Most of my medical career was devoted to assisting patients in pain. The overwhelming majority suffered intractable low back pain, a common yet debilitating malady. There are numerous potential sources for back pain, including bones, intervertebral discs, facet joints, sacroiliac joints, nerves, muscles, tendons, and ligaments. Most physicians, however, have little to no training in distinguishing among these sources and are limited to treating the symptoms rather than the cause. A typical new patient to my practice would have seen several other physicians, often would have already undergone an operation, such as a laminectomy or a spinal fusion, and would have been prescribed a multitude of different drugs, in the most severe cases opioids. While at least 80% of us will experience acute low back pain in our lifetimes, around 8% of all adults will experience persistent or chronic pain. Low back pain is a significant cause of disability in the US, estimated to result in the loss of 149 million days of work annually. The health care costs associated with this problem are enormous – in 2016, low back and neck pain were the most expensive conditions in the US, at a national cost of approximately $134.5 billion. 

This wasn’t always the case. In fact, back pain only became a major health problem nationally during the latter half of the 20th century. A study from the University of North Carolina reported that the prevalence of chronic low back pain impacting function has increased in that state from 3.9% in 1992 to a whopping 10.2% by 2006. Increases are affecting adults across the spectrum regardless of age or other demographic factors. Nationwide, the escalating number of patients seeking care for back pain in recent decades has been likened to an epidemic. The causes are complex, as there are associations with low educational status, obesity, and psychosocial factors such as depression or workplace dissatisfaction. Despite the complexity, it is noteworthy that the possibility of increased genetic susceptibility for this condition has not been considered a contributing factor. Concern that it might play a role led me to research what is known about the influence of genetics on the increasing incidence of complex diseases in general, and to share my findings with others in health care and public policy.

I tend to view human health issues such as this from an evolutionary perspective. After college, I studied ecology and evolutionary biology, eventually receiving a doctoral degree. My training prepared me primarily for academic work, but the university job market was quite limited. Five years after completing my doctorate, I decided that a career change was in order, and I was very fortunate to be accepted as a medical student at the University of North Carolina in Chapel Hill. After medical school, I remained at UNC while I completed a residency in Anesthesiology and Pain Medicine and subsequently joined the medical faculty until my retirement 25 years later. Although my primary occupation was providing care for each of my patients suffering from chronic pain, I was struck by the increasing number of such patients. I began to question if there was an evolutionary explanation.

With my combined expertise as an evolutionary biologist and physician, I made it my mission to discover if genetic changes might contribute to the increase in lower back pain and other chronic ailments. From an evolutionary perspective, we know that the vertebrate spine did not initially evolve to support the upright stance of a species walking on only two legs. Evolutionary alterations in the curvature of the spine have allowed for us to walk on two legs, but not without the risk of excessive forces acting upon the lumbar area (low back), leading to spinal degeneration, nerve symptoms such as sciatica, and chronic pain. Imagine the impact that pain originating from the lumbar spine would have had on our day-to-day lives in the centuries before modern healthcare, analgesic drugs, spinal injections, surgical interventions, physical therapy, and psychological support. For humans in pre-historic times, strength, sturdiness, and mobility were essential attributes for survival, securing a mate, reproducing, and providing for a family. Natural selection would have acted to minimize the inheritance of any susceptibility to low back problems, especially in younger patients. So why are we seeing a nationwide epidemic of low back pain now?

Even 500 years ago, many of us would not have survived to our current age or even come close to growing old. Now, we expect to live a long and healthy life well into our 70’s, 80’s, and even 90’s. In developed countries, medical and public health interventions are so effective at combating threats to survival that many of us live our entire lives rarely having to confront death or face even a single near-death experience. Even when our loved ones pass away, it often takes place within advanced medical facilities or hospice centers that serve as a buffer against the pain and trauma of dealing with it firsthand. But this was not the case throughout nearly all of the hundreds of thousands of years of human existence. Whether from trauma related to human conflict or simply the physical risks of a vulnerable life with numerous environmental hazards and extremes, death was a constant threat and a regular part of life as a human. Until recently, the availability of an adequate food supply or safe water was by no means guaranteed. There was also always a risk of infection that could overwhelm the immune system. Intrinsic disorders, such as diabetes - without diagnosis or medication - caused pain, suffering, disability, and death. The history of high mortality, particularly during childhood, is one of the reasons that humans had characteristically large numbers of children: to compensate for those that would likely be lost. These various threats to our lives reflected the mechanisms of natural selection favoring those best able to survive, with adaptation as a result.

