Over the expanse of evolutionary time, the genomes of virtually every animal species have become riddled with these proviral sequences, the so-called endogenous retroviruses (ERVs). Most ERV sequences have been degraded by the accumulation of mutations but are still recognizable as retroviral in origin. The human genome alone contains hundreds of thousands of HERVs (Human ERVs), outnumbering our genes. Extrapolate these numbers across the entirety of the animal kingdom, and collectively ERV loci may well comprise a “fossil” collection numbering in the hundreds of millions of specimens.
Find out more about paleovirology, the study of extinct viruses, at Small Things Considered. Link -via Boing Boing