One primate doesn’t monkey around when it comes to etiquette.
Marmoset monkeys know when to speak their turn, carry on polite conversations and are quite friendly, a new study suggests. The findings, published in the journal Current Biology, indicate that the species has a lot more in common with humans than previously believed.
"We were surprised by how reliably the marmoset monkeys exchanged their vocalizations in a cooperative manner, particularly since in most cases they were doing so with individuals that they were not pair-bonded with," Asif Ghazanfar, of Princeton University, said in a statement.
"This makes what we found much more similar to human conversations and very different from the coordinated calling of animals such as birds, frogs, or crickets, which is linked to mating or territorial defense."
What Ghazanfar and the study's coauthor Daniel Takahashi did know was that marmosets had two features in common with humans that might make the ideal foundation to carry on good conversation: they're a friendly and they communicate through vocal sounds.
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“Marmosets don’t have the same sophisticated semantic and syntactic skills as humans, nor do they display much evidence of shared intentionality, but they do have in common with humans a cooperative breeding strategy and volubility,” the study said, adding that marmosets communicate with one another when they can’t see each other.
To see if their theory was correct, researchers placed marmosets at opposite corners of a room and separated them with a curtain so they could hear but not see each other. After recording 54 sessions between 10 marmosets in different combinations (some were cagemates while others weren't), researchers found that phee calls -- considered long-distance contact calls between marmosets -- never overlapped. After careful analysis to make sure the calls didn't take place at the same time, the researchers concluded that marmosets don’t interrupt each other when they speak.
“We found that marmosets wait for the vocal exchange partner to finish calling before responding,” the study authors explain. “The consistent waiting period of about 5-6 seconds upon hearing a call establishes a turn-taking rule.”
This time period differs in humans where gaps in conversations last hundreds of milliseconds rather than 3 to 5 seconds in marmosets. Scientists say the slower time scale could be caused by “units of perception” in each species. That is, in humans a word or syllable may be the smallest unit of communication, but for marmosets and other callitrichid species the minimal unit is the entire phee call.
While the latest study shows the advanced nature of marmoset communication, the primates may also be able to shed light on how communication breaks 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," Ghazanfar said.