SYDNEY: Human language may have evolved from the use of gestures by our ape ancestors, and not just from primitive vocalisations, according to a new study.
Only humans and apes use hand or limb gestures to communicate, but until now little was known about how these gestures combine with other forms of communication in apes or what kind of responses they generate.
To learn more, primatologists Frans de Waal and Amy Pollick of the Yerkes National Primate Research Centre in Atlanta, Georgia, studied bonobos and chimpanzees, in captivity. They focused on the way that our closest relatives combine gestures, facial expressions and vocalisations to communicate.
Flexible and complex
As they reveal today in the U.S. journal Proceedings of the National Academy of Sciences (PNAS) the pair found that the use of gestures is highly flexible, complex, and difficult to link to specific contexts. The use of gestures even varied widely between different groups of chimps and bonobos.
“The way they use gestures is extremely variable, especially compared with other forms of communication,” said de Waal. “This makes gesture a possible candidate for symbolic communication in our shared ancestor.”
Facial expressions and vocalisations, on the other hand, are more stereotypical, and are though to be largely instinctive and reactionary in apes. Gesture appears to be more under conscious voluntary control – much like human language, write the authors.
“Far more than facial expressions and vocalisations, gestures are subjected to modification, conventionalisation, and social transmission,” de Waal told Cosmos Online. “This is especially so when compared to their vocalizations and facial expressions, which are more directly tied to emotional and social contexts.”
“Since language is largely voluntary and free of specific contextual situations, these results suggest that manual gestures are a better platform on which to build a language system,” commented Michael Corballis a psychologist at the University of Auckland in New Zealand.
He argues that speech itself is a kind of gestural communication, made up of gestures of the tongue, larynx and lips. “My guess is that gestural language became more facial and less manual as our ancestors usurped the hands for other activities.”
The new study also suggested that – at least in terms of the origin of language – bonobos are more similar to us than chimps. The team found that bonobos are more flexible in their use of gestures, and also responded more frequently to them.
“This may be due in part to bonobos’ deliberate attempts to add critical information to the message they’re trying to send [and] suggests that the bonobo is a better model of symbolic communication in our early ancestors,” said de Waal.
Related findings also published in PNAS today report that the language we speak, can shape the way we perceive colours – leading to different patterns of colour discrimination.
Researchers at Stanford University in California have found that speaking a language with a mandatory distinction between shades of a colour (say light blue and dark blue in Russian, rather than just blue in English) can influence the time taken for the subject to respond in an objective colour test, a result not seen in subjects who speak a language with just one word for the colour.
Ape gestures and language evolution – PNAS
Frans de Waal, Yerkes National Primate Centre, U.S.