Chimpanzees’ gestures bear a striking resemblance to human language, exhibiting two of the same underlying mathematical patterns found in all languages on Earth, researchers at the University of Roehampton have found. The finding suggests that our nearest cousins’ communication is much more like our own than we previously thought. As gestures are important communicative tools for humans, as well as many primates, they are likely to be an important step in the evolution of spoken language, the researchers say.
The team studied 81 wild chimpanzees at play at the Budongo Forest Reserve in Uganda and recorded over 2,000 of their gestures. They categorised the gestures into 58 types, including hand and arm movements such as waving, clapping and poking, as well as full-body movements such as galloping, head butting and somersaulting.
The way the apes used their gestures obeyed two linguistic rules, known as Zipf’s law of abbreviation and Menzerath’s law. Both of these rules are thought to be obeyed by all human languages.
Zipf’s law of abbreviation says that the more frequently we use a word, the shorter it tends to be. For example, the three most commonly used words in the English language are ‘the’, ‘be’ and ‘to’. The chimpanzees most frequently used the gestures of the shortest duration.
Menzerath’s law says that the longer a sequence is, the shorter its constituent parts will be. For humans, this means that the more clauses – or components – in a sentence, the fewer words tend to make up each clause. The equivalent for chimpanzees is that longer ‘sentences’ – or sequences of gestures – tend to be made up of shorter gestures.
“Primate gestural communication is, of course, very different to human language, but our results show that these two systems are underpinned by the same mathematical principles,” said researcher Raphaela Heesen. “We hope that our work will pave the way for similar studies, to see quite how widespread these laws might be across the animal kingdom.”
Both Zipf’s law and Menzerath’s law are examples of a linguistic concept known as compression – an underlying process in the evolution of language that involves reducing the amount of speech – or gestures – required to explain an idea. In general, the most efficient methods of communicating will be developed over time. It is believed that Zipf’s law is present in so many languages because shortening words increases the rate of passing on information. It has also been observed in the language of macaques and dolphins. Menzerath’s law has been seen in geladas, a species of baboon-like monkey native to Ethiopia.
The discovery that these two laws hold in the communication system of chimpanzees gives the first evidence that compression is an important evolutionary factor in animal gestural languages.