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 with a common ancestor to be a monophyletic group. Since it is presumed that one could find a common ancestor from any group of organisms if one goes far enough into the past, this definition implicitly or explicitly constrains what is a legitimate common ancestor, for example by requiring the common ancestor to share a derived trait (synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...

) which defines the group.

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.
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