Scientists: High Time for Medicine to Adapt to Evolution.

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 krausekc@msn.com.

Insanity, a great innovator once observed, is doing the same thing over and over again while expecting different results.  In the March 22, 2010 Newsweek, pediatrician Claire McCarthy bemoaned the medical profession’s failure to contain the epidemic of childhood obesity.  After acknowledging Einstein’s maxim, McCarthy offered what she deemed a practical new solution.  Rather than simply discussing the benefits of exercise and healthy eating with children and their parents, she advised, physicians should scare them with the facts, encourage immediate action, and celebrate their incremental victories.  All well and good, perhaps—but does that really sound like the caliber of change we can expect to produce novel results?

In The Evolution of Obesity (Johns Hopkins, 2009), medical researchers Michael Power and Jay Schulkin suggest a fundamentally different approach.  Absent an understanding of the epidemic’s “how and why,” they reason, all “attempts to modify obesity within individuals will be problematic, if not doomed to failure.”  We should view obesity, they say, less as a pathology and more as an incongruous adaptation.  To confront the predicament—even at the clinical level—physicians must comprehend its underlying biology and, thus, “the evolutionary events and pressures that have shaped our adaptive responses to hunger, food, exertion, and energy stores that, in today’s world, may not be as appropriate as in the past.”

As advances in genetics, genomics, neuroscience, and microbiology mount at a truly awe-inspiring pace, many biologists and some medical experts are stepping forward to insist that the moment has finally arrived for medicine to fully acknowledge its scientific bedrock.  For the benefit of their patients and of the global societies in which they now live, physicians too must appreciate evolution as the organizing principle of all biology.

Peter Gluckman, Alan Beedle, and Mark Hanson, biomedical experts and authors of a new textbook titled Principles of Evolutionary Medicine (Oxford, 2009), appear to agree.  Contrary to their patients’ best interests, they say, physicians generally have settled into “reductionist approaches” to medicine, focusing narrowly on body parts and systems and the immediate or “proximate” causes of disease.  “Ultimate” or evolutionary causes are largely ignored.  But the latter perspective, the authors propose, “not only helps to identify research questions, but also allows engagement with individual patients in ways which promote understanding of their current health status and which also contribute to the design of appropriate interventions in public health.”

Similarly, in the recently published Textbook of Evolutionary Psychiatry: The Origins of Psychopathology (Oxford, 2008), professor of psychiatry Martin Brüne demands “radical revision” of his profession’s current paradigm characterizing knowledge of evolutionary principles as interesting but superfluous.  “If psychiatry wants to survive,” he counsels, “it can no longer be satisfied with a knowledge base that covers just 50 per cent of what is needed for a full comprehension of psychopathological conditions.”  Understanding of the ultimate causes of cognition, emotion, and behavior, he believes, is “absolutely essential” to the intelligent diagnosis and effective treatment of mental disorders.

But despite these lively appeals and the dizzying tempo at which new evolutionary applications to various medical problems are being discovered, no medical school in the United States currently offers a course on evolutionary medicine.  Not one maintains a department of evolutionary biology, or even a single faculty member—apart from geneticists, arguably—specializing in evolutionary applications to medicine.

I asked University of Michigan professor of psychiatry Randolph Nesse—who does specialize in such applications—to assess the situation from his standpoint.  The gap in evolutionary education among physicians, he advises, “is wide and serious.”  By the time they enter practice, most physicians have received far more instruction on quantum physics than in evolutionary biology, and because they lack a solid theoretical foundation, many have no idea why people age or even how cancer arises.  It’s akin to “engineers not understanding the first law of thermodynamics,” he chides, “or thinking that heavier objects fall faster.”

