A chimpanzee has challenged the widely held view that animals do not have language by making up its own words from scratch.
Kanzi, an adult bonobo or pygmy chimpanzee kept at Georgia State University, Atlanta, has come up with four distinct sounds for the things closest to his heart - banana, juice, grapes and yes.
Although the choice of words may be a little predictable, it is the first report of an ape making sounds that seem to have the same meaning across different situations.
The findings have astonished ape experts, who believe Kanzi has come the closest yet to mastering a simple form of speech.
Kanzi has grown up among people and is skilled at communicating with symbols. It understands some spoken English and can respond to simple phrases such as "do you want a banana?", New Scientist reports today.
But its language trainers, Jared Taglialatela and Sue Savage-Rumbaugh, discovered that he also made distinct noises during their "conversations". The team studied 100 hours of video tapes of Kanzi. They were most interested in situations where the chimp's meaning was obvious, such as when it was pointing to the symbol for grapes or eating a banana. The researchers found four noises used by Kanzi in different contexts.
Dr Taglialatela said: "We haven't taught him this. He's doing it all on his own."
Kanzi's "word" for yes stayed the same across a whole range of emotions, suggesting that the noises were not simply the result of differences in the chimp's emotional state.
Kanzi is the latest in a line of primates to challenge the conventional view that animals have no language. Language used to be defined as symbolic communication until another chimpanzee, Washoe, learned to communicate in American Sign Language. Since then, the definition has been refined to put more emphasis on syntax and less on symbols.
The researchers are now trying to discover whether Kanzi is imitating human speech. But they will not consider the chimp to be communicating using the sounds until other chimps respond to the noises.