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In
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
for 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 ...

organism
s, monophyly is the condition of being a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
—that is, a group of
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 mechani ...
composed only 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 ...
(or more precisely an ancestral
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
) and all of its lineal descendants. Monophyletic groups are typically characterised by shared derived characteristics (
synapomorphies 279px, trait states. In phylogenetics, apomorphy and synapomorphy refer to derived characters of a clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are mon ...

synapomorphies
), which distinguish organisms in the clade from other organisms. An equivalent term is holophyly. The word "mono-phyly" means "one-tribe" in Greek. Monophyly is contrasted with
paraphyly 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 ...
and
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 ...
as shown in the second diagram. A ''paraphyletic group'' consists of all of the descendants of a common ancestor minus one or more monophyletic groups. A '' polyphyletic group'' is characterized by
convergent Convergent is an adjective for things that wikt:converge, converge. It is commonly used in mathematics and may refer to: *Convergent boundary, a type of plate tectonic boundary * Convergent (continued fraction) * Convergent evolution * Convergent s ...
features or habits of scientific interest (for example, night-active primates, fruit trees, aquatic insects). The features by which a polyphyletic group is differentiated from others are not inherited from a common ancestor. These definitions have taken some time to be accepted. When the cladistics school of thought became mainstream in the 1960s, several alternative definitions were in use. Indeed,
taxonomist In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxon, taxa (singular ...
s sometimes used terms without defining them, leading to confusion in the early literature, a confusion which persists.Aubert, D. 2015. A formal analysis of phylogenetic terminology: Towards a reconsideration of the current paradigm in systematics. ''Phytoneuron'' 2015-66:1–54. The first diagram shows 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
with two monophyletic groups. The several groups and subgroups are particularly situated as branches of the tree to indicate ordered lineal relationships between all the organisms shown. Further, any group may (or may not) be considered a
taxon 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 mechani ...
by modern
systematics Biological Biology is the natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), o ...
, depending upon the selection of its members in relation to their common ancestor(s); see second and third diagrams.


Etymology

The term ''monophyly'', or ''monophyletic'', derives from the two
Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the diale ...
words (), meaning "alone, only, unique", and (), meaning "genus, species", and refers to the fact that a monophyletic group includes organisms (e.g., genera, species) consisting of all the descendants of a ''unique'' common ancestor. Conversely, the term ''
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 ...
'', or ''polyphyletic'', builds on the ancient Greek prefix (), meaning "many, a lot of", and refers to the fact that a polyphyletic group includes organisms arising from ''multiple'' ancestral sources. By comparison, the term ''
paraphyly 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 ...
'', or ''paraphyletic'', uses the ancient Greek prefix (), meaning "beside, near", and refers to the situation in which one or several monophyletic subgroups are ''left apart'' from all other descendants of a unique common ancestor. That is, a paraphyletic group is ''nearly'' monophyletic, hence the prefix '.


Definitions

On the broadest scale, definitions fall into two groups. *
Willi Hennig Emil Hans Willi Hennig (20 April 1913 – 5 November 1976) was a German German(s) may refer to: Common uses * of or related to Germany * Germans, Germanic ethnic group, citizens of Germany or people of German ancestry * For citizens of German ...

Willi Hennig
(1966:148) defined monophyly as groups based on
synapomorphy 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, phys ...

synapomorphy
(in contrast to paraphyletic groups, based on
symplesiomorphy 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, phy ...
, and polyphyletic groups, based on
convergence Convergence may refer to: Arts and media Literature *Convergence (book series), ''Convergence'' (book series), edited by Ruth Nanda Anshen *Convergence (comics), "Convergence" (comics), two separate story lines published by DC Comics: **A four-par ...
). Some authors have sought to define monophyly to include paraphyly as any two or more groups sharing a common ancestor. However, this broader definition encompasses both monophyletic and paraphyletic groups as defined above. Therefore, most scientists today restrict the term "monophyletic" to refer to groups consisting of all the descendants of one (hypothetical) common ancestor. However, when considering taxonomic groups such as genera and species, the most appropriate nature of their common ancestor is unclear. Assuming that it would be one individual or mating pair is unrealistic for sexually reproducing species, which are by definition interbreeding populations. * Monophyly (also, holophyly) and associated terms are restricted to discussions of taxa, and are not necessarily accurate when used to describe what Hennig called tokogenetic relationships—now referred to as genealogies. Some argue that using a broader definition, such as a species and all its descendants, does not really work to define a genus. The loose definition also fails to recognize the relations of all organisms. According to D. M. Stamos, a satisfactory cladistic definition of a species or genus is impossible because many species (and even genera) may form by "budding" from an existing species, leaving the parent species paraphyletic; or the species or genera may be the result of
hybrid speciation Hybrid speciation is a form of speciation Speciation is the evolution Evolution is change in the Heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the G ...
. * Moreover, the concepts of monophyly,
paraphyly 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 ...
, and
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 ...
have been used in deducing key genes for barcoding of diverse group of species.


See also

*
Clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

Clade
*
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 ...
*
Glossary of scientific naming This is a list of terms and symbols used in scientific names for organisms, and in describing the names. For proper parts of the names themselves, see List of Latin and Greek words commonly used in systematic names. Note that many of the abbreviati ...
*
Monotypic taxon In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...
*
Paraphyly 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 ...
*
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 ...


References


External links

* * * * {{Phylogenetics Phylogenetics de:Kladistik#Verwandtschaftsverhältnisse