An Evolutionary and Functional Perspective on Chronic Disease.

by Kenneth W. Krause.

Kenneth W. Krause is a contributing editor and “Science Watch” columnist for the Skeptical Inquirer.  Formerly a contributing editor and books columnist for the Humanist, Kenneth contributes regularly to Skeptic as well.  He may be contacted at

By any historically informed appraisal, twenty-first century life is pretty darn pleasant for most of us.  We live longer and grow larger than our recent ancestors.  Our offspring survive childhood and adolescence at an unprecedented rate.  We are also cleaner and more comfortable than the richest kings or queens of old.

But are we healthier?  As you read this column, you are likely seated in a position your body never evolved to assume.  You might be nibbling a muffin or donut with your morning coffee, or perhaps sipping a sugary soda with lunch.  When you lower the magazine, how long will it take for your eyes to adjust?  Do you wear thick-soled shoes—perhaps with arch supports—to protect your sensitive feet?

Statistically speaking, most of us suffer from at least one malady our hunter-gatherer forebears rarely experienced.  Are you significantly overweight, for example?  What about your children?  How many of your neighbors, friends, relatives, and co-workers don’t have a problem with allergies, asthma, cavities, flat feet, low back pain, myopia, or insomnia?  Few if any, I’ll wager.

On average, each American spends about eight thousand dollars per year on healthcare—in total, nearly eighteen percent of the nation’s gross domestic product.  And most of that hard-earned money is frittered away on the treatment of completely preventable illnesses, including type II diabetes, some cancers, and heart disease.

Modern medicine has succeeded brilliantly in eradicating most of the infectious diseases that began plaguing our species in the wake of the agricultural revolution.  Today, however, we suffer and die from an entirely different spate of post-agricultural and post-industrial ailments.  These are the infamous “diseases of civilization” that now account for eighty percent of American healthcare spending.  They are projected to cost the global economy $47 trillion over the next twenty years, and to kill twice as many people as all infectious diseases combined.

But both intuition and conventional wisdom invite us to expect as much.  We now live exceptionally long lives, as noted.  And immortality was never an evolutionary option—we have to die of something, if not contagion or malnutrition.  So, perhaps chronic diseases are better characterized as the inevitable illnesses of extended old age, in some cases genetically programmed to wash us away in the wake of our reproductive prime.

Not according to John Ratey, associate professor of psychiatry at Harvard Medical School. He describes type II diabetes, for example, as a “screaming, wailing siren of a warning to our society that something is changing fast, and that we ought to do something about it.”

Indeed, diabetes is a now-common metabolic disorder that used to be quite rare.  While it’s true that genetics play a role in terms of susceptibility, biological inheritance alone seldom explains the disease.  Why is the incidence rate of diabetes now higher in Asia than in America, for instance?  The answer is not that Easterners are getting older.  In fact, what was once referred to as “adult-onset” diabetes is now quickly spreading to younger adults and children.  Nor is it true that Asians have evolved some new diabetes gene or genes.  Rather, Easterners are suffering because they have lately adopted with great and regrettable enthusiasm the typical Western diabetogenic lifestyle marked by poor dietary habits and physical inactivity.

Harvard evolutionary biologist Daniel Lieberman recognizes the self-inflicted, environmentally-based origins of diabetes.  But he also sees the problem of rising incidence rates as one of many unfortunate examples of chronic disease “dysevolution” (harmful change over time).  Modern medicine is not only ineffective at addressing chronic diseases, he insists, but, in combination with cultural apathy, it actually makes them worse in terms of prevalence from one generation to the next by failing to focus on prevention over the mere treatment of symptoms.

First, doctors and patients seldom even try to address such problems until the latter get sick.  Second, doctors usually prescribe only modest weight loss and exercise regimens because they believe their patients will either ignore more challenging and effective advice, or simply fail in its attempted execution.  Finally, physicians tend to prescribe anti-diabetes drugs, like metformin, that are far less effective than intelligent lifestyle changes (and often involve unpleasant side effects).  Thus, we unwittingly perpetuate and even accelerate the cycle of chronic disease by resigning ourselves to the clumsy management of symptoms and, in the end, to failure.

Consider as well dental caries, a causally related but very different and far simpler “mismatch” disease.  Cavities were rare among hunter-gatherers and occur relatively infrequently among non-human apes.  But they spread through the post-agricultural human population like wildfire and, today, afflict nearly 2.5 billion people.  Why?  Again, the excessively sugar-laden and starchy diets now pervading Western culture are inimical to our evolved biology.

And our medical response?  A strategy informed by both genomics and natural history would dictate serious revisions to dietary habit.  Nevertheless, we still consume cereals and processed grains—i.e., cheap calories—by the bucket-load.  So, instead, we’ve decided to brush and floss day after day, and to hire hygienists and dentists to scrape, drill, fill, and replace our teeth as they are slowly eaten away by bacteria that ironically did evolve to dine on refined sugars.

So, as we emphasize technical innovation and symptom treatment—i.e., palliative dental care—over a preventive approach based on evolutionary science, we trigger Lieberman’s dysevolutionary feedback loop.  To our children, we relay a predominantly cultural strategy, allowing the disease to not only persist, but perhaps also increase in both prevalence and intensity as the generations pass.

