LAST TUESDAY I PRESSED little white keyboard squares for eight hours, drove home, helped the kids with their homework, overcooked some chicken breasts, watched Jeopardy, paid Idaho Power, read some paragraphs, switched off the lamp, and thought: You lummox, you didn’t do anything outside all day.

Why berate myself? Because getting outdoors helps me think, feel, and sleep better. Increasingly, science has my back on this. A 2008 University of Michigan study, for example, showed that volunteers who ambled through a campus arboretum improved their short-term memory by about 20 percent.

More recently, Japanese studies have found that regular strolls in the woods can lower depression rates, blood pressure, and levels of the stress hormone cortisol. South Korea is so convinced of the benefits of “forest bathing,” they’re building a $140 million National Forest Therapy Center. Finland is funding similar research.

All of which is both interesting and encouraging. Yet I remain troubled by the language of my own formulation. The words I chose — you didn’t do anything outside — suggest that I didn’t leave the “Inside” to do anything in “Nature.” They imply that a world exists called “Inside” and that it is fully separable from another world called “Outside.”

Implicit within that arrangement is the assumption that “Me” and “Nature” are discrete entities. But the emerging reality is immensely more complicated. “Me” is not some inalienable being that has to remind himself to plant a tulip once in a while before getting back to the real business of watching Alex Trebek. And “Nature” is not some elfin, rejuvenating spa that provides “Me” with a daily dose of fresh oxygen, mental health, and organic broccoli.

Increasingly, the science of microbiology is showing that we carry “Nature” with us everywhere we go. From the moment we emerge from our mothers, we are colonized, seized, and occupied by other entities. We are not, it turns out, walking cleanrooms that ought to be shuttled into Nature for forty-five minutes, then bustled inside and bathed in hand sanitizer.

In truth, no matter how far “Inside” we get, the “Outside” is always with us.

WITNESS: YOUR SKIN HARBORS whole swarming civilizations. Your lips are a zoo teeming with well-fed creatures. In your mouth lives a microbiome so dense — fusospirochetes, Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans — that if you decided to name one organism every second (You’re Barbara, You’re Bob, You’re Brenda), you’d likely need fifty lifetimes to name them all.

When you climb out of bed in the morning, ten times more bacterial cells climb out of bed than do human cells. In your gut, coalitions of hundreds of different species compete for food in a dark, simmering biome alive with as many as 100 trillion microbes. Without them, you die. To even write that you are “you” and the microbes are “them” is, perhaps, a failure of pronouns.

Ultimately, we aren’t individuals; we are big permeable societies. In the ten minutes it takes to read this essay, for example, you’ll inhale about 8 billion dust particles — calcite, gypsum, flame retardant from your carpet, spores from nearby woods. Your next breath might contain slag wool, mica, viruses, pollen, and fragments of an aphid who lived and died three hundred miles away.

Even the brain you use to process these sentences, an organ we have long imagined as a perfectly sterile entity operating above the microbial fray, might be home to beings that aren’t strictly “you.” A 2013 study in Canada found proteobacteria and viruses inside multiple human brains, suggesting that even our minds might be occupied by microbial populations of great richness.

NOT LONG AGO I WAS giving a lecture about narrative structure when a young student asked: “Wait, aren’t there only three kinds of stories? You know, Man versus Man, Man versus Himself, and Man versus Nature?”

“Well,” I began, “those are a bit — ” but my objections felt half-formed. I wondered: What about “Man helps Nature”? What about women? But within seconds, the class had leapt into the discussion, classifying Jack London’s “To Build a Fire” (Man v. Nature) and Star Wars (Man v. Man? Jedi v. Himself?), and we fumbled along for another ten minutes before everyone had to go.

What I should have said is: Look at the little power plants at the center of our cells. Our mitochondria have DNA and RNA entirely separate from our own; they are much closer, genetically, to bacteria than to us. Aren’t they a part of “nature”? And yet aren’t they absolutely a part of being “human”?

I should have said: Look at the viruses. Viruses are no longer understood as evildoers who show up now and then to send us to bed for a week. Viruses flit between species like bees between flowers, picking up genes from one host and plugging them into the genetic material of a new host. With the help of viruses, little snippets of genome can migrate between species, from land to sea, plant to animal, all within the span of a single generation. Because of them, evolution accelerates. We’ve already identified around 100,000 viruses in the human genome, and the vestiges of 150,000 more. Without viruses, can you be you?

At a time when scientists can grow insulin inside the bodies of bacteria, or tiny, perfectly operable human kidneys inside mice, when synthetic biologists are trying to create a kind of E. coli that can transform solar energy into fuel, we’re learning more and more deeply that we are inextricably linked to our ancestors and neighbors, from the maples outside our windows to the bacteria that paddle through our intestines.

Perhaps we are better understood not as “Man” and “Nature” at all, but as aggregates of biological dependencies. Maybe it’s better to think of ourselves as living skyscrapers aswarm with tenants, or as walking coral reefs. Even though more of us now live in cities than do not, even if we spend all day, as I often do, pecking away at a plastic keyboard, all of us are living with “Nature.”

Maybe there really is only one kind of story. We are the “Outside.” And it is us.