cladistics


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cladistics

cladistics (klədĭsˈtĭks) or phylogenetic systematics (fīˌlōjənĕtˈĭk), an approach to the classification of living things in which organisms are defined and grouped by the possession of one or more shared characteristics (called characters) that are derived from a common ancestor and that were not present in any ancestral group (as envisioned by Charles Darwin's idea of “descent with modification”). Developed by Willi Hennig, a German entomologist, in the 1950s, it is a method of reconstructing evolutionary relationships that emphasizes the importance of descent and common ancestry rather than chronology.

Cladistics places species in a group, or clade, based on a shared character. Within a clade, species that share other characters unique to them are grouped together, and so on, until a cladogram (a branching diagram that resembles a family tree) is assembled. For example, all vertebrates make up a clade; all tetrapods (vertebrates that have four limbs with wrists, ankles, toes, and fingers) form their own clade within the vertebrate clade. In this example the vertebrate clade would be considered “primitive” and the tetrapod clade “derived” or “advanced.” In living creatures genetic characters or behaviors as well as more obvious anatomical features might be considered in assembling a cladogram. In paleontology the characters are necessarily skeletal.

Cladistics is especially significant in paleontology, as it points out gaps in the fossil evidence. It is also felt to be more objective than fossil study, which of necessity extrapolates from a limited number of finds that may or may not be representative of the whole.

See also fossil; dating.

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cladistics

Biology a method of grouping animals that makes use of lines of descent rather than structural similarities
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
The spider infraorder Mygalomorphae (Araneae): cladistics and systematics.
Although it is inappropriate to classify soil solely on the basis of parent material, climate and topography (Basinski 1959; Marbut 1951), it does illustrate the potential of cladistics in identifying homologies (i.e.
de Pinna, M.G.G., 1991, "Concepts and Tests of Homology in the Cladistic Paradigm", Cladistics, vol.
Pretarsal structure in the Miridae (Hemiptera) with a cladistic analysis of relationships within the family.
The typology-based system developed by Troll (1964) and Weberling (Weberling, 1965, 1989) has proved to be useful for describing inflorescences (Rua, 1999) as well as for providing characters for cladistic analyses (Nickol, 1995; Rua & Aliscioni, 2002; Tortosa et al., 2004; Reinheimer, 2007).
While cladistics will classify the most parsimonious evolutionary relationship between species by forcing the data into a tree-shaped diagram, it will not provide an appreciation of the relationship between closely related species.
Again and again, he expresses reservations about conventional biology, from cladistics to population genetics.
Appendix 6, "Taxonomy, classification, and the debate about Cladistics" is the best description for students and laymen of Cladistics and of the conflict between Cladistics and traditional classification that this reviewer has seen.
Lepidoptery in Johnson and Coates's brilliant and lucid book unfolds as a history involving extraordinarily interesting people--the Hungarian Zsolt Balint's troubles with European museum nabobs resembles a Nabokovian short story--as well as many adjustments of scientific theories over the past twenty-five years: continental drift, cladistics, and the evolutionary branching of species.