Biologists classify organisms to organize and keep track of the enormous variety of life forms, to better understand evolutionary distances, and to examine the relationships between organisms. Life on earth is incredibly diverse, with millions of different identified species.
The basic system of classification for biology was originally devised by Swedish doctor and botanist Carolus Linnaeus. Linnaeus devised a system in which organisms are grouped under increasingly specific sub-categories, ranging from (at the broadest level) order, to family, genus and species (at the most specific level). For example, humans are classified as "Homo sapiens," with Homo being the genus and sapiens being the species. Linnaeus's basic system of classification is still used by biologists today.