Evidence for the additions of clustered interacting nodes during the evolution of protein interaction networks from network motifs

Table 2 Constraints of topologies on the co-origins of motif constituents

The total number	Age homogeneity rate (%) ^a		Age homogeneity ratio ^b
	Real network	Average of 1000 random networks
5611	43.11	29.51	1.46
50536	22.60	10.12	2.23
2620	39.58	10.05	3.94
400510	10.03	3.63	2.77
331797	13.71	3.65	3.76
4746	16.90	3.65	4.63
55692	24.53	3.64	6.74
5748	35.11	3.66	9.58
1315	39.92	3.61	11.05
504884	11.37	1.32	8.64
4237	12.20	1.33	9.19
399622	13.39	1.33	10.05
71141	18.79	1.34	14.01
9125	31.93	1.34	23.90
632	40.82	1.28	31.87

^a Age homogeneity rate is referred to as the fraction of the motifs whose constituents are of the same age class. ^b Age homogeneity ratio is defined as the ratio of the age homogeneity rate of the real network to its random expectation which is calculated as the average age homogeneity rate of the 1000 random networks (the fourth column). ^c Considering the length limitation of the table, here we only show six representative kinds of topology for 5-motif. Actually for all possible topologies of 5-motifs, the results are consistent (additional file 1: Table S10).

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