Chimpanzees in Context


We have created a themed collection of the ePoster abstracts in collaboration with PeerJ, a respected open access publisher in the biological and medical sciences. To view any of the abstracts for the ePosters that will be presented at Lincoln Park Zoo on the evening of August 19th please visit this site:


Augustin Kanyunyi Basabose(1) and Eiji Inoue(2)

1. Laboratoire de Primatologie, Département de Biologie, Centre de Recherche en Sciences Naturelles de Lwiro, Democratic Republic of Congo

2. Human Evolution Studies Graduate School of Science, Kyoto University, Japan

Assessing the conservation status of a wild chimpanzee population in Kahuzi-Biega National Park, Democratic Republic of Congo, using non-invasive genetic methods  Long-term studies of eastern chimpanzees (Pan troglodytes schweinfurthii) and Grauer’s gorillas (Gorilla beringei graueri) have been conducted over three decades in Kahuzi-Biega National Park, Democratic Republic of Congo. Both apes are sympatric in a small area of montane forest. Because of incomplete habituation, there is little information about the chimpanzees’ population structure, making it difficult to assess their conservation status.  In this context, acquiring information on the Kahuzi chimpanzees is only possible by indirect observation using genetic markers obtained from fecal samples.  The genetic structure in Kahuzi was comparable to that of other chimpanzee populations and reflected the typical female-biased dispersal pattern. A relatively high heterozygosity and negative inbreeding coefficient were observed in microsatellite loci, suggesting that the study community belongs to an outbreeding population. These findings suggest that individuals of the Kahuzi chimpanzee community may have been in reproductive contacts with other individuals from neighboring communities, at least in the recent past. The montane forest of Kahuzi is connected with the lowland rainforest of this park through a corridor which is currently affected by human encroachment. Effort to protect that corridor is needed to enable regular reproductive contacts between chimpanzee populations living on both sides and thus preserve a viable genetic diversity in both populations. Additionally, genetic studies on other chimpanzee communities adjacent to the study group and those ranging in the lowland sector of the park are urgently needed. These studies will provide a broad understanding of Kahuzi chimpanzee genetic structure in comparison with that of the sympatric gorillas to better understand the threats they face and which may negatively impact their long-term survival.

Michael J. Beran(1), Bonnie M. Perdue(2) and Audrey E. Parrish(1)

1. Department of Psychology and Language Research Center, Georgia State University, USA

2. Department of Psychology, Agnes Scott College, USA

Cognitive control in chimpanzees Cognitive control involves a number of executive and regulatory processes including those that allocate attention, manipulate and evaluate available information (and, when necessary, seek additional information), plan future behaviors, and deal with distraction and impulsivity when they are threats to goal achievement. Cognitive control is a hallmark feature of human cognition, and recent comparative tests have shown that some nonhuman animals might share aspects of cognitive control with humans.  Two of the executive processes that constitute cognitive control are metacognition and self-control.  Metacognition refers to “thinking about thinking,” but more specifically it consists of control and monitoring processes that allow individuals to assess what information they have and what information they still need, and then seek information as needed.  Self-control is a regulatory process whereby individuals forego more immediate or easier to obtain rewards for more delayed or harder to obtain rewards that are objectively more valuable. Recent experiments with chimpanzees will be described that demonstrate these cognitive control processes and how they relate to such processes in other primate species. In one experiment, chimpanzees immediately named hidden food items that they already had seen, but they first looked at what the items were before trying to name them in conditions where the hidden item could not be known.  In another experiment, chimpanzees showed confidence in their responses to memory and semantic knowledge tests by moving early to a reward dispenser even before any external signals were given regarding whether their responses were correct or not.  Other experiments have shown that chimpanzees engaged in strategic responding in a self-control task by exhibiting self-distraction as an aid to delay of gratification, allowing them to exceed the performances of monkeys with that task. These demonstrations indicate continuity with human cognitive control capacities, and the performances of chimpanzees in these kinds of tests have implications for considering the nature of the intelligence of these animals and perhaps implications regarding states of conscious awareness in chimpanzees. 

Mollie Bloomsmith(1), Stephen R. Ross(2), Corrine K. Lutz(3), Andrea Clay(1), Maribel Vazquez(4), Sarah Jacobson(2), Kim Neu(1), and Jaine Perlman(1)

1. Yerkes National Primate Research Center, Emory University, USA

2. Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, USA

3. Primate Resources and Research Support, Southwest National Primate Research Center, USA

4. Biomedical Engineering, The City College of New York, USA

A simple chimpanzee welfare assessment tool: application across chimpanzees living in different types of facilities Collecting behavioral data is an essential element of monitoring the welfare of captive chimpanzees no matter where they live, and any comparisons between the varying sites in which chimpanzees live should be based on objectively-collected data. Information collected as a part of standard monitoring programs in chimpanzee facilities was collated through a survey which was designed to compile information related to individual chimpanzee welfare.  The survey includes questions about early rearing history, current social group size, features of enclosures, the presence of species-typical and abnormal behaviors, and use of positive reinforcement training methods. The survey has been completed by behavioral specialists, and could be completed by other staff members. The information in the survey can be drawn from quantitative behavioral data and/or less formal assessments based on staff observations. The survey can be completed for chimpanzees living in laboratories, zoos or sanctuaries. We present data representing a broad range of chimpanzee holding institutions including multiple zoos, laboratories and sanctuaries, and demonstrate the utility of this method to efficiently gather and compare information on chimpanzee welfare across multiple settings. The findings will inform future improvements in behavioral management to address existing behavioral problems in the captive chimpanzee population. 

Sarah Brosnan

Departments of Psychology & Philosophy, Neuroscience Institute, Georgia State University

Michale E. Keeling Center for Comparative Medicine and Research, UT MD Anderson Cancer Center

Cooperative decision-making in non-human primates Humans routinely confront situations that require coordination between individuals, from mundane activities such as planning where to go for dinner, to incredibly complicated activities, such as multi-national agreements.  How did this ability arise, and what prevents success in those situations in which it breaks down?  To understand how this capability evolved across the primate taxa, my lab uses the methodology of experimental economics.  This is an ideal mechanism for the comparative approach as it is a well-developed methodology for distilling complex decision-making in to a series of simple choices, allowing these decisions to be compared across species and contexts using identical methodologies. We have investigated coordination in New World monkeys, Old World monkeys, and great apes, including both chimpanzees and humans.  We find that there are remarkable continuities of outcome across the primates, including humans, however there are also important differences in how each species reaches these outcomes.  For example, while humans and other primates can find the same coordinated outcome, our research indicates that they are using different cognitive mechanisms to do so.  Additionally, in many primates, including humans, cooperation breaks down under conditions of inequity.  However, only humans and chimpanzees seem to be able to rectify inequity, presumably avoiding this breakdown and thereby maintaining a successful cooperative partnership.  This ability is undoubtedly the foundation of the much more complex sense of fairness that evolved uniquely in humans.  By carefully considering both the similarities and differences among species, we can better understand how cooperative decision-making emerged in the primates, and how each species relates to the others.

