Book excerpt: The fascinating evolutionary links between six seemingly unremarkable traits that make us the very remarkable creatures we are. Countless behaviors separate us from the rest of the animal kingdom, but all of them can be traced one way or another to six traits that are unique to the human race-our big toe, our opposable thumb, our oddly shaped pharynx, and our ability to laugh, kiss, and cry. At first glance these may not seem to be connected but they are. Each marks a fork in the evolutionary road where we went one way and the rest of the animal kingdom went another. Each opens small passageways on the peculiar geography of the human heart and mind. Walter weaves together fascinating insights from complexity theory, the latest brain scanning techniques, anthropology, artificial intelligence, cognitive psychology, and robotics to explore how the smallest of changes over the past six million years - all shaped by the forces of evolution -- have enabled a primate once on the brink of extinction to evolve into a creature that would one day create all of the grand and exuberant edifices of human culture. As the story of each trait unfolds, Walter explains why our brains grew so large and complex, why we find one another sexually attractive, how toolmaking laid the mental groundwork for language, why we care about what others think, and how we became the creature that laughs and cries and falls in love. Thumbs, Toes and Tears is original, informative, and delightfully thought-provoking.