Evolutionary Taxonomy - Difference From Cladism

Difference From Cladism

The two approaches differ in the use of the word monophyletic. For evolutionary systematicists, monophyletic means only that a group is derived from a single common ancestor. In phylogenetic nomenclature, there is an added caveat that the ancestral species and all descendants should be included in the group. The term holophyletic has been proposed for the latter meaning. As an example, amphibians are monophyletic under evolutionary taxonomy, since they have arisen from fishes only once. Under phylogenetic taxonomy, amphibians is not monophyletic, in that the amniotes (reptiles, birds and mammals) have evolved from an amphibian ancestor and yet are not considered amphibians. In phylogentic nomenclature such units are rejected as paraphyletic.

The product of evolutionary systematics is a division according to Linnaean taxonomy (which can then be used to form tentative conclusions about phylogeny); the product of a cladistic classification is a cladogram, which can then be used to recommend a taxonomy.

Cladistics collects character data only from the taxa being classified. It does not consider the inferred characters of ancestors.

Evolutionary systematics also differs in method from cladistics. Cladistics involves collecting data and feeding it into a computer program. Evolutionary systematics involves a researcher following flexible guidelines which consider various kinds of evidence (which need not be represented as discrete alternatives).

Other debates between evolutionary systematists and cladists are not about the underlying approach, but on details. One is whether there is a danger of artificial classifications when preparing a classification using molecular phylogeny based on only a single gene or part of a gene. Another is whether it is sufficient to study DNA from chloroplasts, mitochondria, and ribosomes, as opposed to non-ribosomal nuclear DNA.