Bonobos respond to distress in others: consolation across the age spectrum

Abstract

How animals respond to conflict provides key insights into the evolution of socio-cognitive and emotional capacities. Evidence from apes has shown that, after social conflicts, bystanders approach victims of aggression to offer stress-alleviating contact behavior, a phenomenon known as consolation. This other-orientated behavior depends on sensitivity to the other's emotional state, whereby the consoler acts to ameliorate the other's situation. We examined post-conflict interactions in bonobos (Pan paniscus) to identify the determinants of consolation and reconciliation. Thirty-six semi-free bonobos of all ages were observed at the Lola ya Bonobo Sanctuary, DR Congo, using standardized Post-conflict/Matched Control methods. Across age and sex classes, bonobos consoled victims and reconciled after conflicts using a suite of affiliative and socio-sexual behaviors including embracing, touching, and mounting. Juveniles were more likely to console than adults, challenging the assumption that comfort-giving rests on advanced cognitive mechanisms that emerge only with age. Mother-reared individuals were more likely to console than orphans, highlighting the role of rearing in emotional development. Consistent with previous studies, bystanders were more likely to console relatives or closely bonded partners. Effects of kinship, affiliation and rearing were similarly indicated in patterns of reconciliation. Nearby bystanders were significantly more likely to contact victims than more distal ones, and consolation was more likely in non-food contexts than during feeding. The results did not provide convincing evidence that bystander contacts served for self-protection or as substitutes for reconciliation. Overall, results indicate that a suite of social, developmental and contextual factors underlie consolation and reconciliation in bonobos and that a sensitivity to the emotions of others and the ability to provide appropriate consolatory behaviors emerges early in development.

Figure 1. Percentage of agonistic conflicts encountered by different victim and aggressor classes.

Pie charts show the percentage of total agonistic conflicts (N = 356) encountered by different victim (a) and aggressor classes (b) in the bonobo population at the Lola ya Bonobo Sanctuary.

Figure 2. Frequency of first affiliative contacts in conflicts compared to Matched Controls.

Frequency over all observations combined of the first affiliative contact offered by (a) bystander to victims of aggression and (b) between opponents in the first ten minutes immediately following conflicts compared to Matched Controls.

Figure 3. The probability of providing consolation as a function of the bystander proximity to the conflict.

Bar chart indicated means+SD. Asterisk indicates P<0.001.

Figure 4. The effect of bystander age and rearing on providing consolation to victims of aggression.

The graph provides the mean+SEM proportion of conflicts per individual to which they were bystander. Corresponding GLMM models revealed significant effects of both bystander age and rearing (significant differences between juveniles vs adults, adolescents vs adults, mother-reared vs orphans, see Table 2). The asterisk indicates P<0.05.

Figure 5. Rates of victim self-scratching during Post-Conflict periods with or without consolation compared to Matched Controls.

The bar chart indicates mean ± SEM rates of self-scratching by victims during Post-Conflict and (PC) and Matched Control periods (MC). To remove the confounding influence of reconciliation, PCs with reconciliation were removed from analysis. The asterisk indicates P<0.05.