Human relationships are typically organized in layers, with individuals dedicating the most time to a close circle of friends and family, while maintaining looser ties with a broader network of acquaintances. A recent international study indicates that this hierarchical pattern is not exclusive to humans.
Researchers from Utrecht University and Universidad Carlos III de Madrid discovered that chimpanzees and bonobos, our nearest living relatives, also construct social networks that mirror human friendship circles. These findings shed new light on the evolution of complex social relationships.
Great Apes Construct Human‑Like Social Networks
To explore how great apes navigate their social lives, the researchers investigated social grooming behavior across 24 groups of chimpanzees and bonobos. Grooming constitutes one of the most vital social activities for apes, facilitating bond formation and relationship maintenance.
Employing a mathematical model, the team examined how individuals allocated their limited time and social effort among group members.
The results uncovered a familiar pattern: most apes devoted a substantial proportion of their grooming time to a few preferred partners, while sustaining less intensive relationships with many others. This layered structure mirrors the organization of human social circles.
The study also revealed that apes inhabiting larger groups exhibited greater selectivity in allocating their social attention, a trend mirrored in human social networks.
Chimpanzees and Bonobos Adopt Distinct Social Strategies
Although both species displayed human‑like social structures, they did not manage relationships identically.
Bonobos distributed grooming time more evenly across group members, creating a comparatively egalitarian social network, whereas chimpanzees concentrated a larger share of effort on a smaller number of favored companions.
Aging Alters Chimpanzee Friendships
People frequently become more selective in later life, directing attention toward a smaller inner circle of close connections. The researchers observed a comparable pattern among chimpanzees.
With advancing age, chimpanzees increasingly invest in fewer social partners. Bonobos did not exhibit the same narrowing of their social circles over time.
“Possibly, this reflects their more egalitarian social systems. Bonobos appear to inhabit more fluid relationships, forming social bonds that extend beyond group boundaries — a pattern rarely observed in chimpanzees,” explains van Leeuwen.
Clues to the Evolution of Friendship
According to lead author Edwin van Leeuwen, these results suggest that similar principles govern the formation and maintenance of social relationships across multiple species.
“Our findings indicate that the fundamental rules governing how individuals allocate social effort operate across multiple species,” says van Leeuwen. “This reveals deep evolutionary continuity in the organization of complex societies.”
Conversely, the distinctions between chimpanzees and bonobos indicate that multiple evolutionary strategies can underlie the management of social connections.
van Leeuwen notes that comprehension of these patterns could enhance scientists’ understanding of cooperation, social learning, and emotional well‑being in both humans and other animals.
Understanding these patterns may uncover crucial insights for studying cooperation, social learning, and emotional well‑being in both humans and other animals.