Evolution of fast mutating replicators—RNA viruses and the RNA world

In the last two decades, viruses have become the model system to witness evolution in the laboratory. Large population sizes, high mutation rates, and short generation times are the three features that permit to carry out in vitro experiments under controlled conditions. In this contribution we briefly review a number of recent experiments that open new prospectives in our understanding of molecular evolutionary mechanisms, in their dependence with population dynamics and quasispecies organization, and in the interaction between heterogeneous populations and the environment. One of the possible origins of RNA viruses is a hypothetical RNA world, previous to our present DNA world, where information coding and catalytic functions would be simultaneously performed by RNA molecules.