Biological classification

Scientific Classification is a means used by biologists to organize each of the organisms on the planet, based primarily on evolutionary similarity. The system works by placing each organism into a seven-layer 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, when specifiying a species, scientists use the bottom two layers - a system called binomial nomenclature. The seven layers are as follows:

While there are only five kingdoms, there are millions of species.