What is the nature of human uniqueness? Where did "The Human Spark" ignite, and when? And perhaps most tantalizingly, why? In this three-part series, Alan Alda takes these questions personally, visiting with dozens of scientists on three continents, and participating directly in many experiments -- including the detailed examination of his own brain. Bringing his trademark humor and curiosity to face-to-face conversations with leading researchers, he seeks "The Human Spark" -- from archaeologists finding clues in the fossilized bones and tools of our ancestors; to primatologists studying our nearest living relatives to explore what we have in common and what sets us apart; to neuroscientists peering into his mind with the latest brain scanning technologies.