Pross Proves Plato

It is a commonplace in the academy that we learn as much or more from intelligent errors than from the modestly correct.  Addy Pross’ book What is Life? has utterly failed to convince me that the title of his penultimate chapter is correct; i.e., that biology is chemistry.  What he has convinced me of is that Plato was closer to the truth than Aristotle. 

The basic problem that Pross addresses is how to reconcile our understanding of non-living, non-replicating nature (governed by the second law of thermodynamics) with our understanding of organisms and their prebiotic (but replicating) chemical ancestors.  Pross finds the solution in a distinction between two kinds of stability: static stability and dynamic stability.  Water molecules are statically stable: they remain stubbornly what they are over long periods without change.  Bacteria are dynamically stable.  They remain what they are by a process of constant change that keeps bringing the form back into existence. 

Just as the second law of thermodynamics is the driving force that governs all chemical reactions, so all dynamically stable systems like organisms and replicating molecules are governed by a similar law:

Replicating chemical systems will tend to be transformed from (dynamically) kinetically less stable to (dynamically) kinetically more stable.

Once diverse populations of replicators get going in the history of life, more dynamically stable replicators out compete less dynamically stable competitors.  This law governs the evolution of all life up to the present and, presumably, for the duration. 

Here’s where Aristotle and Plato come in.  While they had no viable chemistry, they were very good at thinking about biological form.  Aristotle famously rejected his teacher’s theory of forms as independent entities in favor of the view that form is an abstraction from existing organisms.  How do we understand a horse?  This horse, here, is the real thing.  It consists of a certain collection of materials that realize a certain form.  The form of the horse is an abstraction from really existing horses, but it allows us to sort horses out from other organisms.  Thus it is a species form. 

Aristotle was later drawn to the view that the real thing is not the individual horse but the species, since the one comes and goes but the latter persists.  What persists over time is more robustly real than what does not.  Still, the form is an abstraction from something really embodied now (and always) whether the embodied thing is a horse or all the horses.  The laws that govern the existence and development of each species are specific; there is nothing more general than the species that controls their natures. 

Plato looked at the problem the other way round.  Form was primary; individual organisms (and presumably populations of organisms) are derivative.  Plato’s view was rooted in an analysis of human intelligence.  When we view a tree from a great distance, it looks very small.  As we approach it, it seems to grow larger.  Near the tree, it is very large indeed.  Yet the tree has not changed; what has changed is our perspective.  There is one thing, the individual tree, behind the shifting perspectives and that one thing is more real than the appearances. 

Plato’s great innovation was to extend this analogically to understand what a species is.  When we move from one tree to another, we recognize both of them as in some sense the same thing‑different examples of tree, just as we recognized the various views of a single tree as the same objective thing.  Perhaps this is because there is one thing behind all the individual trees that our minds are getting a dim grasp of.  That is the idea of a tree and it is more real than individual trees because it is not susceptible to change or decay.  It defines what a tree is for all actual trees and for all trees that may or may not come to be in the future. 

This account has been subject to a lot of derision over the millennia, but Plato’s Socrates was always careful to advance it as provisional.  It is not necessarily this, he would say, but something more or less like this.  It is unclear whether he really believed in the idea of a complex object like a tree, or whether the true ideas were more like mathematical principles. 

It strikes me that Pross’ law of dynamic kinetic stability looks a lot like a Platonic form.  It is not a mere abstraction from actual organisms or populations.  It is a logical rule that (if valid) governed all the emergence of all replicators from the Ur-replicating molecules to the replicating elephants.  It will govern all organisms that emerge in the future. 

Aristotle laid down a very good foundation for biology.  I have argued that modern biology is now coming round to his view on a lot of things.  It may be, however, that Plato’s view was correct at a deeper level. 

Metabolism & Replication

In Chapter 5 of What is Life? Addy Pross considers theories of the origin of life on earth.  There is a lot in here to chew on, but I will focus on a couple of themes.  One is the relationship between historical and ahistorical explanations. 

