The brain holds some 10 billion neurons, an truly amazing number. But taken one at a time, there is nothing amazing about a nerve cell. If you stimulate one, it will stimulate other neurons to which it is connected. And that is all that a neuron does. And yet arising from this great mass of simple cells is every one of our mental faculties, including perhaps the most marvelous of all, our use of language. How do neurons take tiny vibrations on the ear drum and somehow capture meanings about the world? How does the brain understand written words and how does it form a reply? In The Ascent of...