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Apes are known for being very intelligent animals, and a new study has revealed yet another similarity to human beings!

Apes use signals to start and end their interactions in the same way people greet each other and say goodbye, the research suggests.

This behaviour hasn't been seen outside the human species until now.

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.

The researchers also found that the way in which apes interact with each other depends on both the type of relationship they have with others and the power dynamics of the group - ie: who's in charge.

They think this could mirror human patterns, where how people greet others often comes down to the nature of their relationship - with a friendly hug or a serious handshake!

Sharing what you want to achieve with others and working together on a common goal leads to a shared sense of responsibility known as 'joint commitment'.

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.

However, unlike previous scientists, they suggest that joint commitment isn't only based on the feeling of responsibility between two participants to fulfil a shared promise.

They believe it also involves the process of setting up the agreement and mutually deciding afterwards that it's been fulfilled, the study suggests.

The researchers wanted to see whether apes had similar entry and exit processes, which they argued would demonstrate the process of joint commitment among apes.

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.

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 length of their entry and exit phases. The authors say this pattern is similar to how humans communicate with others.

"When you're interacting with a good friend, you're less likely to put in a lot of effort in communicating politely," said Raphaela Heesen who is a postdoctoral researcher at Durham University.

Researchers say there's still lots of work to be done in understanding the origin and evolution of joint commitment.

"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," Dr Heesen said.

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