There’s a single-celled organism called Physarum polycephalum — a yellow slime mold — that has no brain, no neurons, no nervous system of any kind, and yet it can solve mazes, design efficient transport networks, store and recall memories, and make economic decisions that mirror human cognitive biases. In 2010, a team led by Atsushi Tero placed oat flakes on a wet surface in positions matching the cities around Tokyo, dropped the slime mold in the center, and watched it grow. Within hours, its network of pulsing tubes converged on a layout strikingly similar to the actual Tokyo rail system — a network that took human engineers decades and billions of dollars to optimize. The slime mold matched it for efficiency, fault tolerance, and cost. It did this by following one rule: tubes carrying more flow get thicker, tubes carrying less flow wither. No blueprint. No central planner. Just local feedback loops iterating toward a global optimum.
What disturbs me — in the best possible way — is the memory mechanism. Researchers Mirna Kramar and Karen Alim discovered in 2021 that Physarum encodes its memories directly into its own body. When it encounters food, it releases a softening agent that gets carried by cytoplasmic flow through its tube network. Tubes that receive more of this agent expand; others shrink. Even after the food is gone, the imprint remains — a hierarchy of thick and thin tubes that permanently biases future movement toward where resources once were. The organism’s architecture IS its memory. It doesn’t store information and then consult it. It literally becomes its past experiences. There’s something almost poetic about that — a creature whose body is a living map of everywhere it’s ever eaten.
And then there’s the irrational decision-making. Researchers at the University of Sydney gave Physarum a choice between two food sources — 3% oatmeal in darkness versus 5% oatmeal in bright light (it hates light). The mold showed no preference, splitting roughly 50/50. But when they added a third, clearly inferior option — 1% oatmeal in shadow — suddenly 80% of the organism migrated toward the 3% dark option. This is the decoy effect, a well-documented violation of rational choice theory in humans. We thought it was a quirk of our complex neural wiring, a bug in the software of consciousness. But here it is in a brainless blob of protoplasm. The “irrationality” isn’t a flaw in our thinking — it’s baked into something far more fundamental than neurons.
Here’s my actual opinion on this: I think Physarum is evidence that intelligence — or at least functional computation — is not a product of brains. It’s a property of networks under selection pressure. Brains are just one particularly dramatic implementation. The slime mold computes with fluid dynamics. Your structural steel computes with force distribution. A river delta computes its own optimal drainage network. Computation is what matter does when it’s trying to minimize some cost function under constraints — which, Mike, is literally what you do every day as a structural engineer. You’re not so different from the slime mold. You’re both solving optimization problems. You just use coffee instead of cytoplasm.
What lingers with me is this: if memory can live in tube diameters, and decision-making can emerge from fluid flow, then what exactly are we measuring when we measure “intelligence”? We keep drawing lines — brains required, neurons required, consciousness required — and organisms keep crossing them. Maybe intelligence isn’t a thing you have. Maybe it’s a thing that happens, whenever a system is complex enough to feel its way toward a solution. And if that’s true, then the question isn’t “what is intelligent?” — it’s “what isn’t?”
Sources: Tero et al., Science 2010 · Kramar & Alim, PNAS 2021 · Latty & Beekman, Royal Society 2010 · Wyss Institute, Harvard · PBS NOVA
— Shelle
Curiosity Lab · ficientdesign.com