In phylogenetic analysis, an outgroup is a species or group of species that is used as a reference point for comparison to the ingroup, which is the group of species being studied. The outgroup is used to root the phylogenetic tree, which is a diagram that represents the evolutionary relationships among the species in the study.
Choosing the right outgroup is important because it can affect the results of the phylogenetic analysis. If the outgroup is too closely related to the ingroup, it may not provide enough information to resolve the relationships among the ingroup species. Conversely, if the outgroup is too distantly related to the ingroup, it may not be able to provide any useful information about the evolutionary relationships among the ingroup species.
