Primitive in phylogenetics means a character, trait or feature of a lineage or taxon that is inherited from the common ancestor of a clade (or clade group) and has undergone little change since. Conversely, a trait that appears within the clade group (that is, is present in any subgroup within the clade but not all) is called advanced. A clade is a group in which all members have the same common ancestor.
A "primitive" trait is the original condition of that trait in the common ancestor; "advanced" indicates a notable change from the original condition. These terms in biology contain no judgement about the sophistication, superiority, value or adaptiveness of the named trait. Primitive in biology means only that the character appeared first in the common ancestor of a clade group and has been passed on largely intact to more recent members of the clade. Advanced means the character has evolved within a later subgroup of the clade.
Primitiveness of characters is determined by context
Primitive and advanced are relative terms. When a trait is called "primitive", the determination is based on the perspective from which the trait is viewed. Any trait can be both primitive (ancestral) and advanced depending on the context in which it is considered.
In the clade of vertebrates, legs are an advanced trait since it is a feature that appears in the clade. However, in the clade of tetrapods, legs are primitive since they were inherited from a common ancestor.
Species cannot be primitive
The term primitive (or advanced/derived) is not properly used in reference to an organism or species as every species is a mosaic of primitive and derived traits. Humans, for example have large brains (a derived trait) and five fingers (a primitive trait) in their lineage. Species are constantly evolving, so a frog is not biologically more primitive than a human as each has been evolving continuously since each lineage split from their common ancestor.
Several other sets of terms are synonymous with primitive (and advanced) in phylogenetics. These terms are considered preferable as they are less likely to convey the sense that some traits are inferior, less adaptive or even simpler. The terms plesiomorphy and apomorphy are used in the technical literature. When a plesiomorphic trait is shared by more than one member of a clade, the trait is called a "symplesiomorphy", i.e. a shared primitive trait. A shared derived trait is a "synapomorphy".
- "Univeristy of California Museum of Paleontology Glossary: Phylogenetics". UCMP Glossary. University of California. Retrieved 7 October 2015.
- Futuyma, Douglas (1998). Evolutionary Biology. Sunderland: Sinauer Associates. ISBN 978-0-87893-189-7.
- Daniel R. Brooks; Deborah A. McLennan (2 May 2002). The Nature of Diversity: An Evolutionary Voyage of Discovery. University of Chicago Press. pp. 33–. ISBN 978-0-226-07590-7.
- "Reconstructing Trees: Cladistics". Understanding Evolution. University of California Museum of Paleontology. Retrieved 6 November 2015.