Forgive me if you’ve covered this already, but… Isn’t it also possible that you have some shortscale homeostatic pair where neither rate changes, but were in fact always just a little miscalibrated relative to each other? Such that the equilibrium point shifts very very slowly over time?
Like, in Harry Potter canon you can cast reparo on an object as often as you break it, but it’s just slightly less than a perfect repair. It’s not a difference you’d notice until you’d repaired the object numerous times.
In general, the “state variables” in biology are counts of identical things (or at least functionally-identical things). So for instance, paralleling your Harry Potter example, DNA is constantly breaking and being repaired. But the imperfections in that repair process aren’t continuous—either the repair is perfect, or a mutation is introduced. Once a mutation is introduced (assuming it’s in something functionally important), we have a functionally different molecule, so it needs to be reflected in a state variable: we need to have a state variable like “mutation count” or counts of specific kinds of mutations. That state variable will be what’s out-of-steady-state on a long (in this case infinite) timescale.
This generalizes: if there are slight differences accumulating over time, then those will have a state variable (like mutation count), and that variable will be out-of-steady-state on a long timescale.
Forgive me if you’ve covered this already, but… Isn’t it also possible that you have some shortscale homeostatic pair where neither rate changes, but were in fact always just a little miscalibrated relative to each other? Such that the equilibrium point shifts very very slowly over time?
Like, in Harry Potter canon you can cast reparo on an object as often as you break it, but it’s just slightly less than a perfect repair. It’s not a difference you’d notice until you’d repaired the object numerous times.
Great question, and it’s a very subtle point.
In general, the “state variables” in biology are counts of identical things (or at least functionally-identical things). So for instance, paralleling your Harry Potter example, DNA is constantly breaking and being repaired. But the imperfections in that repair process aren’t continuous—either the repair is perfect, or a mutation is introduced. Once a mutation is introduced (assuming it’s in something functionally important), we have a functionally different molecule, so it needs to be reflected in a state variable: we need to have a state variable like “mutation count” or counts of specific kinds of mutations. That state variable will be what’s out-of-steady-state on a long (in this case infinite) timescale.
This generalizes: if there are slight differences accumulating over time, then those will have a state variable (like mutation count), and that variable will be out-of-steady-state on a long timescale.