Abstract
AbstractIt is possible to reconsider the origin of biological homochirality in a novel way by formally invoking the standard groupoid approach to stereochemistry in a thermodynamic context that generalizes Landau's spontaneous symmetry breaking arguments. On Earth, limited metabolic free energy may have served as a low temperature analog to 'freeze' the system in the lowest energy state, i.e., the set of simplest homochiral transitive groupoids representing reproductive chemistries. These engaged in a Darwinian competition until a single configuration survived. Subsequent path dependent evolutionary process locked in this initial condition, in spite of increases in available metabolic free energy. Astrobiological outcomes, given higher initial metabolic free energy densities, could well be considerably richer, for example, of mixed chirality. One result would be a complicated distribution of biological chirality across a statistically large sample of extraterrestrial stereochemisty, in marked contrast with published predictions of a racemic average.
Highlights
Amino acids and the backbone of DNA/RNA in living things on Earth are found in only one of the two possible mirrorimage states available to them
Via a statistical thermodynamic construction, that available metabolic energy could well have been the principal determining environmental influence, and that, as a consequence of groupoid symmetries associated with stereochemical structure, a statistically large sampling of extraterrestrial stereochemistries could well be far more complex than Gleiser et al and Wald proposed, i.e., not necessarily racemic on average
At a given level of available metabolic free energy, a particular set of different symmetry schemes can engage in Darwinian competition, leading to subsequent evolutionary lock-in by path dependence. This suggests the possibility of very complicated astrobiological symmetry schemes, if sufficient metabolic free energy is available
Summary
Amino acids and the backbone of DNA/RNA in living things on Earth are found in only one of the two possible mirrorimage states available to them. Attempts to replicate early conditions on Earth – Miller/Urey experiments – always produce ‘racemic’ mixtures having equal amounts of both possible amino acid symmetry forms This conundrum was recently addressed by Gleiser et al (2008), in a computational intensive study adapting Sandars’ (2003) ‘toy model’ of polymerization. Via a statistical thermodynamic construction, that available metabolic energy could well have been the principal determining environmental influence, and that, as a consequence of groupoid symmetries associated with stereochemical structure, a statistically large sampling of extraterrestrial stereochemistries could well be far more complex than Gleiser et al and Wald proposed, i.e., not necessarily racemic on average. 3. Groupoid symmetries and metabolic free energy are, as a consequence of the Darwinian individuality of coding schemes, contexts for, rather than determinants of, the resulting evolutionary processes, including punctuated equilibrium. This suggests the possibility of very complicated astrobiological symmetry schemes, if sufficient metabolic free energy is available
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