The evolution of human papillomavirus (HPV) types predicts carcinogenicity. The evolution of papillomaviruses is very slow. Tissue specificity, natural history, and carcinogenicity of HPVs are generally consistent with evolutionary relationships. HPV species in the alpha genus (left) infect mucosa, including the anogenital region and the oral cavity. The phylogenetic tree is based on the alignment of concatenated early and late open reading frames as described in Schiffman et al. (20). HPV types in the blue clade (which comprises species α1, α8, α10, and α13) include the HPV types that cause genital warts. HPV types in the green clade (which comprises species α2, α3, α4, and α15) cause commensal infections. HPV types in the red clade (which comprises species α5, α6, α7, α9, and α11) (shown in detail on the right) are associated to different degrees with cervical cancer and cervical intraepithelial neoplasia grade 3. The eight types that most commonly cause cervical cancer everywhere in the world belong to species alpha-9 or, to a lesser extent, to alpha-7. The carcinogen group for each HPV type is according to the International Agency for Research on Cancer (19): group 1 = carcinogenic, group 2A = probably carcinogenic, and group 2B = possibly carcinogenic.