Thirty years after Roger Fouts was first introduced to Washoe, a baby chimpanzee from the US Space Programme, they are still together, still conversing through sign language. Fouts made scientific history and fulfilled the age-old human dream of talking to animals. What he learned from these dialogues – as a scientist and as a human being – lies at the heart of this remarkable story of inter-species friendship. Challenging many of our assumptions about non-human primates and their cognitive abilities, On Human Nature is a moving account of Roger Fouts' personal and professional odyssey – from novice researcher to a celebrity scientist to impassioned crusader for the rights of animals.