Along with obesity and heart disease, diabetes and dental caries perhaps epitomize chronic diseases resulting from environmental excess—that is, overuse.  Others, however, stem from individual disuse.  For example, asthma and other immune-related disorders—the incidences of which have tripled since the 1960s in wealthy nations—may result from our recent obsession with cleanliness and, thus, underexposure to certain germs and worms.  Flat feet and plantar fasciitis can afflict people whose foot muscles have weakened due to over-reliance on shoes with stiff soles, heavy cushioning, or arch supports.  Focusing our eyes too long on close objects can elongate our eyeballs and cause myopia, or nearsightedness.  Sitting in comfortable chairs and hunching over desks can cause hip and leg muscle imbalances producing lower back pain.  And how do we typically confront these afflictions?  We treat the symptoms only, with drugs, orthotics, eyeglasses, and, perhaps worst of all, bed rest.

A debilitating bone disease, Osteoporosis demonstrates how age, sex, hormones, exercise, and diet interact to define the later stages of life.  This mismatch disease of disuse was exceedingly rare among seniors until very recently.  Today, however, it causes more than one-third of elderly women in America to fracture their bones.

Skeleton growth is maximized by age twenty in women and twenty-five in men.  Thereafter, bone mass declines as osteoclast activity begins to outpace that of osteoblasts.  Throughout most of life, estrogen serves to minimize damage to women.  Following menopause, however, degeneration accelerates as hormone levels plunge.  Low blood calcium levels also allow osteoclasts to resorb bone tissue.

But just as children can build larger, stronger bones with increased activity, older adults can slow, perhaps even halt or reverse, the degenerative process with vigorous and consistent weight-bearing exercise.  We can also replace calcium-deficient, grain-based diets with more appropriate foods packed with calcium, vitamin D, and protein.  Instead, we are often prescribed estrogen supplements or drugs to slow osteoclast activity.  Once again, however, the side effects of such treatment can prove unpleasant, even to include increased risks of heart disease and cancer.

It is absolutely true that certain forms of early-onset Alzheimer’s disease are strongly associated with genetic inheritance.  Contrary to popular opinion, however, ninety-five percent of all documented Alzheimer’s cases—i.e., those afflicting people over the age of sixty—are not primarily genetic in origin.

According to Jeffrey Bland, biochemist and co-founder of the Institute for Functional Medicine, the infamous ApoE4 gene does not by itself cause Alzheimer’s.  Rather, it merely “describes a susceptibility to the disease that the individual’s choices of lifestyle and diet can affect.”  In other words, inheritance of ApoE4 simply increases susceptibility “to the dangerous effects of diets high in saturated fat and sugar and of a sedentary lifestyle.”

Bland insists that “new paths of inquiry and research” into Alzheimer’s reveal an extended list of major environmental risk factors entirely within our preventive control—diet, chronic inflammation, insulin resistance, elevated blood levels of homocysteine, poor exercise tolerance, lack of brain stimulation, and exposure to toxic substances.  Moreover, he suggests, medical interventions addressing these factors, especially diet, can improve brain function in patients already suffering from the illness.

The landscape of disease has changed dramatically in recent years.  A recent worldwide study measured years lost to both premature mortality and diminished health (Murray 2012).  Between 1990 and 2010, the greatest bump in disability resulted from heart disease, stroke, depression, and metabolic diseases like diabetes—all of which are avoidable through serious environmental and lifestyle changes.  Indeed, incidences of ischemic heart disease rose twenty-nine percent (to jump from the number four to the number one ranking), while rates of stroke and depression increased nineteen and thirty-seven percent, respectively.

As a society and as individuals, we clearly pay woefully inadequate attention to disease prevention.  One large-scale, long-term, and well-controlled study found that sedentary American men who subsequently improved their fitness levels halved their rates of cardiovascular disease (Blair 1995).  According to Lieberman, it costs $18,000 per year to treat one case of heart disease.  Thus, persuading just twenty-five percent more Americans to meet national fitness guidelines could save more than $58 billion per year for care related to heart disease alone.  This equals roughly twice the annual research budget of the National Institutes of Health (of which only five percent is allocated to disease prevention).

In any case, as Bland warns, our current yet outdated medical infrastructure and education system remain geared toward the “pill-for-an-ill” treatment of contagious diseases and acute events.  As such, they are ill-suited to addressing the complexities of those chronic illnesses that are, in fact, today’s predominant health reality.


Blair, S.N., H.W. Kohl, C.E. Barlow, et. al. 1995. Changes in physical fitness and all-cause mortality: a prospective of healthy and unhealthy men. Journal of the American Medical Association. 273(14): 1093-98.

Bland, J.S. 2014. The Disease Delusion: Conquering the Causes of Chronic Illness for a Healthier, Longer, and Happier Life. NY: HarperCollins.

Lieberman, D. 2013. The Story of the Human Body: Evolution, Health, and Disease. NY: Pantheon Books.

Murray, C.J., T. Voss, R. Lozano, et. al. 2012. Disability-adjusted life years (DALYs) for 291 diseases and injuries in 21 regions, 1990-2010; a systematic analysis for the Global Burden Disease Study 2010. Lancet 380(9859): 2179-223.

Ratey, J. and R. Manning. 2014. Go Wild: Free Your Body and Mind from the Afflictions of Civilization. NY: Little, Brown and Company.


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