When I asked Yale University ecologist and evolutionary biologist, Stephen Stearns, to comment, he confided that “resistance is both practical and political.”  The medical curriculum is already packed with essential or at least contributive classes, of course, and is “thought to be functioning well by those teaching it.”  Yet evidence from the front lines seems to suggest glaring deficiencies.  For example, Stearns adds, “The over-prescription of antibiotics, particularly by pediatricians, often for viral infections that do not respond to antibiotics, continues to be widespread despite the fact that the rapid evolution of antibiotic resistance is the best understood example of evolutionary medicine.” The consequences of such uninformed treatment to the patient, he warns, could prove “difficult, expensive, and perhaps insoluble.”

Nesse and Stearns were among four prominent American scientists who organized “Evolution in Health and Medicine,” the Arthur M. Sackler Colloquium of the National Academy of Sciences held on April 2-3, 2009, in Washington D.C.  Their goal, according to Stearns, was to “raise awareness in the medical community that evolutionary biology had helpful insights into medical problems that were being missed by other perspectives.”  The event was covered by Science magazine and the provocative results were released in a multi-paper supplement to the January 26, 2010 Proceedings of the National Academy of Sciences.

In an summary article, “Making Evolutionary Biology a Basic Science for Medicine,” an international team of 13 medical and biological experts, including Nesse and Stearns, argued for more integrative medical education and outlined their specific suggestions.  A more penetrating comprehension of evolutionary processes, they claim, “helps to correct the prevalent dependency on the metaphor of the body as a designed machine.”  To the contrary, the human form is more accurately characterized as a “jury-rigged system” better understood as a series of compromises shaped by natural selection to maximize reproductive viability rather than health.  Only when students are required to overhaul the former, erroneous mindset, the authors insist, will they gain a “deeper understanding of the body and why it is vulnerable to disease.”

So what should every doctor know?  Eschewing actual course recommendations in favor of competency and learning objectives, the team tackled the premedical curriculum first.  In order to understand evolutionary “tradeoffs,” for instance, undergraduates should know that nature has not selected for a thicker distal head on the human radius bone in order to thwart fractures because such an adaptation would limit wrist flexibility.  They should also know how to use comparative data among primates, the authors contend, to show why humans could not have evolved to eat only vegetables—because our shorter guts and smaller teeth were selected to consume more easily digestible fruits and protein-packed meats.

So too should they comprehend the evolutionary explanation for why young women who regularly and vigorously exercise might experience the cessation of sexual cycling—because intense physical exertion was once indicative of severe environmental stress that endangered fetuses and pregnant women, and how women beyond reproductive age can nevertheless influence their inclusive genetic fitness—by caring for their daughters’ children.  These kinds of learning objectives, the team agrees, are “more directly relevant to medicine” than some others proposed by the American Association of Medical Colleges and the Howard Hughes Medical Institute advocating familiarity, for example, with the fairly abstruse principles of quantum mechanics.

While again conceding that medical school curricula are already bursting at their seams, the authors nonetheless propose a challenging set of objectives for professional students as well.  They should grasp the concept of “facultative adaptation,” and know why calorie deprivation and stress during early life can affect later metabolism.  They ought to understand the evolutionary tradeoffs that likely resulted in the uniquely narrow human birth canal that, although dangerous to both mother and child, is essential for proficient bipedalism.  So too should they know how “path dependence” leaves evolved organisms far short of the machine-like ideal—consider, for instance, the often excruciatingly problematic human spine.

Medical students should also be well versed, the authors say, in the co-evolution of hosts and pathogens, and capable of explaining how “arms races” render us vulnerable to disease.  They ought to be familiar with the potentially negative health consequences of antibiotics and modern hygiene practices—allergies, asthma, and autoimmune diseases, for example—that can disrupt important signals our bodies would otherwise receive from the pathogens with which we evolved.  And certainly soon-to-be doctors should appreciate how antibiotic resistance can emerge and spread in dreadfully short periods of time, and when their future patients can safely use drugs that block critical evolutionary defenses like pain sensitivity, fever, anxiety, and depression.

