What does outgroup mean?
An outgroup is a biological group used as a reference when scientists investigate the evolutionary relationships of another group, known as the ingroup. By comparing features or genetic sequences in both groups, researchers can infer which similarities are inherited from a common ancestor and which arose more recently. An effective outgroup generally belongs to a lineage that diverged before the most recent common ancestor of the ingroup, although the appropriate choice depends on the question being studied. The term is also used more broadly in comparative studies to mean a reference group outside the group under examination. In biological usage, an outgroup is therefore not simply an unusual or unrelated organism: it is a strategically selected comparative reference that helps scientists identify ancestral traits and reconstruct evolutionary history.
nounIn evolutionary biology and systematics, a taxon or group of organisms used as a reference for determining the evolutionary relationships of a focal group, called the ingroup. An outgroup is generally understood to have diverged before the ingroup's most recent common ancestor.
- A taxon or lineage outside the focal group in an evolutionary analysis, used as a reference point for inferring ancestral character states and the relationships among ingroup organisms.
"The researchers used the genome of a related species as an outgroup to identify evolutionary changes within the focal group."
"The outgroup sequence was aligned with those of the ingroup species to reconstruct their common ancestry."
"Choosing an outgroup that is too closely related can make the evolutionary tree less informative."
The plural takes the ordinary plural suffix -s.
"The study compared several outgroups to reconstruct the ancestry of the ingroup."
An outgroup is named for standing outside the group whose history is being investigated, but its value comes from making that group's relationships visible.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does outgroup come from?
Outgroup is a compound formed from out and group, following the contrast with ingroup. Its specialized biological meaning developed in comparative systematics, where organisms outside the principal group of interest were used to help determine ancestral and derived character states. The wording is parallel to the older term ingroup, emphasizing the external position of the comparison group.
How outgroup is actually used
The term is chiefly used in evolutionary biology, phylogenetics, and systematics. It is usually written as one word and is distinct from the broader social-science use of out-group for a group excluded from a wider collective.
Easily confused with outgroup
An outgroup is a comparative biological group used to study evolutionary relationships, whereas an outsider is a person who does not belong to a particular group.