When the first scientist opened a human skull to see what was inside, he must have had a shock. From battle wounds he would have known to expect a lump of greyish-pink stuff. He would not have expected to see what looked like three brains: the small cerebellum, or old brain, at the base, which we have long known to control the instinctive and automatic systems, and the huge hemispheres of the cortex, almost completely divided by a deep vertical fissure. This feature has been known for millennia. Yet it was not until the last few decades that science has begun to make any progress towards explaining its purpose and workings.

Progress was long hampered by the impossibility of performing experiments on living human brains, so research was limited to the study of the few sufferers from accidental brain damage. This paucity of experimental data resulted in many controversial and often contradictory theories, and most neurologists carefully avoided the subject. But recent advances in technology have made it possible to record very accurately exactly what is going on in specific areas of the brain, and new drugs can temporarily and harmlessly disable selected areas. As a result, research has burgeoned and become respectable.

This book is also split down the middle. The purpose of the first half is to collate the large body of hard scientific knowledge that now exists to describe the very different function of each hemisphere. The second half speculates on how this knowledge might account for the history of Western civilisation and its present crisis.

What is now known is that each hemisphere has a completely different way of looking at the world. In attempting to summarise these, I shall have to grossly oversimplify, and to leave out altogether the evidence Iain McGilchrist deploys in the 200 pages of Part I (with almost another hundred pages of notes, references and bibliography). I can most economically do this by setting out in two columns, and in no particular order, some of the radically different characteristics of each hemisphere.

The sympathies of readers of Resurgence will lean heavily towards the right-hand column, and so do McGilchrist’s. He takes his title from a story in Nietzsche. A wise spiritual master is selflessly devoted to his people, but as his domain spreads he is obliged to trust emissaries to act on his behalf in the administration of the more distant regions. Eventually, however, the most trusted and powerful of these emissaries comes to lose respect for the master and works to usurp him. Because the emissary is both efficient and unscrupulous, he displaces the master and becomes a tyrant. McGilchrist interprets this as an allegory of the history of human consciousness.

The left hemisphere evolved as the executive wing of the brain, specialised for organisation, security and power, processing the right hemisphere’s raw experience of the world for practical purposes. The phenomenal growth of the frontal lobes enabled us to stand back from our world:

“But this development, permitting as it does a far greater capacity to speculate, to consider the lessons of the past and to project possible worlds into the future, to build projects and schemes for the better governing of the state and for the increase of knowledge of the world at large, requires the ability to record: to make externalised, therefore more permanent, traces of the mind’s workings, to fix, to freeze the constantly passing flow of life on the wing. It requires, therefore, a huge expansion of the realm of the written word, as well as the development of diagrams, formulas and maps; records of observations of nature; and records of the histories of people and states.”

These functions were necessary if humankind was ever to develop such things as “analytic philosophy, the codification of laws, the formalisation of systematic bodies of knowledge”: the “gifts of the left hemisphere have helped us achieve nothing less than civilisation itself, with all that means”. But the contribution of the left hemisphere must be returned to the larger purview of the right, “where everything is understood within its penumbra of significances, in its context – all that encircles it”. Sanity is this dynamic equilibrium.

But it seems that at some point near the beginnings of civilisation the left hemisphere began to enforce its own single vision, dismissing the functions of the right hemisphere (“the lunatic, the lover and the poet”) as symptoms of some mental illness. Disconnected reason came to be the only reliable witness of reality and the only arbiter of truth. (According to Plato the body evolved purely in order to support and transport the head.)

McGilchrist’s demonstration of the damage which has been done (and is increasingly being done by the dominance of left hemisphere operating alone) is masterly and totally convincing. How perfect a template this map of the mind now provides for understanding “the making of the Western world”. It accounts for the greatness of Rome, which “depended more on codification, rigidity and solidity than it did on flexibility, imagination and originality”; for the Dark Ages, when intellect was deployed in constructing “a legalistic framework for divinity”, and when Christianity was transformed into “a force for conformity, abstraction, and the suppression of independent thought”; for the Reformation, when the Flesh was made Word; for the hubris and “dissociation of sensibility” of the Enlightenment, which divorced consciousness from body and feeling, and spawned “the large-scale, rootless, mechanical force of capitalism” and the inhumanity of the Industrial Revolution.

In its “neglect of context … philosophy in the West is essentially a left-hemisphere process”. So is post-modern critical theory:

“The left hemisphere’s grasp of the world is essentially theoretical, and is self-referring. In that respect it gives validity to the post-modern claim that language is a self-enclosed system of signs – but if, and only if, it is a product of the left hemisphere alone. By contrast, for the right hemisphere there is, as Johnson said of theories of literature, always an appeal open to nature: it is open to whatever is new that comes from experience, from the world at large.”

