Mean evolutionary rates for bins of proteins with different number of interactions. Shown for each graph is the range of the number protein-protein interactions for each bin (x-axis) and the mean evolutionary rate (substitutions per site) for each bin (y-axis). (a) S. cerevisiae and S. pombe orthologs. (b) H. pylori strain 26695 and H. pyori strain J99 orthologs. (c) H. pylori strain 26695 and C. jejuni orthologs.