Hannah M. Buchanan-Smith(1), Sarah-Jane Vick(1), F. Blake Morton(1,2) and Elizabeth S. Herrelko(1,3,4)

1. Behaviour and Evolution Research Group, Psychology, School of Natural Sciences, University of Stirling, UK

2. Department of Psychology, Franklin & Marshall College, USA

3. Royal Zoological Society of Scotland, Edinburgh, UK

4. Animal Care Sciences, Smithsonian's National Zoo, USA

Environmental enrichment: our cognitive challenges Chimpanzees are considered to be one of the most cognitively and socially complex species, creating challenges for humans to ensure their captive conditions provide for optimum welfare. The goals of enrichment are to provide an environment to engage in a diversity of species-typical (wild, desired) and motivated behaviors, and increase complexity, behavioral choices and provide opportunities to control aspects of the environment. We measure the success of our enrichment attempts by determining whether animal welfare has improved. In this presentation I shall compare the evidence that our attempts to cognitively enrich chimpanzees and other animals are really cognitive (i.e. engage the animals’ evolved cognitive skills rather than simply occupy them) and successful (i.e. improve welfare). Individual research testing is often regarded as cognitive enrichment, and the voluntary nature of participation, the lack of increase in self-directed behaviors, the activity patterns closer to wild counterparts have been used to support the notion the testing enhances welfare. To extend the evidence I shall compare our data on chimpanzees and capuchins with other mammalian species on which cardiovascular and cortisol data have been collected, to inform methodology and future directions for enrichment which is designed to engage cognitive processes which underlie the performance of complex behaviors. It is also important to explore how return to the group following individual testing may impact on social interactions. Chimpanzees and capuchins are aware of differences in the way they are treated in comparison to others and have been found to comprehend inequality, and responses to conspecifics. I shall review the issues of pitching challenge at the right level, and how human interactions may influence participation for chimpanzees, capuchins and other animals in research testing.

Josep Call
School of Psychology & Neuroscience, University of St Andrews, Scotland
Max Planck Institute for Evolutionary Anthropology, Germany

Communication and coordination in chimpanzees and orangutans  In recent years there has been a substantial amount of work devoted to investigate cooperation in nonhuman primates in experimental settings.  Much of this research has been aimed at pinpointing the motivational and cognitive processes underlying cooperation in the great apes.   Although multiple studies have documented pairs of individuals coordinating their actions to achieve a common goal, communicative exchanges between partners have been rarely observed, even in cases when cooperation broke down due to mis-coordination.  We presented conspecific pairs of chimpanzees and orangutans with two tasks in which communication could substantially enhance performance.  One task required subjects to transfer a tool to their partner and inform her about the location of food while the other task required individuals to take turns touching stimuli presented on a computer screen.  Contrary to previous studies, we observed multiple instances of gesture-based communicative exchanges in both chimpanzees and orangutans.  In some cases, communicative exchanges served to encourage partners to respond while in other cases they provided partners with specific information that they needed to solve the task.  In sum, under suitable conditions both chimpanzees and orangutans spontaneously gesture to conspecifics to initiate and maintain coordination to obtain a mutually beneficial goal.

Colin A. Chapman(1,2,3) and Kim Valenta(1)

1. Department of Anthropology and McGill School of Environment, McGill University, Canada

2. Wildlife Conservation Society, USA

3. Makerere Biological Field Station, Uganda

Chimpanzee conservation: what we know, what we do not know, and ways forward  The world is changing rapidly and on September 30th, 2014 the World Wildlife Fund announced that the world had lost 52% of is biodiversity.  Primate species may also have been lost and it is estimated that close to 50% of the world’s primates are at risk of extinction, with 11% critically endangered.  Chimpanzees (Pan troglodytes) are one of these endangered species and because of their iconic status and phylogenetic closeness to humans, they are a very special endangered species.  It is estimated that chimpanzee populations have experienced a significant reduction in the past 20 to 30 years and overall the population reduction over three generations is estimated to exceed 50%.  This review documents the current threats to chimpanzee populations in such a way as to illustrate what the scientific and conservation communities know and what they do not know.  In doing so, we hope to illustrate the way forward.  We consider the relative strengths of deforestation, the bushmeat industry, disease, and climate change as factors leading chimpanzee population declines.  While the situation we outline is grim, there are a number of promising actions that can be taken, including improved and more extensive law enforcement, reduced impact logging, reforestation associated with carbon storage and reduction in climate change, education and public outreach, and new emerging models for conservation funding.  Chimpanzees are our closest living relatives and are wonderful intelligent animals and we must strive to conserve them. 

Zanna Clay

School of Psychology, University of Birmingham, UK

Vocal communication in Pan: Insights into underlying social awareness and the evolution of language  Despite being very closely related, a growing body of research has revealed some striking differences between chimpanzees and bonobos in regards to their social behavior, development, physiology and even neural anatomy. Given that both species are equally related to humans, these differences highlight the importance of gaining insights from both chimpanzees and bonobos in order to develop balanced models of Hominin evolution. Compared to other domains, relatively little is known about Pan vocal communication, especially that of bonobos. Nevertheless, vocal communication provides a useful window through which we can investigate their underlying social awareness, as well as the socio-cognitive skills that might have supported the evolution of language. This is because language is based on a multitude of capacities, which includes a sophisticated social awareness for detecting, understanding and influencing the mental states of others. In this presentation, I will review recent research that investigates Pan vocal communication, focusing particularly on what this research can reveal to us about underlying social awareness and the kinds of social inferences that chimpanzees and bonobos can make by attending to each other’s vocalizations. Combining insights from both species, I discuss evidence that Pan vocalizations can be used in flexible and intentional ways to pursue certain social and reproductive strategies. Their vocalization are also subject to audience effects, may refer to external events and can be combined together into sequences, whose structure provides information to listeners about features of the external world. Overall, these results highlight a sophisticated social awareness and suggest that many of the skills required for language are firmly rooted in our great ape past.

Katherine A. Cronin

Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, USA

Strategic cooperation by chimpanzees: friend today, foe tomorrow The limitation of chimpanzee cooperation that has been demonstrated in several captive studies contrasts with the extensive cooperative abilities documented in the wild where they are known for their political alliance formation, team hunting and impressive territorial expansions. Some argue that this dichotomy is due to the differences between chimpanzees in captivity and in the wild. Here, I consider the cooperative behavior of chimpanzees studied in a constant environment across different types of social challenges. All studies took place at Chimfunshi Wildlife Orphanage Trust, a sanctuary in Zambia. In one study, chimpanzees were presented with a food acquisition challenge. In this context, competitive motivations dominated and rank differences entirely impeded cooperative solutions. This response was in contrast to robust cooperation observed in cooperatively breeding cotton-top tamarins posed with a similar challenge. In a second chimpanzee study utilizing a territorial defense paradigm, the same chimpanzees coordinated behavior in time and space with several group mates of disparate rank to patrol their boundaries and search for threats. Thus, at least high-ranking chimpanzees assess the need for partners and this affects the likelihood of cooperation. Recent research with humans suggests that the context of the social challenge also affects our own species’ likelihood to cooperate. In this regard, chimpanzees bear more similarity to humans than to cotton-top tamarins in terms of the flexibility with which they respond to social challenges. Importantly, behavioral differences that have been reported between wild and captive chimpanzees may be due, at least in part, to the context-dependent nature of chimpanzee cooperation.

Frans B. M. de Waal  

Living Links, Yerkes National Primate Research Center, USA

Psychology Department, Emory University, Atlanta, USA    

How far have we come: new research on primate altruism and cooperation At our last conference, The Mind of the Chimpanzee, a major point of debate was still if any animals other than us care about the well being of others, and how their cooperation compared with the vastly superior cooperation among humans. This was less than ten years ago, in 2007. Science was pessimistic about the cooperative abilities of apes, the idea of empathy in animals was still meticulously avoided, and negative findings were given ample attention. I will discuss two conclusions from studies I have been involved in: one on chimpanzee favoring cooperation over competition, the other on the neuroscience behind animal empathy, then introduce the speakers, who clearly have moved on since our last meeting. Instead of questioning the prosocial nature of apes, we have moved to studies of how and when prosociality is being expressed, what are the conditions that favor it, and the interplay between competition and cooperation.

