Researchers eavesdropping on marmoset conversations reveal that these small monkeys have rules to govern vocal interactions among themselves -- like us. They know to wait their turn before “talking” and not interrupt, behaviors that are guided by their parents. The findings, published in Proceedings of the Royal Society B last month, may help us understand the evolution of human language. 

As humans grow in the womb and outside of it, we pick up several mechanisms for vocal learning all along the way. During infancy, for example, we start learning to time our babbling based on the behavior of the other person. Many animals also know to take their turn during verbal communication. A couple of years ago, Princeton researchers discovered how marmosets exchanged their vocalizations in a cooperative manner, taking turns producing calls for up to half an hour. They never interrupt each other during monkey conversations. 

To study the learning processes that underlie their conversational turn-taking, a UC San Diego trio led by Cory Miller recorded common marmosets (Callithrix jacchus) interacting with their twin siblings and their parents over the first year of their lives. The marmosets were placed in plastic mesh cages on opposite sides of room, and they couldn’t see each other. “Phee,” “twitter,” “trill,” and “trillPhee” were the most common calls they’d make. “Because marmosets live in dense forests and are very small, it is difficult for them to maintain visual contact,” Miller tells Discover. “These vocal exchanges are essentially social interactions.”

After analyzing 53,363 calls from 10 infants and juveniles, 15,267 calls from two moms, and 7,436 calls from two dads, the team found at least two parallels in language development between the monkeys and us. First, marmoset turn-taking is a learned behavior. Second, marmoset parents guided the development of turn-taking by providing feedback when their young ones make mistakes during these monkey conversations. The most common errors were interrupting the parents and making call types that don’t fit the context, like an ill-placed “phee.”

The responses of young marmosets depend on who they were conversing with. They were less likely to interrupt their mom than their dad, Science reports, and both parents give the kids the silent treatment if they were interrupted. “If marmoset parents do guide the development of turn-taking,” Miller adds, “it would suggest that this ability may have evolved early in our primate ancestry.”

Polite conversation isn’t the only thing we have in common with this species of marmosets: They can learn skills by watching videos too.