Move!: The New Science of Body Over Mind

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Why We Move

That which we call thinking is the evolutionary internalisation of movement.

Rodolfo Llinás

Nothing in biology makes sense except in the light of evolution.

Theodosius Dobzhansky

Some days, the life of a sea squirt sounds almost idyllic. After a brief swim around the ocean while it’s young and still has the energy, the tadpole-like larva finds a rock with a view and settles down for a rest. Once attached, it sets about developing into its adult form, a blob with two tubes. There it will sit for the rest of its life, gently sucking in water through one tube and blowing it out of the other like a small, rubbery bagpipe.

There’s a high price to pay for this lifetime of relaxation. In its larval stage a sea squirt has a simple brain and a basic nerve cord that runs along the length of its tail. It uses these to swim around, searching for a good spot to live, and to coordinate its movements to get there. Once attached, though, glued firmly to the rock by its head, the sea squirt digests almost its entire nervous system, never to make a decision again.

The curious case of the disposable brain tells us something about why we have a nervous system at all. And, before we get to the ‘how to’ aspects of body movement over mind, it’s worth considering why the many body–brain pathways came to exist. The distinguished Colombian neuroscientist Rodolfo Llinás used the sea squirt to make the case that animals originally evolved brains not so that they could think but so that they could move – away from danger and towards where the living is easier, making informed decisions as they go. Movement, Llinás reasoned, is simply too dangerous to attempt without a plan.¹

Sea squirts represent a snapshot of a time in evolution when life was experimenting with whether a nervous system was any more likely to make you survive the rigours of existence. Nervous systems are expensive to run – our own brains gobble up 20 per cent of our body’s entire energy budget despite accounting for only 2 per cent of our body weight. For the sea squirt, the answer was that the investment was worth it for as long as it was on the move, but thereafter, not so much. And when movement is no longer necessary, thinking is surplus to requirements, so the whole system goes in the recycling.

Since this period of evolutionary dithering, most species of animals have opted not only to keep a brain throughout the entirety of their lifespan but also to invest heavily in its architecture. Thinking and movement have been evolving in lockstep ever since. The human brain is by no means the pinnacle of the process of brain development – each creature’s brain is, after all, uniquely adapted to its own way of life – but in terms of investment it is certainly an extreme example. Our brains contain three times as many neurons as our closest living relatives the chimpanzees. In fact, with 86 billion neurons with over 100 trillion connections between them, the human brain is the most complicated object we have ever encountered.

Explanations of how we got this way generally concentrate on our cortex, the wrinkly outer layer of the brain, which is disproportionately large in humans compared with other apes. The wrinkles are actually a product of its size: as the cortex expanded, adding more and more processing power, the only way it could fit into the skull was to repeatedly fold in on itself. Other species with a smaller cortex, such as dogs, cats and chimpanzees, have far fewer folds and wrinkles than us. Some, including mice, rats and marmosets, don’t have any at all – their brains are as smooth as raw, skinned chicken.

Some think that our cortex enlarged to cope with the challenges of finding new ways to think – keeping track of our complex social lives, for example, or predicting where the next meal might show up and working out how to catch it. Then, once we used our big brains to work out how to cook, they got even bigger, because cooking allowed us to extract more calories from our food. All of this added up to an unusually large cortex that allows us to plan, to mentally travel back and forward in time and to come up with ideas for things that have never existed before.

That’s a good synopsis as far as it goes, yet it totally ignores the influence of movement. A new theory adds this vital detail into our origin story, linking the evolution of forward thinking not to abstract computations inside the head but to a growing evolutionary pressure to come up with new ways to move. In this view, the origin of our most impressive mental tricks can be traced even further back in our evolutionary history, to a time before humans existed, when our even more distant ancestors needed to find new ways to get around.

Twenty-five million years ago the common ancestor that we share with other apes split off the evolutionary tree from the monkeys. These early apes lived in the trees like their monkey cousins but were bigger, heavier and clumsier and were in constant danger of falling from the branches. Their solution to this problem was quite sensible: to spend more time bearing their weight on their hands, holding on tightly to branches above in situations where smaller monkeys might have been able to balance. This strategy worked well, and over millions of years (and some shoulder modifications) slowly evolved into an ability to brachiate – swinging arm over arm in the trees at speed, as gibbons do today.

