Monday, November 02, 2009

Darwin Bicententary Part 28: The Mystery of Life’s Origin, Chapter 8



Continuing my consideration of the three online chapters of Thaxton, Bradley and Olson’s book “The Mystery of Life’s Origin”

As far as chapter 8 is concerned I can cut a long story short; Thaxton, Bradley and Olson calculate the Gibbs free energy associated with the formation of the information bearing bio-polymers essential for life. They come to the conclusion that this free energy is positive - as one would expect from a process involving a polymerization that uses energy to form the required molecular bounds and also to work against entropy in order to secure the right molecular configuration. I can see no fundamental flaw or controversy in TB&O’s conservative estimates. At the end of the chapter 7 they draw the conclusion that life’s information bearing bio-polymers are not going to form in near equilibrium conditions. However, they make this final comment:

In the next chapter we will consider various theoretical models attempting to show how energy flow through the system can be useful in doing the work quantified in this chapter for the polymerization of DNA and protein. Finally, we will examine experimental efforts to accomplish biomacromolecule synthesis.

Thus, TB&O leave us with the same cliff hanger that I felt I was left with in the previous chapter: If life has any chance of forming naturally that chance will only be found, if it is to be found at all, in disequilibrium conditions where there is an energy flowing through a system’s subsystems. Thus, it may be possible that this energy flow can be used to produce organic structures with high Gibbs energies …. or perhaps not.

***

Remark
Chapter 8 has a more promising view of the nature of living configurations than the previous chapter. In the previous chapter (as I said) TB&O seem to conflate complexity and order, but in this chapter they tell us (rightly I believe) that living structures are neither highly ordered nor highly disordered and thus classify as something else. They note that the aperiodicity of bio-polymers resemble the aperiodicity of random arrangements of bases, both of which are very different from the high order of crystals, but TB&O then go on to tell us just what distinguishes bio-polymers from random polymers:

Only certain sequences of letters correspond to sentences, and only certain sequences of sentences correspond to paragraphs, etc. In the same way only certain sequences of amino acids in polypeptides and bases along polynucleotide chains correspond to useful biological functions. Thus, informational macro-molecules may be described as being and in a specified sequence. Orgel notes: “Living organisms are distinguished by their specified complexity. Crystals fail to qualify as living because they lack complexity; mixtures of random polymers fail to qualify because they lack specificity”

However, in my view TB&O are still presenting a rather obscure answer to the question of just where living configurations stand in relation to order and disorder, referring only to a mysterious property they call “specified complexity”. To try and clarify this they say:

Yockey and Wickens develop the same distinction, that "order" is a statistical concept referring to regularity such as could might characterize a series of digits in a number, or the ions of an inorganic crystal. On the other hand, "organization" refers to physical systems and the specific set of spatio-temporal and functional relationships among their parts. Yockey and Wickens note that informational macromolecules have a low degree of order but a high degree of specified complexity. In short, the redundant order of crystals cannot give rise to specified complexity of the kind or magnitude found in biological organization; attempts to relate the two have little future.

In referring to a specific set of spatio-temporal and functional relationships among their parts TB&O may be trying to tell us that informational macromolecules are only one component taken from a wider system, a system that as a whole has a configuration that is both highly ordered and yet highly complex. Taking one component out of that system such as an informational macro molecule, yields something that in a standalone sense is highly disordered and yet when placed within the context of the whole working system it is seen to be part of a highly organized system. Thus “specified complexity” is not a vitalistic property intrinsic to a sequence, but a property bestowed extrinsically by virtue of that the sequence having a well defined and orderly role in a much larger spatio-temporal configuration that certainly does not classify as disordered. “Specifity” is itself a configurational property that comes out of the configurational relations between an informational macromolecule and the spatio-temporal configuration in which it is embedded. Hence, we are back to where we were in my post on chapter 7: Biological structures are configurations in time and space, but they are neither highly ordered or nor highly disordered – they inhabit the space between the extremes of order and disorder. Perhaps the terms “complex organization” best describe these configurations. But although crystals are far too an elementary form of organisation to make a close comparison with life, there is, in spite of what TB&O say, a close relation between the process of crystallization and the conjectured process of evolution. But more about that another time.


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