Franklin later said what sparked the idea of the film was Goodall observing "the cannibalizing of young chimpanzees by one particular mad female chimp. She observed actual inter-tribal warfare, not unlike the opening of "2001", between two groups of chimps. The whole ’60s idea of man being the only animal to make war against its own kind was suddenly thrown out the window. Since then, they’ve discovered that lions and other animals do it as well, but that, to me, was a really interesting idea for a good thriller.”