According to a study, the sound communication of chimpanzees is more complex than expected: Our animal relatives also combine calls according to certain rules to a large number of special sound sequences. Further investigations should now clarify the extent to which chimpanzees use these sequences to convey complex information.
In many ways we are very similar – but one important aspect distinguishes humans from their closest relatives in the animal kingdom: monkeys communicate, we use language. Although the animals also sometimes make meaningful sounds, the human system is able to convey highly complex information. Our concept is based on the special combination of sounds into words and words into hierarchically structured sentences. How this special ability came about over the course of evolutionary history is an intriguing question of anthropology. In order to get clues, it therefore makes sense to look at the communication skills of the primates that are our closest relatives: chimpanzees.
Basically, it becomes clear that the complexity of human language is not based solely on an extraordinarily large variety of possible individual sounds that we combine to speak. Because chimpanzees can also produce many different sounds. What is special is the way in which we combine sounds into words in a structured manner and assemble them hierarchically into sentences in order to convey complex information. It was already known in principle that chimpanzees also combine different calls. However, a Franco-German research team has now systematically dealt with the structure and variety of the sound sequences of chimpanzees.
Listened carefully to chimpanzees
The scientists examined recordings of thousands of vocalizations made by members of three groups of wild chimpanzees in Taï National Park in Ivory Coast. “This is the first study as part of a larger project. 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 how our unique language evolved,” says co-author Catherine Crockford of the Institute for Cognitive Sciences CNRS in Bron, Lyon.
As the scientists report, they discovered characteristic features during the structural analysis of the chimpanzee tone sequences. They were able to identify 390 unique sound sequences, which are composed of combinations of up to ten different types of calls from the entire chimpanzee repertoire. The order of the calls follows rules – they were connected in a structured way, the researchers found. It turned out that calls – in combination with certain other calls – always occur at certain positions within the sequence.
Surprisingly complex and structured
“Basically, this ability of chimpanzees to organize discrete units into structured sequences provides a versatile system potentially suitable for expansive meaning generation,” the scientists write. Co-author Tatiana Bortolato from the CNRS Institute of Cognitive Sciences says: “Our results show that the chimpanzee vocal communication system is much more complex and structured than previously thought.”
As the scientists emphasize, with the study they have now laid a basis for further investigations that could shed light on the communication skills of chimpanzees and the origin of human language. “The assembly of words or groups of words into sentences – the syntax – is a feature of human language. In order to fathom their origin, we must first understand how exactly the vocalizations of great apes are structured,” says co-author Emiliano Zaccarella from the Max Planck Institutes for Evolutionary Anthropology and for Human Cognitive and Brain Sciences in Leipzig.
Through further investigations, the team now wants to elucidate in more detail how far the similarities between the characteristics of chimpanzee communication and human language actually reach. They are also planning to investigate an exciting question that almost begs the question: To what extent do our animal relatives use the sound sequences to convey a wider range of information to their fellow animals?
Source: Max Planck Institute for Evolutionary Anthropology, Article: Communications Biology, doi: 10.1038/s42003-022-03350-8