Has Evolution Set Us Up For Chronic Pain?
It is hard to overstate the toll that lower back pain takes on affected individuals and the communities in which they live. Most of us have experienced some sort of back pain, no matter the level of intensity. We may have woken up with our backs feeling awkward or stood up after sitting for too long with our backs needing a good stretch. However, some of us may experience more serious back pains. According to the 2010 Global Burden of Disease Survey, such pain, whether chronic or acute, is one of the ten most common conditions that leads to disability. Sixty to seventy percent of people living in industrialized nations will experience lower back pain at least once in their life, and the prevalence increases with age as intervertebral discs deteriorate over time. Though some incidences of lower back pain have an obvious source (e.g. traumatic injury), not all cases are so easily explained. Some recent studies, however, present an interesting potential culprit: evolution. In the transition to walking on two legs, has evolution set us up for chronic pain?
Our non-human primate relatives suffer from spinal diseases at a much lower rate than we do, prompting researchers to look into a possible reason. One prominent hypothesis that was proposed is that the increased stress placed on our vertebrae by our bipedal motion is to blame. To test this idea, researchers examined vertebrae from humans (bipeds), chimpanzees (knuckle-walking quadrupeds), and orangutans (primates that use all four legs to climb). Significant structural differences were present when comparing the three, indicating that the shape of vertebrae and methods of locomotion are related. Additionally, the researchers found that human vertebrae with visible spinal disease symptoms were closer in shape to chimpanzee vertebrae than healthy human vertebrae were. This suggests that there may be a correlation between vertebrae shape and susceptibility to spinal disease – if so, it could explain the discrepancy between occurrence in non-human primates and humans.
Yet another factor to blame beyond just our means of walking and the shape of our vertebrae is our modern lifestyle. In the industrialized societies where lower back pain is so prominent, we have access to amenities and resources our hunter-gatherer ancestors could never have imagined. We sit in chairs or on couches, often for hours at a time. We have comfortable beds to lay on when we sleep. When it comes time to acquire food, we rarely have to travel far and almost never have to hunt down prey to fill our stomachs. All of these factors encourage a more sedentary lifestyle, which lead to weaker bodies overall but especially weaker backs. This, combined with the increased stress that sitting places on our spines, could explain our increased susceptibility to lower back pain. Hunter-gatherers, on the other hand, were frequently engaging in moderate exercise and rarely sat for extended periods of time. That behavioral sweet spot was very healthy for the human spine, and it was in that environment that our bodies evolved for thousands of years.
But that environment, of course, is not the environment in which we live today. Even current-day subsistence farmers living outside of industrialized regions engage in more repetitive, heavy-load-bearing activities that are more harmful than helpful to the lower back. This situation facing the modern human back has been described as a “mismatch disease,” where our evolutionary adaptations fail to match the needs of our modern society.
When considering all of this, it may seem that we have been dealt a bad hand by evolution. However, it is important to note that our evolutionary history merely puts us at risk for developing lower back pain – it does not definitively cause it or even guarantee it. Indeed, by getting adequate exercise, one can improve flexibility, mobility, and overall strength for a healthier, less painful back.
References:
https://bmcevolbiol.biomedcentral.com/articles/10.1186/s12862-015-0336-y
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4315061/
http://www.who.int/medicines/areas/priority_medicines/Ch6_24LBP.pdf
