THE FORCES DRIVING MOLECULAR EVOLUTION

Competitive replication among RNA or DNA molecules at linear and non-l inear rates of propagation has been reviewed from the perspective of a recent physicochemical model of molecular evolution and the findings are applied to pre-replication, prebiotic and biological evolution. A system of competitively replicating molecules was seen to follow a pat h of least action on both its thermodynamic and kinetic branch, in evo lving toward steady state kinetics and equilibrium for the nucleotide condensation reaction. Stable and unstable states of coexistence, betw een competing molecular species, arise at nonlinear rates of propagati on, and they derive from an equilibrium between kinetic forces. The de novo formation of self-replicating RNA molecules involves damping of these scalar forces, error tolerance and RNA driven strand separation. Increases in sequence complexity in the transition to self-replicatio n does not exceed the free energy dissipated in RNA synthesis. Retrodi ction of metabolic pathways and phylogenetic evidence point to the occ urrence of three pre-replication metabolic systems, driven by autocata lytic C-fixation cycles. Thermodynamic and kinetic factors led to the replication takeover. Biological evolution was found to involve resour ce capture, in addition to competition for a shared resource. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.