Does the ability to reason determine human behavior? If we thought more clearly and rationally, could we avoid such catastrophes as war? These are the quesitons Calne asks in this philosophical and scientific inquiry. “When I was young,” says neurologist Calne (Univ. of British Columbia, Canada), director of the Neurodegenerative Disorders Centre at Vancouver Hospital, “I was taught that education was important because without it we would be doomed to stupid behavior and opinions based upon prejudice.” But if education brought wisdom, he later queried, “how was it possible that Germany, the home of Bach, Beethoven, Brahms, Goethe, Leibniz, and Kant could become a nation driven by hatred and complicit in the worst crimes against humanity?” His exploration for a definition of reason and an answer to his conundrum takes him here through neurology (brain structure and function) and evolution, considers the interweave between reason and social behavior and ethics, and then examines how reason has been invoked in the creation and maintenance of such cultural institutions as commerce, government, religion, art, and science. Calne agrees with the evolutionary evidence that intelligence and reasoning evolved as humans developed social organization, specifically, from the evolutionary need for individuals to cooperate in order to survive. Calne is clear in sorting through all this material: philosophy and psychology provide the principles by which reason operates, but reason itself is simply a tool. It is instinct rather than reason, he argues, which still sets our goals. How we then reach the goals is the part that involves reasoning. The strongest illustration of his argument is the existence of religion: “Reason can discredit religion so readily,” says Calne, “yet religions flourishes. We must conclude that the human needs for religion are very powerful,” And therefore, in striving to solve societal problems, we first have to establish goals that appeal to our instincts and most basic motivations; only then will reason help us find the best way to reach them. Thought-provoking and clear, this is a useful and enjoyable exercise.