Human children rely more on social information than chimpanzees do

Human societies are characterized by more cultural diversity than chimpanzee communities. However, it is currently unclear what mechanism might be driving this difference. Because reliance on social information is a pivotal characteristic of culture, we investigated individual and social information reliance in children and chimpanzees. We repeatedly presented subjects with a reward-retrieval task on which they had collected conflicting individual and social information of equal accuracy in counterbalanced order. While both species relied mostly on their individual information, children but not chimpanzees searched for the reward at the socially demonstrated location more than at a random location. Moreover, only children used social information adaptively when individual knowledge on the location of the reward had not yet been obtained. Social information usage determines information transmission and in conjunction with mechanisms that create cultural variants, such as innovation, it facilitates diversity. Our results may help explain why humans are more culturally diversified than chimpanzees.     

‘Ghost’ experiments and the dissection of social learning in humans and animals

The focus of this review is the experimental techniques used to identify forms of social learning shown by humans and nonhuman animals. Specifically, the ‘ghost display’ and ‘end‐state’ conditions, which have been used to tease apart imitative and emulative learning are evaluated. In a ghost display, the movements of an apparatus are demonstrated, often through the discrete use of fishing‐line or hidden mechanisms, without a live model acting directly upon the apparatus so that the apparatus appears to be operated as if by a ‘ghostly’ agent. In an end‐state condition, an observing individual is shown the initial state of the test apparatus, the apparatus is then manipulated out‐of‐sight and then represented to the individual in its final state. The aim of the ghost display condition is to determine whether individuals are able to emulate by replicating the movements of an apparatus, or perform a task, without requiring information about the bodily movements required to do so (imitation). The end‐state condition is used to identify goal‐emulation by assessing whether the observer can replicate the steps required to solve the task without having been shown the required body actions or task movements. The responses of individuals tested with either the ghost display and/or end‐state conditions are compared to those of further individuals who have observed a full demonstration by either a human experimenter or a conspecific. The responses of a control group, to whom no information has been provided about the test apparatus or required actions, are also compared and evaluated. The efficacy of these experimental techniques employed with humans, nonhuman primates, dogs, rats and birds are discussed and evaluated. The experiments reviewed herein emphasise the need to provide ghost displays and end‐state conditions in combination, along with full live demonstrations and a no‐information control. Future research directions are proposed.     

Multiple classification performance of juvenile chimpanzees,normal children,and retarded children

The cognitive capacities of juvenile chimpanzees, normal children, and retarded children were evaluated by using a nonverbal, Piagetian-type multiple classification task. The three groups of subjects were tested with the same two by two stimulus matrix, which was formed by combining two different colors with two different shapes. On each problem the subjects were required to select one of four stimulus items from the response tray and place it inside the empty cell of the stimulus matrix. It was found that the human and nonhuman primates tested were able to select objects with correct color and shape cues (C⁺/S⁺)significantly more often than the other objects with only color cues correct (C⁺/S^-), only shape cues correct (C^-/S⁺), or neither cue correct (C^-/S^-). Although the two groups of human children were able to select the C⁺/S⁺ objects about 100% of the time by the end of testing, the normal children required significantly fewer problems than the retarded children. The juvenile chimpanzees needed significantly more problems than the human subjects before they consistently selected the C⁺/S⁺ object on the first trial and attained a level of correct responding that was above chance. Moreover, their level of performance did not exceed 70% correct. These data suggest that the human children (both normal and retarded) used a conceptual strategy, while the juvenile chimpanzees employed a perceptual strategy to solve the multiple classification problems. The relationship between language and conceptual problem-solving strategies for Piagetiantype tasks is discussed. Portions of the data reported in this study were presented at the Annual Meeting of the Southern Psychological Association, Atlanta, Georgia, March 15–18, 1978.     

