Scientists who study the evolution of language say wild chimpanzees have a more complex communication system than past research has shown. The researchers say the animal uses more than ten kinds of calls that can be combined into hundreds of different orders or sequences.
The study team made 4,800 recordings of calls produced by members of three groups of chimpanzees that live in Ivory Coast's Taï National Park. The park is one of the last important areas of old-growth tropical forest in West Africa and home to many kinds of plants and animals.
Chimpanzees, along with bonobos, are the closest living relatives to humans. They are intelligent and highly social. Chimpanzees make and use tools and can be taught a small amount of human sign language.
Scientists have long known that chimpanzees use different calls, or vocalizations, in the wild. But the new study offered a deeper understanding of their communication.
Cédric Girard-Buttoz was the lead writer of the study that appeared in the publication Communications Biology.
Girard-Buttoz said of the chimpanzee calls, "It is not a language but it is amongst the most complex forms of communication described in a non-human animal."
The call types included what researchers called 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 orders or sequences.
"In general 'pant grunt' and 'pant hoot' are the most common calls used in these sequences," Girard-Buttoz said.
The order in which the chimpanzees produced the calls appeared to follow rules, although the study did not include ideas about any possible meanings.
Girard-Buttoz said the study was important because it shows the beginning of communication that could have been the starting point of the evolution toward "syntax in our language."
Syntax is the way in which words are put together to form full sentences or phrases.
The researchers want to learn whether the sequences communicate wider meanings. They have suspicions about the possible meanings of some vocalizations.
Girard-Buttoz said researchers need to “explore in detail” the situations surrounding these calls. He added that researchers need to do “playback experiments to see if the suspected meaning matches with the behavioral reaction of chimpanzees when they hear the call."
