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Human language appears very complex compared to other forms of communication observed in the animal world. Scientists are still trying to understand the mechanisms that led to such a difference during evolution. To this end, researchers from the Max Planck Institutes for Evolutionary Anthropology and Cognitive and Brain Sciences in Leipzig, and the CNRS Institute of Cognitive Sciences in Lyon, recorded and analyzed hundreds of hours of vocalizations of wild chimpanzees. . It appears from their study that these primates use perfectly well-structured vocal sequences to communicate with each other.
We are the only species known to communicate via language. Accustomed to speaking like this every day, we tend to forget how extraordinary (and unique) this ability is in the animal world. But the complexity of our language is not due to the number of sounds we produce — less than fifty in most languages. What sets us apart from other species is how we combine these different sounds to form words, and then how we combine the words to form a near-infinite number of sentences with a multitude of different meanings.
Where does this ability come from? To trace the evolutionary origins of our language, a group of researchers took an interest in the vocal productions of other animals and in particular those of primates. The latter use nearly forty different cries to communicate with each other, cries that they do not combine with each other (or very rarely). At least, that’s what the experts thought so far. This new study shows that chimpanzees are actually able to form meaningful vocal sequences from different types of cries.
Communication based on a very precise syntax
The team analyzed thousands of vocalizations (4826 recordings in total, or 900 hours) produced by 46 wild adult chimpanzees from the Taï National Park, located in Côte d’Ivoire. The researchers identified 12 different types of cries that the animals used to form vocal sequences, revealing “a hitherto unknown complexity in their modes of communication”, underlines Cédric Girard-Buttoz, researcher in primatology attached to the Max Planck Institute. and CNRS, and first author of the study.
Chimpanzees were already known to make several distinct sounds: growls, roars, barks and squeals. These are generally issued on a one-off, one-off basis; but sometimes chimpanzees also chain a series of sounds together in the form of a gasp (during which the animal inhales between each sound), as shown in this video by renowned anthropologist Jane Goodall:
The researchers set out to determine, from their recordings, whether some of these typical gasps appeared more often than others. They assume that the structure of a communication system capable of encoding flexible meaning should at least, but not exclusively, require the following three structural capabilities: flexibility (the combination of single-use cries into vocal sequences), order (the positioning of sound units in sequences) and recombination (the combination of independent vocal sequences into longer sequences).
They finally highlighted several combinations repeating themselves regularly: the team identified 390 unique vocal sequences in total, combining two to ten types of calls from their repertoire. ” More than a third of their vocal production comprises at least two units, with 15% of vocal sequences containing three to ten units “, specify the researchers in their article. These cries occurred in predictable ways at certain points in the sequence, following what linguists call “contiguity rules.” Sometimes two sequences would combine to form even longer “sentences”. In other words, chimpanzees would also communicate according to a well-defined syntax.
Sounds emitted differently depending on the context
This is the first time that such a diversity of vocal production has been demonstrated in non-human primates. ” Our results highlight a much more complex and structured vocal communication system in chimpanzees than previously thought. said Tatiana Bortolato, of the Max Planck Institute for Evolutionary Anthropology, and co-author of the study.
The sounds were emitted in a punctual way or in the form of panting according to the contexts, note the researchers. For example, simple grunts are primarily uttered for food, while “panting” grunts are uttered as a submissive greeting vocalization. However, it is possible that the researchers missed some even more subtle building blocks of the cries, which could vary depending on the situation. For example, a hoot emitted in response to a predator may have a subtly different pitch than a hoot emitted during a friendly encounter.
It also remains to understand the meaning of the recorded sentences. The researchers note on this subject that the order of the vocal sequences could be important: indeed, certain sounds tended to appear at the beginning of the sentences, while others were always placed at the end. The team will therefore try to elucidate this mystery and determine whether, from their “language”, chimpanzees are able to widen the range of subjects on which they can communicate with each other, as we do.
This study to explore the complexity of the vocal sequences of wild chimpanzees — which are a socially complex species like humans — could also shed new light on our origins and how our own unique language evolved, says Catherine Crockford, co-author -director of the Taï Chimpanzee Project and co-author of the study.