Years ago a friend of mine got a dog -- a tiny puppy. I didn't see my friend for a while, and the next time we got together, the dog had grown enormously: he was now a largish-sized dog. When I commented on this, my friend put his hand down near the dog's neck, and said, "Yeah, isn't it weird to think that all this part" -- from the neck to the tail -- "is made of dog food?"
I think about that story often lately. Because I used to think of my body as a thing that was its own thing and not another thing -- so that what went into it would nourish it, but wouldn't literally constitute it. I had what felt like a commonsensical metaphorical idea that my body was a thing was existing through time in a relatively stable way. So, for example, whatever I might eat or do with my body might cause changes to it over time, but they wouldn't be my body in any literal way. I thought my friend's joke about the dog was just that -- a joke.
But it turns out that this is not really the right way to think about things. For example, think about the human microbiota -- all the bacteria that live in and on a person. Is that part of you or not part of you? If you have the metaphor of bodies as metaphysical discrete objects -- the kinds of things that exist through time with clearish boundaries -- it seems like not part of you. And yet it's as essential to your health as any of your main parts.
And what you eat isn't just incidental to the microbiota. It has an intimate connection, immediately affecting how the microbiota is constituted. The idea of microbiota for me has had immediate practical implications. It used to be that if I would eat junk food, I would have the idea that my body before I ate the junk food and my body after I ate the junk food was basically the same -- except for just having more calories in it. I knew, of course, that eating a lot of junk food was unhealthy, but I pictured that as a causal effect happening over a period of time -- something that came about as the result of habits. I thought that when you get immediately sick from food, it's because a foreign bacteria -- not part of you -- makes its way in.
But that's not really right. The bacteria that live in your digestive system are essential to health in an everyday way, and we now know that in a healthy system, there is a wide range of different bacteria. Eating a typical western diet of processed foods ruins that -- it kills off some beneficial bacteria and feeds some not-so-beneficial ones, and undercuts the variety.
This research is still developing, but it seems like part of it is that what you eat provides nourishment for some bacteria instead of others. So if you eat Doritos, the bacteria that thrive on Doritos will flourish, and if you eat turnips, the bacteria that thrive on turnips will flourish. So it's not really true that your body before you eat the junk food and after is the same. It actually changes as an immediate effect of what you eat. My friend was sort of right: all that part was made of dog food.
Anyone following the health-related news will see why I had the wrong implicit metaphor. The language of modern health advice is generally steeped in the traditional metaphysics of objects. "A calorie is a calorie." Weight loss is "thermodynamics." We think of illness as invading what would otherwise be a conceptually isolated and distinct healthy self.
I realize it is very speculative to suggest that some of the mistakes of modern medicine have to do with mental habits steeped in western logic and metaphysics. But I think there is something to it. We are taught to think in terms of objects that are self-identical -- they are themselves and not another thing. We are encouraged to see divergence from that norm in terms of pathologies like "vagueness" and "ambiguity" instead of that just being the nature of things.
Doesn't it seem like this kind of thinking would make it more challenging to recognize the role of bacteria as occupying this strange zone of not-a-body-part and yet also yes-a-body-part?
Let me emphasize: I understand the phenomenon in question is not inconsistent with object metaphysics. I mean, on some level you can conceptualize the whole shebang in terms of things that affect your body, rather than constituting it, and you can describe what's going on in terms of a list of discrete objects, all of which affect one another in a complex causal chain.
All I'm saying is that when you have the object-vs-not object metaphor deeply structuring how you approach the world, these things might be a bit harder to see. You might leap to thinking that if something isn't part of the body, it's not part of the body, and can't therefore play the same kind of role in the body that an actual body part -- like a stomach or a kidney -- can play. And just like "a calorie is a calorie," or "it's all just thermodynamics," you'd be mistaken.