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Origin of life? Scientists Rule Out 'Metabolism First' Theory
January 10, 2010
Phenomenica
A new study has rejected the long-held theory that the origin of life stems from a system of self-catalytic molecules capable of experiencing Darwinian evolution without the need of RNA, DNA and their replication.
The research, led by Mauro Santos of Universitat Autònoma de Barcelona, has demonstrated through the analysis of what some researchers name "compound genomes", these chemical networks cannot be considered evolutionary units as they lose properties which are essential for evolution when they reach a critical size and greater level of complexity.
The scientific theories on the origin of life revolve around two main ideas: one focuses on genetics -- with RNA or DNA replication as an essential condition for Darwinian evolution to take place -- and the other on metabolism.
It is clear that both situations must have begun with simple organic molecules formed by prebiotic processes.
The point in which these two theories differ is that the replication of RNA or DNA molecules is a far too complex process which requires a correct combination of monomers within the polymers to produce a molecular chain resulting from the replication, say scientists.
Until now no plausible chemical explanation exists for how these processes occurred. In addition, defenders of the second theory argue that the processes needed for evolution to take place depend on primordial metabolism.
The researchers in this study nevertheless reveal that these systems are incapable of undergoing a Darwinian evolution. For the first time a rigorous analysis was carried out to study the supposed evolution of these molecular networks using a combination of numerical and analytical simulations and network analysis approximations.
Their research demonstrated that the dynamics of molecular compound populations which divide after having reached a critical size do not evolve, since during this process the compounds lose properties which are essential for Darwinian evolution.
The researchers concluded this fundamental limitation of "compound genomes" should lead to caution towards theories that set metabolism first as the origin as life, even though former metabolic systems could have offered a stable habitat in which primitive polymers such as RNA could have evolved.
They say that different prebiotic Earth scenarios can be considered. However, the basic property of life as a system capable of undergoing Darwinian evolution began when genetic information was finally stored and transmitted such as occurs in nucleotide polymers (RNA and DNA).
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