FIG. 1.

A cladistic tree showing the current vision on primate evolution. The probable germ line introductions of retroviruses and cross-species transmission of PcEV are indicated with arrows. Compared to SERV and PcEV, BaEV was more recently introduced into germ lines of the baboon, gelada, mangabey, and the African green monkey (C. aethiops) (17). The branch of Miopithecus was drawn based upon the genetic evidence of the mitochondrial DNA 12S rRNA gene and SERV proviral genes (19). MYA, million years ago.