Watch Horizon online: Episode 1 The Demonic Ape

In a film that is in turns charming, disturbing and poignant, Horizon explores the relationship between science and the chimpanzee. It began with a magical story. A young girl ventured alone into the jungle and befriended a group of chimpanzees. What she saw became the stuff of scientific legend. But then, last year came a terrible tragedy. Frodo, one of the chimpanzees she had helped make famous, killed a human baby. That shocking act brought into focus a huge debate about the relationship between humans and chimps, and what these primates have taught us about the origins of our own behaviour. The saga of how Jane Goodall went into the jungle to study the chimps of Gombe in Tanzania has inspired novels and movies. Her observations revealed that chimpanzees were in many ways like humans. They used tools, had culture and even language. And what's more they had empathy. They were also capable of savage brutality against their own kind. Just like us. In fact many began to think that the origins of aggressive human male behaviour could be traced back to our shared evolutionary ancestry with chimps. In other words, men are genetically programmed to be violent. But then came some disturbing questions.

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