ABSTRACT
In this chapter, we discuss the role of RNA in the major transitions that could have occurred during the origin and early evolution of life on the Earth. The ability of RNA to be a catalyst and the existence of ribozymes are important clues to how life developed. We discuss the RNA world hypothesis, and then, with examples of modern-day and laboratory-derived ribozymes, we discuss how RNA can evolve and search sequence space to discover new functions. Because RNA is a linear polymer of consecutive nucleotides, a network of related sequences can exist for any genotype. We describe the evolutionary pressures that exist to move a population of RNAs through this network and consider how similar networks can interact. Both point mutations and recombination contribute to the means by which new genotypes can emerge and evolve. Overall, these considerations depict a series of transitions that retell the history of how chemistry became biology.
