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|It has been suggested that this article be merged into Monophyletic. (Discuss) Proposed since August 2013.|
Holophyletic is a term posited as a semantically correct replacement for the term monophyletic as used by cladists (which differs from the usage of evolutionary systematists). It originated amidst confusion over the correct definition for monophyletic group; many definitions were available, of varying degrees of restrictiveness, and holophyletic was posited as a term to describe the definition with scientific utility. The least scientifically useful definition for monophyletic, which is arguably the semantically correct one, considers any group of organisms that includes its own common ancestor to be a monophyletic group. A naive view would be to say that one can find a common ancestor from any group of organisms, if one goes far enough into the past. But with a little thought it is obvious that this objection stems from a misunderstanding: the question is not whether a common ancestor exists (it does), but whether the common ancestor is itself contained within the group. A monophyletic group contains its common ancestor; a polyphyletic group does not contain its common ancestor.
The term holophyletic refers specifically to the definition that a group contains the common ancestor, all organisms descended from the common ancestor, and no other organisms.
The term holophyletic has not gained widespread acceptance in the scientific community, probably because the term monophyletic is so widely used with the same widely understood meaning.