It is the most memorable moment of Sir David Attenborough's broadcasting career. A short sequence of his encounter with a group of playful mountain gorillas in a forest clearing in Rwanda. "There is more meaning and mutual understanding in exchanging a glance with a gorilla than any other animal I know," he tells the camera, as a female gorilla observes him from just a few feet away. The footage for his 1979 Life on Earth series was not just unexpected, it said something profound about our