Whether referring to a politician, cheering on an athlete, or telling what friends and family have been up to, names often crop up in everyday human communication. Now researchers say marmoset monkeys use similar tags.
Besides humans, previously only dolphins and elephants were known to use vocal tags for other members of their species.
But now scientists say they have found evidence of the behavior in a non-human primate.
Dr David Omer, co-author of the research from the Hebrew University of Jerusalem, said: “We think that this behavior is important for [marmosets’] social cohesion and therefore it is crucial for their survival.”
“We predict that other non-human primates with the similar social structure of a monogamous family group may have evolved similar behaviors.”
The team said the work could have other implications as well.
“Primate vocalization has long been considered genetically predetermined and inflexible, making it irrelevant to the evolution of human language,” Omer said. “However, our findings challenge this assumption.”
Write in the journal ScienceOmer and colleagues report how they conducted a series of experiments involving a total of 10 marmosets.
Such animals are social primates that live in small family groups and are known to use whistle-like vocalizations called “phee calls” to inform other marmosets of their location.
In each experiment, the team placed a pair of marmosets, with different relationships to each other, in a room and let them interact. They then separated them with a barrier so the monkeys could not see each other, and recorded their calls.
The researchers found that the monkeys naturally engaged in spontaneous phee call chit-chat, taking turns making calls.
However, when they analyzed the vocalizations, they found that the marmosets used different phee calls for each monkey on the other side of the barrier, similar to names in humans.
“We found that marmosets have a behavioral strategy. On the first 20 or so calls, in each session, the variability of the calls was high – meaning they were trying to call different recipients,” Omer said. “After the initial 20 calls [or so] they came together to the call addressing the receiver monkey on the other side of the visual barrier.”
The team added that monkeys within the same family group tended to use similar calls when addressing a given monkey on the other side of the barrier.
“This is evidence for vocal learning,” Omer said. “They learn vocal etiquette from their family members.”
The team also conducted experiments in which three of the monkeys were each exposed to recordings of calls made by others.
The researchers found that the marmosets were more likely to answer calls directed at them, while they also found evidence that recipient monkeys could accurately identify the caller.
“The phenomenon of vocal labeling we report in marmosets is similar to human naming, but there are few important differences,” Omer said. “People can form an infinite combination of vocalizations to form a name. Marmosets use a stereotypical call – a phee call – and modulate the fine acoustic structure of that call to form a unique label for each receiver.’”
Dr Jacob C Dunn, an expert on primate evolution and ecology at Anglia Ruskin University, who was not involved in the study, said the work provided the first preliminary evidence for the persistent vocal labels of others in a non- human primate, and adds the study also suggested marmosets used vocal learning.
Dunn said this is important because the extent to which vocal learning can be found in non-human primates is key to reconstructing the evolution of speech.
“Whether other primates are capable of using vocal labels for others remains to be seen,” he said. “But this study provides exciting evidence of mechanisms that enabled the transition from non-linguistic communication to complex language in our hominin primate ancestors.”
