A basis of our language is the combination of individual words to meaningful word combinations and sentences. Biologists have now observed the first signs of such a compositional syntax in chimpanzees. In certain situations – for example when suddenly confronted with a potentially dangerous snake – these combine alarm and help calls. This sound combination then triggers a corresponding reaction in their conspecifics.
Great apes are our closest relatives in the animal kingdom. Their behavior therefore allows some conclusions to be drawn about our common ancestors and the development into humans. This also applies to language and the question of whether the basic prerequisites for it first arose in the human lineage or in primeval primates. It is clear that great apes also use a wide variety of vocalizations to communicate. They express aggression, well-being or fear and use special alarm sounds to warn their fellows. So far, however, these sounds were primarily considered to be instinct-controlled and not very changeable.
Are chimpanzees combiners?
However, chimpanzees can already master a first stage of real language: the ability to combine individual sounds into new units. We use this compositional syntax, for example, to combine individual words into meaningful sentences or to describe things in more detail – “ball” becomes “red ball”. However, it is unclear when our ancestors developed this ability for compositionality. “So far it has been disputed whether compositional syntax is a unique feature of human communication,” explain Maël Leroux from the University of Zurich and his colleagues. While isolated observations have suggested that some monkey species combine vocalizations, systematic studies are lacking.
That’s why Leroux and his team have now put wild chimpanzees to the test in Uganda. They wanted to know whether these great apes use compositional syntax in specific situations. “Chimpanzees produce whoosh calls when surprised and whaa roars when they need assistance in aggression or when hunting,” explains Leroux. But what happens when primates are surprised by a threat that requires the help of their fellow primates? For their experiment, the biologists hid a rubber snake covered in real python skin in the bushes. When a chimpanzee passed, they pulled a string so that the snake suddenly appeared in front of the chimpanzee. The team then recorded the sounds made by the surprised monkey and observed how their peers responded to its calls.
Alarm and calls for help at the same time
When evaluating the observations, it became apparent that the chimpanzees sometimes only uttered the alarm call Huu when the threatening snake suddenly appeared. In nine out of 21 tests, however, they combined the hoo sound with the waa call for support. “Our observations suggest that the animals combine multiple calls when they face a threat and want to recruit other group members for defense. For example, when encountering a snake,” says Leroux. In fact, the Huu-Waa sound combination caused a specific reaction in the conspecifics of the calling chimpanzee: While they mostly stayed away from mere alarm calls, they rushed over much more often when the call combination was heard.
According to Leroux and his team, these results indicate that chimpanzees show at least the first signs of a compositional syntax: They combine alarm and help calls to warn their fellows and request help. “The meaning of the call combination results from the meaning of its individual parts – this represents a structure similar to the compositional syntax,” the researchers write. This also sheds new light on the origin of this ability: “Humans and chimpanzees shared a common ancestor about six million years ago. So our data suggests that the ability to combine meaningful vocalizations is at least six million years old, if not older,” says Leroux. The combining of sounds could therefore have arisen before the appearance of a real language.
Source: University of Zurich; Specialist article: Nature Communications, doi: 10.1038/s41467-023-37816-y