For Many Years, Biologists Felt That the Highest Level of Classification

question 36

Essay

For many years, biologists felt that the highest level of classification of living organisms was the five kingdoms. Recently, some biologists have proposed that the hierarchical classification of organisms start with three domains, the Bacteria, the Archaea, and the Eucarya. Explain the reasoning behind this proposal and why the Bacteria and the Archaea should be in separate domains even though their members are all prokaryotes.

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Definitions:

Hominin

Any of a group of extinct and living humans. Also called hominid.

Supraorbital Ridge

A prominent ridge of bone located above the eye sockets on the frontal bone of the skull.

First Toe

The big toe on the human foot, which plays a crucial role in balance and walking by bearing much of the weight of the body.

Out-of-Africa Hypothesis

A theory proposing that modern humans originated in Africa and dispersed to other continents, replacing previously existing hominid species.