Brachiation is a complicated way of moving. According to the evolutionary anthropologist Robert Barton, of Durham University, it requires more than just a vague plan of action to stand any chance of getting from A to B safely. Staying safe while swinging through the trees requires an ability to link movement to an understanding of the consequences of your actions at speed – I put my hand here, swing and reach … that one won’t hold my weight, so I’ll grab here and so on – which means being able to formulate and adapt a plan on the fly. In a paper published in 2014 Barton put forward his idea that the development of the extra brain circuitry needed to support this new skill not only led to an improvement in our ancestors’ physical gymnastic skills but also set the stage for our impressive mental gymnastics.²

The circuitry that is in charge of these kinds of super-fast movements is found not in the wrinkly cortex but in the cerebellum – the small, cauliflower-like region that, in diagrams at least, looks as if it’s dangling from the bottom of the rest of the brain. At about the time that the early apes started swinging through the trees, the cerebellum started expanding, becoming disproportionately large compared with the cortex. This trend continued through the evolution of the great apes and accelerated in the branch that led to us.

The way the cerebellum is built seems to have made this expansion a fairly straightforward process. While the rest of the brain’s wiring looks a bit like the organised chaos of an old-fashioned telephone exchange, the cerebellum is more like a well-kept vineyard, with neat rows of neurons linked with super-fast input and output wires. That means that another ‘module’ can be replicated and then bolted on fairly quickly, at least on an evolutionary timescale.

Until recently this finding would have raised a huge ‘so what?’ in evolutionary biology circles. The cerebellum had long been known to be specialised for fine-movement control. It shouldn’t have been terribly surprising that the cerebellum would expand to support a complex new movement skill.

Then in the late 1990s and early 2000s the view of the cerebellum started to change. It was gradually becoming clear that what the cerebellum does for movement it also does for thinking and emotional control. Brain imaging experiments and tracing of neurons throughout the brain revealed that many of the evolutionarily newer cerebellum ‘modules’ wire up to the frontal parts of the cortex, which are in charge of planning and forward thinking and help to fine-tune our emotional reactions. In fact, it turned out that only a small portion of the human cerebellum connects to the movement-generating parts of the rest of the brain. The rest specialises in thinking and feeling.

Barton’s theory is that, when brachiation tied together movement, forward planning and potentially fear of falling from a great height, it set us up for all manner of sequential thinking, from understanding the rules of language and numbers to building simple tools, telling stories and working out how to get to the moon and back. It’s tempting to speculate that it may also underlie the sensations that accompany some of our less successful social interactions: swinging and falling is certainly how it can feel when a conversation suddenly takes a turn for the worse.

The ability to think sequentially is particularly useful for skills that require not only fine sensory motor control but also a capacity to work out a sequence of actions that will lead you to your goal – central to the ability to knit a scarf or think through a series of moves in chess. It could also explain how chimpanzees can work out the sequence of movements that will allow them to adapt a twig to fish for termites. ‘Our capacity to work out how to achieve a goal by stringing together a sequence of actions is kind of the basis of our causal understanding of the world,’ says Barton.

Blame the ancestors

Twig technology aside, the other great apes haven’t done a great deal with their expanded forward-planning skills. Humans, though, took the ball and ran with it in a big way. One potential reason for this is that when our ancestors split off from the other apes, they started adopting a very different lifestyle, one in which they spent far less time in the trees and started roaming longer distances on the ground in search of food. The mental and physical demands of this new lifestyle brought about another crunch point in evolution, where new ways of moving and thinking came together and worked hand in hand to increase the species’ chances of survival. As a result, being physically active started to become non-negotiable to keep the brain working at peak capacity.

It’s worth a quick aside at this point to remember that evolution doesn’t work with an endgame in mind. Our minds and bodies didn’t get to be the way they are today because evolution had a plan to make us the cleverest, most self-aware species on the planet. We got here because the changes that brought us to this point must have provided some kind of survival advantage when they first appeared. Each of them had to be useful from the start, and they stuck around because they continued to supply benefits.

Use it or lose it, then, is a rule of evolution in general, but in terms of our physiological responses to movement it applies to us especially. It’s well known that our ability to exercise – our cardiovascular fitness, our muscle strength and so on – is directly linked to how much we as individuals have challenged those systems in the past. That isn’t the case for all species: bar-headed geese, for example, manage a 3,000-kilometre migration each year with no training at all. The physiological changes that build them stronger flight muscles and a bigger, more efficient heart are triggered not by months of intense training but by the change of season and a lot of extra food.³ It’s the stuff of dreams – imagine if the shortest day heralded not only the coming spring but also an increasingly fit and toned beach body, just in time for summer (but only if you ate enough pizza).

Unfortunately, our bodies aren’t built that way, and it seems that the same ‘use it or lose it’ rules apply to the brain. According to David Raichlen, who studies human evolution at the University of Southern California, this is a feature that can be traced to a point in time, around 4 million years ago, when our ancestors stopped being ape-like animals who sat around in the trees all day eating fruit, and started to explore.

