What’s Ape: Chimps say hello and goodbye when they meet, just like us

You may have been told that it’s rude to start eating before everyone is ready, or that you shouldn’t leave the table before your guests have finished. As it turns out, apes are no different.

Like us, chimpanzees and bonobos make a common gesture that signifies the start and end of a social interaction – a mutual gaze or a vocal signal is enough to show they’re ready to play, for example.

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

“Joint commitment is the driving force, the glue, of our joint actions, whether at large scale, like long-term projects, or small scale, such as lunch,” explained one of the study’s authors Dr Raphaela Heesen, from Durham University.

Though many animals cooperate to achieve a goal, scientists thought a joint commitment had to involve a sense of obligation. However, when Heesen and colleagues noticed two bonobos making gestures at one another after their grooming had been interrupted, the team proposed a new definition: that joint commitment requires an agreement to be set up beforehand, and then ended at a mutually decided time. If so, then the behaviours they’d witnessed between the bonobos could be seen as the agreed return to their prior commitment to grooming each other.

Using footage of over 1,200 ape interactions, such as grooming and playing, the team showed that the two species did communicate before and after a joint activity, using gestures such as holding hands, touching each other or butting heads, as well as vocalisations, mutual gazing and facial expressions.

Before playing with their friends, bonobos exchanged mutual gazes

90 per cent of the time, while two chimpanzees would communicate that they were ready to start 69 per cent of the time. The two ape species would perform exit signals even more often than on entry, with 92 per cent of bonobo and 86 per cent of chimpanzee interactions ending with some form of gesture or gaze.

What if the two apes couldn’t agree on the end of an interaction? “We very rarely observed such cases of disagreement,” said Heesen. “When we did, the two individuals communicated before coming to a mutual agreement to end.”