Bonobo juveniles hugging each other (Pan paniscus). Lola Ya Bonobo Santuary, Democratic Republic of ...

Social Theory

Study reveals a surprising similarity between bonobos and humans

Once again, animals show humans are not so unique.

Anup Shah

For far too long, researchers believed humans were alone in their ability to engage in a sociological concept known as joint commitment.

Joint commitment is the understanding that by working together as a collective, we can accomplish more than we could as individuals acting alone.

Essentially, joint commitment is the glue holding human civilization together.

But a new study published in Science Advances reveals we are not alone in our commitment to cooperation. Bonobos engage in joint commitment, too, and in a surprisingly similar manner to humans.

A bonobo holding a partner.Dr. Raphaela Heesen

Sociology 101— Joint commitment is just one aspect of "shared intentionality" among humans, which essentially means shared behaviors in activities, including cooperative communication, understanding another's perspective, understanding roles in social interactions, and providing mutual aid.

Researchers previously assumed these higher-level cognitive skills were the preserve of humans. They based this assumption on past tests on great apes, chimpanzees, and bonobos, which involved artificial games to test their level of joint commitment.

These tests found inconsistent results. It's possible that the artificial nature of these experiments affected the outcome.

"Some experiment[s] indeed showed that joint commitment tests in bonobos are more successful than with chimpanzees, but these experiments always involved human experimenters who interacted with subjects," Raphaela Heesen, lead author on the study and a post-doctoral research associate at Durham University, tells Inverse.

This time, the researchers chose to interrupt pairs of bonobos while they were engaged in a more natural social activity: grooming.

Bonobos are special among non-human primates — past research suggests these apes develop human-like social interactions and deep bonds.

"Bonobos are documented to be more socially tolerant and egalitarian than chimpanzees and other great apes, which is why we assumed that they would be the best candidate species to study joint commitment beyond humans," Heesen says.

If joint commitment exists among bonobos, then bonobos may understand there is an implied social contract when undertaking joint activities with another bonobo.

A bonobo carrying another partner.Dr Raphaela Heesen

Not only that that, but they may also understand there are consequences for breaking this commitment — so they would have to communicate accordingly to mitigate potential disputes.

The researchers theorized that bonobos, like humans, understand the concept of "face threats" — a concept similar to the need to save face — which entails the risk of partners feeling disrespected if they are kept waiting for too long or otherwise wronged.

Put another way: Bonobos should abide by the politeness theory, which is common among humans.

"Politeness theory in humans states that our actions will be calibrated to key dimensions of the social relationship via acts of politeness," Heesen explains.

These acts of politeness tend to occur when there's a difference in social rank between the two interacting partners, or if the partners are unfamiliar with each other.

"For example, you are more polite to your boss compared to your sibling," Heesen says. "So, the two dimensions that increase politeness acts in humans are social distance and power difference."

The politeness theory predicts bonobos would behave the same way — if they understand joint commitment.

The experiment — The researchers tested their hypothesis by interrupting pairs of bonobos as they groomed one another. In the first arm of the experiment, the researchers observed how bonobo pairs reacted to an untargeted interruption to the grooming activity — such as the opening of a door to the bonobos' holding cell, or making a loud noise.

In the second arm of the experiment, the researchers targeted their interruptions towards specific bonobos. In this instance, a zookeeper called out the name of a specific bonobo and gave them a food reward, temporarily distracting them from the task of grooming — or being groomed, if they are the recipient.

An example of targeted interruption in the experiment.Dr Raphaela Heesen

The researchers tracked what the bonobos did after they were interrupted — did they resume their grooming activities, or did they communicate upon stopping (or resuming) their grooming?

The researchers also looked at how interruptions of solitary activity, too — the bonobo grooming alone or playing by themselves — and compared the apes' reactions to interrupting the shared activity of one bonobo grooming another.

If the bonobos resumed activities more often in the shared setting versus the solitary one, it may indicate a level of joint commitment — a social contract between the two apes.

The researchers recorded their observations on camera and also inputted their results into statistical models to test their hypothesis.

The results — Between May and August 2018, the researchers observed 88 untargeted and targeted interruptions of 17 bonobos going about their business in a zoological park in France.

The results were largely in line with their predictions, Heesen says.

"Our study is the first to show that bonobos seem to engage in joint commitment when interacting with other bonobos naturally during social grooming," Heesen says.

The researchers drew upon a few different observations to support their hypothesis.

Bonobos were "less likely to resume a solitary than a social activity, suggesting that their motivation to resume social interactions goes beyond a mere desire to complete an unfinished task, but entails a sense of commitment toward the partner or the joint action itself," Heesen and her colleagues write in the paper.
A bonobo sitting by themselves.Dr. Raphaela Heesen

This behavior is similar to studies of human children. When children play with another child, they are more likely to tell them if they need to leave, or otherwise communicate when they return, than if they are merely playing alongside another child.

Intriguingly, targeted bonobos were more likely to communicate to resume activities with their partner after an interruption than untargeted bonobos, suggesting the targeted bonobos feel a sense of personal responsibility to their peer.

Bonobos were also "more likely to communicate at the time of suspension when they were socially distant and subordinate in rank," Heesen says. This is further evidence their behavior follows the terms of politeness theory.

"These results suggest that bonobos have some awareness of the social consequences linked to breaking joint commitments and adjust their communication efforts according to the identity of their partner," Heesen says.

The findings offer clues to the evolution of this social behavior, hinting it may be more common among non-human primates than we think, the researchers say.

Next steps — The study is a tantalizing indication that bonobos and humans may be more alike than we first thought. But more data is needed to fully understand the true extent of joint commitment in bonobos.

One outstanding question stems from the fact humans seem to demonstrate a greater degree of joint commitment than bonobos, according to the study. For example, a past study found 3-year-old children resisted the temptation to break a joint commitment in favor of personal rewards about 70-80 percent of the time. This does not seem to be true for bonobos, which showed this behavior only 3 percent of the time, according to the data.

The researchers also don't fully understand the nuances of bonobo communication. For example, humans use specific signals and language when temporarily stopping an activity — “sorry, I’ll be right back” — versus resuming an activity — “sorry for keeping you waiting”.

Bonobos might have similarly specific signals for suspension and resumption of joint commitment, but there are not enough data to say what these might be, Heesen says. But we may soon know the answer.

"We would like to analyze signal types used for suspending and reinstating activities in bonobos in a larger sample, and whether these are significantly different," Heesen says.

"That would then indicate a more complex understanding of joint commitment in this species."

Abstract: Joint action is central to human nature, enabling collectives to achieve goals otherwise unreachable by individuals. It is enabled by humans’ capacity to understand and engage in joint commitments. Joint commitments are evidenced when partners in interrupted joint actions reengage one another. To date, there is no clear evidence whether nonhuman animals understand joint commitment, suggesting that only humans experience it. Here, we revisit this claim by interrupting bonobos engaged in social activities. Bonobos reliably resumed the activity, and the likelihood of resumption was higher for social compared to solitary activities. Furthermore, communicative efforts deployed to suspend and resume social activities varied depending on partners’ social relationships and interactive roles. Our results suggest that bonobos, like humans, engage in joint commitment and have some awareness of the social consequences of breaking it.
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