From the treatise on tapeworms by Marcus Bloch, 1782 (Courtesy Wellcome Library)

I first set eyes on the original version of this engraving while seated on a hard wooden chair—was it from the middle ages?—at the Université Montpellier in southern France. “Worm heads so cute,” I wrote in my notes, sure that I would be able to use the information later. At last that time has come. All week I have been working on a chapter for a book about eighteenth-century reproduction. When the editor asked me to write something related to my specialization in the history of childbirth, I refused. “I want to wax poetic about worms and dead body parts instead. Take it or leave it.” Luckily, he took it, for my research on tapeworms ultimately led me to the topic of this post: the idea that the human body is an ecosystem.

An ecosystem is a complex set of relationships among living resources. We typically think of human beings benefitting from, destroying, or being harmed by various ecosystems. But I am not referring to the rather commonplace notion that people participate in and impact a larger world that includes plants, animals, water, soil, pollutants, and so on. I am pointing to the human body as itself an ecosystem, consisting of micro-organisms, protozoa and god knows what else living in and around flesh. Thinking along these lines is more challenging, able to undermine the assumption that something distinctive can be isolated and identified as a human body.

A research project launched in 2008 is helping to create this radically new body or lack thereof. The International Human Microbiome Consortium combines the efforts of scientists in, among other places, Australia, Canada, Europe, and the United States, to characterize the microbial communities—billions of bacteria, fungi, protozoa, and viruses—at various sites on the human body (http://www.human-microbiome.org/). Using DNA sequencing techniques and platforms, these researchers are participating in the field of metagenomics, studying how the complex relationships between microbes and humans can impact both illness and health. This approach is at odds with the traditional model of disease as a kind of germ warfare, in which bacteria are posited as enemy invaders. [So please put the fucking wet wipes down!] Researchers are increasingly recognizing the necessity and value of many forms of bacteria which aid in, for example, digestion and the generation of vitamins.

These fascinating developments have the potential to alter the conceptual category of “human” by challenging its boundaries. Many official explanations of the microbiome continue to distinguish “them” from “us,” referring to bacteria and other creatures as parasites that colonize human hosts. Yet the differences between the human and supposedly non-human realms of the microbiome become blurred when research reveals that bacteria have co-evolved with human bodies, adapting to co-exist on certain parts of them. The bacteria under my arm, for example, are more similar to those under your arm than to those currently nestled, snug as a bug, behind my left knee. I don’t know how you feel about this buggish information, but it blows my mind! When I told PDDs about the microbiome, she was disgusted. “I am never licking anyone behind their knee again!” she affirmed. Then she reached into her ponytail and removed a pencil from it. Just to be clear: it was a long red pencil, not the short mini-golf type. “Did you know that was in your hair?” I asked. “Nope,” PDDs replied flatly before continuing with her hanging leg raises. I then killed myself laughing, but I should be more sympathetic. PDDs is exhausted by training and dieting for an upcoming figure competition, so her ecosystem is a fucking mess right now.

Back to the matter at hand [a microbially covered hand that should stay that way]: these crucial bacteria clearly guard against disease, while providing essential nutrients and health benefits. For instance I just learned that breast milk contains sugars that infants cannot digest, meant to support the important bacteria living inside the child’s intestines. Can this child’s body truly be separated from its microbiome? Are the two entities fundamentally different? Or is the human body even more complex, expansive, and encompassing than scientists have previously imagined it to be?

Here I must admit that approaching the human body as an ecosystem is not entirely novel. Various early modern researchers were also interested in what might be called the inhabitants of the body, studying lice, worms, and other entities that lived in or on human flesh. Hooray! Journalist Virginia Hughes makes a strong case for linking this past with present conditions by arguing that “scientists have been curious about our bacterial cohabitants since 1683, when when Antonie [sic] van Leeuwenhoek, using a microscope he had built himself, examined his own dental plaque only to discover ‘little living animacules, very prettily a-moving.’” (Pop Sci text). By reconfirming Leeuwenhoek’s title as the “father of bacteriology,” she enforces a progressive narrative of scientific discovery, in which knowledge steadily increases over time. Leeuwenhoek, however, did not consider his animalcules in terms of either bacteria or contagion, concepts that were arguably invented by Louis Pasteur and Robert Koch during the second half of the nineteenth century but evident much earlier in the eighteenth-century work of botanist Richard Bradley, who posited that microscopic living agents caused infectious diseases. Leeuwenhoek and most of his colleagues adhered to the longstanding humoural understanding of the body—each person was composed of a unique combination of four fluids (phlegm, blood, yellow bile, and black bile)—at odds with the biomedical model that informs the methods of participants in the International Human Microbiome Consortium. The metagenomic techniques used by the twenty-first century scientists approach the human body as an open text that can be altered at will “largely through sooner-rather-than-later technoscientific interventions not only for treatment but also increasingly for improvement” (Biomedicalization: Technoscience, Health, and Illness in the U.S.). The ultimate goal of the Consortium’s research is to remake nature by, for instance, developing bacterial transplants, whereby a person suffering from disease would receive an influx of “good” organisms in order to balance his or her own bodily ecosystem. Fecal transplants are already helping those suffering from colitis, something that fills me with awe rather than disgust. No doubt you feel the same way.

In contrast, Leeuwenhoek was not primarily interested in medical treatments. An amazing inventor, he created some of the most powerful microscopes of his day. Like any man would, he briefly pondered what use these machines could be before jacking off onto a glass slide and then picking his teeth to have a look see. Leeuwenhoek deployed microscopic lenses to create drawings of mysterious creatures, rendering visible the formerly invisible while linking his “pretty” worm-like organisms with both movement and life. I hope you, glorious readers, have enjoyed this history of the body lesson, for it is sadly about to end. Ahem: In my opinion, the most significant link between early modern and contemporary practices is to be found in their similar challenge to the definition of human flesh and the basis of its reproduction.