Review of Rob Dunn's new book The Wild Life of Our Bodies: Predators, Parasites, and Partners That Shape Who We Are Today:
For most of human history, we lived in proximity to countless other species. We evolved in concert with these life forms; everything from the tiniest microbes to the most fearsome predators shaped the bodies and brains we’re walking around with today. “What happens,” Dunn asks, “when humans leave behind the species their bodies evolved to interact with, whether they be cheetahs, diseases, honeybees, or giant sucking worms?”
The answers Dunn provides aren’t pretty. Without these other life forms, he argues, many features of our own bodies have “become anachronistic or worse.” The unlikely Exhibit A: Crohn’s disease, a chronic inflammation of the bowel that is on the rise in developed nations. Crohn’s and other autoimmune disorders are most common in exactly those places where public health seems to be most advanced—where, for instance, the intestinal parasites that plagued humans for much of history, such as hookworms and tapeworms, have become staggeringly rare. What if, scientists wondered, the absence of these parasites was somehow leaving us more vulnerable to various maladies of the immune system?
Soon, other researchers were linking most or all autoimmune diseases to our missing parasites—as well as many allergy and asthma cases. Reintroducing intestinal worms has been shown to alleviate the symptoms of inflammatory bowel syndrome, diabetes, heart disease, and multiple sclerosis. Whatever the exact mechanism—scientists are still working it out—intestinal parasites appear to help train the immune system to work properly. (Perhaps, without parasites, the immune system looks for something else to attack—such as the body itself.) But prescribing parasites is still a counterintuitive and controversial idea that doctors and patients find hard to swallow.
The disappearance of our intestinal parasites is but one stop on Dunn’s breathtakingly broad look at the other species that have shaped human evolution. He moves seamlessly from the physiology of the digestive system to the circuitry of the brain. He explains, for instance, how the disappearance of most of the animals that preyed on humans has left us with outdated fear circuitry.
For most of human history, we lived in proximity to countless other species. We evolved in concert with these life forms; everything from the tiniest microbes to the most fearsome predators shaped the bodies and brains we’re walking around with today. “What happens,” Dunn asks, “when humans leave behind the species their bodies evolved to interact with, whether they be cheetahs, diseases, honeybees, or giant sucking worms?”
The answers Dunn provides aren’t pretty. Without these other life forms, he argues, many features of our own bodies have “become anachronistic or worse.” The unlikely Exhibit A: Crohn’s disease, a chronic inflammation of the bowel that is on the rise in developed nations. Crohn’s and other autoimmune disorders are most common in exactly those places where public health seems to be most advanced—where, for instance, the intestinal parasites that plagued humans for much of history, such as hookworms and tapeworms, have become staggeringly rare. What if, scientists wondered, the absence of these parasites was somehow leaving us more vulnerable to various maladies of the immune system?
Soon, other researchers were linking most or all autoimmune diseases to our missing parasites—as well as many allergy and asthma cases. Reintroducing intestinal worms has been shown to alleviate the symptoms of inflammatory bowel syndrome, diabetes, heart disease, and multiple sclerosis. Whatever the exact mechanism—scientists are still working it out—intestinal parasites appear to help train the immune system to work properly. (Perhaps, without parasites, the immune system looks for something else to attack—such as the body itself.) But prescribing parasites is still a counterintuitive and controversial idea that doctors and patients find hard to swallow.
The disappearance of our intestinal parasites is but one stop on Dunn’s breathtakingly broad look at the other species that have shaped human evolution. He moves seamlessly from the physiology of the digestive system to the circuitry of the brain. He explains, for instance, how the disappearance of most of the animals that preyed on humans has left us with outdated fear circuitry.
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