Evolutionary systematics

From Palaeos

SYSTEMATICS

Evolutionary Systematics, also called Gradistic Taxonomy, gives an a dynamic evolutionary slant to the static Linnean system. It is based on a combination of branching and divergence. Most old books on paleontology were based on this paradigm. Evolutionary Systematics was formulated by such "grand old men" of paleontology as Ernst Mayr and G. G. Simpson. This approach accepts the Hennigian cladistic methodology as adequate for reconstructing phylogenetic trees, but retains paraphyletic groups (e.g. "Reptilia").

Also, unlike Cladistics, with it's reliance on a proposed Most Recent Common Ancestor that is never actually described or discovered (a missing link that is always missing), Evolutionary systematics gives illustrations of the actual evolution of one species or higher taxon into another.

Admittedly, Evolutionary Systematics suffers from a number of shortcomings. For example the use of several very different criteria (phylogeny, divergence, adaptational level) to define particular taxa, as well as inconsistencies inherent in the paraphyletic approach (e.g. separating Class Aves (Birds) from the Archosauria). This, together with the greater rigor and precision of the Cladistic (Phylogenetic) approach has meant that over the past decades, Evolutionary Systematics has greatly declined with cladistics becoming the dominant paradigm.

[edit] A critique of Evolutionary Systematics, from Glossary of Phylogenetic Systematics by Günter Bechly

Evolutionary Systematics: The so-called "Evolutionary Systematics" is a syncretistic approach to biological systematics, which was especially endorsed by ERNST MAYR and SIMPSON. Although the proponents of this approach mostly accepted the Hennigian methodology as adequate technique for the reconstruction of phylogenetic trees, they strongly objected against a strictly cladistic classification, since they wanted to use paraphyletic groups in their classifications. These paraphyla (e.g. "Reptilia") were a direct corollary of their desire to assign a higher categorical rank (e.g. class) to a monophyletic taxon with numerous autapomorphies (e.g. birds), than to its sister group (e.g. crocodiles), if the latter has retained numerous symplesiomorphies with other groups (e.g. lizards). This desire was justified by the greater "evolutionary divergence" compared to the common ancestor, and the possession of a new "adaptational level". Except the difficulty to define and measure "evolutionary divergence" and "adaptational level", the main problem of this approach is the extreme arbitrariness in the classification and delimitation of paraphyla: Should animals been divided in "Protozoa" (paraphyletic) versus Metazoa (monophyletic), or rather in "Invertebrata" (paraphyletic) versus Vertebrata (monophyletic), or better in "Protostomia" (paraphyletic) versus Deuterostomia (monophyletic); should one likewise divide Vertebrata in "Pisces" (paraphyletic) versus Tetrapoda (monophyletic), or in "Anamnia" (paraphyletic) versus Amniota (monophyletic), or maybe even in non-mammals (paraphyletic) and Mammalia (monophyletic), which curiously was never proposed yet. Even the exclusion of man from the kingdom of animals as separate kingdom (regnum) "Psychozoa" has been proposed and would be absolutely compatible with the principles of "Evolutionary Systematics". The grouping of crocodiles and birds as sistergroups in a monophyletic taxon Archosauria has been dismissed as absurd by evolutionary systematists, while they accepted a group like Deuterostomia without any protest, although it is including such divergent organisms as sea-cucumbers and man. A further critique against Phylogenetic Systematics was the mere conjecture that it shall completely neglect the evidence from symplesiomorphic characters, although they are important homologies, too. This statement is of course nonsense, since all homologous characters are recognized and used in Phylogenetic Systematics, and symplesiomorphic characters are therefore not neglected at all, but are recognized on that hierarchical level on which they do represent a synapomorphy... A more general problem of "Evolutionary Systematics" is the circumstance that several very different criteria are used for the construction of a classification (phylogeny, divergence, adaptational level), but in the resulting system it is not recognizable which criteria have been used for a particular taxon. Because of the mentioned problems and the theoretical, practical and heuristic superiority of Phylogenetic Systematics, the number of proponents of "Evolutionary Systematics" has strongly declined in the past decades."