' actions as compared to puppets' actions. Across models, they copied contact actions more than no-contact actions. While children imitate causally irrelevant actions from puppet models to some extent, their social learning from puppets does not necessarily match their social learning from real-world social agents, such as children or adults. RESEARCH HIGHLIGHTS: We examined children's over-imitation from adult, child, and puppet models to validate puppetry as an approach to simulate non-hierarchical interactions. Children imitated adults and child models at slightly higher rates than puppets. This effect was present regardless of whether the irrelevant actions involved physical contact to the reward container or not. In our study children's social learning from puppets does not match their social learning from human models.

Brain structure and function: a multidisciplinary pipeline to study hominoid brain evolution.

To decipher the evolution of the hominoid brain and its functions, it is essential to conduct comparative studies in primates, including our closest living relatives. However, strong ethical concerns preclude in vivo neuroimaging of great apes. We propose a responsible and multidisciplinary alternative approach that links behavior to brain anatomy in non-human primates from diverse ecological backgrounds. The brains of primates observed in the wild or in captivity are extracted and fixed shortly after natural death, and then studied using advanced MRI neuroimaging and histology to reveal macro- and microstructures. By linking detailed neuroanatomy with observed behavior within and across primate species, our approach provides new perspectives on brain evolution. Combined with endocranial brain imprints extracted from computed tomographic scans of the skulls these data provide a framework for decoding evolutionary changes in hominin fossils. This approach is poised to become a key resource for investigating the evolution and functional differentiation of hominoid brains.

Chimpanzees organize their social relationships like humans.

Human relationships are structured in a set of layers, ordered from higher (intimate relationships) to lower (acquaintances) emotional and cognitive intensity. This structure arises from the limits of our cognitive capacity and the different amounts of resources required by different relationships. However, it is unknown whether nonhuman primate species organize their affiliative relationships following the same pattern. We here show that the time chimpanzees devote to grooming other individuals is well described by the same model used for human relationships, supporting the existence of similar social signatures for both humans and chimpanzees. Furthermore, the relationship structure depends on group size as predicted by the model, the proportion of high-intensity connections being larger for smaller groups.

The ontogeny of children's social emotions in response to (un)fairness.

Humans have a deeply rooted sense of fairness, but its emotional foundation in early ontogeny remains poorly understood. Here, we asked if and when 4- to 10-year-old children show negative social emotions, such as shame or guilt, in response to advantageous unfairness expressed through a lowered body posture (measured using a Kinect depth sensor imaging camera). We found that older, but not younger children, showed more negative emotions, i.e. a reduced upper body posture, after unintentionally disadvantaging a peer on (4,1) trials than in response to fair (1,1) outcomes between themselves and others. Younger children, in contrast, expressed more negative emotions in response to the fair (1,1) split than in response to advantageous inequity. No systematic pattern of children's emotional responses was found in a non-social context, in which children divided resources between themselves and a non-social container. Supporting individual difference analyses showed that older children in the social context expressed negative emotions in response to advantageous inequity without directly acting on this negative emotional response by rejecting an advantageously unfair offer proposed by an experimenter at the end of the study. These findings shed new light on the emotional foundation of the human sense of fairness and suggest that children's negative emotional response to advantageous unfairness developmentally precedes their rejection of advantageously unfair resource distributions.

Expanding the understanding of majority-bias in children's social learning.

Prior experiments with children across seven different societies have indicated U-shaped age patterns in the likelihood of copying majority demonstrations. It is unclear which learning strategies underlie the observed responses that create these patterns. Here we broaden the understanding of children's learning strategies by: (1) exploring social learning patterns among 6-13-year-olds (n = 270) from ethnolinguistically varied communities in Vanuatu; (2) comparing these data with those reported from other societies (n = 629), and (3) re-analysing our and previous data based on a theoretically plausible set of underlying strategies using Bayesian methods. We find higher rates of social learning in children from Vanuatu, a country with high linguistic and cultural diversity. Furthermore, our results provide statistical evidence for modest U-shaped age patterns for a more clearly delineated majority learning strategy across the current and previously investigated societies, suggesting that the developmental mechanisms structuring majority bias are cross-culturally highly recurrent and hence a fundamental feature of early human social learning.

