Chimpanzees. They’re our closest genetic relatives, with DNA over 98 per cent the same as ours. We’ve asked them to test our vaccines, check the safety of our space flights and even help us make fun of ourselves. Chimpanzees can learn from those around them in ways many other animals can’t - and when they’re captive they become even more human-like, sometimes with tragic results. This story investigates the horrific case of Charla Nash who was brutally attacked by her friend’s pet chimp, Travis and asks why such a tragedy happened..