Melissa Emery Thompson

Department of Anthropology, University of New Mexico, USA

Chimpanzee reproduction in context: a lifespan perspective  Chimpanzees and other great apes are notable for their very slow life histories in comparison with other primates. Examinations of ape life histories have focused primarily on quantifying reproductive milestones in efforts to characterize interspecific and population variation. Even this presents significant challenges due to the long periods of study required and potential for sampling bias. Still needed are examinations of the dynamic properties of life histories, and particularly the interactions between slow reproduction and a long lifespan. I draw from the Kibale Chimpanzee Project, Uganda, and other long-term research studies to outline what we know about changes in reproductive biology and behavior across the lifespan in female chimpanzees. Data on this species clearly indicate that energy availability constrains multiple parts of the reproductive process, from timing of dispersal to the duration of postpartum amenorrhea. With age, reproductive function declines and mortality risk increases, but females experience some compensating effects from enhanced social status, attractiveness, and maternal experience. These relationships raise several important unanswered questions. How should females prioritize increased reproductive rates versus longer life? Do individuals exhibit different strategies, or merely respond to different levels of constraint? Are these tradeoffs fundamentally the same as in shorter-lived species, or are ape life histories qualitatively different from other primates?

Brian Hare

Department of Evolutionary Anthropology, Duke University, USA

Who is nicer, bonobo or chimpanzee? Bonobos (Pan paniscus) are remarkable in their preference for sharing with strangers. Chimpanzees (Pan troglodytes) are unusual for helping in more instrumental contexts.  Both species appear to have their own unique profile of contexts and partners that encourage or prevent sharing and helping.  I will present a series of experimental studies comparing the sharing and helping behavior in bonobos and chimpanzees. Future observational and experimental comparisons of bonobos and chimpanzees will provide an unparalleled opportunity to understand how species-specific prosocial preferences are formed. The most exciting work will reveal the processes that shape these different prosocial profiles during evolution and across ontogeny. 

Daniel Haun(1), Katherine Cronin(2), Edwin van Leeuwen(3)

1. Department of Early Child Development and Culture, University of Leipzig & Leipzig Research Center for Early Child Development, Germany

2. Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, USA

3. Department of Psychology and Neuroscience, University of St. Andrews, UK

Group-level variation in chimpanzee social behavior  Investigating of the variation of human behavior across diverse contexts provided by different social groups has revealed differences and similarities that helped define the human species. In the same way, group-level variation in chimpanzee behavior can help us to describe the species with added depth. Furthermore, differences in the structure of group-level variability between humans and chimpanzees provide both questions and answers about the differences between these sister-species. We will present a set of studies investigating differences in social behavior across four captive groups of chimpanzees living at Chimfunshi Wildlife Orphanage, Zambia, that inhabit similar physical environments. Data show that these groups, even when similar in size and composition, vary in their co-feeding tolerance and social network structure. We will also discuss the stability of these group differences across time and across changes in group composition and compare them to the variation found across human social groups. Finally I will present a first outlook on the next set of studies investigating the relationship between group differences in social behavior and group-level variation in prosociality and social learning. Overall future research should utilize the varying contexts for chimpanzee behavior created, not by ecological characteristics or task demands, but by other chimpanzees.

Satoshi Hirata

Wildlife Research Center, Kyoto University, Japan

Welfare of ex-biomedical chimpanzees in Japan and the role of research at Kumamoto Sanctuary, Japan In Japan, invasive biomedical research of chimpanzees has been abolished.  My talk describes the background of this change and the welfare-oriented activities at Kumamoto Sanctuary, the first sanctuary in Japan that is home to ex-biomedical chimpanzees. In 1998, a total of 136 chimpanzees who had been used or to be used for biomedical purposes were kept at three different facilities in Japan. In addition to hepatitis studies, other invasive studies such as those for genetic treatment were about to start. Researchers and zoo-related professionals coordinated to end such invasive studies after a decade of effort. At that time, one of the biomedical research facilities was transformed into the first sanctuary for retired chimpanzees, which is now called Kumamoto Sanctuary. In 2012, the last three chimpanzees kept at a biomedical facility were transferred to Kumamoto Sanctuary, which meant the end of biomedical chimpanzee research in Japan. While the main aim of Kumamoto Sanctuary is to promote the welfare of the resident chimpanzees, researchers also engage in behavioral and cognitive studies to investigate the nature of these apes. Participation in cognitive studies by the chimpanzees is always voluntary, thus it can be regarded as a form of behavioral or cognitive enrichment. Some other applied research such as measurement of hair cortisol or of cardiac electrograms have been conducted to understand chimpanzee psychobiology. Both basic research to understand the nature of chimpanzees and applied research to monitor the chimpanzees’ wellbeing play important roles in promoting welfare of the chimpanzees.

Catherine Hobaiter

School of Psychology and Neuroscience, University of St Andrews, UK

Gestural communication in Pan: tracing the origins of language Language is the most complex system of animal communication described to date. However, the emergence of language within the human lineage through a single recent genetic leap is extremely implausible. Instead, its precursors were likely present in the communication of our evolutionary ancestors, and are likely shared by our modern great ape cousins. All great apes, including humans, employ a rich repertoire of vocalizations, facial expressions, and gestures with which to communicate. Great ape gestural repertoires are particularly elaborate, with chimpanzees and bonobos employing over 60 different gesture types intentionally: that is towards a recipient and with a specific goal in mind. Intentional usage is a key feature of language and has rarely been described in other species. It allows us to ask not only what information is encoded in ape gestures, but what do apes mean when they use them? I will review recent research on the gestural communication of great apes, with a particular focus on wild Pan populations. I will describe the range of gesture types and their meanings, exploring whether these are consistent across signallers, populations, and species. I will examine the ways in which gestures can be combined into sequences, either with other gestures or with other signal types. From this evidence I will address key questions: do we find evidence that gestures can be employed with syntactic-like structure? And are they used strategically to achieve particular social goals? Together, these data suggest that many of the core features of modern human language are also present across the living great apes.

Gottfried Hohmann

Department of Primatology, Max-Planck-Institute for Evolutionary Anthropology, Germany 

Temporal patterns of development in bonobos and chimpanzees  Bonobos display a suite of behavioral traits that combines moderate intensity of male aggression with co-dominance between the sexes and reduced predictability of female fecundity. While some of these traits separate bonobos from closely related chimpanzees, little is known about how these differences emerge. Various studies suggested that compared to chimpanzees, bonobos are characterized by developmental delay and retention of juvenile traits into adulthood. Such a heterochrony in development may reflect a general difference in the timing of maturation with one species maturing consistently earlier than the other. Alternatively, the difference in adult phenotypes of the two Pan species may be due to differences in the expression of age-specific traits in behavior and morphology. Here, we present data on somatic growth and sexual maturation collected from wild and captive bonobos to explore the timing of developmental changes in bonobos and compare this with corresponding information from chimpanzees. We found that development of some traits is delayed in bonobos while others occur at the same time as, or emerge earlier than, in chimpanzees. Moreover, results indicate obvious sex-differences in development. In spite of marked differences in the expression of traits of adulthood, males were found to be similar in the temporal pattern of development whereas females of both species differ with regard to the timing of developmental changes. Female bonobos seem to grow faster and reach puberty at a younger age than chimpanzees. In spite of this, females of both species terminate somatic growth at a similar time and give birth to their first infant at a similar age. The results indicate that species-differences in maturing individuals are most obvious during adolescence and more prominent in females than in males. The implications of the differences in temporal pattern of early development for female life history will be discussed.             

