We emphaseised the features which living things have in common. For example that all are made of cells and carry out life processes. Here and in Appendix I we concentrate on differences. The Appendix introduces you to the remarkable range which make up the living world.
THE NEED FOR CLASSIFICATION
biologist have so far studied and named over 1500000 different types of organisms and it is likely that several times that number remains to be studied and named. It would be impossible to deal with such large numbers unless we classified organism in some ways.
To classify means to arrange or organize things into group its something we do all the time. For example, in a school library we usually arrange the books according to subject. We might group all the regional geography books together and if there are many break them down further into those above continent's and countries.
When biologist classify living things they place them in a series of group according to their similarities and differences. This classification is based on careful and detailed study of each type of organisim
The species is the basic unit of biological classification. For example, all dogs are placed in the species canis familiaris, and all lions in the specie Pantera leo.
A specie is a group of individual which can be breed together to produce fertile offspring.
Species are arranged in a series of increasingly larger group, depending on the number and nature of features their members share species with many features in common are placed in same genus (plural: genera). Genera with common features are placed in the same family, and so on. The kingdom is the largest group used in biological classification. As we move from genus to Kingdom, each group include a larger number of species, but these have a fewer features in common.
A clarification and classification of living things based on comon features is useful in several ways. For example if you are told that an animal is a mammal, you already know quite a lot about it you know that is has all the features common mammal has outlined on page 441. It also have all the features common to vertebrates (page 409) and to animal as a whole (page5).
We sometimes find considerable variety within a species. For example, all the animal in on earth are varieties of dog. Though they look so different, they are still placed in the same species because they can breed together to produce fertile offspring.
Horse and donkeys can also breed together, but the offspring they produce, called a mule, is infertile (cannot give rise to offspring). Horses(Equus caballus) and donkeys (Equus asinus) are therefore classified as separate species
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THE BINOMIAL SYSTEM
species are named by the binomial system which was devised by the Swedish biologist linnaeus (1707-1798).he gave every species two names ; a generic name and a specific name. The generic name is common to all animal species in a genus. For example Equus caballus (the horse), Equus asinus (the donkey), Equus burchelli (the common zebra), are different species belonging to the same genus
Note that generic name is always written fist and start with a capital letter. When we refer to several species belonging to the same genus, we need only write the generic name in full on the first occasion e.g Equus caballus, E. Asinus and E. Burchelli.
The characteristic features of the main animal and plant groups and of the fungi, bacteria and viruses are set out in appendix 1 page 402. We recommend that you to look through the appendix to get in an idea of the variety of life on earth, but do not attempt to study it in detail at this stage. You will however, find it useful to refer to this appendix each time an animal, or plant species, or group, with which your are unfamiliar, is mentioned.
Today there is generally agreement among biology as to how orgsnisims should be classified. How many Kingdom should we have; two, five or more? We shall return to this question in chapter 29. That is it
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