Chimpanzees Build Friend Groups That Look a Lot Like Ours, Study Finds

Think about your own social life for a second. You probably have one or two people you consider your absolute closest friends, a slightly bigger group you hang out with regularly, and then a wider circle of people you know and get along with but do not spend as much time with. Scientists call this a layered social network, and for a long time, many researchers assumed it was something unique to humans. A new study published in the journal iScience is challenging that idea in a pretty compelling way. It turns out that chimpanzees and bonobos, our closest living relatives in the animal kingdom, organize their friendships in strikingly similar layers.

Researchers from Utrecht University in the Netherlands and Universidad Carlos III de Madrid in Spain studied 24 groups of chimpanzees and bonobos across different locations. To measure how strong the bonds were between individual apes, the team focused on grooming behavior. Grooming is when one ape carefully combs through another's fur, removing dirt and parasites — tiny organisms that live on a host animal. For great apes, grooming is far more than just hygiene. It is one of the primary ways they build and maintain social bonds, similar to the way humans might strengthen a friendship by spending quality time together or checking in on someone regularly.

Using a mathematical model — a set of equations that helps scientists spot patterns in large amounts of data — the researchers mapped out exactly how each ape distributed its grooming time across its group. The results were clear. Most apes invested a large portion of their grooming effort into a small number of preferred partners, while keeping lighter, less frequent connections with many others. This mirrors the way human social circles are structured almost exactly. The study also found that apes in larger groups became more selective about who received their social attention, which is a pattern researchers have also seen in human communities.

Although both chimpanzees and bonobos showed this layered structure, they managed it differently. Bonobos spread their grooming time more evenly across group members, creating what researchers describe as a more egalitarian social network — meaning relationships that are more equal and less concentrated around a tiny few. Chimpanzees, on the other hand, directed a greater share of their effort toward a smaller number of favored companions. These differences reflect the broader personalities of each species. Bonobos are known for their cooperative, flexible social style, while chimpanzees tend to have more competitive, rank-based social environments.

One of the most interesting findings involves how age affects social behavior. Many adults report that as they get older, they stop trying to maintain huge networks of acquaintances and instead invest more deeply in a small number of close, trusted relationships. Scientists observed the same shift in chimpanzees. Older chimpanzees increasingly concentrated their grooming on fewer partners, narrowing their inner circle over time. Bonobos did not show the same pattern. Lead researcher Edwin van Leeuwen suggests this may be connected to the fact that bonobos live in more fluid social groups, with bonds that can extend beyond their immediate community — something rarely seen in chimpanzees.

So why does any of this matter beyond being a fascinating fact about apes? According to Van Leeuwen, understanding these shared patterns across species can shed light on how cooperation, social learning, and emotional well-being evolved over millions of years. The fact that chimpanzees, bonobos, and humans all independently arrived at similar strategies for managing social connections suggests that there may be deep evolutionary rules — built-in tendencies passed down through our shared ancestry — that guide how social animals build relationships. In other words, the impulse to have a best friend and a broader social world around them might be something far older and more fundamental than anyone previously realized.

Source: ScienceDaily