Taxonomists group living things into a hierarchy that moves from general to specific. Organisms found in the same Kingdom are related, but not closely related. Presently, scientists accept that there are five Kingdoms of living organisms: Animalia, Plantae, Protoctista, Fungi, and Monera. The Animalia, Plantae, Fungi and Protoctista are part of the Domain Eukarya. The Kingdom Monera contains two Domains: the Eubacteria and Archea. Currently, there is some of debate among scientists with respect to the Kingdom level of classification because the use of DNA-based technology has allowed us to look more closely at the genetic relationships between organisms.
Each Kingdom is divided into smaller groups called Phyla (singular Phylum) that contain more closely related organisms. Each Phylum, in turn, is subdivided into smaller groups called Classes. A Class is composed of many Orders, which contain a number of Families. A Family of living things is made up of Genera (singular Genus). Finally, each Genus is divided into the smallest and most closely related group of organisms called the species.
The smallest grouping in the taxonomy hierarchy is the species, which contains organisms that are very closely related. In order to be classified in the same species, the organisms must be able to produce viable (fertile) offspring. The species level is the most reliable and useful to scientists.
The following diagram illustrates the taxonomic relationships accepted by many scientists today:
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