Theory of mind in animals is an extension to non-human animals of the philosophical and psychological concept of theory of mind (ToM), sometimes known as mentalisation or mind-reading. It involves an inquiry into whether non-human animals have the ability to attribute mental states (such as intention, desires, pretending, knowledge) to themselves and others, including recognition that others have mental states that are different from their own. [1] [2] [3] To investigate this issue experimentally, researchers place non-human animals in situations where their resulting behavior can be interpreted as supporting ToM or not.
The existence of theory of mind in non-human animals is controversial. On the one hand, one hypothesis proposes that some non-human animals have complex cognitive processes which allow them to attribute mental states to other individuals, sometimes called "mind-reading" while another proposes that non-human animals lack these skills and depend on more simple learning processes such as associative learning; [4] or in other words, they are simply behaviour-reading.
Several studies have been designed specifically to test whether non-human animals possess theory of mind by using interspecific or intraspecific communication. Several taxa have been tested including primates, birds and canines. Positive results have been found; however, these are often qualified as showing only low-grade ToM, or rejected as not convincing by other researchers.
The term "theory of mind" was originally proposed by Premack and Woodruff in 1978. [2] [5] Early studies focused almost entirely on studying if chimpanzees could understand the knowledge of humans. This approach turned out not to be particularly fruitful and 20 years later, Heyes, reviewing all the extant data, observed that there had been "no substantial progress" in the subject area. [6]
A 2000 paper [7] approached the issue differently by examining competitive foraging behaviour between primates of the same species (conspecifics). This led to the rather limited conclusion that "chimpanzees know what conspecifics do and do not see". [8]
In 2007, Penn and Povinelli wrote "there is still little consensus on whether or not nonhuman animals understand anything about unobservable mental states or even what it would mean for a non-verbal animal to understand the concept of a 'mental state'." They went on further to suggest that ToM was "any cognitive system, whether theory-like or not, that predicts or explains the behaviour of another agent by postulating that unobservable inner states particular to the cognitive perspective of that agent causally modulate that agent's behaviour". [9]
In 2010, an article in Scientific American acknowledged that dogs are considerably better at using social direction cues (e.g. pointing by humans) than are chimpanzees. [10] In the same year, Towner wrote, "the issue may have evolved beyond whether or not there is theory of mind in non-human primates to a more sophisticated appreciation that the concept of mind has many facets and some of these may exist in non-human primates while others may not." [5] Horowitz, working with dogs, agreed. [11]
In 2013, Whiten reviewed the literature and concluded that regarding the question "Are chimpanzees truly mentalists, like we are?", he stated he could not offer an affirmative or negative answer. [8] A similarly equivocal view was stated in 2014 by Brauer, who suggested that many previous experiments on ToM could be explained by the animals possessing other abilities. They went on further to make reference to several authors who suggest it is pointless to ask a "yes or no" question, rather, it makes more sense to ask which psychological states animals understand and to what extent. [12] At the same time, it was suggested that a "minimal theory of mind" may be "what enables those with limited cognitive resources or little conceptual sophistication, such as infants, chimpanzees, scrub-jays and human adults under load, to track others' perceptions, knowledge states and beliefs." [13]
In 2015, Cecilia Heyes, Professor of Psychology at the University of Oxford, wrote about research on ToM, "Since that time [2000], many enthusiasts have become sceptics, empirical methods have become more limited, and it is no longer clear what research on animal mindreading is trying to find" and "However, after some 35 years of research on mindreading in animals, there is still nothing resembling a consensus about whether any animal can ascribe any mental state" (Heyes' emphasis). Heyes further suggested that "In combination with the use of inanimate control stimuli, species that are unlikely to be capable of mindreading, and the 'goggles method' [see below], these approaches could restore both vigour and rigour to research on animal mindreading." [1]
Specific categories of behaviour are sometimes used as evidence of animal ToM, including imitation, self-recognition, social relationships, deception, role-taking (empathy), perspective-taking, teaching and co-operation, [5] however, this approach has been criticised. [6] Some researchers focus on animals' understanding of intention, gaze, perspective, or knowledge, i.e. what another being has seen. Several experimental methods have been developed which are widely used or suggested as appropriate tests for nonhuman animals possessing ToM. Some studies look at communication between individuals of the same species (intraspecific) whereas others investigate behaviour between individuals of different species (interspecific).
