A new study has found that marmosets can communicate with each other by name and understand when they are addressed, adding to the list of species that exhibit such behavior and becoming the first non-human primate to do so.
The monkeys use special calls known as “phee-calls” to call to each other, a “highly cognitive” behaviour pattern that scientists say has previously only been observed in humans, dolphins and elephants.
The discovery, made by a team from Hebrew University, is outlined in a study published Thursday in the journal Science.
“This is the first time we’ve seen this in non-human primates,” David Omer, an assistant professor at the university’s Safra Brain Sciences Center (ELSC) and lead author of the paper, told CNN on Thursday.
The tree-dwelling primates are highly social animals and live in small groups in South America, but the researchers collected the data at a university animal facility in Israel.
“The experiment was very simple,” Omer told CNN. “We just put two marmosets in the same room and put a visual barrier between them.
“When you do that, they start to engage in spontaneous dialogue.”
Omer’s team recorded natural conversations between pairs of marmosets and their interactions with a computer system, leading them to conclude that the marmosets were addressing specific individuals with “phee calls.” What’s more, the animals could understand when they were being called and responded more accurately in those situations.
Ten marmosets from three different family groups were recorded communicating throughout the process, highlighting “the complexity of social communication among marmosets,” Omer added in the press release.
“Until now, we thought that non-human primate vocalization was a genetically determined and inflexible type of communication. But now we see that marmosets have the ability to produce an extremely flexible vocabulary,” he told CNN.
The study notes that marmosets are heavily reliant on vision but also exhibit a “complex array of social calls,” one of which is the “phee call.” The calls are often used to communicate when they are out of sight from each other.
In addition to using different calls for different individuals, marmosets were also found to be able to distinguish between calls directed at them and those not directed at them.
These were previously interpreted as a method of “self-location” – in other words, a way of communicating their location to others. But the new study showed that the sounds were used as “specific calls to label and address specific individuals,” according to Omer.
The study also found that marmosets from the same family group use “similar sound labels to address different individuals” and also use “similar sound features to encode different names.” This practice is similar to the use of names and dialects in humans, according to the study.
Interestingly, the learning pattern can also be seen in unrelated adult marmosets, suggesting that they learn sound tags and dialects from other members of the same group.
“We can definitely say that there is a learning process here. They are learning the names of their family members. We can also say that it is not genetic,” Ömer told CNN.
Ömer and his colleagues believe their research provides new insights into how human language and social communication evolved.
“Until now, we thought that human language was a big bang event that came out of nowhere and only appeared in humans. That completely contradicts the theory of evolution,” he told CNN.
“This finding, along with other findings, suggests for the first time that there are precursors to language development in non-human primates and that we may find evidence for an evolutionary process.”
Another study earlier this year found that African elephants can address each other with personal connotations that are similar to the personal names humans use.
The study’s lead author, Mickey Pardo, an animal behaviorist and postdoctoral researcher at Cornell University in New York, told CNN that the marmoset paper was “a very comprehensive experimental study” that “challenges the long-held but outdated idea that humans are the only primate capable of vocal learning.”
But Pardo expressed reservations about the idea that “different marmosets would use the same name for the same recipient.” He said his team had reached a similar conclusion in elephant studies before conducting further research that refuted their findings.
“The more species we can discover that have names or similar names, the more opportunity we have to use the comparative method to learn about the selection pressures that may have driven the evolution of names in our own species,” he said.
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