The three current hypotheses for virus origin, e.g. Reduction hypothesis (regressive hypothesis) Nasir A, Kim KM, Caetano-Anollés G. Viral evolution: Primordial cellular origins and late adaptation to parasitism. The fundamental premise of the regressive hypothesis for the origin of viruses is viruses were once independent cells that became dependent on host cells The plaque assay for determining viral titer measures only infectious viral particles This states that some viruses may have evolved from bits of RNA or DNA that escaped from the genes of larger organisms . However, many components of how this process might have occurred are a mystery. One major contention against the hypothesis is that it fails to explain why even the smallest of cellular parasites do not resemble viruses in any way. A virus is a tiny infectious agent that reproduces inside the cells of living hosts.When infected, the host cell is forced to rapidly produce thousands of identical copies of the original virus. Therefore, choices (F), (G), and (H) are all eliminated. Uses Video Gaming for Military Training. The discovery of which of the following living organisms would provide the most support for the Regressive Evolution Hypothesis?F. A third hypothesis posits a system of self-replication similar to that of other self-replicating molecules, probably evolving alongside the cells they rely on as hosts; studies of some plant pathogens support this hypothesis. The fundamental premise of the coevolution hypothesis for the origin of viruses is. Adopted a LibreTexts for your class? Also known as the escape hypothesis and the vagrancy hypothesis, it also hypothesizes that the escape could have come from plasmids or transposons. But there are problems with all of these hypotheses: the regressive hypothesis did not explain why even the smallest of cellular parasites do not resemble viruses in any way. Viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. However, many components of how this process might have occurred are a mystery. Virus (venom-name given) are the small microorganisms with different structures and forms. They lend support to this “regressive” hypothesis, as their dependence on parasitism is likely to have caused the loss of genes that enabled them to survive outside a cell. The regressive, or reduction, hypothesis asserts that viruses are remnants of cellular organisms; The virus-first hypothesis states that viruses coevolved with their current cellular hosts. However, many components of how this process might have occurred are a mystery. Viruses have short generation times, and many—in particular RNA viruses—have relatively high mutation rates (on the order of one point mutation or more per genome per round of replication). The evolutionary origin of the SVG coating … Escapist or progressive hypothesis. Under the hypothesis, there was a chimeric scenario in which different types of primordial and selfish replicons resulted in the emergence of viruses by recruiting host proteins for virus formation. Extracellular parasites with DNA resembling a known virus G. Extracellular parasites with unique RNA nucleotide sequences H. Intracellular parasites with DNA resembling a known virus J. Intracellular parasites with unique RNA nucleotide sequences For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. Microbiologists generally agree that certain bacteria that are obligate intracellular parasites, like Chlamydia … The evolution of viruses is speculative as they do not fossilize; biochemical and genetic information is used to create virus histories. The hypothesis of origin of "leglessness" in snakes, because it posits LOSS of characters as homology. viruses may have originated as mobile genetic elements such as transposons or plasmids (small, circular DNA fragments). One possible hypothesis, called devolution or the regressive hypothesis, proposes to explain the origin of viruses by suggesting that viruses evolved from free-living cells. HIV/AIDS. The Regressive Hypothesis In contrast to the progressive process just described, viruses may have originated via a regressive, or reductive, process. Devolution or regressive hypothesis. Nonetheless, several hypotheses or theories have been built on these basic assumptions. Although biologists have accumulated a significant amount of knowledge about how present-day viruses evolve, much less is known about how viruses originated in the first place. Mob Genet Elements. The virus-first hypothesis has been revived in the last decade by Wolfram Zillig who suggested that viruses originated in the prebiotic word, using the primitive soup as a host (Prangishvili et al., 2001). CURRENT HYPOTHESIS OF ORIGIN OF VIRUS • 3 hypotheses 1. The food source also gave rise to lipid-like molecules that could self-assemble into vesicles that, in turn, could enclose or envelope replicons. This regressive or reduction hypothesis states that the existing viruses evolved from more complex, possibly free-living cellular organisms (independent life forms) over time through a loss of essential functional genes . Below are the two modern hypotheses of the origins of viruses: Also called the bubble theory, the coevolution hypothesis presents a scenario before