Evolution in open systems: bistability and the origin of molecular asymmetry.

Abstract

MOLECULAR asymmetry in biological systems is believed to have evolved, through some autocatalytic process (including enzymes and macromolecules) characterized by absolute stereospecificity, from one parent asymmetric molecule formed by some very rare event occurring only once during evolution1, or alternatively through the induction of asymmetry by optically active crystals, circularly polarized light or by a hypothetical local or general physical inequality of left and right2. However, there is an alternative “cybernetic” mechanism, a spontaneous generation and self-propagation of asymmetry as a consequence of kinetic bistability in the course of the evolution of open systems. Open systems can exist in a stable steady state, where parameters remain constant in time, although the system is not in thermodynamic equilibrium3. Far from thermodynamic equilibrium, such systems have an intrinsic tendency to evolve into instabilities and dissipative structures4. In special conditions there may be more than one possible steady state. A necessary condition for this is the presence of at least one feedback loop4. An autocatalytic5 chemical reaction in a flow reactor6–9 is a simple chemical example of such a system; it can exist in a non-reacting state (without autocatalyst) or in a reacting state. In the non-reacting (“extinct”) state, inoculation with the autocatalyst will induce an instability resulting in a transition (“chemical mutation”10) into the reacting state.