Classification
Taxonomy
Taxonomy is the name given to the area of science of putting living organisms into catagories, and then giving them scientific names. This is important because it allows us to see how 'related' two creatures are and it also means that species can be refered to with a name that is common across all languages.
The system of classifying is hierarchical (there is a hierarchy), meaning that there are groups, and then groups within groups, and so on (much like the navigation of this site). At the top are the kingdoms, and then we 'zoom in' and get more and more specific until we have an individual species. The levels of classification are as follows.
The levels of classification are based on the evolutionary history of species (a bit like a family tree), and it is said to be phylogenetic [fi-lo-jen-et-ic].
At the very origins of Taxonomy with Carl Linnaeus in the 1700s, creatures were classified based on their appearance and geographic distribution; however, the fairly recent discovery of genes means that more precision can be used, and many species have been reclassified.
All species are given a scientific name called a binomial name, this consists of two words and takes the form Genus Species; for example, humans are in the genus Homo, and are the species Sapiens, therefore the binomial name is Homo Sapiens.
The Five Kingdoms
The very top layer of classification are the kingdoms, and there are now agreed there are 5 of these (originally two: plant and animal). Below these kingdoms are listed with a brief description of common features.
| Kingdom | Traits | Includes... |
|---|---|---|
| Animalia | All are eukaryotes; the cells do not have walls; and they cannot make their own food. | Worms, insects, sponges, birds, humans. |
| Fungi | All feed by extracellular digestion, single celled fungi are called yeast. | Mushrooms, moulds, yeast. |
| Monera (Prokaryotae) | All organisms here are prokaryotic, mainly reproduce by binary fission (splitting in half). | Bacteria (E Coli, Penicillin, MRSA), algae. |
| Plantae | Plants, cells have cell wall, most produce their own food by photosynthesis. | Mosses, ferns, flowering plants, trees |
| Protoctista | This catagory is the miscellaneous kingdom for species that can't be put in the others. One important thing is that Protostista are all eukaryotes. | Algae, amoeba, and malarial parasites. |
Speciation
Defining a species is difficult: but one of the most common is: a population of similar individuals that can mate and produce fertile offspring (ie. they can themselves reproduce). For example, a horse and donkey can mate and produce offspring: the mule, but mules are sterile.
New species are a result of isolation and natural selection. There are various types of isolation but in general it is when part of the population becomes seperated so that they can no longer breed.
New species evolve when members of a species become isolated. During this isolation, natural selection occurs so that allele and phenotype frequency change, and eventually differences become so great that a seperate species is formed.