Thibaud Gruber

Social network analysis shows direct evidence for social transmission of tool use in wild chimpanzees.

Network-based diffusion analysis demonstrates that a novel tool-use behavior, “moss-sponging”, spread via social learning in a wild East-African chimpanzee community.

Wild Chimpanzees Rely on Cultural Knowledge to Solve an Experimental Honey Acquisition Task

Population and group-specific behavioral differences have been taken as evidence for animal cultures, a notion that remains controversial. Skeptics argue that ecological or genetic factors, rather than social learning, provide a more parsimonious explanation. Work with captive chimpanzees has addressed this criticism by showing that experimentally created traditions can be transmitted through social learning. Recent fieldwork further suggests that ecological and genetic factors are insufficient to explain the behavioral differences seen between communities, but the data are only observational. Here, we present the results of a field experiment that compared the performance of chimpanzees (P. t. schweinfurthii) from two Ugandan communities, Kanyawara and Sonso, on an identical task in the physical domain-extracting honey from holes drilled into horizontal logs. Kanyawara chimpanzees, who occasionally use sticks to acquire honey, spontaneously manufactured sticks to extract the experimentally provided honey. In contrast, Sonso chimpanzees, who possess a considerable leaf technology but no food-related stick use, relied on their fingers, but some also produced leaf sponges to access the honey. Our results indicate that, when genetic and environmental factors are controlled, wild chimpanzees rely on their cultural knowledge to solve a novel task.

A comparison of bonobo and chimpanzee tool use: evidence for a female bias in the Pan lineage

Chimpanzees, Pan troglodytes, are the most sophisticated tool-users among all nonhuman primates. From an evolutionary perspective, it is therefore puzzling that the tool use behaviour of their closest living primate relative, the bonobo, Pan paniscus, has been described as particularly poor. However, only a small number of bonobo groups have been studied in the wild and only over comparably short periods. Here, we show that captive bonobos and chimpanzees are equally diverse tool-users in most contexts. Our observations illustrate that tool use in bonobos can be highly complex and no different from what has been described for chimpanzees. The only major difference in the chimpanzee and bonobo data was that bonobos of all age–sex classes used tools in a play context, a possible manifestation of their neotenous nature. We also found that female bonobos displayed a larger range of tool use behaviours than males, a pattern previously described for chimpanzees but not for other great apes. Our results are consistent with the hypothesis that the female-biased tool use evolved prior to the split between bonobos and chimpanzees.

Community-specific evaluation of tool affordances in wild chimpanzees

The notion of animal culture, defined as socially transmitted community-specific behaviour patterns, remains controversial, notably because the definition relies on surface behaviours without addressing underlying cognitive processes. In contrast, human cultures are the product of socially acquired ideas that shape how individuals interact with their environment. We conducted field experiments with two culturally distinct chimpanzee communities in Uganda, which revealed significant differences in how individuals considered the affording parts of an experimentally provided tool to extract honey from a standardised cavity. Firstly, individuals of the two communities found different functional parts of the tool salient, suggesting that they experienced a cultural bias in their cognition. Secondly, when the alternative function was made more salient, chimpanzees were unable to learn it, suggesting that prior cultural background can interfere with new learning. Culture appears to shape how chimpanzees see the world, suggesting that a cognitive component underlies the observed behavioural patterns.

Vocal Recruitment for Joint Travel in Wild Chimpanzees

Joint travel is a common social activity of many group-living animals, which requires some degree of coordination, sometimes through communication signals. Here, we studied the use of an acoustically distinct vocalisation in chimpanzees, the ‘travel hoo’, a signal given specifically in the travel context. We were interested in how this call type was produced to coordinate travel, whether it was aimed at specific individuals and how recipients responded. We found that ‘travel hoos’ were regularly given prior to impending departures and that silent travel initiations were less successful in recruiting than vocal initiations. Other behaviours associated with departure were unrelated to recruitment, suggesting that ‘travel hoos’ facilitated joint travel. Crucially, ‘travel hoos’ were more often produced in the presence of allies than other individuals, with high rates of recruitment success. We discuss these findings as evidence for how motivation to perform a specific social activity can lead to the production of a vocal signal that qualifies as ‘intentional’ according to most definitions, suggesting that a key psychological component of human language may have already been present in the common ancestor of chimpanzees and humans.

Female bonobos use copulation calls as social signals

During mating events, females of many primate species produce loud and distinct vocalizations known as ‘copulation calls’. The adaptive significance of these signals is considered to be in promoting the callers direct reproductive success. Here, we investigated copulation calling in bonobos (Pan paniscus), a species in which females produce these vocalizations during sexual interactions with partners of both sexes. Females were more likely to call when mating with males than with females. We also observed a positive relationship between the likelihood of calling and partner rank, regardless of partner sex. Sexual activity generally increased with swelling size (an indicator of reproductive state) and, during their peak swelling, females called more with male than with female partners. Female bonobos are unusual among the non-human primates in terms of their heightened socio-sexuality. Our results suggest that in this species, copulation calls have undergone an evolutionary transition from a purely reproductive to a more general social function, reflecting the intrinsic evolutionary links between vocal behaviour and social cognition.

