Biologists divide living things into specific classes. This classification, known as taxonomy, dates back to Carolus Linnaeus in the 18th century. The classification system that Linnaeus constructed has been expanded and revised, but is still in use today.

This system of classification contains hierarchical categories. Living things are first divided into kingdoms, such as the animal and plant kingdoms. Kingdoms are then subdivided into phyla, which are then further subdivided. Classification takes the following form, in descending order:

–>kingdom

—>phylum (plural phyla)

—>class

—>order

—>family

—>genus (plural genera)

—>species

Most biologists today accept the existence of five separate kingdoms. In addition to the plant and animal kingdoms, they regard fungi, monera (single-celled