RNA: the first replicator?

We do not know what the earliest ancestral replicating molecule was; however, several lines of evidence point to RNA.

• RNA is simpler than DNA, being single stranded.

• 'Prebiotic soup' experiments have more readily yielded the nucleotide U than T.

• In the 1980s it was discovered that RNA can act not only as a replicator but also as an enzyme (in which capacity it is called a ribozyme), catalyzing certain kinds of reaction that contribute to replication. No fully autocatalytic replicating RNA system -one in which the RNA acts as a ribozyme to catalyze its won replication - has (at the time of writing) been discovered; but such a system would require no fundamentally new properties beyond what has already been found.

Research in this area is moving rapidly; the technology was developed in 1994 to select for new ribozymes in vitro , and the discovery of a fully autocatalytic system is probably only a matter of time.