Viral evolution
In addition, because viruses typically produce many copies in an infected host, mutated genes can be passed on to many offspring quickly.
[5] It has been suggested that new groups of viruses have repeatedly emerged at all stages of evolution, often through the displacement of ancestral structural and genome replication genes.
A recent study based on comparisons of viral protein folding structures, however, is offering some new evidence.
From an astrobiological perspective, it has therefore been proposed that on celestial bodies such as Mars not only cells but also traces of former virions or viroids should be actively searched for: possible findings of traces of virions in the apparent absence of cells could provide support for the virus-first hypothesis.
These DNA sequences are the remnants of ancient virus genes and genomes that ancestrally 'invaded' the host germline.
These sequences are a valuable source of retrospective evidence about the evolutionary history of viruses, and have given birth to the science of paleovirology.
The mutation rates for many viruses have been measured, and application of a molecular clock allows dates of divergence to be inferred.
[18] Viruses evolve through changes in their RNA (or DNA), some quite rapidly, and the best adapted mutants quickly outnumber their less fit counterparts.
[19] The way viruses reproduce in their host cells makes them particularly susceptible to the genetic changes that help to drive their evolution.
Other viruses change more slowly as mutations in their genes gradually accumulate over time, a process known as antigenic drift.
[24] Through these mechanisms new viruses are constantly emerging and present a continuing challenge in attempts to control the diseases they cause.
[27] The morbilliviruses, for example, are a group of closely related, but distinct viruses that infect a broad range of animals.
[31] Phage T4 may have diverged in evolution from a common ancestor of bacteria and eukaryotes or from an early evolved member of either lineage.
