https://www.cnn.com/2021/08/20/world/apes-social-interaction-greetings-scn/index.html

Just like people, chimpanzees and bonobos aren't ones for leaving without saying goodbye.

Apes purposefully use signals to begin and end social interactions --
behaviors not
typically seen outside of humans until now, according to a new study
published in the
journal iScience.

Researchers analyzed more than 1,200 interactions with groups of chimps
and bonobos
in zoos and found that they commonly exchange gazes or swap gestures to
share their
intentions about social interactions. Those gestures included touching
each other,
holding hand and even butting heads.

Bonobos exchanged "hello" signals prior to playing 90% of the time and
chimps 69% of
the time, according to the study, and goodbyes were even more common.

Scientists say the apes' ability to signal hellos and goodbyes indicates something much
bigger than politeness. It shows that chimpanzees and bonobos can
communicate a
mutual sense of obligation towards each other.


https://www.cell.com/iscience/fulltext/S2589-0042(21)00840-3

Summary
Many social animals interact jointly, but only humans experience a
specific sense
of obligation toward their co-participants, a joint commitment. However,
joint
commitment is not only a mental state but also a process that reveals
itself in
the coordination efforts deployed during entry and exit phases of joint
action.
Here, we investigated the presence and duration of such phases in N = 1,242 natural play and grooming interactions of captive chimpanzees and bonobos.
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.

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