Lydia M Hopper

Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, USA

Chimpanzee social learning: a comparative perspective Chimpanzees, like many primate species, can learn new skills from observing others. In this talk I will provide a review of my research in which I have compared chimpanzees’ social learning mechanisms and strategies with those reported for other primate species, including humans, when tested using comparative methods. ‘Ghost displays’ lack an agent and discriminate social learning mechanisms. Comparing learning from a live model with agency, to that from a ghost display, has revealed that there appears to be an interplay between the complexity of the novel task and the need for a social demonstration. For chimpanzees, as for other primate species and human children, a social model appears necessary for learning more complex tasks. Social support, which aids exploration, is only sufficient for learning simpler tasks. Eye-tracking techniques, used to detect the elements to which subjects attend when observing a model, have revealed that seeing a model with agency demonstrate a task increases chimpanzees’ and human infants’ memory of the events they observed. This suggests that a model may facilitate learning by increasing a subject’s memory for, and understanding of, a model’s goals and/or the mechanics of the task. Although both chimpanzees and children can learn from ghost displays, chimpanzees appear less likely to copy the exact details of a demonstration. Reduced matching fidelity, however, promotes innovation and discovery of novel skills. Thus, social learning is only beneficial if individuals are selective over when and who they copy. Specifically, when chimpanzees are uncertain as to how to solve a task they are more likely to rely on social information, and low-ranking individuals also show a stronger reliance on social learning, copying older and more dominant individuals.

Tatyana Humle

Durrell Institute of Conservation and Ecology, School of Anthropology and Conservation, University of Kent, UK

Contextualising coexistence between people and chimpanzees: challenges and opportunities  Wild chimpanzees face numerous threats, including habitat loss and fragmentation, hunting and capture, and disease, especially zoonosis, responsible for concerning declines in populations across much of their range. Albeit variable across subspecies, these main threats resonate across Africa in terms of trends and patterns.  This talk aims to contextualise our understanding of the differing challenges and opportunities facing chimpanzee conservation today. Drawing from various case studies and publications, especially focused on Guinea and Sierra Leone in West Africa, I address questions about the relationship between conservation and large-scale development, especially extractive industries and commercial agriculture, in the context of avoidance, mitigation and offset strategies, between landscape changes and people-chimpanzee co-existence, and between the conservation of populations and the preservation of individuals in the context of law enforcement and in situ education efforts. Opportunities are highlighted in terms of the necessity for interdisciplinary, multidisciplinary and multiscale approaches and methodologies, a better understanding of conflicting values and perceptions, and more research focused around chimpanzee adaptations and responses to the dynamic socio-ecological landscapes in which they occur both inside and outside protected areas. This overview aims to highlight gaps and prospects for future research and conservation efforts, while also stressing the influence of human-human conflicts in hampering current initiatives and the urgent need for disseminating research findings, conservation successes and failures, and methodologies in range countries.

Cheryl D. Knott

Department of Anthropology, Boston University, USA

Ecology and the energetics of reproduction in the hominoids  The hominoids exemplify selection for slow life histories, characterized by late age at first reproduction, long inter-birth intervals and long lifespans. However, the relationships among life history variables such as body size, mortality and ecological variability, that apply between broad taxonomic groups, are more complex among these closely related species. Chimpanzees, for example, appear to have higher energy availability than do orangutans and correspondingly have shorter inter-birth intervals. However, the comparison does not apply to mountain gorillas, who have a lower quality diet than do either chimpanzees or orangutans, yet have the shortest inter-birth intervals of all the great apes. In this case, stability in the food supply may be a key factor. In this paper I examine differences between chimpanzees and the other great apes in terms of ecological variability and discuss what factors may have selected for differences in life history between these species. I discuss the comparative research that reveals common hominoid patterns in how reproductive effort, measured in terms of ovarian hormone production and successful conception, has a graded relationship with variance in energy balance. Further, to improve our understanding of hominoid reproductive ecology, I outline how we might better quantify ecological variability, energetics and the factors that influence conversion of food into metabolizable energy. The relationship between ecology and reproductive effort can vary at the species, sub-species, population or individual level. Thus, I explore how we can better understand what factors have selected for life history adaptations, vs. how selection for phenotypic plasticity can allow reproductive output to respond to both developmental influences and current ecological circumstances. Data are drawn from the literature, from my long-term study of wild orangutans at Gunung Palung National Park in Borneo, and from comparative studies between different ape species and populations.

Elizabeth V. Lonsdorf

Department of Psychology and Biological Foundations of Behavior Program, Franklin and Marshall College, USA

Growing up chimpanzee: studies of behavioral development in a comparative perspective  Chimpanzees and other great apes have an extended period of development relative to most other mammals. Offspring are nutritionally dependent on their mother through infancy until weaning between the ages of three to five, but remain behaviorally dependent (i.e. continually traveling and socializing with) through the juvenile years, until at least the age of eight.  Attempts to study the factors that influence developing offspring in the wild have been hampered by a lack of long-term datasets, but these have recently become available.  I will draw on data from a long-term study of chimpanzee mother-infant interactions from Gombe Stream Research Centre, Tanzania, to present and discuss developmental trajectories of several key behaviors, including distinct sex differences that begin to manifest in early infancy.  Sex differences in behavior and developmental trajectories in human children are of great interest to researchers in a variety of fields of study, and a persistent topic of discussion and debate is the relative contribution of biological versus social influences to such differences.  Given the relative lack of overt socialization by mother and others, chimpanzees are an important study species for understanding the biological and evolutionary roots of sex differences in human development. 

Lydia V. Luncz(1,2), Roman Wittig(2), Christophe Boesch(2)

1. School of Anthropology, University of Oxford, UK

2. Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Germany

Culture in a nutshell: social influence on percussive tool selection in wild chimpanzees  In the Taï National Park in Côte d’Ivoire, three neighboring chimpanzee (Pan troglodytes verus) groups are habituated to the presence of humans, offering the unique opportunity to search for culturally-influenced behavior by simultaneously minimizing the effect of ecological and genetic influence. Our recent research has shown that these neighboring groups display striking between-group variation in their behavioral repertoire including many fundamental aspects of their social life such as communication, hunting styles and foraging. One of the most remarkable differences between groups is hammer selection during percussive nut-cracking. Chimpanzees in Taï crack several nuts species using wooden and stone tools. Their main target nut is Coula edulis which they can feed on up to four hours per day during the high season, from November until March. Despite similar nut hardness and availability of raw materials in each groups’ territory, preference of tool material and tool size differs between groups. Interestingly, these tool preferences remains stable and persist over time despite frequent female migration between groups. To investigate the underlying reasons for the establishment and maintenance of diversity we studied the behavior of newly immigrated group members. Using archaeological methods, we investigated previous tool preferences in the females’ original groups. By recovering used tool remains at abandoned nut-cracking sites we reconstructed tool selection patterns of these females’ group prior to immigration. Comparing these patterns with direct observations after immigration, we demonstrate that new females were conforming to the tool selection pattern of their new community. Differences in the efficiency of tool properties suggest that these immigrants are exposed to costs or benefits in personal foraging success. Nevertheless conformity is observed repeatedly during migrating events in chimpanzees as well as other animal species (for example vervet monkeys and birds), highlighting the importance of group belonging in wild animals.

