ΔD and interaction densities between age groups in the original and collapsed protein interaction network. We calculate the ΔD value and the normalized interaction densities for an S. cerevisiae literature curated network, using the taxonomic distribution of EggNOG orthologous groups to determine protein age. Round network nodes correspond to proteins whereas oval network nodes correspond to protein families. Different colors indicate different families. If we remove all edges between paralogs, the ΔD value decreases and the normalized interaction densities for this network show that the strongest effect is in interactions between proteins of age AE/BE. It turns out that mainly interactions between homologous components of the Spliceosome have been removed in this age category. We then continue to remove all edges that are redundant on a protein family level, thus collapsing the network into a network where nodes are no longer proteins, but protein families. We show that ΔD is decreased dramatically in this network. There is neither a specific family nor age group overrepresented among the nodes that have edges removed.