Like humans, chimpanzees have the ability to combine vocalizations to create larger, more meaningful forms of communication. According to UZH researchers, this ability may be much older from an evolutionary point of view than previously thought. The ability to combine words into larger, meaningful phrases is a fundamental feature of human language, where the meaning of the whole phrase is related to the meanings of the parts that make it up. However, the origin and evolutionary development of this ability remains unclear.

Chimpanzees, our closest living relatives, are known to make a range of different sounds to direct their social and ecological lives, and in some cases combine these calls into larger strings. Researchers from the University of Zurich (UZH) have demonstrated that these combinations are understood by chimpanzees by conducting carefully controlled experiments with wild chimpanzees in Uganda.

Chimpanzees respond most strongly to combinations of calls.

“Chimpanzees produce an ‘alarm’ when surprised and a ‘bark’ when they potentially recruit their own species during aggression or hunting,” says Mael Leroux, a doctoral student in the Department of Comparative Linguistics at UZH and who led the study. “Our behavioral observations suggest that chimpanzees combine these calls when threatened, such as encountering a snake, when recruiting group members is advantageous, but experimental validation has so far been lacking.”

The researchers showed chimpanzees the snake patterns and were able to derive a combination of calls. Most importantly, the chimpanzees responded more strongly to playing the combination than to alarm-huu or waa-bark alone.

“This makes sense, because the threat to recruitment is an urgent event, and it means that listening chimpanzees really do conflate the meanings of individual calls,” adds Simon Townsend, the study’s last author and UZH Professor.

Primate roots of the composition

An important implication of the new findings is that they may shed light on the evolutionary roots of the compositional nature of language.

“The last time humans and chimpanzees had a common ancestor was about 6 million years ago. Our data therefore suggest that the ability to assemble meaningful vocalizations has potentially existed for at least 6 million years, if not longer,” says Townsend.

“These data provide an intriguing insight into the evolutionary emergence of language,” added Leroux. In short, this indicates that compositionality predates language itself, but ideally further observation and experimental work in other monkey species would be central to confirming this.