Restorative Justice in Children.

An important, and perhaps uniquely human, mechanism for maintaining cooperation against free riders is third-party punishment. Our closest living relatives, chimpanzees, will not punish third parties even though they will do so when personally affected. Until recently, little attention has been paid to how punishment and a sense of justice develop in children. Children respond to norm violations. They are more likely to share with a puppet that helped another individual as opposed to one who behaved harmfully, and they show a preference for seeing a harmful doll rather than a victim punished. By 6 years of age, children will pay a cost to punish fictional and real peers, and the threat of punishment will lead preschoolers to behave more generously. However, little is known about what motivates a sense of justice in children. We gave 3- and 5-year-old children--the youngest ages yet tested--the opportunity to remove items and prevent a puppet from gaining a reward for second- and third-party violations (experiment 1), and we gave 3-year-olds the opportunity to restore items (experiment 2). Children were as likely to engage in third-party interventions as they were when personally affected, yet they did not discriminate among the different sources of harm for the victim. When given a range of options, 3-year-olds chose restoration over removal. It appears that a sense of justice centered on harm caused to victims emerges early in childhood and highlights the value of third-party interventions for human cooperation.

No third-party punishment in chimpanzees.

Punishment can help maintain cooperation by deterring free-riding and cheating. Of particular importance in large-scale human societies is third-party punishment in which individuals punish a transgressor or norm violator even when they themselves are not affected. Nonhuman primates and other animals aggress against conspecifics with some regularity, but it is unclear whether this is ever aimed at punishing others for noncooperation, and whether third-party punishment occurs at all. Here we report an experimental study in which one of humans' closest living relatives, chimpanzees (Pan troglodytes), could punish an individual who stole food. Dominants retaliated when their own food was stolen, but they did not punish when the food of third-parties was stolen, even when the victim was related to them. Third-party punishment as a means of enforcing cooperation, as humans do, might therefore be a derived trait in the human lineage.

Grooming network cohesion and the role of individuals in a captive chimpanzee group.

Social network analysis offers new tools to study the social structure of primate groups. We used social network analysis to investigate the cohesiveness of a grooming network in a captive chimpanzee group (N = 17) and the role that individuals may play in it. Using data from a year-long observation, we constructed an unweighted social network of preferred grooming interactions by retaining only those dyads that groomed above the group mean. This choice of criterion was validated by the finding that the properties of the unweighted network correlated with the properties of a weighted network (i.e. a network representing the frequency of grooming interactions) constructed from the same data. To investigate group cohesion, we tested the resilience of the unweighted grooming network to the removal of central individuals (i.e. individuals with high betweenness centrality). The network fragmented more after the removal of individuals with high betweenness centrality than after the removal of random individuals. Central individuals played a pivotal role in maintaining the network's cohesiveness, and we suggest that this may be a typical property of affiliative networks like grooming networks. We found that the grooming network correlated with kinship and age, and that individuals with higher social status occupied more central positions in the network. Overall, the grooming network showed a heterogeneous structure, yet did not exhibit scale-free properties similar to many other primate networks. We discuss our results in light of recent findings on animal social networks and chimpanzee grooming.