The Knower-Guesser method has been used in many studies relating to animal ToM. [6]
The competitive feeding paradigm approach is considered by some as evidence that animals have some understanding of the relationship between "seeing" and "knowing". [1]
In one suggested protocol, chimpanzees are given first-hand experience of wearing two mirrored visors. One of the visors is transparent whereas the other is not. The visors themselves are of markedly different colours or shapes. During the subsequent test session, the chimpanzees are given the opportunity to use their species-typical begging behaviour to request food from one of the two humans, one wearing the transparent visor and the other wearing the opaque. If chimpanzees possess ToM, it would be expected they would beg more often from the human wearing the transparent visor.
A method used to test ToM in human children has been adapted for testing non-human animals. The basis of the test is to track the gaze of the animal. One human hides an object in view of a second human who then leaves the room. The object is then removed. [14]
Many ToM studies have used nonhuman primates (NHPs). One study that examined the understanding of intention in orangutans (Pongo pygmaeus), chimpanzees (Pan troglodytes) and children showed that all three species understood the difference between accidental and intentional acts. [15]
There is controversy over the interpretation of evidence purporting to show ToM in chimpanzees. [16]
Chimpanzees were unable to follow a human's gaze to find food hidden under opaque bowls, but were able to do so when food was hidden in tubes that the experimenter was able to look into. This seems to suggest that chimpanzees can infer another individual's perception depending on the clarity of the mechanism through which the individual has gained that knowledge. [17]
Attempts to use the "Goggles Method" (see above) on highly human-enculturated chimpanzees failed to demonstrate they possess ToM. [9]
In contrast, chimpanzees use the gaze of other chimpanzees to gain information about whether food is accessible. [7] Subordinate chimpanzees are able to use the knowledge state of dominant chimpanzees to determine which container has hidden food. [18]
Young chimpanzees were shown to reliably help researchers perform tasks that involved reaching (such as picking up dropped items that the researcher struggled to retrieve), without specific prompting. This suggests that these chimpanzees were able to understand the researcher's intentions in these cases and acted upon them. [19] [20]
In a similar study, chimps were provided with a preference box with two compartments, one containing a picture of food, the other containing a picture of nothing. Neither were actually related to the contents of the box. In a foraging competition game, chimpanzees avoided the chamber with the picture of food when their competitor had chosen one of the chambers before them. [21] [22]
Captive bonobos such as Kanzi have been reported to show concern for their handlers’ well-being. [23] Bonobos also console other bonobos who are victims of aggressive conflicts and reconcile after participating in these conflicts. [24] Both of these behaviors suggest some semblance of ToM through an attribution of mental states to another individual.
Chimpanzees have passed the False Belief Test (see above) involving anticipating the gaze of humans when objects have been removed. Infrared eye-tracking showed that the chimpanzee subjects’ gaze were focused on where the experimenter would falsely believe the object /subject to be, rather than focusing on its actual location of which the chimps were aware. This seems to suggest that the chimpanzees were capable of ascribing false belief to the experimenter. [25]
Evidence for ToM | Present in Chimps? | Present in Bonobos? | References |
---|---|---|---|
Attribution to Perception/Knowledge | |||
Using human gaze to find food hidden under opaque bowl | No | Call et al., 1998 | |
Using human gaze to find food hidden in tube open to human | Yes | Call et al., 1998 | |
Remembering what human had seen and inferring target of attention | Yes | Yes | MacLean & Hare, 2012 |
Attribution to Intention | |||
Helping humans retrieve objects when reaching | Yes | Warneken & Tomasello, 2008 | |
Consoling victims of conflict and reconciling after participating in these conflicts | Yes | Clay & Waal, 2013 | |
Attribution of False Belief | |||
Anticipating that human will look in wrong location based on false belief | Yes | Yes | Krupenye et al., 2016 |
In one approach testing monkeys, rhesus macaques (Macaca mulatta) are able to "steal" a contested grape from one of two human competitors. In six experiments, the macaques selectively stole the grape from a human who was incapable of seeing the grape, rather than from the human who was visually aware. [26] Similarly, free ranging rhesus macaques preferentially choose to steal food items from locations where they can be less easily observed by humans, or where they will make less noise.[ citation needed ]
The authors also reported that at least one individual of each of the species showed (weak) evidence of ToM. [27]