Coordination strategies of chimpanzees and human children in a Stag Hunt game

Much of human cooperation takes place in mutualistic contexts in which the main challenge for individuals is how to coordinate decisions. In the current studies, we compared the abilities of chimpanzees and young children to coordinate with a partner in two versions of a Stag Hunt game. When risks were low (the hare was of low value) and information was cheap (the partner''s behaviour was readily observable), partners of both species were able to successfully coordinate on the higher value stag more than 90% of the time. By contrast, when the risks were raised and observing the partner was more difficult, the chimpanzees became less successful, whereas the children compensated, and so remained highly successful, by communicating more often and more specifically. This pattern of results is consistent with the hypothesis that humans evolved unique skills of coordination and communication in the context of especially risky coordination problems.     

Dialects in wild chimpanzees?

Chimpanzees emit a loud, species-typical long distance call known as the pant hoot. Geographic variation between the pant hoots of chimpanzees living in two neighboring populations, the Mahale Mountains and Gombe Stream National Parks, Tanzania, was examined. Analysis of six acoustic features revealed subtle differences in the way chimpanzees from the two populations called. Individuals from the Mahale study site uttered one section of their pant hoots at a faster rate and with shorter elements than animals from Gombe Stream. In addition, individuals at Mahale delivered broader-band, higher pitched “climax” elements than males from Gombe. While genetic factors, anatomical differences, variations in the use of calls at the two sites, and changes in calling over time may account for the variability between populations, we suggest the additional possibility that differences in pant hooting may be due to learning. © 1992 Wiley-Liss, Inc.     

Inhibition of social behavior in chimpanzees under high-density conditions

This is the first study to investigate the short-term effects of high population density on captive chimpanzees (Pan troglodytes). Subjects of the study were 45 chimpanzees living in five different groups at the Yerkes Regional Primate Research Center. The groups were observed under two conditions: 1) when they had access to both the indoor and outdoor sections of their enclosures; 2) during cold days when they were locked into the indoor runs, which reduced the available space by more than half. Under the high-density condition, allogrooming and submissive greetings decreased, but juvenile play increased. Remarkably, the rate of various forms of agonistic behavior, such as aggression, bluff charge, bluff display, and hooting, occurred less frequently under the high-density condition. This general decrease in adult social activity, including agonistic behavior, can be interpreted as an inhibition strategy to reduce opportunities for conflict when interindividual distances are reduced. This strategy is probably effective only in the short run, however. Behavioral indicators of anxiety, such as rough scratching and yawning, showed elevated rates, suggesting increased social tension under the high-density condition. Am. J. Primatol. 41:213–228, 1997. © 1997 Wiley-Liss, Inc.     

The scope of culture in chimpanzees, humans and ancestral apes

More studies have focused on aspects of chimpanzee behaviour and cognition relevant to the evolution of culture than on any other species except our own. Accordingly, analysis of the features shared by chimpanzees and humans is here used to infer the scope of cultural phenomena in our last common ancestor, at the same time clarifying the nature of the special characteristics that advanced further in the hominin line. To do this, culture is broken down into three major aspects: the large scale, population-level patterning of traditions; social learning mechanisms; and the behavioural and cognitive contents of culture. Each of these is further dissected into subcomponents. Shared features, as well as differences, are identified in as many as a dozen of these, offering a case study for the comparative analysis of culture across animal taxa and a deeper understanding of the roots of our own cultural capacities.     

Observational learning in orangutan cultural transmission chains

Field reports suggest that orangutans acquire local traditions by observing neighbouring conspecifics. However, there is little direct evidence of social learning to support this conclusion. The present study investigated whether orangutans would learn a novel foraging method through observation of a conspecific in a diffusion-chain paradigm testing for the spread of the behaviour. A foraging box with two possible methods for extracting food was used to investigate the transmission of a foraging tradition among zoo-living subjects. In a socially housed group of five orangutans, the dominant male was trained to use one technique exclusively to retrieve food. He then performed this technique in the presence of another group member, who was then allowed to forage. After several trials, the observer became the model for the next individual. A second experimental group of six individuals was introduced to the alternative method. The model-seeded technique was successfully transmitted along both experimental chains, with significant preferences for the model method. These results are consistent with claims for social transmission of foraging methods in wild orangutans.     

