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A clade (), also known as a monophyletic group or natural group, is a group of
organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological me ...

organism
s that are
monophyletic 300px, A cladogram of the primates, showing a ''monophyletic'' taxon: ''the simians'' (in yellow); a ''paraphyletic'' taxon: ''the prosimians'' (in cyan, including the red patch); and a ''polyphyletic'' group: ''the night-active primates, i.e., ...
– that is, composed of a
common ancestor Common descent is a concept in evolutionary biology Evolutionary biology is the subfield of biology that studies the evolution, evolutionary processes (natural selection, common descent, speciation) that produced the Biodiversity, diversity ...
and all its
lineal descendants A lineal descendant, in legal usage, is a blood relative in the direct line of descent – the children Biologically, a child (plural children) is a human being between the stages of childbirth, birth and puberty, or between the Development ...
- on a
phylogenetic tree A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree (graph theory), tree showing the evolutionary relationships among va ...

phylogenetic tree
. Rather than the English term, the equivalent
Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation with") is "an appa ...

Latin
term ''cladus'' (plural ''cladi'') is often used in taxonomical literature. The common ancestor may be an individual, a
population Population typically refers the number of people in a single area whether it be a city or town, region, country, or the world. Governments typically quantify the size of the resident population within their jurisdiction by a process called a ...

population
, or a
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
(
extinct Extinction is the termination of a kind of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by ...
or
extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the endling, last individual o ...
). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect
evolutionary history The history of life on Earth traces the processes by which living and fossil organisms evolved, from the earliest emergence of life to the present. Earth formed about 4.5 billion years ago (abbreviated as ''Ga'', for ''Year#SI prefix multiplier ...
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 In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
that are not clades; that is, taxa that are not
monophyletic 300px, A cladogram of the primates, showing a ''monophyletic'' taxon: ''the simians'' (in yellow); a ''paraphyletic'' taxon: ''the prosimians'' (in cyan, including the red patch); and a ''polyphyletic'' group: ''the night-active primates, i.e., ...
. Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that
fungi A fungus (plural: fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as ...

fungi
are closer relatives to animals than they are to plants,
archaea Archaea ( ; singular archaeon ) constitute a domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a pa ...

archaea
are now considered different from
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of biological cell The cell (from Latin ''cella'', meaning "small room") is the basic structural, functional, and biological unit of all known organisms. Cells are the sm ...

bacteria
, and multicellular organisms may have evolved from archaea. The term "clade" is also used with a similar meaning in other fields besides biology, such as
historical linguistics Historical linguistics, also termed diachronic linguistics, is the scientific study of language change Language change is variation over time in a language A language is a structured system of communication used by humans, including s ...
; see Cladistics § In disciplines other than biology.


Etymology

The term "clade" was coined in 1957 by the biologist
Julian Huxley Sir Julian Sorell Huxley (22 June 1887 – 14 February 1975) was an English evolutionary biologist, eugenicist, and internationalist. He was a proponent of natural selection Natural selection is the differential survival and reprodu ...
to refer to the result of
cladogenesis Cladogenesis is an evolutionary splitting of a parent species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defi ...
, the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from
Bernhard Rensch Bernhard Rensch (21 January 1900 – 4 April 1990) was a German evolutionary biologist and ornithologist Ornithology is a branch of zoology that concerns the "methodological study and consequent knowledge of birds with all that relates to the ...
. Many commonly named groups –
rodent Rodents (from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republi ...

rodent
s and
insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

insect
s, for example – are clades because, in each case, the group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s that split off after the end of the period when the clade
Dinosaur Dinosaurs are a diverse group of reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) a ...

Dinosaur
ia stopped being the dominant terrestrial
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
s 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as
chipmunk Chipmunks are small, striped rodents Rodents (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, kn ...

chipmunk
or
ant Ants are eusocial Eusociality (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population i ...

ant
, each of which consists of even smaller clades. The clade "rodent" is in turn included in the mammal,
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
and animal clades.


History of nomenclature and taxonomy

The idea of a clade did not exist in pre-
Darwinian Darwinism is a theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as obser ...