Janet Mann, Eric Patterson

Department of Biology, Georgetown University, USA

Look no hands! Parallels and differences between dolphin and chimpanzee tool-use  Chimpanzees and bottlenose dolphins share a very distant evolutionary history but converge on traits such as large brains, slow life histories, extended social learning, high social complexity, and fission-fusion societies. When tool-use, a trait rarely favored in marine environments for ecological, phylogenetic, and physiological reasons, does occur at sea, it provides comparative insights into not only the conditions that favor tool-use, but also how tool-use behaviors are maintained, spread, and become ‘cultural’. In Shark Bay, Australia, bottlenose dolphins detach marine sponges from the seafloor and wear them over their beaks for protection while ferreting fish from an abrasive and cluttered seafloor. This highly specialized form of tool-use is limited to approximately 4% of the population, the ‘spongers’, which have been extensively studied for over 30 years.  Like some chimpanzee tool-use, the behavior is female biased. As with chimpanzee tool-use, tool-use in dolphins is vertically transmitted from mother to offspring, but while virtually 100% of daughters become tool-users, only 50% of sons fully adopt the technique. This is curious given that both chimpanzees and dolphins nurse their offspring for an extended period of time (dolphins: mean 4 years, range 3-8 years) during which they spend considerable time alone with their offspring. In both chimpanzees and dolphins, social learning plays a key role in development of tool-use and recent evidence suggests lifelong learning and the development of expertise (peaking mid-life) in tool-use. By placing chimpanzee tool-use in context with what is known about dolphin tool-use we gain vital insights into the role that life history, learning, ecology and social dynamics play in the evolution of tool use.

Georgia Mason

Animal Biosciences, University of Guelph, Canada

Why do captive animals – including chimpanzees – perform abnormal repetitive behaviors, and how can we identify pathological forms? Many captive animals, including chimpanzees, perform a diverse array of abnormal repetitive behaviors (ARBs) that are rare or absent in the wild. To humans their appearance can range from amusing to disturbing, and in the latter cases it is often hard not to infer poor well-being or mental health in the animals that perform them. However, ARBs are biologically heterogeneous. Some seem merely to be normal activities redirected to unusual substrates and/or performed at elevated levels due to low behavioral competition. When these seem to be good motivational substitutes for normal behavior, and do not covary with indicators of poor welfare, we may conclude these are adaptive responses that should attract little concern. Kneading by cats and coprophagia in chimpanzees are likely examples. Other ARBs likewise seem to derive from normal behavior patterns, but reflect sub-optimal current environments that present animals with insoluble problems. Their performance would also seem to have few benefits for the performer. Such ‘maladaptive’ behaviors do indicate poor welfare, in the form of motivational frustration; likely examples include corner-digging by caged gerbils and scrabbling in farmed mink. Finally, others may reflect central nervous system malfunction (especially of the prefrontal cortex, dorsal striatum and/or nucleus accumbens), induced by deprivation rearing, inadequate diets, disease, or chronic stress.  Measurable correlated changes in brain function and behavioral organization (e.g. perseveration) are necessary - albeit not sufficient - for identifying these. Also required is evidence that such animals show correlated impairments (compared to a control group known a priori to be normal) in foraging, nest-building, social/sexual interactions, physical health, or maternal care. To date the clearest examples of this come from humans, rhesus monkeys, mice, horses, and mink.  In male mink for example, high levels of stereotypic behaviour predict reduced success with females in the mating season. Stereotypic behaviours that markedly interfere with normal activities in this way (or, alternatively, that result in bodily injury) would trigger a diagnosis of Stereotypic Movement Disorder in humans, according to the APA’s DSM-V.  These types of principle illustrate how we might translate our knowledge from other species to objectively identify pathological ARBs in chimpanzees:

Jorg J.M. Massen

Department of Cognitive Biology, University of Vienna, Austria

The social lives and cooperative skills of corvids  The social intelligence hypothesis argues that large brains have evolved in parallel with an increased complexity in the social environment, since maneuvering successfully through such a complex social world requires advanced socio-cognitive skills, such as the ability to cooperate. While this hypothesis could theoretically be applied to any given species or taxon, such advanced socio-cognitive skills have mainly been tested in non-human primates, most notably in chimpanzees. However, to truly test the influence of social complexity on socio-cognitive skills and required brain size, we need to exclude confounding effects of common ancestry, ideally by also testing animals outside our own phylogenetic lineage. Among birds, corvids are known for their large relative brain size, and recent studies are slowly uncovering the complexity of their social environment. Raven flocks, for example, show high fission-fusion dynamics, much like chimpanzee groups. The results of a series of our experiments revealed that the cooperative skills of ravens are in fact also comparable to those of chimpanzees. However, ravens’ prosocial tendencies are relatively low to non-existent, whereas this remains a debated subject regarding chimpanzees. In contrast, some of our most recent work on azure-winged magpies shows that this cooperatively breeding corvid does behave prosocially towards group members. By comparing corvids with different breeding styles, we test an extension to the social brain hypothesis that also originates from primatology; namely, that cooperative breeding leads to more inter-individual tolerance and to the evolution of extreme prosocial tendencies, such as those observed in humans. Consequently, I would like to argue that to test evolutionary hypotheses about the evolution of intelligence, we need comparative work that also encompasses species of different orders or even classes.

Tetsuro Matsuzawa (1,2,3)

1. Institute for Advanced Study, Kyoto University, Japan

2. Primate Research Institute, Kyoto University, Japan

3. Japan Monkey Centre, Japan

Communication in chimpanzees and bonobos: Semantics and syntactics This session addresses three important aspects relating to the origin of human language: gestural communication vs. vocal communication; semantics and syntactics; and comparison of chimpanzees and bonobos.  Hobaiter reviews recent research on gestural communication in great apes, especially wild populations of chimpanzees. She tackles fundamental questions, for example, are gestures used in sequential arrangements somewhat similar to syntax in language? Taglialatela proposes that differences in feeding ecology may have led to bonobos becoming relatively more reliant on vocal communication than chimpanzees, resulting in selection for greater vocal control and flexibility. Clay discusses results of studies investigating vocal communication in bonobos and chimpanzees. From hearing each other’s vocalizations: what social information do they gain? What can these findings tell us about their social awareness and knowledge of others’ mental states? Townsend and Slocombe talk about functionally-referential food calls in chimpanzees. Drawing evidence from studies in the wild and captivity, both observational and experimental, they suggest that chimpanzees use food calls flexibly, and that structure and use is modulated through learning from others.  The first “understanding chimpanzees” symposium was held in Chicago in 1986. This is the 30th anniversary of that landmark symposium.  There were no presentations on bonobos thirty years ago.  Topics included ape-language studies focused on the human-centric question: could great apes learn human language or master language-like skills?  There were no studies focused on communication in wild populations.  The present session shows clearly the trend of investigation into communication capacity in chimpanzees and bonobos: from artificial to more natural media; from laboratory studies to encompassing the wild.  As a whole, the session will provide the opportunity to think about the emergence of human language in the context of hominid evolution, focusing particularly on chimpanzees and bonobos.

William C McGrew

Division of Biological Anthropology, Deptartment of Archaeology & Anthropology, University of Cambridge, UK

Chimpanzee social life: is fission-fusion the key? The single-most important factor in the daily social lives of Pan troglodytes may be fission-fusion dynamics, yet this feature has been understudied. It cannot be investigated thoroughly in zoo or lab, by definition. Typically, field researchers report descriptive analyses of party size or composition (e.g. nursery group, consortship), yet the details of timing and make-up of individuals’ co-activities mostly are ignored. How much time do A & B spend together and what do they do then? Individuals may not meet for hours, days or even weeks, so there is probably huge variation in these basic affordances. (The chimpanzee pattern differs from some other primates’ fission-fusion, in which group members disperse and convene daily at sleeping sites.) Given this social milieu, such variation in sociality has implications for competition, cooperation, and especially social learning opportunities. The topic and its ramifications seem ripe for modern network-based analyses. The relative valence of stressors and relaxers likely varies with this diversity in companionship, probably affecting both behaviour and its physiological substrates. The extent to which social learning of elementary technology skills is transmitted must depend upon exposure to models, which in turn is a function of social dynamics, both within and across groups. Semi-free-ranging chimpanzee groups living in closer daily proximity and lacking migratory exchange with neighbours may show enhanced patterns of social relations than their free-ranging counterparts. The extent to which corvids do or do not converge with chimpanzees in these patterns may help to explain variation in behaviour across that much more diverse avian radiation.  

