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Primates are capable of high levels of cognition; some make tools and use them to acquire foods and for social displays; some have sophisticated hunting strategies requiring cooperation, influence and rank; they are status conscious, manipulative and capable of deception; they can recognise kin and conspecifics; they can learn to use symbols and understand aspects of human language including some relational syntax, concepts of number and numerical sequence.
Studies in primate cognition
Theory of mind
Premack and Woodruff's 1978 article "Does the chimpanzee have a theory of mind?" sparked a contentious issue because of the problem of inferring from animal behavior the existence of thinking, of the existence of a concept of self or self-awareness, or of particular thoughts.
Non-human research still has a major place in this field, however, and is especially useful in illuminating which nonverbal behaviors signify components of theory of mind, and in pointing to possible stepping points in the evolution of what many claim to be a uniquely human aspect of social cognition. While it is difficult to study human-like theory of mind and mental states in species which we do not yet describe as "minded" at all, and about whose potential mental states we have an incomplete understanding, researchers can focus on simpler components of more complex capabilities.
For example, many researchers focus on animals' understanding of intention, gaze, perspective, or knowledge (or rather, what another being has seen). Part of the difficulty in this line of research is that observed phenomena can often be explained as simple stimulus-response learning, as it is in the nature of any theorizers of mind to have to extrapolate internal mental states from observable behavior. Recently, most non-human theory of mind research has focused on monkeys and great apes, who are of most interest in the study of the evolution of human social cognition.
There has been some controversy over the interpretation of evidence purporting to show theory of mind ability—or inability—in animals. Two examples serve as demonstration: first, Povinelli et al. (1990) presented chimpanzees with the choice of two experimenters from which to request food: one who had seen where food was hidden, and one who, by virtue of one of a variety of mechanisms (having a bucket or bag over his head; a blindfold over his eyes; or being turned away from the baiting) does not know, and can only guess. They found that the animals failed in most cases to differentially request food from the "knower." By contrast, Hare, Call, and Tomasello (2001) found that subordinate chimpanzees were able to use the knowledge state of dominant rival chimpanzees to determine which container of hidden food they approached.
Tomasello and like-minded colleagues who originally argued that great apes did not have theory of mind have since reversed their position. Povinelli and his colleagues, however, maintain that Tomasello's group has misinterpreted the results of their experiments. They point out that most evidence in support of great ape theory of mind involves naturalistic settings to which the apes may have already adapted through past learning. Their "reinterpretation hypothesis" explains away all current evidence supporting attribution of mental states to others in chimpanzees as merely evidence of risk-based learning; that is, the chimpanzees learn through experience that certain behaviors in other chimpanzees have a probability of leading to certain responses, without necessarily attributing knowledge or other intentional states to those other chimpanzees. They therefore propose testing theory of mind abilities in great apes in novel, and not naturalistic settings. Kristin Andrews takes the reinterpretation hypothesis one step further, arguing that it implies that even the well-known false-belief test used to test children's theory of mind is susceptible to being interpreted as a result of learning.
The modelling of human language in animals is known as animal language research. There have been many examples of modelling of human language through entrainment in primates. Most notably are Nim Chimpsky, a chimpanzee; Koko, a gorilla and Kanzi, a bonobo. Cognitive abilities are also demonstrated through the natural communication through vocalizations performed by non-human primates in the wild, with sophisticated systems of alarm calls and emotional vocalizations as well as adaptive behavioural responses to other animal's calls.
Modeling of human language
The experiment called Project Nim was one of the first experiments that aimed to show nonhuman primates could be taught a human form of language. The experiment conducted on the chimpanzee dubbed "Nim Chimpsky" took place in the 1970s and was the idea of Herbet S. Terrace, to try to disprove the notion put forth by Noam Chomsky, for whom the chimp was named, stating that language is an exclusively human ability. Nim was taught 125 signs in his life, and constantly impressed those he met with his ability to seemingly understand human nature and his mischievous behaviours. Similar experiments took place on two other primates, Koko and Kanzi. Koko was able to learn many signs, as well as some novel vocalizations to indicate emotional state. Kanzi learned to model human language in an entirely different way. He was able to learn 348 geometrical symbols that represented different words, and to combine symbols in a type of proto-grammar to convey meaning and understanding. His keepers also claim that he understands the meaning of up to 3,000 human words. These examples of stunning cognition demonstrate the near-human ability of some trained primates to learn and retain the ability to communicate with humans.
