Getting from an RNA world to modern cells just got a little easier

Our understanding of the early steps in the evolution of life is hampered by a Catch‐22: Darwinian selection leading to longer genomes requires as prerequisite increased replicative fidelity. Yet a genome at capacity cannot increase in size; it will be catastrophically mutated out of existence if fidelity has not already increased. Traditionally the problem has been considered for genotypes but can be downsized if multiple genotypes specify the same phenotype. Kun and colleagues1 put empirical meat on theoretical bone by analysing ribozyme mutagenesis data, concluding that modest replication fidelities could permit a primordial genome with up to 100 genes. BioEssays 28: 105–108, 2006. © 2006 Wiley periodicals, Inc.