Chimpanzees may learn how to use some of their calls from the adults around them, in a surprising parallel with how human children learn words, finds a study from the CNRS Institute of Cognitive Sciences, University of Warwick and Taï Chimpanzee Project.
We learn what words mean from the people around us, and different communities use different sounds for the same thing. English speakers say 'dog' and French speakers say 'chien', and these sounds would work just as well if they were suddenly swapped. Until now, scientists have assumed chimpanzee calls are not like this: largely instinctive and fixed by biology, but the new study tests this for the first time.
The study, published in PNAS , focuses on the raspberry: an unvoiced sound made by chimpanzees, much like a person blowing a raspberry with their lips. The team compared how 91 chimpanzees, aged from birth to 55 years, used the raspberry call. They studied four communities of wild chimpanzees in Taï National Park, Ivory Coast, and four communities of orphaned, peer-raised chimpanzees at Tacugama Chimpanzee Sanctuary in Sierra Leone.
Wild chimpanzees used the raspberry almost exclusively while grooming others. The juveniles at the sanctuary used it across a much wider range of social situations. If the raspberry was purely an instinctive call, groups would be expected to use it in similar ways wherever they grew up. The differences suggest chimpanzees learn not only to make a call, but when and why to use it.
Richard Moore, a philosopher at the University of Warwick and co-author of the study, said: "In everyday communication, we use the words that we do only because our peers do too. It's communal practice that fixes their meaning, rather than features of the words themselves. The discovery that this is true not just for natural languages but also some chimpanzee calls means there's more continuity between chimpanzees' vocal learning and our own than we previously suspected."
The team then found that when an adult chimpanzee was introduced to one of the sanctuary groups, the group's use of the raspberry gradually became more consistent and began to resemble the newcomer's. This suggests adults act as role models, helping a community settle on shared patterns of communication.
The researchers say it is the first time this kind of learned, agreed use has been shown in chimpanzee calls. The link between the sound and its use appears to be passed on from one chimpanzee to another, not built in at birth.
Unlike humans, chimpanzees struggle to learn entirely new call sounds. But the findings suggest they can learn the functions of calls they already make, offering new insight into how communication develops and is passed between generations. "Even aspects of chimpanzee vocal communication that seemed fixed and unlearned may be shaped by learning, suggesting that there is still much to discover about their vocal repertoire," said Antoine Valet, first author of the study.
Senior author, Catherine Crockford, CNRS Institute of Cognitive Sciences, Lyon said: "If the raspberry is learned, why do different populations use it in similar ways? One possibility is that, whilst grooming, as chimpanzees use their lips to extract parasites from another's fur, it may be easier to generate a vocalisation that uses similar lip movements, a call that is known to prolong grooming bouts. Communities may have found this useful independently, but that wouldn't change the fact that the call is a convention. We need more research to test it."
Roman Wittig, Director of the Taï Chimpanzee Project and a senior author of the study, said: "Preserving wild chimpanzee populations is critical if we want to continue to understand the extent to which chimpanzees learn and perpetuate their vocal communication."
