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Historical contingency and the futility of reductionism: Why chemistry (and biology) is not physics

The views expressed are those of the author and are not necessarily those of Scientific American.


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Even an omniscient being like Dr. Manhattan from Watchmen could not have predicted the result of life's accidents (Image: Christian Fearing Godman)

The reductionist zeitgeist of physics cannot “explain” chemistry any more than “entropy” explains the inexorable march of life from birth to death. It’s important to understand what we mean when we say that physics cannot explain chemistry. Physics of course accounts for chemistry in the trite sense that molecules are composed of atoms. But then physics also “accounts for” human behavior since the brain is ultimately composed of atoms too. Yet we have no clue how to get from atoms to things like jealousy and musical creativity. When we say that A explains B, it usually means there is an unbroken and logical thread of continuity connecting A to B by way of which the properties of A are manifestly demonstrated in B. This physics cannot do even in the highly reductionist realm of chemistry, let alone in “higher” realms like neuroscience and sociology. These days emergence has become a fashionable word that’s often thrown around to describe any kind of complexity, but the emergence of chemical and biological properties that cannot be deduced from their underlying physics is in fact quite real.

There are several reasons why the reductionist approach in science doesn’t always work, but one of the most important ones was alluded to by the physicist and writer Jeremy Bernstein in a Wall Street Journal review of a biography of George Gamow and Max Delbruck:

Some sciences are more unruly than others. Here’s a parable to illustrate what I mean. Imagine that when the first life form appeared there was a super intelligent freak. If this freak had had a complete knowledge of the laws of physics, what could it have predicted? Quite a lot. All atomic nuclei consist of neutrons and protons, and the number of protons determines each element’s chemical nature. Knowing this, the freak could have predicted all the elements that could possibly exist, along with their respective characteristics. Suppose that it also knew all the laws of biology, including the “central dogma,” which explains how genes are expressed as proteins. Even so, it could not have predicted the existence of giraffes, nor even the fact that my brother and I share only half our genes. Both of these are evolutionary accidents. If it had not been for random mutation there would be no giraffes, and my brother and I might have shared all our genes, as male bumblebees do. Biology is not like physics.

This paragraph succinctly drills down to one of the fundamental limitations of physics-based reductionism and it’s a point that applies to chemistry as well. It’s a very important one. The problem is that reductionism cannot account for the role of historical contingency and accident. Even if an all-powerful being could account for all biological scenarios emerging from an initial state of the universe, it could never tell us why one particular scenario is preferred over others. As Bernstein says, evolutionary accidents by definition cannot be predicted from starting conditions because they depend on chance and opportunity.

In addition function can never be uniquely derived from reductionism even if structure is. For instance in his book “Reinventing the Sacred”, the complexity theorist Stuart Kauffman makes a powerful argument that even if one could derive the structure of the human heart from string theory in principle, string theory would never tell us that its most important function is to pump blood. The function of biological organs arose as an adaptive consequence of the countless unpredictable constraints that molded them during evolution. In addition the evolution of both structure and function was a mix-and-match process that depended as much on chance encounters as on strict adaptation. All this can never be captured in a reductionist worldview.

The same principle applies to chemistry. Evolution has fashioned many unique molecules that underpin life’s machinery. The question facing many chemists and especially chemists working on the origins of life is, why this particular molecule and not that one? Here are some more specific conundrums: Why are there only twenty amino acids, why are there alpha amino acids instead of beta or gamma amino acids (which have extra carbon atoms), why is amino acid stereochemistry (molecular “handedness”) L while sugar stereochemistry is D, why does DNA consist of a very specific set of four nucleotides and no other, why did nature choose phosphates in the construction of so many important biomolecules (the chemist Frank Westheimer comes close to answering this question), why does a given protein fold into only one unique functional structure, why is water is the only solvent known to sustain life, and in general why are the myriad small and large molecules of life what they are. In retrospect of course one could provide several arguments for the existence of these molecules based on stability, function and structure but there is no way to predict these parameters prospectively.

The fact is that an all-powerful, super-reductionist freak would have been useless in accounting for the unique existence of life’s chemical precursors. This is because there is nothing in the nature of these molecules which dictates that their presence should have been uniquely determined. For instance we now know from chemical studies that beta and gamma amino acids can also fold into the kind of helix and sheets motifs that are ubiquitous for alpha amino acids. They also have other favorable properties like chemical diversity which might have made them better building blocks compared to alpha amino acids. Yet for some reason they were discarded during evolution. Why? We could come up with several arguments. For instance because of their floppiness, maybe the higher order versions had to pay an unacceptable entropic penalty that could not compensate for their folding propensity. Or maybe a reaction called the Strecker reaction that is thought to produce alpha amino acids could never be superseded by beta amino acid-forming chemical reactions. Or perhaps alpha amino acids shield hydrophobic or water-hating side chains much better than their longer chain counterparts. These are all cogent reasons, and yet I am sure we could find an equal number of arguments against alpha amino acids if we searched hard enough. The truth is that the ultimate failure to find an explanation for the existence of alpha amino acids is a powerful reminder of the importance that chance and circumstance played in the evolution of both biomolecules as well as living organisms. Reductionism does not help us in tracing a path through this random, probabilistic landscape of evolution. The identities of life’s fundamental building blocks were shaped by chance followed by Darwinian natural selection.

