Evolution and Classification of Life

Classification of Life:

Two Kingdom System:

Carolus Linnaeus (1707-1778) distinguished two kingdoms of living things as –
i. Regnum Animale for animals
ii. Regnum Vegetabile for plants

Three Kingdom System:

With the discoveries of more and more microbes scientists like R.Owen and John Hogg (1866) first proposed a third kingdom system and following their proposals Ernst Haeckel (1866) published three kingdom classification of life.

Four Kingdom System:

The discovery and development of electron microscopes revealed a sharp distinction between unicellular prokaryotes and unicellular and multicellular eukaryotes. On this basis, H.F Copeland (1938) proposed a four-kingdom classification. The scheme of his classification is as follows –

Five Kingdom System:

At this stage, after the publication of stainer and Van Niel’s scheme (1960) the earlier demands of moving fungi out of Plantae gained much ground and gave much importance to this contention Robert Whittaker (1969) proposed an additional kingdom for Fungi. As a result, a five-kingdom classification developed.

Six Kingdom System:

From the seventh decade of the last century studies at a molecular level, i.e, gene level were so progressed that it was felt necessary that a comparative genic study should be the primary factor in classification. They further stressed that taxonomic ranks should show a monophyletic or at least partially monophyletic relationship. Based on such rRNA gene study comparatively, Carl Woese (1977) proposed three domain and six kingdom classifications. The kingdom Monera was divided into Eubacteria and Archebacteria as there exist many genetic differences between the two. The scheme of C. Woese is as follows –

Seven Kingdom System:

Cavalier-Smith (2004) published Six kingdom classification based on evolution. The scheme is as follows –

Modifying the classification published in 2004 Cavalier Smith published another classification in 2009 in which the term kingdom was abolished and instead subgroups were proposed. The scheme is as follows –