In the 25th year of the BBC's Natural History Unit - a series in 26 parts
Narrator
David Attenborough 13: Protowords
The vocalisations made by East African vervet monkeys are thought to correspond to specific objects and events in the external world - a property usually reserved for human speech.
Robert Seyfarth of the University of California at Berkeley and Tom Strusacker of the New York Zoological Society Investigate whether species other than man evolved the ability to make systematic use of vocal signals.
Producer MICHAEL BRIGHT BBC Bristol