Scientists exploring the evolutionary origin of language have detected a vocal communication system among wild chimpanzees more complex and structured than previously known, with a dozen call types combined into hundreds of different sequences.
The researchers made more than 4800 recordings of vocalisations produced by members of three groups of chimpanzees inhabiting Ivory Coast's Tai National Park, one of the last major remnants of old-growth tropical forest in West Africa and home to a rich array of plants and animals.
Chimpanzees, which along with their cousins the bonobos are the closest living genetic relatives to people, are intelligent and highly social apes that make and utilise tools and can be taught some basic human signing from sign language.
Scientists have long known that chimpanzees use various vocalisations in the wild, but the new study offered a comprehensive examination of this intra-species communication.
"It is not a language but it is amongst the most complex forms of communication described in a non-human animal," said behavioural ecologist Cedric Girard-Buttoz of French research agency CNRS's Institute for Cognitive Science and lead author of the study.
The call types included a grunt, a panted grunt, a hoo sound, a pant hoot, a bark sound, a panted bark, a pant, a scream, a panted scream, a whimper, a panted roar and the non-vocal lip smack and raspberry sounds.
The researchers determined that these call types were used in 390 different sequences.
The order in which the chimpanzees produced the calls appeared to follow rules and structure, though the study did not include conclusions about any potential meanings.
"The key finding is the ability of a primate other than humans to produce several structured vocal sequences and to recombine small sequences with two calls into longer sequences by adding calls to it," Girard-Buttoz said.
"It is important because it shows the premise of structured communication which could have been the foundation of the evolution towards syntax in our language."
The researchers want to learn whether the various sequences communicate a wider range of meanings in the complex social environment of the chimpanzees.
The researchers are not certain whether chimpanzee vocal communication may be similar to the beginnings of language in the human evolutionary lineage.
Humans and chimpanzees share a common ancestor but split into separate lineages perhaps seven million years ago.
The study was published this week in the journal Communications Biology.
Australian Associated Press
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