Marmoset couples gradually sound more alike
Just as humans unconsciously pick up words, accents and speech habits from the people around them, marmoset monkeys make their calls sound more and more alike when they bond together. This curious discovery reveals the evolutionary roots of the mechanisms that support social learning, cooperation and communication.
By the NCCR Evolving Language
A pair of marmosets vocalizing. © Nikhil Phaniraj
Humans naturally adapt their speech when they spend time with a group. We pick up new idioms, accents, or adjust our speaking rate without realizing it. This vocal learning process allows cohesion in human groups, enabling complex cooperation. In the animal kingdom, there is growing evidence of a more subtle related behaviour called vocal accommodation, where individuals adjust their voices to sound more like their social partners.
In a new study published in Proceedings Royal Society B, researchers from the University of Zurich and the NCCR Evolving Language investigated whether marmoset monkeys could also modify their calls to match those of their partners, in a process of vocal accommodation. Understanding the biological roots and the cognitive processes involved in such a mechanism could help us figure out the foundations of human language and how it evolved.
Dynamic patterns of vocal accommodation
Researchers from the University of Zurich recorded 7 coupled pairs of marmosets to analyse how similar the vocalizations of partners were. While many previous studies only compared vocalizations before and after animals formed a bond, in their study, Nikhil Phaniraj and his team collected data consistently over the course of pair formation. “This allowed us to observe how vocal changes unfolded through time, almost like watching a movie, instead of looking at two snapshots,” the first author says.
The analysis, accompanied by mathematical modelling of the acoustic trajectories taken by marmosets to sound more similar to each other, showed that in marmoset pairs, both partners appear to continuously track changes in each other’s calls and make adjustments to their own calls over time. “It’s an ongoing, interactive process,” Nikhil Phaniraj explains. “In a sense, the marmosets were having a vocal dance, with each partner constantly adjusting to the other’s moves.”
With these results, the team of researchers can say more confidently that marmosets exhibit a dynamic form of vocal learning, with more sophisticated cognitive processes than previously thought. “This raises the possibility that some of the building blocks needed for more advanced vocal learning abilities are more widespread in the animal kingdom than we once thought,” says the researcher.
A need to accommodate?
Marmosets are a highly cooperative species, and work together to raise offsprings for example. This means their relationships and communication system are quite complex. “They are a fascinating species to study how relationships develop and communication changes as they form,” Nikhil Phaniraj says.
According to the study, marmosets accommodate their vocalizations to their partner’s, but the researchers have yet to explore the reasons for this. “Across many species, vocal accommodation seems to be linked to social relationships: individuals that cooperate often become more similar in how they vocalize,” Nikhil Phaniraj explains. Adjusting the calls could help reinforce the bonds and facilitate coordination. It could also be that this phenomenon allows a third party to recognize a bonded pair. “Further testing, with playback experiments, should be done in the future to confirm,” the researcher adds.
The team is now investigating what happens when one member of a pair fails to accommodate its partner’s calls. “We are interested in understanding not just how vocal accommodation occurs, but also how other marmosets respond when the vocal expectations are met or violated,” says Nikhil Phaniraj. By identifying the biological and social mechanisms that drive vocal accommodation, researchers can better understand how it could have provided a foundation for more advanced forms of vocal learning in humans.
