14 TALKBACK INSIGHT
Humans: a very unusual great ape āWe often say the reason people get lower back pain is because we became bipeds and being a biped is a stupid way to use your back,ā says Harvard evolutionary biologist Daniel Lieberman, taking careful aim at some of his fellow scientists who maintain that humans never really adapted to being upright. āBut actually that doesnāt make any sense, because if back pain is so difficult, such a challenge, natural selection surely would have acted to lessen the prevalence and severity of back pain.ā Thereās no doubt about it: we are an unusual type of great ape. Not only are we furless but we can stand in a fully upright stance with fully extended ankle, knee and hip joints in such a way that our thigh bones are aligned with the bones of our lower legs to form flexible, continuous vertical columns. Intriguingly, as anatomists have discovered, this allows a well-coordinated person with an extended S-shaped spine to stand for hours, their body weight transmitted through their feet to the centre of the Earth, using only seven percent more energy than while lying on the ground. By contrast, our closest living relatives, furry bonobos and chimpanzees, with their slightly C-shaped spines, can stand on their hind legs without using their forelimbs for support, but only for relatively short periods because of the high energy costs used in counteracting the pull of gravity on their unstable, semi-flexed bodies. Compared with other apes, we are unusual in another respect ā we are capable of walking upright for miles, and, if need be, to run for miles. The exact details of how our ancient ancestors managed to stand upright and then used that capability to travel on the surface of the planet, as well as standing on tiptoe, bending down, and twisting their heads,
ā¦we have lost the ability to move freely and easily as most of us did as young children TALKBACK l ISSUE 3 2015
SeĆ”n Carey has some ideas why our bodies were made for walking, running, stretching, twisting, bending ā anything but sitting stillā¦
shoulders and waists, in order to obtain food and manipulate other objects, is still the subject of much debate among paleoanthropologists and evolutionary biologists. One thing we do know for sure is that when we are standing fully upright, swaying slightly, there is more weight in front of the spine than behind it and so a bipedal human anywhere in the world ā London commuter, Siberian nomad or east African hunter-gatherer ā has a tendency to fall forwards. Thatās why evolution has provided a neat mechanism through which the muscles in the neck, back and legs (the so-called extensor or anti-gravity musculature) keep us erect with the minimum amount of effort. But uprightness in humans, which also lends itself to biomechanically efficient
locomotion, has a downside. The big problem for most of us who live in the so-called advanced economies is that we never, ever manage to come up to our full height; instead we droop or collapse, and in so doing create stiffness throughout the body. Furthermore, that mal-coordination affects kinaesthesia ā the ability to sense oneself in position and movement. The result is that we have lost the ability to move freely and easily as most of us did as young children, and as people who maintain a traditional foraging lifestyle still do. Back to Daniel Lieberman: āIf you start asking people who work with huntergatherers, most people say yes, actually come to think of it, I donāt really recall anybody saying that they had back pain. Iāve never seen anybody have back pain in the hunter-gatherer context.ā