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Cladistics is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived characteristics (synapomorphies) that are not present in more distant groups and ancestors. However, from an empirical perspective, common ancestors are inferences based on a cladistic hypothesis of relationships of taxa whose character states can be observed. Theoretically, a last common ancestor and all its descendants constitute a (minimal) clade. Importantly, all descendants stay in their overarching ancestral clade. For example, if the terms worms or fishes were used within a strict cladistic framework, these terms would include humans. Many of these terms are normally used paraphyletically, outside of cladistics, e.g. as a 'grade', which are fruitless to precisely delineate, especially when including extinct species. Radiation results in the generation of new subclades by bifurcation, but in practice sexual hybridization may blur very closely related groupings.
In biological phylogenetics, a clade, also known as a monophyletic group or natural group, is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. In the taxonomical literature, sometimes the Latin form cladus is used rather than the English form.
In biology, phylogenetics is the study of the evolutionary history and relationships among or within groups of organisms. These relationships are determined by phylogenetic inference methods that focus on observed heritable traits, such as DNA sequences, protein amino acid sequences, or morphology. The result of such an analysis is a phylogenetic tree—a diagram containing a hypothesis of relationships that reflects the evolutionary history of a group of organisms.
In taxonomy, a grouping is paraphyletic if it consists of the grouping's last common ancestor and most of its descendants, but excludes a few monophyletic subgroups. The grouping is said to be paraphyletic with respect to the excluded subgroups. In contrast, a monophyletic grouping includes a common ancestor and all of its descendants. The terms are commonly used in phylogenetics and in the tree model of historical linguistics. Paraphyletic groups are identified by a combination of synapomorphies and symplesiomorphies. If many subgroups are missing from the named group, it is said to be polyparaphyletic.
Systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees. Phylogenies have two components: branching order and branch length. Phylogenetic trees of species and higher taxa are used to study the evolution of traits and the distribution of organisms (biogeography). Systematics, in other words, is used to understand the evolutionary history of life on Earth.
Emil Hans Willi Hennig was a German biologist and zoologist who is considered the founder of phylogenetic systematics, otherwise known as cladistics. In 1945 as a prisoner of war, Hennig began work on his theory of cladistics, which he published in German in 1950, with a substantially revised English translation published in 1966. With his works on evolution and systematics he revolutionised the view of the natural order of beings. As a taxonomist, he specialised in dipterans.
A cladogram is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to descendants, nor does it show how much they have changed, so many differing evolutionary trees can be consistent with the same cladogram. A cladogram uses lines that branch off in different directions ending at a clade, a group of organisms with a last common ancestor. There are many shapes of cladograms but they all have lines that branch off from other lines. The lines can be traced back to where they branch off. These branching off points represent a hypothetical ancestor which can be inferred to exhibit the traits shared among the terminal taxa above it. This hypothetical ancestor might then provide clues about the order of evolution of various features, adaptation, and other evolutionary narratives about ancestors. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational phylogenetics are now very commonly used in the generation of cladograms, either on their own or in combination with morphology.
The International Code of Phylogenetic Nomenclature, known as the PhyloCode for short, is a formal set of rules governing phylogenetic nomenclature. Its current version is specifically designed to regulate the naming of clades, leaving the governance of species names up to the rank-based nomenclature codes.
In cladistics or phylogenetics, an outgroup is a more distantly related group of organisms that serves as a reference group when determining the evolutionary relationships of the ingroup, the set of organisms under study, and is distinct from sociological outgroups. The outgroup is used as a point of comparison for the ingroup and specifically allows for the phylogeny to be rooted. Because the polarity (direction) of character change can be determined only on a rooted phylogeny, the choice of outgroup is essential for understanding the evolution of traits along a phylogeny.
In phylogenetics, long branch attraction (LBA) is a form of systematic error whereby distantly related lineages are incorrectly inferred to be closely related. LBA arises when the amount of molecular or morphological change accumulated within a lineage is sufficient to cause that lineage to appear similar to another long-branched lineage, solely because they have both undergone a large amount of change, rather than because they are related by descent. Such bias is more common when the overall divergence of some taxa results in long branches within a phylogeny. Long branches are often attracted to the base of a phylogenetic tree, because the lineage included to represent an outgroup is often also long-branched. The frequency of true LBA is unclear and often debated, and some authors view it as untestable and therefore irrelevant to empirical phylogenetic inference. Although often viewed as a failing of parsimony-based methodology, LBA could in principle result from a variety of scenarios and be inferred under multiple analytical paradigms.
Jacques Armand Gauthier is an American vertebrate paleontologist, comparative morphologist, and systematist, and one of the founders of the use of cladistics in biology.
Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional approach, in which taxon names are defined by a type, which can be a specimen or a taxon of lower rank, and a description in words. Phylogenetic nomenclature is currently regulated by the International Code of Phylogenetic Nomenclature (PhyloCode).