In a multi-species study, it was shown that chimpanzees, bonobos and orangutans passed the False Belief Test (see above). [25]
In 2009, a summary of the ToM research, particularly emphasising an extensive comparison of humans, chimpanzees and orang-utans, [28] concluded that great apes do not exhibit understanding of human referential intentions expressed in communicative gestures, such as pointing. [29]
Grey parrots (Psittacus erithacus) have demonstrated high levels of intelligence. Irene Pepperberg did experiments with these and her most accomplished parrot, Alex, demonstrated behaviour which seemed to manipulate the trainer, possibly indicating theory of mind. [30]
Ravens are members of the family Corvidae and are widely regarded as having complex cognitive abilities. [31] [32] Other studies indicate that ravens recall who was watching them during caching, but also know the effects of visual barriers on what competitors can and can not see, and how this affects their pilfering. [33]
Ravens have been tested for their understanding of "seeing" as a mental state in other ravens. [34] The researchers further suggested that their findings could be considered in terms of the "minimal" (as opposed to "full-blown") ToM recently suggested. [13]
Using the Knower-Guesser approach, ravens observing a human hiding food are capable of predicting the behaviour of bystander ravens that had been visible at both, none or just one of two baiting events. The visual field of the competitors was manipulated independently of the view of the test-raven. [35]
Scrub jays are also corvids. Western scrub jays (Aphelocoma californica) both cache food and pilfer other scrub jays' caches. They use a range of tactics to minimise the possibility that their own caches will be pilfered. One of these tactics is to remember which individual scrub jay watched them during particular caching events and adjust their re-caching behaviour accordingly. [36] One study with particularly interesting results found that only scrub jays which had themselves pilfered would re-cache when they had been observed making the initial cache. [37] This has been interpreted as the re-caching bird projecting its own experiences of pilfering intent onto those of another potential pilferer, and taking appropriate action. [8] [38]
Domestic dogs (Canis familiaris) show an impressive ability to use the behaviour of humans to find food and toys using behaviours such as pointing and gazing. The performance of dogs in these studies is superior to that of NHPs, [39] however, some have stated categorically that dogs do not possess a human-like ToM. [12] [40]
Similarly, dogs preferentially use the behaviour of the human Knower to indicate the location of food. This is unrelated to the sex or age of the dog. In another study, 14 of 15 dogs preferred the location indicated by the Knower on the first trial, whereas chimpanzees require approximately 100 trials to reliably exhibit the preference. [39] [29]
An experiment at the University of Bristol found that one out of ten pigs was possibly able to understand what other pigs can see. That pig observed another pig which had view of a maze in which food was being hidden, and trailed that pig through the maze to the food. The other pigs involved in the experiment did not. [41] [42]
A 2006 study found that goats exhibited intricate social behaviours indicative of high-level cognitive processes, particularly in competitive situations. The study included an experiment in which a subordinate animal was allowed to choose between food that a dominant animal could also see and food that it could not; those who were subject to aggressive behaviour selected the food that the dominant animal could not see, suggesting that they are able to perceive a threat based on being within the dominant animal's view – in other words, visual perspective taking. [43]
The chimpanzee, also known as simply the chimp, is a species of great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close relative the bonobo was more commonly known as the pygmy chimpanzee, this species was often called the common chimpanzee or the robust chimpanzee. The chimpanzee and the bonobo are the only species in the genus Pan. Evidence from fossils and DNA sequencing shows that Pan is a sister taxon to the human lineage and is humans' closest living relative. The chimpanzee is covered in coarse black hair, but has a bare face, fingers, toes, palms of the hands, and soles of the feet. It is larger and more robust than the bonobo, weighing 40–70 kg (88–154 lb) for males and 27–50 kg (60–110 lb) for females and standing 150 cm.
The bonobo, also historically called the pygmy chimpanzee, is an endangered great ape and one of the two species making up the genus Pan. While bonobos are, today, recognized as a distinct species in their own right, they were initially thought to be a subspecies of Pan troglodytes, due to the physical similarities between the two species. Taxonomically, the members of the chimpanzee/bonobo subtribe Panina—composed entirely by the genus Pan—are collectively termed panins.
