Young Marmosets Learn Not to Interrupt

A pair of black-tufted marmosets. Image Credit: Miguelrangeljr via Wikimedia Commons // CC BY-SA 3.0

Human children aren’t the only primates that are eager to interrupt their parents’ conversations. Baby marmosets do it, too.

Learning to take turns in conversation is an important aspect in the evolution of communication, scientists from the University of California, San Diego argue in a new study. You can’t understand what someone else is saying if you can’t hear them, after all. 

Similar to polite humans, the common marmoset—a pocket-sized monkey species native to Brazil—doesn’t make noise when one of its brethren is talking. But just like in people, this behavior isn’t automatic: it has to be learned in childhood. 

Researchers from UCSD’s Cortical Systems and Behavior Laboratory studied the vocalization patterns of 10 young marmosets (five pairs of twins) and two sets of parents over the first year of the infants’ lives, recording the “conversations” the juvenile marmosets had with their parents when they couldn’t see each other. In the wild, marmosets keep in contact through high-pitched “phee” calls when they are separated. 

The elder marmosets guided the behavior of their young by responding when they made the right vocalization, and ignoring them when they did something uncouth. When the young marmosets interrupted their parents’ calls, their parents would simply not respond for several seconds, teaching them that that behavior was inappropriate in that context. If the marmosets did not interrupt, they were more likely to receive a response to their call.

A common marmoset. Image Credit:  Leszek Leszczynski via Wikimedia Commons // CC BY 2.0 

“When a parent produces a vocal response to their child, it provides a potential positive reinforcement, affirming an interest in continuing the vocal exchange,” the researchers write. “The absence or delay of a response would, therefore, communicate that the behavior of the offspring was not appropriate.”

Furthermore, if the young marmosets produced the wrong sound (not a “phee” vocalization) for the context, their parents were more likely to interrupt them, seemingly a corrective measure.

Interestingly, young marmosets were significantly more likely to interrupt their father than their mother, though there’s not a clear explanation for why. Furthermore, the young marmosets’ “conversations” with their siblings didn’t change as much over time as their vocalizations with their parents did, suggesting that the primates tailor their voices to the social context.

The researchers were unable to distinguish whether the marmoset parents were aware that they were actively teaching their offspring proper behavior, or if they were exhibiting normal behavior that happened to direct social learning.