phylogenetics In biology, phylogenetics (; from Greek language, Greek wikt:φυλή, φυλή/wikt:φῦλον, φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary his ...

, a primitive (or ancestral) character, trait, or feature of a lineage or

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 nam ...

is one that is inherited from the

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 comm ...

of a

clade A clade (), 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. Rather than the English term, ...

(or clade group) and has undergone little change since. Conversely, a trait that appears ''within'' the clade group (that is, is present in any subgroup within the clade but not all) is called advanced or derived. A

is a group of organisms that consists of a common ancestor and all its lineal descendants. A primitive trait is the original condition of that trait in the common ancestor; advanced indicates a notable change from the original condition. These terms in biology contain no judgement about the sophistication, superiority, value or adaptiveness of the named trait. "Primitive" in biology means only that the character appeared first in the common ancestor of a clade group and has been passed on largely intact to more recent members of the clade. "Advanced" means the character has evolved within a later subgroup of the clade. Phylogenetics is utilized to determine evolutionary relationships and relatedness, to ultimately depict accurate evolutionary lineages. Evolutionary relatedness between living species can be connected by descent from common ancestry. These evolutionary lineages can thereby be portrayed through a phylogenetic tree, or cladogram, where varying relatedness amongst species is evidently depicted. Through this tree, organisms can be categorized by divergence from the common ancestor, and primitive characters, to clades of organisms with shared derived character states. Furthermore, cladograms allow researchers to view the changes and evolutionary alterations occurring in a species over time as they move from primitive characters to varying derived character states. Cladograms are important for scientists as they allow them to classify and hypothesize the origin and future of organisms. Cladograms allow scientists to propose their evolutionary scenarios about the lineage from a primitive trait to a derived one. By understanding how the trait came to be, scientists can hypothesize the environment that specific organism was in and how that affected the evolutionary adaptations of the trait that came to be. Other, more technical, terms for these two conditions—for example, "plesiomorphic" and "synapomorphic"—are frequently encountered; ''see'' the table below.

Usage

At least three other sets of terms are synonymous with the terms "primitive" and "advanced". The technical terms are considered preferable because they are less likely to convey the sense that the trait mentioned is inferior, simpler, or less adaptive (e.g., as in

lower Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Gloucestershire, England See also *Nizhny Nizhny (russian: Ни́жний; masculine), Nizhnyaya (; feminine), or Nizhneye (russian: Ни́� ...

and

higher plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They a ...

s). The terms "plesiomorphy" and "apomorphy" are typically used in the technical literature: for example, when a plesiomorphic trait is shared by more than one member of a clade, the trait is called a symplesiomorphy, that is, a shared primitive trait; a shared derived trait is a

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

. The amount of variation of characters can assist in depicting greater relatedness amongst species, and conversely show the lack of relatedness between species. Analysis of character variation also aids in distinguishing primitive characters from derived characters. The term derived and primitive, or ancestral, is used in reference to characters and character state. In doing so, a derived character is depicted as a character procured through evolution from the previous ancestral state, and persisting due to fixation of derived alleles. Whereas, a primitive character is one that is originally present in the ancestral population. Primitive characters are avoided as they depict the ancestral character state. Conversely, derived characters depict the alteration of characters from the ancestral state because selection favored organisms with that derived trait.

Primitiveness of characters is determined by context

"Primitive" and "advanced" are relative terms. When a trait is called primitive, the determination is based on the perspective from which the trait is viewed. Any trait can be both primitive (ancestral) and advanced (derived) depending on the context.

Examples

In the

of vertebrates, legs are an advanced trait since it is a feature that appears in the clade. However, in the clade of tetrapods, legs are primitive since they were inherited from a common ancestor. The terms "primitive" and "advanced", etc., are not properly used in referring to a species or an organism as any species or organism is a mosaic of primitive and derived traits. Using "primitive" and "advanced" may lead to "ladder thinking" (compare the Latin term ''

scala naturae The great chain of being is a hierarchical structure of all matter and life, thought by medieval Christianity to have been decreed by God. The chain begins with God and descends through angels, humans, animals and plants to minerals. The great c ...

'' 'ladder of nature'), which is the thought that all species are evolving because they are striving toward supremacy. When this form of thinking is used, humans are typically considered perfect and all other organisms are of less quality than them. This can cause the misconception of one species being an ancestor to another species, when in fact both species are extant. ''Homo sapiens'', for example have large brains (a derived trait) and five fingers (a primitive trait) in their lineage. Species are constantly evolving, so a frog is not biologically more primitive than a human as each has been evolving continuously since each lineage split from their common ancestor.

References

{{Phylogenetics, state=collapsed Evolutionary biology