Chimpanzees incorporate calls to communicate new meanings

Similar to humans, chimpanzees incorporate vocalizations into communicatively meaningful structures. UZH researchers think this ability may be evolutionarily more ancient than previously thought.

The main feature of human language is our ability to combine larger words compositional phrases i.e. where the meaning of the whole is related to the meaning of the parts. However, where this ability came from or how it developed is unclear.

Chimpanzees, our closest living relatives, are known to produce a number of different vocalizations to regulate their social and ecological life and, under certain circumstances, combine these calls into larger sequences. By conducting careful, controlled experiments with wild chimpanzees in Uganda, researchers from the University of Zurich (UZH) showed that this combination is understood by the chimps.

Chimpanzees react the strongest to calling combinations

“Chimpanzees produce an ‘alarm-huus’ when startled and a ‘waa-bark’ when potentially recruiting conspecifics during aggression or hunting,” said Maël Leroux, a postdoctoral student in UZH’s Department of Comparative Linguistics, who led the study. “Our behavioral observations show that chimpanzees incorporate these calls when faced with a threat where recruiting group members is advantageous, such as when encountering snakes, but until now experimental verification has been lost.”

The researchers presented the chimpanzees with a model snake and were able to elicit combination calls. Critically, the chimps responded most strongly to repeated playback of the combination than to hearing “alarm-huu” or “waa-bark” alone. “This makes sense because threats requiring recruitment are urgent events and suggests chimpanzee listening actually incorporates the meaning of individual calls,” added final study author and UZH professor Simon Townsend.

The roots of primate compositionality

An important implication of these new findings is the potential light they can shed on the evolutionary roots of language compositional properties. “The last humans and chimpanzees shared a common ancestor roughly 6 million years ago. Therefore, our data suggest that the capacity to incorporate meaningful vocalizations is potentially at least 6 million years old, if not older,” said Townsend. “These data provide an interesting glimpse into the evolutionary emergence of language,” adds Leroux. In short, this points to compositionality originating before the appearance of language itself, although continued observation and experimental work, ideally in other great ape species, will be critical to confirming this.