Chimpanzees' Communicative Gestures Share Similarities to Spoken Human Language

The gestures and posture of Chimpanzees have been found to obey some of the basic principles that undermine all spoken languages. The new research from the  University of Roehampton demonstrates that modern human language has deep evolutionary roots. 

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Linguistic researchers analyzed hundreds of video recordings of chimpanzees living in Uganda's Budongo Forest reserve categorizing the sounds used in 58 types of playful gesture. 

While previous research had already proved that the two rules common to all forms of human communication – Zipf's law of abbreviation, and Menzerath law on the complexity of linguistic constructs are applicable to the Chimpanzees' communication when they are in large spaces. There were gaps missing about chimpanzees in close proximity to each other. 

Gestures more important than sounds

In close quarters the animals use less vocal language and rely more heavily on physical gestures. Zipf’s law notes the inverse relationship between how often we use a word, and it's ranking with respect to other words. According to Zipf the second most repeated word in any language will be used half as often as the first. 

The rule is named after the linguist George Kingsley Zipf who also discovered that the higher a word is in use, the more abbreviated it happens to be. For example, have a look at English among the top five words are the, be, and, of, and a. 

Pretty short words, especially when compared to some of the words ranks around 500; value, international, building, and action. Interestingly, these rules aren’t just applicable to English, they have been shown to be evident in the sounds produced by macaques and dolphins too. 

Deep roots to cross-species linguistics

This new research suggests that there are some fundamentals of language that cross species. The new research also proves the rules extend to non-verbal communication of chimpanzees, too. 

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However, initially, the researchers thought this wasn't the case. When they first looked at the 2,137 measured gestures for their video recordings, they found no clear relationship between the duration of specific instances of each sign and its frequency of use. 

But when those gestures were categorized into groups, and their duration averaged out clear pattern began to emerge. It was clear that each expression type had a frequency, and following Zipf’s law of abbreviation, the more often the chimps used it, the shorter that expression group tended to be on average. 

One exception the team found thought was whole body gestures which defied any correlation to known linguistic rules. "Universal principles do not necessarily produce universal patterns," the researchers write, suggesting the law might still be at work on some level but masked by other driving forces. 

Gestures share similarities to words

Menzerath's law was also found to be true among the highly physical gestures and body posturing of the chimpanzees. The law notes that large language structures are made of smaller ones. Long words, for example, have numerous components based on shorter, simpler terms. 

Once again, the researchers could start to see correlations to the rule and the gestures after they have been grouped. Analyzing the groupings showed that chimpanzees built long visual expressions from shorter units. The laws show that there is a shared tendency to compress language into a more efficient form. 

Meaning why would human or chimpanzees put more effort into vocalizing or gesturing than we need to. The same group of researchers will now turn their attention to bonobos to see if the same laws apply in their language too.