Every living thing has to solve the same problem: harvest enough energy to rebuild itself, and keep doing it. Fail once and it dies. That sounds too obvious to be worth saying, but I've come to think something surprising falls out of taking it completely seriously.
Strip biology down to almost nothing — forget DNA, cells, genes, selection, ecosystems, intelligence, even chemistry — and imagine only a machine that repeatedly harvests energy, spends it rebuilding itself, and repeats. The rule is brutally simple: whatever it harvests has to cover the cost of remaking itself. If it gathers less than that, even once, it's gone. That's the entire model, and my claim is that a surprising amount follows from the single inequality at its heart, harvest ≥ cost of rebuilding.
Say the machine harvests ten units and rebuilding costs six. The remaining four aren't just extra — they're slack, and slack is the only energy available for anything beyond staying alive. Every new structure, every improvement, every specialization has to be paid for out of it. No slack, no innovation. This reframes complexity in a way I find useful: complexity isn't free, it's accumulated maintenance, and each additional component is another recurring bill. So the question was never whether a system can become more complex. It's whether it can generate enough extra surplus to pay for that complexity indefinitely.
Now add a second machine that doesn't harvest at all but lives off the first one's surplus. At first this looks like a good deal, since the second machine skips the hardest job there is — finding energy. But if it consumes more than it gives back, it raises the survival threshold for the pair, and lean years the first machine would have weathered alone now kill both of them. A purely parasitic arrangement lowers long-term viability. What I find striking is that no morality entered the picture to make this happen. Nobody chose to cooperate. The arithmetic simply won't support a relationship that permanently takes out more than it puts in, and in a genuinely closed system, exploiters eventually remove themselves by removing whatever was keeping them alive.
Give the second machine something useful to do instead — gathering materials, repairing damage, making harvesting easier. If its contribution saves more energy than it costs to keep running, the total surplus goes up. Not despite the specialization but because of it: cooperation literally produces more free energy. And that new surplus can fund further specialization, which can produce still more surplus, and so on, until the thing compounds. Which points at something I hadn't quite seen before working through it. Cooperation and complexity aren't two separate evolutionary trends. Cooperation is how complexity gets paid for.
It's tempting to ask why evolution favours complexity at all, but maybe that's the wrong question, and the better one is which kinds of complexity can afford their own upkeep. Most can't. Every new part raises the bill, and only the parts whose contribution beats their maintenance cost leave any budget for the next round. That quietly filters toward systems built out of mutually supporting pieces, with no purpose required and no built-in direction toward progress — just accounting.
Every bargain has its price, though. As parts specialize they give up independence. Your heart can't digest food, your stomach can't pump blood, your neurons can't clear their own waste. Each becomes extraordinarily good at one thing and completely dependent on the rest, so capability and fragility rise together. This isn't a flaw in the design; it's the same arithmetic wearing a different face. The specialization that creates surplus is the specialization that creates dependence, and there's no path to unlimited complexity that doesn't also raise systemic risk.
The same logic scales up. Agriculture produced a surplus, the surplus let people stop growing food, and that freed-up energy paid for scientists, engineers, doctors, teachers, artists, governments, universities. Modern civilization is more or less accumulated specialization financed by surplus. When the surplus grows, societies diversify; when it contracts, all that complexity gets hard to hold together. Civilization isn't an exception to biology so much as the same accounting running at a larger scale.
I want to be clear about what this is. The model is deliberately minimal. It says nothing about how the first self-maintaining system got started, it doesn't replace evolutionary theory, and it ignores information, spatial structure, randomness, population dynamics — most of what actually makes biology hard. It's a toy. But toys earn their keep when they expose structure hidden under the complexity, and what I'm hoping this one shows is a single thread running through things we usually study apart: why living things die, why cooperation emerges, why specialization works, why complexity grows, and why that same growth breeds fragility. All of them seem to turn on the same quantity — the surplus left over above the cost of staying alive.
Maybe that's already well known somewhere under a different name. Maybe it's wrong. Or maybe this small accounting identity earns a place next to the more familiar tools we use to think about living systems. I'd like to know where readers think the logic holds, where it breaks, and whether something like it already exists in the literature.
