|MadSci Network: General Biology|
Hello, 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 group. Some References for Further Info: SparkNotes: Viruses http://www.sparknotes.com/biology/microorganisms/viruses/summary.html a> International Code of Zoological Nomenclature http://www.iczn.org/ IUCN Red List Ė Threatened and Endangered Species http://www .iucn.org/themes/ssc/red_list_2004/main_EN.htm Kingdoms of Life http://www.palaeos.com /Kingdoms/kingdoms.htm Textbooks: Biology by Campbell and Reece Evolutionary Analysis by Freeman and Herron
Try the links in the MadSci Library for more information on General Biology.