Responses to novel foods in captive chimpanzees

Hesitancy to eat novel foods hampers the immediate enlargement of the diet but serves to limit the risk of ingesting toxic foods. Neophobia has been systematically investigated in only a few primate species, in which it appears to be affected by social influences. Surprisingly, little is known about neophobia in chimpanzees. We studied the response of eight adult captive chimpanzees to 16 foods (foods commonly eaten by humans and never tasted before by chimpanzees). Each novel food was presented twice to the chimpanzee by a familiar or an unfamiliar human. Between the two trials the human ate the food face to face with the chimpanzee (demonstration). Results showed that some foods were almost unanimously accepted, whereas others were not. Moreover, there were marked interindividual differences in food acceptance and consumption; chimpanzees ranged from being almost completely neophobic to accepting almost all foods. Familiarity with the human and the human's demonstration did not affect responses to the foods. The humans' predictions concerning the chimpanzees' acceptance of the different foods were rather good; furthermore, in seven cases out of eight the humans' preferences did not correlate with their predictions on the chimpanzees' preferences. The finding that most captive chimpanzees are initially cautious toward novel foods supports the little information there is regarding this subject in wild chimpanzees. However, the lack of influence of the humans' familiarity and demonstration on the response to food by the chimpanzees calls for more naturalistic studies, in which social influences are provided by group members. Since novel stimuli provide sensory stimulation and elicit exploration and social interest, occasional presentation of novel foods could be a promising and cheap device for feeding enrichment. Zoo Biol 21:539–548, 2002. © 2002 Wiley‐Liss, Inc.     

Effects of early rearing conditions on problem‐solving skill in captive male chimpanzees (Pan troglodytes)

Early rearing conditions of captive chimpanzees characterize behavioral differences in tool use, response to novelty, and sexual and maternal competence later in life. Restricted rearing conditions during early life hinder the acquisition and execution of such behaviors, which characterize the daily life of animals. This study examined whether rearing conditions affect adult male chimpanzees' behavior skills used for solving a problem with acquired locomotion behavior. Subjects were 13 male residents of the Chimpanzee Sanctuary Uto: 5 wild‐born and 8 captive‐born. A pretest assessed bed building and tool use abilities to verify behavioral differences between wild‐ and captive‐born subjects, as earlier reports have described. Second, a banana‐access test was conducted to investigate the problem‐solving ability of climbing a bamboo pillar for accessing a banana, which might be the most efficient food access strategy for this setting. The test was repeated in a social setting. Results show that wild‐born subjects were better able than captive‐born subjects to use the provided materials for bed building and tool use. Results of the banana‐access test show that wild‐born subjects more frequently used a bamboo pillar for obtaining a banana with an efficient strategy than captive‐born subjects did. Of the eight captive‐born subjects, six avoided the bamboo pillars to get a banana and instead used, sometimes in a roundabout way, an iron pillar or fence. Results consistently underscored the adaptive and sophisticated skills of wild‐born male chimpanzees in problem‐solving tasks. The rearing conditions affected both the behavior acquisition and the execution of behaviors that had already been acquired. Am. J. Primatol. 72:626–633, 2010. © 2010 Wiley‐Liss, Inc.     