the emergence of life forms. Viruses are ancients. DNA is not mentioned as a component of the earliest virus particles in this hypothesis… The emerging field called virus molecular systematics attempts to do just that through comparisons of sequenced genetic material. viruses were once independent cells that became dependent on host cells. Three types of hypotheses have been proposed to explain the origin of viruses: the “ virus first ” hypothesis in which viruses originated before cells, the “ regression hypothesis ”, in which cells or proto-cells evolved into virions by regressive evolution and the “ escape hypothesis ”, in which fragments of cellular genomes (either from prokaryotes or eukaryotes) became infectious. The emerging field of paleovirology has provided a set of methodologies for studying the evolution of ancient viruses. Henceforth, there were two paths of development for replicons due to evolutionary pressure: merging with a vesicle, which eventually gave rise to cells, and entering the vesicle to use its resources until depletion, which gave rise to viruses. Note that this assertion was based on the analyses of the evolution of the replicative and structural modules of viruses. Note that although they do not form physical fossils, some of them leave their genetic materials within the DNA of the hosts they infected. [ "article:topic", "authorname:boundless", "showtoc:no" ], https://bio.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fbio.libretexts.org%2FBookshelves%2FIntroductory_and_General_Biology%2FBook%253A_General_Biology_(Boundless)%2F21%253A_Viruses%2F21.1%253A_Viral_Evolution_Morphology_and_Classification%2F21.1B%253A_Evolution_of_Viruses, 21.1A: Discovery and Detection of Viruses, information contact us at info@libretexts.org, status page at https://status.libretexts.org, Describe the difficulties in determining the origin of viruses. In my research I found three theories of virus origin; the theories include the progressive hypothesis, the regressive hypothesis, and the virus-first hypothesis. Regressive, or reduction hypothesis: Viruses started as independent organisms that became parasites. However, a considerable number of scientists have rejected the virus-first hypotheses for the simplest reason that it violates one of the basic definitions or characteristics of a virus. However, many components of how this process might have occurred are a mystery. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. The discovery of which of the following living organisms would provide the most support for the Regressive Evolution Hypothesis?F. Viruses infecting cells from the three domains of life, Archaea, Bacteria and Eukarya, share homologous features, suggesting that viruses originated very early in the evolution of life. Escape hypothesis (progressive hypothesis) 3. In my research I found three theories of virus origin; the theories include the progressive hypothesis, the regressive hypothesis, and the virus-first hypothesis. How Does the ECHELON Surveillance System Works? 2009. The Progressive Hypothesis. We strongly believe that research and consultancy form the backbone of informed decisions and actions. Viruses: • Defination: • An infective agent that typically consists of a nucleic acid molecule in a protein coat, is too small to be seen by light microscopy, and is able to multiply only within the living cells of a host. There are now two modern hypotheses that are under consideration. The chimeric-origin hypothesis also asserts that new groups of viruses have repeatedly emerged at all stages of the evolution of life, often through the displacement of ancestral structural and genome replication genes. “Origin of Viruses: Primordial Replicators Recruiting Capsids from Hosts.”, Nasir, A., Kim, K. M., and Caetano-Anollés, G. 2012. Effectiveness in Drugs and Vaccines, Effectiveness of L-carnitine in Weight Loss and Muscle Building, Studies: Effects of Chronic Stress in the Brain, Precision Medicine vs. Personalized Medicine: The Difference, Cytokine Storm: Definition, Causes, and Effects, ECHELON Program Explained: Global Surveillance Network, Role of Elvis Presley in Popularizing Polio Vaccination, Explainer: Why Did The Great Leap Forward Fail, Why and How the U.S. However, many components of how this process might have occurred are a mystery. Note that plasmids are DNA that can move between cells while transposons are DNA bits that replicate and move within the genes of a cell. Essentially, it argues that viruses predated primitive forms of life, and they contributed to the emergence of cellular life. Virus SARS-CoV-2, a member of the subfamily Coronavirinae Virus classification (unranked): Virus Realms Duplodnaviria Monodnaviria Riboviria Varidnaviria A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. The regressive hypothesis asserts that viruses are remnants of cellular organisms that adapted themselves to a parasitic replication strategy. While most findings agree that viruses don’t have a single common ancestor, scholars have yet to find one hypothesis about virus origins that is fully accepted in the field. A position paper by M. Krupovic, V. V. Dolja, and E. V. Koonin published in 2019 presented and proposed the chimeric-origin hypothesis. Another popular hypothesis that seeks to explain the origin of the virus is the cellular origin theory. Esploro embraces the responsibility of doing business that benefits the customers and serves the greater interests of the community. The Regressive Hypothesis Viruses may have evolved from more complex, possibly free living organisms that lost genetic information over time, as they adapted a parasitic approach to replication. B. At the heart of our business is a pronounced commitment to empower business, organizations, and individuals through our informative contents. 