In a new book, "Sublime Dreams of Living Machines," University of Missouri-St. Louis history professor Minsoo Kang traces the complicated relationship humans have had with the mechanical man, as a symbol and an actual entity, throughout European history. We're fascinated by machines that can imitate humans, he says, but also feel an existential discomfort around them—an uneasiness that stems from their ability to obscure what seems like a fundamental truth of the universe, the line between the living and the inanimate.