Kanzi and Panbanisha understand English. Loulis can have conversations in sign language with his mother. Sheba is able to look into two bins containing oranges and tell you how many there are in total. Darrell knows that if you cut half a banana in two you get a quarter. Nothing special except that Kanzi, Panbanisha, Loulis, Sheba and Darrell are all chimpanzees. 

 In the late 1960s and early 1970s, teaching apes to communicate using the linguistic systems which humans had designed for them was a popular pursuit among psychologists and linguists. They were trying to uncover the origins of human speech and to discover whether the possession of grammar set us apart from our closest biological relatives. But in the 1980s, the work of pioneer researchers who seemed to have taught apes to communicate with human beings was attacked as charlatanism.

Now opinion is moving back in favour of the idea that apes can indeed talk to us. Horizon looks at the latest developments in the chimpanzee language laboratories of America - and visits some of the original subjects, now in their teens and 20s. Can chimpanzees really communicate with humans?
What does this tell us about the evolution of human language and thought?
Director Jenny Jones
Series editor Jana Bennett
An Orlando productionfor BBCtv