Can't get there from here

In the 10 August Nature, Burch and Chao find that two populations of an RNA virus, derived from a single ancestral phage, repeatedly evolve towards different fitness maxima (Nature 2000, 406:625-628). The average fitness of one of the final phage populations is actually lower than that of the starting clone, suggesting that the original individual was at the peak of a local maximum of fitness. The existence of these different and non-overlapping solutions to maximizing fitness suggests that the evolvability of an RNA virus is determined by which advantageous genotypes are within its mutational neighborhood.