For my third and final comment on the emergence and evolution of early life for the week, I’ll come back to something I mentioned last week: the Royal Society’s Philosophical Transactions in biology has a special discussion series out in the October 29th issue on “Conditions for the emergence of life on the early Earth.”
Among them, I found Joshua Jortner’s summary and reflections piece to be a good place to start in both reading and commenting on the series. Among the areas that Jortner address include (a) a search for a complete definition of life, a la Schrodinger, so as to reduce the discussion to the most fundamental component that had to have developed during abiogenesis itself; (b) the possible roles and mechanisms of self-organization (self-assembly) in both chemical and biological evolutionary processes; (c) refining of our operational and mechanistic descriptions of necessary conditions and constraints for emergent life; and (d) our knowledge of the chemical universe and what pre-organic resources emergent life may have utilized. Both top-down and bottum-up approaches are considered in examining the properties of emergent life as well.
What I found most interesting in Jortner’s review was his discussion of self-organization/assembly in chemical and biological evolution – we can conceive of a modest continuum from self-assembling chemistries to biological processes (even if we don’t know what those steps might be), as it is indeed difficult to establish a criteria for distinguishing self-assembly in chemistry and in biology. Jortner writes:
Eigen (1971, 1996), Yates (1987), Lehn (2002a, b, 2003) and Heckl (2004) advanced and developed the concept of self-organization (self-assembly) and proposed that it resulted in the evolution of biological complex matter, which rests on the elements, as follows: (i) Molecular structure formation of (living and non-living) matter is driven by molecular interactions and operates on a huge diversity of possible strutural combinations. (ii) Prior to the biological evolution, the chemical evolution took place, performing a selection on molecular diversity, leading to the embedment of structural information in chemical entitites. (iii) The implementation of the concepts of molecular information pertains to information storage at the molecular level and the retrieval, transfer and processing of information at the supramolecular level. (iv) The formation of supramolecular structures in induced by molecular recognition (based on non-covalent intermolecular interactions, e.g. H-bonding, van der Waals interactions, charge transfer in donor-acceptor sequences and interactions in ion coordination sites). This includes self-organization, which allows adaptation and design at the supramolecular level. (v) Self-organization involves selection in addition to design at the supramolecular level, and may allow the ‘target-driven selection of the fittest’ (Lehn, 2003), leading to biologically active substances.
Unfortunately, this is almost exclusively at the theoretical level, however – but it seems pretty plausible to me. David Deamer’s contribution to the series of articles expanding on the topics of self-assembly processes in the prebiotic environment as well. Deamer examines the roles of mineral surfaces as organizing events, with an energy source (thermal energy, in multiple geothermal sites in the US and Russia), to examine the fate of a mixture of organic compounds in a natural setting.
Deamer’s experiments don’t accomplish much more than a brief, initial assessment of general chemical conditions. This is inevitable, as one study can’t tell us much, but still intriguing. I hope that Deamer and colleagues follow up this study, in the tradition of Miller and Urey (1953), with many more like it. Perhaps then the theoretical possibilities surrounding abiogenesis and self-organization can be realized and reproduced, with implications for identifying life on other planets.