What isn't social tolerance? The past, present, and possible future of an overused term in the field of primatology.

In the past four decades, the term social tolerance has been utilized to describe, explain, and predict many different aspects of primates' sociality and has been measured with a large range of traits and behaviors. To date, however, there has been little discussion on whether these different phenomena all reflect one and the same construct. This paper opens the discussion by presenting the historical development of the term social tolerance and a structured overview of its current, overextended use. We argue that social tolerance has developed to describe two distinct concepts: social tolerance as the social structure of a group and social tolerance as the dyadic or group-level manifestation of tolerant behaviors. We highlight how these two concepts are based on conflicting theoretical understandings and practical assessments. In conclusion, we present suggestions for future research on primate social tolerance, which will allow for a more systematic and comparable investigation of primate sociality.

Early Trauma Leaves No Social Signature in Sanctuary-Housed Chimpanzees (Pan troglodytes).

Negative early experiences can have detrimental effects on social functioning in later life, both in humans as well as in other socially-living animals. In zoo-housed chimpanzees, recent evidence suggests that there may be a lingering signature of early trauma on individuals' social interaction tendencies as measured by social proximity and grooming. Here, we address whether a similar effect would be observable in chimpanzees living under semi-wild conditions in an African sanctuary. By analysing party size, close proximity and social grooming, we show that in this specific sanctuary, chimpanzees that suffered early trauma (n = 42) were socially indistinguishable from chimpanzees who were born and raised by their mothers in the sanctuary (n = 36). Our findings indicate that chimpanzees may not be irreversibly affected by early social trauma, possibly owing to rehabilitation in stable social groups in a semi-natural environment. Beyond identifying sanctuaries as valuable rehabilitation centres for orphaned chimpanzees, this study demonstrates a remarkable social flexibility in one of our closest living relatives.

Conformity decreases throughout middle childhood among ni-Vanuatu children: An intracultural comparison.

Multiple studies have shown that children conform to majorities in perceptual judgment tasks against their better knowledge. However, these studies report contradictory results about how conformity develops over age. Here, we study variation in conformity over the course of middle childhood: we examined potential informational and normative motivations underlying conformity, as well as intracultural variability in their age patterns. We measured conformity in both a public and a private setting among 5- to 11-year-olds from eight different communities in Vanuatu (n = 125, 59 boys), a highly diverse society in the South Pacific. We also explored whether selected sociodemographic variables help to explain individual variation in children's conformity. Conformity is lower in both public and private settings the older ni-Vanuatu children are, with conformity in public settings being subject to more developmental and intracultural variation. We infer that normative conformity is more variable than informational conformity. Moreover, we find that children in higher school classes conform less. Our study combines a developmental perspective with an intracultural comparison, and demonstrates that both the publicness of the experimental situation and intracultural variability are important for the understanding of the age patterns of conformity. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Games and enculturation: A cross-cultural analysis of cooperative goal structures in Austronesian games.

While most animals play, only humans play games. As animal play serves to teach offspring important life-skills in a safe scenario, human games might, in similar ways, teach important culturally relevant skills. Humans in all cultures play games; however, it is not clear whether variation in the characteristics of games across cultural groups is related to group-level attributes. Here we investigate specifically whether the cooperativeness of games covaries with socio-ecological differences across cultural groups. We hypothesize that cultural groups that engage in frequent inter-group conflict, cooperative sustenance acquisition, or that have less stratified social structures, might more frequently play cooperative games as compared to groups that do not share these characteristics. To test these hypotheses, we gathered data from the ethnographic record on 25 ethnolinguistic groups in the Austronesian language family. We show that cultural groups with higher levels of inter-group conflict and cooperative land-based hunting play cooperative games more frequently than other groups. Additionally, cultural groups with higher levels of intra-group conflict play competitive games more frequently than other groups. These findings indicate that games are not randomly distributed among cultures, but rather relate to the socio-ecological settings of the cultural groups that practice them. We argue that games serve as training grounds for group-specific norms and values and thereby have an important function in enculturation during childhood. Moreover, games might server an important role in the maintenance of cultural diversity.

