-
1735
Carl Linnaeus establishes two kingdoms: Vegetabilia (plants); Animalia (similar to that of Aristotle, 2000 years earlier) -
1866
Ernst Haeckel proposes a kingdom for protists and establishes a three-kingdom approach: Protista; Plantae; Animalia -
1937
Édouard Chatton characterizes the distinction between prokaryotic and eukaryotic cells and coins these terms, thus establishing the two-empire system—Prokaryota and Eukaryota as the top level of classification -
1938
Herbert Copeland proposes establishing the prokaryotes (bacteria and archaea, formerly classified together as a phylum of protists) as Kingdom Monera, thus adding a fourth kingdom to the two-empire system -
1969
Robert Whittaker proposes a separate kingdom for fungi, given their distinct differences from plants, and the five-kingdom approach is established: Monera; Protista; Plantae; Fungi; Animalia (readers can access the full story of Whittaker's work, and its consequences, here) -
1977
Carl Woese proposes a six-kingdom approach within the two-empire system, by subdividing Monera into two kingdoms: Kingdom Eubacteria and Kingdom Archaebacteria -
1990
Carl Woese proposes a revision to the two-empire, six-kingdom approach to a three domain approach, with the term domain being accepted as the highest rank: Domain Bacteria, Domain Archaea, Domain Eukarya -
Period: to
1990 to 2015
Several other combinations of kingdoms, super-kingdoms, and empires were proposed. Today, the system most widely accepted by biologists is the three-domain approach proposed in 1990 (the number of kingdoms is an open question)