Distances, sizes and superessential reactions found in random minimal metabolic networks subject to different environmental demands.(A) Distribution of genotype distance between pairs of minimal metabolic networks viable under the same environmental demands. (B) Average size (closed circles) and average number of superessential reactions (open circles) of 1000 minimal metabolic networks as a function of environmental demands S on a network. The number of superessential reactions was obtained by counting the number of reactions common to 100 minimal metabolic networks generated with the same set of sulfur sources. For each data point, we used 10 different sets of sulfur sources with size S. Error bars represent the standard deviations of the distributions.