The left hemisphere, dealing as it does with the familiar, quantifiable and predictable, suffers, when cut off from the stimulus of new experience from the right hemisphere, from boredom and alienation, which are characteristic of modernism in the arts. Denied the pleasure which derives from creativity and emotional experience, it seeks happiness in the form of entertainment and cheap thrills:

“Today all the available sources of intuitive life – cultural tradition, the natural world, the body, religion and art – have been so conceptualised, devitalised and “deconstructed” by the world of words, mechanistic systems and theories constituted by the left hemisphere that their power to help us see beyond the hermetic world that it has set up has been largely drained from them.”

The symptoms of many of the forms of mental disorder which have become prevalent since the Industrial Revolution, most notably schizophrenia, are exaggerated manifestations of ‘normal’ left-hemisphere dominance in the modern Western World. The right hemisphere is the seat of religious experience, but religious experience defined as unique, personal and grounded in life in the body and the world. D.H. Lawrence wrote that belief is “a profound emotion that has the mind’s connivance”. It is the proper job of the left hemisphere to make sure that the right does not stray into superstition and mysticism. But the disconnected left seems to appropriate religious experience, dehumanise it, codify it, and transform it into theology, doctrine and dogma and, ultimately, in line with its habitual aggressive exclusivity, into fanatical fundamentalism.

The right hemisphere is the seat of imagination. This new knowledge of the two hemispheres vindicates many unorthodox imaginative thinkers who deduced the split consciousness: Montaigne, Goethe, Hegel, Nietzsche, Scheler, Heidegger, Wittgenstein, Merleau-Ponty. The left hemisphere has marginalised the arts as mere entertainment, but Schlegel called the warring worldviews the poetic and the non-poetic:

“The non-poetic view is the one which considers that once the senses have perceived things and intellect has determined what they are, everything is settled once and for all … The poetic view is the one which continues to interpret them and never assigns any limit to their plenitude.”

And Wittgenstein came to believe that poetry was truer than philosophy. Indeed for thousands of years poets have accurately described the split in the human psyche. Most of the greatest writers in the Western canon have written about it; in some cases, about little else. Of course they knew nothing of the two hemispheres, but they knew from experience, their own and the inherited racial experience of myth and literature, that man is an almost fatally split creature – hence the primacy of tragedy. Had they known what we now know of the hemispheres, it would have made no difference to the way they wrote, since abstractions and generalisations are death to imagination. They would still have expressed their ideas (possibly even conceived them in the first place) as characters and metaphors.

There is a perpetual dialogue or conflict throughout Western literature between opposites, each of which embodies several characteristics we can now associate with the hemispheres. The Prometheus of myth and in Aeschylus is an embodiment of left-hemisphere hubris, unable (for all his fabled foresight) to see beyond short-term usefulness that the gift of fire would inevitably lead to atom bombs. Creon versus Antigone, Oedipus versus Tiresias in Sophocles, Pentheus versus Dionysos in Euripides are all dialogues between left and right hemispheres, with the sympathies of the writer invariably with the right. That dialogue has continued ever since, between the Round Table and the Green Knight, for example. It is central in Shakespeare, between Adonis and Venus, Malvolio and Sir Toby, Angelo and the Duke, Greeks and Trojans, Romans and Egyptians, and within all the tragic heroes, culminating with Prospero versus Sycorax. Blake calls the two hemispheres Heaven and Hell, Urizen and Los, single and fourfold vision.

It is Coleridge’s dialogue with his banished ‘natural man’, who insists on being heard as the Ancient Mariner. It is the basis of Yeats’ journey to and retreat from Byzantium. It is a constant theme in Lawrence, who wrote: “Man’s nature is balanced between spontaneous creativity and mechanical-material activity.” It is the battle between Piggy and Simon within the mind of Ralph in Golding’s Lord of the Flies, between the New Men and the Neanderthals in The Inheritors. McGilchrist, strangely, never mentions Ted Hughes, who came closest of all:

“The story of the mind exiled from Nature is the story of Western Man. It is the story of his progressively more desperate search for mechanical and rational and symbolic securities, which will substitute for the spirit-confidence of the Nature he has lost.”

What all these writers and thinkers were talking about, without, of course, realising it, was the battle between the hemispheres. Now their prescience is substantiated with the evidence that the split of which they wrote is not only a metaphor.

Keith Sagar is the author of Literature and the Crime against Nature and many books on D.H. Lawrence and Ted Hughes.