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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., the lorises and the tarsiers'' (in red) In
cladistics Cladistics (, from Greek language, Greek , ''kládos'', "branch") is an approach to Taxonomy (biology), biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evi ...
for a group of
organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synonym for "Outline of life forms, life form". Organ ...
s, monophyly is the condition of being a
clade A clade (; from grc, , ''klados'', "branch"), 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 descen ...
—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 mechanism ...
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 In biology, a population is a number of all the organisms of the same group or 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 biodiv ...
) and all of its lineal descendants. Monophyletic groups are typically characterised by shared derived characteristics (
synapomorphies
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, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two— monophyletic subgroups. The group is said to be paraphyletic ''with r ...
and
polyphyly 300px, Cladogram of the primates, showing a monophyly (the simians, in yellow), a paraphyly (the prosimians, in cyan, including the red patch), and a polyphyly (the night-active primates, the lorises and the tarsiers, in red). A polyphyletic gr ...
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 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 , based on completely sequenced genomes. A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolution ...

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 by modern systematics#Definition and relation with taxonomy, systematics, 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 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 300px, Cladogram of the primates, showing a monophyly (the simians, in yellow), a paraphyly (the prosimians, in cyan, including the red patch), and a polyphyly (the night-active primates, the lorises and the tarsiers, in red). A polyphyletic gr ...
'', 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, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two— monophyletic subgroups. The group is said to be paraphyletic ''with r ...
'', 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 (1966:148) defined monophyly as groups based on synapomorphy (in contrast to paraphyletic groups, based on symplesiomorphy, and polyphyletic groups, based on convergent evolution, convergence). 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. * Moreover, the concepts of monophyly,
paraphyly In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two— monophyletic subgroups. The group is said to be paraphyletic ''with r ...
, and
polyphyly 300px, Cladogram of the primates, showing a monophyly (the simians, in yellow), a paraphyly (the prosimians, in cyan, including the red patch), and a polyphyly (the night-active primates, the lorises and the tarsiers, in red). A polyphyletic gr ...
have been used in deducing key genes for DNA barcoding, barcoding of diverse group of species.


See also

* Clade * Crown group * Glossary of scientific naming * Monotypic taxon * Paraphyly * Polyphyly


References


External links

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