History, Reviews, Science.

The physical sublety of life

I recently re-read portions Erwin Schroedinger's amazing little book What is Life?, which was a post-war stimulus for a number of physicists to switch from physics to biology and look hard for a physical understanding of living organisms.

This book is famous for exploring the idea of a molecular code, provided by an ‘aperiodic solid,’ that would control a living cell and provide the basis for the highly repeatable life cycles observed for all living organisms.  Of course, this is a high level and ‘blind’ description of today’s understanding of the role of DNA.  This is seemingly contrary to the acquired and perceived wisdom of physicists and chemists, whose deep and precise explanations of the behavior of atoms and molecules rests on an order that comes from an underlying atomic disorder, always expressed and understood statistically in terms of massive numbers of atoms which move ceaselessly.  Here a few molecules are postulated to provide order for a vast collection of molecules called a biological cell.

Schrödinger published this nearly ten years before the structure of DNA was characterized. Some of the people who gave birth to molecular biology, many of them initially physicists, claim to have been stimulated to move into the field by this book, such as Watson, Crick, Perutz, and Wilkins, Cavendish scientists all.  The book was intended as at most a heuristic exploration of the application of physical models to living systems, and given the responses of early molecular biologists, this is indeed how it was received. 

Schrödinger, the great quantum physicist, is at his best with his accessible explanation for the application of the 2nd Law of Thermodynamics to living systems and a thought-provoking discussion on the statistical vs. the dynamical approach to physical modeling.


Erwin Schrödinger. PD-US.


Schrödinger’s discussion on this subject touches on the differences between the energetics of simple solids and collections of atoms, whose interactions are governed by the Laws of Thermodynamics, which he labels ‘order from disorder‘, and living organisms, which show a persistent pattern of ‘order from order.’  The Laws of Thermodynamics are applicable to all systems, living and non-living.  In a solution of simple chemicals, these laws provide clear and reliable predictions.  In a living cell, they provide some basic understanding, but much else is going on in a cell than in a solution of simple chemicals.  Living systems are governed by additional order not ordinarily found in the beaker:  Control systems of proteinaceous enzymes themselves controlled by the cell’s master molecules, the nucleic acids.

-Oregon Scribbler,

Typical anti-evolution application of 2nd Law of Thermodynamics. Oregon Scribbler.


Consider the well-worn argument of anti-evolutionists that the 2nd Law of Thermodynamics makes impossible the evolutionary model of change.  Two different and apparently related arguments are usually presented:  The first is that the known physical laws governing chemical energetics, the Laws of Thermodynamics, show that far too much energy and time would be required to simply randomly form a complex collection of biological molecules that are needed to make up the first precursor living, functioning, and reproducing cell from which all other living organisms would evolve.   The second is that once living and reproducing cells were present, the same energetic limitations would preclude a viable model of mutation of genetic material in sufficient quantity or in sufficient time to allow for the evolution of a precursor life form into all of the known living organisms, past and present.

The first argument addresses what scientists today refer to as abiogenesis, the development of living organisms from non-living material or systems.  The anti-evolution argument has real merit here, and in fact the nascent field of abiogenesis is little more than highly and sometimes intriguingly speculative ‘science’:  scientists doing work in that field generally acknowledge this, and make similar statistical arguments themselves regarding the great complexity of forming a living cell strictly from inanimate sources.  The old chicken-or-the-egg problem remains intractable:  In Schrödinger’s terms this can be stated as the construction of the first system that exhibits ‘order from order‘ from a general environment dominated by ‘order from disorder‘ behavior.

But anti-evolutionist’s attempts to extend this argument to living and evolving organisms is much more problematic.  Living cells, in order to metabolize and reproduce, must in every second of their existence seemingly violate these basic energetic rules, rules based on the underlying random and ceaseless thermal atomic motion.  Every living cell exists and thrives despite the physical expectation that collections of atoms cannot by the Laws of Thermodynamics alone be energetically efficient enough to take energy from outside the cell and use it to maintain the high order needed for every second of metabolic activity that is the signature of life.  

So how does a cell beat the odds, so to speak?  In a word, enzymes.  Living cells are highly ordered from inception, and maintain the requisite orderliness by taking in energy from the environment (directly from the Sun, or indirectly via the food chain) and very efficiently using that energy by catalyzing the thousands of biochemical reactions needed to sustain life. Catalysis is the well-characterized chemical phenomenon whereby a ‘helper’ atom or molecule, when present, vastly speeds up a chemical reaction without itself becoming part of the end product of the reaction.  In biochemistry, these catalysts are folded proteins called enzymes, or short RNA molecules called ribozymes.

This enzymatic process is controlled by a cell’s genetic material, in a very complex and still only partly characterized process of genetic expression in a cell. This catalytic world has much more efficiency and thereby more capacity for genomic change necessary for the evolution of populations than the simplistic arguments based on the 2nd Law of Thermodynamics suggested by anti-evolutionists would allow.

Anti-evolutionists who blithely make this argument don’t seem to understand that if it is true, it would apply more generally to the entirety of a living cell, rendering it incapable of carrying on the activity of life.  If their application of the 2nd Law of Thermodynamics to biological evolution, as opposed to abiogenesis, was accurate, there would be no one alive to argue about it:  They and the rest of life would not exist.

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