Watching others pays off: Attentive macaques benefit from observing their group mates interacting

Monkeys constantly observe and evaluate their social environment. It stands to reason that the social and mental abilities required to do so were favored by evolution. After all, these abilities should influence how an animal interacts with its conspecifics and, as a result, what social position it can attain within the group’s hierarchy. Researchers from the DPZ and the University of Göttingen have now investigated whether this widely held assumption is correct by studying 46 wild male Assamese macaques in Thailand.

At the start of the two-year study, the team recorded how long the macaques watched other conspecifics in their vicinity during social interactions. They distinguished between two types of interactions: friendly, for example, when the animals groomed each other, and aggressive, when they fought. In total, they recorded more than 440 situations in which a macaque watched two other males interact with one another.

From friends, to rank, and finally mating success

The analysis revealed that males who spent more time observing friendly interactions had closer social bonds with certain other males by the end of the first year. Stronger bonds then led to higher ranks in the dominance hierarchy by the end of the second year. And those who were significantly higher in the hierarchy mated about 20 percent more often.

Julia Ostner, head of the “Social Evolution in Primates” research group at the DPZ, explains: “It’s important to understand that simply watching doesn’t result in additional matings for the males. Rather, our analyses suggest that curiosity made it easier for the macaques to form the right alliances so they could then climb the social hierarchy together. Ultimately, it was this social success that made the higher mating success possible.”

Learn from friendly situations and be cautious with aggressive ones

Animals that observed friendly interactions for longer periods also interfered in social situations more frequently. The information gained from their observations may have helped them decide when and how to get involved. Sometimes they joined a friendly encounter; other times, they disrupted a friendly interaction perhaps to prevent two rivals from forming an alliance in the first place. Both approaches are thought to help strengthen their own position in the dominance hierarchy.

In contrast, observing aggressive interactions did not correlate with social bonding or dominance success. Although males looked more often at fights than at friendly interactions, how long they looked had no effect on their subsequent rank in the group hierarchy. A different mechanism appears to be at work here: managing one’s own risk. During fights, all males appear to watch just as closely, as none of them wants to be drawn into the conflict against their will. Because the animals show little variation in this behavior, it does not give any of them an advantage.

Sofia Pereira, the first author of the study, concludes: “We consider it unlikely that animals that are simply more socially skilled form stronger bonds and, independently of that, also achieve higher dominance ranks. The statistical models suggest instead that one leads to the other: Those who observe others form closer social bonds. These lead to a higher rank and, ultimately, to greater mating success.”

Studies like these help us understand how social intelligence has evolved over time. Humans, too, keep a close eye on who gets along with whom and who is arguing. If it turns out that this observation provides a measurable advantage in other primates, it offers a clue as to why this ability has become established in our relatives – and possibly in ourselves as well.