Great apes keep their closest friends close, just like humans

Chimpanzees and bonobos arrange their relationships in concentric circles that look a lot like ours. Just like us, these apes invest most of their time in a few close friends while keeping looser ties with the rest.

They lavish attention on a few close partners, keep warm ties with a broader set, and maintain looser links at the edges – patterns that shift with group size and, for chimps, with age.

In a recent study, researchers from Utrecht University and Universidad Carlos III de Madrid set out to test whether human-style “friendship layers” are uniquely ours or shared with other primates.

The results of the study point to common rules for managing limited social time and energy, while also spotlighting clear differences between our two closest ape cousins.

Grooming as social currency

To map relationship structure, the team analyzed social grooming – the primary way great apes invest in bonds – across 24 groups of chimpanzees and bonobos.

Using a mathematical model that treats time and attention as finite resources, they asked how individuals allocate effort across partners. 

The pattern that emerged will look familiar to anyone with an inner circle and an outer one. Most apes poured intense grooming into a handful of partners and spread lighter contact over many others.

Just as in human networks, bigger groups pushed individuals to be choosier, concentrating effort where it matters most.

The species split was striking. Bonobos divided their grooming more evenly across group mates, reflecting a broadly egalitarian style.

Chimpanzees focused more time on fewer partners, tightening their core. That contrast persisted even after accounting for group size, hinting at different social strategies rather than simple crowding effects.

Apes become more selective about friends

Human social circles often narrow with age as people invest more deeply in fewer relationships.

The researchers found the same trajectory in chimpanzees: older chimps became more selective, intensifying bonds with a smaller set. Bonobos, by contrast, showed no clear age-related pruning. Their networks stayed relatively even.

Why the difference? “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,” said study lead author Edwin van Leeuwen.

Shared rules, different solutions

At the heart of the study is a simple idea: brains and bodies can only support so many strong ties, so individuals triage.

The fact that apes and humans appear to follow similar allocation rules suggests a deep evolutionary logic to how complex societies organize themselves.

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

Yet chimps and bonobos get there by different routes. Chimpanzees invest heavily in a few key relationships – alliances that can pay off in cooperation, coalitionary support, and access to resources. 

Bonobos, with their more tolerant, female-centered societies, spread the wealth, maintaining a web of moderate ties that can bridge subgroups and ease tensions.

Both strategies can stabilize group life. Each has trade-offs for information flow, conflict management, and resilience to shocks.

Apes have layered social networks

Layered networks shape what individuals know and do. Tight inner circles are fertile ground for trust, coordination, and rapid help. Outer circles are conduits for novelty – new techniques, different foods, fresh social information.

In apes, as in humans, that mix of deep and broad ties can determine how cooperation scales, how traditions spread, and who gets included or left out.

Those dynamics shift as circumstances change. In larger groups, the cost of maintaining many intense ties rises, so both species became more selective. In older chimps, the payoff seems to tilt toward depth over breadth.

Bonobos, whose relationships flow more readily across subgroups, may buffer that pressure by leaning on a wider, more even web.

Well-being across species

The authors argue that recognizing these structural commonalities can sharpen research on well-being, learning, and social stress across species. 

Those insights have practical echoes. For captive management and conservation, designing spaces and routines that respect species-typical layering could reduce anxiety and aggression and improve group stability.

For field researchers, mapping layers may predict where innovations will appear and how quickly they’ll spread.

A window onto our own evolution

The new results nudge a long-running debate: are human friendship layers a cultural artifact or a biological constraint? The ape data back the latter. 

Even without language or social media, great apes partition their limited social budgets into nested circles.

The specifics – who sits in the inner ring, how fast ties turn over, whether aging narrows the core – depend on species and context. But the overarching logic, the team argues, is shared.

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

Seen that way, human networks aren’t an exception; they’re a variation on a primate theme. And that makes the differences between chimps and bonobos especially instructive: two closely related species, two stable social strategies, one set of underlying rules.

“Understanding these patterns may reveal crucial insights for studying cooperation, social learning, and emotional well-being in both humans and other animals,” Van Leeuwen concluded.

The study is published in the journal iScience.

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