Self-Organization of Macromolecules

Evolution seems to occur in bursts, separated by relatively quiescent periods. From the simpler prokaryotes (organisms without a nuclear membrane around their genetic material) the fully nucleated eukaryote came—but how rapidly? Prokaryotic evolution was preceded by the chemical evolution leading to polynucleotide self-replication, although no fossils are recognized from that period. Auto-catalysis must have been required at that stage. But autocatalytic chemical processes are not simple, in vitro. Today there is enormous structural variability of biopolymers and polynucleotide synthesis can occur on several different levels of increasing efficiency (faster rates). Systems for these syntheses are complex; models of them have ten-dimensional kinetic equation systems, even in fitting data from simple experiments. Under restricted conditions, these equations show stationarity of relative polynucleotide concentrations. However, a relatively simple equation system predicts an early phase of exponential growth followed by linear growth of polynucleotide concentrations. Very general equations governing the growth of polynucleotide concentrations can be analyzed, but that analysis is much simplified by studying systems having constant total nucleotide concentration. With increasing degrees of realism in the simulations, models predict that: (1) the polynucleotide having the largest excess of synthesis over degradation becomes dominant; (2) if only a few copying errors are made, a whole “quasispecies” of polynucleotides comes to dominate; (3) if many errors are made, the system merely drifts, thus limiting the length of duplicatable polymers; (4) other results will be obtained, such as symmetric self-replication, hypercyclic cooperation, “frozen accidents,” Eigen and Schuster’s elementary hypercycle, the gamelike dynamics of Maynard Smith, or Lotka-Volterra dynamics.