At least 1.5 million different kinds of Animal have been identified by scientists and more are identified every year. The total number of animals in existence may be as high as thirty million, which means that the task of identifying and locating all the Planet Earth's fauna may never be complete. In order to make sense of this diversity, biologists use formal classification systems, in which all the past and present known life is named and organised into groups. Each type of animal is given a unique species name and placed into the group where the species to which its evolutionary development suggests that it is most closely related.Modern scientific classification dates back to the work of a Swedish botanist and explorer called Karl Linnaeus (18th Century). He devised a system whereby all organisms are classified by two part scientific names written in Latin. The first part of the name refers to the genus to which the animal belongs and the second part denotes its species; this system remains in force today and is understood by scientists all over the world. As well as labelling all living things it shows exactly where a species fits into the living planet.
In scientific classification the species is the basic unit. Species are organised into groups called genera and these are organised into families. This system of groups continues working upwards through orders, classes, phyla and finally into kingdoms. Kingdoms are the largest group and also the highest level in the hierarchy.Each of the groups in the hierarchy has a common ancestor, which becomes increasingly remote from a species with each higher level of the hierarchy. Identification of the groups is an important part of the classification process and often involves difficult and complicated research.
Traditionally species are defined as groups of living things that share a set of characteristics and that are able to interbreed in the wild. It is sometimes difficult to determine if a group fits the definition so scientists prefer to determine species by examining genetic data. However genetic data does not solve all the classification problems because it still has to be decided if two animals' genes are close enough to warrant their being classed as one species.
Nearly all of today's animal groups were identified before genetic analysis became available. The groups were established on the basis of anatomical evidence both in living species and in those species preserved as fossils. Anatomical studies can be useful in tracing the path of evolution because they can show how certain body parts have been modified, sometimes greatly, for different uses.
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