Evolutionary origin of protein interactions in seven signaling pathways in study. Protein interactions in the seven signaling pathways in study were divided into “Evo-groups” according to the origins of the corresponding components. A blank in the right side represents that there are no protein originating in this evo-group. For each pathway, the proportion of interactions in each evolution stage to all the interactions in this pathway is shown in different shades of green. A darker green colour stands for a larger proportion.