Lesson 2: The Persistence Test Prologue Consider two things left in a field for a year. The first is a bicycle. Steel frame, rubber tires, a chain that was recently oiled. The second is a bacterium — a single cell, one ten-thousandth the size of a pinhead, with no moving parts you could see under anything but the most powerful microscope. Come back a year later. The bicycle will be on its way to ruin — the chain seized, the tires cracked, the frame beginning to surrender to rust. The bacterium, if conditions permitted, will have become millions of bacteria. It will have found energy, repaired itself, and made copies. It will, in some meaningful sense, have grown. The atoms in both objects obey exactly the same laws of physics. And yet something has happened to the bacterium that did not happen to the bicycle. Something that physics, on its own, has no language to describe. In this lesson, we find that language. For centuries, science has operated under an unspoken assumption about what it means for something to exist. To exist, in the scientific sense, has meant to be physical — to be composed of matter and energy, subject to forces, measurable by instruments. This is the doctrine of physicalism, and it has served science brilliantly wherever it has been applied to the nonliving world. The problem appears when we ask a deceptively simple question about living things: why do certain configurations of matter persist while others do not? A rock persists. A star persists, for billions of years. These are not puzzling cases — the forces holding them together are well understood. But a bacterium persists in a different and more interesting way. It doesn’t merely hold together; it actively maintains itself. When it is damaged, it repairs. When it runs low on resources, it seeks more. When conditions are right, it reproduces. It does all of this through a logic — a set of organized responses to information about its environment — that has no counterpart in the rock or the star. This difference has been sitting at the center of biology for over a century, mostly unacknowledged. We observe it constantly. We depend on it for every medical treatment, every understanding of disease and health. And yet we have no official scientific framework for saying what it is. The physical description captures the mechanism but not the logic that governs it. To build that framework, we need to start at the very beginning: with what it means for something to exist at all. We propose that existence is not a property exclusive to physical matter, but a status — one that can be earned by meeting two conditions. The first condition is persistence. An entity must maintain its identity or configuration over time, resisting the pressure of entropy. It need not be made of the same matter from moment to moment. It needs to remain, in the most practical sense, itself. The second condition is systematic interaction. An entity must engage with the world according to consistent principles — not randomly, but in ways that can be described and studied. We call this the persistence test. A rock passes it. A star passes it. But notice what else passes it. Consider the heart. The physical cells of a heart are constantly being replaced — the matter is in flux. Yet the function, the pumping of blood, persists across decades. It interacts systematically with the lungs, the muscles, the circulatory system, according to principles we can describe with precision. By the criteria we have just established, the pumping exists. Not as a poetic description of chemistry. As a persistent entity in its own right — one that has survived because organisms that lost it did not. This is a modest but consequential claim. We are not yet saying anything about minds, or experience, or consciousness. We are saying something much simpler: that when a biologist identifies a function — the heart pumps, the liver filters, the immune system defends — they are not speaking loosely. They are identifying something real. Something that persists, interacts systematically, and can be studied scientifically. Note what the persistence test does not claim. Abstract constructs — mathematical objects, logical forms, hypothetical entities — don’t pass it. A platonic solid neither persists through time nor interacts with the world. The test is deliberately grounded: it admits only what actually maintains itself and engages with reality. Functional entities qualify not because we can describe them abstractly, but because they do something real in the world and would be missed if they disappeared. That something is what functional science is built to study. And in our next lesson, we will establish the rigorous basis for taking it seriously alongside the physical world it inhabits. Epilogue The bicycle rusts. The bacterium persists. We began with that contrast, and now we can say more precisely what it means. The bicycle has no response to entropy. It is subject to physics and nothing else. When the forces of dissolution come for it, it has no recourse. The bacterium has a response. Not a conscious one, not a deliberate one — but a functional one. A logic, built up over billions of years of trial and error, that learned, in the most primitive sense of the word, to hold on. Not forever. Not without cost. But enough to persist, and in persisting, to pass that logic on. We are the inheritors of that logic. Every function in your body — every system that maintains, repairs, responds, and adapts — is a link in a chain that reaches back to the first chemical networks that learned to hold on. We have not yet explained how that chain was built, or what it produced when it reached us. That is the work ahead. But we have established the first thing: that the logic is real. That function exists. And that a science which ignores it is missing half of nature. Contents This is a public episode. If you would like to discuss this with other subscribers or get access to bonus episodes, visit thefunctionalmind.substack.com
