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Project Progress

A universal aspect of living systems on Earth is their homochirality: Life uses dextrorotary sugars and levorotary amino acids. The reasons for this are hotly debated and not close to being settled. However, the leading idea is that autocatalytic reactions grew exponentially fast at the origin of life, and whatever chiral symmetry breaking was accidentally present became amplified subsequently. For this argument to be viable, it has to be shown that autocatalysis can indeed amplify homochirality. Secondly, one must consider the potentially confounding effects of spatial extension, which could give rise to spatial heterogeneity in the pattern of chiral symmetry breaking. We have succeeded in providing an improved formulation of the famous homochirality model of F.C. Frank, one that removes an unphysical requirement and moreover includes the inevitable and important stochasticity arising from chemical reactions. The mathematics shows that homochirality can arise by a previously unnoticed mechanism – the stabilization of homochirality into states that are least affected by noise. This mechanism is different from potential-based mechanisms for bistability, because it is the noise itself that generates the symmetry breaking. We have also succeeded in formulating this stochastic model with spatial extension. Our preliminary result is that the autocatalytic mechanism for homochirality does not seem to be stable in space: life would self-organize into local domains where homochirality was present, but of a different sign in neighbouring domains. If our ongoing research confirms this result, then it will cast doubt on the autocatalytic proposal for homochirality.