Study may throw light on origins of human language
The use of gestures by chimpanzees was first demonstrated by field studies carried out in the 1960s and 1970s, and work on captive animals has shown that these gestures are part of an intentional, goal-orientated behaviour common to all the great apes. While this behaviour overlaps with human language, it is absent from most animal communication systems and evidence for it is also lacking for the vocalisations of great apes.
There has been considerable interest in a potential common origin of great ape gestures and components of human language and, therefore, in the actual meaning of the gestures. Surprisingly, little work has been carried out in this area. In a new report, published in the journal Current Biology, researchers Catherine Hobaiter and Richard Byrne from the School of Psychology & Neuroscience, University of St Andrews, have presented the first systematic study of meaning in wild chimpanzee gestural communication. They have found that individual gestures have specific meanings, independently of who is making them, as is the case with words in human language. They have also provided a partial ‘lexicon’.
The field studies were conducted in the Budongo Forest in Uganda, and more than 80 chimpanzees were observed. The researchers recorded the interactions of the chimpanzees and analysed 4,531 instances of gestural communications between the animals, noting the motions they used and how other chimpanzees responded. Some 36 gestures were analysed, and some 15 different meanings were identified. Some of the gestures are unambiguous: for example ‘leaf-clipping’ is only used to signal sexual attraction.
However, many are associated with up to three meanings: for example, ‘grab’ is used for ‘stop that’, ‘’climb on me’, and ‘move away’. This ambiguity may be apparent rather than real, and may arise in part from the difficulty for human observers in discerning subtle variations in the nature of the gesture. It is evident to a human recipient whether or not a gentle touch is intended to make them move or stay where they are, but such distinctions are very difficult to perceive visually. Gestures were also employed towards two or three very similar outcomes: for example, ‘push’ is used for both ‘move away’ and ‘stop that’.
Researchers found considerable variation in whether an intended meaning was signalled by a single gesture type or several gestures of apparently equivalent meaning. This was particularly common in social negotiations, where a degree of persuasion was required. By contrast, meanings typically conveyed by a single gesture were often well defined: for example ‘initiate grooming’ is signalled by a big loud scratch.
Hobaiter, C. & Byrne, R., The Meanings of Chimpanzee Gestures. Current Biology 24, 1-5 (2014).