Best-selling author and psychiatrist Iain McGilchrist says that we each have two brains, not one, and that the future of civilisation hangs on the relationship between them. Each brain – what we normally think of as the left and right hemispheres – can operate independently and sees a radically different version of the world. The extent to which we rely on one or the other shapes civilisation. Across many different areas of society, he argues, the west has lost the broader vision of what humans are and how they relate to the rest of life, in favour of a narrow, machine-like view.

McGilchrist first put this thesis forward in a 400-page book, The Master and His Emissary, which took him 20 years to write. It went on to sell over 100,000 copies. Now, 10 years later, a well-crafted documentary, The Divided Brain, follows McGilchrist as he meets supporters and critics of his ideas. The result is a fascinating ode to the power of art, Nature, and holistic thinking based on the latest neuroscience. The softly spoken McGilchrist, who taught English at Oxford before retraining to become a psychiatrist, is often pictured on camera walking on the coastal hills near his home on the Isle of Skye. He talks viewers through experiments showing that the difference between the hemispheres, contrary to popular belief, is not what they do, but how they do it.

The left hemisphere – the ‘emissary’ in his metaphor – divides and conquers the world with sharply focused precision, but neglects context. It has overthrown the right hemisphere – the rightful master – which deals in meaning and the big picture. As a result, the west is an enormously powerful and wealthy civilisation that fails to understand how it fits into the whole.

The Divided Brain grounds these lofty ideas in the personal stories of people who, due to tumours or strokes, have damaged parts of their brains, and those of the doctors who treat them. Alongside the scientists, it features interviews with actor John Cleese, a fan of the book, as well as former Archbishop of Canterbury Rowan Williams and Leroy Little Bear, an Indigenous leader from Canada.

McGilchrist’s ideas remain controversial to some scientists who prefer to see the brain as a computer, but to its credit the documentary includes some of this criticism. The power of the two-brain idea – whether it turns out to be scientific truth or metaphor – is that it gives a language and an easy-to-grasp image to something many people understand intuitively. Although the film doesn’t have all the answers, it throws new light on some of the biggest questions of our time. Why does the education system steer children towards increasingly specialised knowledge and undervalue drama and art? Why are many economists so focused on abstract mathematical models that ignore reality? And why don’t more people recognise that humans are entirely dependent on the climate and the rest of life for survival?

McGilchrist is keen to stress that he is not anti-science and would like to see a balance between the right and left hemi­spheres. The task he sets us is nothing less than a fundamental shift in how we conceive of human beings and the world and our relationship with it. The alternative, he suggests, is the collapse of civilisation. But it’s not all bleak. Making an analogy with people who through rehabilitation recover after strokes, he says that western civilisation can do the same, if only it recognises the need and moves in the right direction.

Nat Dyer is a freelance writer based in London. He tweets at @natjdyer