Scientists have struggled for centuries to pinpoint the qualities that distinguish humans from the millions of other animal species with which we share the vast majority of our DNA. Now, we explore those traits once thought to be uniquely human to discover their evolutionary roots. Neanderthals 'R' Us - Is there a Neanderthal in your family tree? Recently, geneticists shocked the scientific community when they announced they'd found evidence suggesting that ancient humans may have interbred with Neanderthals. Watch as David Pogue delves into his own genetic makeup. Stone Age Language Mystery - Could two of our species' defining achievements--tool use and language--be intimately connected? Anthropologists are studying what happens in the brain when people make stone tools; their results suggest that language and tool use might go hand in hand. Evolution of Laughter - Humans may be the only species that appreciates jokes, but we're not the only one that laughs. We'll meet researchers who are tickling baby chimps, bonobos, and orangutans to record their giggling and uncover the evolutionary roots of laughter.