The genus Pan consists of two extant species: the chimpanzee and the bonobo. Taxonomically, these two ape species are collectively termed panins. The two species were formerly collectively called "chimpanzees" or "chimps"; if bonobos were recognized as a separate group at all, they were referred to as "pygmy chimpanzees". Together with humans, gorillas, and orangutans they are part of the family Hominidae. Native to sub-Saharan Africa, chimpanzees and bonobos are currently both found in the Congo jungle, while only the chimpanzee is also found further north in West Africa. Both species are listed as endangered on the IUCN Red List of Threatened Species, and in 2017 the Convention on Migratory Species selected the chimpanzee for special protection.
Apes are a clade of Old World simians native to sub-Saharan Africa and Southeast Asia, which together with its sister group Cercopithecidae form the catarrhine clade, cladistically making them monkeys. Apes do not have tails due to a mutation of the TBXT gene. In traditional and non-scientific use, the term ape can include tailless primates taxonomically considered Cercopithecidae, and is thus not equivalent to the scientific taxon Hominoidea. There are two extant branches of the superfamily Hominoidea: the gibbons, or lesser apes; and the hominids, or great apes.
Franciscus Bernardus Maria "Frans" de Waal is a Dutch primatologist and ethologist. He is the Charles Howard Candler Professor of Primate Behavior in the Department of Psychology at Emory University in Atlanta, Georgia, director of the Living Links Center at the Yerkes National Primate Research Center at Emory, and author of numerous books including Chimpanzee Politics (1982) and Our Inner Ape (2005). His research centers on primate social behavior, including conflict resolution, cooperation, inequity aversion, and food-sharing. He is a member of the United States National Academy of Sciences and the Royal Netherlands Academy of Arts and Sciences.
Animal cognition encompasses the mental capacities of non-human animals including insect cognition. The study of animal conditioning and learning used in this field was developed from comparative psychology. It has also been strongly influenced by research in ethology, behavioral ecology, and evolutionary psychology; the alternative name cognitive ethology is sometimes used. Many behaviors associated with the term animal intelligence are also subsumed within animal cognition.
Dog intelligence or dog cognition is the process in dogs of acquiring information and conceptual skills, and storing them in memory, retrieving, combining and comparing them, and using them in new situations.
The California scrub jay is a species of scrub jay native to western North America. It ranges from southern British Columbia throughout California and western Nevada near Reno to west of the Sierra Nevada. The California scrub jay was once lumped with Woodhouse's scrub jay and collectively called the western scrub jay. The group was also lumped with the island scrub jay and the Florida scrub jay; the taxon was then called simply scrub jay. The California scrub jay is nonmigratory and can be found in urban areas, where it can become tame and will come to bird feeders. While many refer to scrub jays as "blue jays", the blue jay is a different species of bird entirely.
Cognitive specialization suggests that certain behaviors, often in the domain of social communication, are passed on to offspring and refined to be maximally beneficial by the process of natural selection. Specializations serve an adaptive purpose for an organism by allowing the organism to be better suited for its habitat. Over time, specializations often become essential to the species' continued survival. Cognitive specialization in humans has been thought to underlie the acquisition, development, and evolution of language, theory of mind, and specific social skills such as trust and reciprocity. These specializations are considered to be critical to the survival of the species, even though there are successful individuals who lack certain specializations, including those diagnosed with autism spectrum disorder or who lack language abilities. Cognitive specialization is also believed to underlie adaptive behaviors such as self-awareness, navigation, and problem solving skills in several animal species such as chimpanzees and bottlenose dolphins.
The concept of the evolution of morality refers to the emergence of human moral behavior over the course of human evolution. Morality can be defined as a system of ideas about right and wrong conduct. In everyday life, morality is typically associated with human behavior rather than animal behavior. The emerging fields of evolutionary biology, and in particular evolutionary psychology, have argued that, despite the complexity of human social behaviors, the precursors of human morality can be traced to the behaviors of many other social animals. Sociobiological explanations of human behavior remain controversial. Social scientists have traditionally viewed morality as a construct, and thus as culturally relative, although others such as Sam Harris argue that there is an objective science of morality.
