Understanding our humanity-the very essence of who we are and how we live our lives-is one of the deepest mysteries and biggest challenges in modern science. Why do we have bad moods? Why are we capable of having such strange and vivid dreams? How can metaphors and symbols in our language hold such a powerful sway on our thoughts and actions? As we learn more about the mechanisms of human behavior through evolutionary biology, neuroscience, anthropology, psychology, sociology, and other related fields, we're discovering just how intriguing the human species is. And while scientists are continually uncovering deep similarities between our behavior and that of other animals, they're also finding a wealth of insights into everything that makes us unique from any other species on Earth.