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A model of prebiotic replication discussed by Szathmary and Maynard Smith (1997) is refined in accordance with Lifson's (1997) theory on the crucial stages in the origin of animate matter. The refined model accounts for two processes associated with replication: (1) Replicators always decompose at some rate. (2) Replicators deplete their reactants at a rate equal to the rate of their own replication. Consequently, replicators and their reactants are linked by a non-linear feedback process that keeps them within limits and leads them toward a steady state. The model suggests that: (a) All competing replicators, including those which replicate at sub-exponential "parabolic" and super-exponential "hyperbolic" rates, are subject to natural selection. (b) Survival/extinction is determined by positive/negative net-replication irrespective of the mechanism of replication. (c) Being fit/unfit is the consequence of survival/extinction rather than its cause. In other words, natural selection and survival of the fit is the outcome of continual extinction of the unfit., (Copyright 1999 Academic Press.)