Basal (phylogenetics)
Encyclopedia
In phylogenetics
, a basal clade
is the earliest clade to branch in a larger clade; it appears at the base of a cladogram
.
A basal group forms an outgroup to the rest of the clade, such as in the following example:
The word "basal" is preferred to the term "primitive", which may carry false connotations of inferiority or a lack of complexity.
The term basal can only be correctly applied to clades of organisms, not to individual traits possessed by the organisms—although it can be misused in this manner in technical literature. While the term "basal" applies to clades, characters or traits are usually considered derived
if they are absent in a basal group, but present in other groups. This assumption only holds true if the basal group is a good analogy for the last common ancestor of the group.
As an example, the flowering plant family Amborellaceae
is considered the most basal lineage
of extant angiosperms.
In animal family Hominidae
, the gorillas are an outgroup to chimpanzees, bonobos and humans. These four species form a clade, the subfamily Homininae
, of which gorillas are the basal member.
However, in the family Hominidae, the orangutans form an outgroup to the subfamily Homininae, the clade to which gorillas, chimpanzees, bonobos and humans all belong.
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
, a basal clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
is the earliest clade to branch in a larger clade; it appears at the base of a cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
.
A basal group forms an outgroup to the rest of the clade, such as in the following example:
The word "basal" is preferred to the term "primitive", which may carry false connotations of inferiority or a lack of complexity.
The term basal can only be correctly applied to clades of organisms, not to individual traits possessed by the organisms—although it can be misused in this manner in technical literature. While the term "basal" applies to clades, characters or traits are usually considered derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
if they are absent in a basal group, but present in other groups. This assumption only holds true if the basal group is a good analogy for the last common ancestor of the group.
As an example, the flowering plant family Amborellaceae
Amborellaceae
Amborella is a genus of rare understory shrubs or small trees endemic to the island of New Caledonia. The genus consists of only a single species, Amborella trichopoda, and is the only member of the family Amborellaceae. Wood of Amborella lacks the vessels characteristic of most flowering plants...
is considered the most basal lineage
Lineage (evolution)
An evolutionary lineage is a sequence of species, that form a line of descent, each new species the direct result of speciation from an immediate ancestral species. Lineages are subsets of the evolutionary tree of life. Lineages are often determined by the techniques of molecular systematics.-...
of extant angiosperms.
In animal family Hominidae
Hominidae
The Hominidae or include them .), as the term is used here, form a taxonomic family, including four extant genera: chimpanzees , gorillas , humans , and orangutans ....
, the gorillas are an outgroup to chimpanzees, bonobos and humans. These four species form a clade, the subfamily Homininae
Homininae
Homininae is a subfamily of Hominidae, which includes humans, gorillas and chimpanzees, and some extinct relatives; it comprises all those hominids, such as Australopithecus, that arose after the split from orangutans . Our family tree, which has 3 main branches leading to chimpanzees, humans and...
, of which gorillas are the basal member.
However, in the family Hominidae, the orangutans form an outgroup to the subfamily Homininae, the clade to which gorillas, chimpanzees, bonobos and humans all belong.