Abstract:

Theory of mind refers to the ability of individuals to speculate about other people's mental states and make causal explanations for their behaviors. Comparative studies using non-human primates is an important way to explore the essence, origin and evolution of theory of mind. This article reviews a large number of empirical studies and demonstrate that nonhuman primates exhibit some basic theory of mind components, including joint attention, goal understanding and level-1 perspective-taking. Nonhuman primates can follow or attract the attention of other individuals, understand the behavior of other individuals based on potential goals and intentions, and judge whether other individuals perceive something from their perspective.

The paper explains the above conclusions from the perspective of evolutionary continuity hypothesis. Species that appeared earlier in the primate evolutionary lineage have been shown to have basic theory of mind. Phylogenetic reconstruction proved that theory of mind has deep evolutionary roots in primates. Research from neuroscience is consistent with this view. Brain imaging studies have shown that non-human primates and humans rely on common brain regions for mind-reading tasks. On the one hand, there are obvious anatomical and connectivity similarities between these parts of the human and non-human primate brains. On the other hand, these areas of the human brain have undergone significant expansion over the course of evolution. So theory of mind has evolutionary continuity across primate lineages. The similarity between nonhuman primates and humans in theory of mind stem from shared descent.

The paper also concludes that non-human primates are unable to achieve second-order perspective selection and false belief understanding as humans do. The submentalizing hypothesis, vicarious representation hypothesis, minimal theory of mind hypothesis and awareness relations hypothesis attempt to explain the differences. Although specific views and perspectives vary, these theories all emphasize that there is a primary representational system before a mature theory of mind is mastered by the individual, and these representational systems lay the foundation for the development of a complete theory of mind. However, non-human primates only have a primary representation system, and they are unable to form representations of other individuals' psychological beliefs about the external world. Belief representation is an important dividing point between non-human primates and humans in theory of mind. Unfortunately, there is no single hypothesis that can explain all the current empirical research. One possibility is that higher-level theory of mind depend on many different sub-processing mechanisms. Different task paradigms depend on different processing mechanisms, thus resulting in seemingly contradictory performance of non-human primates in different experimental modes. The differences and related explanations between non-human primates and human psychological theories in theory of mind need to be tested more fully in future studies.

For humans, theory of mind is a psychological mechanism that plays an important role in both competitive and cooperative scenarios. Non-human primates, on the other hand, seem to be more likely to initiate mind-reading in competitive situations, and competitive activities lead to more pronounced use of theory of mind. They are more likely to perceive competitive intentions from others than cooperative intentions or shared intentions. One reasonable speculation is that during human evolution, specific social pressures led humans to develop sensitivity to shared intentions. Theory of mind is further improved when individuals are able to establish common goals and coordinate with each other for common goals. Future research should focus on this hypothesis, and further explore the influence of shared intention on the development of primate theory of mind through empirical research.

The relationship between language and theory of mind is another topic that needs to be explored in the future. On the one hand, a higher level of theory of mind allows the individual to step into the perspective of the person he is communicating with, allowing him to understand the true meaning of the sender of the information senders. So the improvement of mind-reading ability in humans may have been a key shift in the evolution of language. Theory of mind is an important basis for the realization of complex language. On the other hand, language system provides a necessary tool for mental representation system. When represented in language, subjects can encode complex nested recursive relationships. Future research should focus on the relationship between the characteristics of non-human primates' theory of mind and their communication systems, and seek enlightenment for revealing the mysteries of human theory of mind and language evolution through comparative studies of different non-human primates.

Furthermore, as an important social cognitive feature, theory of mind is bound to be closely related to the social ecological environment of a species. In the future, more comparative studies on differences can enable researchers to explore the relationship between theory of mind and social attributes, and also enable researchers to test whether each sub-component of theory of mind has different social driving factors, providing important basis for understanding the evolutionary mechanism of theory of mind.

Key words: non-human primates, theory of mind, joint attention, perspective-taking, false belief