A helpful review of common scientific terms Nov 18, 2011 4:53:08 GMT -9
Post by grrraaahhh on Nov 18, 2011 4:53:08 GMT -9
According to a precise set of rules laid down by the ICZN and the ICBN, the scientific name of every taxon is almost always based on one particular specimen, or in some cases specimens. Types are of great significance to biologists, especially to taxonomists. Types are usually physical specimens that are kept in a specially designated type collection in a museum research collection, or are a particular plant sample in a herbarium. Usually types are a physical example of the taxon, but failing that, an image of an individual of that taxon can be used. This material is the "type" or "types" of that taxon. Describing species and appointing type specimens is part of scientific nomenclature and alpha taxonomy.
When identifying material, a scientist attempts to apply a taxon name to a specimen or group of specimens based on his or her understanding of the relevant taxa, based on (at least) having read the type description(s), preferably based on an examination of all the type material of all of the relevant taxa. If there is more than one named type that all appear to be the same taxon, then the oldest name takes precedence, and is considered to be the correct name of the material in hand. If on the other hand the taxon appears never to have been named at all, then the scientist or another qualified expert picks a type specimen and publishes a new name and an official description.
This process is crucial to the science of biological taxonomy. People's ideas of how living things should be grouped changes and shifts over time. How do we know that that that we call "Canis lupus" is the same thing, or approximately the same thing, as what they will be calling "Canis lupus" in 200 years time? It is possible to check this because there is a particular wolf specimen preserved in a museum somewhere, and everyone who uses that name – no matter what else they may mean by it – will mean that particular specimen.
Depending on the nomenclature code applied to the organism in question, a type can be a specimen, a culture, an illustration, a description, or a taxon.
For example, in the research collection of the Natural History Museum in London, there is a bird specimen numbered 1818.104.22.168. This is a specimen of a kind of bird commonly known as the Spotted Harrier, which currently bears the scientific name Circus assimilis. This particular specimen is the holotype for that species; the name Circus assimilis refers, by definition, to the species of that particular specimen. That species was named and described by Jardine and Selby in 1828, and the holotype was placed in the museum collection so that other scientists might refer to it as necessary.
Note that at least for type specimens there is no requirement for a "typical" individual to be used. Genera and families, particularly those established by early taxonomists, tend to be named after species that are more "typical" for them, but here too this is not always the case and due to changes in systematics cannot be. Hence, the term name-bearing type or onomatophore is sometimes used, to denote the fact that biological types do not define "typical" individuals or taxa, but rather fix a scientific name to a specific operational taxonomic unit. Type specimens are theoretically even allowed to be aberrant or deformed individuals or color variations, though this is rarely chosen to be the case, as it makes it hard to determine to which population the individual belonged.
The usage of the term type is somewhat complicated by slightly different uses in botany and zoology. In the PhyloCode, type-based definitions are replaced by phylogenetic definitions.