Help! Is there an evolutionary biologist in the house?
Meanwhile, valuable evolutionary applications to medicine are being discovered at a dizzying rate. That many doctors fail to appreciate evolution as the central organizing principle of all biology, some experts contend, is an embarrassment to the profession and a dangerous disservice to the patients who depend on it. So, as awe-inspiring advances in genetics, genomics, biotechnology, and neuroscience mount, biologists around the world are stepping forward to insist that the fateful moment has arrived for medicine to fully embrace its scientific bedrock.
On April 2-3, 2009, the National Academy of Sciences in Washington, DC, held an Arthur M. Sackler Colloquium titled, "Evolution in Health and Medicine." According to organizer Stephen Stearns, Yale University ecologist and evolutionary biologist, the objective 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's provocative results were released in a multi-paper supplement to the January 26, 2010, Proceedings of the National Academy of Sciences.
"Resistance," Stearns confided to me, "is both practical and political." Medical curricula are already packed with essential or at least contributive classes, of course, and are "thought to be functioning well by those teaching it." Yet evidence from the front lines seems to betray some glaring deficiencies. For example, Stearns noted, "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 patients, he warned, could prove "difficult, expensive, and perhaps insoluble."
Co-organizer Randolph Nesse, University of Michigan professor of psychiatry, considers the gap in evolutionary education among physicians "wide and serious." By the time they enter practice, he told me, 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 says, "or thinking that heavier objects fall faster than lighter ones."
In the summary PNAS article, "Making Evolutionary Biology a Basic Science for Medicine," an international team of thirteen medical and biological experts, including Nesse and Stearns, argued for more integrative medical education and offered specific suggestions. A more penetrating comprehension of evolutionary processes, they argued, "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 com promises shaped by natural selection to maximize reproductive viability rather than health. Only when medical students are required to correct the former, erroneous mindset, the authors insist, will they gain a "deeper understanding of the body and why it is vulnerable to disease."
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 settle 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."
Principles offers physicians (and their concerned patients) eight possible pathways by which to conceive of and address a given medical condition from an evolutionary perspective. The most common and perhaps easily understood mechanism results from conspicuous "mismatches" between our slowly evolving genomes and our rapidly shifting cultural circumstances. A wide variety of common but often serious pathologies--everything from lactose intolerance and myopia to obesity and addiction--are thought to arise from these clashes.
Gluckman emphasizes infant formula feeding, a cultural innovation promoted most ardently in the 1970s, as a particularly notorious example. Nutritionally distinct from breast milk, formula is said to have caused obesity, reduced cognitive ability, and even increased infant mortality among children in the developed world. In Israel, the authors note, infants were left brain damaged or brain dead because their formulas lacked the thiamine, or vitamin B1, their mothers might otherwise have provided.
In addition to the patient's course of illness, the authors urge physicians to consider two much deeper historical levels when evaluating a problem. First, developmental history from the point of conception can reveal how plasticity and disruption have influenced the patient's phenotype. Second, evolutionary history--since the inception of hominins, Homo sapiens, agriculture, and perhaps the patient's specific ancestral or cultural lineage--can deliver genetic and other more intuitive clues revealing altered risk levels and potential treatments. A more "holistic approach," they conclude, "will pay enormous dividends for medicine and amply repay the effort needed to adopt it."
Similarly, in the Textbook of Evolutionary Psychiatry: The Origins of Psychopathology (Oxford, 2008), Martin Brune, professor of psychiatry at the University of Bochum, Germany, demands "radical revision" of his professions current paradigm characterizing knowledge of evolutionary principles as interesting but superfluous. "If psychiatry wants to survive as a medical discipline," he counsels, "it can no longer be satisfied with a knowledge base that covers just 50 percent 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 treatment of mental disorders.
According to Brune, psychiatrists frequently presume that proximate factors like early development and neurochemistry can fully explain mental pathology. But a more complete investigation of any given behavior, he urges, will also include an attempt to trace its evolutionary roots and an analysis of its potential adaptive value. Though once selected for some benefit, psychopathological symptoms often reflect "extremes of variation" that have become maladaptive, or "dysfunctional," because of their inappropriate frequency, intensity, or context.
Take fear, for example--clearly an ancient and highly adaptive trait. When expressed under circumstances posing no objective threat, however, fear becomes pathological anxiety. But when we ask the appropriate evolutionary question--here, why it might be "cheaper" for a person in actual danger to be more rather than less frightened than necessary--we can see why it makes good selective sense to lower the threshold of release. This nimble evolutionary induction, Brune proposes, might explain why so many psychopathological conditions involve anxiety.
Though primarily crafted for academic settings, both Gluckman and Brune are accessible to frequent readers of this column. Utterly gorged with cutting-edge medical research and fascinating insight into the broader human condition, these generalized yet meticulous texts will leave readers feeling invested and eager for a great deal more--which is amply provided by either of two brilliant, multi-author, multi-topic anthologies.
