VIRAL EVOLUTION Viruses are considered ancient and many are RNA-containing particles. Because they are not cellular, they are not necessarily thought of as life forms by modern scientists. They mutate to a great degree and respond easily to natural selection, resulting in adaptation. Many offspring are made at a time, even though they are not able to reproduce without some kind of host. Mutations get passed to the progeny quite easily. There are many diseases that are caused by viral organisms. Viruses can infect all three domains of life, which may mean they existed at the time of the first universal common ancestor. They have likely arisen many times over the course of history, with new viruses being developed even today. There are three theories about how viruses originated and evolved: 1. Viruses came first. It is possible, because of their simplicity that viruses predated all cellular forms of life. They code for proteins that are completely unrelated to any known cellular proteins but, because they require a host, many do not believe this hypothesis. 2. Degeneracy theory. This is the idea that viruses were once smaller cells that parasitized bigger cells during the course of time. Support for this theory is the presence of larger viruses that have genetics similar to bacteria. It does not explain why small intracellular parasites do not resemble viruses at all. 3. Vagrancy or escape theory. This is the idea that viruses evolved from pieces of DNA that escaped other cells. It doesn’t explain the complexity of viruses in terms of their capsids and other structures. 4. Coevolution theory. This is the theory that says that viruses existed near hydrothermal vents and were able to self-replicate. They evolved at the same time as cells have. 5. Chimeric origins theory. This involves the idea that viruses started out as part of the primordial gene pool, making it a cross between the virus first and escape theories. Viruses mutate to a greater degree than other organisms. This is very true especially for RNA viruses, such as HIV/AIDS. Vital proteins are fold super families that show similar folding even if the DNA sequence is not the same. There are 4 types of fold super families in viruses that correspond with the three domains and one that probably predates the splitting off of the domains. The proteome of a virus suggests it is old indeed.
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