You might expect it at a human high school but friendship-sabotage happens in the wild too. New research, recently published on Royal Society Open Science, suggests that chimpanzees and wild sooty mangabeys actively try to stop their friends from making other friends.
Like humans, both species of primate form large and complex social networks. Within these groups, individuals build strong, long-term relationships, which are mutually beneficial to those involved. These friendships can evolve over time – especially if one individual decides to become best mates with someone else.
However, whereas chimpanzees tend to be more flexible in their friendships and will happily form close bonds with group members outside their biological family, mangabeys, a member of the Old World monkey family, are far more kin-orientated. Chimps are also much more likely to use these relationships as a power move as their friendships play a larger role in the outcome of aggression than those of mangabeys.
To better understand the nature of primate relationships, researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, studied grooming interactions between two groups of chimpanzees and one group of mangabeys, in Taï National Park, Côte d'Ivoire.
They chose to research grooming behavior because both species of primate use grooming as a way to build and maintain relationships and alliances. Every now and then, a bystander will butt in and change the outcome of these bonding sessions.
The anthropologists observed which individual would groom with who, which individuals would intervene, who they tried to get access to, and their success rate. Every time a bystander interrupted, the researchers would note the target of their attention and the outcome. They then used this information to assess how it affected group dynamics.
"We found that in both species, bystanders are often very specific in their interventions, targeting grooming interactions of their friends, of individuals that are close to them in rank and groom someone high-ranking, and of dyads that do not yet have a strong relationship with each other," Alexander Mielke, first author of the study, explained in a statement.
There was one difference between the chimpanzee and mangabey communities. Because mangabeys don't like to be groomed by more than two other monkeys, interventions tend to involve only high ranking individuals. Chimps, however, are more inhibited and grooming takes place with multiple group members. This means high ranking individuals weren't always as successful at separating groomers as they had been in the mangabey community.
What this study shows is that primates are aware of ranks and relationships within their network. They're also ok with using this info to change the social dynamic within that network. But whether this is influenced by feelings of jealousy – as they do in human relationships – waits to be seen.