Figure 1.

Left-hand side: the state-space for a fitness landscape with three forward-mutations and no back-mutations. Each node, i, is a particular genotype. The replication rate of each genotype is ri. Right-hand side (discussed in Section 6): The state-space can be expanded to include mutational histories. Each two-mutation state is split into 2! = 2 states while the three-mutation state is split into 3! = 6 states. The node is now identified by a vector which conveys the mutational history of a particular path through the landscape.