The Linnaean Hierarchy and the Evolutionization of Taxonomy, with Emphasis on the Problem of Nomenclature

During the post-Darwinian history of taxonomy, the Linnaean hierarchy has maintained its role as a means for representing hierarchical taxonomic relationships. During the same period, the principle of descent has taken on an increasingly important role as the basis for reformulated versions of fundamental taxonomic concepts and principles. Early in this history, the principle of descent provided an explanation for the existence of taxa and implied a nested, hierarchical structure for taxonomic relationships. Although an evolutionary explanation for taxa contradicted the Aristotelian context within which the Linnaean hierarchy was developed, the nested, hierarchical structure of taxonomic rela· tionships implied by evolution was compatible with the practical use of the Linnaean hierarchy for conveying hierarchical relationships and seems to have reinforced this practice. Later changes associated with the development of taxon concepts based on the principle of descent led to changes in the interpretation of the Linnaean categories as well as certain modifications related to use of the Linnaean hierarchy in representing phylogenetic relationships. Although some authors questioned use of the Linnaean hierarchy in phylogenetic taxonomies, most continued to use it in one form ot artother. More recently, taxonomists have considered the relevance of the principle of descent to nomenclature. They have found fundamental inconsistencies between concepts of taxa based on that principle and methods currently used to define taxon names, which are based on the Linnaean hierarchy. Although these inconsistencies can be corrected without totally eliminating the Linnaean hierarchy, the necessary changes would greatly reduce the importance of that hierarchy, particularly in the area of nomenclature. Moreover, the earlier development of taxon concepts based on the principle of descent effectively proposed taxonomic categories of greater theoretical significance than those of the Linnaean hierarchy. The historical trend of granting increasing importance to the principle of descent has reduced the significance of the Linnaean hierarchy to the point where it may no longer be worth retaining.