Humans often organize their relationships in layers, spending the most time with a small number of close friends and family, but maintaining weak ties with a large number of acquaintances. New international research suggests this pattern is not unique to people.
Researchers from Utrecht University and Carlos III de Madrid University have discovered that our closest living relatives, chimpanzees and bonobos, also form social networks similar to human friendship circles. This discovery provides new insights into how complex social relationships evolved.
Great apes build human-like social networks
To investigate how great apes manage their social lives, researchers examined the social grooming behavior of 24 groups of chimpanzees and bonobos. Grooming is one of the most important social activities among great apes, helping to strengthen bonds and maintain relationships.
The research team used a mathematical model to analyze how individuals allocate their limited time and social effort among other members of their group.
The results revealed a familiar pattern. Most apes spent the majority of their grooming time with a small number of preferred partners and maintained less intensive relationships with many others. This hierarchical structure is very similar to the way human social circles are organized.
The study also found that apes living in larger groups tend to be more selective about where they focus their social attention, a trend also observed in human social networks.
Chimpanzees and bonobos take different approaches
Although both species exhibited social structures similar to humans, they did not manage relationships in exactly the same way.
Bonobos distributed grooming time more evenly among group members, forming more egalitarian social networks. In contrast, chimpanzees focused much of their effort on a small number of friendly allies.
These differences reflect broader differences in the social behavior of the two species.
Chimpanzee friendships change with aging
As people grow older, they often become more selective about their relationships, focusing on the close ties of a smaller inner circle. Researchers found a similar pattern in chimpanzees.
As chimpanzees get older, they invest in fewer social partners. However, bonobos did not experience the same narrowing of their social circles over time.
“Perhaps this is due to bonobos’ more egalitarian social system. Bonobos seem to have social bonds that transcend group boundaries and live together in more fluid relationships, which is rarely seen in chimpanzees,” van Leeuwen explains.
Clues to the evolution of friendship
Lead author Edwin van Leeuwen said the results suggest that similar principles govern how social relationships are formed and maintained across species.
“Our findings suggest that the basic rules that determine how individuals allocate their social effort apply across species,” van Leeuwen says. “This reveals deep evolutionary continuity in how complex societies are organized.”
At the same time, the differences between chimpanzees and bonobos suggest multiple evolutionary strategies for managing social connections.
Van Leeuwen points out that understanding these patterns can improve scientists’ understanding of cooperation, social learning, and mental well-being between humans and other animals.
“Understanding these patterns may provide important insights for studying cooperation, social learning, and emotional well-being in humans and other animals.”
