What makes us human? And how did we get here? It's only human to want to know. These two renowned paleo-anthropologists have unlocked enormous gaps in our origin story. Each of them discovered some of the most significant prehistoric bones ever found in east Africa. For Donald Johanson it was Lucy. For Richard Leakey it was Turkana Boy. These skeletons helped explain how, why and when our ape ancestors evolved, grew bigger brains, and started walking on two legs. We hear the fascinating tales of their discoveries, but we also learn their personal origin stories, and what led each of them to try to solve some of humankind's greatest mysteries.