Monkeys 'take turns in conversation'
Marmoset monkeys take it in turns to "talk" in a pattern very similar to human conversation, according to scientists.
Researchers recorded the sounds of the marmosets as they called to one another from behind a curtain.
Each animal would call, then wait for the other to respond before calling again.
The results suggest an "alternative evolutionary route" for our own conversational turn-taking.
They are reported in the journal Current Biology.
It is something we take for granted in our conversations, but taking it in turns to talk and listen is crucial for us to effectively exchange information through what we say.
Somewhat mysteriously though, we do not see an obvious origin in our closest primate relatives - the chimpanzees.
Chimps are not very vocal and tend to use their repertoire of gestures to communicate, so it is widely accepted that these manual gestures provided the foundations for the co-operation inherent in our own communication.
But Dr Asif Ghazanfar from Princeton University set out to look for evidence of a vocal route for this co-operation, by looking at vocal exchanges in marmosets.
He explained that he chose marmosets precisely because, unlike chimps, they are very vocal.
It is one of two main characteristics the monkeys share with humans, Dr Ghazanfar said.
"They're [also] co-operative breeders - so they help one another take care of their offspring.
"That's an important characteristic because it leads to greater pro-sociality (meaning the animals, like us, carry out behaviours that are intended to benefit others)."
The lead researcher, Daniel Takahashi, recorded marmosets calling to one another from opposite corners of a room. The animals were separated by a curtain, so each could hear but not see the other.
The recordings revealed that the marmosets would wait for about five seconds after the other finished calling to respond - seemingly following "unspoken rules of conversational etiquette".
Dr Ghazanfar explained that there were two ideas for why the animals followed these rules.
"One is, if you're out of sight of your group members and want to establish contact with another, you only know if you've established that contact if their response is contingent on your own," he explained to BBC News.
"And the other hypothesis is that these calls they exchange might have information content [that needs to be digested]."
Dr Ghazanfar says that our own conversational turn-taking might have evolved via a similar route - although on a parallel branch of the evolutionary tree.
This provides an alternative explanation to the somewhat "mysterious step" it is suggested occurred as the patterns in chimp-like gestural exchanges evolved into the patterns of our own vocal communication.
The team hopes that continued study of the marmosets will help to reveal more about why our own conversation can sometimes break down.
"We are currently exploring how very early life experiences in marmosets - including those in the womb and through to parent-infant vocal interactions - can illuminate what goes awry in human communication disorders," said Dr Ghazanfar.