We humans like to think that our mastery of language sets us apart from the communication abilities of other animals, but a revealing new analysis of chimpanzees might force a rethink just how unique our powers of speech really are.
In a new study, researchers analyzed nearly 5,000 recordings of calls from wild adult chimpanzees in Taï National Park in Ivory Coast (aka Ivory Coast).
When they examined the structure of the calls captured on the recordings, they were surprised to find 390 unique voice sequences – much like different types of sentences, assembled from combinations of different call types.
Compared to the virtually endless possibilities of human sentence construction, 390 distinct sequences might not seem too wordy.
Yet until now, no one really knew that nonhuman primates had so many different things to say to each other, because we’ve never quantified their communication abilities so thoroughly.
“Our findings highlight a vocal communication system in chimpanzees that is much more complex and structured than previously thought,” says animal researcher Tatiana Bortolato from the Max Planck Institute for Evolutionary Anthropology in Germany.
In the study, the researchers wanted to measure how chimpanzees combine single-use calls into sequences, order those calls into sequences, and recombine independent sequences into even longer sequences.
While chimpanzee call combinations have been studied before, until now the sequences that make up their entire vocal repertoire have never been the subject of broad quantitative analysis.
To remedy this, the team captured 900 hours of voice recordings made by 46 wild mature western chimpanzees (Pan troglodyte verus), belonging to three different communities of chimpanzees in the Taï National Park.
By analyzing the vocalizations, the researchers identified how vocal calls could be uttered individually, combined in two-unit (bigrams) or three-unit (trigrams) sequences. They also mapped the networks of how these utterances were combined, as well as examining how different types of frequent vocalizations were ordered and recombined (e.g., bigrams into trigrams).
A total of 12 different types of calls were identified (including growls, gasps, hoots, barks, squeals and whines, among others), which seemed to mean different things, depending on how they were used. , but also according to the context in which the communication took place.
“Simple grunts, for example, are primarily emitted during feeding, while panting grunts are primarily emitted as a submissive greeting vocalization,” the researchers explain in their paper, led by co-first authors Cédric Girard-Buttoz. and Emiliano Zaccarella.
“Simple hoos are issued for threats, but gasping hoos are used in inter-party communication.”
In total, the researchers found that these different types of calls could be combined in different ways to make up 390 different types of sequences, which they believe might actually be an underestimate, given that new sequences of vocalization were still being found as researchers reached their limit of field records.
Even so, the data so far suggest that chimpanzee communication is much more complex than we thought, which has implications for the sophistication of the meanings generated in their utterances (and provides new clues to the origins of language). human).
“The chimpanzee vocal system, consisting of 12 types of calls used flexibly as single units, or in bigrams, trigrams, or longer sequences, offers the potential to encode hundreds of different meanings,” the researchers write. .
“Although this possibility is significantly less than the infinite number of different meanings that can be generated by human language, it nevertheless offers a structure that goes beyond that traditionally considered probable in primate systems.”
The next step, the team says, will be to record even larger datasets of chimpanzee calls, to try to assess how much the diversity and order of spoken sequences are related to the generation of meaning. versatile, which was not taken into account in this study.
There’s a lot more to be said, in other words – by both chimpanzees and scientists.
“This is the first study of a larger project,” says lead author Catherine Crockford, research director at the CNRS Institute of Cognitive Sciences, France.
“By studying the richly complex vocal sequences of wild chimpanzees, a socially complex species like humans, we hope to shed new light on understanding where we came from and how our unique language evolved.”
The findings are reported in Communications Biology.