Figure 4.

The average number of combination partners of group-specific domains. This figure illustrates the difference in the number of combination partners among each group-specific domain in extant species. Each line shows average number of combination partners of group-specific domains in extant species in deuterostomes, invertebrates, fungi, plants, and protists. Euk, Ani, Opi, Deu, Pla, Fun, Lan, Alg, Ins, and Nem refer to eukaryote, animal, opisthokonta, deuterostome, plant, fungus, land plant, alga, insect, and nematode specific domains, respectively. Com indicates the domain shared by eukaryotes and prokaryotes. These are ordered along with the hierarchy of species, which implies the age of domains. Domains in Deu, Fun, Lan, Ins, and Nem also include domains specific to respective subgroups of them because these numbers are very small. Species* in the graph of Protists refers to each group of protists such as alveolata and euglenozoa. The outlier in Deuterostomes (C. familiaris) reflects the incompleteness of its its genome sequence, and the difference among distributions for three plants reflect their distant evolutionary relationship. The hierarchical classification of groups and the numbers of their specific domains are shown in Figure 3, and all information for respective species and group-specific domains is provided in Additional data files 2 to 6.