In his book The Wild Life of Our Bodies: Predators, Parasites, and Partners That Shape Who We Are Today, biologist Rob Dunn presents a compelling perspective about how, in spite of the tremendous progress in human civilization, our lifestyle, in particular our interaction with other species, continues to be guided (and occasionally misguided) by primitive cues from our ancient brains.
Evolution has played a big role in shaping the flora and fauna of today. Many phenotypes that offered survival strategies in the past and were responsible for nature selecting us no longer offer an evolutionary advantage and yet influence our natural instinct. Our preference for sugary, salty, or fatty foods, for example, may have been an evolutionary trait that allowed our ancestor, the hunter-gatherer, to be physically prepared for dark times involving acute food shortage. Agriculture (the reinvention of which seems to be a recurring event in space and time) and animal domestication may have been survival routes that prevented a population from being completely wiped out during the dark times. Unlike most adult mammals, a majority of humans today exhibit the ability to digest lactose. Unlike its wild, colossal predecessor the Aurochsen, modern cows are smaller and docile. The selection of these traits may be explained by a kind of mutualism that offered a survival strategy to both species. Aurochsen provided milk—a reliable food source. Humans cleared grasslands for the Aurochsen to graze and warded away their competitors.
We are primitive creatures. Our adrenal glands and amygdalae alert us against predators evoking a flight or fight response. We obsessively disinfect our bodies and our living spaces and shirk away from germs and parasites. A household disinfectant wipes out a spectrum of germs that extends much beyond the handful of harmful ones. An antibiotic not only kills the pathogenic bacterium targeted but also decimates populations of friendly bacteria which we otherwise depend on. A propensity toward xenophobia seems to be more predominant in regions stricken with infectious diseases. It is possible that it may be been a behavioral adaptation that helped guard one's tribe against deadly pathogens carried by other tribes. The primary idea this book is trying to convey is that (largely due to our ancient instincts) we shun other species much more than needed in our modern lives.
Evidence in support of the idea that our tendency to isolate ourselves from other species, even potential mutualists, may offer serious disadvantage can be found in the recent emergence of a variety of autoimmune disorders such as Asthma or Crohn's disease. In Crohn's disease, for example, the immune system attacks the gut, "an internal turf war in which the immune system always wins." The occurrence of this disease is highly correlated with urban living. Amongst city-dwellers, a sedentary worker leading a protected, indoor work life is more likely to suffer from Crohn's than a construction worker who spends his time outdoors. One compelling theory that fit these observations was that our immune systems are prepared in anticipation for microbes and, in their absence, attack our own cells. It has been demonstrated that microbes within us release toxins that mitigate our immune responses. In a move to outwit the microbe, our immune system may secrete a higher dose of antitoxins than necessary. Now, it is possible that, in the complete absence of the anticipated foreign species, the immune system overreacts assailing our own bodies in the process. As a spectacular example in support of this idea, Joel Weinstock fed a concoction containing a suspension of whipworm eggs and charcoal (to mask the eggs) in Gatorade to a group of critically ill Crohn's patients. By the 24th week of the study 24 out of 25 patients were doing better! Thus "Weinstock rewilded human guts and cured sick patients who had previously had little hope of getting better."
Dunn makes an important point in this book. The discovery of antibiotics and our improved grasp on infectious diseases has ushered in a movement against all germs. More often than not, to our biased minds, "a green pesticide-treated lawn is more healthy than one abounding in biodiversity." Just as rewilding our gut offers benefits that we only recently realized, rewilding our cities by introducing diverse flora and fauna may offer unique advantages – not only evolutionary but also economic. Dunn envisions cities cleansed of pollutants where skyscrapers are sites of large-scale indoor hydroponics yielding fruits and vegetables that feed the population. Dunn imagines “green walls of wild species in each and every city, even rare species, among which flit hummingbirds, butterflies, and bees.” He says “whether we notice or not, (we) are still and always will be where the wild things are.”