Time scale of Poxvirus evolution

Unlike in vertebrates and RNA viruses, the molecular clock has not been estimated so far for DNA viruses. The extended conserved central region (102 kb) of the orthopoxvirus genome and the DNA polymerase gene (3 kb) were analyzed in viruses representing several genera of the family Poxviridae. Analysis was based on the known dating of the variola virus (VARV) transfer from Western Africa to South America and previous data on the phylogenetic relatedness of modern West African and South American isolates of VARV. The mutation accumulation rate was for the first time estimated for these DNA viruses at (0.9–1.2) × 10^?6 substitutions per site per year. It was assumed that poxviruses diverged from an ancestor approximately 500,000 years ago to form the recent species and that the ancestor of the genus Orthopoxvirus emerged approximately 300,000 years ago and gave origin to the modern species approximately 14,000 years ago.