A clade (from Ancient Greek: κλάδος, klados, "branch") is a group of organisms that consists of a common ancestor and all its lineal descendants, and represents a single "branch" on the "tree of life". The common ancestor may be an individual, a population, a species (extinct or extant), and so on right up to a kingdom and further. Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over the last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic. Some of the relationships between organisms that the molecular biology arm of cladistics has revealed are that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria, and multicellular organisms may have evolved from archaea.
1 Etymology 2 History of nomenclature and taxonomy 3 Definitions 4 Clades and phylogenetic trees 5 Terminology 6 In popular culture 7 See also 8 Notes 9 References 10 External links
The term "clade" was coined in 1957 by the biologist
Early phylogenetic tree by Haeckel, 1866. Groups once thought to be more advanced, such as birds ("Aves"), are placed at the top.
The idea of a clade did not exist in pre-Darwinian Linnaean taxonomy,
which was based by necessity only on internal or external
morphological similarities between organisms – although as it
happens, many of the better known animal groups in Linnaeus' original
Gavialidae, Crocodylidae and Alligatoridae are clade names that are here applied to a phylogenetic tree of crocodylians.
A clade is by definition monophyletic, meaning that it contains one
ancestor (which can be an organism, a population, or a species) and
all its descendants.[note 1] The ancestor can be known or
unknown; any and all members of a clade can be extant or extinct.
Clades and phylogenetic trees
Main article: Phylogenetics
Main article: Cladistics
The science that tries to reconstruct phylogenetic trees and thus
discover clades is called phylogenetics or cladistics, the latter term
The relationship between clades can be described in several ways:
A clade located within a clade is said to be nested within that clade. In the diagram, the hominoid clade, i.e. the apes and humans, is nested within the primate clade. Two clades are sisters if they have an immediate common ancestor. In the diagram, lemurs and lorises are sister clades, while humans and tarsiers are not. A clade A is basal to a clade B if A branches off the lineage leading to B before the first branch leading only to members of B. In the adjacent diagram, the strepsirrhine clade, including the lemurs and lorises, is basal to the hominoids, the apes and humans. Some authors have used "basal" differently, using it to mean a clade that is "more primitive" or less species-rich than its sister clade; others consider this usage to be incorrect.
In popular culture
Adaptive radiation Binomial nomenclature Biological classification Cladistics Crown group Monophyly Paraphyly Phylogenetic network Phylogenetic nomenclature Phylogenetics Polyphyly
^ A semantic case has been made that the name should be "holophyletic", but this term has not acquired widespread use. For more information, see holophyly.
^ a b Dupuis, Claude (1984). "Willi Hennig's impact on taxonomic
thought". Annual Review of Ecology and Systematics. 15: 1–24.
^ a b Palmer, Douglas. Evolution: the story of life. University of
California Press: Berkeley. 2009. p. 13
^ Pace, N.R. (May 18, 2006). "Time for a change". Nature. 441 (7091):
289. Bibcode:2006Natur.441..289P. PMID 16710401.
^ Huxley, J. S. (1957). "The three types of evolutionary process".
Nature. 180: 454–455. doi:10.1038/180454a0.
^ a b Huxley, T.H. (1876): Lectures on Evolution. New York Tribune.
Extra. no 36. In Collected Essays IV: pp 46-138 original text w/
^ Brower, Andrew V. Z. (2013). "Willi Hennig at 100". Cladistics.
^ a b ”
Look up clade in Wiktionary, the free dictionary.
Evolving Thoughts: Clade DM Hillis, D Zwickl & R Gutell. "Tree of life". An unrooted cladogram depicting around 3000 species. Phylogenetic systematics, an introductory slide-show on evolutionary trees University of California, Berkeley
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