Marmosets may have more sophisticated communication than we first thought, with individuals even having names.
The monkeys have been observed using special vocal calls, dubbed "phee calls," to identify one another in communication, according to a new paper in the journal Science.
This discovery places monkeys among the scant ranks of species known to use names, which until now only included humans, dolphins and elephants.
According to the paper, the researchers made this discovery by recording the vocal interactions of the marmosets in pairs and a marmoset conversing with a computer. They found that these "phee" calls were used only when talking to another individual marmoset and different between individuals, indicating that they were a form of a name.
"We found that marmoset monkeys use phee calls to vocally label their conspecifics, distinguish between phee calls that were directed at them as opposed to nondirected calls, and can respond correctly to the caller's identity. These results could not be explained by a variation in calls between sessions," the researchers wrote in the paper.
Additionally, they discovered that the monkeys responded more accurately when a phee call was directed at them.
"This discovery highlights the complexity of social communication among marmosets," study co-author David Omer, a researcher at the Safra Center for Brain Sciences at Hebrew University in Israel, said in a statement. "These calls are not just used for self-localization, as previously thought— marmosets use these specific calls to label and address specific individuals."
The researchers also discovered that the marmosets appeared to use similar labels within family groups, even if the individual was not a blood relative but was present with the family. This suggests that they have a form of dialect and that the vocal labels are learned from other members of the group.
"We observed that monkeys from the same family group tend to use similar calls to vocally label others and use similar acoustic features to encode the identity of others. Additionally, family members' calls addressing the same receivers were significantly more similar than calls addressing different receivers," the researchers wrote.
"These similarities were observed even among individuals who are not genetically related, which implies that vocal learning may occur among adult members of a family group."
The scientists suggest that this may have arisen to help the monkeys keep in touch in their native rainforest homes, where they may not have been able to see each other very well and, therefore, not have been able to identify family members visually.
"Marmosets live in small monogamous family groups and take care of their young together, much like humans do," said Omer. "These similarities suggest that they faced comparable evolutionary social challenges to our early pre-linguistic ancestors, which might have led them to develop similar communicating methods."
This discovery may also have implications regarding how human speech and social communication arose, as the marmosets may have evolved brain areas associated with language similar to those in humans.
"The vocal labeling of others that we report here represents a learned, highly flexible call production that requires brain mechanisms for representations of others as discrete concepts, vocal learning, imitation, and modification of the acoustic fine structure of calls," the researchers wrote.
"These mechanisms might be similar to those that facilitated the evolutionary transition from nonlinguistic communication to language in our prelinguistic humanoid ancestors."
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References
Oren, G., Shapira, A., Lifshitz, R., Vinepinsky, E., Cohen, R., Fried, T., Hadad, G. P., & Omer, D. (2024). Vocal labeling of others by nonhuman primates. Science, 385(6712). https://doi.org/10.1126/science.adp3757
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