Theory 08/Biological control/Physiology
The Regulation Energy Floor
The energy cost of biological regulation has a floor set by the ratio of signalling molecules to noise, so tighter control is always more expensive and organisms should be found operating near, not far below, that floor.
01What is already known
Control theory gives the cost of precision; physiology gives the budget. What is missing is a quantitative statement of where real organisms sit relative to the theoretical minimum. Measurements of signalling noise and metabolic cost are now good enough to ask.
02The mechanism
Maintaining a variable near a set point requires measuring it. Measurement requires molecules, and molecular counts are noisy. Reducing noise requires more molecules, which costs energy. The trade-off sets a floor: the cheapest regulator that achieves a given precision. Organisms that regulate more tightly than needed waste energy; those that regulate less tightly risk failure.
03Predictions
- Measured regulation cost should scale with achieved precision in the way the floor predicts, across systems from bacterial chemotaxis to mammalian glucose control.
- Organisms should cluster near the floor rather than at arbitrary points above it.
- Systems under energy stress should relax precision rather than maintain it at higher cost.
04Refutation
If precision is achieved at costs far below the predicted floor — implying a signalling mechanism not counted by the model — the floor is not binding.
Combine measurements of signalling molecule counts, noise in the regulated variable, and metabolic cost in the same system. The floor is a line in that space, and the test is where organisms sit relative to it.