Figure 2

Models of biological network evolution. Network evolution models can be grouped into three categories depending on how the models 'grow' the network. The green, blue and black nodes represent a selected node in the network, a new node added to the network, and the rest of the network, respectively. Red, gray and black lines represent gained, lost and unchanged interactions, respectively. Orange circles are different clusters, a parameter specific for the crystal growth model. From the starting network, the evolutionary models expand the network in different ways. The steps each model makes can be followed by reading the figure from top to bottom.