Book excerpt: From the bestselling author of The Man Who Mistook His Wife for a Hat, a collection of essays that displays Oliver Sacks's passionate engagement with the most compelling ideas of human endeavor: evolution, creativity, memory, time, consciousness, and experience. "Curious, avid and thrillingly fluent." —The New York Times Book Review In the pieces that comprise The River of Consciousness, Dr. Sacks takes on evolution, botany, chemistry, medicine, neuroscience, and the arts, and calls upon his great scientific and creative heroes--above all, Darwin, Freud, and William James. For Sacks, these thinkers were constant companions from an early age. The questions they explored--the meaning of evolution, the roots of creativity, and the nature of consciousness--lie at the heart of science and of this book. The River of Consciousness demonstrates Sacks's unparalleled ability to make unexpected connections, his sheer joy in knowledge, and his unceasing, timeless endeavor to understand what makes us human.