The Evolution of Posture and the Origins of Back Pain: a Return to Primal Posture

It’s been argued that our back pain shows that evolution hasn’t yet completed our transition to upright posture. But this isn’t right. Rather, it is our failure to use our spines as intended that is the problem.

As usual, Darwin was right. He famously was the first to recognize that humans are just a snapshot in a long process that began with far simpler organisms that emerged from the mists of time. But Darwin had more to say. He also got important details of how this happened right.

As the scientists of Darwin’s time tried to fill in our origin story, they could all agree that our large brain and our upright posture were the two features that set us apart from our primate cousins.

But which of these traits appeared first?

Darwin surmised that our upright posture predated the explosive growth of our brains, and although his contemporaries disagreed with him, we now know Darwin was right about this crucial chronology. Darwin reasoned that upright posture freed our hands to make tools, a development that he believed then encouraged the growth of our immense brains.

Well, Darwin wasn’t always right. Anthropologists now know that the real driver of our upright posture was the immense increase in efficiency provided by walking with a balanced upright posture. Chimpanzees use four times as much energy with their knuckle walking gait than do humans with their signature upright, graceful walk. This difference has profound implications for lifestyle: chimps in the wild rarely travel more than a mile in a day, while our hunter gatherer forebears thought nothing of a 10-mile stroll. Of course, the chimp approach also has its advantages. Because chimps have four limbs in contact with the ground, they get twice the traction and can run twice as fast as a human for short distances. But in the long-distance contest of hunting and gathering the human approach proved the better strategy: there are now 8 billion humans on earth, while fewer than a million chimps remain in the wild.

Today it’s difficult to see just how daring Darwin’s proposal was at the time, but a century later Stephen Jay Gould observed¹: “Upright posture is the surprise, the difficult event, the rapid and fundamental reconstruction of our anatomy. The subsequent enlargement of our brain is, in anatomical terms, a secondary epiphenomenon, an easy transformation embedded in a general pattern of human evolution.”

But how exactly did we humans develop upright posture over a mere million years after 400 million years of quadrupedal locomotion? It turns out that balancing an 11-pound head on top of an upright spine requires an S-shaped curve. Early apes were able to get around with a spine that had a single, uniform, forward curve because they could bear some of their weight on their forelimbs. But humans’ upright gate required adding a reverse curve to the lower spine (our “lumbar lordosis”), a change that in turn required humans add two lumbar vertebrae to the bottom end of their spines.

We can get a glimpse of how this transition occurred when we compare contemporary human spines which uniformly have 5 lumbar vertebrae to those of contemporary chimps, who have to get by on just 3 or sometimes 4 lumbar vertebrae.

Evolution never stops, however, and even today humans are exploring different tweaks to their lumbar anatomy. For example, a minority of people have individual vertebral anatomy (Smhorl nodes) that retain some chimpanzee like characteristics, and these individuals are slightly more prone to painful back problems such as disc herniation.²

Only a fraction of back pain is due to the occasional vertebral flirtation with an earlier design, however. Rather, careful epidemiologic work³ shows that the vast majority of low back pain has no anatomical cause. The medical terms used are “nonspecific” or “idiopathic”, reflecting the fact that doctors simply don’t understand the origin of their patients’ discomfort. Fortunately, most episodes of back pain resolve within a week or two regardless of the treatment prescribed⁴. Unfortunately, such episodes are prone to recur.

When physicians can’t point to an anatomic cause for pain, they the refer to that pain as “functional”. That is, the pain is the result of misuse of one’s body. And we don’t have to look to far back in history to see how we humans went off the rails and began to abuse our spines. Since the advent of agriculture about 10,000 years ago our posture, and our general health, have declined. There is considerable anthropological research showing that early farmers experienced reduced height, diminished bone strength, increased infectious disease burden, and poorer nutritional status compared to their hunter-gatherer predecessors.⁵ This idea is perhaps best captured in a single graphic:

But there is some good news: Note that we are ourselves the authors of our back pain, so we have the power to rewrite the ending. For example, because sitting is powerfully associated in non-specific back pain, we can arrange to sit less, or to sit for shorter periods of time.

Or even to avoid sitting altogether. In his fascinating book Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding, the Harvard professor Daniel Lieberman suggests that we should squat rather than sit. Because squatting is an “active resting posture” it keeps muscles engaged and so mitigates the health risks associated with slumped, static sitting.

And for those for whom squatting is not appealing, or perhaps no longer even possible, there are other ways to stay active while sitting. A number of companies now make office chairs specifically designed to keep your core muscles engaged, and your posture erect, by requiring continuous micro adjustments to stay seated in a balanced way. In effect these chairs make sitting more like walking, and so improve posture and increase metabolic rate.

Variously call active sitting or dynamic sitting, these chairs break with standard ergonomic chairs that seek to support every body part. By requiring us to rely on our intrinsic skeletal structure for support rather than on the backrests, armrests, footrests and lumbar support designed into standard “ergonomic” chairs, active chairs aim to give us back our birthright primal posture while still allowing us to still answer mountains of email.

¹From "Our Greatest Evolutionary Step," in The Panda's Thumb. [London: Penguin, 1980]

²The ancestral shape hypothesis: an evolutionary explanation for the occurrence of intervertebral disc herniation in humans

³Non‐spinal low back pain: Global epidemiology, trends, and risk factors

⁴Evidence-based interventions to treat chronic low back pain: treatment selection for a personalized medicine approach

⁵Hunter-gatherers as models in public health