The Importance of Movement: From Evolution to Motion Sickness
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Modern humans spend a lot more time sitting down than ever before. Manual-labour jobs have largely been replaced by office jobs. Cars and other means of transport mean we can travel while sitting down. The Internet means it is possible to spend practically your whole life sitting down, what with telecommuting, online banking and shopping. Obscene sums are spent on ergonomically designed office chairs. Sitting too long on an airplane can even be fatal. It seems odd, but very little movement is damaging.
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Because moving is important. Humans are good at it and we do it a lot, as evidenced by the fact that, as a species, we have pretty much covered the surface of the earth, and actually been to the moon. Walking two miles a day has been reported as being good for the brain, but then it’s probably good for every part of the body. Our skeletons have evolved to allow long periods of walking, as the arrangement and properties of our feet, legs, hips and general body layout are ideally suited to regular ambulation. But it’s not just the structure of our bodies; we’re seemingly ‘programmed’ to walk without even getting the brain involved.
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There are nerve clusters in our spines that help control our locomotion without any conscious involvement. These bundles of nerves are called pattern generators, and are found in the lower parts of the spinal cord in the central nervous system. These pattern generators stimulate the muscles and tendons of the legs to move in specific patterns to produce walking. They also receive feedback from the muscles, tendons, skin and joints – such as if we’re walking down a slope – so we can adjust the manner of movement. This may explain why an unconscious person can wander about, in the phenomenon of sleepwalking. This ability to move around without thinking about it – whether fleeing dangerous environments, finding food sources, pursuing prey or outrunning predators – ensured our survival. The first organisms to leave the sea and colonize the land led to all air-breathing life on earth; they wouldn’t have done so if they’d stayed put.
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But here’s the question: if moving is integral to our well-being and survival, and we’ve evolved sophisticated biological systems to ensure it happens as easily as possible, why does it sometimes make us throw up? This is known as motion sickness. It’s the brain that’s responsible for this, not the stomach. What possible reason could there be for our brains to conclude, in defiance of aeons of evolution, that going from A to B is a legitimate cause for vomiting? Actually, the brain isn’t defying our evolved tendencies. It’s the numerous systems and mechanisms we have to facilitate motion that are responsible. Motion sickness occurs only when you’re travelling by a vehicle. Here’s why. Humans have a sophisticated array of senses and neurological mechanisms that give rise to proprioception, the ability to sense how our body is currently arranged, and which parts are going where. Put your hand behind your back and you can still sense the hand, know where it is and what rude gesture it’s making, without actually seeing it. That’s proprioception.
