Thesis (doctoral)--Lund University, 1999. / Includes bibliographical references (p. 287-306). Also available on the Internet.

付記する学位プログラム名: 霊長類学・ワイルドライフサイエンス・リーディング大学院 / 京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22295号 / 理博第4609号 / 新制||理||1661(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 古市 剛史, 教授 湯本 貴和, 教授 濱田 穣 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24470号 / 理博第4969号 / 新制||理||1709(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 古市 剛史, 准教授 Huffman Michael Alan, 教授 今井 啓雄 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

<p>Humans are natural politicians. We obsessively collect social information that is both observable (e.g., about third-party relationships) and unobservable (e.g., about others’ psychological states), and we strategically employ that information to manage our cooperative and competitive relationships. To what extent are these abilities unique to our species, and how did they evolve? The present dissertation seeks to contribute to these two questions. To do so, I take a comparative perspective, investigating social decision-making in humans’ closest living relatives, bonobos and chimpanzees. In Chapter 1, I review existing literature on theory of mind—or the ability to understand others’ psychological states—in these species. I also present a theoretical framework to guide further investigation of social cognition in bonobos and chimpanzees based on hypotheses about the proximate and ultimate origins of their species differences. In Chapter 2, I experimentally investigate differences in the prosocial behavior of bonobos and chimpanzees, revealing species-specific prosocial motivations that appear to be less flexible than those exhibited by humans. In Chapter 3, I explore through decision-making experiments bonobos’ ability to evaluate others based on their prosocial or antisocial behavior during third-party interactions. Bonobos do track the interactions of third-parties and evaluate actors based on these interactions. However, they do not exhibit the human preference for those who are prosocial towards others, instead consistently favoring an antisocial individual. The motivation to prefer those who demonstrate a prosocial disposition may be a unique feature of human psychology that contributes to our ultra-cooperative nature. In Chapter 4, I investigate the adaptive value of social cognition in wild primates. I show that the recruitment behavior of wild chimpanzees at Gombe National Park, Tanzania is consistent with the use of third-party knowledge, and that those who appear to use third-party knowledge receive immediate proximate benefits. They escape further aggression from their opponents. These findings directly support the social intelligence hypothesis that social cognition has evolved in response to the demands of competing with one’s own group-mates. Thus, the studies presented here help to better characterize the features of social decision-making that are unique to humans, and how these abilities evolved.</p> / Dissertation

No description available.

<p>What makes our minds human? How did they evolve to be this way? This dissertation presents data from two complementary lines of research driven by these orienting questions. The first of these explores the `what' of human cognitive evolution through comparative studies with chimpanzees and bonobos. The general aim of these studies is to understand which aspects of cognition are unique to humans, and which are shared with our closest living relatives. Chapters 2-3 test the hypothesis that humans have unique cognitive skills for reasoning about the attention of other individuals (theory of mind), and unique motivation to use these skills in cooperative contexts with conspecifics. In Chapter 2 I show that understanding others' attention is unlikely to be the `small difference that makes the big difference', as some researchers have proposed. However, my data support the possibility that species differences in the ontogeny of these skills may have robust consequences for the adult cognitive phenotype. In Chapter 3 I show that (contrary to previous reports) nonhuman apes are also motivated to engage in some simple triadic social activities, which resemble those characteristic of human children. Again however, I identify important differences between humans and other apes in their spontaneous preferences for these types of activities, and their attitudes toward a partner when cooperative behaviors are interrupted. The second half of this dissertation (Chapters 4-5) explores the `why' and `how' of cognitive evolution. Chapter 4 outlines the kind of research questions and methods that comparative psychologists will need to embrace in order to use the comparative method to its full potential in the study of cognitive evolution. Chapter 5 provides a proof of principle for this approach using a dataset including 33 species tested on two cognitive tasks measuring inhibitory control. Here I show that cognitive skills for inhibitory control are closely related to phylogeny across species, and strongly predicted by absolute (but not relative) brain size. Further, I show that two of the other leading hypotheses put forth to explain primate intelligence, namely sociality and diet, do not predict cognitive skills on these tasks. These data illustrate the power of the comparative method for understanding cognitive evolution, and provide a starting point for future studies embracing this approach. Collectively, this research refines our understanding of how human cognition differs from that of other primates, and illustrates the utility of studying cognitive evolution from an explicitly phylogenetic comparative framework.</p> / Dissertation

