Natural conflict resolution in brown capuchin monkeys
(Cebus apella)

Project's summary

In the past four decades, the study of primate's social behaviour has rapidly developed into one of the most interesting areas of research, connecting biological and social sciences. These studies have shed light on the richness and diversity of primate social organization and consequently provided researchers with tools to understand how natural selection shapes psychology and social organization in group-living mammals, allowing scientists to go further in understanding human behavioural evolution.

Social relationships can be conceptualised as the result of a sequence of interactions between two individuals. Competition, social attraction and cooperation are the main principles governing interactions among primates. These often conflicting tendencies are integrated into a cohesive system of social relationships, although traditionally most attention has been given to the inequalities resulting from dominance relationships. Nowadays there is an emphasis on more positive features of social behaviour, such as coordination, negotiation, reconciliation and cooperation.

To enjoy the benefits of sociality, group living animals must overcome the cost of conflicts. Knowledge of how animals manage these conflicts it's essential for understanding the dynamics of social systems, since the conflict of interests may compromise the benefits of group living, especially when it escalates to aggression.
With this project we propose to collect and interpret several kinds of information about post-conflict interactions, in a captive group of brown capuchin monkeys (Cebus apella), using direct observation techniques, throughout a period of approximately six months. The importance of this study resides in the fact that most works on reconciliation have been done in chimpanzees and Old World monkeys, and consequently very little is known about conflict management in New World monkeys. This project will able us to do intra- and interspecies comparisons, improving this way our knowledge of reconciliation and step a little further in the comprehension of how evolution shaped conflict resolution mechanisms.

Goals of the project

The main goals of this project are to study: (1) the variables that affect the occurrence of reconciliation (e.g. kinship, dominance, gender, age); (2) the behaviour patterns used for reconciliatory purposes; and (3) the relation between dominance style and conflict management, in a captive group of brown capuchin monkeys (Cebus apella), housed at the Lagos Zoo. This approach will allow us to test current theories on non-human primate reconciliation, using multivariate analysis to examine the role of multiple factors affecting reconciliation frequency, the potential dependency between these variables, and the relative contribution of specific conciliatory patterns.

Relationship with the state of the art

After reconciliation was defined, in 1979 by de Waal and van Roosmalen, as a friendly reunion between former opponents not long after an aggressive conflict, it as been documented in more than twenty primate species (Aureli & de Waal, 2000), including prosimians, monkeys, apes and humans.

The term reconciliation implies that affiliative contacts between former opponents serve as mean to repair the relationship disturbed by the preceding conflict (Aureli, 1997). The Valuable Relationship Hypothesis (de Waal & Aureli, 1997) lies on this assumption: according to this theory, the tendency to reconcile depends on the quality of the relationship, with opponents being more likely to reconcile when their relationship is highly valuable.

More recently, advances in the study of animal emotionality have led Maestripieri (1992) to propose that certain self-directed behaviours (e.g. self-groom, self-scratch) are reliable indicators of anxiety in primates. The use of these behavioural indicators allowed the investigation of the role of reconciliation in reducing uncertainty after agonistic interactions- Uncertainty-Reduction Hypothesis (Aureli & van Schaik, 1991). This hypothesis states that reconciliation functions as mechanism that reduces both victim's and aggressor's anxiety, therefore, allowing a faster termination of the stress response and preventing negative consequences of a prolonged activation.

Although having different predictions these two hypotheses have been integrated by Aureli (1997), by showing that post-conflict anxiety is higher after conflicts between individuals with strong affiliative relationships.

Even tough reconciliation is very common on the primate order, the work of Kappeler (1993) on lemurs provides an example of a highly social species (Lemur catta) that appears to the lack behavioural mechanisms to cope with the dispersive effects of conflicts. These results suggest that reconciliation might not be a necessary consequence of group living, and that the type of dominance relationships might be linked somehow with conflict management.

Thierry (2000) attempted to classify the 22 macaque species into grades ranging from despotic to egalitarian, and link the different dominance styles with the patterns of conflict management characteristic of each species: despotic species with infrequent post-conflict affiliation on one side, and on the other side, egalitarian species with more frequent post-conflict affiliation.

As the knowledge on reconciliation expands, comparative studies are increasing in number an importance. Inter- and intraspecies comparisons are very important since they allow to the study the evolution of reconciliation (Call et al., 1999). Nevertheless, there have been few studies that analyse the effect of more than a restrict number of variables at a time on the occurrence of reconciliation. Adding to this, most of what we now know about post-conflict behaviour comes from studies on chimpanzees and other Old World species. As far as we know, there are only two published studies focusing on reconciliation on brown capuchins: the first relates the occurrence of reconciliation with the presence or absence of an attractive food (Verbeek & de Waal, 1997), and the second, relates mother-offspring relationship quality with the development of reconciliation (Weaver & de Waal, 2003). Both of them indicate that reconciliation in Cebus apella does happen.

The importance of improving our knowledge of this species social behaviour comes from the fact that, although being distantly related to humans and other apes, capuchin monkeys have the largest relative brain size of any nonhuman primate, and are one of the few known species that uses tools and hunts other vertebrates.