Great apes say hello and goodbye in show of social bonds

A new study has shown for the first time that chimps and bonobos social interact with each other in common signals and gazes as a show of greetings and goodbyes.

It’s the first time these social bonds have been seen in great apes.

Until now, researchers believed that only humans experienced a specific sense of obligation towards each other in encounters when they arrive and exit Great apes exchange signals and gaze with each other before entering and exiting.

The joint action structure resembles that of humans and indicate an underlying joint commitment.

Imagine that you have a lunch meeting with your friend. Once you and your friend agree to meet at a certain time, you both value your lunch commitment; this means that you wouldn’t let your friend wait, nor would you leave your friend in the middle of the lunch,” explained one of the study’s authors Dr Raphaela Heesen, a researcher in human and great ape communication at Durham University.

“If your phone is ringing while you’re eating, then you’d probably try to avoid the interruption after all, or would excuse yourself to pick up the call, then return to your friend once done. Once you are done eating and you are both ready to leave, you will not do this abruptly but go through the process of saying good bye and wishing your friend well.”

Heesen says that this is an example of a joint action with a common goal, in which you and your friend are mutually aware of the obligations linked to your lunch meeting.

“Joint commitment is the driving force, the glue, of our joint actions, whether at large (long-term research projects) or small scale (lunch).”

Though many animals do cooperate to achieve a goal, scientists have believed until recently that the sense of commitment felt by individuals when engaging in a social activity was limited to humans alone.

However, when Heesen and colleagues noticed two bonobos making gestures at one another after their grooming had been interrupted, the team began to wonder if a joint commitment relied on more than just a mutual obligation.

The apes frequently exchanged mutual gaze and communicative signals prior to and after engaging in joint activities with conspecifics, demonstrating entry and exit phases comparable to those of human joint activities.

Although rank effects were less clear, phases in bonobos were more moderated by friendship compared to phases in chimpanzees, suggesting bonobos were more likely to reflect patterns analogous to human “face management”. This suggests that joint commitment as process was already present in our last common ancestor with Pan.

Humans say goodbye with verbal gestures, apes also make a vocal signal and gaze at each other to show they’re about to begin grooming, or that they want to stop playing.

These signals could represent the start and end of a mutual agreement, which researchers say challenges the current idea that only humans make these joint commitments.

“We did very rarely observe such cases of disagreement,” said Heesen. “In the cases that we did, the two individuals communicated before coming to the mutual agreement that they were ready to exit from the interaction!”

The study also looked at whether social status and relationship played a part in joint commitment. While the chimps weren’t affected by differences in these social standings, bonobos did change their actions based on how close they were with their partner.

When grooming or playing with an individual they weren’t close to, the bonobos spent more time setting up and concluding the activity. Researchers say this could be similar to what we humans consider to be “social etiquette” or “politeness”.

“When you’re interacting with a good friend, you’re less likely to put in a lot of effort in communicating politely,” said Heesen.

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