5. Devolution or regressive hypothesis. This is known as Regressive hypothesis. The Regressive Hypothesis, also known as the Reduction Hypothesis, states viruses are the remains of the cellular organisms; The Virus-First Hypothesis says that the viruses evolved simultaneously with their cellular hosts. The researchers have now sequenced all or part of the DNA and/or RNA of the known varieties of viruses, including the largest (pox- and herpesviruses) and the smallest (gemini- and other ssDNA viruses). The devolution or the regressive hypothesis suggests that viruses evolved from free-living cells. There’s the progressive and regressive hypothesis–both assuming cells existed before the very first virus. Have questions or comments? However, tracing their origins through conventional paleoethology is impossible because they do not form physical fossils. However, many components of how this process might have occurred remain a mystery. It also explains that the replication modules of viruses came from the primordial genetic pool. Another hypothesis puts forward the idea that viruses may have once been small cells that became parasites of larger cells. As technology advances, scientists may develop and refine further hypotheses to explain the origin of viruses. The regressive hypothesis ('degeneration hypothesis', (Dimmock, Easton, and Leppard 2007) or 'reduction hypothesis': (Mahy and Regenmortel 2009) they come from small cells that previously parasitized larger cells. Extracellular parasites with DNA resembling a known virus G. Extracellular parasites with unique RNA nucleotide sequences H. Intracellular parasites with DNA resembling a known virus J. Intracellular parasites with unique RNA nucleotide sequences And definitely the can be spreads by many means. A. The escape hypothesis did not explain the complex capsids and other structures on virus particles. 5. Efficacy vs. Nicolae Sfetcu: What came first: the virus or the cell? Over time, they shed genes that did not help them parasitize, and … Legal. A. One such hypothesis, the “devolution” or the regressive hypothesis, suggests that viruses evolved from free-living cells, or from intracellular prokaryotic parasites. Regressive hypothesis Viruses might have evolved in a regressive way, which states that virus might have been smaller cells that parasitized larger cells and as they gain parasitism the genetic information that was not necessary for replication was lost or it was lost before they develop parasitism and loss of genetic material associated with reproduction might have been a driving force in the adaptation of … This hypothesis proposes to explain the origin of viruses by suggesting that viruses evolved from free-living cells. However, viruses do not fossilize, so researchers must conjecture by investigating how today’s viruses evolve and by using biochemical and genetic information to create speculative virus histories. Investigations of their evolution have revealed many characteristics that allow them to thrive, including their high mutation rate. Profolus operates as a media and publication unit of Esploro Company. “Viral Evolution: Primordial Cellular Origins and Late Adaptation to Parasitism.”. Krupovic, M., Dolja, V. V., and Koonin, E. V. 2019. The escapist or the progressive hypothesis suggests that viruses originated from RNA and DNA molecules that escaped from a host cell. The second model is called the regressive hypothesis, sometimes also called the degeneracy hypothesis or reduction hypothesis. Eventually, it was unable to replicate independently and adopted an obligate parasitic lifestyle for multiplication. Regressive Hypothesis Another hypothesis puts forward the idea that viruses may have once been small cells that became parasites of larger cells. The new branch of virus molecular systematics helps in understanding the distant relationships of and origins of many important groups of viruses. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. This hypothesis proposes to explain the origin of viruses by suggesting that viruses evolved from free-living cells. A second hypothesis (called escapist or the progressive hypothesis) accounts for viruses having either an RNA or a DNA genome and suggests that viruses originated from RNA and DNA molecules that escaped from a host cell. Traditionally, theories of viral evolution belong to one of three groups: the virus-first hypothesis, the regression hypothesis and the escaped genes hypothesis. Genetic sequencing of modern viruses and hosts have helped draw and connect interrelationships between different groups, subfamilies, and families of viruses.