Scientists organize living organisms into groups because it is easier to study organisms that have certain shared features. The act of organizing different types of living things into groups is called classification, and taxonomy is the scientific study of these classifications.
Taxonomic classification also helps scientists group together living organism that have a similar evolutionary histories. The main groupings used for classification purposes are domain, kingdom, phylum, class, order, family, genus and species. Different phyla and classes can be subdivided into subphyla and subclasses.
The Domain Eukarya consists of the four kingdoms: Protista, Fungi, Plantae and Animalia. Eukaryotes contain cells with a distinct nucleus. Each of these kingdoms further subdivides different living organisms according to the different evolutionary characteristics they share. For example, the kingdom consists of birds, fish, reptiles and mammals.