Compositional inheritance: comparison of self-assembly and catalysis.

Genetic inheritance in modern cells is due to template-directed replication of nucleic acids. However, the difficulty of prebiotic synthesis of long information-carrying polymers like RNA raises the question of whether some other form of heredity is possible without polymers. As an alternative, the lipid world theory has been proposed, which considers non-covalent assemblies of lipids, such as micelles and vesicles. Assemblies store information in the form of a non-random molecular composition, and this information is passed on when the assemblies divide, i.e. the assemblies show compositional inheritance. Here, we vary several important assumptions of previous lipid world models and show that compositional inheritance is relevant more generally than the context in which it was originally proposed. Our models assume that interaction occurs between nearest neighbour molecules only, and account for spatial segregation of molecules of different types within the assembly. We also draw a distinction between a self-assembly model, in which the composition is determined by mutually favourable interaction energies between the molecules, and a catalytic model, in which the composition is determined by mutually favourable catalysis. We show that compositional inheritance occurs in both models, although the self-assembly case seems more relevant if the molecules are simple lipids. In the case where the assemblies are composed of just two types of molecules, there is a strong analogy with the classic two-allele Moran model from population genetics. This highlights the parallel between compositional inheritance and genetic inheritance.