Humans are not the only species capable of polite conversation with each party allowing the other a turn to speak -- marmosets do it too, U.S. researchers say. The monkeys will engage one another for as long as 30 minutes at a time in vocal turn-taking, the researchers report in the 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,\" Princeton University scientist Asif Ghazanfar said. \"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.\" The finding shows marmosets are distinctive in their vocal habits, the researchers said, 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!\" The researchers said marmosets have two features in common with people: They are generally friendly with one another and they communicate primarily by producing vocal sounds. Those are features likely to promote the self-monitored give and take that a good conversation requires, they said. In experiments, the researchers found marmosets don\'t call at the same time, but rather each will wait for about 5 seconds after the other is finished calling before responding. In other words, the researchers said, they appear to follow a set of unspoken rules of conversational etiquette.