In 1976, the Princeton psychologist Julian Jaynes published the provocative Origin of Consciousness in the Breakdown of the Bicameral Mind, which argued that human self-awareness was invented in ancient Greece. His evidence consisted mainly of the Iliad, which describes its heroes as listening to the voices of the gods as they come down from Mount Olympus. Jaynes argued that these voices were emanations from inside the mind, triggered by the "breakdown" of the wall between the brain hemispheres. When the articulate left hemisphere first gains access to the dreamlike impressions of the right, a flood of new thoughts needs to be explained. This led, in Jaynes's view, to the invention of a pantheon of bickering gods, which eventually morphed into an acute consciousness of the self.
While Jaynes's speculative theory remains just that—an intriguing idea with little supporting evidence—it left a lasting mark on psychology. Thinkers in the field readily took up his central vision of human nature as a pitched battle between the two halves of the brain, each operating with a distinct set of desires and talents. That primordial conflict surfaces anew in The Master and His Emissary, a hugely ambitious work by Iain McGilchrist, a former fellow at All Souls College, Oxford, who studied literature before becoming a medical doctor. Like Jaynes, McGilchrist interprets human history as an unresolved quarrel between the left and right hemispheres. "It follows that the hemispheres need to co-operate," he writes, "but I believe they are in fact involved in a sort of power struggle, and that this explains many aspects of contemporary Western culture."
McGilchrist spends the first half of the book reviewing decades of scientific research, giving a fascinating overview of experiments led by Roger Sperry, who studied the behavior of patients whose corpora callosa had been severed (one patient would put on his clothes with his left hand while his right hand was busily taking them off), and from there moving on to more recent research on patients who have suffered trauma to either their left or their right brain. When asked to draw a house, left-brain-dominant subjects provide lots of detail (wrinkles in the curtains, bricks) but don't always make sense—the roof might be upside down, for instance. People with the use of only their right brain, on the other hand, get the architecture right but lack particulars. It's the difference between seeing the forest and the trees.
These distinct hemispheric talents lead McGilchrist to invert Jaynes's hypothesis. While Jaynes argued that the Greek gods were invented to explain the breakdown of the bicameral mind—our hemispheres were finally able to listen to each other—McGilchrist argues the opposite: He interprets the internal voices the Greeks projected onto Mount Olympus "as being due to the closing of the door, so that the voices of intuition now appear distant, 'other'; familiar but alien, wise but uncanny." The emanations of the right hemisphere became both holy and neglected, abstract.
Even to the layperson, this is fascinating research, and McGilchrist eloquently weaves the evidence into a larger narrative about the modular mind. Unfortunately, the book's second half finds McGilchrist embarking on a whirlwind tour of human history, from ancient Greece to post-modernism, interpreting everything from the melancholy music of the Renaissance to the Industrial Revolution in terms of the sides of the brain. Too often his arguments feel thin, such as when he suggests that the invention of the modern factory "enabled the left hemisphere to make its most audacious assault yet on the world."
When it comes to the hemispheres, McGilchrist isn't shy about playing favorites. He describes the left hemisphere as being "parasitic" on the right and blames the left's supposed selfishness for a wide variety of social ills, pinpointing its ability to construct clever excuses for bad behavior. "The left hemisphere is not keen on taking responsibility," he writes. "If the defect might reflect on the self, it does not like to accept it."
Unfortunately, such generalizations obscure more than they reveal; the mind remains too mysterious to become an all-encompassing explanation for the past. Although McGilchrist laments the atomization of human nature—the reduction of the soul into its neural correlates—he often falls victim to the same mistake, as he struggles to interpret thousands of years of history, philosophy, and culture in terms of two hillocks of cellular mush. In reality, the brain is the universe's largest knot; our behavior is determined not by one hemisphere in isolation but by the interactions of the brain as a whole. Oddly enough, McGilchrist's reductionism is pure left hemisphere, with its love of detail and theoretical abstraction, yet his urgent message is about embracing the right brain's metaphors and generosity. I'm not sure which side of the brain would appreciate the irony in that.