Fig. 2. The bluebell tunicate.

      To Wolpert, and many like-minded scientists, the tunicate is sending us an important message from our evolutionary past, telling us that if you do not need to move, you do not need a brain. The tunicate, they say, informs us that the brain is fundamentally very practical, that its main role is not to engage in pure thought but to plan and execute physical movement. What is the point, they ask, of our sensations, our memories, our cognitive abilities, if these do not lead at some point to action, be it walking, or reaching, or swimming, or eating, or even writing? If we humans did not need to move then perhaps we too would prefer to ingest our brain, a metabolically expensive organ, consuming some 20 per cent of our daily energy. Scientists who believe the brain evolved primarily to control movement – Wolpert calls himself and his colleagues ‘motor chauvinists’ – argue that thought itself is best understood as planning; even higher forms of thought, such as philosophy, the epitome of disembodied speculation, proceed, they argue, by hijacking algorithms originally developed to help us plan movements. Our mental life, they argue, is inescapably embodied. Andy Clark, a philosopher from Edinburgh, has put this point nicely when he states that we have inherited ‘a mind on the hoof’.

      To understand the brain, therefore, we need to understand movement. Yet that has turned out to be a lot harder than anyone imagined, harder in a sense than understanding the products of the intellect. We tend to believe that what belongs in the pantheon of human achievement are the books we have written, the theorems we have proved, the scientific discoveries we have made, and that our highest calling involves a turning away from the flesh, with its decay and temptation, and towards a life of the mind. But such an attitude often blinds us to the extraordinary beauty of human movement, and to its baffling mystery.

      Such is the conclusion drawn by many engineers who have tried to model human movement or to replicate it with a robot. They have quickly come to a sobering realisation – that even the simplest of human movements involves a mind-boggling complexity. Steven Pinker, for example, points out that the human mind is capable of understanding quantum physics, decoding the genome and sending a rocket to the moon; but these accomplishments have turned out to be relatively simple compared to the task of reverse-engineering human movement. Take walking. A six-legged insect, even a four-legged animal, can always keep a tripod of three legs on the ground to balance itself while walking. But how does a two-legged creature like a human do it? We must support our weight, propel ourselves forward, and maintain our centre of gravity, all on the ball of a single foot. When we walk, Pinker explains, ‘we repeatedly tip over and break our fall in the nick of time’. The seemingly simple act of taking a step is in truth a technical tour de force, and, he reports, ‘no one has yet figured out how we do it’. If we want to observe the true genius of the human nervous system, we should therefore look not so much to the works of Shakespeare or Mozart or Einstein, but to a child building a Lego castle, or a jogger running over an uneven surface, for their movements entail solving technical problems which for the moment lie beyond the ken of human understanding.

      Wolpert has come to a similar conclusion. He points out that we have been able to program a computer to beat a chess grandmaster because the task is merely a large computational problem – work out all possible moves to the end of the game and choose the best one – and can be solved by throwing a lot of computing power at it. But we have not yet been able to build a robot with the speed and manual dexterity of an eight-year-old child.

      Our physical abilities are awe-inspiring, and they remain so even when compared to those of the animals. We tend to think that as we evolved out of our bodies and into our larger brains we left physical prowess behind, with the brutes. We may have a larger prefrontal cortex relative to brain size than any animal, but animals outclass us in pretty well any measure of physical performance. We are not as large as an elephant, not as strong as a gorilla, nor as fast as a cheetah. Our nose is not nearly as sensitive as a dog’s, nor our eyes those of an owl. We cannot fly like a bird, nor can we swim underwater for as long as a seal. We get lost easily in the forest and end up walking in circles, while bats have radar and monarch butterflies have GPS. The gold medals for physical achievement in all events therefore go to members of the animal kingdom.

      But is this true? We need to look at the question from another angle. For what is truly extraordinary about humans is our ability to learn physical movements that do not in some sense come naturally, like dancing ballet, or playing the guitar, or performing gymnastics, or piloting a plane in an aerial dogfight, and to perfect them. Consider, for example, the skills displayed by a downhill skier who, in addition to descending a mountain at over 90 miles an hour, must carve turns, sometimes on sheer ice, at just the right time, a few milliseconds separating a winning performance from a deadly accident. This is a remarkable achievement for a species that took to the slopes only recently. No animal can do anything like this. Little wonder that Olympic events draw such large crowds – we are witnessing a physical perfection unequalled in the animal world.

      Remarkable feats of physical prowess can also be viewed in the concert hall. The fingers of a master pianist can disappear in a blur of movement when engaged in a challenging piece. All ten fingers work simultaneously, striking keys so rapidly that the eye cannot follow, yet each one can be hitting a key with varying force and frequency, some lingering to hold the note, others pulling back almost instantly, the whole performance modulated so as to communicate an emotional tone or conjure up a certain image. The physical feat by itself is extraordinary, but to think that this frenzied activity is so closely controlled that it can produce artistic meaning almost beggars belief. A piano concert is an extraordinary thing to watch and hear.

      Humans have always dreamed of breaking the bonds of terrestrial enslavement, and in sport, as in music and dance, we have come close to succeeding. Our incomparable prowess led Shakespeare to sing of our bodies, ‘In form and moving how express and admirable! In action how like an Angel!’ We have to wonder, how did we develop this physical genius? How did we learn to move like the gods? We did so because we grew a larger brain. And with that larger brain came ever more subtle physical movements, and ever more dense connections with the body.

      The brain region that experienced the most explosive growth in humans was, of course, the neo-cortex, home to choice and planning. The expanded neo-cortex led to the glories of higher thought; but it should be pointed out that the neo-cortex evolved together with an expanded cortico-spinal tract, the bundle of nerve fibres controlling the body’s musculature. And the larger neo-cortex and related nerves permitted a