Figure 5

Changes of domain combination networks during evolution. (a) Log-log plot of the degree distribution i.n the domain combination networks of H. sapiens, T. cruzi, S. cerevisiae, A. thaliana, and estimated ancestral species. Dots represent empirical data, and lines and values of γ were obtained by least squares fitting of the cumulative distribution. (b) Difference between domain combination networks of extant species and their union networks. The bold line indicates the values of γ for domain combination networks of extant species, and the dashed line indicates the values for union networks. (c) Changes of domain combination networks and union networks in lineages of S. cerevisiae and H. sapiens during evolution. Bold and dashed lines indicate γ of domain combination networks and union networks, respectively, for estimated ancestors and extant species. It should be noted that the horizontal axis does not indicate the actual time in evolution but the divergence points of each lineage. I to VII indicate the last common ancestors at each divergence point in the H. sapiens lineage and suggest divergence times as follows: I, opisthokonta-plant-protist (1,230 to 1,250 million years ago); II, animal-fungi (965 to 1,050 million years ago); III, deuterostome-protostome (656 to 750 million years ago); IV, mammal-fish (350 to 450 million years ago); V, primate-rodent (80 to 90 million years ago); VI, human-chimpanzee (6 to 7 million years ago); VII, extant human [33-36]. Unexpectedly, the periods between divergence points turned out more or less the same (200 to 300 million years), except for the period between VI and VII.