John C. Mitani(1), Kevin E. Langergraber(2), Kevin B. Potts(3)

1. Department of Anthropology, University of Michigan, USA

2. School of Human Evolution and Social Change, Arizona State University, USA

3. Department of Biology, Augsburg College, USA

Chimpanzee conservation: multiple challenges yet reason for hope As one of humankind’s closest living relatives, chimpanzees generate considerable interest on the part of scientists and lay people alike.  Despite the fascination that chimpanzees create, they remain critically endangered across the African continent and are a high priority for conservation.  In this session, four scholars will review the challenges, both old and new, that chimpanzees face with regard to their conservation.  Collectively, these talks also highlight some of the actions and management strategies that are being implemented to ensure that chimpanzees continue to survive in their natural environmental and social settings.  Exponential growth of the human population exacerbates many of the problems associated with maintaining populations of wild chimpanzees and makes it increasingly difficult to carry out effective conservation plans.  Nevertheless, the situation is not entirely bleak.  I use our long-term study of chimpanzees at Ngogo in the Kibale National Park, Uganda, to show how one community of chimpanzees has thrived and continued to grow in the midst of widespread decline in chimpanzee numbers elsewhere.  Additional work reveals that Ngogo is not an unusual situation, as novel genetic capture-recapture data indicate that there are several other large communities of chimpanzees scattered throughout the Kibale Park.  This latter finding is especially surprising given the long history of intensive primate field research at Kibale and underscores the paucity of information that we have about the densities and distributions of these animals who we are all working hard to save. 

David Morgan(1) Crickette Sanz(2), Eric Lonsdorf(3), Samantha Strindberg(4), Hjalmar S. Kühl(5,6), Roger Mundry(5)

1. Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, USA

2. Department of Anthropology, Washington University, USA

3. Department of Biology, Franklin & Marshall College, USA

4. Wildlife Conservation Society, Republic of Congo

5. Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Germany

6. German Centre for Integrative Biodiversity Research, Germany

Modern environmental challenges to the ecological flexibility of chimpanzees  Chimpanzees have a long evolutionary history of adjusting to fluctuating environments, but basic questions remain as to how this species copes with modern environmental disturbances like industrial logging. Most studies of chimpanzees and forestry have compared areas with different logging histories, rather than detailing the responses of populations to extraction as it occurs. In this study, we documented the arrival, progression, and departure of forestry activities in northern Republic of Congo. Our aim was to not only describe the impacts of logging on chimpanzees, but also to determine the factors driving their abundance and compare their responses with those of western gorillas who reside in sympatry with chimpanzees throughout most of central Africa. We surveyed ape nests and human signs encountered along line transects over the course of an eight-year study. A total of 12,467 nests were detected over 1,068 km of transects, and complemented by information on ape ecology from ongoing studies of habituated apes and tree distribution from forestry inventories. Abundance of chimpanzee was predicted by human impacts and feeding trees and gorilla abundance was predicted by stage of logging and heterogeneity of vegetation. Chimpanzees also shifted away from forestry to nearby “refuge areas” of lower human disturbance, whereas gorillas were attracted to the dense undergrowth of logged habitat. Contrasting the socio-ecological needs of these coexisting apes was very informative in interpreting their responses to environmental instability, as chimpanzees can be considered specialists belonging to the omnivore guild (but consuming mostly fruit) and gorillas are generalists belonging to the folivore guild (consuming mostly herbs). Together, these results demonstrate the importance of the ecological flexibility and advanced cognitive capacities of chimpanzees in coping with environmental disturbance. Results are being used to develop evidence-based conservation initiatives to mitigate identified threats and ensure the preservation of our closest living relative.

Jill D. Pruetz(1), Stephanie Bogart(2), Stacy Lindshield(1)

1. Department of Anthropology, Iowa State University, USA

2. Human and Evolutionary Biology, University of Southern California, USA

Savanna chimpanzees at Fongoli, Senegal, use tools to reconcile an extreme environmentChimpanzees in the Fongoli community in Senegal live in harsh savanna environments and are the first such population to be habituated and longitudinally studied. We provide information on the Fongoli chimpanzees’ tool behavior collected over the course of 10 years (2006-2015) in these hot, dry and open habitats. Fongoli chimpanzees rely on tool use during foraging to successfully combat the extreme pressures they face in the savanna-woodland mosaic of southeastern Senegal, the northernmost extent of the species’ range. While the tool kit of chimpanzees here is less varied than that of some forest-living chimpanzees, tool behavior is frequent as well as instrumental for their survival in this environment. Data collected between February 2010-July 2014 reveal chimpanzees used tools to forage on 66.5% of days. Tool-assisted hunting behavior, where apes target the nocturnal Galago senegalensis as their main vertebrate prey, has been recorded in 75% of calendar months, but is concentrated in the early rainy season (June-July). With over 350 cases recorded, we can now examine individual differences in success rates and tool-making techniques. Fongoli chimpanzees spend more time feeding on invertebrate prey than chimpanzees elsewhere, and we will discuss aspects of their termite-fishing and ant-dipping behavior. Termite fishing is the most common type of tool use, being recorded in all months. Using stone or wood anvils to crack open baobab fruits is a significant behavior for Fongoli chimpanzees, second only to termite-fishing in terms of frequency, allowing them to access one of their most important food items. While the behaviors we describe are unique at Fongoli or rare (in form or frequency) in other communities, it is likely that ongoing efforts to habituate savanna chimpanzees in Senegal and East Africa will also reveal patterns of differences between these and forest-dwelling apes.

Anne Pusey

Department of Evolutionary Anthropology, Duke University, USA

Ontogeny, reproduction and life histories at ape field sites The comparative study of ape life histories is of particular interest for the insights that this can provide into the evolution of human life history as well as life history evolution more generally.  Yet, because of the very slow pace at which ape lives unfold, a good understanding of patterns of ontogeny, age-specific reproduction and longevity can only be obtained by continuous observation of known individuals over periods that approach or even exceed the length of a single human researcher’s working life.  The talks in this section are all based on data painstakingly collected by numerous researchers over several decades.  At several sites the original researcher has produced academic offspring who have continued study at that site or started new studies. This is particularly true for Gombe, where Jane Goodall began the longest continuous ape study in 1960 and has nurtured three generations of academic descendants who continue their studies both at Gombe and elsewhere. In this talk I reflect briefly on the growth of our knowledge of chimpanzee life history as studies have lengthened and proliferated over the last 56 years.

Stephen R. Ross

Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, USA

Chimpanzee Welfare:  the intersection of science and policy The measure, assessment and evaluation of psychological wellbeing of captive chimpanzees remain a critical topic of study.  This is especially relevant today in the midst of monumental shifts in policy relating to the use and housing of this species.  Moreso than ever before, scientists and managers have at their disposal a range of evaluative tools to aid in welfare assessments and such activities are vital to advancing the way we care for chimpanzees in the broad range of housing in which they are currently managed.  A comparative approach – across sites, between species, and accounting for individual variability – seems a particularly fertile approach for determining both proximate and ultimate influences on chimpanzee welfare, and in this session, we realize some of the potential of such approaches.  Satoshi Hirata demonstrates that changes for captive chimpanzees are afoot around the world, as he describes the transition of a biomedical research center to a chimpanzee sanctuary in Japan and how research plays a vital role in the assessment and promotion of chimpanzee welfare there.  Hannah Buchanan-Smith continues on this theme and provides a comparative perspective on the degree to which voluntary research is able to play an enriching role for a variety of captive animals.  Mollie Bloomsmith fully leverages the variability in chimpanzee housing in the United States by providing an assessment of management factors and behavioral outcomes for chimpanzees living in zoos, sanctuaries and laboratories in this country.  Georgia Mason also delves into behavioral indicators of wellbeing, specifically abnormal repetitive behaviors, and provides a broad taxonomic context for such behaviors in relation to what we know about their expression in a range of other species.  Together, these presentations demonstrate the importance of an evidence-based approach to improving chimpanzee welfare, and while I assert that progress in augmenting housing standards should not suffer from “paralysis by analysis”, it is clear that such research will be essential to determine the most effective means to improve the environments in which chimpanzees live.

