MadSci Network: General Biology

Re: questions on 5 kingdoms and classfication

Date: Thu Mar 3 12:21:34 2005
Posted By: Shannon DeVaney, Grad student, Ecology and Evolutionary Biology, University of Kansas
Area of science: General Biology
ID: 1108816376.Gb


Iíll try to answer all of your questions. First, letís go over the five 
kingdoms of the traditional classification. They are Monera (all 
prokaryotes, including the bacteria), Protista (including protozoans and 
algae), Fungi, Plantae, and Animalia. You are right to say that viruses 
are alive in a sense, but not usually classified in those 5 kingdoms. 
There is uncertainty whether viruses should be considered living things, 
as they are unable to reproduce by themselves, and (more importantly) 
they lack a key characteristic of life: growth. 

In biology, something is not accepted as a new species until a formal 
description of the species has been published in a scientific journal. 
The person who writes the description (who may or may not be the person 
who discovered the species) chooses the name. There are extensive rules 
for naming species and higher groups; for animals, the rules are laid out 
in the International Code of Zoological Nomenclature. 

I am not entirely sure what you mean by species that are extinct before 
they can be classified, but I would guess you mean species that were 
never discovered by humans before they went extinct, and left no evidence 
(e.g., fossils) behind. We know a lot about dinosaurs based on fossils, 
and are able to describe and name species and classify them into higher 
groups despite never having seen a living dinosaur. On the other hand, 
most species leave no fossils, so plenty of species that have gone 
extinct, whether in recent times or the ancient past, are species that we 
never knew about, and will now never know anything about. Even today, we 
have discovered only a small fraction of the species that are now on the 
planet, but many of those are going extinct every day. 

Most biologists now feel that the traditional five-kingdom classification 
is inappropriate, as it does not reflect the actual patterns of 
diversity, particularly when you look at DNA sequence data. The most 
common system advocated today is a three-domain system comprising the 
domains Bacteria, Archaea, and Eucarya. Both Bacteria and Archaea were 
placed in Monera in the old system, but itís clear that they are very 
different groups; in fact, Archaea is more closely related to Eucarya 
than to Bacteria. Eucarya was split into four kingdoms in the old system, 
but those old kingdoms did not reflect real groups of closely related 
species, and it makes the most sense to consider the Eucarya a single 

Some References for Further Info:

SparkNotes: Viruses

International Code of Zoological Nomenclature

IUCN Red List Ė Threatened and Endangered Species http://www

Kingdoms of Life


Biology by Campbell and Reece

Evolutionary Analysis by Freeman and Herron

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