In Evolutionary Medicine and Health: New Perspectives (Oxford, 2008), biological anthropologists Wenda Trevathan (New Mexico State), E. O. Smith (Emory), and James McKenna (Notre Dame) have assembled twenty-three original essays contributed by forty-four experts from Australia, France, Norway, Switzerland, the U.K., and the United States "Highlighting diet and nutrition, sex and reproduction, and social disorders and chronic diseases, the editors have judiciously chosen to address specific health concerns of critical interest to the public at large.
Which is not to imply that more complicated medical issues were ignored. For example, in "Genes, Geographic Ancestry, and Disease Susceptibility," Douglas Crews and Linda Gerber, public health experts from The Ohio State and Cornell Universities, respectively, discuss three means of determining disease risk through personalized medicine--self-reported race and ethnicity, geographic ancestry, and individual profiles. They also compare each model's medical utility, and, of course, explain how the relevant debate should be guided by evolutionary principles.
Though commonly exploited by modern clinicians and researchers, "race," the authors confirm, is merely a social construct that "does not reflect any specific biological reality." As such, its therapeutic merit is severely limited. And why would any medical professional armed with even the most basic working knowledge of natural history suppose otherwise? As Crews and Gerber point out, we have no reason to believe that disease-promoting genes have been subjected to the same evolutionary pressures as those for skin color or hair texture, or that such alleles are in any way linked.
Methods drawing upon geographic ancestry are much preferred. Scientists have discovered many genes that predispose specific populations to diabetes, hypertension, and obesity, for example. But while a few such alleles are indeed unique to those groups, the authors caution, "most are shared to some degree across populations." Thus, the most accurate reflectors of natural selection and genetic drift are individual DNA profiles.
"The molecular revolution," Crews and Gerber summarize, "has provided new and powerful tools for profiling one's genetic risks [for chronic degenerative conditions] and for understanding gene-environment and gene-culture interactions predisposing individuals, families, and groups to specific conditions." Unfortunately, the revolution's clinical potential has yet to be seriously developed--perhaps in part because its scientific foundation remains somewhat obscure to so many clinicians and researchers.
An equally diverse suite was collected by Stearns and Jacob Koella, biologist at the Imperial College London, in the second edition of Evolution in Health and Disease (Oxford, 2008). Although evolution can't provide easy answers to every medical dilemma, say Stearns, Nesse, and Harvard biologist David Haig in the text's opening and introductory chapter, evolutionary thinking can provide precious insight and even "save lives" when physicians prescribe antibiotics, administer vaccinations, advise couples having difficulty conceiving, and treat cancer, among many other things.
Patients might want their doctors to know, for example, why Western women experience demonstrably higher rates of cancer than women living without contraception in pre-industrial cultures. More menses, of course, mean more cell divisions and a greater likelihood of dangerous mutations. Physicians and researchers need to recognize, as the authors point out, that "there is nothing biologically normal about the regular monthly period." Developing contraceptives that don't induce periods but do provide the appropriate level of estrogen for maintaining bone strength and avoiding osteoporosis may be the best solution.
And perhaps all pediatricians should recognize the value of worms. Having evolved in human guts to downregulate our immune responses, certain parasites have also reduced child susceptibility to autoimmune diseases by flagging the production of antibodies. But because modern environments have become so antiseptic, autoimmune diseases have made dramatic comebacks as worm infestations have waned. This rather peculiar evolutionary mismatch, Stearns, Nesse, and Haig instruct, "helps to explain the current epidemics of asthma, type I diabetes, and even leukemia." But certain informed doctors, they note, have actually made headway by treating children with parasitic fauna.
Of course scientists have no desire to completely overhaul medical school curricula. Instead they suggest modest yet substantive contributions where evolutionary material would be clearly helpful. A free, intelligent, and continuing dialogue between biology and medicine would no doubt benefit both disciplines. But well-informed patients inclined to take responsibility for their own health and fitness will be the biggest winners. Inherently predictive, evolutionary thinking emphasizes prevention over treatment and, as such, personal empowerment over dependence or helplessness.
You can learn more at the Evolution and Medicine Review (http://evmedreview.com). The next "Good Book" will further explore evolutionary applications to medicine in two critical contexts--women's health and the now global epidemic of obesity.
Kenneth W. Krause is a contributing editor and books editor/columnist for the Humanist, and a contributing editor and science columnist for Skeptical Inquirer. He publishes frequently in Skeptic and Wisconsin Lawyer as well. He may be contacted at email@example.com.
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||THE GOOD BOOK|
|Author:||Krause, Kenneth W.|
|Article Type:||Book review|
|Date:||Jul 1, 2010|
|Previous Article:||Wonders, not miracles.|
|Next Article:||Eyes Wide Open.|