Darwinian
Linnaean taxonomy Linnaean taxonomy can mean either of two related concepts: # the particular form of biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying ...
, 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
Systema Naturae ' (originally in Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic ...
(notably among the
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
groups) do represent clades. The phenomenon of
convergent evolution Convergent evolution is the independent evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; eithe ...
is, however, responsible for many cases where there are misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary
tree of life#REDIRECT Tree of life The tree of life is a fundamental widespread mytheme or archetype in many of the world's mythology, mythologies, religion, religious and philosophy, philosophical traditions. It is closely related to the concept of the s ...
. The publication of Darwin's
theory of evolution Evolution is change in the Heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the Gene expression, expressions of genes that are passed on from parent to offsp ...

theory of evolution
in 1859 gave this view increasing weight.
Thomas Henry Huxley Thomas Henry Huxley (4 May 1825 – 29 June 1895) was an English biologist Francesco Redi, the founder of biology, is recognized to be one of the greatest biologists of all time A biologist is a professional who has specialized knowledge ...

Thomas Henry Huxley
, an early advocate of evolutionary theory, proposed a revised taxonomy based on a concept strongly resembling clades,Huxley, T.H. (1876): Lectures on Evolution. ''New York Tribune''. Extra. no 36. In Collected Essays IV: pp 46-13
original text w/ figures
/ref> although the term ''clade'' itself would not be coined until 1957 by his grandson,
Julian Huxley Sir Julian Sorell Huxley (22 June 1887 – 14 February 1975) was an English evolutionary biologist, eugenicist, and internationalist. He was a proponent of natural selection Natural selection is the differential survival and reprodu ...
. For example, the elder Huxley grouped birds with reptiles, based on fossil evidence. German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of
cladistics Cladistics (; ) is an approach to biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared ch ...

cladistics
. He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on a "ladder", with supposedly more "advanced" organisms at the top.”Evolution 101"
page 10
Understanding Evolution website. University of California, Berkeley. Retrieved 26 February 2016.
Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to
naming Naming is assigning a name A name is a term used for identification by an external observer. They can identify a class or category of things, or a single thing, either uniquely, or within a given context. The entity identified by a name is call ...

naming
, however, this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a
rank Rank is the relative position, value, worth, complexity, power, importance, authority, level, etc. of a person or object within a ranking A ranking is a relationship between a set of items such that, for any two items, the first is either "ranked ...
can be named) because there are not enough ranks to name a long series of nested clades. For these and other reasons,
phylogenetic nomenclature In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, ...
has been developed; it is still controversial. As an example, the full current classification of ''
Anas platyrhynchos The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa, and has been introduced species, introduced to New Zealand, Australia, Peru, Bra ...

Anas platyrhynchos
'' (the mallard duck) has 40 clades from ''
Eukaryota Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...
'' down: see https://species.wikimedia.org/wiki/Anas_platyrhynchos and click on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade
Dracohors Dracohors is a clade of Dinosauriformes, dinosauriform archosaurs that includes dinosaurs and Silesauridae, silesaurids. The oldest known dracohortian is ''Asilisaurus'', dating to about 245 million years ago in the Anisian age of the middle Trias ...

Dracohors
, which was made by
haplology Haplology (from Greek "simple" and , "speech") is defined as the elimination of an entire syllable A syllable is a unit of organization for a sequence of speech sounds. It is typically made up of a syllable nucleus (most often a vowel A ...
from Latin "draco" and "cohors", i.e. "the
dragon A dragon is a large, serpent Serpent or The Serpent may refer to: * Snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote Amniotes (fro ...

dragon
cohort Cohort or cohortes may refer to: * Cohort (educational group), a group of students working together through the same academic curriculum * Cohort (floating point), a set of different encodings of the same numerical value * Cohort (military unit), ...
"; its form with a suffix added should be e.g. "dracohortian".


Definition

A clade is by definition
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...

monophyletic
, meaning that it contains one ancestor (which can be an organism, a population, or a species) and all its descendants. 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''. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct.


Clades and phylogenetic trees

The science that tries to reconstruct phylogenetic trees and thus discover clades is called
phylogenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...

phylogenetics
or
cladistics Cladistics (; ) is an approach to biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared ch ...

cladistics
, the latter term coined by
Ernst Mayr Ernst Walter Mayr (; 5 July 1904 – 3 February 2005) was one of the 20th century's leading evolutionary biologists File:Francesco Redi.jpg, Francesco Redi, the founder of biology, is recognized to be one of the greatest biologists of all ti ...
(1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called ''
cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics Cladistics (, from Greek language, Greek , ''kládos'', "branch") is an approach to Taxonomy (biology), biological classification in whi ...

cladogram
s''; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in
phylogenetic nomenclature In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, ...
: node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions).


