Lineage-specific gene duplications were also observed in the primate IR-IFITM genes. The IFITM1 genes from some primate species form an individual sub-group located at the basal position of the primate IR-IFITM sub-clade (Fig. 3) . IFITM1, IFITM2 and IFITM3 have miscellaneous functions including cell adhesion, antiproliferation, tumor suppression and embryonic development. Apart from these biological functions, human IFITM1, IFITM2 and IFITM3 have a broad-spectrum of antiviral activity, possibly brought on by inhibiting the viral entry processes [14, 18, 39] . In particular, human IFITM3 and IFITM2 appear to have higher antiviral activity than IFITM1 [14] and IFITM3 has been reported to inhibit virus replication in other mammals [40] . These findings suggest that after IFITM1 occurrence, the generation of IFITM2 and IFITM3 might be associated with host defense against various virus infections.