Sister group

Sister group, also sister taxon or Adelphotaxon, is a term used in cladistics. Two taxa that have a common ancestral species only them, are sister groups (as Mitfahren in the book Richard Dawkins': Stories from the origin of life called ).

Sister groups on the type level are called sister species. Based on a phylogenetic study, two species are only known sister species, if they are each other's closest relatives, descended from immediate common ancestor.