Human language is unique. However, the potential of another primate's vocal communication is clearly underestimated: Chimpanzees combine a dozen different calls into hundreds of vocal sequences - and by no means randomly.
Chimpanzee vocal communication appears to be more sophisticated than previously thought. Researchers recorded thousands of vocalizations by wild chimpanzees in Ivory Coast. The analysis revealed that the great apes can combine twelve different calls into hundreds of different sound sequences. This combination of calls is based on certain rules, writes the team from the Max Planck Institutes for Evolutionary Anthropology (MPI-EVA) and for Human Cognitive and Brain Sciences (MPI-CBS) in Leipzig and the CNRS Institute for Cognitive Sciences in Lyon in the journal "Communications Biology".
This means that the sound communication of chimpanzees is less dissimilar to human language than previously thought: Humans combine sounds according to certain rules into words, which in turn are assembled into sentences according to certain principles. Most human languages contain fewer than 50 sounds. For comparison, some non-human primates use up to 38 calls.
Researchers recorded thousands of calls from 46 individuals from three chimpanzee communities in Ivory Coast's Taï National Park. They identified twelve different calls, which the animals combined into 390 different sound sequences. These sequences usually consisted of two to three calls, but not uncommonly up to ten.
The calls are combined quite flexibly, but not indiscriminately. Accordingly, some calls - in combination with certain others - often appear at similar positions in a sequence. This points to certain principles according to which sequences are created. However, the team emphasizes that the database is far from sufficient to determine the meaning of the sound sequences.
The study therefore documents for the first time the diversity of such call sequences for non-human primates. "Our results show that the chimpanzee's vocal communication system is much more complex and structured than previously thought," says co-author Tatiana Bortolato, who conducts research in both Lyon and Leipzig. The group writes, however, that the great apes' vocal communication probably does not come close to the complexity of human language.
"By exploring the complexity of the phonetic sequences of free-ranging chimpanzees, a species with a complex social life similar to that of humans, we hope to learn more about where we come from and how our unique language evolved," says lead author Catherine Crockford.