Key insights into the evolutionary origins of human social behavior can be gained via study of our closest living relatives, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). Despite being equally related to humans, these two species differ importantly in aspects of their morphology, physiology, behavior, and cognition. Morphological comparisons reveal numerous traits in bonobos that can be viewed as paedomorphic, or juvenile, relative to chimpanzees. Meanwhile, comparisons of endocrinology in the two species suggest that aspects of steroid physiology have changed significantly in bonobos in line with their reductions in male mating competition. Based on this evidence, I tested the hypothesis that behavioral and cognitive differences between bonobos and chimpanzees derive from changes in their 1) developmental trajectories of behavioral and cognitive traits and 2) neuroendocrine influences on behavior and cognition. I tested this hypothesis by studying semi free-ranging populations of bonobos and chimpanzees. First, I found that bonobos retained juvenile levels of food sharing and social inhibition into adulthood, leading them to differ from chimpanzees in these traits as adults. Second, I found that bonobos showed muted elevations in their levels of testosterone from infancy to adulthood in comparison to chimpanzees, suggesting that numerous aspects of development differ between these two species. Third, I found that male bonobos and chimpanzees differ in their immediate neuroendocrine shifts surrounding competition, implicating changes in proximate mechanisms influencing social behavior between the two species. Fourth, I found that patterns of cognitive development in these two apes differed significantly from those of human children. These results provide substantial support for my hypothesis that phenotypic differences between bonobos and chimpanzees evolved via shifts in bonobo development and neuroendocrine physiology. More broadly, they illustrate how behavioral and cognitive evolution can occur through changes in ontogenetic trajectories and neuroendocrine mechanisms. These findings thus show the merits of integrating ultimate and proximate levels of analysis in studies of the evolution of human behavior and cognition. / Human Evolutionary Biology

<p>Humans are champions of prosociality. Across different cultures and early in life, humans routinely engage in prosocial behaviors that benefit others. Perhaps most strikingly, humans are even prosocial toward strangers (i.e. xenophilic). This is an evolutionary puzzle because it cannot be explained by kinship theory, reciprocal altruism or reputation. The parochialism hypothesis proposes that this extreme prosociality is unique to humans, is motivated by unselfish motivation and evolved through group selection made possible by human culture and warfare. The first impression hypothesis, on the other hand, proposes that xenophilia can evolve to promote the selfish benefits that accrue from extending one's social network. It predicts that 1) nonhuman species can evolve prosociality toward strangers when the benefit of forming new relations is higher than the cost, 2) the motivation for prosociality can be selfish, and 3) encounters with strangers can be a positive social event since strangers represent potential social partners. This dissertation presents three sets of experiments designed to test these predictions with bonobos (Pan paniscus), a species known for reduced xenophobia. These experiments showed, first, that bonobos voluntarily shared monopolizable food with a stranger and helped the stranger to obtain out-of-reach food. Second, the observed prosociality was driven by a selfish motivation to initiate an interaction with the stranger in close proximity and an other-regarding motivation to benefit the stranger. Third, an involuntary yawning task and a voluntary choice task show converging results that bonobos attribute positive valence to completely unknown strangers by default. These experiments support the three core predictions of the first impression hypothesis and challenge the view that intergroup competition is crucial to the origin of prosociality toward strangers in our species. Instead, the first impression hypothesis proposes that xenophilia in bonobos is probably an adaptation to initiating non-kin cooperation. Because female bonobos are highly cooperative even though they are the dispersing sex, xenophilia might function to quickly establish cooperative relationships with new immigrants. This suggests that xenophilia and reciprocity are likely two complementary aspects of non-kin cooperation: the former explains its initiation while the latter explains its maintenance. Similarly, xenophilia in humans is likely a result of the increasing need for cooperation among non-kin due to enhanced fission-fusion dynamics, population expansion, obligate cooperative foraging and greater dependence on cultural knowledge.</p> / Dissertation