Terminology

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 Apes (Hominoidea ) are a branch Image:Tree Leaves.JPG, The branches and leaves of a tree. A branch ( or , ) or tree branch (sometimes referred to in botany as a ramus) is a woody structural member connected to but not part of the central ...

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 Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is neces ...
'' 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 Strepsirrhini or Strepsirhini (; ) is a suborder of primate A primate ( ) (from Latin , from 'prime, first rank') is a eutherian mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting ...

strepsirrhine
/
prosimian Prosimians are a group of primate A primate ( ) (from Latin , from 'prime, first rank') is a eutherian mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class ...
clade, is basal to the
hominoids Apes (Hominoidea ) are a branch Image:Tree Leaves.JPG, The branches and leaves of a tree. A branch ( or , ) or tree branch (sometimes referred to in botany as a ramus) is a woody structural member connected to but not part of the central ...
/
ape Apes (Hominoidea ) are a branch The branches and leaves of a tree. A branch ( or , ) or tree branch (sometimes referred to in botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of bi ...

ape
clade. However, in this example, both Haplorrhine as prosimians should be considered as most basal groupings. It is better to say that the prosimians are the sister group to the rest of the primates. This way one also avoids unintended and misconceived connotations about evolutionary advancement, complexity, diversity, ancestor status, and ancienity e.g. due to impact of sampling diversity and extinction. Basal clades should not be confused with stem groupings, as the latter is associated with paraphyletic or unresolved groupings.


Clade age

The age of a clade is measured as in two ways,
crown '' File:서봉총 금관 금제드리개.jpg, The Seobongchong Golden Crown of Ancient Silla, which is 339th National Treasure of South Korea. It is basically following the standard type of Silla's Crown. It was excavated by Swedish Crown Pri ...
age and stem age. The crown age of a clade refers to the age of the common ancestor of all of the species in the clade. The stem age of a clade refers to the time that that clade descended from an ancestor, common to it and its
sister A sister is a woman A woman is an adult female Female (symbol: ♀) is the sex of an organism, or a part of an organism, that produces non-mobile ovum, ova (egg cells). Barring rare medical conditions, most female mammals, including fema ...
clade. The clade's stem age will be either the same or older than its crown age.


In popular culture

''Clade'' is the title of a novel by
James Bradley James Bradley (1692–1762) was an English astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as star ...
, who chose it both because of its biological meaning and also because of the larger implications of the word. An episode of ''
Elementary In computational complexity theory, the complexity class ELEMENTARY of elementary recursive functions is the union of the classes : \begin \mathsf & = \bigcup_ k\mathsf \\ & = \mathsf\left(2^n\right)\cup\mathsf\left(2^\right)\ ...
'' is titled " Dead Clade Walking" and deals with a case involving a rare fossil.


See also

*
Adaptive radiation In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic inte ...
*
Binomial nomenclature In taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only ...
*
Biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...
*
Cladistics Cladistics (; ) is an approach to biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular ...

Cladistics
*
Crown group In phylogenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, p ...
*
Monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...
*
Paraphyly In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and all its descendants, but excluding a few—typically only one or two—Monophyly, monophyletic subgroup ...
*
Phylogenetic network A phylogenetic network is any graph used to visualize evolutionary relationships (either abstractly or explicitly) between nucleotide sequences, gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to descri ...
*
Phylogenetic nomenclature In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, ...
*
Phylogenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...

Phylogenetics
*
Polyphyly A polyphyletic group or assemblage is a set of organisms, or other evolving elements, that have been grouped together based on characteristics that do not imply that they share a common ancestor that is not also the common ancestor of many othe ...


Notes


References


Bibliography

*


External links


Evolving Thoughts: "Clade"
* DM Hillis, D Zwickl & R Gutell.

. An unrooted cladogram depicting around 3000 species.
"Phylogenetic systematics, an introductory slide-show on evolutionary trees"
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public In public relations Public relations (PR) is the practice of managing and disseminating information from an individual or an organization ...

University of California, Berkeley
{{Evolution Biology terminology Philosophy of biology Phylogenetics 1950s neologisms