This role of contingency and accident is one of the most important reasons why the reduction of chemistry and biology to physics will not work. Even if reductionism could provide us a list of all possible scenarios in chemical and biological evolution, it could never tell us which one would be preferred and for what reason. This is yet another reason why chemistry and biology are not physics.

This is a revised and updated version of a post on The Curious Wavefunction blog.

Ashutosh Jogalekar About the Author: Ashutosh (Ash) Jogalekar is a chemist interested in the history and philosophy of science. He considers science to be a seamless and all-encompassing part of the human experience. Follow on Twitter @curiouswavefn.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. jaspevacek 3:02 pm 03/27/2013

    Physics::chemistry::biology
    Letters::words::paragraphs (or maybe even novels!)

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  2. 2. curiouswavefunction 3:09 pm 03/27/2013

    Yes, that’s a good analogy. The words and paragraphs are made up of letters but they have a meaning of their own that’s more than the sum of the letters.

    Link to this
  3. 3. tmonk 4:44 pm 03/27/2013

    Read a book on chaos theory and after you understand it, you might reconsider.I think it may help you.You posit not testable hypothesis.You only follow the adage-that it is easier to blow up a house than to built one.

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  4. 4. Joetheplumber 7:42 pm 03/27/2013

    But there is a point to saying that our understanding at a larger scale (ex: Biology) is only one of possible outcomes given everything we know at a smaller scale (Chemistry, or Physics).

    Curious that you mention chaos theory, but I think you could say the exact opposite if you read quantum theory. If the act of observing a particular phenomena collapses its probability function, then if we knew everything about the atoms and molecules of a system we would necessarily have altered its larger-scale properties.

    An example of this is plant photosynthesis, where a single photon can travel through multiple channels (http://www.scientificamerican.com/article.cfm?id=when-it-comes-to-photosynthesis-plants-perform-quantum-computation). If we knew everything about the motion of individual particles in the cell we would collapse the wave function and change the nature of the the cell as a whole.

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  5. 5. Cpoov 9:32 pm 03/27/2013

    I suggest that before rejecting reductionism you read Kurt Godel’s incompleteness theorem. It succinctly proves that understanding all of the axioms and rules of a system does not allow predictability in emergent properties. If the universe is mathematical, then it is also impossible to predict outcomes!

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  6. 6. N a g n o s t i c 2:57 am 03/28/2013

    Physics is an ongoing exercise, and has yet to come up with a unified explanation of the Universe. Why does the author regard physics as qualitatively different from chemistry or biology? Physics cannot reliably explain what the local weather will be like a week from now.

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  7. 7. curiouswavefunction 7:47 am 03/28/2013

    Chaos is actually an excellent example of a phenomenon rife with emergent properties.

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  8. 8. Scottcha 1:45 pm 03/28/2013

    Good article, but predicting what will happen is not the same as reductionism, which only purports to describe a given situation in terms of its components. Stanford’s cell simulator describes cellular biology in terms of the constituent chemicals, which is reductionism at its best. But they never claim to have predicted the existence of cells given the basic chemicals. You are talking about the limits of predictions. As Yogi Berra said, predictions are hard to make — especially about the future!

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  9. 9. M Tucker 2:05 pm 03/28/2013

    Ash, you make some very interesting points in your piece. But, do you ever get into any lively discussions with those who study bioenergetics? I have, in the past, heard some claim that the OOL comes under their purview. It is hard to get away from the all encompassing influence of physics.

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  10. 10. alexmenchus 3:29 pm 03/28/2013

    Most of the above comments are weird and irrelevant to the topic of the article. Everyone just want to trot out their pet theories (QM, Goedel’s theorem, chaos etc), without any attempt to understand the science behind what they’re writing about.
    As for the article itself, let me quote the Belgian physicist Jean Bricmont: “Despite frequent claims to the contrary, reductionists are quite happy not to explain carburetors directly in terms of quarks… Many people simply cannot swallow mechanical and reductionist explanations. They need some vital spirit, some teleological principle or some other animist view. Putting philosophical considerations aside, I believe that what we understand well, we understand in mechanical and reductionist terms. There is no such thing as a holist explanation in science.” (‘Science of Chaos or Chaos in Science?’ http://arxiv.org/abs/chao-dyn/9603009).