At the time the climate in East Africa was becoming cooler and drier, and tropical forest was giving way to woodland and savannah. This made food more difficult to find and forced our ancestors to forage further afield. Under these circumstances, evolution would have favoured those who could stand up straighter to walk or run long distances in search of food.⁴

Those who were not only able to walk and run long distances but also to make intelligent decisions – finding their way to where the best forage is found, remembering the way back to base and so on – were even more likely to survive and pass on their genes. Around 2.6 million years ago, when hunting skills were added to gathering, thinking on our feet became yet more critical. Now our ancestors not only had to forage widely and wisely but also had to work together to outwit and bring down larger prey. And so these two selection pressures – to walk further and think better – were tied together in the unique evolutionary history of our species.

As a result, says Raichlen, our physiology became fixed so that, when we exercise, the brain responds by physically adding more capacity.⁵ The hippocampus, a part of the brain that is involved in spatial navigation and memory, responds to physical exercise by adding new cells – essentially adding capacity to the brain’s memory banks. If this new capacity is then called upon in future foraging or hunting bouts, it is more likely to be retained. New neurons are only part of this brain-boosting process. The extra capacity also requires more blood vessels, which allow for more fuel and oxygen to flow around the brain, helping it to do its job.

On the flip side, if the new memory banks are left idle, the brain will begin to make energy savings, removing any architecture that isn’t strictly necessary and trimming unused capacity to claw back some of its energy budget and divert it to where it’s needed.

The upshot of all this is that, while our closest relatives among the great apes get away with being couch potatoes, moving only if they can’t possibly avoid it and suffering no physical or mental repercussions for their laziness, we, like the sea squirt before us, can’t. The specific challenges of survival as a hunter–gatherer tied the nuts and bolts of our mental capacity to our levels of activity.

Sitting around is no longer an option for humankind if we want a healthy body and mind: that ship sailed when our ancestors gave up a life of fruit in the trees. As for how much we need to move, studies of the Hadza people, modern hunter–gatherers who live in northern Tanzania, have found that women walk almost 6 kilometres per day, while men cover 11.5 kilometres, the equivalent of 8,000–15,000 steps. If we take this as a rough guide to what our bodies evolved to do, it means that getting your steps in is non-negotiable for a fully functioning brain. If you don’t like it, take it up with Homo erectus, the species of ancient humans that started the whole sorry business.

On the upside, the evolutionary pressures that link moving and thinking are the very same ones that make moving feel good – including the well-known endorphin boost, which makes exercise feel effortless, even euphoric, and encourages us to keep going when we start to get tired. On the other hand, it raises the worrying possibility that, if our minds are there to help us move – and we don’t – perhaps we risk a future as a race of couch-bound filter-feeders, our hard-earned brains turned to mush.

It’s too soon to panic, though. Humans are nothing if not adaptable. What we need to do is use that adaptability to spring into action once again, to unglue ourselves from the sofa, get up and remember how good it feels to move.

Travelling without moving

The final part of our moving, thinking and feeling story is more difficult to pin down to a particular point in our evolutionary history, not least because we can’t see it happening in our own heads, let alone those of other species. But we do know that it must have happened, because at some point we became able to move not just physically but also virtually, inside our mind’s eye.

Whether other species can do this too is very much a moot point. There is some evidence of what looks a lot like thinking ahead in some species. In 2009 a captive chimpanzee called Santino was seen calmly piling up rocks in his compound at Furuvik Zoo in Sweden, which he would later hurl at visitors in what looked a lot like a premeditated attack.⁶ Similarly scrub jays, one of the cleverest members of the crow family, cache food to eat later. In experiments where they were fed boring kibble and then occasionally given something more exciting, they seemed to plan ahead and store more of the good stuff for later, when plain rations would presumably return.⁷ While some call this evidence of forward thinking, other scientists insist that it doesn’t prove that they are preparing for the needs of their future selves. Until we find a way to talk to the animals, we will never know for sure.

We do know, however, that humans definitely can relive the past and plan for the future. The ability to imagine things that have never been, mentally to travel back and forth in time to learn from the past and to plan for the future is very much a human speciality, and it all comes down to what Rodolfo Llinás calls the ‘evolutionary internalisation of movement’. From Llinás’s point of view, thinking and moving are basically the same kind of thing. The only difference is that movement has a final stage that makes it real to the outside world too.

The advantages of this ability are obvious. Unlike moving, thinking is invisible and risk-free, allowing us to explore the world in our own minds, trying things out for size and updating them based on new information before we risk life and limb. Something similar is true for emotions. The whole point of emotions is to stir us into action to change something that isn’t right in the world: the word ‘emotion’ comes from the Latin for ‘to