The Linnaean Hierarchy and 'Extensional Thinking'

摘要

The Linnaean Hierarchy has been opposed from a number of different perspectives, but most of this oppositionwas based upon the confusion of two aspects of every taxon—extension and intension. These aspects account for its dualnature of simultaneous change and constancy. "Constancy" is apparent only in the differences that exist among groups oforganisms; these differences appear in the very first origin of taxa and persist throughout their entire evolutionary history.The sequence of differences over time is the only basis upon which to judge the history of the organic world. The Linnaeansystem addresses this sequence by attempting to distribute these differences among hierarchical levels. Taxonomichierarchical levels, or ranks, do not imply a rigid adherence to certain kinds of characters, since characters can change their rank during group evolution. As such, taxonomic levels can serve only as a tool to coordinate chaotically segregatedgroups of organisms.