Marginally stable chemical systems as precursors of life.

Current research on the origin of life aims at finding the simplest entity that can undergo spontaneous Darwinian evolution toward increasing replication efficiency. Here I consider some of the models of self-replicating molecular systems, and I show that they exhibit a distinct feature, namely, an infinity of stationary states forming a continuous curve; i.e., they are only marginally stable. I show that, in marginally stable chemical systems, thermodynamic fluctuations induce a drift directed toward increasing replication efficiency. This drift represents a form of evolution, taking place slowly, cooperatively, in macroscopic volumes of water.