The Role of Retroviruses in Cellular Evolution

Retroviruses originated over 400 million years ago, and were present throughout most or all of vertebrate evolution. Integration of a provirus into host-cell DNA is an essential step in the retrovirus replication cycle, which can produce persistent infections and chronic diseases that reduce host fitness. Integration is also inherently mutagenic, with a spectrum of phenotypic consequences, and if integration occurs in the germline, the result is an endogenous retrovirus (ERV) that can be passed on to the organism’s descendants. Thus, retroviruses have a dual role in vertebrate evolution, as agents of selection and as sources of genetic and phenotypic variation.