If not for a horse, would Alexander have been the Great? William, the Conqueror? Richard, the Lionhearted? If not for their awesome mounts, would the Spaniards have had their way with the New World? Would Paul Revere have spread the word? Would the West have been won?

It is hard to comprehend how far horse power has carried us, difficult to imagine, in our era of mechanical wizardry and speed, what role the horse has played in shaping human history. This is the challenge Juliet Clutton-Brock takes up in her book, a splendid blend of natural and social history that recounts the horse's story as it has figured in—and transfigured—our own.

By drawing on biological, archaeological, and historical evidence, Clutton-Brock describes the wild horse and the wild ass, from their widespread distribution at the end of the last Ice Age to their near extinction today. She shows how these beasts, once hunted for meat, were drafted for work and domesticated as humans began to grasp the possibilities of riding horseback. This discovery, with the speed, distance, and power it offered, transformed the course of history. This elegant tale of the horse and donkey, wonderfully written and handsomely illustrated, revives the true meaning of "horse power."

Throughout his remarkable career, Donald Pfaff has demonstrated that by choosing problems and methods with care, biologists can study the molecular mechanisms of brains more complex than those of fruit flies, snails, roundworms, and other invertebrates. His half century in the lab, starting with his discovery of hormone receptors in the brains of mammals and leading to the first detailed account of a neural circuit for mammalian behavior, puts him in a unique position to survey the origins and development of behavioral neurobiology and the current state of research. How the Vertebrate Brain Regulates Behavior offers a close-up, conversational perspective on scientific struggles and successes throughout a fifty-year quest to understand how behavior is regulated in a complex organism.

In graduate school, when Pfaff expressed a desire to study behavioral regulation, his advisor suggested focusing on hormones. Pfaff’s investigation into the hormonal basis of female sexual behavior in laboratory rats led him to a comprehensive appreciation of how hormone-dependent neurons work through neural circuits to produce discrete behaviors among all vertebrates. This breakthrough, along with other researchers’ findings, established a link between molecular biology and neuroscience that opened up a fruitful new field of inquiry.

Pfaff’s approach is to focus on one solvable problem and explore it from many angles. He begins with a single observed behavior and traces its regulation through a series of biological mechanisms—from hormones to genes to neural circuits. Pfaff’s relentless pursuit of his goals continues to inspire neuroscientists today.