Neurophysiologist Calvin (The Ascent of Mind: Ice Age Climate and the Evolution of Intelligence, 1990, etc.) continues to explore the human mind in a lively, erudite fashion, this time drawing on evolutionary biology, ethology, linguistics, and neuroscience. He begins by distinguishing consciousness, or awareness, from intelligence (""the high-end scenery of neurophysiology"" encompassing foresight, speed, and creativity) and then considers the likely evolution of human intelligence. He argues that syntax, the structuring of relative relationships in a mental model of things, is what human levels of intelligence are mostly about, and to understand why humans are so intelligent, we need to understand how our primate ancestors evolved syntax from the more limited communicative abilities of apes. Calvin argues that not only did a Darwinian process shape a better brain over two million years, but that the same process operating within the brain might explain how the brain gives shape to thoughts and makes decisions. An image emerges of cerebral codes that copy themselves, compete with other cerebral codes, and develop new variations. Calvin tries to help the nonscientist along with clever illustrations and analogies, such as his Rube Goldberg--style mechanical ""Vacuum-Lifter Package-Carrying System"" to explain how sentences are understood, but close attention is required at all times. In his concluding chapter he considers some of the implications of artificial intelligence, i.e., a computer that simulates brain processes and is capable of abstraction, imagery, talking, planning, and decision making. What values would we want these silicon beings to have, and how would humans fare in competition with them? Challenging and rewarding. As always, Calvin's thinking about thinking gives plenty of food for thought.