Tool use by non-humans is a phenomenon in which a non-human animal uses any kind of tool in order to achieve a goal such as acquiring food and water, grooming, combat, defence, communication, recreation or construction. Originally thought to be a skill possessed only by humans, some tool use requires a sophisticated level of cognition. There is considerable discussion about the definition of what constitutes a tool and therefore which behaviours can be considered true examples of tool use. A wide range of animals, including mammals, birds, fish, cephalopods, and insects, are considered to use tools.
Joint attention or shared attention is the shared focus of two individuals on an object. It is achieved when one individual alerts another to an object by means of eye-gazing, pointing or other verbal or non-verbal indications. An individual gazes at another individual, points to an object and then returns their gaze to the individual. Scaife and Bruner were the first researchers to present a cross-sectional description of children's ability to follow eye gaze in 1975. They found that most eight- to ten-month-old children followed a line of regard, and that all 11- to 14-month-old children did so. This early research showed it was possible for an adult to bring certain objects in the environment to an infant's attention using eye gaze.
Primate cognition is the study of the intellectual and behavioral skills of non-human primates, particularly in the fields of psychology, behavioral biology, primatology, and anthropology.
Josep Call is a Spanish comparative psychologist specializing in primate cognition.
Culture and social cognition is the relationship between human culture and human cognitive capabilities. Cultural cognitive evolution proposes that humans’ unique cognitive capacities are not solely due to biological inheritance, but are in fact due in large part to cultural transmission and evolution. Modern humans and great apes are separated evolutionarily by about six million years. Proponents of cultural evolution argue that this would not have been enough time for humans to develop the advanced cognitive capabilities required to create tools, language, and build societies through biological evolution. Biological evolution could not have individually produced each of these cognitive capabilities within that period of time. Instead, humans must have evolved the capacity to learn through cultural transmission. This provides a more plausible explanation that would fit within the given time frame. Instead of having to biologically account for each cognitive mechanism that distinguishes modern humans from previous relatives, one would only have to account for one significant biological adaptation for cultural learning. According to this view, the ability to learn through cultural transmission is what distinguishes humans from other primates. Cultural learning allows humans to build on existing knowledge and make collective advancements, also known as the “ratchet effect”. The ratchet effect simply refers to the way in which humans continuously add on to existing knowledge through modifications and improvements. This unique ability distinguishes humans from related primates, who do not seem to build collaborative knowledge over time. Instead, primates seem to build individual knowledge, in which the expertise of one animal is not built on by others, and does not progress across time.
Deception in animals is the transmission of misinformation by one animal to another, of the same or different species, in a way that propagates beliefs that are not true.
Number sense in animals is the ability of creatures to represent and discriminate quantities of relative sizes by number sense. It has been observed in various species, from fish to primates. Animals are believed to have an approximate number system, the same system for number representation demonstrated by humans, which is more precise for smaller quantities and less so for larger values. An exact representation of numbers higher than three has not been attested in wild animals, but can be demonstrated after a period of training in captive animals.
The cooperative pulling paradigm is an experimental design in which two or more animals pull rewards toward themselves via an apparatus that they cannot successfully operate alone. Researchers use cooperative pulling experiments to try to understand how cooperation works and how and when it may have evolved.
Brian Hare is a professor of evolutionary anthropology at Duke University. He researches the evolution of cognition by studying both humans, our close relatives the primates, and species whose cognition converged with our own. He founded and co-directs the Duke Canine Cognition Center.
Inequity aversion in animals is the willingness to sacrifice material pay-offs for the sake of greater equality, something humans tend to do from early age. It manifests itself through negative responses when rewards are not distributed equally between animals. In controlled experiments it has been observed, to varying degrees, in capuchin monkeys, chimpanzees, macaques, marmosets, dogs, wolves, rats, crows and ravens. No evidence of the effect was found in tests with orangutans, owl monkeys, squirrel monkeys, tamarins, kea, and cleaner fish. Based on mixed results in experimental studies it may be concluded that some bonobos, baboons, gibbons, and gorillas are inequity averse. Disadvantageous inequity aversion, which occurs when the animal protests as it gets a lesser reward than another animal, is most common. But advantageous inequity aversion has been observed as well, in chimpanzees, baboons and capuchins: the animal protests when it gets a better reward. Scientists believe that sensitivity to inequity co-evolved with the ability to cooperate, as it helps to sustain benefitting from cooperation. There is little evidence for inequity aversion in non-cooperative species.
{{cite journal}}
: CS1 maint: multiple names: authors list (link)