Crickette Sanz(1,2), David Morgan(2,3)

1. Department of Anthropology, Washington University, USA

2. Wildlife Conservation Society, Republic of Congo

3. Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, USA

Sex differences in foraging among sympatric chimpanzees and gorillas in northern CongoNiche separation between the sexes has been documented in many species, and often relates to body mass dimorphism and reproductive status. Division of labor is much less common and involves delegation of tasks to individuals with cooperative roles. Although division of labor has been associated with many potential advantages, the evolutionary origins of these sex differences remain debated. We examine sex differences in the foraging strategies of adult chimpanzees and gorillas residing within the shared environment of the Goualougo Triangle, Republic of Congo. Ecological and social opportunities were assessed to determine if they differentially influence male and female foraging, particularly with regard to the evolution of technology. While body size and strength are important factors in some contexts, social setting was also found to have a large effect on ape foraging. Our results highlight the distinct and yet complementary roles of males and females within great ape societies.

Jared P. Taglialatela

Department of Ecology, Evolution, and Organismal Biology, Kennesaw State University, USA

Ape Cognition and Conservation Initiative, USA

A comparison of socio-communicative behavior in chimpanzees and bonobos  A fundamental characteristic of human language is multimodality and humans use multiple signaling channels concurrently when communicating with one another.  For example, people frequently produce manual gestures while speaking, and the words a person perceives are impacted by visual information.  However, humans also have the ability to rely exclusively on speech, allowing complex communication with individuals that are not in direct view or physical proximity.  This level of vocal control and flexibility is unique among primates – and indeed exceedingly rare among mammals.  It is unclear what selection pressures led to this phylogenetically unprecedented capacity for autonomous speech.  Given that speech and the soft-tissue that supports it do not leave well-preserved marks in the fossil record, the study of variation in communicative behavior in extant nonhuman primates – particularly chimpanzees and bonobos - is critical for understanding the evolutionary origins of human sociality and communication.   Despite being closely related – diverging from a common ancestor only approximately 1 million years ago – bonobos and chimpanzees exhibit some notable behavioral differences.  One of the most striking, but least studied, differences between these species are their vocal repertoires.  We hypothesize that differences between the Pan species’ feeding ecology may have favored bonobos to become increasingly reliant on vocalizations, as opposed to other modalities, to communicate with conspecifics and mediate social interactions.  The subsequent selection for increased vocal control and flexibility that occurred in bonobos, as compared to chimpanzees, may have been similar to those selection pressures faced by early hominins.  For this talk, I will review species differences in the socio-communicative behavior of chimpanzees and bonobos and discuss their neurobiological and genetic foundations.

Claudio Tennie

School of Psychology, University of Birmingham, UK

Chimpanzee tool-use: cultural, but not culture-dependent  Understanding chimpanzee tool cultures offers important insights into the evolution of human culture. I will argue that chimpanzee – as well as early hominin – tool cultures consist of chains of uniform reinventions. The evolved cognitive skills of chimpanzees potentially enable them to individually reinvent all tool-use behaviors shown by any other chimpanzee anywhere else (excluding human-trained behavior). In reality, no individual chimpanzee will likely exhibit all of these behaviors. Instead, the specific set of reinventions that is realized in any chimpanzee population (i.e. their culture) is socially mediated in that each individual is much more likely to reinvent tool use behaviors they have already come in contact with. Even so, each individual chimpanzee will still have to generate the behavior anew – i.e. reinvent it – fueled by evolved cognitive skills. The resulting uniformity of behaviors within chimpanzee groups can then create a powerful illusion: it may instead appear to be based on imitations of the behavior. But it is unlikely that imitation is the driver behind this uniformity, given the growing evidence of uniform reinventions outside populations (the “latent solution project”) and the poor imitative skills of wild-type chimpanzees (and other non-human great apes). Reinventions are not limited to non-human great apes. They also appear in other animals – and in our own species. We have recently shown that human children spontaneously reinvent tool-use behaviors shown by wild chimpanzee and orangutans, suggesting that the underlying evolved skills were shared by our last common ancestor. Yet in contrast to chimpanzee tool use, modern human tool use also includes variants that no individual could ever independently reinvent. These behaviors cannot occur unless they are culturally transmitted (directly via high-fidelity transmission; and/or indirectly via “cultural intelligence” – i.e. a positive influence loop of culture on cognition). They are, in other words, culture-dependent – whereas, I will argue, chimpanzee tool-use culture is not. The same is possibly true for all non-human animals (and indeed also for the tools used and made by early hominins).

Masaki Tomonaga

Primate Research Institute, Kyoto University, Japan

How chimpanzees perceive faces: an update after nine years of investigation  Faces play a special role in primate communication and social cognition, and as such they are processed in a different manner to other types of visual stimuli. We have been studying perception and cognition of faces in chimpanzees from the standpoint of comparative cognitive science. We initially reported some results at the last Chimpanzee Symposium (“The Mind of the Chimpanzee, 2007) and now, nine years later, I present the latest results from our continuing research project. First, as in humans, chimpanzees process facial stimuli in a holistic manner. When we see a non-facial object containing similar spatial configurations to faces (top-heavy patterns), we readily perceive it as a ‘face’. This phenomenon, often called ‘pareidolia’, was also observed in chimpanzees. In addition, when the spatial configuration of a face-like object was manipulated, the chimpanzee’s performances deteriorated, compared to when the same manipulation was applied to other types of stimuli. Secondly, chimpanzees tried to find facial configurations in noise patterns in which facial images did not exist. These results further support the notion that face processing in chimpanzees is holistic. Thirdly, faces include important social information such as gaze.  In a visual search task, in which chimpanzees were required to detect attentional state an attentive state, they showed quicker detection of an inattentive state than humans. Fourthly, we know that the physical features of human and chimpanzee eyes are different as humans have very high-contrast sclera and pupils, but chimpanzees do not. Interestingly, when humans are shown faces of different species with human eyes (“Planet of the Apes effect”), we find them less abnormal than faces of humans with eyes of different species (“Alien Eyes effect”). However, chimpanzees did not show such a heterospecific eyes effect in their visual search performance. These results have implication for understanding visual communication in chimpanzees. 

Simon W. Townsend(1) and Katie E. Slocombe(2)

1. Department of Psychology, University of Warwick, UK

2. Department of Psychology, University of York, UK

Chimpanzee food calling: implications for the evolution of human semanticity  The emergence of human language is arguably one of the major evolutionary transitions in the history of life though elucidating its origins is non-trivial. Unpacking the phylogenetic roots of language, through investigating the communication skills of non-human primates, can however, shed important light on the evolution of key linguistic features. Over the last 50 years, a number of studies have demonstrated that primates are capable of producing vocalizations that refer to objects and events in the external world. Whilst these so called ‘functionally-referential calls’ (FRCs) have been argued to represent potential precursors to the semantic vocal labels used in human language, they also occur in more distantly related non-primate species, and key differences between primate and human referential abilities persist. Specifically, very few studies have investigated the proximate psychological mechanisms underlying the production of these calls and whether, as in language, producers have flexible control over the use and acoustic structure of FRCs. Over the last five years we have systematically addressed this question in the functionally-referential food calls of chimpanzees (Pan troglodytes). Using observational and experimental techniques, in both the wild and captivity, we have begun to demonstrate that chimpanzee food calling is not hardwired and reflexive, but flexibly used and modifiable, at the structural level, through social learning. These data indicate that the similarities between human and chimpanzee referential abilities transcend the surface level and suggest the cognitive building blocks underpinning human semanticity may be evolutionarily more ancient than previously thought.

