In
cladisticsCladistics is a form of biological systematics which classifies living organisms on the basis of shared ancestry...
, an
outgroup is a (monophyletic) group of organisms that serves as a reference group for determination of the
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
ary relationship between three or
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In
cladisticsCladistics is a form of biological systematics which classifies living organisms on the basis of shared ancestry...
, an
outgroup is a (monophyletic) group of organisms that serves as a reference group for determination of the
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
ary relationship between three or
more monophyletic groups of organisms.
The choosen 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:
- Human
Humans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s, chimpanzeeChimpanzee, 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 — gorillaGorillas are the largest of the living primates. They are ground-dwelling and predominantly herbivorous. They inhabit the forests of central Africa. Gorillas are divided into two species and either four or five subspecies...
s
- Placental mammals, Marsupial
Marsupials are an infraclass of mammals, characterized by a distinctive pouch , in which females carry their young through early infancy.- History :...
s — MonotremeMonotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals ....
s
- Tetrapoda, Actinopterygii
The Actinopterygii constitute the class of the ray-finned 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 the class Sarcopterygii...
— ElasmobranchiiElasmobranchii is the subclass of cartilaginous fish that includes skates, rays , and sharks .-Evolution:Fossilised shark teeth are known from the early Devonian, around 400 million years ago. During the following Carboniferous period, the sharks underwent a period of diversification, with many...
- Chordate
Chordates 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, EchinodermEchinoderm, there are seven main classes of Echinoderms which are brittle stars, basket stars, sea urchins, sand dollars, sea lilies, feather stars, and sea cucumbers...
s — Mollusks