Communication in the wild
Communication of animals in the wild has been studied extensively. Calls with specific intent, such as alarm calls or mating calls has been observed in many orders of animals, including primates. A study done on East African Vervet monkeys showed that in the wild this species was able to produce at least 5 acoustically different alarm calls in response to danger, and that other monkeys responded differently according to which alarm had been sounded. This indicated a clear communication that there is a predator nearby and what kind of predator it is, eliciting a specific response. A different species of monkeys, the wild Campbell's monkeys have also been known to produce a sequence of vocalization that require a specific order to elicit a specific behaviour in other monkeys. Changing the order of the sounds changes the resulting behaviour, or meaning, of the call. Diana monkeys were studied in a habituation-dishabituation experiment that demonstrated the ability to attend to the semantic content of calls rather than simply to acoustic nature. Primates have also been observed responding to alarm calls of other species. Crested Guinea fowl, a ground-dwelling fowl, produce a single type of alarm call for all predators it detects. Diana monkeys have been observed to respond to the most likely reason for the call, typically a human or leopard, based on the situation and respond according to that. If they deem a leopard is the more likely predator in the vicinity they will produce their own leopard-specific alarm call but if they think it is a human, they will remain silent and hidden.
There are many reports of primates making or using tools, both in the wild or when captive. Chimpanzees, gorillas, orangutans, capuchin monkeys, baboons, and mandrills have all been reported as using tools. The use of tools by primates is varied and includes hunting (mammals, invertebrates, fish), collecting honey, processing food (nuts, fruits, vegetables and seeds), collecting water, weapons and shelter.
Tool making is much rarer, but has been documented in orangutans, bonobos and bearded capuchin monkeys. Research in 2007 shows that chimpanzees in the Fongoli savannah sharpen sticks to use as spears when hunting, considered the first evidence of systematic use of weapons in a species other than humans. Captive gorillas have made a variety of tools. In the wild, mandrills have been observed to clean their ears with modified tools. Scientists filmed a large male mandrill at Chester Zoo (UK) stripping down a twig, apparently to make it narrower, and then using the modified stick to scrape dirt from underneath its toenails.
There is some controversy over whether tool use represents a higher level of physical cognition. Some studies suggest primates could use tools due to environmental or motivational clues, rather than an understanding of folk physics or a capacity for future planning.
In 1913, Wolfgang Köhler started writing a book on problem solving titled The Mentality of Apes (1917). In this research, Köhler observed the manner in which chimpanzees solve problems, such as that of retrieving bananas when positioned out of reach. He found that they stacked wooden crates to use as makeshift ladders in order to retrieve the food. If the bananas were placed on the ground outside of the cage, they used sticks to lengthen the reach of their arms.
Köhler concluded that the chimps had not arrived at these methods through trial-and-error (which American psychologist Edward Thorndike had claimed to be the basis of all animal learning, through his law of effect), but rather that they had experienced an insight (sometimes known as the Eureka effect or an "aha" experience), in which, having realized the answer, they then proceeded to carry it out in a way that was, in Köhler's words, "unwaveringly purposeful."
Asking questions and giving negative answers
In the 1970s and the 1980s there had been suggestions that apes are unable to ask questions and to give negative answers. According to numerous published studies, apes are able to answer human questions, and the vocabulary of the acculturated apes contains question words. Despite these abilities, according to the published research literature, apes are not able to ask questions themselves, and in human-primate conversations questions are asked by the humans only. Ann and David Premacks designed a potentially promising methodology to teach apes to ask questions in the 1970s: "In principle interrogation can be taught either by removing an element from a familiar situation in the animal's world or by removing the element from a language that maps the animal's world. It is probable that one can induce questions by purposefully removing key elements from a familiar situation. Suppose a chimpanzee received its daily ration of food at a specific time and place, and then one day the food was not there. A chimpanzee trained in the interrogative might inquire "Where is my food?" or, in Sarah's case, "My food is?" Sarah was never put in a situation that might induce such interrogation because for our purposes it was easier to teach Sarah to answer questions".
A decade later Premacks wrote: "Though she [Sarah] understood the question, she did not herself ask any questions—unlike the child who asks interminable questions, such as What that? Who making noise? When Daddy come home? Me go Granny's house? Where puppy? Sarah never delayed the departure of her trainer after her lessons by asking where the trainer was going, when she was returning, or anything else".
Despite all their achievements, Kanzi and Panbanisha also have not demonstrated the ability to ask questions so far. Joseph Jordania suggested that the ability to ask questions could be the crucial cognitive threshold between human and other ape mental abilities. Jordania suggested that asking questions is not a matter of the ability of using syntactic structures, that it is primarily a matter of cognitive ability.
g factor of intelligence in primates
The general factor of intelligence, or g factor, is a psychometric construct that summarizes the correlations observed between an individual’s scores on various measures of cognitive abilities. First described in humans, the g factor has since been identified in a number of nonhuman species.
Primates in particular have been the focus of g research due to their close taxonomic links to humans. A principal component analysis run in a meta-analysis of 4,000 primate behaviour papers including 62 species found that 47% of the individual variance in cognitive ability tests was accounted for by a single factor, controlling for socio-ecological variables. This value fits within the accepted range of the influence of g on IQ.
However, there is some debate as to the influence of g on all primates equally. A 2012 study identifying individual chimpanzees that consistently performed highly on cognitive tasks found clusters of abilities instead of a general factor of intelligence. This study used individual-based data and claim that their results are not directly comparable to previous studies using group data that have found evidence for g. Further research is required to identify the exact nature of g in primates.
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