Effects of Neutral Selection on the Evolution of Molecular Species

We introduce a new model of evolution on a fitness landscape processing a tunable degree of neutrality. The model allows us to study the general properties of molecular species undergoing neutral evolution. We find that a number of phenomena seen in RNA sequence-structure maps are present also in our general model. Examples are the occurrence of "common" structures which occupy a fraction of the genotype space which tends to unity as the length of the genotype increases, and the formation of percolating neutral networks which cover the genotype space in such a way that a member of such a network can be found within a small radius of any point in the space. We also describe a network can be found within a small radius of any point in the space. We also describe a number of new phenomena which appear to be general properties of naturally evolving systems. In particular, we show that the maximum fitness attained during the adaptive walk of a population evolving on such a fitness landscape increases with an increasing degree of neutrality, and is directly related to the fitness of the most fit percolating network.