In “The Great Opportunity,” an Evolutionary Applications paper published in 2008, Nesse and Stearns argue that evolutionary biology provides physicians with “an otherwise missing paradigm” that could help them “make sense of why disease exists at all, what environments increase the risk, and how treatments work.”  Although the regrettable medical trend is to “just carry out protocols,” they advise, “[b]etter decisions come from doctors who understand the ecology of immune responses, the evolutionary reasons for polygenic diseases, the phylogeny of cancer cells, and the origins of antibiotics,” among other principles.

Only a few years ago, for example, medical students were erroneously instructed that pathogens tend to coexist with their hosts because killing them would be counterproductive.  But a more nuanced evolutionary view recognizes that virulence is leveled to maximize transmission.  If bedridden hosts will do the trick—think cholera victims who suffered from diarrhea prior to modern sanitation—then virulence levels might be high.  If not, pathogens could indeed benefit from healthier, more ambulatory hosts capable of infecting others more directly.  Then again, the authors reiterate, modern sanitation practices can bear deleterious effects on human health as well.  Many scientists believe that certain autoimmune diseases, including asthma, diabetes, and childhood leukemia, can result from the absence of helminth parasites that until very recently evolved in our guts.

So too might hospital directors who currently choose to rotate antibiotics hoping to prevent resistance by exposing bacteria to changing selective regimes benefit from a more sophisticated knowledge of evolutionary science.  “At least in principle,” Nesse and Stearns propose, “hospitals would do better to use a mix of different drugs on different patients simultaneously, rather than to cycle through [them] over time.”  And perhaps medical staff should pay closer attention to the current evolutionary debate on whether influenza kills directly or through the effects of released inflammatory agents.  “If the former is true,” the authors warn, “anti-inflammatory drugs will increase death rates, if the latter is true it will decrease them.”

And evolutionary insights might one day spur medical researchers to conquer even the most universal and seemingly intractable malady in natural history—aging.  Though currently misunderstood as the inevitable result of wearing body parts, aging is actually an evolutionary tradeoff that almost always favors reproductive success among the young over lifespan.  In the March 25, 2010 issue of Nature, however, biochemist Cynthia Kenyon calculates that, relative to our common ancestor with nematodes, “over evolutionary time mutations have increased [the human] lifespan more than 2,000-fold.”

More specifically, she notes, in very harsh environments or under severe dietary restrictions, certain regulatory genes in many species, including some primates, can actually shift focus to extend lifespan in order to preserve youthful organisms for future reproductive opportunities.  So perhaps animal longevity can be unleashed, and the diseases of aging ameliorated, simply by tweaking a few genes.  Though in nature these shifts represent a rare exception to an otherwise clear evolutionary rule, as Nesse and Stearns cautiously observe, “The ancient dream of extending lifespan no longer seems like just a dream.”

Consistent with recommendations widely agreed upon at the Sackler Colloquium, scientists urge the AAMC, the HHMI, and the Institute of Medicine to convene with evolutionary biologists to address these issues further.  The science is very difficult, they agree.  Every new evolutionary hypothesis must be assessed rigorously and with exacting skepticism, especially those pertaining to cognition and emotion.  In the introductory article to the PNAS supplement, “Evolutionary Perspectives on Health and Medicine,” the Colloquium’s organizers ask whether the increased investment can be justified.  Evolutionary principles, they conclude, “are already saving lives, reducing suffering, and can help us to avoid major unpleasant scientific surprises.”

Indeed, the most profound advantage of evolutionary thinking in medicine might be its distinctively predictive quality.  Perhaps a renovated medical perspective accounting for natural selection and other evolutionary processes could propel medicine in an entirely new direction that, to the unambiguous benefit of patients (though maybe not initially to the healthcare and pharmaceutical industries), emphasizes anticipation and prevention over belated treatment.

To learn more, consult The Evolution and Medicine Review (http://evmedreview.com).

 

 

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