How Sophisticated is Chimpanzee Speech?

By Iva Fedorka

The ways that animals communicate with each other may be simple compared to human language.

Researchers at the Max Planck Institutes for Evolutionary Anthropology (MPI-EVA) and for Cognitive and Brain Sciences (MPI-CBS) in Leipzig, Germany, and the CNRS Institute for Cognitive Sciences in Bron, Lyon, France, recorded the vocalizations of chimpanzees in Taï, Ivory Coast for clues to language development in humans.

They made 4,826 recordings (980 hours) of 46 wild adult chimpanzees in three different communities, all of whom were habituated to human observation.

Let’s Talk

Evolutionary science has not yet explained the origins of human language, which uniquely and flexibly combines sounds into words and words into a limitless number of sentences. And although the sequences produced by other animals seem relatively limited, most studies to-date haven’t examined the full flexibility and structure of vocal sequences in other animals.

Humans use language by combining sounds to form words and then using the words to produce structured sentences. To understand the origin of language, researchers have typically compared the vocal production in primates and other animals to that in humans.

The complexity of human language does not lie in the number of sounds we make (below 50 in most languages), but in the way we combine those sounds to express ourselves. Non-human primates use nearly as many different calls to communicate but had not been observed to routinely combine them into vocal sequences.

Chimpanzees were found to communicate with each other using 38 different calls, up to ten call types, and hundreds of varying sequences. The combination of specific calls seemed to predictably recur in certain positions in the sequence.

Observations

“Observing animals in their natural social and ecological environment reveals a previously undiscovered complexity in the ways they communicate,” first author Cédric Girard-Buttoz told ScienceDaily. “Syntax is a hallmark of human language and in order to elucidate the origin of this human ability it is crucial to understand how non-human primate vocalizations are structured,” adds Emiliano Zaccarella, another lead author of the study.

“Our findings highlight a vocal communication system in chimpanzees that is much more complex and structured than previously thought,” says co-author Tatiana Bortolato who recorded the vocalizations in the forest. “This is the first study in a larger project. By studying the rich complexity of the vocal sequences of wild chimpanzees, a socially complex species like humans, we expect to bring fresh insight into understanding where we come from and how our unique language evolved,” Catherine Crockford, senior author on the study, points out.

Findings

Chimpanzees produced 390 unique vocal sequences. These included two single units voiced as a “bigram” sequence, and some of which were then embedded in three-unit “trigram” sequences (trigrams). Bigrams showed positional and transitional regularities within trigrams and certain bigrams occurred at the beginning or end of a trigram or with other specific units.

• The single-unit calls of chimpanzees seem specific in a range of contexts, including alarm, hunting, feeding, and greeting
• Chimpanzees use single units within numerous vocal sequences in loud calls (pant hoot) and in sequences voiced during feeding, nesting, fusion, greeting, and travel
• The acoustic structure of calls within a vocal sequence is the same as when they are single calls

These characteristics give chimpanzees a suitable vocal system for further study.

Conclusions

The authors postulate that a language system that communicates flexible meanings requires at least:

• Flexibility – most sounds or calls in the vocal repertoire can be combined with most of the others
• Ordering – Single units within sequences follow specific rules or patterns
• Recombination – independent short sequences are combined into longer sequences

Although there is no evidence that non-human species demonstrate all three characteristics, the authors believe that previous studies may not have looked for them in the same way. Researchers have heretofore rarely evaluated the entire vocal repertoire of non-singing species, so drawing definitive conclusions about animal vocal sequences may be premature.

The meaning of the study was not assessed nor has a quantitative examination of vocal sequence patterning been conducted. The authors intend to further investigate the meaning of these complex and structured vocal sequences and whether chimpanzees regularly increase the range of topics they “talk” about.