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  11. 11. K.D. Koratsky 4:22 pm 03/28/2013

    Generally, counter-reductionists are those who do not like the conclusions we humans are presented with. That is, with the existence of simple, universal explanations for much (or especially all) we see around us, we humans lose out freedom to create realities of our choosing.

    When you argue against physics-based reductionism you appear to alter context severely, intentionally or otherwise. I doubt there are many physicists that claim physics “accounts for” chemical or biological phenomena, but there will near universal agreement that physics sets the rules by which the chemical and biological realms must conform.

    In other words, within the hierarchically constructed material world, the chemical realm is built upon, but cannot transcend, the physical realm, and in turn the biological realm is built upon the chemical and physical realms below, and so on. But no higher level of organization can defy the laws of those realms below.

    Meanwhile, the evolutionary realm allows for reduction to the utmost level in the way that counter-reductionists fear the most. For this model both encompasses and dictates what exists and what does not throughout the universe (and other universes if a multiverse exists).

    In other words, the early physical realm was built of the fundamental forces of self-organization, from quarks and gluons up. That which could sustain an existence in one hierarchical form or another amidst the surrounding destructive forces did so. All else in effect perished (e.g., the original antimatter that is thought to have been in equal proportion to the matter that was created did not make the cut).

    Then, when the physical realm finally gave rise to the chemical realm on planets, such as earth, molecular self-organization was subject to the same forces of natural selection. The apparent absences of hafnium and rhenium (numbers 72 and 75 on the periodic table) on earth serves as a good case in point. Based on the basic atomic number sequence it seems we should be able to find these elements, but they apparently do not have what it takes to hold up to the destructive forces that surround them.

    Of course, the extremely diverse yet precarious nature of biological existence leaves it even more vulnerable to selection-based forces. With those at the top of the hierarchy typically being the most vulnerable of all (which explains why mass extinctions strongly disfavor those at the higher levels of the food chain), they are also the most subject to contingent destructive forces

    The role of contingency and accident present no obstacle whatsoever to such reductionism. With the force of self-organization being pervasive, variable destructive events serve to scramble things up more than usual, sometimes giving rise to new biotechnologies as the demise of the old guard can give upstarts a better chance to display their potential.

    Indeed, the history of species is a lesson in the development of solutions to deal with contingency while self-organization gives rise to higher levels of structures–each of which must be evermore adept at dealing with contingency than the last.

    In short, while randomness is an element of evolutionary development, it is not the basis for it. The basis is the combination of universal self-organization which has also given rise to the destructive forces within the universe that oppose self-organization–creating an eternal tug of war with the end result being certain trends within the evolutionary realm (described as selection vector universal, or SVUs, in my book) that have increasingly led to the advancement of species–physical, chemical, and biological.

    Then again, the need to deal with contingency for organismic structures has led them to include random elements (with bell curve dynamics being central) in their adaptive systems in strategic ways–which means randomness as such has also been selected for in such cases.

    K.D. Koratsky, Author of Living With Evolution or Dying Without It: A Guide to Understanding Humanity’s Past, Present, and Future.

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  12. 12. gesimsek 6:21 pm 03/28/2013

    I think the question we must ask is where did this law of evolution come from. Since it is obvious that laws of physics do not explain why there is such law. If laws of physics do not have any purpose the law of evolution with a purpose to adapt and improve should have a different source.

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  13. 13. Dr.d 9:50 pm 03/28/2013

    It is disappointing to see how the radical extremists ‘beliefs’,whether theoreticians or psycho-social practitioners ignore what should be obvious about nature, the human as an actor/protagonist/observer of existential reality and the role language plays in objectively describing the physical sense-phenomenology or explaining the metaphysical relevant elements that resist being framed into a consistent representation in language terms. It both extreme ‘beliefs’ ignore that reality is inside a physical human brain who reports his ‘beliefs’ about quotidian existence in space-time in an adopted language. It is sad to see a theoretician speculating about a mental representation content coded in a language with a total ignorance of the brain structure and function where the language coding (symbols, sentences, etc.)is taking place. No more surprising is to witness the same theorist invoking -tongue in cheek- the magic of spontaneous ‘self organization’ in blatant ignorance of the self-evident laws of nature about systems tending naturally to a minimum of free potential energy thereby ignoring entropy, etc. Trying to reconcile the need for both the phenomenological ontology and the language based epistemolgy as an inseparable epistemontological unit whole is almost as difficult as reconciling classical macrophysics with relativity. The psycho social practitioners likewise ignore that the theorist are in a better perspective to see what may be of no relevance/interest to the practitioner psych therapist, as evident in the confirmed predictive value of the probability prognosis. What both radical views are ignoring is that a physical human brain is at the center of the universe. No human brain, no reality to report The psycho-social practitioner knows that first and foremost he has to keep that human observer healthy, happy and accepted in his ‘pack’ or he will reflexly do it even in a state of unconsciousness. This rationale has been discussed ‘ad nauseam’ and you can see it all in my blog:

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