Homeostasis versus equilibrium

I want to make a quick distinction between the concepts of homeostasis and equilibrium. It can be easy to think of these two ideas as being the same thing, because both are mechanisms that drive a system that is in a state of change toward a system that is no longer changing. But understanding why they're different can change some low-level lines in our rational operating system code. Bear with me for a second as we cover the basic ground you probably already know. There are subtleties in these definitions we'll pull out if you give me a moment. The payoff should not just be in understanding biological systems better, but also hopefully in understanding larger systems like families, communities, and society as a whole.

Let's start with equilibrium. This is the simple idea that things tend to become more uniform over time unless there's something preventing that from happening.

This sentence is an example of an initial state that has not reached equilibrium.
This sentence is an example of a final state that has reached equilibrium.

I won't belabor the point for this audience. I think in school this idea was the one I was first exposed to, mostly in general physics or chemistry classes. Two chemicals when first exposed to each other start out like the top sentence above, and end up like the bottom one over time. They'll go through an initial period of change, but at a certain point they won't change anymore unless you intentionally perturb the system from the outside.

Homeostasis is the idea that the system is stable and will remain so as long as conditions don't change. If you're reading this in a space that has normal air conditioning you're probably comfortable. Your body is at homeostasis with its surroundings. This, despite the fact that your core body temperature is somewhere in the range of 98 F (around 37 C), and your AC is almost certainly set far below that temperature.

Your body is maintaining homeostasis by actively opposing equilibrium. Many interesting biological processes consist of the body attempting to maintain that homeostasis, or its reaction when homeostasis is interrupted. That's why it's so much more interesting than equilibrium.

It's also easier to work with. Take the example of the two colored sentences above. The first is the 'initial state' of the system, and the second is the 'final state'. But think about how absurd the idea of an 'initial state' is in the context of a complex biological system. The 'initial state' might be said to be the state that the cell was in when it first divided from its parent cell. Except that it was maintaining homeostasis all throughout that period. And so was that cell's parent cell, and so on back through time back to the first cell (we assume). In other words, much of biology is done under complex conditions where a uniform 'initial condition' like the colored sentence above is as absurd a concept as a 'final condition'.

In a physics experiment I can set up objects on a table (or accelerate particles in a collider) and watch what happens from the beginning of my experiment to the end of it. The things that happened to those objects (or particles) before the experiment began are less important than whether I created conditions to ensure they entered the experiment with the same initial properties. In biology, we expect a certain natural variation because of complex 'histories' we can never control. We can't fix it; we can only compensate for that variation by randomly assigning treatment groups and hoping we collect enough data that the law of averages cancels out the variation. (We calculate our hopes with Fisherian statistics, not just blind luck. We're not barbarians!)

So from a biological perspective it's less interesting whether a system is in equilibrium, than whether it's in homeostasis. And along which axis. Here's a brief list of some systems that any given cell continuously maintains homeostasis of:
  • Metabolic rate
  • Replication/division
  • Ions into and out of the cell (a partial list includes: sodium, potassium, chloride, calcium, phosphate, sulphate, magnesium)
  • Transport into/out of the nucleus
  • Protein degradation
  • Protein production
  • DNA packing
  • Cell membrane plasticity
  • Cell 'skeleton' (actin)
  • Cell 'skeleton' (microtubules)
  • Intracellular transport
  • Extracellular sensation
  • Intercellular communication
  • pH
Each of those bullet points represents whole systems of mechanisms designed to keep the cell functional even when it's doing nothing sitting there under the microscope. The correct analogy here would be to think of what a city needs to keep going even if you shut down all its non-essential activities. Homeostasis is an active process. Equilibrium is a passive process. And they often work at cross purposes.

Now, why should we care so much about this distinction? How does expressly understanding this concept help us understand biology better - and potentially also ourselves better? We would want to start by being able to identify a system that is in homeostasis versus one that is in equilibrium. In other words, does the system maintain stability because of active processes that keep it where it's at or does it revert back to stability despite active forces attempting to push it away from the steady-state?

I think here is where many systems that people often characterize as being in equilibrium are better understood as being in homeostasis, and this knowledge should change the way we treat them. Look at it from a relationship level in a marriage. Does the marriage stay strong despite outside influences trying to tear it apart without any effort on the part of the participants? Obviously not. To maintain the status quo requires effort on the part of the participants to drive back toward stability.

What about in communities? Neighbors and neighborhoods don't come together and coordinate activities without active work behind the scenes. Indeed, community organizations don't act as though they do. (For example, the recent 'wear a mask' campaigns are entirely about driving toward a new steady-state condition through active intervention.)

Next, at a society-wide level when we look to current conditions we should ask whether we're driving toward equilibrium or toward homeostasis. When things aren't changing (politics has always been divisive) we might ask whether that's part of the homeostasis. If we look back at the history of politics in the USA, we see a striking uniformity in how vicious the political gamesmanship has been all along. People have constantly complained that the strident nature of political discourse in their day was about to reach the breaking point.

