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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 , ''kládos'', "branch") is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships ...
for a group of
organism In biology, an organism (from Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the properties of life. It is a synonym for "life form". Organisms are classified by taxonomy into groups such as ...
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 monophyletic—that is, composed of a common ancestor and all its lineal descendants - on a phylogenetic tree. R ...
—that is, a group of
taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name ...
composed only of a
common ancestor Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the last universal commo ...
(or more precisely an ancestral
population In biology, a population is a number of all the organisms of the same group or species who live in a particular geographical area and are capable of interbreeding. The area of a sexual population is the area where inter-breeding is possible bet ...
) and all of its lineal descendants. Monophyletic groups are typically characterised by shared derived characteristics (
synapomorphies 279px, trait states.">Phenotypic trait">trait states. In phylogenetics, apomorphy and synapomorphy refer to derived characters of a clade: characters or traits that are derived from ancestral characters over evolutionary history. An apomorphy is a c ...

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 resp ...
and
polyphyly 300px, Cladogram of the primates, showing a monophyly (the simians, in yellow), a paraphyly">monophyly.html" style="text-decoration: none;"class="mw-redirect" title="primates, showing a monophyly">primates, showing a monophyly (the simians, ...
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 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 series Converge ...
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 (circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given ...
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 evolutionary rela ...

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, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name ...
by modern
systematics Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic trees ...
, 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 used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic period ...
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">monophyly.html" style="text-decoration: none;"class="mw-redirect" title="primates, showing a monophyly">primates, showing a monophyly (the simians, ...
'', 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 resp ...
'', 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 biologist who is considered the founder of phylogenetic systematics, also known as cladistics. In 1945 as a prisoner of war, Hennig began work on his theory of cladistics, whi ...

Willi Hennig
(1966:148) defined monophyly as groups based on
synapomorphy 279px, trait states.">Phenotypic trait">trait states. In phylogenetics, apomorphy and synapomorphy refer to derived characters of a clade: characters or traits that are derived from ancestral characters over evolutionary history. An apomorphy is a c ...

synapomorphy
(in contrast to paraphyletic groups, based on
symplesiomorphy File:Cladogram imaginary birds.jpg, Imaginary cladogram. The yellow mask is a plesiomorphy for each living masked species, because it is ancestral. It is also a symplesiomorphy for them. But for the four living species as a whole, it is an apomorp ...
, and polyphyletic groups, based on
convergence Convergence may refer to: Arts and media Literature *''Convergence'' (book series), edited by Ruth Nanda Anshen *"Convergence" (comics), two separate story lines published by DC Comics: **A four-part crossover storyline that united the four Weirdo ...
). 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 where hybridization between two different species leads to a new species, reproductively isolated from the parent species. Previously, reproductive isolation between two species and their parents was thoug ...
. * 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 resp ...
, and
polyphyly 300px, Cladogram of the primates, showing a monophyly (the simians, in yellow), a paraphyly">monophyly.html" style="text-decoration: none;"class="mw-redirect" title="primates, showing a monophyly">primates, showing a monophyly (the simians, ...
have been used in deducing key genes for of diverse group of species.


See also

*
Clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic—that is, composed of a common ancestor and all its lineal descendants - on a phylogenetic tree. R ...
*
Crown group upright=1.5, Two distinct crown groups (in red) are illustrated, connected by an ancestor (black circle). The two groups form a larger crown group (lilac). In phylogenetics, the crown group or crown assemblage is a collection of species, composed ...
*
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 "unispec ...
*
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 resp ...
*
Polyphyly 300px, Cladogram of the primates, showing a monophyly (the simians, in yellow), a paraphyly">monophyly.html" style="text-decoration: none;"class="mw-redirect" title="primates, showing a monophyly">primates, showing a monophyly (the simians, ...


References


External links

* * * * {{Phylogenetics
PhylogeneticsPhylogenetics is the taxonomical classification of organisms based on how closely they are related in terms of evolutionary differences. Bioinformatics Subfields of evolutionary biology Biological classification Categor ...
de:Kladistik#Verwandtschaftsverhältnisse