The ability to understand similarities and analogies is a fundamental aspect of human advanced cognition. Although subject of considerable research in comparative cognition, the extent to which nonhuman species are capable of analogical reasoning is still debated. This study examined the conditions under which tufted capuchin monkeys (Cebus apella) acquire a same/different concept in a matching-to-sample task on the basis of relational similarity among multi-item stimuli. We evaluated (i) the ability of five capuchin monkeys to learn the same/different concept on the basis of the number of items composing the stimuli and (ii) the ability to match novel stimuli after training with both several small stimulus sets and a large stimulus set. We found the first evidence of same/different relational matching-to-sample abilities in a New World monkey and demonstrated that the ability to match novel stimuli is within the capacity of this species. Therefore, analogical reasoning can emerge in monkeys under specific training conditions.

The abstract concept of equivalence is considered one of the bases of higher-order cognition, and it has been the subject of considerable research in comparative cognition. This study examined the conditions under which tufted capuchin monkeys (Cebus apella) are able to acquire an identity concept. Six capuchin monkeys were trained to solve a visual matching-to-sample (MTS) task on the basis of perceptual identity. The acquisition of the identity rule was inferred from the subject's ability to solve transfer tests with novel stimuli. We evaluated the ability of the capuchin monkeys to match the shape of novel stimuli after training with both several small stimulus sets (Experiment 1) and a large stimulus set (Experiment 2). Moreover, we examined the ability of capuchins to transfer the concept to novel visual dimensions, such as colour and size and to transfer to novel spatial arrangements of the stimuli (Experiment 2). We demonstrated that the ability of capuchins to match novel stimuli was improved by increasing the number of stimuli used during training (Experiments 1 and 2) and that after a widely applicable identity concept based on the stimulus shape was acquired, the capuchins were able to match stimuli according to an identity rule based on both the colour and size of the stimuli and when the spatial arrangement of the stimuli was varied (Experiment 2). This study is the first to demonstrate that the size of the training set affects the acquisition of an abstract identity concept in an MTS task in non-human primates.

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According to the thesis of natural mindreading (NMRT), mindreading-i.e., the capacity to attribute mental states to predict and explain behavior-is an intrinsic component of the human biological endowment, thus being innately specified by natural selection within particular neurocognitive structures. In this article, we challenge the NMRT as a phylogenetic and ontogenetic account of the development of the socio-cognitive capacities of our species. In detail, we argue that basic capacities of social cognition (e.g., the traces of early systems of bodily ornamentation within the archeological record, and infants' selective attention at others' beliefs in spontaneous-response false belief tasks) do not involve meta-representational mindreading but are better explained by appealing to situated embodied capacities acquired in social interaction. While we acknowledge that more flexible capacities of social cognition (e.g., those implied by the use of political emblems in industrialized societies, or by 4-year-olds' success in elicitedresponse false belief tasks) involve genuine mindreading, we argue that this ability is elicited and scaffolded by linguistic communication. We conclude that mindreading has emerged as the outcome of a highly derivative long-term constructivist process of biocultural becoming that led to a relatively recent restructuring of the human mind in multiple worldly locations at different times. In particular, we conjecture that humans gradually converged on establishing linguistic practices allowing the understanding of others' actions in terms of mental reasons. These practices were bequeathed to further generations, and continue nowadays to scaffold the acquisition of mindreading in early childhood.