On the Emergence of RNA

Whether there was an RNA world or not, it is indisputable that there was RNA; when, where, and how is yet to be settled. The question of whether pristine RNA assembled directly from its components (prebiotic clutter), or whether it was a descendant of simpler ancestral system(s), is central to the ongoing debate about RNA's origins. In this review, we look at the facts that suggest RNA is an emergent system and that each component of RNA may have been decided at the level of the oligomer/polymer, and not at the level of the prebiotic clutter, nor at the level of monomer nucleotides. The critical interdependence of RNA's components - ribofuranose, phosphodiester backbone, and purine-pyrimidine base-pairing - for the functioning of RNA seems to be evident, and manifests itself only at the level of the polymer. Based on the power of such nuanced selections at the polymer level, and coupling it with the reality of the prebiotic mixtures at the monomer level, a scenario is presented wherein the combinatorial interactions of diverse prebiotic (systems) chemistry leads first to chimeric-heterogeneous (aka pre-RNA) systems, which can usher in a homogeneous system (RNA), capable of further evolution.