An elegant, entertaining collection of 18 short essays by our favorite neurobiologist. The gifted Sapolsky, a professor at Stanford who mostly studies baboons, is a spirited, witty guide to understanding evolution, what makes us what we are, the interaction between genes and environment, the limits of knowledge and other big questions, all of which he tackles with humor and deft prose. These chapters originally appeared in Natural History, The Sciences, Discover and other magazines.  (ATP17, $14.00)