  We investigate the evolutionary dynamics of a finite population of RNA
sequences adapting to a neutral fitness landscape. Despite the lack of
differential fitness between viable sequences, we observe typical properties of
adaptive evolution, such as increase of mean fitness over time and punctuated
equilibrium transitions. We discuss the implications of these results for
understanding evolution at high mutation rates, and extend the relevance of the
quasispecies concept to finite populations and time scales. Our results imply
that the quasispecies concept and neutral drift are not complementary concepts,
and that the relative importance of each is determined by a combination of
population size and mutation rate.