Wayne Paul Maddison, is a professor and Canada Research Chair at the departments of zoology and botany at the University of British Columbia, and the Director of the Spencer Entomological Collection at the Beaty Biodiversity Museum.
Kirk J. Fitzhugh is the curator at the Natural History Museum of Los Angeles County, a position he has held since 1990. His research focuses on the systematics of polychaetes and on the philosophical foundations of evolutionary theory. Fitzhugh is a critic of DNA barcoding methods as a technical substitute for systematics. He attends Willi Hennig Society meetings where he has argued that "synapomorphy as evidence does not meet the scientific standard of independence...a particularly serious challenge to phylogenetic systematics, because it denies that the most severely tested and least disconfirmed cladogram can also maximize explanatory power." His graduate supervisor was V. A. Funk, from the U.S. National Herbarium, National Museum of Natural History, Smithsonian Institution MRC. He completed his doctoral thesis on Systematics and phylogeny of Sabellid polychaetes in 1988 while he was a research scientist at the LA County museum He married a lawyer named Nancy E. Gold in 1989.
The Society of Systematic Biologists (SSB) started as the Society of Systematic Zoology in 1947. A temporary constitution was adopted at the first meeting on 28 December 1947. The updated "biologists" organization become incorporated on August 9, 1971.
The Systematics Association is a charitable organisation based in the UK founded in 1937 for the promotion of the study of systematics and taxonomy. It publishes research, organises conferences, and provides competitive research funds for systematics research.
Quentin Duane Wheeler is an American entomologist, taxonomist, author and newspaper columnist, and is the founding director of the International Institute for Species Exploration. He was the fourth President of the State University of New York College of Environmental Science and Forestry, in Syracuse, New York until his retirement. Other positions have included: professor of entomology at Cornell University and Arizona State University; Keeper and Head of Entomology at the Natural History Museum in London; and Director of the Division of Environmental Biology at the National Science Foundation.
Transformed cladistics, also known as pattern cladistics is an epistemological approach to the cladistic method of phylogenetic inference and classification that makes no a priori assumptions about common ancestry. It was advocated by Norman Platnick, Colin Patterson, Ronald Brady and others in the 1980s, but has few modern proponents. The book, Foundations of Systematics and Biogeography by David Williams and Malte Ebach provides a thoughtful history of the origins of this point of view.
Kevin de Queiroz is a vertebrate, evolutionary, and systematic biologist. He has worked in the phylogenetics and evolutionary biology of squamate reptiles, the development of a unified species concept and of a phylogenetic approach to biological nomenclature, and the philosophy of systematic biology.
Joel Lester Cracraft, is an American paleontologist and ornithologist. He received a PhD in 1969 from Columbia University.
References
- 1 2 "Willi Hennig Society". Willi Hennig Society. Retrieved August 2, 2012.
- ↑ Carpenter, J. M. (1986). "Robust cladistification: Report on the fifth annual meeting of the Willi Hennig Society". Cladistics. 2 (2): 187–194. doi:10.1111/j.1096-0031.1986.tb00451.x. S2CID 83823801.
- ↑ Schuh, R. T. (1981). "Willi Hennig Society: Report of First Annual Meeting". Syst. Zool. 30 (1): 76–81. doi:10.2307/2992305. JSTOR 2992305.
- ↑ Felsenstein, J. (2001). "The troubled growth of statistical phylogenetics" (PDF). Syst. Biol. 50 (4): 465–467. doi: 10.1080/10635150119297 . PMID 12116645.
- ↑ Fink, S. V. (1982). "Report on the Second Annual Meeting of the Willi Hennig Society". Systematic Zoology. 31 (2): 180–197. JSTOR 2413036.
- ↑ Funk, V. A. (2001). "SSZ 1970-1989: A view of the years of conflict". Syst. Biol. 50 (2): 153–155. doi:10.1093/sysbio/50.2.153. JSTOR 3070835. PMID 12116925.
- ↑ Hennig, Willi (1999). Phylogenetic Systematics - translated by Davis, D. & Zangerl, R. University of Illinois Press. p. 280. ISBN 978-0252068140.
- ↑ Claridge, M. F. (1995). "Primary Title: Introducing systematics Agenda 2000". Biodiversity and Conservation. 4 (5): 451–454. doi:10.1007/BF00056335. S2CID 32782553.
- ↑ Butler, D.; Gee, H.; Macilwain, C. (1998). "Museum research comes off list of endangered species". Nature. 394 (6689): 115–117. Bibcode:1998Natur.394..115B. doi:10.1038/28009. S2CID 5474202.
- ↑ Daly, M.; Herendeen, P. S.; Guralnick, R. P.; Westneat, M. W.; McDade, L. (2012). "Systematics Agenda 2020: The Mission Evolves". Syst Biol. 61 (4): 549–552. doi:10.1093/sysbio/sys044. PMC 3376376 . PMID 22492540.
- ↑ "Cladistics". doi:10.1111/(ISSN)1096-0031.
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