The importance of prebiotic chemistry in the RNA world.

In vitro selection experiments have clearly demonstrated that RNA can perform many of the functions necessary to support an RNA world. Moreover, it appears that novel functions could have readily evolved from existing functional RNA molecules. Therefore, diverse molecular ecosystems could potentially have arisen from an initial, small population of functional replicators. These findings suggest that the sequences of living systems may have been determined in part by chance occurrences at origins. Any extrapolations linking sequences (as opposed to functions) obtained in the laboratory to what may have occurred ca. 4 billion years ago are tenuous at best. Thus, perhaps the best way to understand origins is not by examining relatively unconstrained sequence information, but by examining the inherent constraints imposed by prebiotic chemistry.