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Apes communicate to start and end social interactions, study suggests

By Nina Massey, PA Science Correspondent
Apes use signals to start and end interactions in much the same way that humans greet each other and say goodbye, a study suggests.

This behaviour had not been observed outside the human species until now.

Researchers also found that social and power dynamics between interacting apes affected the communication efforts used.

They suggest this mirrors patterns similar to human politeness.

Raphaela Heesen, a postdoctoral researcher at Durham University, said: “We were able to launch rockets and land on the moon because we have the ability to share our intentions, which allows us to achieve things so much bigger than a single individual can achieve alone.

“This ability has been suggested to be at the heart of human nature.”

Sharing intentions and working together on a common goal leads to a mutual sense of obligation otherwise known as joint commitment.

Researchers said they are seeing evidence in great apes that might challenge the long-held claim that joint commitment is unique to humans.

Past experiments of joint commitment found that human children protested when an experimenter abruptly stopped playing with them.

Offering toys or vocalising, the children tried to re-engage the adult in their previously agreed-upon play.
The researchers witnessed a similar situation between two bonobos who were interrupted while grooming but then used gestures to resume the interaction with each other.

The team wanted to learn more about how and when joint commitment emerged in the human lineage.
Unlike previous scientists, they proposed that joint commitment is not solely based on the feeling of obligation between two participants to fulfil a shared promise.

It also involves the process of setting up the agreement and mutually deciding afterwards that the agreement has been fulfilled, the study published in the journal iScience suggests.

Something as simple as entering a conversational commitment with eye contact and a “hello” and then signalling that a conversation is wrapping up with repeating “OK, sounds good” or a “goodbye” are examples of this process.

The researchers set out to see if great apes had similar entry and exit processes, which they argued would demonstrate the process of joint commitment.

After analysing 1,242 interactions within groups of bonobos and chimpanzees in zoos, they found that the apes frequently gazed at and communicated with each other to start and end interactions.

Bonobos exchanged entry signals and mutual gaze before playing 90% of the time and chimps 69% of the time.

Exit phases were even more common, with 92% of bonobo and 86% of chimpanzee interactions involving exits.

Signals included gestures like touching each other, holding hands or butting heads, or gazing at each other, before and after encounters like grooming or play.

Factors like how close the apes were to each other socially or who had more power were also considered.
The closer bonobos were to each other, the shorter the duration of their entry and exit phases, if they existed at all.

The authors say this pattern is similar to how humans communicate with others.

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

According to the research, the level of friendship and strength of social bonds did not seem to affect the chimpanzees’ entries and exits.

Researchers say there is still a lot of work to do to understand the origin and evolution of joint commitment.

Dr Heesen said: “Behaviour doesn’t fossilise. You can’t dig up bones to look at how behaviour has evolved. But you can study our closest living relatives: great apes like chimpanzees and bonobos.

“Whether this type of communication is present in other species will also be interesting to study in the future.”

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