From prelife to life: how chemical kinetics become evolutionary dynamics.

Life is that which evolves. Living systems are the products of evolutionary processes and can undergo further evolution. A crucial question for the origin of life is the following: when do chemical kinetics become evolutionary dynamics? In this Account, we review properties of "prelife" and discuss the transition from prelife to life. We describe prelife as a chemical system where activated monomers can copolymerize into macromolecules such as RNA. These macromolecules carry information, and their physical and chemical properties depend to a certain extent on their particular sequence of monomers. We consider prelife as a logical precursor of life, where macromolecules are formed by copolymerization, but they cannot replicate. Prelife can undergo "prevolutionary dynamics", including processes such as mutation, selection, and cooperation. Prelife selection, however, is blunt: small differences in rate constants lead to small differences in abundance. Life emerges with the ability of replication. In the resulting evolutionary dynamics, selection is sharp: small differences in rate constants can lead to large differences in abundance. We also study the competition of different "prelives" and find that there can be selection for those systems that ultimately give rise to replication. The transition from prelife to life can occur over an extended period of time. Instead of a single moment that marks the origin of life, prelife may have seeded many attempts for the origin of life. Eventually life takes over and destroys prelife.