The combination of sounds emitted by chimpanzees in the wild appears to follow an order that has similarities to the grammar of our species, claims a new study published by European researchers.
Scientists still haven’t been able to assign meaning to primate “phrases,” but the work is an important first step toward understanding the links between the communication capabilities of other great apes and the origin of human language.
Data on the subject have just been published in the specialized journal Communications Biology. Coordinated by Cédric Girard-Buttoz, from the Marc Jeannerod Institute of Cognitive Sciences, in France, the work was based on the analysis of more than 900 hours of recordings of the sounds emitted by chimpanzees from the Taï National Park, in Côte d’Ivoire. In all, the “voices” of 46 adult monkeys are present in the recordings, always made in natural contexts.
Studies on the language skills of chimpanzees have been going on for several decades, but most often they focus on teaching animals the rudiments of human sign languages. In part, this has to do with the fact that the conformation of the musculature and the bones of the animals’ throats simply does not allow them to reproduce sounds with the same flexibility as the animal. Homo sapiens.
In addition, there is, of course, the cognitive issue. With brains that are, on average, a third of ours, apes seem to have fundamental limitations when it comes to understanding how language works. Thus, the results of studies with sign languages ​​are relatively disappointing.
The “volunteer” chimpanzees and bonobos can learn a few hundred signs, but they fail to combine them in a way that resembles the meaning structure that differentiates, for example, the phrase “The boy saw the dog” from “The dog saw the boy”, something that human children from the age of two or three are already able to understand.
However, this type of experiment is often done in contexts far removed from the animals’ natural behavior, which is why the analysis by Girard-Buttoz and her colleagues is valuable. Starting from a list of the different types of vocalizations emitted by chimpanzees (a total of 12 sounds), the European team began to sift through the recordings in search of some characteristics that could indicate more sophisticated forms of communication.
The number one trait rated by scientists is flexibility, that is, the ability to combine most individual sounds with any others. Number two is ordering, which corresponds to the fact that certain units tend to appear in certain positions in the vocalization.
In the case of Portuguese, for example, it is normal to say “the boy”, not “menino o” (although other languages ​​place the equivalent of the article “o” after, not before, the noun). Item three, recombination, has to do with the ability to use individual sounds already combined — two of them, for example, that scientists call “bigrams” — to form even longer “sentences” with three or more elements.
Using these criteria, the scientists found that 67% of chimpanzee “talks” consist of a single type of sound, emitted once or several times in a row. In the remaining cases, more than one type of call was combined. In general, they were the so-called “bigrams”, but there are also records of up to ten different sounds emitted together, in a total of 390 unique sequences of sounds (again, it is possible to compare them to different “phrases”). That is, this already satisfies criterion one, that of flexibility.
To test criterion two, the preferred order of sounds, the study authors specifically looked at “bigrams,” the combination of two different types of vocalization. One more point for chimpanzees: the researchers found that at least nine of the sound units have a clear tendency to appear in typical positions at the beginning or end of “sentences.”
An example is the sound they dubbed “pant-scream”. It was recorded in 67 “bigrams” in the second position, being preceded by a “pant hoot” (or “gasping hoot”) in 60 of these cases. Only in 7 occurrences another sound came before it.
Finally, with regard to criterion three, Girard-Buttoz’s team verified that most of the “bigrams” are also used by animals in vocalizations with three elements (the “trigrams”), and that, in these trios of sounds different in sequence, there also appears to be a preferred order, with certain “bigrams” appearing with a higher frequency than expected in certain positions.
There are few studies of similar scope to the European team’s on the vocalizations of other primates, but what is known so far suggests they may have discovered something unique. “For now, only the vocal systems of humans and chimpanzees appear to encompass the three structural features we propose,” the scientists write.
Now comes the most difficult and slow work: showing that these characteristics can correspond to a range of senses that animals are capable of understanding.
