The Origin of Life

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      I’m a big fan of the RNA world hypothesis myself.

      The compelling feature of RNA World is that a primordial molecule provided both catalytic power and the ability to propagate its chemical identity over generations. As the catalytic versatility of these primordial RNA molecules increased due to random variation and selection, metabolic complexity began to emerge. From that stage, RNA had roles in both control of metabolism and continuity across generations, as it does today. Depending on which function one prefers to emphasize, these overall models have been called “Control First” or “Genetics First.” In either case, the proliferation of metabolism depended on RNA being there first.

      Adherents have come to call the other possibility “Metabolism First” (though by this they have meant many slightly different things). In our version of Metabolism First, the earliest steps toward life required neither DNA nor RNA, and may not even have involved spatial compartments like cells; the earliest reactions could have occurred in the voids of porous rock, perhaps filled with organic gels deposited as suggested in the Oparin-Haldane model. We believe this early version of metabolism consisted of a series of simple chemical reactions running without the aid of complex enzymes, via the catalytic action of networks of small molecules, perhaps aided by naturally occurring minerals. If the network generated its own constituents—if it was recursive—it could serve as the core of a self-amplifying chemical system subject to selection. We propose that such a system arose and that much of that early core remains as the universal part of modern biochemistry, the reaction sequences shared by all living beings. Further elaborations would have been added to it as cells formed and came under RNA control, and as organisms specialized as participants in more complex ecosystems.

      Networks of synthetic pathways that are recursive and self-catalyzing are widely known in organic chemistry, but they are notorious for generating a mass of side products, which may disrupt the reaction system or simply dilute the reactants, preventing them from accumulating within a pathway. The important feature necessary for chemical selection in such a network, which remains to be demonstrated, is feedback-driven self-pruning of side reactions, resulting in a limited suite of pathways capable of concentrating reagents as metabolism does. The search for such self-pruning is one of the most actively pursued research fronts in Metabolism First research.

      Jesus: Hey, Dad? God: Yes, Son? Jesus: Western civilization followed me home. Can I keep it? God: Certainly not! And put it down this minute--you don't know where it's been! Tom Robbins in Another Roadside Attraction

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