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 email@example.com.
Why is it so bloody important that non-scientists understand the basic facts of evolution—or at least of natural selection? It isn’t just a matter of enforcing pre-historical accuracy, of course. And contrary to what many of our secularist colleagues apparently believe, the point is not merely to relegate literalist religion to its dark and dismal place.
Evolutionary science is critical here and now—in rural America, for example, where more than a third of us have grown morbidly obese and can’t seem to figure out why, much less how to solve the problem. It matters in big cities too, where trusted health care professionals—also non-scientists, by the way—mistakenly assume that cleaner is always better. Indeed, evolution is important worldwide, as previously insulated human populations expand and instinctively xenophobic cultures clash.
In The Wild Life of Our Bodies, biologist Rob Dunn, describes a fascinating yet genuinely alarming suite of evolutionary mismatches between our primeval biology on the one hand, and our swiftly advancing culture on the other. To what effect? “The more we distance ourselves from our evolutionary history,” he contends, “the more we seem to feel the pull of uncut strings.”
But the ensuing tangle is more complicated than the brand of vague despondency that typically inspires middle-aged tax attorneys to fire up the RV for a quick “back-to-nature” campaign through the Black Hills of South Dakota. Far more seriously, Dunn says, extrication from our proper ecological context has triggered a novel barrage of truly challenging maladies—everything from allergies, diabetes, and heart disease to autism and a host of social disorders.
As health-conscious circles expand in the developed world, many now recognize the basic relationship between evolution and weight control (or, more accurately, body composition). Familiarity with the diets and habits of our Pleistocene ancestors notifies us that two features of our current lifestyle—a surplus of rich, easily digestible food and absurdly relaxed exercise habits—have left us so overstuffed (yet undernourished) that we’ve had to redesign our doorways, office chairs, elevators, airplane seats, and, unsurprisingly, our hospital beds.
But few of us appreciate the immense nutritional impact of our microbiomes. For instance, Bacteroides thetaiotaomicron—one of many species of microbe native to our guts—churns out at least 400 vegetable-processing enzymes that humans would otherwise lack. These creatures allow us to extract thirty percent more calories from our food, for better or worse, and absent their beneficent presence, we couldn’t possibly produce sufficient quantities of vitamins B or K, the latter of which permits blood coagulation.
Yet we persist in attempting to create “germ-free” environments. According to Dunn, however, recent studies show that the antibiotics contained in hand sanitizers and soaps, for example, provide no benefit in terms of disease prevention. But, unfortunately, they do initiate the evolution of antibiotic resistance, and they do furnish a warm, open house for bad bacteria when they kill the good ones. “Our frequent use of antibiotics,” the author warns, “will progressively make each bit of food less nutritious and give each pathogen to which we are exposed a better chance of taking over our body.”
Life expectancies in developed countries have increased for decades. But in some ways we have also grown sicklier. Exceedingly rare prior to 1950, Crohn’s disease, for example, now afflicts 600,000 people in the U.S. alone. Marked by obnoxious and persistent symptoms associated with immune system attacks on the gut, Crohn’s has also lately emerged in rapidly modernizing regions of India and China.
Scientists have proposed various causes for these disturbing trends. Pollution, toothpaste, refrigerator bacteria, and hypochondria have all been blamed for Crohn’s insurgence. But in 1995, University of Iowa medical researcher Joel Weinstock began to reflect upon the tendency of contemporary, affluent societies to disfavor certain species, including those helpful to humans.
While nearly half of all U.S. children had gut worms into the 1940s, almost none possess them now. Weinstock wondered whether humans had begun to “miss” the so-called parasites with which we evolved—so much in fact that our guts never learned to properly function without them. And just maybe, he thought, the antihelminthics we take to kill the worms—like antibiotics and antiseptics, aren’t all they are commonly cracked up to be.
In 1999, Weinstock received permission to perform an experiment on twenty-nine Crohn’s patients. Each was given a glass of Gatorade spiked with nematodes—pig whipworm eggs specifically. In less than six months, all but one patient was feeling better, and twenty-one of the remaining twenty-five were in remission (four had dropped out along the way). Re-wilding their guts, according to Dunn, had “cured sick patients who had previously little hope of getting better.”
How so? At this point no one knows for sure. Weinstock thinks that gut worms, which in many cases are both tolerable and insurmountable, induce our immune systems to partially acquiesce in order to save precious energy. As such, they also prevent various immune responses from launching heightened and prolonged attacks that can easily result in serious damage. Our worms, in other words, initiate a valuable intestinal peace.
By contrast, Dunn emphasizes certain compounds produced by many species of gut worm that mimic those created by our own cells. In so doing, they might signal and to some degree suppress the immune system. Perhaps our immune system evolved, the author infers, to deliver a stronger response than otherwise appropriate because our bodies “assumed”—and continue to assume—the presence of parasite-generated suppressive influences. In short, modern immune systems run amok by overcompensating for these teensy-weensy wriggling ghosts of the past.
Either way, the “hygiene hypothesis” generally predicts that countless people could benefit—in some cases enormously—from the corporeal reintroduction of mutualist species that most practitioners of modern medicine still consider “dirty.” But the “old medical model,” Dunn argues, “in which we just scrub the rest of life off our bodies, is wrong.” A deeper, more respectful grasp of evolutionary science, it seems, could go a long way toward that model’s long-belated renovation.
In recent years, researchers have begun to inquire whether humans possess a behavioral immune system as well—one that in the past may have helped us to avoid disease, but now leads to inapposite feelings of disgust, and perhaps ultimately to collectivism, xenophobia, and even war. Emotional disgust evolved, Dunn vies, as an effective means of isolating ourselves from disease-related stimuli.
But the instinct was imperfectly honed. Clearly, subconscious disgust can cause us to shun the aged, the disabled, and carriers of non-infectious diseases, like obesity. But some scientists now speculate that, especially in less educated and connected societies, it can steer us toward tribalism, the rejection of liberal democracy and free enterprise, and violent clashes between seemingly incompatible cultures.
Many, including myself, were drawn to evolutionary science because of its explanatory power—it’s intensely satisfying “a-ha!” moments. But as Dunn’s new book makes very plain, the discipline’s practical applications are far more valuable. Yes, certain ideological factions continue to resent speakers, writers, and educators who assertively “push” evolution on society. The truth may not be enough for them, but the health and survival of the species should be.