The origin of the RNA world

It now seems almost certain that there once was an RNA World, that is a world in which RNA functioned as a genetic polymer and supported enzyme‐like catalytic activity. Peptides may or may not have been important in this world but, if they were, they could not have been made by a process similar to modern day protein synthesis. The origin of the RNA World, therefore, has become a major focus of work on the origin of life. It is possible that RNA was the first replicating molecule that supported a complex “biological” organization. We will first discuss attempts to understand the origin of non‐enzymatic nucleotide synthesis, nucleotide polymerization and polynucleotide replication. We will conclude that despite substantial successes, the obstacles to the prebiotic synthesis and replication of RNA are formidable. In response to the difficulties faced by an “RNA first” scenario, many researchers have begun to investigate simpler systems that might have evolved first, and then “invented” RNA. These efforts have revealed a substantial number of novel polymers that have simpler backbones than that of RNA but still form pairing structures more or less related to RNA. This rapidly advancing field will be reviewed.