(Literary Masterpieces, Critical Compilation)

Throughout most of recorded history, the relative status of the human heart and the human brain was clear and mostly unquestioned. An observer at an ancient Egyptian embalming ceremony, for instance, would have seen the priests use a hooklike tool to perfunctorily scrape out the cadaver's brain through the nose and then pack the resulting empty skull with clean cloth before burial. The heart, by contrast, was carefully preserved in the body. As the seat of the soul and all intelligence, the heart was considered crucial for entering the afterlife, where it was weighed by the gods to determine whether the dead merited paradise or destruction.

Even if one fast-forwards thirty-six hundred years to the world of science and medicine in Europe, the brain is still considered a mostly incidental organ. Philosopher Thomas Hobbes, who consorted with such great thinkers as Galileo, summed up the accepted view when he wrote: “For what is the heart but a spring; and the nerves but so many strings; and the joints but so many wheels, giving motion to the whole body, such as was intended by the artificer?” Hobbes considered the heart “the fountain of all senses,” and taught that the rate of the heart's blood flow determined whether a person felt pleasure or pain, anger or fear.

A contemporary of Hobbes, a young physician named Thomas Willis, was about to forever overturn that established hierarchy of anatomy—from considering the brain as, in philosopher Henry More's view, “something like a bowl of curds” to enthroning it as the seat of the modern soul. As contemporary psychologist and author Oliver Sacks (whose medical writings were the basis of the popular 1990 film Awakenings) has written, “Willis was the first man to come to grips with the human brain, to see how different parts of it had different functions, and how the human soul could be embodied in it.”

The historical setting for Willis's research was as dramatic and contradictory as the discoveries themselves. Though historians would later refer to the period as England's “century of genius,” it was also an era of revolution and persecution in which most people's lives were, in Hobbes's best-known phrase, “nasty, brutish, and short.”

Willis and his close-knit group of colleagues, who came to be called the Oxford Circle, were viewed as dangerous heretics by the religious establishment of the day. By persevering in their experiments they risked being officially branded as atheists, which at the time could place both their careers and their survival in jeopardy.

This sprawling and multilayered story finds an able and eloquent teller in young science writer Carl Zimmer, winner of numerous journalism awards and author of a monthly essay in Natural Historymagazine, a prestigious forum he inherited from the late Stephen Jay Gould. Zimmer has a natural gift for putting complex topics into accessible language and for bringing a scene to life in short order. These gifts are put to the test many times over in Soul Made Flesh, as its narrative ricochets along wildly branching pathways: from the medical practices of ancient Greece to astronomy to modern brain-scan machines and antipsychotic pharmaceuticals. It is to Zimmer's great credit as a storyteller that the numerous digressions only occasionally leave the reader impatient to return to the main tale.

Thomas Willis thrived amid the vigorous stir of ideas and discussion made possible by the polymath collection of talents represented in the Oxford Circle. At the age of thirty-nine, he was a well-respected physician and author during the watershed events of 1660, when King Charles assumed the throne of England after years of bloody uprisings and revolution. Willis, now with friends in high places, had more freedom than usual to explore—at least in his lectures—new scientific theories that did not necessarily jibe with the accepted wisdom of such legendary authorities as Galen, the Greek physician whose ideas still dominated European medicine some fifteen hundred years after his death.

Ironically, that freedom and intellectual stimulation led Willis at first to doubt, and then to become severely disillusioned with, his formidable earlier achievements. It was of this time period that Willis would later recall:

I seemed to myself like a painter that had delineated the head of a man, not after the form of a master, but at the will of a bold fancy and pencil…. [I] had not followed that which was most true, but what was most convenient, and what was desired rather than what was known. Thinking on these things seriously with myself, I awaked at length sad, as one out of a pleasant dream…. I determined with myself seriously to enter presently upon a new course, and to rely on this one thing, not to pin my faith on the received opinions of others, nor on the suspicions and guesses of my own mind, but for the future to believe nature and ocular demonstrations.

His new...

(The entire section is 2024 words.)