New Research Reveals Chimpanzees and Bonobos Have “Friend Groups” Just Like Humans Do

Great apes share human-like social circles, but chimpanzees and bonobos differ in how selectively they maintain close social bonds.

A new international study led by researchers from Utrecht University and Universidad Carlos III de Madrid suggests that chimpanzees and bonobos organize their social lives in ways that closely resemble human relationship patterns. By examining social grooming behavior, the researchers found that both species form layered social circles similar to those seen in humans.

The analysis also revealed clear differences between the two apes: chimpanzees tend to focus their grooming on a smaller number of partners, becoming increasingly selective as they age, while bonobos spread their social attention more evenly.

In human societies, people typically divide their social lives into distinct layers, with a small inner circle of close family and friends, surrounded by wider circles of friends, acquaintances, and more distant contacts. Scientists have long debated whether this structured pattern of social relationships is unique to humans or shared with other primates.

Social grooming

To explore this question, lead author Edwin van Leeuwen and his colleagues analyzed social grooming, a key way great apes build and maintain relationships, across 24 groups of chimpanzees and bonobos. Using a mathematical model, the team assessed how each individual allocated its limited time and social effort among group members.

The results showed that most apes invested heavily in a few close partners while keeping weaker connections with many others, closely matching the layered structure of human social networks. Apes living in larger groups were especially selective in how they distributed their grooming. Among the two species, bonobos stood out for their more even sharing of grooming time, whereas chimpanzees concentrated their social effort on fewer individuals.

More selective with age

When people get older, their inner circle becomes smaller, as they interact more intensely with fewer other people. The new results show that chimpanzees also become more selective with age. Bonobos, however, did not show this age-related narrowing of their inner circle. “Possibly, this is due to their more egalitarian social systems. Bonobos appear to live together in more fluid relationships, with social bonds that transcend group boundaries, something we rarely see in chimpanzees,” explains Van Leeuwen.

Evolutionary pathways

“Our findings suggest that the fundamental rules that guide how individuals allocate social effort apply across multiple species,” says Van Leeuwen. “This reveals deep evolutionary continuity in how complex societies are organized.”

At the same time, the differences between chimpanzees and bonobos reveal that there are multiple evolutionary pathways to managing social relationships. Van Leeuwen: “Understanding these patterns may reveal crucial insights for studying cooperation, social learning, and emotional well-being in both humans and other animals.”

Reference: “The physics of sociality: Investigating patterns of social resource distribution among the Pan species” by Edwin J.C. van Leeuwen, Diego Escribano, Zanna Clay, Marcel Eens, Jean-Pascal Guéry, Daniel B.M. Haun, Stephanie Kordon, Suska Nolte, Nicky Staes, Jeroen M.G. Stevens, Jonas Torfs, José A. Cuesta and Angel Sánchez, 24 October 2025, iScience.
DOI: 10.1016/j.isci.2025.113507

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