“Terrain theory” advocates use an image of two goldfish bowls, one in which the water is green, and in the other the water is clear. It always comes with a slogan: “Don’t medicate the fish, clean the tank!” I’ve been staring at that image for a few days now because I knew there’s something wrong with it, but I couldn’t quite figure out what that something was or how to put it into words.

“Terrain Theory” is an “alternative model of health” promoted by the US Secretary of Health and Human Services, Robert F. Kennedy Jr. The idea behind it is short, easy to understand, simple to the point of childishness, and utterly, fatally wrong: if you lived in a healthy world, you wouldn’t need vaccines and antibiotics.

But goddamn is that fish lonely.

Terrain Theory is presented as an alternative to germ theory; the essential idea is that human body is a “terrain” that hosts lots of other micro-organisms, and that illness isn’t the introduction of inimical organisms, it’s when the terrain becomes “unbalanced” in some way, making one exhibit symptoms.

Like all zombie ideas, this one has a clear grain of truth. A healthy gut is undistracted and can handle small incursions of foodborne illness without making you ill. A healthy immune system can fight off a lot of familiar diseases. (The word “familiar” there is doing a lot of work!) Strong muscles and bones make a healthy old age more likely. We take great pains to keep our food fresh, our water clean, and we’re slowly learning the necessity of keeping our air decontaminated.

But goddamn is that fish lonely.

The reason we do things like keep our food fresh and our water clean is because they can harbor dangerous bacteria and other germs. Infections are a matter of numbers and statistics: a small incursion of viri can be handled by your immune system, but if enough get into you, some will sneak past the guards and give you fever and chills and worse. A small amount of hostile bacteria in a dish too-long among the leftovers will die in your stomach acid, but if enough get into you, you’ll be spending tomorrow on the porcelain throne. That threshold is different for everyone, depending on a host of factors that depend on front-line defenses in your respiratory and digestive systems as well as the entire layered defense system of your bloodstream and tissues. (For example, I almost never seem to get foodborne illness, but my wife is much more sensitive; on the other hand, I seem to catch every virus my nose encounters, but she never catches the flu or a cold.)

Terrain Theory is the bizarre idea that at the microbial level, predator/prey dynamics don’t exist. That no invasive species would cause a boom/bust cycle inside your body, turning it into a battlefield as it seeks out its prey and the body fights back.

What makes the image so wrong is that the fish is lonely. It never sees other fish. It’s nowhere near its niche of evolutionary adaptation. They evolved to live in slow-moving streams in the mountainous regions of China, not pristine clean goldfish bowls.

You and I don’t live in a perfectly clean world. We’re not Howard Hughes, holed up in our air-filtered bunkers. We live among other human beings, some of whom will encounter other human beings that have diseases, and they may transmit those to us, via air, via touch, via intimacy. There’s only so much cleaning we can do in a day, and unlike RFK Jr. we can’t hire other people to do it.

What Terrain Theory advocates don’t understand is that there is no perfectly immune human being, not even close. At the microbial level all of nature is trying to figure out how to live within us or eat us, and they evolve one Hell of a lot faster than we do; we produce new offspring about three times in our lifespans, and each of those three has some shatteringly small chance to develop a novel immunity they might pass on to their children. Inside you, an average of thirty-five trillion bacteria are reproducing every three days, and every one of those has its own shatteringly small chance to develop into something deadly inimical… but you get 3 chances in 70 years and they get 70,000,000,000,000 chances every week.

What’s worse is that you can’t live without them. Some of those bacteria are actually as essential to your well-being, speaking of “terrain,” as mammals and birds are to the health of a forest. Microbiome gut bacteria help regulate blood sugar and bowel health, and I’m sure we’ll find even more functions they and we have evolved together to provide them with a mobile survival platform and us with a better immune system.

Terrain theory takes a single idea how we live healthier lives, “we should live with a reasonable amount of cleanliness,” and tries to claim that it’s the only idea. That somehow the microscope was not only unnecessary but an evil addition to our arsenal of tools with which we defend ourselves from sickness and death. Throwing out medication and vaccination as “dispensable modern inventions humanity never needed before” ignores the centuries of pain and suffering disease inflicted even on those warlords who kept for themselves the lion’s share of clean water and fresh food.

I’m not a monk. And, quite likely, neither are you. We eat, drink, breath, kiss, and even have sex with other human beings, and every contact gives the microbial world in which we live and of which we are hosts another chance at moving from one body to another. Terrain Theorists can avoid good food, good friendship, and good messy sex all they want, but they’re sadder– and sicker– people for doing so.