(redirected from Sister group)
Also found in: Dictionary, Thesaurus, Medical.
Related to Sister group: Sister taxon


(klədĭs`tĭks) or

phylogenetic systematics

(fī'lōjənĕt`ĭk), an approach to the classificationclassification,
in biology, the systematic categorization of organisms into a coherent scheme. The original purpose of biological classification, or systematics, was to organize the vast number of known plants and animals into categories that could be named, remembered, and
..... Click the link for more information.
 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 DarwinDarwin, Charles Robert,
1809–82, English naturalist, b. Shrewsbury; grandson of Erasmus Darwin and of Josiah Wedgwood. He firmly established the theory of organic evolution known as Darwinism.
..... Click the link for more information.
'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 paleontologypaleontology
[Gr.,= study of early beings], science of the life of past geologic periods based on fossil remains. Knowledge of the existence of fossils dates back at least to the ancient Greeks, who appear to have regarded them as the remains of various mythological creatures.
..... Click the link for more information.
 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 fossilfossil,
remains or imprints of plants or animals preserved from prehistoric times by the operation of natural conditions. Fossils are found in sedimentary rock, asphalt deposits, and coal and sometimes in amber and certain other materials.
..... Click the link for more information.
; datingdating,
the determination of the age of an object, of a natural phenomenon, or of a series of events. There are two basic types of dating methods, relative and absolute.
..... Click the link for more information.


Biology a method of grouping animals that makes use of lines of descent rather than structural similarities
References in periodicals archive ?
Their taxon sample lacked representatives from the beetle suborder Archostemata and the supra-ordinal group Neuropterida (Orders Megaloptera, Neuroptera and Raphidioptera); thought to be the sister group to Coleoptera alone or to Coleoptera + Strepsiptera (Weigmann et al.
The present analysis also resolves Brachyelytrum either as the sister group of Pooideae (a relationship previously detected by Clark et al.
They compared the sequence with those of Neanderthals and modern humans to determine that the Denisovans were a sister group to the Neanderthals, descended from the same ancestral population that had separated earlier from the ancestors of present-day humans.
The finds alter the story of human evolution, suggesting the Neanderthals had an Asian sister group that broke away on their own evolutionary path before dying out.
It ruled Home Secretary Jacqui Smith had acted illegally when she refused to remove the NCRI's sister group, the People's Mojahedin Organisation of Iran (PMOI), from the blacklist.
Brother and sister group Same Difference are 4-1 to be voted off first .
The ARD television debate pits Schroeder and his Greens party ally foreign minister Joschka Fischer against conservative Christian Democrat leader Angela Merkel and Edmund Stoiber, head of her party's Bavariaonly sister group, the Christian Social Union.
He is a founding member of AVIEN and its sister group AVIEWS, in addition to being a member of AVAR (Association of anti Virus Asia Researchers) and a reporter for the WildList organization.
Asilisaurus is part of a sister group to dinosaurs known as silesaurs.
Its sister group Gam-Anon helps families of addicts through the recovery process and offers a vital lifeline.
Bahinia's teeth look enough like those of Eosimias, to place both creatures in the same evolutionary family, which may have been a sister group of the family that includes Amphipithecus, Jaeger's group says.
The ratings also consider the group's ownership by its Superior-rated life/health parent, American National, and the synergies that are being enhanced with its sister group, ANPAC.