Prelinguistic development of children and chimpanzees

What was unique about our laboratory was the detailed simulation of a human rearing environment for infant chimpanzees, together with continuous, intensive observation and recording of behavioral development. Communication in American Sign Language (ASL) was integrated into this procedure in a way that simulates the teaching of vocal and gestural languages to human children. The result is a comprehensive longitudinal record of the stage by stage development of two-way communication in sign language and its relation to basic aspects of behavioral development such as: locomotion, manipulative skills, observational learning, and social play. In the longitudinal records of five infant chimpanzees, we can trace the patterns of development and also examine the consistency of individual differences through the first five years. The central question is the relation between developing skills in the use of American Sign Language and the rest of behavioral development. To analyze factors that influence development, we have compared records for infant chimpanzees reared in the crossfostering laboratory with records for chimpanzees reared in the wild by their own mothers and chimpanzees reared in cages under conventional laboratory conditions, as well as with records of development for human children, reared in homes and reared in institutions.     

An evaluation of the efficacy of video displays for use with chimpanzees (Pan troglodytes)

Video displays for behavioral research lend themselves particularly well to studies with chimpanzees (Pan troglodytes), as their vision is comparable to humans', yet there has been no formal test of the efficacy of video displays as a form of social information for chimpanzees. To address this, we compared the learning success of chimpanzees shown video footage of a conspecific compared to chimpanzees shown a live conspecific performing the same novel task. Footage of an unfamiliar chimpanzee operating a bidirectional apparatus was presented to 24 chimpanzees (12 males, 12 females), and their responses were compared to those of a further 12 chimpanzees given the same task but with no form of information. Secondly, we also compared the responses of the chimpanzees in the video display condition to responses of eight chimpanzees from a previously published study of ours, in which chimpanzees observed live models. Chimpanzees shown a video display were more successful than those in the control condition and showed comparable success to those that saw a live model. Regarding fine-grained copying (i.e. the direction that the door was pushed), only chimpanzees that observed a live model showed significant matching to the model's methods with their first response. Yet, when all the responses made by the chimpanzees were considered, comparable levels of matching were shown by chimpanzees in both the live and video conditions.     

Innovation in chimpanzees

The study of innovation in non‐human animals (henceforth: animals) has recently gained momentum across fields including primatology, animal behaviour and cultural evolution. Examining the rate of innovations, and the cognitive mechanisms driving these innovations across species, can provide insights into the evolution of human culture. Especially relevant to the study of human culture is one of our closest living relatives, the chimpanzee (Pan troglodytes). Both wild and captive chimpanzees demonstrate an impressive ability to innovate solutions to novel problems, but also a striking level of conservatism in some contexts, creating a unique and at times puzzling, picture of animal innovation. Whilst the animal innovation field is rife with potential for expanding our knowledge of human and non‐human cognition and problem‐solving, it is undermined by a lack of consistency across studies. The field is yet to settle on a definition of the term ‘innovation’, leading to studies being incomparable across and even within the same species. Here, we fill two gaps in the literature. First, we discuss some of the most prevalent definitions of ‘innovation’ from different fields, highlighting similarities and differences between them. Secondly, we provide an up‐to‐date review of accounts of innovations in both wild and captive chimpanzees. We hope this review will provide a resource for researchers interested in the study of innovation in chimpanzees and other animals, as well as emphasising the need for consistency in the way in which innovations are reported.     

Poliomyelitis and skeletal asymmetry in Gombe chimpanzees

Skeletons of free-ranging chimpanzees from Gombe National Park, Tanzania allow assessment of the effects of long-term, unilateral upper limb paralysis due to the infectious viral disease, poliomyelitis. Comparison of left and right upper limb bone weights, lengths, joint areas, and diaphysial diameters between two adult females with long-term, partial paralysis and a group of unaffected adult Gombe chimpanzees show that the disease caused considerable asymmetries in the skeleton. Detailed analyses of mineral content and diaphysial cross-sectional geometry of the humerus in the affected females show individual differences. The analysis extends to consideration of bone-muscle relationships and peripheral and central nervous system involvement. For each individual, sex, estimated age at death, and behavioral information during life are known from field studies. The impact of the disease on survival and reproductive outcome of the affected individuals is discussed.     

