Biological Classification - Modern System

Modern System

Whereas Linnaeus classified for ease of identification, the idea of the Linnaean taxonomy as translating into a sort of dendrogram of the Animal- and Plant Kingdoms was formulated toward the end of the 18th century, well before the On the Origin of Species was published. Among early works exploring the idea of a transmutation of species was Erasmus Darwin's 1796 Zoönomia and Jean-Baptiste Lamarck's Philosophie Zoologique of 1809. The idea was popularised in the Anglophone world by the speculative, but widely read Vestiges of the Natural History of Creation, published anonymously by Robert Chambers in 1844.

With Darwin's theory, a general acceptance that classification should reflect the Darwinian principle of common descent quickly appeared. Tree of Life representations became popular in scientific works, with known fossil groups incorporated. One of the first modern groups tied to fossil ancestors were birds. Using the then newly discovered fossils of Archaeopteryx and Hesperornis, Thomas Henry Huxley pronounced that they had evolved from dinosaurs, a group formally named by Richard Owen in 1842. The resulting description, that of dinosaurs "giving rise to" or being "the ancestors of" birds, is the essential hallmark of evolutionary taxonomic thinking. As more and more fossil groups were found and recognized in the late 19th and early 20th century, palaeontologists worked to understand the history of animals through the ages by linking together known groups With the modern evolutionary synthesis of the early 1940s, an essentially modern understanding of evolution of the major groups was in place. The evolutionary taxonomy being based on Linnaean taxonomic ranks, the two terms are largely interchangeable in modern use.

Since the 1960s a trend called phylogenetic nomenclature (or cladism) has emerged, inspired by the cladistic method. The salient feature is arranging taxa in a hierarchical evolutionary tree, ignoring ranks. If a taxon includes all the descendants of some ancestral form, it is called monophyletic. Groups that have descendant groups removed from them (e.g., dinosaurs, with birds as offspring group) are termed paraphyletic, while groups representing more than one branch from the tree of life are called polyphyletic. A formal code of nomenclature, the International Code of Phylogenetic Nomenclature, or PhyloCode for short, is currently under development, intended to deal with names of clades. Linnaean ranks will be optional under the PhyloCode, which is intended to coexist with the current, rank-based codes.