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Scarcity has been found to intensify value, positive or negative, rather than simply enhancing it. Some researchers have proposed that scarcity affects value by increasing how much attention is paid to a stimulus. We conceptualized sustained attention as stronger engagement and operationalized a situation of scarcity by telling participants who were choosing between two objects that the object that was chosen would then be replaced (Replenish) or not replaced (Scarce). To distinguish sustained attention-stronger engagement in a situation of scarcity from grabbing attention (salience from distinctiveness), the choice was between one option with a single instance (solitary-high salience) and a second option with several duplicates (abundant-low salience). We predicted that stronger engagement from a situation of scarcity would, first, intensify the value of the chosen item regardless of whether it was solitary or abundant, with positive items becoming more positive and negative items becoming more negative, and second, the stronger engagement from the situation of scarcity would transfer intensification to another separate object in the same setting. The results of Studies 1 and 2 supported both of these predictions. Study 3 tested a boundary condition for these scarcity–engagement effects in terms of how real participants experienced the choice items to be, where ‘realness’ is another source of engagement strength. As expected, the scarcity–engagement effect on intensifying value was replicated for participants who experienced the activity as real but was eliminated for those who did not.

In recent years, the presence of stable individual variation in animal behaviour has been corroborated by studies across a wide variety of taxa and research disciplines. Reconciliation, or postconflict affiliation between former opponents, is a behavioural domain in which individual differences have not been systematically studied. Using a long-term data set comprising over 2000 conflict and postconflict observations in two groups of outdoor-housed chimpanzees, Pan troglodytes, we provide evidence for stable individual variation in reconciliation and test several hypotheses on how this postconflict mechanism relates to social switching behaviour. Results of generalized multilevel models revealed that individual differences remained a substantial source of variation in reconciliation after controlling for a number of situational variables (e.g. the nature of the relationship between opponents) shown by previous research to influence its occurrence. We further demonstrated a positive association between an individual's conciliatory tendency and three separate indices of social switching behaviour, proposing that individual differences in reconciliation may reflect a more fundamental motivation to switch between different social states. In addition to a discussion of potential motivational underpinnings, we provide an impetus for future work to consider how reconciliation relates to the broader constructs and themes identified within animal personality research. To the extent that individual differences in other aspects of conflict and postconflict repertoires exhibit temporal and cross-situational consistency, they too should inform our understanding of animal personalities. Delineating how these and other dimensions of sociality are in part driven by stable individual variation not only has implications for how social interactions themselves unfold, but ultimately for the fitness of the individuals therein.

In contrast to a wealth of human studies, little is known about the ontogeny and consistency of empathy-related capacities in other species. Consolation—post-conflict affiliation from uninvolved bystanders to distressed others—is a suggested marker of empathetic concern in non-human animals. Using longitudinal data comprising nearly a decade of observations on over 3000 conflict interactions in 44 chimpanzees (Pan troglodytes), we provide evidence for relatively stable individual differences in consolation behaviour. Across development,individuals consistently differ from one another in this trait, with higher consolatory tendencies predicting better social integration, a sign of social competence. Further, similar to recent results in other ape species, but in contrast to many human self-reported findings,older chimpanzees are less likely to console than are younger individuals. Overall, given the link between consolation and empathy, these findings help elucidate the development of individual socio-cognitive and -emotional abilities in one of our closest relatives.