HiSET Science: Historical and Current Biological Classification Systems of Organisms

Historical and Current Kingdom Systems
In 1735 Carolus Linnaeus devised a two-kingdom classification system. He placed all living things into either the Animalia kingdom or the Plantae kingdom. Fungi and algae were classified as plants. Also, Linnaeus developed the binomial nomenclature system that is still used today. In 1866, Ernst Haeckel introduced a three-kingdom classification system, adding the Protista kingdom to Linnaeus's animal and plant kingdoms. Bacteria were classified as protists and cyanobacteria were still classified as plants. In 1938, Herbert Copeland introduced a four-kingdom classification system in which bacteria and cyanobacteria were moved to the Monera kingdom. In 1969, Robert Whittaker introduced a five-kingdom system that moved fungi from the plant kingdom to the Fungi kingdom. Some algae were still classified as plants. In 1977, Carl Woese introduced a six-kingdom system in which in the Monera kingdom was replaced with the Eubacteria kingdom and the Archaebacteria kingdom.

Domain Classification System
In 1990, Carl Woese introduced his domain classification system. Domains are broader groupings above the kingdom level. This system consists of three domains- Archaea, Bacteria, and Eukarya.
All eukaryotes such as plants, animals, fungi, and protists are classified in the Eukarya domain. The Bacteria and Archaea domains consist of prokaryotes. Organisms previously classified in the Monera kingdom are now classified into either the Bacteria or Archaea domain based on their ribosomal RNA structure. Members of the Archaea domain often live in extremely harsh environments.