Scientists have discovered that monkeys have far more complex vocal capabilities than had previously been thought.
The finding – that monkeys have complex vocal tracts like humans – suggests that they could be capable of reshaping them to produce more articulate sounds.
During studies of the Diana monkey, a researcher at the University of St Andrews, in collaboration with scientists from the US and Germany, realised that their varied alarm calls would be impossible without a complex tract. The evidence disproves the current theory that non-human primates have vocal tracts resembling simple tubes incapable of sophisticated articulation.
The finding, to be published in the Journal of Human Evolution, may shed light on how and when human speech evolved. Until now, humans were thought to be unique amongst primates in their capacity to reshape their vocal tracts during speech production.
Researcher Dr Klaus Zuberbühler of the University of St Andrews is a psychologist with an interest in animal communication. He has spent several years studying the alarm calls of the Diana monkey in West Africa. Diana monkeys are a handsome, brightly coloured species and their loud calls carry up to one kilometre. It has already been demonstrated that they have developed different warning calls for different predators.
He said: “Previous models of animal sound production always assumed the vocal tract was like a uniform tube. This explained why a lot of animal vocalisations had a very simple acoustic structure.”
“The human vocal tract is different because it consists of various flexible tubes of different sizes. This explains how we can produce such a range of different sounds that are important for speech.”
Dr Zuberbühler and fellow researchers Tobias Riede, Babis Hatzikirou (Berlin’s Humboldt University) and Ellen Bronson (The Baltimore Zoo), used acoustic data and anatomical evidence to demonstrate the complexities. The team generated a computer model that simulates the patterns observed in the vocalisations of Diana monkeys.
It is the first time that such evidence has been presented and the team believe that the study demonstrates that some of the basic anatomical structures of the throat necessary for talking have been present in primates for millions of years.
“With Diana monkey calls, it is clear there must be at least three different tubes to be able to produce the acoustic patterns they make,” said Dr Zuberbühler.
“The suggestion is that they can change the size of these tubes to produce the sounds they do. This is in some senses equivalent to how speech production takes place in humans.”
The team are now looking for similar complexities in the vocal tracts of chimpanzees, our closest relatives in the animal kingdom.
NOTE TO EDITORS:
DR ZUBERBÜHLER IS AVAILABLE FOR INTERVIEW ON 01334 462080 OR EMAIL firstname.lastname@example.org
JPEGS OF THE DIANA MONKEY ARE ALSO AVAILABLE FROM THE PRESS OFFICE – CONTACTS BELOW.
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