A new study shows that chimpanzee gestural communication and human language follow the same linguistic patterns


Author of the image: Catherine Hobaiter

The researcher Ramon Ferrer, from the Relational Algorithmics, Complexity and Learnability Laboratory (LARCA) at the UPC, participated with foreign researchers in a study on linguistic laws in chimpanzees’ gestural communication. The study revealed that data compression underpins animal gestural communication.

May 07, 2019

Published in Proceedings B of the Royal Society, the study has provided evidence that linguistic laws in human language, such as Menzerath's law and Zipf's law, are also found in the gestures of chimpanzees. The research was carried out by an international team of researchers: Ramon Ferrer, from the Relational Algorithmics, Complexity and Learnability Laboratory (LARCA) at the Universitat Politècnica de Catalunya · Barcelona Tech (UPC); Stuart Semple, from the University of Roehampton; Raphaela Heesen, from the University of Roehampton and the University of Neuchâtel; and Catherine Hobaiter, from the University of St Andrews.

In human language, Menzerath’s law predicts that “the greater the whole, the smaller its constituents”. Thus, for example, in words with more syllables the average syllable length is shorter, and in clauses with more words the average word length is shorter. Additionally, Zipf's law of abbreviation predicts a negative relationship between the length of words and how often they are used. Both laws are named after their discoverers, linguists Paul Menzerath and George Kingsley Zipf.

Following Menzerath’s law, a negative relationship between number and mean duration of gestures in sequences was found, as already discovered in the last study by the UPC researcher Ramon Ferrer and other scientists on the vocal sequences of male geladas. They initially did not find the negative relationship between gesture duration and the frequency of use predicted by Zipf’s law of abbreviation, but this relationship was seen in specific subsets of the repertoire.

The researchers Catherine Hobaiter and Raphaela Heesen were living with a community of chimpanzees in the Democratic Republic of the Congo, where they recorded and witnessed their communication patterns. According to the researcher Ramon Ferrer, “the scientists were recording the community of chimpanzees, who are used to the presence of humans, which made the analysis possible”. Ramon Ferrer, a professor at the Department of Computer Science, which belongs to the Barcelona School of Informatics, was one of the promoters of this research and collaborated with the scientific team that segmented the recordings to extract gesture patterns and later analysed them for the study.

The results of this work open the door to new research on animal language. “We started this research in 2009 by studying the law of abbreviation in dolphin surfacing behaviour, based on similar studies carried out in dolphins and birds with regard to this and other laws”, explains Ferrer. In addition to analysing the chimpanzees’ sequences, the authors of this study also support the idea that Menzerath’s and Zipf’s laws reflect compression, the information theory principle of minimising code length.

Compression provides a way to improve coding efficiency and is applied (to save space or memory) in many systems created by humans, such as digital pictures and videos, and in data storage in general. The researchers point out that, apart from the results of their own work, patterns consistent with Menzerath's law and other laws have been found at the molecular level: in genes, proteins and genomes. Therefore, they propose that compression underpins biological information systems in a very broad sense, from molecules to animal behaviour, human language and music.