Historical explanations of abiotic genesis concern the question of how life actually did emerge from inorganic matter.  Ahistorical explanations concern how organically complex systems could have emerged, given some propitious set of circumstances.  If we knew how life did emerge, it would obviously help us understand the physical processes that made such an event possible.  Likewise, if we understood how life could have emerged it would help us determine what to look for in the geological record.  Unfortunately, we don’t have plausible answers to either question.  This reminds me of an old joke.  There are two ways for a man to deal with a woman.  Nobody knows either one of them. 

The second theme is the dichotomy involving metabolism first accounts of the origin of life and replicator first accounts.  Metabolism is the regulation of chemical reactions that makes all organic processes possible.  Materials have to be exchanged with the environment and transformed within cells.  Energy must be acquired and expended for this to happen. 

Metabolism first explanations of life’s origin hold that it begins with a holistic, autocatalytic reaction among inorganic chemicals.  Suppose that molecule A catalyzes molecule B; B catalyzes C; C, D; and D in turn catalyzes A.  You know have a potentially self-sustaining cycle.  Perhaps that’s how life got started: digestion precedes reproduction. 

Replicator first accounts look to molecules that can replicate themselves.  Chain A-B-C can catch an additional A, which catches a B, which catches a C.  At that point the C-A connection breaks, and we have two A-B-C molecules. 

In existing organisms, metabolism and replication support one another.  It is very unclear how either could get going by itself, let alone both of them independently.  If Pross’ survey is fair, no one knows how either could climb “uphill” against the second law in order to produce even the simplest organisms. 

I keep waiting for some sign of how a reductionist account of life might be possible, as Pross promised.  I haven’t got to the end yet, but I am getting rather near it.  Meanwhile, I am sticking with Aristotle.  Life looks to me as if it were ontologically irreducible to the same laws that seem to govern inorganic matter.  I am not arguing for some deus ex machina.  I think, rather, that the appearance of life tells us something about inorganic matter that we could not possibly guess were life not in evidence. 

The Uphill, the Downhill, & the Corner Round

I have been walking up high of late, in the Bighorn Mountains of Wyoming.  I haven’t had much time for reading or for this blog, but I did pick up Addy Pross’ What is Life again tonight. 

Pross argues that there is a law governing “dynamic kinetic systems” (i.e., living organisms) that is analogous to the second law of thermodynamics.  Systems governed by the second law tend toward more chemically, physically, and especially thermal stable states.  Here is the second law:

The entropy of an isolated system never decreases. 

That is to say, an isolated system (one in which no additional energy is supplied) tends toward thermal equilibrium.  An ice cube floating in a glass of scotch represents a highly order system (low entropy): the cold and the warm stuff are neatly separated.  As the ice melts, the system becomes steadily less ordered until it reaches equilibrium (high entropy). 

Systems governed by Pross’ analogous law tend toward more stable replication.  Here is Pross’ new law:

Replicating chemical systems will tend to be transformed from (dynamically) kinetically less stable to (dynamically) kinetically more stable. 

This law would underwrite the course of evolution.  Ants, for example, are very kinetically stable so they remain in their form for a very long period in evolutionary history.  Okay. 

All material transformations, including all that go on in living organisms, are governed by the second law.  Only replicators are governed by the Pross law.  Replicators include all organisms but also replicating molecules like RNA. 

Here is an analogy that I think captures this point.  Consider an alley that slopes slightly downhill.  It ends in an intersection with a second alley that slopes from right to left.  A boulder rolling down the first alley will always go left when it reaches the junction, because boulders always roll downhill. 

A man walking down the first alley is just as much subject to the laws of gravity as the boulder.  Nonetheless, the man may turn right at the junction and walk uphill.  In order to accomplish this task, the solitary walker must expend stored reserves of energy.  If he wants to keep resisting gravity, he will eventually have to replenish his store of energy‑perhaps at the pub atop the hill. 

The existence of uphill walkers, while scrupulously observant of the second law of thermodynamics, seems to depend also on Pross’ second law.  Organisms exist in forms that are more dynamically stable in the environmental niches that they occupy than the forms from which they evolved. 

