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.
References:
1. Hobaiter, C. & Byrne, R.,
The Meanings of Chimpanzee Gestures. Current Biology 24, 1-5
(2014).
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