Yet it rarely does. Perhaps that's because a political system in contention is actually a healthy system in a homeostatic condition. But if we understand the system through the lens of that metaphor, we should also understand that to keep that political system in balance requires active effort on our part. One-party rule has yielded disastrous consequences throughout the history of the USA as well as many other nations. But on the other extreme, allowing partisan conflicts to escalate too much is a recipe for disastrophe, civil unrest, and even civil war.

It can be difficult to judge through the long eye of history whether the current moment is the same as past decades, or whether we're witnessing something new. But the difficulty here isn't in judging whether something is in equilibrium or homeostasis. Rather the difficulty is in judging whether we're in a state of change or whether we're just witnessing the active processes of homeostasis continuously keeping the forces of equilibrium at bay.

If you believe we're in the middle of some major changes, I would ask whether you think the system is driving toward equilibrium or homeostasis? (Because the system is going to drive toward one or the other - even if 'equilibrium' ends up being cities reduced to rubble.) By which, I mean do you think is driven by passive forces, like water flowing down hill, or active forces? Those two mechanisms drive toward dramatically different outcomes.

Finally I think this concept can help us build a system of homeostasis that represents the world we want to live in. When we recognize that homeostasis is an active process, we stop looking forward to a time when all enemies are conquered and the galaxy is finally at peace. I know many partisans on both Left and Right who believe that they're engaged in a temporary struggle. They imagine a future victory for their side once "the public realizes [X]" or "when demographics shift" or "once we pass legislation finally dealing with [problem Y]". But politics isn't driving toward equilibrium. The best we can hope for are periods of homeostasis punctuated by periods of change. There was no 'initial state' of our nation or any other nation, and there is no 'final state' we're driving toward.

But life is like that. You can have temporary wins, like a hunter-gatherer taking down an elk for the tribe. But the very idea of a 'victory over all elk kind' is itself disastrous for both the elk and the food situation for the tribe. I think there's a certain romance of the idea of equilibrium. It's clean. It doesn't change. It feels simpler than homeostasis, which requires constant care to maintain. But ultimately equilibrium is our enemy. It's not where we want to be. The only way we achieve it is by dying. Meanwhile, the drive toward homeostasis - pushing back the passive forces of equilibrium that would destroy us - is a description of what it means to be alive.


  1. Very thought provoking, and since you directed a question specifically at me, I'll take a crack at answering it, though this just represents my first off the cuff thoughts, I suspect that the longer I think about it the more depth I'll discover in this analogy.

    My initial thought is to compare cultural evolution to regular evolution. The reason a cell has all of those homeostatic process is that if any of those values end up deviating by very much the cell is in trouble, and it might very well perish. Turning to cultures, they develop their own homeostatic processes which also serve to ensure their survival. Some of these might be labeled as traditions or religion, and while not as concrete as the process in a cell they serve a similar function.

    But of course culture is always changing as well, and arguably cultural evolution happens much faster than biological evolution, but wouldn't survival still be the ultimate arbiter of whether something "works"?

    Which means that in our current situation, we've got various processes that are doing their best to maintain homeostasis, government, laws, traditions. And just because that's what they're trying to do doesn't mean that they're good. Just that they're to be expected.

    I think the goal with the disruption is to achieve a new and better homeostasis, But from where we're at it's hard to imagine what that would be. And I assume that lots of cultures when attempting to cross the valley into another local maxima end up perishing before they arrive, or the maxima ends up being illusory or of lower elevation than the one they were just at.

    As far as equilibrium, how is that not just entropy? The thing we're always fighting against always and everywhere?

    So in answer to the question, I think everyone who has an opinion imagines that their either driving towards a new condition of homeostasis, or they're protecting one they already imagines exists, but that if they're not careful they'll upset things and we'll end up with more entropy/equilibrium.

    In any event that's just my initial thoughts on the subject.

    1. Thanks for the kind words. Bringing the concept of 'cultural evolution' is indeed interesting, as we have less confidence in whether cultural changes will prove to be pro-adaptive over the long term, versus biological evolution.

      I'd like to distinguish between the mechanism that drives a system toward homeostasis and the homeostatic condition itself, and to distinguish both of these from the actual work the system performs. I think these distinctions can provide a bit more clarity as we analogize toward social systems. But first, let's start with a specific biological system as an example: ion balance.

      Cells generally keep a fairly high intracellular concentration of potassium ([in/out] ~120mM /~20mM) but the opposite concentration of sodium ([in/out] ~20mM/~120mM). This means they actively pump potassium into the cell and sodium outside the cell, and because they're pumping against the gradient it requires energy for them to do this. Since the ions are both positively charged, the exchange doesn't result in a net change in the cell's overall electrical charge. But why go to all this work? What does it do for the cell?

