Summary
The sequence from the two-kingdom system up to Cavalier-Smith's six-kingdom system can be summarized in the table below.
Linnaeus 1735 |
Haeckel 1866 |
Chatton 1925 |
Copeland 1938 |
Whittaker 1969 |
Woese et al. 1977 |
Woese et al. 1990 |
Cavalier-Smith 1993 |
Cavalier-Smith 1998 |
---|---|---|---|---|---|---|---|---|
2 kingdoms | 3 kingdoms | 2 empires | 4 kingdoms | 5 kingdoms | 6 kingdoms | 3 domains | 8 kingdoms | 6 kingdoms |
(not treated) | Protista | Prokaryota | Monera | Monera | Eubacteria | Bacteria | Eubacteria | Bacteria |
Archaebacteria | Archaea | Archaebacteria | ||||||
Eukaryota | Protoctista | Protista | Protista | Eukarya | Archezoa | Protozoa | ||
Protozoa | ||||||||
Chromista | Chromista | |||||||
Vegetabilia | Plantae | Plantae | Plantae | Plantae | Plantae | Plantae | ||
Fungi | Fungi | Fungi | Fungi | |||||
Animalia | Animalia | Animalia | Animalia | Animalia | Animalia | Animalia |
Note that the equivalences in this table are not perfect. For example, Haeckel placed the red algae (his Florideae, modern Florideophyceae) and blue-green algae (his Archephyta, modern Cyanobacteria) in his Plantae.
The kingdom-level classification of life is still widely employed as a useful way of grouping organisms, notwithstanding some problems with this approach:
- Kingdoms such as Bacteria represent grades rather than clades, and so are rejected by phylogenetic classification systems.
- The most recent research does not support the classification of the eukaryotes into any of the standard systems. As of April 2010, no set of kingdoms is sufficiently supported by research to attain widespread acceptance. In 2009, Andrew Roger and Alastair Simpson emphasized the need for diligence in analyzing new discoveries: "With the current pace of change in our understanding of the eukaryote tree of life, we should proceed with caution."
Read more about this topic: Kingdom (biology), Systems of Classification
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