Outgroup
Encyclopedia
In cladistics
or phylogenetics
, an outgroup is a (monophyletic) group of organisms that serves as a reference group for determination of the evolution
ary relationship among three or more monophyletic groups of organisms.
The chosen outgroup is hypothesized to be rather closely related to the other groups, but less closely than any single one of the other groups is to each other. The evolutionary conclusion from this is that the outgroup branched from the parent group before the other two groups branched from each other.
Some examples, with outgroup on the right:
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
or phylogenetics
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...
, an outgroup is a (monophyletic) group of organisms that serves as a reference group for determination of the evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary relationship among three or more monophyletic groups of organisms.
The chosen outgroup is hypothesized to be rather closely related to the other groups, but less closely than any single one of the other groups is to each other. The evolutionary conclusion from this is that the outgroup branched from the parent group before the other two groups branched from each other.
Some examples, with outgroup on the right:
- HumanHumanHumans are the only living species in the Homo genus...
s, chimpanzeeChimpanzeeChimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:...
s — gorillaGorillaGorillas are the largest extant species of primates. They are ground-dwelling, predominantly herbivorous apes that inhabit the forests of central Africa. Gorillas are divided into two species and either four or five subspecies...
s - Placental mammals, MarsupialMarsupialMarsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
s — MonotremeMonotremeMonotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals...
s - Tetrapoda, ActinopterygiiActinopterygiiThe Actinopterygii or ray-finned fishes constitute a class or sub-class of the bony fishes.The ray-finned fishes are so called because they possess lepidotrichia or "fin rays", their fins being webs of skin supported by bony or horny spines , as opposed to the fleshy, lobed fins that characterize...
— ElasmobranchiiElasmobranchiiElasmobranchii is a subclass of Chondrichthyes or cartilaginous fish, that includes the sharks and the rays and skates .-Evolution:... - ChordateChordateChordates are animals which are either vertebrates or one of several closely related invertebrates. They are united by having, for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail...
s, EchinodermEchinodermEchinoderms are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone....
s — Mollusks