Chimpanzees consider alternative possibilities.

Humans reason not only about actual events (what is), but also about possible events (what could be). Many key operations of human cognition involve the representation of possibilities, including moral judgment, future planning, and causal understanding1. But little is known about the evolutionary roots of this kind of thought. Humans' closest relatives, chimpanzees, possess several cognitive abilities that are closely related to reasoning about alternatives: they plan for the future2, evaluate other's actions3, and reason causally4. However, in the first direct test of the ability to consider alternatives, Redshaw and Suddendorf5 claim that chimpanzees are not able to represent alternative possibilities. Here, using a novel method, we challenge this conclusion: our results suggest that, like human cognition, chimpanzee thought is not limited to what is, but also involves reasoning about what could be the case.

Observing others' joint attention increases 9-month-old infants' object encoding.

In direct interactions with others, 9-month-old infants' learning about objects is facilitated when the interaction partner addresses the infant through eye contact before looking toward an object. In this study we investigated whether similar factors promote infants' observational learning from third-party interactions. In Experiment 1, 9-month-old typically developing infants from mixed socioeconomic backgrounds from urban Germany (N = 32, 13 female) were presented with four types of videos showing one object and two adults. The scenarios varied systematically regarding the eye contact between the adults (eye contact or no eye contact), and the adults' object-directed gaze (looking toward or away from the object). To assess infants' encoding performance we measured their looking times when seeing the familiarized object subsequently next to a novel object, interpreting an enhanced novelty preference as reversely indicating greater encoding of the familiarized object. Infants showed an increased novelty preference, but only after observing a joint attentional setting during which two adults attended to the familiarized object together (following eye contact). In Experiment 2, we found an identical pattern of results in a matched first-party design in which 9-month-old infants (N = 32, 16 female) were directly addressed by one single adult on screen. Infants' encoding was only enhanced when the adult made eye contact with the infant before looking at an object. Together, this suggests that the capacity to learn through observing others' interactions emerges already in the first postnatal year, and that it may depend on similar factors as infants' learning through direct social engagement. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Out of the empirical box: A mixed-methods study of tool innovation among Congolese BaYaka forager and Bondongo fisher-farmer children.

Tool innovation has played a crucial role in human adaptation. Yet, this capacity seems to arise late in development. Before 8 years of age, many children struggle to solve the hook task, a common measure of tool innovation that requires modification of a straight pipe cleaner into a hook to extract a prize. Whether these findings are generalizable beyond postindustrialized Western children remains unclear. In many small-scale subsistence societies, children engage in daily tool use and modification, experiences that theoretically could enhance innovative capabilities. Although two previous studies found no differences in innovative ability between children from Western and small-scale subsistence societies, these did not account for the latter's inexperience with pipe cleaners. Thus, the current study investigated how familiarity with pipe cleaners affected hook task success in 132 Congolese BaYaka foragers (57 girls) and 59 Bondongo fisher-farmers (23 girls) aged 4-12 years. We contextualized these findings within children's interview responses and naturalistic observations of how pipe cleaners were incorporated into daily activities. Counter to our expectation, prior exposure did not improve children's performance during the hook task. Bondongo children innovated significantly more hooks than BaYaka children, possibly because they participate in hook-and-line fishing. Observations and interviews showed that children imagined and innovated novel uses for pipe cleaners outside the experimental context, including headbands, bracelets, and suspenders. We relate our findings to ongoing debates regarding systematic versus unsystematic tool innovation, the importance of prior experience for the ontogeny of tool innovation, and the external validity of experimental paradigms.