All that seems reasonable; however, it still seems to me that dynamic stability is a very different kettle of fish from thermodynamic stability.  The latter needs only material and efficient causation, as Aristotle described them.  The latter, this rock bumped that rock and made it move, is underwritten in modern physics by the second law.  Pross’ law of dynamic kinetic stability requires Aristotle’s other two causes: formal (it is this kind of organism) and final (it is up to something). 

The big problem for modern biology is how to reconcile the two pairs of Aristotelian causation.  Pross’ highly critical discussion of theories about the origin of life illustrates this very well. 

Addy Pross' Non-Reductionist Reductionism

To a man who makes shoes, the whole world is made of leather.

That proverb, Chinese in origin if I remember correctly, came to mind tonight as I read more of Addy Pross’ What is Life.  This is one of those beautiful little books that bare the soul of a complex science to amateurs like me.  Pross clearly intends to answer the question in a reductionist fashion.  Biology, he dares to say at one point, is just another branch of chemistry.  Well, the whole world is made of chemicals.  Is biology really reducible to chemistry?  No.

In chapter 4: ‘Stability and Instability’, Pross gives us a tour of basic chemistry.  Chemical reactions move “downhill,” i.e., from states of higher free energy to states of lower free energy.  Sometimes, I gather, they have to get over a “hump,” and in those cases a catalyst is required. 

To employ my own analogy, an avalanche occurs when an unstable sheet of snow begins to slide downhill.  The catalyst may have been some fool yodeling.  The result is a ton of snow on top of a group of helpless skiers, at which point the situation is distressingly more stable than the original state. 

Similarly, a mixture of hydrogen and oxygen gas is higher in energy than water.  It requires a spark (the catalyst) to get the former to combine into the latter, but once the combination has happened water is relatively stable.  Good thing, that.  Two cheers for the second law of thermodynamics. 

Pross then makes a distinction between two kinds of stability: static and dynamic.  Water molecules are statically stable.  Once formed, a molecule of water remains materially what it is pretty much forever.  A river, by contrast, is dynamically stable.  The Thames River has been flowing, he tells us, for around thirty million years—longer than there has been an England.  Yet the water in it is constantly renewed.  As Heraclitus famously observed, you can’t step in the same river twice. 

Self-replicating molecules (e.g., RNA) are capable of achieving dynamic stability.  They form and decay by a constant exchange of basic building blocks.  In one experiment, more robust RNA chains emerged from less robust versions.  All populations of living organisms achieve some measure of dynamic stability.  Cyanobacteria have been in business for more than two billion years!  That makes geography look short sighted. 

Pross goes all in by arguing that the stability achieved by such populations of organisms is more than analogous to the chemical stability governed by the second law of thermodynamics (which just states that isolated molecular systems always go from less stable to more stable states).  He proposes a version of the second law for dynamic stability:

Replicating chemical systems will tend to be transformed from (dynamically) kinetically less stable to (dynamically) kinetically more stable. 

So the elegant symmetry of chemical reactions is reproduced at the level of organic systems.  Thus is biology consumed by chemistry. 

Color me underwhelmed.  Granted, I am only half way through the book; however, it seems to me that dynamic stability just isn’t another version of static stability.  It is a whole ‘nuther’ animal, as we would say down South.  To be sure, everything going on in living organisms has to obey the laws of thermodynamics.  Organisms, however, obey rules that are not derived from those chemical laws.  The stability of populations in a given ecosystem incorporates chemical stability but it is not reducible to the laws of chemistry.  Biology is a more comprehensive science than chemistry.  Sorry. 

Nonetheless, I am very grateful to Pross for this argument.  I think that he has conceded all the ground he hoped to occupy.  I also think that his dynamic stability is pretty much what Aristotle was aiming at in his treatment of the soul.  Aristotle’s soul is precisely the communication of organic form over time by means of a constant exchange of matter (and I would add, energy) with the outside world.  Aristotle was a vehement opponent of reductionism.  Pross’ reductionism isn’t reductionism at all, thus confirming the Philosopher’s point.