The Need for Classification
After 3 billion years of evolution, millions of different kinds of organisms now exist. If we are to talk about them and to study them, then it is important that each has its own name.
From the earliest times, man has grouped organisms into basic, everyday, units; e.g. oaks, cats and pigs. As time went on, and scholarship emerged, these units began to be called genera (singular, Genus), and by the time of the Middle Ages, their names were being written in Latin. Thus oaks were placed in the Genus Quercus, cats in Felis and pigs in Sus.
Before 1750, scholars added a series of descriptive terms to the name of a Genus when they wanted to refer to a single member (species) of a Genus. These strings of up to 15 words were known as polynomials. The European bee, for example, carried the name Apis pubescens, thorace subgriseo, abdomine fusco, pedibus posticis glabris utrinque margine ciliatis. Not only were these names profoundly cumbersome, they were also imprecise since any scholar could change them as they saw fit.
The Binomial System
The Swedish biologist Carolus Linnaeus (1707-1778) offered a solution to naming organisms that we still use to this day. Linnaeus had the ambition to catalogue all known organisms and to do so he used the polynomial system. However, from 1750 onwards he also included in his catalogues short-hand names consisting of just two words. Under this new binomial system the honey bee was to be known simply as Apis mellifera.
The binomial system uses the Genus and a descriptive specific epithet. For example our own species is called Homo sapiens where the epithet sapiens means wise.
An international association of taxonomists establishes the scientific names of organisms to a precise set of rules. The names are the same throughout the world, and can be used, without fear of confusion, in all languages.
The Taxonomic Hierarchy
Mans appetite for organising things is insatiable, and once species have been named, they are grouped into a hierarchy of categories, each of which is known as a TAXON (hence the notion of taxonomy).
First the species are grouped into genera, and then the genera into larger more inclusive categories known as families which reflect perceived relationships between the groups included. For example, genera of oaks (Quercus), beeches (Fagus) and chestnuts (Castanea) all belong to the family Fagaceae.
Families are grouped into orders, orders into classes, classes into phyla (singular phylum) and phyla into kingdoms, the most inclusive units of all.
These are the major taxa but in some cases they may be split further; for example, you will come across infra-classes, sub-orders and sub-species to name but a few!
Take a look at the case of the Orkney vole to see an example of a fairly full hierachical classification.
Some Useful Rules