L’information "identité individuelle" est essentielle chez les espèces fortement sociales car elle permet la reconnaissance individuelle et la différenciation des partenaires sociaux dans de nombreux contextes tels que les relations de dominance, les relations mère-jeunes, la défense territoriale, ou encore participe à la cohésion et coordination de groupe. Chez de nombreuses espèces, le canal audio est l’une des voies les plus efficaces de communication dans des environnementscomplexes et à longue distance. Les vocalisations sont empreintes de caractéristiques acoustiques propres à la voix de chaque individu. La combinaison entre ces signatures vocales individuelles et la connaissance sociale accumulée sur les congénères peut grandement favoriser la valeur sélective des animaux, en facilitant notamment les prises de décisions sociales les plus adaptées. Le but de ma recherche est d’étudier le codage et décodage de l’information "identité individuelle" du système vocal de communication du bonobo, Pan paniscus. Premièrement, nous avons recherché la stabilité des signatures vocales des cinq types de cris les plus courants du répertoire du bonobo. Nous avons trouvé que, bien que ces cinq types de cris aient le potentiel de coder l’information individuelle, les cris les plus forts émis dans des contextes d’excitation intense et de communication à longue distance ont les signatures vocales individuelles les plus marquées. Deuxièmement, nous avons étudié l’effet de la familiarité sociale et des liens de parenté sur les caractéristiquesacoustiques qui codent l’information individuelle dans un type de cri "bark". Nous avons mis en évidence l’existence d’une forte convergence vocale. Les individus apparentés et familiers, et indépendamment l’un de l’autre, présentent plus desimilarités vocales qu’entre des individus non apparentés et non familiers. Enfin, dans une troisième étude, nous avons testé la capacité des bonobos à utiliser l’information "identité individuelle" codée dans les vocalisations pour discriminer la voix d’anciens partenaires sociaux avec qui ils ne vivent plus. Par une série d’expériences de repasse, nous avons démontré que les bonobos étaient capables de reconnaître la voix d’individus familiers sur la seule base de l’acoustique, et cela même après des années de séparation. L’ensemble de ce travail de thèse montre que le codage et décodage de l’information "identité individuelle" chez le bonobo est un système dynamique, sujet à modification avec l’environnement social mais suffisamment fiable pour permettre la reconnaissance individuelle au cours du temps. En conclusion cette étude participe à une meilleure compréhension du système de communication vocale chez un primate non-humain forestier, au réseau social unique et complexe / Identity information is vital for highly social species as it facilitates individual recognition and allows for differentiation between social partners in many contexts, such as dominance hierarchies, territorial defence, mating and parent-offspringidentification and group cohesion and coordination. In many species vocalisations can be the most effective communication channel through complex environments and over long-distances and are encoded with the stable features of an individual’s voice. Associations between these individual vocal signatures and accumulated social knowledge about conspecifics can greatly increase an animal’s fitness, as it facilitates adaptively constructive social decisions. This thesis investigates the encoding and decoding of identity information in the vocal communication system of the bonobo, Pan paniscus. We firstly investigated the stability of vocal signatures across the five most common call types in the bonobo vocal repertoire. Results showed that while all call types have the potential to code identity information, loud calls used during times of high arousal and for distance communication have the strongest individual vocal signatures. Following the first study, we investigated if social familiarity and relatedness affect the acoustic features that code individual information in the bark call type. Overall, we found strong evidence for vocal convergence, and specifically, that individuals who are related and familiar, independently from one another, are more vocally similar to one another than unrelated and unfamiliar individuals. In a final study we tested if bonobos are capable of using the encoded identity information to recognise past group members that they no longer live with. Through a series playback experiments we demonstrated that bonobos are capable of recognising familiar individuals from vocalisations alone even after years of separation. Collectively, the results of this thesis show that the encoding and decoding of identity information in bonobo vocalisations is a dynamic system, subject to modification through social processes but robust enough to allow for individual recognition over time. In conclusion these studies contribute to a better understanding of the vocal communication system of a non-human primate species with a unique and complex social network

A central issue in the study of primate communication is the extent to which individuals adjust their behaviour to the attention and signals of others, and manipulate others’ attention to communicate about external events. I investigated whether 13 chimpanzees (Pan troglodytes spp.), 11 bonobos (Pan paniscus), and 7 orangutans (Pongo pygmaeus pygmaeus) followed conspecific attention and led others to distal locations. Individuals were presented with a novel stimulus, to test if they would lead a conspecific to detect it in two experimental conditions. In one the conspecific faced the communicator, while another required the communicator to first attract the attention of a conspecific. All species followed conspecific attention, but only bonobos in conditions that required geometric attention following and that the communicator first attract the conspecific‘s attention. There was a clear trend for the chimpanzees to selectively produce a stimulus directional ‘hunching’ posture when viewing the stimulus in the presence of a conspecific rather than alone (the comparison was statistically non-significant, but very closely approached significance [p = 0.056]), and the behaviour consistently led conspecifics to look towards the stimulus. An observational study showed that ‘hunching’ only occurred in the context of attention following. Some chimpanzees and bonobos consistently and selectively combined functionally different behaviours (consisting of sequential auditory-stimulus-directional-behaviours), when viewing the stimulus in the presence of a non-attentive conspecific, although at species level this did not yield significant effects. While the design did not eliminate the possibility of a social referencing motive (“look and help me decide how to respond”), the coupling of auditory cues followed by directional cues towards a novel object, is consistent with a declarative and social referential interpretation of non-verbal deixis. An exploratory study, which applied the ‘Social Attention Hypothesis’ (that individuals accord and receive attention as a function of dominance) to attention following, showed that chimpanzees were more likely to follow the attention of the dominant individual. Overall, the results suggest that the paucity of observed referential behaviours in apes may owe to the inconspicuousness and multi-faceted nature of the behaviours.