In addition to diet-driven pressures on our gut ecosystem, research suggests that the Western obsession with killing germs, via broad antimicrobial agents such as antibiotics, might also be driving microbial diversity down, leaving fewer and fewer microbes to homestead in our GI river valley[i]. Though the cleanliness of early humans leaves much to be desired by our current Western standards, scientists speculate that, by virtue of their being the hairy unwashed, early humans had an even more diverse microbiota than we do now. While we are not sure what the implications are of having lesser or greater microbial diversity on the species level, Martin Blaser postulates that, by virtue of being too clean, we are actually weakening our immune systems because we lack the contact with a variety of microbes to train it[ii]. The thought is that exactly how an ecosystem relies on a vast reservoir of organisms (which can be reduced to genetic material) to enable it to endure despite any fluctuations or stress, the health of our holobionts hinge on the variety of species filling a myriad of niches in the gut.
Generally speaking, if you have a wide diversity of species, then your system has the potential for good microbial competition and checks and balances against pathogens within your gut as well as theoretical access to a wider assortment of beneficial genes, thus making you a healthier organism. If your gut market lacks diversity, then you are stuck with a limited set of metabolic abilities that relies on the functions of only a few microbes that may or may not have the genetic pool to adequately support your human system as well as support defense against colonization by other less helpful microbes. Therefore, it is safe to say that if your gut has low microbial diversity, your holobiont will have less protection from ecosystem disease.
Scientists have begun to speculate that since the germ theory paradigm shift and the ensuing focus on sterile environments and anti-microbial agents, we are rapidly losing diversity with each successive generation. According to this theory, the humans just figuring out agriculture most likely housed many more different microbes than ours in their guts, and ours will house many more than our great-great grandchildren. However, though diversity sounds great, we need to be careful in focusing on a specific microbial profile as the indicator of human holobiont health for every individuals. We each possess a unique fingerprint of our microbial community, and that uniqueness needs to be taken into account. Noted plant ecologist, Charles Peters reminds us that “maintaining biodiversity is less important than maintaining a functioning ecosystem[iii].” Gut explorers, scientists, and health professionals all need to hold this wisdom in mind as we learn more and more about the human holobiont.
Our holobionts are dynamic and as such are always in a state of minor flux (though over time, the system does stay remarkably stable). Diet change, age, and illness can cause our microbial community to shift in population—sometimes for the worse. Like any ecosystem, our corporeal river valley can be subject to pollution and rejuvenation, flooding (illnesses) and times of peace. But by learning more about our gut inhabitants and how they function in our metabolism as well as encouraging genetic diversity, we can keep our holobiont healthy and thriving.