A Comparison Between Bonobos and Chimpanzees: A Review and Update

Chimpanzees (Pan troglodytes) and bonobos (P. paniscus) are our closest living relatives, with the human lineage diverging from the Pan lineage only around five to seven Mya, but possibly as early as eight Mya.1–2 Chimpanzees and bonobos even share genetic similarities with humans that they do not share with each other.2 Given their close genetic relationship to humans, both Pan species represent crucial living models for reconstructing our last common ancestor (LCA) and identifying uniquely human features. Comparing the similarities and differences of the two Pan is thus essential for constructing balanced models of human evolution.3

Apes have culture but may not know that they do

There is good evidence that some ape behaviors can be transmitted socially and that this can lead to group-specific traditions. However, many consider animal traditions, including those in great apes, to be fundamentally different from human cultures, largely because of lack of evidence for cumulative processes and normative conformity, but perhaps also because current research on ape culture is usually restricted to behavioral comparisons. Here, we propose to analyze ape culture not only at the surface behavioral level but also at the underlying cognitive level. To this end, we integrate empirical findings in apes with theoretical frameworks developed in developmental psychology regarding the representation of tools and the development of metarepresentational abilities, to characterize the differences between ape and human cultures at the cognitive level. Current data are consistent with the notion of apes possessing mental representations of tools that can be accessed through re-representations: apes may reorganize their knowledge of tools in the form of categories or functional schemes. However, we find no evidence for metarepresentations of cultural knowledge: apes may not understand that they or others hold beliefs about their cultures. The resulting Jourdain Hypothesis, based on Molière’s character, argues that apes express their cultures without knowing that they are cultural beings because of cognitive limitations in their ability to represent knowledge, a determining feature of modern human cultures, allowing representing and modifying the current norms of the group. Differences in metarepresentational processes may thus explain fundamental differences between human and other animals’ cultures, notably limitations in cumulative behavior and normative conformity. Future empirical work should focus on how animals mentally represent their cultural knowledge to conclusively determine the ways by which humans are unique in their cultural behavior.

Great Apes Do Not Learn Novel Tool Use Easily: Conservatism, Functional Fixedness, or Cultural Influence?

Animal culture has been of interest for decades but the concept remains controversial. Many researchers feel that animal behavior should not be granted the label “culture” because the latter includes more than “simple” behavioral variation. In recent years, the study of animal culture has been concerned mainly with social learning mechanisms, often claimed to be human specific, which led to the uniqueness of human culture. In addition, failure to innovate novel cultural behavior as often as humans is usually explained by psychological mechanisms presented as more parsimonious, such as conservatism or functional fixedness. However, it is unclear how cognitively complex these mechanisms are in the first place. Here, I analyze recent data obtained with wild chimpanzees (Pan troglodytes schweinfurthii) and wild-born orangutans (Pongo abelii) using the honey-trap experiment, in which individuals must devise a solution to reach inaccessible honey. I compare behavior of apes that developed a tool-based solution in the task with those that did not, and test whether conservatism and functional fixedness can explain individual variation in ape behavior. I find evidence of conservatism, with apes relying on their existing knowledge, and evidence of functional fixedness, with this knowledge potentially preventing them from innovating. However, the apes showed large intraspecific variability. I discuss the two mechanisms through a representational perspective to tackle their cognitive complexity. Understanding how conservatism and functional fixedness interact with ape cultural knowledge to limit innovation of novel tool use appears necessary to understand the full extent of ape cultures and how they compare to human cultures.

Territorial reactions of male Yellowhammers (Emberiza citrinella) toward a specific song structure

Male songbirds assess their rivals by listening to their songs and, in some species, are especially sensitive to certain parts of the song. Yellowhammers (Emberiza citrinella) sing songs with different structures consisting of an initial phrase of stereotyped and repeated notes in a trill, and a terminal phrase, present or not, which consists of low or high frequency whistles that we called elements. We analyzed 1,055 songs from 25 different males and found that four different structures could be distinguished in a French Yellowhammer population. We found that the frequency ranges of the elements were more constant across individuals than the ranges of the notes, and among them, the low frequency element was nearly twice as conserved as the high frequency element. Then, in the wild, we tested the territorial responses of males to the four different structures and found that the full song structure, which is composed of the initial phrase followed by a high frequency element and a low frequency element, induced stronger territory defence responses from the males than any of the other structures. As only the structure containing the initial phrase and the low frequency element also induced a strong response, we propose that the main element responsible for the enhanced reaction of the males is the low frequency element, which is consistent with the fact that it is more conserved than the other constituents.