Evolutionary Grade - Grades and Phylogenetic Nomenclature

Grades and Phylogenetic Nomenclature

With the rise of phylogenetic nomenclature, the use of evolutionary grades as formal taxa has come under debate. Under a strict phylogenetic approach, only monophyletic taxa are recognized. This differs from the more traditional approach of evolutionary taxonomy. The difference in approach has led to a vigorous debate between proponents of the two approaches to taxonomy, particularly in well established fields like vertebrate palaeontology and botany. The difference between the statement "B is part of A" (phylogenetic approach) and "B has evolved from A" (evolutionary approach) is, however, one of semantics rather than of phylogeny. Both express the same phylogeny, but the former emphasizes the phylogenetic continuum while the latter emphasizes a distinct shift in anatomy or ecology in B relative to A.