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 ?
from Peter Greenaway's film, other cladists see phylogenetics today
Cladists are adamant in allowing only derived traits as putative adaptations; characters maintained in their ancestral states need no further explanation (e.g., Coddington 1988, 1990; Baum and Larson 1991; Brooks and McLennan 1991).
The last thirty years of systematics has seen a vigorous controversy between cladists and other systematicists.
For this reason de Queiroz and Gauthier's definition should be called an "autapomorphy-based" definition, in order to distinguish it from "synapomorphy-based" definitions used by cladists (e.g., Nixon & Carpenter, 2000).
The progress of the cladists from a tiny initial core of heretics to the dominant school was documented in David Hull's Science as a Process [1988].
King's disdain for the use of phylogenetic methods overtly manifests itself in this chapter: "The born-again cladists who have not only constructed their own language, think their own logic, and are obsessed with phylogenetic relationships to the exclusion of all else, now require their own species definitions" (p.