Outside group

When I decide system relations of the single system group of creatures more than three in cladistics or phylogenesis, outside group (がいぐん, outgroup) is a group to refer to. The outside group adds a root to genealogical tree, and the systematic position relations of the inner group wanting to know the system relations are used though they are decided. Can decide the polarity of the form and essence change only from existence root genealogical tree [¹]; save it, and is essential when the choice of the outside group understands the evolution of the form and essence state along the system.

The outside group is closely related, however it chooses the thing that it is thought that I am distantly related each other than the group of the group among other throats in other groups of the inner group. The kind of the outside group has an inner group and a common ancestor, and the conclusion of the evolution study derived from these system relations is that it is older than the common ancestor of each group of the inner group. Or, in the outside group, sisters group of the inner group is distantly related [²].

Table of contents

Choice of the outside group

It is most suitable, and the group must satisfy two following conditions.

1. It must not be included in the inner group
2. It must be closely related with an inner group in the meaningful group which I can compare

Thus, it is appropriate, and a group must be a thing in the outside in clarity of クレード wanting to know the system relations. I will really start a wrong conclusion in the evolution of a system and the form and essence state when I made existence root genealogical tree when it is included in the inner group and chooses a group. It is typically a necessary thing to satisfy the second condition in the molecular phylogenesis because sequence of DNA obtained from the outside group or the protein succeeds in alignment with the sequence obtained from the inner group.

Example

Inner group	Outside group
Hominoid	New world colander
Existence Placentalia	Marsupialia
Chordate	Echinoderm
Angiosperm	Gymnospermae

Because scoring does a form and essence state same as one or more outside group, in all examples, the system of the creature in the inner group is made an existence root.

Allied item

• Sisters group

Footnote

1. ^ Farris, J. S. (1982). "Outgroups and Parsimony." Systematic Biology 31 (3): 328–334. doi: 10.1093/sysbio/31.3.328. ISSN 1063-5157. 
2. ^ David A. Baum; Stacey D. Smith (2013). Tree Thinking: An Introduction to Phylogenetic Biology. Roberts. p. 175. It is http://books.google.com/books?id=zW_ApwAACAAJ. ISBN 978-1 - 936,221-16-5 

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