I Contain MultitudesBy Ed YongEcco, 2016  Shortly before a stroke consumed his speech and a few years before his last breath was had, my paternal grandfather shared an answer to a question I had yet to pose. “The meaning of life,” he began with an expectant grin to a teenage me, “is relationships.” I’ve yet to figure if he copped the phrase from his late-in-life hero Jiddu Krishnamurti or if it was something he arrived at in the frequent unguarded musings he entertained so near the precipice of his own cognitive dissolution. Whatever the case, the seed of an expansive idea had been planted in me and it still bears surprising fruit decades on. Understanding who we are and how we relate to others is one of the most essential exercises of the contemplative mind. But my grandfather was more than a humanist. He pondered his relationship to the stars, to the tall palms and violaceous jacaranda on our street, to the air we breathe and the things we eat.Ed Yong similarly marvels at our varied relationships with other beings in “I Contain Multitudes,” but the ones he finds are too small to gaze with an unaided eye. His debut book combs microbiology, a bit of a contemporary underdog in the life sciences, to understand beings that are like living ancestors inhabiting nearly every square meter of Earth. His imperative is no less than wanting to show us “what the animal kingdom really looks like and how much more wondrous it becomes when you see it as the world of partnerships that it actually is.”Yong understands that our popular conception of microbes and their function in our world has been blighted by misinformation, fear mongering, and arrogance. Part of the blame sits with the language we use to describe microbes. For centuries, microbes have mostly been cast as villains, miscreants, and harbingers of death, but in reality, “there is no such thing as a good microbe or a bad microbe.” The same Helicobacter pylori that molests us with ulcers and stomach cancer also reduces the risk of esophageal cancer. The discovery of the germ theory buttressed our linguistic assault of microbes, but we’ve clearly overreached, sterilizing our homes and office spaces as if they were operating theaters, thus banishing even the silent majority of tender, ambient microbes that regulate our immune health.Yong’s examples of microbial relationships throughout the animal kingdom are a salve for our misconceptions. It turns out that bottling these relationships into fixed identities is not particularly useful. Terms like mutualist, pathogen, and parasite are not permanent attributes but rather relate a particular state of affairs between two organisms at a particular point in space and time. In other words, like our understanding of much else in the world, context matters. Even symbionts aren’t “for free… they need to be fed, housed, and transmitted, all of which costs energy.” Microbes are in fact inhabitants of complex ecosystems, parts of a greater whole and participants in numerous, simultaneous transactions. More important than naming the relationships is understanding the nuances and dynamism of the transactions. To more clearly appreciate their place in the world, we must broaden our view of microbial relationships and contextualize them in the framework of ecosystems.One of the most elegant examples of the complexities of life and death in a microbial ecosystem is that of coral reefs. In tepid waters, coral harbor a very dense and diverse microbiome, but as the world’s seas have acidified, once tame occupants have contributed to the downward death spiral of grand sweeps of reefs, stripping their landlords of the very means by which they were nourished. As a result, algae bloom, fish and sharks retreat, and bacterial diversity within reefs plummets. It is here that Yong bedevils us with this Shakespearean idea: “every symbiosis is underlain with hostility and only by proper regulation and often elaborate adjustment can the state of mutual benefit be maintained.” Betrayal, it seems, is never too far from the surface.Studying the dynamism of these transactions in the living theaters of the real world is one of the great challenges of microbial research, even when the negotiations are close to home. Human milk oligosaccharides (HMOs) are long chains of sugars that are the third largest component of human milk, yet surprisingly, human babies cannot digest these sugars. Instead, HMOs exclusively nourish the bacteria that compose the gut microbiome of babies. One of these bacteria, Bifidobacteria infantis, secretes silaic acid, which has been shown to affect infant brain growth. That a bacteria is such an early ally in human development makes us understand why Yong’s book has a philosophical tilt. If such microscopic beings are essential to who we become, then who am “I” precisely?There is a great joy in reading scientists, physicians, and educators explain the outer and inner world to a lay audience in a manner that expands our sense of who we are and what brought us here. Oliver Sacks was an elegant cataloger of the beautiful and strange depths of the brain and Siddhartha Mukherjee entangles us in the meaning of DNA and its mutations. These authors bring a form of spirituality to their work, if that word is to mean both an inward and outward examination of who we are and how we relate to other beings, absent a clarion call from the cosmos.If who we are includes the multitudes of microscopic organisms that we house and feed, which in turn help regulate our immunity and sculpt our destinies, then what constitutes the individual? Some microbiologists would like us to reconceptualize the boundaries of self by using new definitions like holobiont, meaning a collection of organisms that spends large parts of their lives together in interconnected webs. Perhaps what is called for is not new terminology, but rather a reawakened appreciation of the profound interconnectedness of all living things. As Yong puts it, “our microbiome has wide reaching tendrils that root us in the wider world.” To recognize this, to observe the interrelatedness of all life, is the outcome of both deep religious thought and deep scientific thought. It is through books like Yong’s that indulge us in expansive journeys of the known world that we can enlarge our sense of self and our tangled relationships in a way that heightens our spirit.