The ability to understand the mental states of others may not be a unique property of humans, and studying this in our relatives may elucidate its evolution in us. Photo credit: Andrey Tikhonovskiy via Unsplash
An exploration of the current evidence for Theory of Mind in animals
Theory of mind (ToM) is the ability to understand that others have mental states (e.g beliefs, knowledge and desires) that are different from our own. Developing a ToM is important for communicating and forming social relationships and thus, is critical to facilitating complex social lives of humans. Indeed, ToM have been confirmed in humans using a variety of tests such as the famous Sally-Anne test, a psychological test based on a story involving two children named Sally and Anne. The task goes as follows: Sally hides marbles in a box and leaves the room. While Sally is out Anne moves the marbles to a basket. Participants are then asked where Sally will look for the marbles when she returns to the room. If the answer is the “box”, it is taken as evidence of ToM as it demonstrates that the participant understands that others have their own internal beliefs. Whilst the child knows that the marbles are in the basket, they understand that Sally does not know. Several studies have shown that children usually pass this test by around the age of four. However, it remains debated whether these results translate to non-human animals.
One of the main challenges of studying ToM in animals is that they cannot explicitly tell us what they are thinking. Such methodological puzzles make the extant theories and data very debatable. However, evidence suggesting that some animals may also have ToM is slowly accumulating. The aim of this article is to review some of these studies.
Observational evidence
One main source of evidence in support of ToM in animals originates from observations of wild behaviour, particularly observations of deception. Deception is an interesting cognitive ability because in order to “lie”, an animal needs to understand the perspectives of others and anticipate their beliefs, requiring ToM. One type of deception that may be evidence of ToM is tactical deception, the use of an animal’s normal behaviour to deceive others. Whiten and Byrne (1988) analysed potential acts of deception in wild primates. One example of such an act is the deceptive use of alarm calls which are normally used to alert others the presence of predators. Some chimpanzees instead use these alarm calls when being chased by other chimpanzees to distract them and end the chase.
Whiten and Byrne found that apart from one other group (the Cercopithecinae, a subfamily of Old World Monkeys), all examples of tactical deception that could be explained by ToM were in the great apes. These results are potentially evidence of ToM and suggest that ToM may also be limited to certain animal groups. However, observations are not strong evidence for ToM as they have a number of limitations, including that the behaviour may have occurred by chance, could be the result of previous learning, or could be due to poor data collection by the experimenter. Instead, controlled experimental approaches are needed to provide strong evidence for ToM.
Experimental evidence
False belief test models
One experimental approach used to test for ToM are false-belief test models. A false-belief test model is an experimental paradigm designed to assess whether a subject can attribute false beliefs to others, determining the ToM. An example of this is by Povinelli et al. (1990), who conducted a guesser-knower task where chimps observe two people in a room. One person, the guesser, exits the room and the other person, the knower, hides the food in one of two boxes. The guesser returns and then both guesser and knower point to the box they think the food is in. The chimp then has to pull a lever to select a box. It is proposed that if the chimp has ToM they will select the box the knower is pointing at, and this is what Povinelli et al’s results show.
However, there is a killjoy explanation for these results—the chimp is selecting the human informant they are more familiar with. To try and test this hypothesis the experiment was repeated, but this time with the guesser wearing a paper bag over their head, so the chimp is exposed to the knower and the guesser for the same amount of time. The results of this experiment were the same as the first, with all chimps selecting the knower’s choice of box.
However, there is still an alternative explanation for these results. The performance of the chimps was by chance during the first two blocks of trials, and therefore it is possible the chimps learned which humans to select via associative learning. Additionally, chimps failed in further tests which tried to replicate the results. So, these experiments do not provide convincing evidence of ToM in chimps. Another issue with these experiments is that they are potentially expecting too much from the test animal. The chimps are expected to not only know about others but also pull a lever, which is an unnatural action for them. Therefore, there is a need to corroborate these findings with ToM experiments that are designed to suit the ecology of the test animal.
Competitive feeding paradigms
An alternative experimental approach is using a competitive feeding paradigm. During such, two individuals, with differing knowledge of the location of resources, compete. If an ‘informed’ individual uses a resource that the ‘uninformed’ individual cannot see, it is assumed that the ‘informed’ has a ToM, and understands the perspective of the ‘uninformed’. Hare et al. (2000) conducted these tests on chimps—an informed individual could see two food sources whereas, an uninformed only saw one. There were a number of observations suggesting that informed knew the uninformed could not see the hidden food. For example, four individuals only took the food once the uninformed moved away, and one individual waited until the uninformed turned its back to take the food, all suggesting ToM.
These results suggest chimps know what knowledge conspecifics (members of the same species) have, and by extension that the chimps have ToM. However, there is an alternative explanation for these results. It is possible that the informed individual’s choice of food is driven by behavioural cues from the uninformed, not due to ToM. Therefore, this highlights how complex social behaviour does not necessarily require ToM and on its own does not prove that chimps have ToM.
Experience Projection Paradigms
A more successful approach has been Experience Projection Paradigms (EPPs) where test subjects project their experience onto others. One example of an EPP is a desire attribution experiment by Ostojić et al. (2013) which tested whether the food males chose to feed females reflected knowledge of female desires. Females were fed wax moth or meal worm larvae until satiation, and some males observed this feeding. When males observed female feeding, they fed the female less of the food the female had previously eaten, e.g. if the female was fed wax moth larvae, males fed them less wax moth larvae and more meal worm larvae.
Aside from the desire attribution experiment, there is little strong evidence for ToM in animals.
When males could not observe feeding, they showed no preference for what food they fed the female. Importantly, males did not show the same bias in food choice when feeding themselves as when they fed females. These findings suggest that male jays knew what the females wanted, providing evidence of ToM. These results cannot be explained by behaviour reading as when males did not observe female feeding, they showed no preference in food choice. This is a well-constructed study that might provide evidence for ToM as it is hard to explain the results with behaviour reading.
Current evidence and future directions
Aside from the desire attribution experiment, there is little strong evidence for ToM in animals. However, this lack of evidence does not mean that animals do not have ToM. Heyes (2015) suggested that the problems facing research on ToM are both theoretical and methodological. Firstly, there is no clear definition of what it means to have a ToM, making it difficult to produce clear alternative hypotheses to ToM. Additionally, there are a lack of effective methods to discriminate between ToM and killjoy explanations such as behaviour reading or associative learning. However, the desire attribution experiment shows that if carefully designed studies are able to exclude alternative explanations, they may provide strong evidence for ToM. Thus, to effectively test for ToM in animals, future studies are needed that have clear hypotheses, careful experimental design and consideration of alternative explanations.
Studying ToM in close relatives of humans could provide insights into the evolutionary precursors of our social cognition, helping to reconstruct the evolution of human cognition.
Importance of ToM in animals
Studying ToM in animals is essential for understanding the evolutionary origins of ToM, as well as the mechanisms underlying it. Studying ToM in close relatives of humans could provide insights into the evolutionary precursors of our social cognition, helping to reconstruct the evolution of human cognition. For example, if ToM is found in apes it would suggest that any unique human abilities such as language are not required for ToM to evolve. Furthermore, investigating distantly related species can indicate whether ToM has evolved convergently, enabling investigation into the potential selective pressures that drive its evolution. Understanding ToM in animals could thus elucidate the evolution of human cognition and provide insights into the development of our sociality.