A potent effect of observational learning on chimpanzee tool construction

Although tool use occurs in diverse species, its complexity may mark an important distinction between humans and other animals. Chimpanzee tool use has many similarities to that seen in humans, yet evidence of the cumulatively complex and constructive technologies common in human populations remains absent in free-ranging chimpanzees. Here we provide the first evidence that chimpanzees have a latent capacity to socially learn to construct a composite tool. Fifty chimpanzees were assigned to one of five demonstration conditions that varied in the amount and type of information available in video footage of a conspecific. Chimpanzees exposed to complete footage of a chimpanzee combining the two components to retrieve a reward learned to combine the tools significantly more than those exposed to more restricted information. In a follow-up test, chimpanzees that constructed tools after watching the complete demonstration tended to do so even when the reward was within reach of the unmodified components, whereas those that spontaneously solved the task (without seeing the modification process) combined only when necessary. Social learning, therefore, had a powerful effect in instilling a marked persistence in the use of a complex technique at the cost of efficiency, inhibiting insightful tool use.     

Innovative social behavior in chimpanzees (Pan troglodytes)

We present evidence of agonistic buffering in captive chimpanzees, recorded from 1993 until 2005, mainly from ad libitum sampling in over 2000 hr of observation. A total of 33 agonistic buffering episodes were analyzed for context and effects of this complex social behavior. Agonistic buffering was directed at the whole chimpanzee colony as they supported an individual who initially received aggression from the alpha male, independently of the victim's age, sex or social rank. Chimpanzee agonistic buffering behavior is compared with that in other nonhuman primate species, and we describe some particularities of chimpanzee agonistic buffering: the status of the buffers used-socially important offspring such as those from the alpha female-and the social rank of the adult male responsible for the buffering episode-alpha male. Possible functions for this behavior in chimpanzees are suggested as appeasement of group members in a particularly crowded captive setting, and/or as a "forced reconciliation" mechanism. Chimpanzees exhibit behavioral flexibility by adapting themselves to new social and physical situations and use novel behavior to achieve social benefits.     

Species and sex differences in the screams of chimpanzees and bonobos

We examined screams of chimpanzees and bonobos to investigate interspecific and intraspecific variability in call structure. Measurement of 11 acoustic features of screams revealed differences between and within species. One-way analyses of variance and discriminant function analyses show that the calls of chimpanzees and bonobos differ primarily in spectral characteristics. Spectral features also account for acoustic differences between the sexes. These acoustic variations may be attributable to differences in body size and social dispersion between the two species and sexes. The effectiveness with which an acoustic feature could be used to discriminate the two species and female bonobos from male bonobos is negatively associated with its relative variability. These data are consistent with the hypothesis that optimal signals for group identification vary little within groups but differ widely between groups.     

Molecular analyses of the intestinal microbiota of chimpanzees in the wild and in captivity

Little information is available regarding the intestinal bacteria of chimpanzees in the wild, due to the technical difficulties of studying intestinal bacteria in the field. In this study, molecular-based bacterial analyses were performed to overcome this difficulty because polymerase chain reaction (PCR)-based methods, such as temperature gradient gel electrophoresis (TGGE) and amplified ribosomal DNA restriction analysis (ARDRA), of the bacterial 16S rRNA gene can be applied to ethanol-fixed fecal samples. The common presence of bacteria belonging to the Clostridium rRNA sub-group XIVa, such as Ruminococcus obeum and Eubacterium sp., was indicated for Bossou wild chimpanzees by ARDRA. TGGE on partial 16S rDNA followed by hierarchical clustering analysis showed a systematic difference in the composition of intestinal microbiota between wild and captive chimpanzees. However, several TGGE bands commonly shared by wild and captured chimpanzees were excised, and their sequences were obtained. They were suggested to be the Clostridium leptum subgroup bacteria, Lactobacillus gasseri-like bacterium, and Bifidobacterium pseudocatenulatum- or B. catenulatum-like bacterium. These may be considered as common intestinal bacteria for chimpanzees, and may be transmitted vertically over generations.