  Biological evolution in a sequence space with random fitnesses is studied
within Eigen's quasispecies model. A strong selection limit is employed, in
which the population resides at a single sequence at all times. Evolutionary
trajectories start at a randomly chosen sequence and proceed to the global
fitness maximum through a small number of intermittent jumps. The distribution
of the total evolution time displays a universal power law tail with exponent
-2. Simulations show that the evolutionary dynamics is very well represented by
a simplified shell model, in which the sub-populations at local fitness maxima
grow independently. The shell model allows for highly efficient simulations,
and provides a simple geometric picture of the evolutionary trajectories.
