Scientific classification is a means used by biologists to organize each of the organisms on the planet, based primarily on evolutionary similarity as determined by visual observation. This system was devised by Carolus Linnaeus (1707-1778).
The system works by placing each organism into a layered hierarchy of groups. Each group at a given layer is composed of a set of groups from the layer directly below. Therefore, in theory, one needs know only the lowest layer (species) of a particular organism in order to uniquely determine the other six layers. In practice, however, many species actually have the same species designation, so when specifiying a species, scientists use the bottom two layers - a system called binomial nomenclature.
The layers are as follows:
Additional classification is possible. Intermediate ranks are sometimes created by adding prefixes like super-, infra-, and sub- to those listed above. Sometimes tribes, which lie between families and genera, and races, which lie below species, are also used. In Horticulture, species modified by selective breeding are frequently called varieties. An example of a variety is the Peace Rose, a hybrid Tea Rose. The term varieties is also sometimes used in place of subspecies (see the Human classification example below, where variety is used to distinguish us and our ancestors, back to about 130,000 years ago, from the Neanderthals).
Could add a description of the difficulty in classifying microbes: their features are derived from direct visual observation, but include such procedural characteristics as Gram stain type, motility, ability to form spores, etc. However, given an unknown bacterium with a given set of characteristics, it is in general not possible to predict its phylogeny, toxicity, etc. Other methods, using genes, their DNA, and several types of RNA, are under development.
While there are only five kingdoms, there are millions of species.
Examples Of Biological Classification
The fruit fly so familiar in genetics laboratories is Drosophila melanogaster. Its complete classification, as well as that of humans, is as follows
Fruit Fly
| Domain | Eukaryota |
| Kingdom | Animalia |
| Phylum | Arthropoda |
| Class | Insecta |
| Order | Diptera |
| Family | Drosophilidae |
| Genus | Drosophila |
| Species | Drosophila melanogaster |
Human
| Domain | Eukaryota |
| Kingdom | Animalia |
| Phylum | Chordata |
| Class | Mammalia |
| Order | Primates |
| Family | Hominidae |
| Genus | Homo |
| Species | Homo sapiens |
Group Suffixes
Taxa above the genus level are often given names derived from the type genus. The suffixes used to form these names depend on the kingdom, and sometimes the phylum and class, as follows:
| Plants | Algae | Fungi | Animals | |
|---|---|---|---|---|
| Division/Phylum | -phyta | -phyta | -mycota | |
| Subdivision/Subphylum | -phytina | -phytina | -mycotina | |
| Class | -opsida | -phyceae | -mycetes | |
| Subclass | -idae | -phycidae | -mycetidae | |
| Order | -ales | -ales | -ales | -formes (birds, fish) |
| Suborder | -ineae | -ineae | -ineae | (plural of the genus, e.g. Lari) |
| Family | -aceae | -aceae | -aceae | -idae |
| Subfamily | -oideae | -oideae | -oideae | -inae |
| Tribe | -eae | -eae | -eae | -ini |
| Subtribe | -inae | -inae | -inae | -ina |
See also: