Introduced and narrated by David Attenborough
Koko is the first gorilla to learn sign language. At 8 years old she has a vocabularly of over 400 signs. She talks to Californian psychologist PENNY PATTERSON; argues, even lies. But does Koko understand as much as Penny claims? Do her abilities really challenge the traditional view of man's uniqueness?
Produced by BARBET SCHROEDER
Editor PETER JONES BBC Bristol