      It provides the cell with a significant amount of potential energy it can use to make very rapid changes. If the cell wants to import something across the plasma membrane (a process that usually takes a lot of energy, and more so the larger the object to transport) it can use the ion gradient to help it perform this work. If a cell wants to send an electrical signal (like with muscles and neurons), it can open the flood gates for one type of ion and rapidly change its electrical charge. This sends signals much more quickly than normal chemical diffusion. In other words, the cell works against entropy/equilibrium because the homeostatic conditions it's driving toward allow it to do something useful. Not having that homeostasis - or not being able to reset/reestablish homeostatic conditions after a triggering event - can prevent the system from doing important work. That's effectively what's happening in the muscles of these goats with myotonia congenita: https://www.youtube.com/watch?v=we9_CdNPuJg

      Let's take that to the social analogy. First let's distinguish between the homeostatic system (ion balance from the analogy above) from the mechanisms that drive homeostasis (the ion pumps in the cellular analogy). I submit that one homeostatic mechanism most societies need to maintain is a healthy public discourse. I can't imagine a public discourse whose emotional content is entirely dispassionate, or where everyone is in agreement, outside a fictional utopia. I think a certain amount of perpetual disagreement is part of maintaining a healthy public discourse. Note that this is entirely different from seeing public disagreement as problematic. It's not some aberrant condition that we need to solve; it's a basal state we should learn to be comfortable with, and indeed to use to perform important pro-social work.

      Of course, too much anger could be as problematic as too little. As could an inability to return to homeostasis. Like the myotonic goats, we could easily find ourselves paralyzed - unable to perform the important work we need public discourse to help us perform - if the system is unable to return to homeostasis.

      This is all distinct from the actual work we want to do with public discourse - which might be changes to policies or public attitudes about a variety of subjects.

    2. Finally, there's the question of which mechanisms we should encourage to promote homeostasis and which are problematic. This is where the biology is much easier. We can look at myotonic goats and see they have a problem in an important ion channel that works in other kinds of goats. In other words, we can look to biological systems that function normally, and trust that evolved proteins are there for good reason.

      Social mechanisms are more difficult. For example, people disagree as to which restrictions on freedom of expression are required to help drive homeostasis, and which prevent it. Much of my personal opinion on this debate revolves around realizing we're not attempting to drive toward uniformity of thought/agreement (an absolute state of equilibrium). We want instead to maintain a healthy homeostasis where pro-social work is possible, and that change of focus often leads me to make different judgments about restrictions than those who are driving toward equilibrium. What about other mechanisms, such as protests, riots, press freedoms, libel/slander laws, restricting hostile foreign influences, public shaming, etc.? To what extent are each of these mechanisms helping or harming our system's ability to achieve homeostasis?

    3. Certainly I agree that a healthy discourse is necessary, I think my record is pretty clear on that. And I also agree that discourse entirely free of emotion is probably not healthy, though I would contend that the ideal set point is much closer to minimum emotion than maximum emotion, and in particular I'm not sure anger would be very high on my list of useful emotions even if I'm agreeing that a certain amount of emotion is necessary.

      If your argument is that anger is similar to releasing the ion gradient. That it gives us a short burst of civic energy we might not otherwise have. Then I suppose that's as good an analogy for the place of anger as anything else, but while the cell naturally returns to an overabundance of potassium, what mechanism is there for society to return to calm after the initial flash of anger? Perhaps that's the most important homeostatic mechanism of all? I've spent a lot of time thinking about how things calmed down in the early to mid 70s, and I'm not sure I have a good answer, but most of the answers I have come up with were very specific to that time (inflation, Nixon's impeachment, Vietnam) rather than some universal societal process.

    4. I'm not confident in any of this when it comes to extending the analogy to societal concerns, especially since it's not my area of expertise. Certainly the first place you'd go to test these ideas would be international comparisons.

      My concern with how the anger is playing out is if it's released in a way that no useful work can be done with it. This is not to say that the nation should capitulate to the whims of the mob, but that SOMETHING should come of all this activity to address the source of the anger. This is where a better study of the mechanisms of homeostasis might be helpful. If we understood them better, we might be able to predict whether current trends will release tensions by doing useful work or not.

      In particular, I'm concerned that novel aspects of modern activism will break established mechanisms of change so they no longer function to achieve anything except a temporary release of anger. For example, how does the leaderless nature of social media organized movements change political action?

    5. One possibility is that without a representative to speak for the movement there will be no way for them to negotiate political compromises. It will become an all-or-nothing approach, such that either the mob is ignored and it perpetuates, or it's appeased and victory sows the seeds of a reactionary mob.

  2. Not a comment on this post. A few SSCers set up a forum for SSC OT-style discussion at https://www.datasecretslox.com/ . I'm writing here in case you haven't heard about it.


Post a Comment

Popular posts from this blog

A better addiction

Covid-19: Epidemiology is useful

Open Questions: The Origin of Life