Andrew Whiten

School of Psychology and Neuroscience, University of St Andrews, Scotland

Learning and cognition in chimpanzees: rise of the social mind  The last ten years have seen a bumper crop of exciting new studies in primate cognition, and as in the decades before, innovative methods and discoveries concerning chimpanzees have often led the way in this. Two examples that illustrate this, as well as the rise of ‘social mind’ as a pervading focus of research this century, are theory of mind, and cultural transmission. Twentieth century skepticism about the first of these was overturned in more recent times by innovative approaches revealing surprisingly sophisticated understanding of others, aspects of which are further elucidated in Call’s contribution to the symposium focusing on communications engineered by chimpanzees to facilitate cooperation and coordination. Turning to cultural transmission, my own research and that of Hopper and others presented in this symposium pioneered cultural diffusion experiments and other approaches such as ghost experiments, that were the first to demonstrate the emergence and maintenance of multiple tradition and the underlying social learning processes. This focus on social cognition is rounded out by Tomonaga’s ingenious experiments on the special psychological processes called upon by face perception. Of course none of this is to say that physical cognition is undermined; to the contrary this domain has seen its share of recent new discoveries and Beran describes advances in the subject of cognitive control. In all these areas, pioneering work has been done first with chimpanzees, profoundly influencing later research with other primates and non-primates. The studies grouped in this symposium have been executed almost exclusively in captive contexts that most readily accommodate the intricate control conditions necessary to these studies, but I suggest it is finally important to remember that field experiments on cognitive issues, whilst challenging, are increasingly being undertaken and yielding important results; some are perhaps likely to be addressed by papers in other symposia of this meeting. 

Roman M. Wittig, Catherine Crockford

Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Germany

Chimpanzee friends: formation, maintenance and benefits of social bonds in wild chimpanzees  Chimpanzees, like some other social mammals, can form close and enduring social bonds, where dyads with close social bonds are those that engage in high rates of affiliative and cooperative behaviors. Maintaining social bonds leads to greater reproductive success, health and longevity. However, underlying mechanisms promoting this effect are still ambiguous, especially for non-kin, non-sexual bonds. One possibility is that bond partners buffer the negative effects of physical and psychological stress, where prolonged cortisol release is associated with reduced fertility, health and longevity. Another may be that direct benefits are derived from cooperative exchange, which may be emotionally rather than cognitively mediated through oxytocin, a key neuropeptide in social bonding. Here we investigate these possibilities in wild chimpanzees, known for their close social bonds with both, kin and non-kin, using hormonal and behavioral data from multiple communities in Budongo Forest, Uganda, and Taï National Park, Côte d’Ivoire. First we look into how chimpanzees form and maintain bonds measuring urinary oxytocin levels following behaviors that have been associated with bonding. Further, we examine also chimpanzees urinary glucocorticoid levels following several cooperative events, including those considered to be stressors (potentially dangerous encounters with rival groups or food competition contexts), or relaxers (grooming interactions), and contrast them with socially neutral (resting, feeding) situations. Our results suggest that the combination of engaging in cooperative behaviors with bond partners, rather than with non-bond partners, was associated with hormonal profiles likely to facilitate both cooperation and stress reduction. Discussing our results suggests that the relationship between bond partners is more than just a high frequency of socio-positive interactions, but rather describes a ‘trusting’ relationship – similar to human friendships.

Richard Wrangham(1), Kathelijne Koops(2)

1. Department of Human Evolutionary Biology, Harvard University, USA

2. Anthropological Institute & Museum, University of Zurich, Switzerland

Chimpanzee tool use in a comparative perspective: sex differences, ecological significance and cultural transmission This session addresses three big themes in chimpanzee tool use: sex differences, ecological significance and mechanisms of cultural transmission. It approaches these topics from three directions each of which offer prospects for testing hypotheses about adaptive significance and causal mechanisms. First is the comparison of different chimpanzee populations, each with their own set of cultural traditions of food collection. Sanz & Morgan introduce the richest dataset yet known on tool use by forest-living chimpanzees, while Pruetz et al document tool use among the best-studied savanna chimpanzees. Second is the comparison of different species. Sanz & Morgan present a novel comparison of striking differences in foraging strategies among sympatric chimpanzees and gorillas, thereby offering an unusually well controlled opportunity for testing hypotheses about the evolution of behavioral sex differences among apes. By contrast Mann & Peterson compare tool use in two distant relatives, bottlenose dolphins and chimpanzees, probing for parallels and differences in patterns of cultural transmission. Third is an experimental approach presented by Tennie that assesses similarities and differences in cultural transmission between chimpanzees and humans. These methods give promise of insights into several questions that are critical for understanding how human culture came to differ from that of chimpanzees. What can sex differences in the behavior of chimpanzees and other species tell us about the evolution of sex differences in human behavior, or even about the sexual division of labor? Are there differences between non-human and human cultures that can inform us about human cultural evolution? And, uniting the two themes, how can insights about chimpanzees or other cultural species help explain the evolution of sex differences in cultural behavior. Feeding ecology and tool use are informative arenas in which to explore these questions because they critically influence human adaptive success, as they often do for non-humans as well.


Shinya Yamamoto(1,2), Kirsty Graham(3), Kimberley J Hockings(4), Takeshi Furuichi(5), Tetsuro Matsuzawa(5)

1. Graduate School of Intercultural Studies, Kobe University, Japan

2. Wildlife Research Center, Kyoto University, Japan

3. School of Psychology & Neuroscience, University of St Andrews, UK

4. Anthropology Centre for Conservation, Environment and Development, Oxford Brookes University, UK

5. Primate Research Institute, Kyoto University, Japan

Cooperation in dyads and in groups among chimpanzees and bonobos Cooperation is a hallmark of humans and our society is sustained by various kinds of prosocial behaviors such as helping, sharing, and group coordination. Our closest relatives, chimpanzees and bonobos, demonstrate similar behaviors, which suggest the evolutionary basis for human cooperation. Meanwhile, we have accumulating evidence for differences between these two Pan species, revealing that each species has its respective advantages and outperforms the other in some specific forms of cooperation. Investigation of these differences will lead to a better understanding of how cooperation evolved. In our previous studies, we suggested that chimpanzees are good at understanding a conspecific’s problem-solving situation and can help according to the partner’s need, but they seldom provide help proactively. Several studies have suggested that bonobos outperform chimpanzees in dyadic cooperation such as food sharing and joint action. This seems to be due to bonobos’ high social tolerance and peaceful nature. Then, the subsequent question is about cooperation in a group setting. We have compared group coordination of chimpanzees and bonobos in a dangerous situation. Both wild chimpanzees in Bossou, Guinea, and wild bonobos in Wamba, Democratic Republic of Congo, are known to cross villagers’ roads when travelling within forests divided by roads. Analyzing the way they crossed the roads, we found chimpanzees demonstrated more cooperative and coordinated actions than bonobos in a similar situation. Chimpanzees, especially adult males, turned around and waited for others frequently, while in bonobos such cooperative behaviors were not so conspicuous and observed predominantly in mothers toward their offspring. Chimpanzees may outperform bonobos on cooperation in group settings, which might have co-evolved with competitive inter-group relationship found in chimpanzees rather than in bonobos. Thus cooperation in dyads and in groups might have formed through different evolutionary processes.

Lester E. Fisher Center for the Study and Conservation of Apes
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