Abstract: We presented small groups of chimpanzees with two collective action situations, in which action was necessary for reward but there was a disincentive for individuals to act owing to the possibility of free-riding on the efforts of others. We found that in simpler scenarios (experiment 1) in which group size was small, there was a positive relationship between rank and action with more dominant individuals volunteering to act more often, particularly when the reward was less dispersed. Social tolerance also seemed to mediate action whereby higher tolerance levels within a group resulted in individuals of lower ranks sometimes acting and appropriating more of the reward. In more complex scenarios, when group size was larger and cooperation was necessary (experiment 2), overcoming the problem was more challenging. There was highly significant variability in the action rates of different individuals as well as between dyads, suggesting success was more greatly influenced by the individual personalities and personal relationships present in the group.

Abstract: Humans have many cognitive skills not possessed by their nearest primate relatives. The cultural intelligence hypothesis argues that this is mainly due to a species-specific set of social-cognitive skills, emerging early in ontogeny, for participating and exchanging knowledge in cultural groups. We tested this hypothesis by giving a comprehensive battery of cognitive tests to large numbers of two of humans' closest primate relatives, chimpanzees and orangutans, as well as to 2.5-year-old human children before literacy and schooling. Supporting the cultural intelligence hypothesis and contradicting the hypothesis that humans simply have more “general intelligence,” we found that the children and chimpanzees had very similar cognitive skills for dealing with the physical world but that the children had more sophisticated cognitive skills than either of the ape species for dealing with the social world.

Abstract: In the current study two groups of young chimpanzees (4–6 and 8–9 years old) were given a T-bar and a food item that could only be reached by using the T-bar. Experimental subjects were given the opportunity to observe an adult using the stick as a tool to obtain the food; control subjects were exposed to the adult but were given no demonstration. Subjects in the older group did not learn to use the tool. Subjects in the younger group who were exposed to the demonstrator learned to use the stick as a tool much more readily than those who were not. None of the subjects demonstrated an ability to imitatively copy the demonstrator's precise behavioral strategies. More than simple stimulus enhancement was involved, however, since both groups manipulated the T-bar, but only experimental subjects used it in its function as a tool. Our findings complement naturalistic observations in suggesting that chimpanzee tool-use is in some sense «culturally transmitted» — though perhaps not in the same sense as social-conventional behaviors for which precise copying of conspecifics is crucial.

Abstract: Description
Ever since Charles Darwin first formulated his theories on evolution, much research has been conducted in primate cognition. In this book, Michael Tomasello and Josep Call review what is already known about the cognitive skills of nonhuman primates, and assess the current state of our knowledge. They integrate empirical findings on the topic from the beginning of the century to the present, placing this work in theoretical perspective. The first part examines the way primates adapt to their physical world, mostly for the purpose of foraging. The second part lokos at primate social knowledhe and focuses on the adaptations of primates to their social world for purposes of competation and cooperation. In the third section, the authors construct a general theory of primate cognition, distinguishing the cognition in primates from that of other mammals (human in particular). Their broad-ranging theory should provide a guide for future research. Primate Cognition is an enlightening exploration of the cognitive capacities of our nearest primate relatives. It is a useful resource for a eide range of researchers and students in psychology, behavioral biology, primatology, and anthropology.

Abstract: At around 1 year of age, human infants display a number of new behaviors that seem to indicate a newly emerging understanding of other persons as intentional beings whose attention to outside objects may be shared, followed into, and directed in various ways. These behaviors have mostly been studied separately. In the current study, we investigated the most important of these behaviors together as they emerged in a single group of 24 infants between 9 and 15 months of age. At each of seven monthly visits, we measured joint attentional engagement, gaze and point following, imitation of two different kinds of actions on objects, imperative and declarative gestures, and comprehension and production of language. We also measured several nonsocial-cognitive skills as a point of comparison. We report two studies. The focus of the first study was the initial emergence of infants' social-cognitive skills and how these skills are related to one another developmentally. We found a reliable pattern of emergence: Infants progressed from sharing to following to directing others' attention and behavior. The nonsocial skills did not emerge predictably in this developmental sequence. Furthermore, correlational analyses showed that the ages of emergence of all pairs of the social-cognitive skills or their components were interrelated. The focus of the second study was the social interaction of infants and their mothers, especially with regard to their skills of joint attentional engagement (including mothers' use of language to follow into or direct infants' attention) and how these skills related to infants' early communicative competence. Our measures of communicative competence included not only language production, as in previous studies, but also language comprehension and gesture production. It was found that two measures-the amount of time infants spent in joint engagement with their mothers and the degree to which mothers used language that followed into their infant's focus of attention-predicted infants' earliest skills of gestural and linguistic communication. Results of the two studies are discussed in terms of their implications for theories of social-cognitive development, for theories of language development, and for theories of the process by means of which human children become fully participating members of the cultural activities and processes into which they are born.