Among other things, human adaptation over the millennia has led to an advanced intellect and physical dexterity that far surpasses any other species. Moreover, we have used these abilities to improve our lives in ways that circumvent the mechanisms of natural selection. The process began over 10,000 years ago but has escalated exponentially over the past 200 to 300 years. We now cultivate the food we need, construct dwellings and workplaces with tightly controlled environments, and create social structures and networks that help support the less fortunate among us. We have increased our understanding of human biology and pathology, so much so that public health measures and advanced medical care allow us to avoid or treat many of the maladies that affected us historically. Modern health care is truly a marvel of human accomplishment! We have not yet conquered every disease, but most humans today can be assured a profoundly better quality and duration of life than our progenitors. However, as this revolution in human mastery over our environment progressed, little thought was given to the fact that the world we crafted for ourselves dramatically changed the parameters of natural selection on our species. But then, what does it matter?

In this book, I will make the case that it does matter, with significant implications for the future of our genetic well-being. The proposition that the human genome (our entire collection of DNA) could deteriorate without historical natural selection is not new. This fear contributed in part to the advancement of eugenics during the early 20th century. Thankfully, many eugenic practices, ranging from forced sterilization to genocide, were ultimately recognized as ethically reprehensible. They exploited the desire to optimize our genes as an excuse for racially biased and morally repugnant interventions. Although these practices are rightfully rejected, that does not mean the genetic concerns were unfounded. Our distaste for past eugenic practices should not blind us to the potential for genetic decline, regardless of how uncomfortable it may be to acknowledge. Some of our most revered evolutionary authorities, such as Hermann Joseph Muller and Theodosius Grigorovich Dobzhansky, expressed concerns about our genetic health decades ago. Since then, profound advances in genetics shed further light on those concerns. In view of this progress, it is appropriate to reexamine whether changes in our genetic makeup in the absence of historical natural selection may be affecting our viability and susceptibility to disorders such as chronic low back pain[1].

In the following chapters, we will take a closer look at natural selection as it was throughout most of our history and how it has changed in recent evolutionary times. We will review some basic concepts of human genetics and explore how our DNA has been molded by natural selection as well as other processes. These considerations will lead us to some difficult questions: What are the possible long-term implications of recent changes in natural selection? Can these changes provide a partial explanation for increases in maladies such as chronic low back pain?  Is the “quality” of our genetic blueprint at risk? What can/should we do to minimize the potential impact on human well-being?

Sources:

Dieleman, Joseph L. et al. 2020. US health care spending by payer and health condition, 1996-2016. Journal of the American Medical Association 23(9): 863-884.

Dobzhansky, Theodosius and Gordon Allen 1956. Does natural selection continue to operate in modern mankind? American Anthropologist 58: 591-604.

Freburger, Janet K. 2009. The rising prevalence of chronic low back pain. Archives of Internal Medicine 169(3): 251-258.

Muller, H. J. 1950. Our load of mutations. The American Journal of Human Genetics 2(2): 111-176.

Patrick, Nathan et al. 2014. Acute and chronic low back pain. Medical Clinics of North America 98: 777-789.

[1] Despite discussion of these issues in the academic literature, I believe that the general public is largely unaware of the possibility that genetic vulnerability may account for an increased incidence of human disease, and I have found that none of the physicians with whom I have discussed this issue were aware of the literature supporting such concerns. The desire to raise awareness of this issue has been my primary motivation for writing this book.