This classifies organisms based on their evolutionary history. Closely related organisms are grouped together. Organisms in the same group have a more recent common ancestor with each other than with organisms not in their group. If organisms are closely related they will typically show physical similarities.
A hierarchial system has been devised for all living organisms. Each grouping in the system is a taxon, bigger taxa contain smaller taxa. Within each taxon, organisms are more similar to each other and more closely related than to organisms outside that taxon.
The hierarchy of biological classification is as follows:
There are five kingdoms. Phylum is where organisms have radically different body plans. Class is where diversity within the phyla allows for a further division. Family is where the level of differences are less obvious. Genus is where each family is further sub-divided into genera.
Taxas are discreet, this means that something is either in one taxon or another. It can not be in more than one taxon.
Reasons for a classification system
- A phylogenetic classification system allows us to infer evolutionary relationships. If two organisms are so similar that we put them in the same taxon, we infer that they are closely related.
- If a new animal is discovered, we predict some of its other characteristics based on our general understanding with animals that share the same characteristics as the ones we already know.
- When describing the health of an ecosystem or the rate of extinction is the geological record, conservationists find it more useful to count families rather than species
Our classification system is based upon our current knowledge. When our knowledge advances, the system may need to change. As new organisms are discovered, new groups may need to be created or adjusted.