Marmoset mother and daughter, Bhumi and Belle
David Omer Lab
Marmosets use distinctive calls to other monkeys in their family group, similar to the way humans call each other – they are the first non-human primates known to make such calls. The discovery shows that marmoset communication is more complex than previously thought and could help tell us more about how human language evolved.
“Until recently, people thought of human language as a peculiar phenomenon that suddenly appeared out of nowhere,” says David Omer of the Hebrew University of Jerusalem, “and we’re starting to see evidence that this isn’t the case.”
Marmoset (Calitrix jackass) live in tight-knit, monogamous family groups nestled in the dense rainforest canopy, and communicate their location and other information to one another using high-pitched song melodies that carry through the leaves. Listen below.
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Omer and his team analyzed how the high-pitched “fee” calls help the monkeys map their social circles in their brains. In the lab, they recorded the fee calls exchanged between pairs of marmosets separated by a screen. They paired 10 marmosets from three different families in various combinations and used artificial intelligence to classify more than 50,000 calls according to subtle acoustic differences. They then observed how the three marmosets responded to the fee calls recorded in the lab and directed at themselves and other marmosets.
The team found that the marmosets make 16 subtle acoustic changes to their “fee” calls, depending on which monkey they’re calling, to encode specific information about who they’re addressing. They sprinkle these monkey-specific modulations throughout the calls — the human equivalent of inserting a sound in the middle of a sentence to announce a friend’s name. The marmosets on the receiving end of these calls respond much more quickly and reliably to those directed at them than to others, meaning they understand when they’re being addressed, Omer says.
This initial analysis also suggests that family members use similar identifying labels for the same monkeys, as if they were designations unique to them, like personal names, rather than just vague identifiers.
If marmosets really do use unique names, they must have learned how to produce the specific acoustic properties of those names, says Daniel Yasumasa Takahashi of the Federal University of Rio Grande do Norte in Brazil. This means that marmosets have a more flexible vocalization system than previously thought, he says. But to really prove that marmosets are learning each other’s unique identifiers, researchers would need to discover that the marmosets didn’t know these identifiers before joining a social group, but rather learned them by listening to and imitating the conversations of other monkeys.
These findings also raise the question of whether marmosets can vocally name other objects, which could help pinpoint when naming people, places and objects is a fundamental property of language and therefore may help pinpoint when it began to evolve.
A growing body of research suggests that a variety of unrelated animals may use identifiers to refer to one another, including several species of parrots, African savanna elephants, and possibly Egyptian fruit bats. This suggests that name calling emerged independently in the tree of life, and that there may be similar social selection pressures in the biology and societies of these animals that cause names to evolve, says Michael Pardo of Colorado State University, whose research has led to the discovery that bottlenose dolphins have such identifiers.
“Many animals have much more developed cognitive abilities and much richer social lives than historically has been realized,” he says.
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