lunes, 6 de septiembre de 2010

Does the phylogenetic Species Category exist in virus?

Jiménez- Silva C. L.
Universidad Industrial de Santander.
Laboratorio de Sistematica y Biogeografia

Phylogenetic specie is the smallest diagnosable group identified as an ancestor-descendant populations evolving separately from others (Cacraft, 1983). The species can be considered a species level, among all those available in the hierarhy Phylogenetic. Only monophyletic groups can be recognized and formally named taxa. This principle is based on the groups which include all the descendants of a single common ancestor are the only groups with real and natural existence in relation to the evolutionary process (De Luna and Mishler, 1996). The real existence of the species gives genealogical relationships with other group of organisms, their historical behavior, so it is considered that the species are different because they have diverged evolutionarily. Wiley (1978) supports this assertion by suggesting that the species is a single lineage of ancestral-descendant populations, they retain their identity from other lineages and have their own evolutionary tendencies and historical fate.

According to the above and the ontological status of phylogenetic species suggests that instead of viewing species as natural kinds we should think of them as individuals (Ghiselin, 1974 and Hull, 1978). Given the class/individual distinction, Ghiselin and Hull argue that species are individuals, not classes. Their argument assumes that the term ‘species’ is a theoretical term in evolutionary theory, so their argument focuses on the role of ‘species’ in that theory. Here is Hull's version of the argument, which can be dubbed the ‘evolutionary unit argument.’ Since Darwin, species have been considered units of evolution. The "individuals" can you discover connectors or space - time, ie, the status of "individual" at a time and place particle is linked to another state at another time and space site for historical connections (Dupré 2001, Reydon de 2003, y Crane 2004). From this concept and its ontological status is to intend whether the phylogenetic Species exist in virus Category.

The idea that species are individuals has a number of implications. For one, the relationship between an organism and its species is not a member/class relation but a part/whole relation. An organism belongs to a particular species only if it is appropriately causally connected to the other organisms in that species. The organisms of a species must be parts of a single evolving lineage (Hull, 1978). If belonging to a species turns on an organism's insertion in a lineage, then qualitative similarity can be misleading. Two organisms may be very similar morphologically, genetically, and behaviorally, but unless they belong to the same spatiotemporally continuous lineage they cannot belong to the same species.

Virus Species

The international Committee on taxonomy of viruses (ICTV) endorsed the following definition of virus species: a virus species is a polythetic class of viruses that constitutes a lineage of replication and occupies a particular ecological niche (Van Regenmortel & Mahy, 2004). This definition applies for viruses like units called "classes", in a biological classification scheme, an individual organism or a virus can be a member of several abstract classes like a species or a genus. Class membership must be distinguished from the so-called ‘‘part-whole’’ relationship which exists only between two concrete objects, one being a part of the other in the way, for instance, that cells and organs are parts of an organism. It is not possible for a concrete object like a virus to be ‘‘part’’ of an abstract entity like a species (similarly a thought cannot be part of an object). The mixing of logical categories has led to much debate in viral taxonomy (Bos, 2003; Van Regenmortel, 2003).

A class is defined by properties that are constant and immutable. This allows members of such a class to be recognized with absolute certainty since one or more property is necessarily present in every member of the class. Virus families, for instance, are universal classes because they consist of members, all of which share a number of defining properties that are both necessary and sufficient for class membership. Allocating a virus to a family is thus an easy task since a few structural or chemical attributes will suffice to allocate the virus to a particular family. (Van Regenmortel, 2006).

Classifying viruses consists in inventing taxonomic classes like particular families or species and allocating individual viruses to these classes in order to achieve some order whereby similar viral agents are grouped together. The failure to distinguish between real objects such as organisms and viruses and the mental constructions and abstractions needed to build up any classification system has been a fertile source of confusion in taxonomy (Van Regenmortel, 2003) Distinguishing between real, tangible objects like viruses (i.e. concrete individuals) and mental constructs like virus species and genera (i.e. classes) that exist only in the mind is a basic requirement for clear thinking. Although a taxonomic class is defined by properties possessed by concrete objects, it is an abstract, conceptualized collection, i.e. a mental construct.

Returning to the phylogenetic species concept, this raises the real Existence of the species Conceived as discrete units, ie, restricted in space and time. Inconsistent with the vision Referred to by (ICTV), Which Takes the virus species as a class being these, units exist independent and unrestricted that teporales or spatial boundaries. If we encuena that "classes" are abstractions, ie, a mental construct, missing reality. The concept proposed by De Luna and Mishler (1996), on the phylogenetic concept where raise the species as a group with real existence in relation to the natural evolutionary process. The virus species is not wonderful to hang phylogenetic species category and be closer to a nominalist concept (real missing) or phenetic.

Bos, L., 2003. Virus nomenclature; continuing topicality. Arch. Virol. 148, 1235–1246.

Crane, J. 2004, “On the Metaphysics of Species”, Philosophy of Science, 71: 156–173

Cracraft, J. 1983. Species concepts and speciation analysis. Current Ornithology, 1, 159–187.

Dupré, J., 2001, “In Defense of Classification”, Studies in the History and Philosophy of Biology and the Biomedical Sciences, 32: 203–219.

Ghiselin, M., 1974, “A Radical Solution to the Species Problem”, Systematic Zoology, 23: 536–544

Hull, D., 1978, “A Matter of Individuality”, Philosophy of Science, 45: 335–360
Reydon, T., 2003, “Species Are Individuals Or Are They?” Philosophy of Science, 70: 49–56.

Van Regenmortel, M.H.V. and Mahy, B.W.J., 2004. Emerging issues in virus taxonomy. Emerg. Infect. Dis. 10, 8–13.

Van Regenmortel, M.H.V., 2003. Viruses are real, virus species are man-made taxonomic constructions. Arch. Virol. 148, 2481–2488.

Van Regenmortel, M.H.V., 2006. Virologists, taxonomy and the demands of logic. Arch. Virol. 151, in press.

Wiley, E. O.,1978. The evolutionary species concept reconsideres. Syst. Zool., 27: 17-26.

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