Understanding the evolution of self-awareness, which is defined as the capacity to reflect on oneself as an individual, in nonhuman animals holds far-reaching implications for understanding the evolution of consciousness, cognition and ethical considerations that shape the treatment of animals. The mirror self-recognition test, which was developed in the 1970s, has been widely used to assess individual self-recognition, often equated with a certain level of self-awareness and higher-order cognition. In this review, the findings from mirror self-recognition and related tests, such as ecologically adapted, nonvisual modality and body-awareness paradigms, were synthesized. A total of 89 studies on 62 species from 17 orders were included, and significant conceptual, methodological and taxonomic biases inherent in the mirror self-recognition paradigm were highlighted. Such biases include anthropocentric assumptions about the universality of visual self-recognition, the binary pass or fail structure of the test and the over-representation of ‘large-brained’ species. In addition, the STRANGE framework reveals how subject-level variables, such as rearing history and personality, can influence outcomes. Although this review focuses on the mirror self-recognition test as a widely applied standard paradigm for assessing self-awareness, the conceptual, methodological and taxonomic biases discussed are broadly relevant across the fields of animal cognition and behaviour. By highlighting these pervasive biases, this review aims to raise awareness among animal behaviour researchers and encourage the design of future studies that address these limitations by testing a broader range of species, developing more ecologically relevant testing paradigms and transparently reporting the STRANGEness of study subjects. By addressing long-standing biases in the field of animal behaviour, we can develop a richer and more nuanced understanding of the diverse evolutionary drivers of self-awareness across the animal kingdom. • Review identifies the key biases in mirror self-recognition studies across taxa. • Large-brained species are overrepresented, limiting the generalizability of results. • Nonvisual and ecologically adapted tests provide broader insights into self-awareness. • Inclusive and bias-aware approaches are necessary in animal behaviour research.
Priestley et al. (Sun,) studied this question.