Humans aren't the only species that knows how to carry on polite conversation. Marmoset monkeys, too, will engage one another for up to 30 minutes at a time in vocal turn-taking, according to evidence reported in the Cell Press journal Current Biology.

"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," says Asif Ghazanfar of Princeton University.

"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."

In other words, both people and marmosets appear to be willing to "talk" to just about anyone, and without any rude interruptions. The discovery makes marmosets rather unique, the researchers say, noting that chimps and other great apes "not only don't take turns when they vocalize, they don't seem to vocalize much at all, period!"

Ghazanfar and first author of the study Daniel Takahashi were especially interested in marmosets because of two features they hold in common with people: they are generally friendly with one another and they communicate primarily by producing vocal sounds. The scientists suspected that those features would support the self-monitored give and take that a good conversation requires.

To find out, they placed marmosets in opposite corners of a room in which they could hear but not see each other and recorded the exchanges that ensued. They found that marmosets don't call at the same time, but rather wait for about 5 seconds after one is finished calling to respond. In other words, they follow a set of unspoken rules of conversational etiquette.

Further study of the marmosets could help to explain not only why humans communicate with each other as they do but also why 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," Ghazanfar says.

Current Biology, Takahashi et al.: "Coupled oscillator dynamics of vocal turn-taking in monkeys."