Evolution
Since they are much smaller than the tiniest colloidal fragments forming sedimentary rocks that fossilize plants and animals, viruses do not create fossils in the conventional sense. However, endogenous viral elements (EVEs) are found in the genomes of many organisms. These DNA strands are the surviving parts of ancient virus genomes and genes that once "invaded" the host germline. Hundreds to thousands of sequences derived from ancient retroviruses, for instance, can be found in the genomes of most vertebrate species. In addition to giving rise to paleobiology, these sequences are a valuable source of retroactive data regarding the evolutionary history of viruses. When two viruses of similar strains infect the same cell, many viruses (such as the influenza A virus) can "shuffle" their genes with the genes of the other viruses. New and more virulent strains frequently emerge due to this phenomenon, known as genetic shift. Other viruses evolve more slowly as antigenic drift or the accumulation of mutations in their genes over time occurs.Transmission
Evolution has allowed viruses to maintain their infectious existence. The ability to spread has been given to viruses by their quick mutation rates and natural selection. The evolution of virus transmission is one way that viruses have been able to spread. The virus can pick up a new host using the:- Transmission by droplet—transmitted through bodily fluids.
- It was spread through the air or airborne transmission.
- Waterborne transmission involves an agent moving from a host, contaminating the water, and ingesting a new host.
- Vector transmission: information is taken in by a carrier and delivered to a new host.
