Guillén Salazar, Federico

Our capacity to attribute mental states to others, or theory of mind (ToM), affects the way in which we manage social interactions. Likewise, the social scenario in which we find ourselves probably influences our use of ToM. In this study, 6-year-old children and adult women participated in pairs in a task where participants needed to infer their partner’s behavior considering the partner’s visual perception (Experiment 1), knowledge (Experiment 2), and false belief (Experiment 3) regarding the placement of rewards under cups. The results were analyzed according to the temporal direction of the inference (past or future behavior of the partner), the social context (competition or cooperation), and—in the case of women—the type of social relationship with their partner (another adult or their own child). Children solved only the visual perception task, and adults solved the three tasks but performed better in the visual perception task than in the false belief task, suggesting that not only developmental issues but also differences in the intrinsic difficulty of the tasks underlie children’s results. The temporal direction of the inference, in contrast, did not influence their results. Whereas children performed better in the competition context, adults performed better in the cooperation context in one experiment. Moreover, women avoided competing against their own child, and even cooperated with her or him when this was against their own interest, suggesting that cooperation between mothers and children might have been a key driving force in the evolution of ToM in our species.

Gaze sensitivity allows us to interpret the visual perspective of others, inferring their intentions and attentional states. In order to clarify the evolutionary history of this ability, we assessed the response of free-ranging Japanese macaques (Macaca fuscata) to human gaze in three contexts: threat (Experiment 1), cooperation (Experiment 2), and competition (Experiment 3). Subjects interpreted the direct gaze of an approaching human as a sign of threat, showing a greater flight initiation distance and more threats towards the human in this condition than when the human gazed in another direction. Subjects also adapted their behavior to the attentional cues of a human who gave them food, by for example moving into his visual field. However, the macaques did not seem to take the visual perspective of a human competing with them over food, as they failed to first retrieve the food that was not visible to the human (i.e., located behind an opaque barrier). Our results support the idea that Japanese macaques can respond to a human’s gaze flexibly depending on the context. Moreover, they highlight the importance of studying animal behavior across different species and contexts to better understand the selective pressures that might have led to its evolution.

Spontaneous yawning is a widespread behaviour in vertebrates. However, data on marine mammals are scarce. In this study, we tested some hypotheses on the functions of yawning in a captive group of South American sea lions (Otaria favescens). According to the Dimorphism Hypothesis, species showing low levels of sexual dimorphism in canine size do not show sex diferences in yawning distribution; this was supported by our fndings, since yawning did not difer between the sexes. Yawning was more frequently performed during resting/sleeping contexts, thus supporting the Drowsiness Hypothesis. Yawning and self-scratching are considered reliable indicators of short-term anxiety in sea lions, since they immediately increased after conficts both in aggressors and victims (Social Distress Hypothesis supported). In the long-term, yawning was not correlated with individuals’ dominance status, thus showing that anxiety is similarly experienced by dominants and subordinates. The last two fndings can be explained by the social competition of this species, that involves individuals independently from their sex, age or ranking status. Therefore, the exposure to frequent stressful events can induce similar levels of anxiety in all the subjects (Resource Inequity Hypothesis supported). In conclusion, spontaneous yawning in sea lions seems to share similar functions with other social mammals, suggesting that this behaviour is a possible plesiomorphic trait.