Metabolic networks have diverse phenotypes in their neighborhood. (A) Cumulative number of novel phenotypes encountered in the neighborhoods of evolving metabolic networks of different sizes and subject to different environmental demands. (B) The average pairwise genotype distance found in populations of evolving metabolic networks. Each population consists of 100 individual metabolic networks. (C) Number of novel phenotypes found in the (1-mutant) neighborhood of random metabolic networks of different size N and subject to different environmental demands S. Each data point is an average over 200 metabolic networks (20 random walks for 10 different sets of environmental demands, with the same number S of required sulfur sources).