Systematics Taxonomic inertia

Taxonomy and Nomenclature

Phylogeny and Systematics
   Systematics - History of ideas
      The Great Chain of Being
      Linnaean taxonomy
      The Tree of Life
      Evolutionary systematics
      Molecular phylogeny

   Taxonomy - Definitions
   Taxonomic inertia
   Phylogenetic nomenclature
   The Incompatibility of the Cladistic and Linnaean Systems

Taxonomy serves two purposes in biology - first, to express the relationships of organisms; second, to facilitate communication between researchers. Unfortunately, these two aims are not always compatible with each other - while communication would usually be perhaps best served by a stable, unchanging structure, taxonomies are often required to change to better reflect increased knowledge about evolutionary relationships.

Taxonomic changes generally take a while to enter the general parlance - this may be referred to as taxonomic inertia. The most common cause of this is simply the time taken for the new taxonomy to become widely known - after all, not everyone who would be affected by the changes will learn about them the very day the paper is published, especially if they don't make a habit of following the taxonomic literature. However, sometimes am old taxonomy will remain in place long after changes have had time to disseminate. Some reasons for this are given below.

First, the organisms involved may have been particularly widely known under the old name, and there may be popular or economic issues with taking up the new taxonomy. The widespread persistence of the name Brontosaurus, despite it being a later synonym of Apatosaurus, is a familiar example of this. Cases such as this are particularly abundant in the horticultural world - plants are much more widely known buy their scientific names than animals, and many gardeners do not take kindly to having to remember to look for something different when they go to the garden centre. The genus Azalea was sunk into Rhododendron a number of years ago, but people did not start referring to their azaleas as rhododendrons. Other widely misused genera are Cosmos (a synonym of Bidens) and Datura (generally used to refer to the trumpet-flowered trees and shrubs that have been separated off into the genus Brugsmansia - Datura sensu stricto is a genus of herbaceous plants including the noxious Jimson weed). Interestingly, in 2005 the Commision on Botanical Nomenclature agreed to officially change the type species of the genus Acacia, in order that economically important species might remain as Acacia when the previously polyphyletic genus was divided.

Second, there may be difficulties in applying the new taxonomy. For instance, a taxonomic revision of members of the small insect order Zoraptera, previously all placed in the single genus Zorotypus, established a number of genera based on characters of the wing venation. However, wings are absent or unknown for many species of Zoraptera (zorapterans usually live as small colonies of wingless individuals in rotting logs, with winged individuals only produced as dispersers when the colony becomes overcrowded or begins to lose its habitat). As the new taxonomy is therefore unusable for most members of the order, the single genus Zorotypus is still used.

Sometimes there are particular barriers to dissemination of new taxonomies. For many years until the end of the Cold War, researchers in Eastern Europe and the Soviet Union were isolated from their peers in western countries. In many cases (for instance, many protozoa), researchers on both sides developed taxonomies in parallel for the organisms they were working on.

Finally, and fairly obviously, researchers may simply not think the new taxonomy is worth adopting. The DNA-DNA hybridisation studies on bird phylogeny by Sibley and Ahlquist lead to the proposal of a new classification for birds differing significantly from the traditional system established by Wetmore in the 1950s. However, right from its proposal there were doubts cast on the studies' methodology and results, and the new classification did not gain wide acceptance. While most researchers were willing to accept that there were problems with retaining the Wetmore classification, they did not accept the Sibley and Ahlquist classification as solving those issues. The Wetmore classification continues to be widely used by default, until a more robust alternative is developed. - CKT061013

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