What is it that makes us human? That's the question that sends Alan Alda on a quest across three continents in search of what he calls the human spark -- one thing that, for whatever reason, caused mankind to become what it is. From caves in France to rock shelters in South Africa, Alda and a team of producers seek out scientists who have thoughts on what separates us from the rest of the planet's inhabitants. "Chimps are smart as a whip, but they're not us," Alda says. "Why aren't they?" The hunt for the answer to that question, he promises, "will be fascinating."